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CHAPTER 5Hand/Wrist Musculoskeletal Disorders(Carpal Tunnel Syndrome, Hand/WristTendinitis, and Hand-Arm VibrationSyndrome): Evidence for Work-Relatedness

Musculoskeletal disorders (MSDs) of the hand/wrist region have been separated into three componentsfor the purpose of this review: (a) Carpal Tunnel Syndrome (CTS), (b) Hand/Wrist Tendinitis, and (c)Hand-Arm Vibration Syndrome (HAVS). Each of these are described with regard to the evidence forcausality between workplace risk factors and development of MSDs.

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CHAPTER 5aCarpal Tunnel Syndrome

SUMMARY Over 30 epidemiologic studies have examined physical workplace factors and their relationship to carpaltunnel syndrome (CTS). Several studies fulfill the four epidemiologic criteria that were used in this review,and appropriately address important methodologic issues. The studies generally involved populationsexposed to a combination of work factors, but a few assessed single work factors such as repetitivemotions of the hand. We examined each of these studies, whether the findings were positive, negative, orequivocal, to evaluate the strength of work-relatedness using causal inference.

There is evidence of a positive association between highly repetitive work alone or in combination withother factors and CTS based on currently available epidemiologic data. There is also evidence of a positiveassociation between forceful work and CTS. There is insufficient evidence of an association between CTSand extreme postures. Individual variability in work methods among workers in similar jobs and the influenceof differing anthropometry on posture are among the difficulties noted in measuring postural characteristicsof jobs in field studies. Findings from laboratory-based studies of extreme postural factors support a positiveassociation with CTS. There is evidence of a positive association between work involving hand/wristvibration and CTS.

There is strong evidence of a positive association between exposure to a combination of risk factors (e.g.,force and repetition, force and posture) and CTS. Based on the epidemiologic studies reviewed above,especially those with quantitative evaluation of the risk factors, the evidence is clear that exposure to acombination of the job factors studied (repetition, force, posture, etc.) increases the risk for CTS. This isconsistent with the evidence that is found in the biomechanical, physiological, and psychosocial literature.Epidemiologic surveillance data, both nationally and internationally, have also consistently indicated thatthe highest rates of CTS occur in occupations and job tasks with high work demands for intensive manualexertion–for example, in meatpackers, poultry processors, and automobile assembly workers.

INTRODUCTIONIn 1988, CTS had an estimated populationprevalence of 53 cases per 10,000 currentworkers [Tanaka et al. (in press)]. Twentypercent of these individuals reported absencefrom work because of CTS. In 1994, theBureau of Labor Statistics (BLS) reported thatthe rate of CTS cases that result in “days awayfrom work” was 4.8 cases per 10,000workers. The agency also reported that themedian number of days away from work forCTS was 30, which is even greater than themedian reported for back pain cases [BLS1995]. In 1993, the incidence rate (IR) forCTS workers’ compensation cases was 31.7cases per 10,000 workers; only a minority ofthese cases involved time off of work

[Washington State Department of Labor andIndustry 1996]. These data suggest that about5 to 10 workers per 10,000 workers will misswork each year due to work-related CTS.

In recent years, the literature relatingoccupational factors to the development of CTS has been extensively reviewed by numerous authors [Moore 1992; Stock1991; Gerr et al. 1991; Hagberg et al. 1992;Armstrong et al. 1993; Kuorinka and Forcier 1995; Viikari-Juntura 1995]. Most of these reviews reach a similarconclusion—work factors are one of the important causes of CTS. One review [Moore 1992] found the evidence

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more equivocal, but stated that theepidemiologic studies revealed a fairlyconsistent pattern of observations regarding thespectrum and relative frequency of CTS[among other musculoskeletal disorders(MSDs)] among jobs believed to be hazardous.The epidemiologic studies which form the basisfor these reviews are outlined in Tables 5a–1 to5a–4 of this chapter.

Thirty studies of occupational CTS are listed onTables 5a–5. Twenty-one are cross-sectionalstudies, six are case-control, and three involvea longitudinal phase; all have been publishedsince 1979. We included one surveillance study[Franklin et al. 1991] because it has beenincluded in many of the earlier reviews. The fewearlier studies of CTS identified were clinicalcase series, or did not identify work place riskfactors and were not included in the tablesrelated to CTS.

OUTCOME AND EXPOSUREMEASURESIn four of 30 studies listed in Tables 5a–1 to5a–4, CTS was assessed based on symptomsalone; in another nine studies, the casedefinition was based on a combination ofsymptoms and physical findings.Electrophysiological tests of nerve functionwere completed in 14 studies. Electrodiagnostictesting (nerve conduction studies) has beenconsidered by some to be a requirement for avalid case definition of CTS, as is similarly usedfor a clinical diagnosis in individuals with CTS.A few studies which have looked at therelationship of occupational factors to CTShave used a health outcome based onelectrodiagnostic testing alone [Nathan et al.1988; Schottland et al. 1991; Radecki 1995.]However, some authors [Nilsson 1995;Werner et al. 1997] have discouraged the use

of labeling workers as having “CTS” or“median nerve mononeuropathy” based onabnormal sensory nerve conduction alone(without symptoms). The reason for this view isillustrated in a recent prospective study byWerner et al. [1997]. On follow-up six toeighteen months after initial evaluation, theyfound that asymptomatic active workers withabnormal sensory median nerve function (byNerve Conduction Studies [NCS]) were nomore likely to develop symptoms consistentwith CTS than those with normal nervefunction. Studies which have used nerveconduction tests for epidemiologic field studieshave employed a variety of evaluation methodsand techniques [Nathan et al. 1988, 1994b;Bernard et al. 1993; Osorio et al. 1994].Normal values for nerve conduction studieshave also varied from laboratory to laboratory.NCS results have been found to vary withelectrode placement, temperature, as well asage, height, finger circumference and wrist ratio[Stetson 1993], suggesting that “normal” valuesmay need to be corrected for those factors.

Several epidemiologic studies have used asurveillance case definition of CTS basedon symptoms in the median nerve distributionand abnormal physical examination findingsusing Phalen’s test and Tinel’s sign, and havenot included NCS. Two recent studies[Bernard et al. 1993; Atterbury et al. 1996]looked at CTS diagnosis based onquestionnaire and physical examination findingsand its association with the “gold standard” ofnerve conduction diagnosed medianmononeuropathy. Both studies foundstatistically significant evidence to support theuse of an epidemiologic CTS case definitionbased on symptoms and physical examination(not requiring NCS) for epidemiologic surveillance studies. Nathan

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[1992a] also found a strong relationshipbetween symptoms and prolonged sensorymedian nerve conduction. (It is important tonote here that a case definition used forepidemiologic purposes usually differs from oneused for medical diagnosis and therapeuticintervention.)

Researchers have relied on a variety ofmethods to assess exposure to suspectedoccupational risk factors for CTS. Thesemethods include direct measurement,observation, self-reports, and categorization byjob titles. Most investigators agree that use ofobservational or direct measurement methodsincreases the quality (both the precision andaccuracy) of ergonomic exposure assessments,but these methods also tend to be costly andtime consuming. In general, misclassificationerrors tend to dilute the observed associationsbetween disease and physical workload[Viikari-Juntura 1995].

REPETITIONDefinition of Repetition for CTSFor our review, we identified studies thatexamined repetition or repetitive work for thehand and wrist for CTS as cyclical or repetitivework activities that involved either 1) repetitivehand/finger or wrist movements such as handgripping or wrist extension/flexion, ulnar/radialdeviation, and supination or pronation. Most ofthe studies that examined repetition or repetitivework as a risk factor for CTS had severalconcurrent or interacting physical workloadfactors. Therefore, repetitive work should beconsidered in this context, with repetition asonly one exposure factor, accompanied byothers such as force, extreme posture, and, lesscommonly, vibration. Studies Reporting on the Association

of Repetition and CTSNineteen studies reported on the results of theassociation between repetition and CTS. Several studies in Table 5a-1 quantitativelymeasured [Moore 1992; Chiang et al. 1990,1993; Silverstein et al. 1987] or observed[Stetson et al. 1993; Nathan et al. 1988,1992a; Barnhart et al. 1991; Osorio et al.1994] and categorized repetitive hand and wristmovements in terms of: a) the frequency orduration of tasks pertaining to the hand/wrist, b)the ratio of work-time to recovery time, c) thepercentage of the workday spent on repetitiveactivities, or d) the quantity of work performedin a given time. The rest of the studies generallyused job titles or questionnaires to characterizeexposure.

Studies Meeting the Four Evaluation CriteriaFive epidemiologic studies of the hand/wristarea addressing repetitiveness and CTS[Chiang et al. 1990, 1993; Moore and Garg1994; Osorio et al. 1994; Silverstein et al.1987] met the four criteria. Chiang et al. [1990]studied 207 workers from 2 frozen foodprocessing plants. Investigators observed jobtasks and divided them into low or highrepetitiveness categories of wrist movementbased on cycle time, as previously described bySilverstein et al. [1987]. Jobs were alsoclassified according to whether or not workers’hands were exposed to cold work conditions.The resulting exposure groups were:Group 1–Not Cold, Low Repetitiveness(mainly office staff and technicians);Group 2–Cold Exposure or HighRepetitiveness; and Group 3–Cold Exposureand High Repetitiveness. CTS diagnosis wasbased on abnormal clinical examination andnerve conduction studies. Prevalence of CTS

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was 3% in Group 1, 15% in Group 2, and 37%in Group 3. Statistical modeling that alsoincluded gender, age, length of employment,and cold resulted in an odds ratio (OR) of 1.87(p=0.02) for CTS among those with highlyrepetitive jobs. The OR for CTS among thoseexposed to cold conditions and highrepetitiveness was 3.32 (p=0.03). The authorscautioned that cold exposure may have at leastpartially acted as a proxy for forcefulhand/wrist exertion in this study group.

Chiang et al. [1993] studied 207 workers from8 fish processing factories in Taiwan. Jobs weredivided into 3 groups based on levels ofrepetitiveness and force. The comparison group(low force/low repetitiveness) was comprisedof managers, office staff, and skilled craftsmen(group 1). The fish-processing workers weredivided into high repetitiveness or high force(group 2), and high force and highrepetitiveness (group 3). Repetition of upperlimb movements (not specifically the wrist) wasdefined based on observed cycle time[Silverstein et al. 1987]. CTS was defined onthe basis of symptoms and positive physicalexamination findings, ruling out systemicdiseases and injury. CTS prevalence for theoverall study group was 14.5%. CTSprevalence increased from group 1, to group 2,and to group 3 (8.2%, 15.3%, and 28.6%,respectively), a statistically significant trend (p<0.01).Repetitiveness alone was not a significantpredictor of CTS (OR 1.1). Statistical modelingshowed that women in this study group had ahigher prevalence of CTS than men (OR 2.6,95% confidence interval [CI] 1.3–5.2).Because the proportion of women varied byexposure group (48%, 75%, and 79% fromgroup 1 to 3), further analyses were limited to

females. The OR for repet-itiveness was 1.5(95% CI 0.8–2.8), con-trolling for oralcontraceptive use and force.

Moore and Garg [1994] evaluated 32 jobs in apork processing plant and then reviewed pastOSHA illness and injury logs and plant medicalrecords for CTS cases in these job categories.A CTS case required the recording ofsuggestive symptoms (numbness and tingling)combined with electrodiagnostic confirmation(as reported by the attendingelectromyographers) of a case. Incidence ratios(IRs) were calculated using the full-timeequivalent number of hours worked reportedon the logs. The exact number of workers wasnot reported. Exposure assessment includedvideotape analysis of job tasks forrepetitiveness and awkward postures. Theforce measure was an estimate of the percentmaximum voluntary contraction (%MVC)based on weight of tools, and parts andpopulation strength data adjusted for extremeposture or speed. Jobs were then categorizedas hazardous or safe (for all upper extremityMSDs, not for CTS), based on exposure dataand the judgment of the investigators. Thehazardous jobs had a relative risk (RR) forCTS of 2.8 (95% CI 0.2–36.7) compared tothe safe jobs. Due to the lack of data fromindividual workers, the study was unable tocontrol for common confounders. Potential forsurvivor effect (79% of the workforce was laidoff the year prior to the study), a limited latencyperiod (8–32 months), and the potential forincomplete case ascertainment (underreportingis known to be a problem with OSHA illnessand injury logs) limit confidence in this estimate.This study did not specifically address therelationship between repetitiveness and CTS.No significant association was identified

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between repetitiveness and the grouped “upperextremity musculoskeletal disorders,” but therewas very little variability in repetitiveness (31 ofthe 32 jobs had a cycle time less than 30seconds).

Osorio et al. [1994] studied 56 supermarketworkers. Exposure to repetitive and forcefulwrist motions was rated as high, moderate, orlow, following observation of job tasks. TheCTS case definition was based on symptomsand nerve conduction studies. CTS-likesymptoms occurred more often (OR 8.3, 95%CI 2.6–26.4) among workers in the highexposure group compared to the low exposedgroup. The odds of meeting the symptom andNCS-based CTS case definition among thehigh exposure group were 6.7 (95% CI0.8–52.9), compared to the low exposuregroup.

Silverstein et al. [1987] studied 652 workers in39 jobs from 7 different plants (electronics,appliance, apparel, and bearing manufacturing;metal casting, and an iron foundry).Investigators divided jobs into high or lowrepetitiveness categories, based on analysis ofvideotaped job tasks of 3 representativeworkers in each job. High repetitiveness wasdefined as cycle time less than 30 seconds or atleast 50% of the work cycle spent performingthe same fundamental movements. Jobs werealso divided into high or low force categoriesbased on EMGs of representative workers’forearm flexor muscles while they performedtheir usual tasks. EMG measurements wereaveraged within each work group tocharacterize the force requirements of the job.High force was defined as a mean adjustedforce >6 kg. Jobs were then classified into 4groups: low force/low repetitiveness, high

force/low repetitiveness, low force/highrepetitiveness, and high force/highrepetitiveness. Fourteen cases (2.1%prevalence) of CTS were diagnosed based onstandardized physical examinations andstructured interviews.

The OR for CTS in highly repetitive jobscompared to low repetitive jobs, irrespective offorce, was 5.5 (p<0.05) in a statistical modelthat also included age, gender, years on the job,and plant. The OR for CTS in jobs withcombined exposures to high force and highrepetition was 15.5 (p<0.05), compared tojobs with low force and low repetition. Age,gender, plant, years on the job, hormonalstatus, prior health history, and recreationalactivities were analyzed and determined not toconfound the associations identified.

Studies Meeting at Least One CriterionFourteen additional studies met at least one ofthe criteria.

Barnhart et al. [1991] studied ski manufacturingworkers categorized as having repetitive ornonrepetitive jobs based on observationalexposure methods for hand/wrist exposure. Theparticipation rate for this study was below70%. Three different case definitions were usedfor CTS based on symptoms, physical examfindings, and NCS using the mean median-ulnardifference in each group. Each case definitionused the NCS results. The authors reported asignificant prevalence ratio (PR) of 2.3 for themean median-ulnar sensory latency nervedifference among those in repetitive jobscompared to those in non-repetitive jobs.However, the difference was found in the ulnarrather than in the median nerve. The mediannerve latencies were not statistically differentbetween the two groups.

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Baron et al. [1991] studied CTS in 124grocery store checkers and 157 other grocerystore workers who were not checkers. TheCTS case definition required symptoms thatmet pre-determined criteria on a standardizedquestionnaire and physical examinations. TheOR for CTS among checkers was 3.7 (95%CI 0.7–16.7), in a model that included age,hobbies, second jobs, systemic disease, andobesity. Participation rates at the work siteswere higher among the exposed group(checkers: 85% participation, non-checkers:55% participation). After telephone interviewsin which 85% of the non-checkers completedquestionnaires, investigators reported that theproportion of non-checkers meeting the casedefinition did not increase.

Cannon et al. [1981] in a case-control study ofaircraft engine workers did not find a significantassociation with the performance of repetitivemotion tasks (OR 2.1, 95%CI 0.9–5.3), butfound a significant association with self-reported use of vibrating hand tools, history ofgynecologic surgery, and an inverse relationshipwith years on the job. One must assume fromthe article that “repetitive motion tasks” weredefined by job title. The diagnosis of CTS wasbased on medical and workers’ compensationrecords.

In English et al.’s [1995] case-control study ofupper limb disorders diagnosed in orthopedicclinics, the case series included 171 cases ofCTS and 996 controls. Exposure was based onself-reports; repetitiveness was defined as amotion occurring more than once per minute.The logistic regression model of CTS foundsignificant associations with height (negative),weight (positive), presentation at the clinic as aresult of an accident (negative), and two

occupational factors: 1) uninterrupted shoulder rotation with elevatedarm (OR 1.8, 95% CI 1.2–2.8) and 2)protection from repeated finger tapping (OR0.4, 95% CI 0.2–0.7). The authors note thatthe latter observation presented “difficulties ofinterpretation.” Limitations of this study concernthe lack of exposure assessment for repetition,and the questionable reliability for reported limbmovements as an accurate measure ofrepetition.

Feldman et al. [1987] studied electronicworkers at a large manufacturing firm using aquestionnaire survey and biomechanical jobanalysis. Four work areas with 84 workerswere identified as “high risk” with highlyrepetitive and forceful tasks. Workers in thesehigh risk areas had physical examinations andNCS. Sixty-two workers from the high riskarea had repeat NCS one year later.Comparing these high risk workers to theothers, one can calculate ORs for symptoms ofnumbness and tingling [OR 2.26 (p<0.05)] anda positive Phalen’s sign [2.7 (p<0.05)].Longitudinal NCS of workers in the high riskarea showed significant worsening in themedian motor latency and sensory conductionvelocity in the left hand, and motor changesover a year’s period, which the authorsattributed to work exposure. A limitation of thisstudy concerns inadequate exposureinformation about the extent of workerexposure to repetitive and forceful work.

McCormack et al. [1990] studied 1,579 textileproduction workers and compared them to 468other nonoffice workers, a comparison groupthat included machine maintenance workers,transportation workers, cleaners, andsweepers. The textile production workers weredivided into four broad job categories based onsimilarity of upper extremity exertions. No

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formal exposure assessment was conducted.Health assessment included a questionnaire andscreening physical examination followed by adiagnostic physical examination. CTS wasdiagnosed using predetermined clinical criteria.The severity of cases was also reported asmild, moderate, or severe. The overallprevalence for CTS was 1.1%, with 0.7% inboarding, 1.2% in sewing, 0.9% in knitting,0.5% in packaging/folding, and 1.3% in thecomparison group. None of the differenceswere statistically significant. A statistical modelthat also included age, gender, race, and yearsof employment showed that CTS occurredmore often among women in this study(p<0.05). Interpretation of these data,especially with a low prevalence disorder likeCTS, is difficult since gender varied with job(94% of boarding workers were female,compared to 56% in the comparison group),and the comparison group (machinemaintenance workers, transportation workers,cleaners and sweepers) may have also beenexposed to upper extremity exertions.Interactions among potential confounders werenot addressed, but they are suspected becauseof significant associations between race andthree MSDs.

Morgenstern et al. [1991] mailedquestionnaires to 1,345 union grocery checkersand a general population group. Exposure wasbased on self-reported time working as achecker. Symptoms of CTS were significantlyassociated with age and the use of diuretics,and nonsignificantly associated with averagehours worked per week, and years worked asa checker. A positive CTS outcome was basedon the presence of all four symptoms: pain inthe hands or wrist, nocturnal pain, tingling in thehands or fingers, or numbness. The estimatedattributable fraction of CTS symptoms toworking as a checker was about 60%, using

both a general population comparison groupand a low exposed checker group. Thelimitations of this study are: 1) the use of anoverly sensitive health outcome measure, forexample, 32% of the surveyed populationreported numbness; and 2) the use of self-reported exposure.

Nathan et al. [1988] studied median nerveconduction of 471 randomly selected workersfrom four industries (steel mill, meat/foodpackaging, electronics, and plasticsmanufacturing). Median nerve sensory latencyvalues were adjusted for age for statisticalanalyses. Thirty-nine percent of the studysubjects had impaired sensory nerveconduction, or “slowing” of the median nerve.The five exposure groups were defined asfollows: Group 1 is very low force, lowrepetition (VLF/LR); Group 2 is low force,very high repetition (LF/VHR); Group 3 ismoderate force, moderate repetition (MF/MR);Group 4 is high force/moderate repetition(HF/MR); and Group 5 is very high force/highrepetition (VHF/HR). There was no significantdifference between Group 1 and Group 2, thegroups that had the greatest differences inrepetition. The authors reported a significantlyhigher number of subjects with median nerveslowing in Group 5 (VHF/HR) compared toGroup 1 (VLF/LR), but not in other groups,using a statistical method described as a“pairwise unplanned simultaneous testprocedure” [Sokal and Rohlf 1981]. Theauthors also reported that when individualhands were the basis of calculations rather thansubjects, Group 3 had a significantly higherprevalence of median nerve slowing.Calculations of the data using PRs and chi-squares [Kleinbaum et al. 1982] resulted insignificantly higher prevalences of median nerve

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slowing in each of Groups 3, 4, and 5(moderate to high repetition, with moderate tovery high force) compared to Group 1(VLR/LF). PRs are 1.9 (95% CI 1.3–2.7), 1.7(95% CI 1.1–2.5), and 2.0 (95% CI 1.1–3.4)for Groups 3, 4, and 5, respectively. Aconservative (Bonferroni) adjustment of thesignificance level to 0.0125 for multiplecomparisons [Kleinbaum et al. 1982] wouldresult in Group 5 no longer being statisticallysignificantly different from Group 1 (p=0.019),but Group 4 (p=0.009), and Group 3(p=0.000) remain statistically significantlyhigher than Group 1 in prevalence of mediannerve slowing.

In 1992, Nathan et al. [1992a] reported on afollow-up evaluation in the same study group.Sixty-seven percent of the original studysubjects were included. Hands (630), ratherthan subjects, were the basis of analysis in thisstudy. Novice workers (those employed lessthan 2 years in 1984) were less likely to returnthan non-novice workers (56% compared to69%, p=.004). Maximum latency differences inmedian nerve sensory conduction weredetermined as in the Nathan et al. [1988] study.The authors state that there was no significantdifference in the prevalence of median nerveslowing between any of the exposurecategories in Nathan et al. [1988] using thesame statistical method described in the Nathanet al. 1988 study. However, calculations usingcommon statistical methods result in thefollowing PRs for slowing: Group 3–1.5 (95%CI 1.0–2.2), Group 4–1.4 (95% CI 0.9–2.1),and Group 5–1.0 (95% CI 0.5–2.2),compared to Group 1. Group 5 had the sameprevalence of slowing (18%) as Group 1 in1989. In 1984 the prevalence of slowing was29% in Group 5, and 15% in Group 1. The

drop in prevalence of median nerve slowing inGroup 5 between 1984 and 1989 might beexplained by the higher drop-out rate amongcases in Group 5 compared to Group 1 (PR2.9, 95% CI 1.3–6.6). This was not addressedby the authors.

Punnett et al. [1985] compared the symptomsand physical findings of CTS in 162 womengarment workers and 76 women hospitalworkers such as nurses, laboratory technicians,and laundry workers. Eighty-six percent of thegarment workers were sewing machineoperators and finishers (sewing and trimming byhand). The sewing machine operators weredescribed as using highly repetitive, low forcewrist and finger motions, whereas finishingwork also involved shoulder and elbowmotions. The exposed garment workersprobably had more repetitive jobs than most ofthe hospital workers. CTS symptoms occurredmore often among the garment workers (OR2.7, 95% CI 1.2–7.6) compared to the hospitalworkers. There was a low participation rate(40%) among the hospital workers.

Schottland et al. [1991] carried out acomparison of NCS findings in poultry workersand job applicants as referents. No exposureassessment was performed, and applicantswere not excluded if they had prioremployment in the plant. Results indicated thatthe right median nerve sensory latency wassignificantly longer in 66 female poultry workerscompared to 41 female job applicants. In thesetwo groups of women there were lesspronounced differences in the left mediansensory latency. The latencies in the 27 malepoultry workers did not differ significantly fromthe 44 male job applicants, although the powercalculations presented in the paper noted

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limited power to detect differences among maleparticipants. The OR for percentage of femalepoultry workers who exceeded the criteriavalue for the right median sensory latency is2.86 (95% CI 1.1–7.9). The major limitationsof this study are the absence of detailedinformation on exposure and the inclusion offormer poultry workers into the applicantgroup, as well as the inadequate sample size,and the personal characteristics of theseworkers. This study found a significantassociation between highly repetitive, highlyforceful work and abnormal NSC consistentwith CTS. It does not allow analysis ofrepetition alone.

Stetson et al. [1993] used measurements ofsensory nerve conduction velocity of themedian nerve as indicators of nerve impairmentor CTS; clinical examination results were notreported in this article. Three groups werestudied: a reference group of 105 workerswithout occupational exposure to highly forcefulor repetitive hand exertions, 103 industrialworkers with hand/wrist symptoms, and 137asymptomatic industrial workers. Exposure wasassessed with a checklist by trained workers.Factors considered included repetitiveness(Silverstein criteria), force defined by theweight of an object that is carried or held,localized mechanical stress, and posture.Exposure assessments were available on 80%of the industrial workers. Most of the industrialworkers were on repetitive jobs (76%), aminority carried more than ten pounds some ofthe time (32%), and gripped more than sixpounds at least some of the time (44%). Theanalysis controlled for several confoundersincluding age, gender, finger circumference,height, weight, and a square-shaped wrist. Inthe comparison of the asymptomatic to

symptomatic industrial workers, the meanexposure for the symptomatic industrialworkers was nonsignificantly slightly greater forall exposure factors except for repetitiveness.The median sensory amplitudes weresignificantly smaller (p<0.01) and latencies longer (p<0.05 ) forindustrial workers with exposure to high gripforces compared to those without. Meansensory amplitudes were significantly smaller(p<0.05) and motor and sensory latencies weresignificantly longer (p<0.01) in the industrialasymptomatic workers compared to the controlgroup. These findings for the motor latenciesare similar to Feldman et al. [1987]. Since mostof the industrial workers were exposed torepetitive work, it is not clear whether thisstudy population allowed a comparisonbetween repetitive and non-repetitive work.Overall this study suggests that repetitive workcombined with other risk factors is associatedwith slowing of median nerve conduction. The Wieslander et al. [1989] case-controlstudy used self-reported information collectedvia telephone interview about the duration ofexposure (number of years and hours perweek) to several work attributes includingrepetitive work. Definitions for these workattributes were not provided. Three categoriesof duration of exposure were defined for eachattribute (<1 year,1–20 years, and >20 years), but the asymmetryof the categories was not explained. Asignificant OR for reporting repetitivemovements of the wrist comparing CTSpatients to hospital referents (OR 4.6) andgeneral population referents (OR 9.6) wasreported, but only among those employedgreater than 20 years. Those employed from1–20 years compared to the referent

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population had elevated ORs for repetitivemovements of the wrist (1.5 for CTS patientscompared to hospital referents, and 2.3compared to population referents), but thesewere not significant. Jobs with increasingnumbers of work risk factors gave increasingORs (from 1.7 to 7.1) among CTS cases whencompared to referents; these were statisticallysignificant when there were two or more riskfactors. Given the limited quality of theexposure data and findings (repetition is asignificant risk factor only after 20 years ofexposure), this is only suggestive of arelationship between repetition alone and CTS. Studies Not Meeting Any of the CriteriaLiss et al. [1995] conducted a mail surveyconcerning CTS among 2,124 Ontario dentalhygienists compared to 305 dental assistantswho do not scale teeth. Both groups had a lowresponse rate (50%). The age adjusted ORwas 5.2 (95% CI 0.9–32) for being told by aphysician that you had CTS and 3.7 (95% CI1.1–1.9) using a questionnaire-based definitionof CTS. The major limitations of this study arethe low participation rate, the lack of a detailedexposure assessment for repetitiveness, andself-reported health outcome.

Strength of Association—Repetitionand CTSThree of the five studies that met all four criteriaevaluated the effect of repetitiveness alone onCTS: Chiang et al. [1990], Silverstein et al.[1987], and Chiang et al. [1993].

Chiang et al. [1990] reported an OR of 1.9(p<0.05) for CTS among those with highlyrepetitive jobs. The OR for CTS among thoseexposed to high repetitiveness and cold was3.32 (p<0.05). The additional effect attributed

to cold may be at least partially explained byforceful motions among workers who were alsoexposed to cold. Force was not evaluated inthis study.

Silverstein et al. [1987] reported an OR of 5.5(p<0.05) for repetition as a single predictor ofCTS. Among workers exposed to highrepetition and high force, the OR was 15.5(p<0.05).

Chiang et al. [1993] reported a significant trendof increasing prevalence of CTS with increasingexposure to repetition and/or force (8.2%,15.3%, and 28.6%, p<0.05). Repetition (of thewhole upper limb, not the wrist) alone did notsignificantly predict CTS (OR 1.1).

In summary, three studies that met all fourcriteria reported ORs for CTS associated withrepetition. The statistically significant ORs forCTS attributed to repetition alone ranged from1.9 to 5.5. The statistically significant ORs forCTS attributed to repetition in combination withforce or cold ranged from 3.3 to 15.5. Gender,age, and other potential confounders wereaddressed and are unlikely to account for theassociations reported.

Five other studies observed job tasks, thengrouped them into categories according toestimated levels of repetitiveness combinedwith other risk factors [Feldman et al. 1987;Moore and Garg 1994; Nathan et al. 1988,1992a; and Osorio et al. 1994]. CTS casedefinitions reported here required more thansymptom-defined criteria. Moore and Garg[1994] reviewed medical records; Nathan et al.[1988] and Osorio et al. [1994] performednerve conduction studies.

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Feldman et al. [1987] reported an OR of 2.7(p<0.05) for a positive Phalen’s test amongworkers in high exposure jobs, compared tolow exposure jobs.

Moore and Garg [1994] reported an OR of2.8 (0.2, 36.7) for CTS among workers in“hazardous” jobs compared to workers in“nonhazardous” jobs.

Nathan et al.’s [1988] data result in PRsfor four groups with varying levels ofrepetitiveness and force from very low (VL) tovery high (VH), compared to a very low force,low repetition group (VLF/LR): LF/VHR versus VLF/LR: 1.0 (95% CI0.5–2.0)MF/MR versus VLF/LR: 1.9 (95% CI1.3–2.7)HF/MR versus VLF/LR: 1.7 (95% CI 1.1–2.5)VHF/HR versus VLF/LR: 2.0 (95% CI1.1–3.4).

Nathan et al. [1992a] data, a 5-year follow-upof the 1988 study, result in PRs for thefollowing groups:LF/VHR versus VLF/LR: 1.0 (95% CI 0.6–1.9) MF/MR versus VLF/LR: 1.5 (95% CI 1.0–2.2)HF/MR versus VLF/LR: 1.4 (95% CI 0.9–2.1)VHF/HR versus VLF/LR: 1.0 (95% CI 0.5–2.2).

Osorio et al. [1994] reported an OR of 6.7(95% CI 0.8–52.9) for CTS among workers inhigh exposure jobs, compared to workers inlow exposure jobs. Using a symptom-basedcase definition, the OR for the same

comparison groups was 8.3 (95% CI 2.6–26.4).

To summarize, three of the five studiesreviewed resulted in statistically significantpositive findings for CTS associated withcombined exposures. Feldman et al. [1987]reported an elevated OR for CTS with highcombined exposure. Nathan et al.’s [1988]data resulted in elevated PRs for CTS amongthe three highest combined exposure groups.Nathan et al.’s [1992a] data resulted in anelevated PR for CTS among one of the highcombined exposure groups. There wasevidence of survivor bias in the highestexposure group.

The following studies used job title or jobcategory to represent exposure torepetitiveness combined with other exposuresand defined CTS based on physicalexamination [Baron et al. 1991, McCormack etal. 1990, Punnett et al. 1985] or nerveconduction studies [Schottland et al. 1991].

Baron et al. [1991] reported an OR of 3.7(95% CI 0.7–16.7) for CTS, defined bysymptoms and physical examination, amonggrocery checkers compared to other groceryworkers.

McCormack et al. [1990] reported thefollowing ORs for CTS among workers in eachof four broad job categories that wereconsidered exposed, compared to acomparison group of maintenance workers andcleaners that was considered to have lowexposure:Boarding versus Low: 0.5 (95% CI 0.1–2.9)Sewing versus Low: 0.9 (95% CI 0.3–2.9)

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Packaging versus Low: 0.4 (95% CI 0.0–2.4)Knitting versus Low: 0.6 (95% CI 0.1–3.1)

Punnett et al. [1985] reported an OR of 2.7(95% CI 1.2–7.6) for CTS among garmentworkers versus hospital workers.

Schottland et al. [1991] reported an OR of2.86 (95% CI 1.1–7.9) for prolonged rightmedian sensory latency among female poultryworkers, compared to female applicants for thesame jobs. No significant differences wereidentified among males.

In summary, two of the four studies reviewedabove reported significantly elevated ORs forCTS or median sensory nerve conductionslowing.

Wieslander et al. [1989] reported an OR forCTS (surgical cases, confirmed by NCS) of2.7 (95% CI 1.3–5.4) among those with self-reported exposure to repetitive wrist movement>20 years, compared to hospital referents, and4.5 (95% CI 2.0–10.4), compared topopulation referents. Significant OR s for CTSamong those with combined job risk factorsranged from 3.3 to 7.1.

The remaining two studies relied on self-reported symptoms and self-reportedexposures from mail [Morgenstern et al. 1991]or telephone surveys [Liss et al. 1995]. Dataquality and response rates limit interpretation offindings.

In conclusion, among the studies that measuredrepetition alone, there is evidence that repetitionis positively associated with CTS. The majorityof studies provide evidence of a strongerpositive association between repetition

combined with other job risk factors and CTS.

Temporal Relationship: Repetitionand CTS The question of which occurs first, exposure ordisease, can be addressed most directly inprospective studies. However, study limitationssuch as survivor bias can cloud theinterpretation of findings. In our analysis ofNathan et al.’s [1992a] data, 2 of 3 groups thatwere exposed to forceful hand/wrist exertionswere more likely to have median nerve slowingwhen nerve conduction testing was repeated 5years later. The highest exposure group had thesame prevalence of slowing as the lowestexposure group in 1989, whereas they had ahigher prevalence rate in 1984. As discussedabove, this apparent decrease in prevalenceover 5 years can probably be explained by ahigher drop-out rate among cases in the highestexposure group, compared to the lowestexposure group. These interpretations of thedata differ from those of the authors. Furtherstudy is needed to clarify these issues.However, to our knowledge, there is noevidence demonstrating that those with CTSwould be more likely to be hired in jobs thatinvolve high exposure to repetitive hand/wristexertions and combined job risk factors,compared to those without CTS. In fact,employment practices tend to exclude newworkers with CTS from jobs that requirerepetitive and intensive hand/wrist exertion.

Feldman et al. [1987] reported longer medianmotor (but not sensory) latencies amongworkers with combined exposure to hand/wristexertion, compared to nerve conductionfindings in the same group one year earlier.

Cross-sectional studies provide evidence that

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exposure occurred before CTS, by using casedefinitions that exclude pre-existing cases, andby excluding recently hired workers from thestudy. The studies that provide evidence thatrepetitive and combined job exposures areassociated with CTS followed these practices,therefore the associations identified cannot beexplained by disease occurring beforeexposure.

Consistency in Association forRepetition and CTS One study [English et al. 1995] reported astatistically significant negative associationbetween repetitive work and CTS. The specificexposure was self-reported repeated fingertapping; the investigators stated that they haddifficulty interpreting this finding. All of the otherstatistically significant findings pointed to apositive association between repetitive workand CTS. The non-significant estimates of RRwere also mostly greater than one. Coherence of Evidence for RepetitionOne of the most plausible ways that repetitivehand activities may be associated with CTS isthorough causing a substantial increase in thepressure in the carpal tunnel. This in turn caninitiate a process which results in eitherreversible or irreversible damage to the mediannerve [Rempel 1995]. The increase in pressure,if it is of sufficient duration and intensity, mayreduce the flow of blood in the epineuralvenules. If prolonged, this reduction in flowmay affect flow in the capillary circulation,resulting in greater vascular permeability andendoneural and synovial edema. Because of thestructure of the median nerve and the carpaltunnel, this increase in fluid and resultingincrease in pressure may persist for a longperiod of time. If the edema becomes chronic,

then it may trigger a fibrosis which damages thefunction of the nerve. The interplay betweenacute increases in pressure and chronic changesto the nerve could partially explain why there isnot a stronger correlation between symptoms ofCTS and slowing of the median nerve. Bothsymptoms and slowing of the median nerve arelikely to have both acute and chroniccomponents in many cases of CTS.

The work determinants of pressure in thecarpal tunnel are wrist posture and load on thetendons in the carpal tunnel. For example, thenormal resting pressure in the carpal tunnel withthe wrist in a neutral posture is about 5millimeters of mercury (mmHg), and typing withthe wrist in 45E of extension can result in anacute pressure of 60 mmHg. Substantial loadon the fingertip with the wrist in a neutralposture can increase the pressure to 50 mmHg.A parabolic relationship between wrist postureand pressure in the carpal tunnel has beenfound. In laboratory studies of normal subjects,elevated carpal tunnel pressures quickly returnto normal once the repetitive activity stops;patients with CTS take a long time for thepressure to return to their baseline values. Oneof the supporting observations for this model isthat at surgery for CTS, edema and vascularsclerosis (fibrosis due to ischemia) are common[Rempel 1995].

This model of the etiology of work-related CTSis consistent with two observations from theepidemiological literature. First, it illustrateswhy both work and nonwork factors such asobesity may be important because anything thatincreases pressure in the carpal tunnel maycontribute to CTS. Second, it explains whyrepetitiveness independent of wrist posture andload on the flexor tendons may not be a major

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risk factor for CTS.

Exposure-Response Relationship forRepetitionEvidence of an exposure-response relationshipis provided by studies that show a correlationbetween the level or duration of exposure andeither the number of cases, the illness severity,or the time to onset of the illness. Silverstein etal. [1987] showed an increasing prevalence ofCTS signs and symptoms among industrialworkers exposed to increasing levels ofrepetition and forceful exertion. Thisrelationship was not seen when repetition alonewas assessed. Similar findings on an exposure-response relationship were reported by Chianget al. [1993], Osorio et al. [1994], Wieslanderet al. [1989], and by Stock [1991] in herreanalysis of the Nathan et al. [1988] data.

Morgenstern et al. [1991] and Baron et al.[1991] reported increased prevalence of CTSwith increasing length of time working as agrocery cashier.

Conclusions Regarding RepetitionBased on the epidemiologic studies notedabove, especially those with quantitativeevaluation of repetitive work, the strength ofassociation for CTS and repetition has beenshown to range from an OR of 2 to 15. Thehigher ORs are found when contrasting highlyrepetitive jobs to low repetitive jobs, and whenrepetition occurred in combination with highlevels of forceful exertion. Those studies withcertain epidemiologic limitations have also beenfairly consistent in showing a relationshipbetween repetition and CTS. The evidencefrom those studies which defined CTS basedon symptoms, physical findings, and NCS islimited, due to the variety of methods used

[Nathan et al. 1988; Stetson et al. 1993;Barnhart et al. 1991].

There is evidence of a positive associationbetween highly repetitive work alone and CTS.There is strong evidence of a positiveassociation between highly repetitive work incombination with other job factors and CTS,based on currently available epidemiologicdata.

FORCE AND CTSDefinition of force for CTSThe studies reviewed in this section determinedhand/wrist force exposure by a variety ofmethods. Some investigators [Armstrong andChaffin 1979; Chiang et al. 1993; Silverstein etal. 1987] measured force by EMGs ofrepresentative workers’ forearm flexor muscleswhile they performed their usual tasks. EMGmeasurements were averaged within each workgroup to characterize the force requirements ofthe job; jobs were then divided into low or highcategories if the average force was above orbelow a cutoff point. Moore and Garg [1994]estimated force as %MVC, based on weight oftools and parts and population strength data,adjusted for extreme posture or speed. Jobswere then predicted to be either hazardous orsafe (for any upper extremity musculoskeletaldisorder), based on exposure data andjudgment. Stetson et al. [1993] estimatedmanipulation forces based on weights of toolsand parts and systematically recordedobservations of one or more workers on eachjob. Jobs were then ranked according to gripforce cutoffs. Nathan et al. [1988, 1992a] andOsorio et al. [1994] estimated relative levels offorce (e.g., low, moderate, high) afterobservation of job tasks. McCormack et al.[1990] grouped jobs into broad job categories

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based on similarity of observed job tasks; onejob group (boarding) required forcefulhand/wrist exertions. Baron et al. [1991] andPunnett et al. [1985] used job title as asurrogate for exposure to forceful hand/wristexertions.

Much of the epidemiologic data on CTS andforce overlaps with those studies discussed inthe above section on repetition. Repetitivework is frequently performed in combinationwith external forces, and much of theepidemiologic literature has combined thesetwo factors when determining association withCTS.

Studies Reporting on the Associationof Force and CTSEleven studies reported results on theassociation between force and CTS. Theepidemiologic studies that addressed forcefulwork and CTS tended to compare workinggroups by classifying them into broadcategories based on estimates of theforcefulness of hand/wrist exertions incombination with estimated repetitiveness. Inmost studies the exposure classification was anordinal rating (e.g., low, moderate, or high); insome studies job categories or titles were usedas surrogates for exposure to force exertions.

Studies Meeting the Four Evaluation CriteriaFour studies that evaluated the relationshipbetween forceful hand/wrist exertion and CTSmet all four criteria: Chiang et al. [1993],Moore and Garg [1994], Osorio et al. [1994],Silverstein et al. [1987]. Chiang et al. [1993]studied 207 workers from 8 fish-processingfactories in Taiwan. Jobs were divided into 3groups based on levels of force andrepetitiveness. The comparison group (low

force/low repetitiveness) was managers, officestaff, and skilled craftsmen. The fish-processingworkers were divided into high force or highrepetitiveness (group 2), and high force andhigh repetitiveness (group 3). Hand forcerequirements of jobs were estimated byelectromyographs of forearm flexor muscles ofa representative worker from each groupperforming usual job tasks. High force wasdefined as an average hand force of >3 kgrepetition of the upper limb (not specifically thewrist) was defined based on observed cycletime [Silverstein et al. 1987]. CTS was definedon the basis of symptoms and positive physicalexamination findings, ruling out systemicdiseases and injury. CTS prevalence for theoverall study group was 14.5%. CTSprevalence increased from group 1 to group 3(8.2%, 15.3%, and 28.6%), a statisticallysignificant trend p<0.01). Statistical modelingshowed that women in this study group had ahigher prevalence of CTS than men (OR 2.6,95% CI 1.3–5.2). Force also significantlypredicted CTS (OR 1.8, 95% CI 1.1–2.9), butnot repetitiveness. Because the proportion ofwomen varied by exposure group (48%, 75%,and 79% from groups 1 to 3), the possibility ofan interaction between gender and jobexposure exists, but this was not statisticallyexamined. In an analysis limited to females, the2 significant predictors of CTS were oralcontraceptive use (OR 2.0, 95% CI 1.2–5.4),and force (OR 1.6, 95% CI 1.1–3.0). Concernover interpretation of these findings is raisedbecause oral contraceptive use varies with age,and age may vary with job exposures.

These potential interactions were not examined,and women’s ages by job group were notreported.

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Moore and Garg [1994] evaluated 32 jobs in apork processing plant and then reviewed pastOSHA 200 logs and plant medical records forCTS cases in these job categories. IRs werecalculated using the full-time equivalent (FTE)number of hours worked as reported on thelogs. The exact number of workers was notreported. Exposure assessment includedvideotape analysis of job tasks forrepetitiveness and awkward postures. Theforce measure was an estimate of the %MVC,based on weight of tools and parts andpopulation strength data, adjusted for extremeposture or speed. Jobs were then predicted tobe either hazardous or safe (for all UpperExtremity MSDs), based on exposure data andjudgment. CTS was determined by reviewingOSHA 200 logs and plant medical records.The proportion of CTS in the overall studygroup during the 20 months of caseascertainment was 17.5 per 100 FTEs. If theoccurrence of CTS did not vary over thisperiod, the proportion of CTS in a 12-monthperiod would be 10.5 per 100 FTEs. Thehazardous jobs had a RR for CTS of 2.8 (0.2,36.7) compared to the safe jobs. Potential forsurvivor effect (79% of the workforce was laidoff the year before the study), limited latencyperiod (8-32 months), and the potential forincomplete case ascertainment (underreportingis common on OSHA 200 logs, and logs werenot reviewed for the first 12 months of thestudy) limit confidence in this estimate. One ofthe more hazardous jobs, the Ham Loaders,required extreme wrist, shoulder and elbowposture and was rated 4 on a 5-point scale forforce, yet there was no observed morbidity.Since this job did not start until 1989, theperiod of observation for musculoskeletaldisorders for this job was only 8 months. Other

jobs studied allowed for up to a 32-monthlatency period. The possibility of differentialcase ascertainment between exposed andunexposed jobs exists, both because ofdifferent observation periods, as well as thelikelihood that turnover may have been greaterin the exposed jobs. It is also unclear whetheremployees worked full-time or part-time hours.

Osorio et al. [1994] studied 56 supermarketworkers. Exposure to repetitive and forcefulwrist motions was rated as high, moderate, orlow, following observation of job tasks (97%initial concordance with 2 independentobservers). The CTS case definition was basedon symptoms and nerve conduction studies.CTS-like symptoms occurred more often (OR8.3, 95% CI 2.6–26.4) among workers in thehigh exposure group compared to the lowexposed group. The odds of meeting thesymptom and NCS-based CTS case definitionamong the high exposure group were 6.7 (95%CI 0.8–52.9), compared to the low exposuregroup.

Silverstein et al. [1987] measured force byelectromyographs of representative workers’forearm flexor muscles while they performedtheir usual tasks. EMG measurements wereaveraged within each work group tocharacterize the force requirements of the job;jobs were then divided into high or lowcategories if the mean adjusted force wasabove or below4 kg. Jobs were then classified into 4 groupsthat also accounted for repetitiveness: lowforce/low repetitiveness, high force/lowrepetitiveness, low force/high repetitiveness,and high force/high repetitiveness. Fourteencases (2.1% prevalence) of CTS were

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diagnosed based on standardized physicalexaminations and structured interviews.

The OR for CTS in high force jobs comparedto low force jobs, irrespective of repetitiveness,was 2.9 (p>0.05). The plant- adjusted OR forCTS in jobs with combined exposures to highforce and high repetition was 14.3 (p<0.05),compared to jobs with low force and lowrepetition. Age, gender, plant, years on the job,hormonal status, prior health history, andrecreational activities were analyzed anddetermined not to confound the associationsidentified. The OR for CTS in jobs withcombined exposure from the multiple logisticanalysis was 15.5 (95% CI 1.7–142.)

Studies Meeting at Least One CriterionBaron et al. [1991] studied CTS in 124grocery store checkers and 157 other grocerystore workers who were not checkers. TheCTS case definition required symptoms thatmet pre-determined criteria on a standardizedquestionnaire. Physical examinations were alsoperformed, but participation rates at the worksites were higher among the exposed group(checkers: 85% participation, non-checkers:55% participation). Telephone interviews tonon-checkers resulted in questionnairecompletion by 85% of the non-checkers.Based on a questionnaire case definition, theOR for CTS among checkers was 3.7 (95%CI 0.7–16.7), in a model that included age,hobbies, second jobs, systemic disease, andobesity.

McCormack et al. [1990] studied 1,579 textileproduction workers compared to 468 othernonoffice workers, a comparison group thatincluded machine maintenance workers,transportation workers, cleaners, and

sweepers. The textile production workers weredivided into four broad job categories based onsimilarity of upper extremity exertions. TheBoarding group required the most physicalexertion. No formal exposure assessment wasconducted. Health assessment included aquestionnaire and screening physicalexamination followed by a diagnostic physicalexamination. CTS was diagnosed usingpredetermined clinical criteria. The severity ofcases was also reported as mild, moderate orsevere. The overall prevalence for CTS was1.1%, with 0.7% in Boarding, 1.2% in Sewing,0.9% in Knitting, 0.5% in Packaging/Folding,and 1.3% in the comparison group. None ofthe differences were statistically significant. Astatistical model that also included age, gender,race, and years of employment showed thatCTS occurred more often among women in thisstudy (p<0.05). Interpretation of these data,especially with a low prevalence disorder likecarpal tunnel syndrome, is difficult since gendervaried with job (e.g., 94% of Boarding workerswere female, compared to 56% in thecomparison group), and the comparison groupmay have also been exposed to upper extremityexertions (machine maintenance workers,transportation workers, cleaners andsweepers). Interactions among potentialconfounders were not addressed, but they aresuspected because of significant associationsbetween race and three musculoskeletaldisorders.

Nathan et al. [1988] studied median nerveconduction of 471 randomly selected workersfrom four industries (steel mill, meat/foodpackaging, electronics, and plasticsmanufacturing). Jobs were grouped into 5relative levels of force (from very light to veryhigh) after observation of job tasks. Jobs were

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also rated for repetitiveness (5 levels). Thirty-nine percent of the study subjects had impairedsensory conduction, or “slowing” of the mediannerve. The 5 exposure groups were defined asfollows: Group 1 is very low force, lowrepetition (VLF/LR); Group 2 is low force,very high repetition (LF/VHR); Group 3 ismoderate force, moderate repetition (MF/MR);Group 4 is high force/moderate repetition(HF/MR); and Group 5 is very high force/highrepetition (VHF/HR). The most logicalcomparisons to evaluate the effect of forcewould be Groups 3, 4, and 5 (moderate, high,and very high force) compared to Group 1 (lowforce). Group 2 jobs are not a goodcomparison because they are very highlyrepetitive, which may confound thecomparisons. The authors reported asignificantly higher number of subjects withmedian nerve slowing in Group 5 (VHF/HR)compared to Group 1 (VLF/LR), but not inother groups, using an uncommon statisticalmethod (pairwise unplanned simultaneous testprocedure [Sokal and Rohlf 1981]). Theauthors also reported that when individualhands were the basis of calculations rather thansubjects, Group 3 had a significantly higherprevalence of median nerve slowing.Calculations of the more familiar PRs and chi-squares [Kleinbaum et al. 1982], using thepublished data, result in higher prevalences ofmedian nerve slowing in each of Groups 3, 4,and 5, compared to Group 1 (PRs: 1.9, 95%CI 1.3–2.7; 1.7, 95% CI 1.1–2.5; and 2.0,95% CI 1.1–3.4, respectively). A conservativeadjustment (Bonferroni) of the significance levelto 0.0125 for multiple comparisons [Kleinbaumet al. 1982] would result in Group 5 no longerbeing statistically significantly different fromGroup 1 (p=0.019), but Group 4 (p=0.009)and Group 3 (p=0.000) remain statistically

significantly higher than Group 1 in prevalenceof median nerve slowing.

In 1992 Nathan et al. [1992a] reported on afollow-up evaluation in the same study group.Sixty-seven per cent of the original studysubjects were included. Hands (630), ratherthan subjects, were the basis of analysis in thisstudy. Novice workers (those employed lessthan 2 years in 1984) were less likely to returnthan non-novice workers (56% compared to69%, p=0.004). Probable CTS was defined onthe basis of symptoms reported during astructured interview and a positive Phalen’s orTinel’s test. Maximum latency differences inmedian nerve sensory conduction weredetermined as in the 1984 study. The authorsstate that there was no significant difference inthe prevalence of slowing between any of theexposure categories in 1989. However,calculations using common statistical methodsshow significantly higher prevalences of slowingin Group 4 (PR 1.4, 95% CI 0.9–2.1)compared to Group 1. Group 3's prevalence ofslowing was 26% compared to Group 1's18%, but this difference was not statisticallysignificant (p=0.07). Group 5 had the sameprevalence of slowing (18%) as Group 1 in1989; the prevalence of slowing in Group 5was 29% in 1984. The drop in prevalence ofslowing in Group 5 between 1984 and 1989might be explained by the higher drop-out rateamong cases in Group 5 compared to Group 1(PR 2.9, 95% CI 1.3–6.6). This was notaddressed by the authors.

Punnett et al. [1985] compared the symptomsand physical findings of CTS in 162 womengarment workers and 76 women hospitalworkers such as nurses, laboratory technicians,and laundry workers. Eighty-six percent of the

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garment workers were sewing machineoperators and finishers (sewing and trimming byhand). The sewing machine operators weredescribed as using highly repetitive, low forcewrist and finger motions, whereas finishingwork also involved shoulder and elbowmotions. The exposed garment workers likelyhad more repetitive jobs than most of thehospital workers. CTS symptoms occurredmore often among the garment workers (OR2.7, 95% CI 1.2–7.6) compared to the hospitalworkers. There was a low participation rate(40%) among the hospital workers.

Stetson et al. [1993] conducted nerveconduction studies on 105 administrative andprofessional workers, and 240 automotiveworkers. Hand/wrist forces were estimatedbased on weights of tools and parts andsystematically recorded observations of one ormore workers on each job. Jobs were thenranked according to grip force cutoffs: <6 lb,>6 lb, >10 lb. Median nerve measures differedamong the groups: index finger sensoryamplitudes were lower and distal sensorylatencies were longer among automotiveworkers in jobs requiring grip force >6 lb and>10 lb, compared to those requiring less than 6lb (p<0.05 for all). At the wrist, median sensoryamplitudes were also lower and distal mediansensory latencies were also longer among the>6 lb, and the >10 lb exposure groups (p<0.05for 3 of 4 differences). Age, height, and fingercircumference were included in statisticalmodels. The automotive workers were thendivided into two groups, symptomatic (n=103)and asymptomatic (n=137), based on whetheror not they met standard interview criteria forCTS symptoms. When comparisons weremade to the administrative and professionalworkers, 15 of 16 measures of median and

ulnar nerve function showed lower amplitudesand longer latencies (p<0.05) among theasymptomatic automotive workers; differenceswere greater between the symptomaticautomotive workers and the white collarworkers. The symptomatic automotive workershad lower amplitudes and longer latencies for 5of 6 median sensory measures (p<0.05),compared to the asymptomatic automotiveworkers; there were no significant differences inulnar nerve function between these two groups.Asymptomatic automotive workers had“healthier” median nerves than automotiveworkers with CTS symptoms, but there wereno differences between these 2 groups in ulnarnerve function, suggesting that the casedefinition was specific for CTS.

Of the studies that addressed CTS, almost allexamined occupations and jobs in which forcewas combined with another exposure factor(such as repetition or awkward postures).Chiang et al. [1993] estimated exposure tohand/wrist force independent of repetitivenessand found statistically significant RRs for CTSranging from 1.6 to 1.8. Estimates of RR thatwere not statistically significant ranged from 0.4to 6.7 [McCormack et al. 1990; Osorio et al.1994]. Relative risk estimates for CTS amongworkers exposed to a combination of forcefuland repetitive hand/wrist exertions ranged from1.0 to 15.5 [Nathan et al. 1988, 1992a;Silverstein et al. 1987].

Study limitations may impact the interpretationof findings. One limitation to consider is gendereffect. Of the studies listed above reportingstatistically significant associations betweenforceful hand/wrist exertions and CTS, gendereffect was controlled for in the analyses. Otherpotential limitations such as selection factors

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impact the interpretation of the studiesreviewed. Survivor bias can be a concern. Ifworkers with CTS are more likely to leave jobsthat require forceful and repetitive hand/wristexertions than jobs without those demands,then the workers in the highest risk jobs may be“survivors” (those who did not get CTS). Ouranalysis of Nathan’s [1992a] data from afollow-up of industrial workers shows thatcases (with median nerve slowing) were morelikely to drop out of the most highly exposedgroup than the unexposed group, which mightexplain why the RR for high exposuredecreased from 2.0 to 1.0 over a 5-yearperiod. Survivor bias results in anunderestimate of the RR.

Refined or exact measures of exposure toforceful hand/wrist exertions are not alwaysused in epidemiologic studies (e.g., sometimesexposure is based on job category and notactual forceful measurements); this can result insome study subjects being assigned to thewrong exposure category. When this occurs,the usual effect is again to underestimate the RRbetween exposure groups.

Stetson et al. [1993] did not report RRestimates for exposure variables, but theyreported that median sensory amplitudes weresignificantly smaller and distal sensory latencieswere significantly longer in groups with forcefulhand exertions (p<0.05). Age, height, andfinger circumference were included in statisticalmodels.

Temporality, Force and CTS

Temporal issues can usually best be addressedusing longitudinal studies. However, study

limitations, such as survivor bias, can cloud thefindings of even prospective studies. In our re-analysis of Nathan et al.’s [1992a] data, 2 of 3groups exposed to forceful hand/wrist exertionswere more likely to have median nerve slowingwhen nerve conduction testing was repeated 5years later. The highest exposure group had thesame prevalence of slowing as the lowestexposure group in 1989, whereas there hadbeen a higher prevalence rate in 1984. Asdiscussed above, this apparent decrease inprevalence over 5 years can likely be explainedby survivor bias. Our interpretations of the datadiffer from those of the author. Further study isneeded to clarify these issues. To ourknowledge, there is no evidence that workerswith pre-existing CTS are more likely to seekor to be employed in jobs with high forcerequirements. We believe that employmentpractices would, if they had any influence, tendto exclude new hires with CTS from jobs withhigh force requirements for the hand/wrist.

Case definitions in most of the cross-sectionalstudies excluded cases that occurred beforeworking on the current job. This limits CTScases studied to those that occurred followingcurrent exposure. Several of the studiesreviewed also required a minimum time periodof working on the job before counting CTScases. This increases the likelihood thatexposure to forceful hand/wrist exertionoccurred for a sufficient length of time todevelop CTS. There is evidence that CTS is also attributableto nonwork causes (hobbies, sports, othermedical conditions, and hormonal status inwomen, etc.). One issue which deals withtemporality is whether those withnonwork-related CTS would be more likely tobe hired into jobs requiring more forceful

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hand/wrist exertions than those without CTS.Again, it seems unlikely that those withpre-existing CTS would be preferentially hiredinto jobs requiring highly forceful hand/wristexertions.

Consistency of Association for Forceand CTS

Most of the statistically significant estimates ofRR for CTS among workers with exposure toforceful hand/wrist exertions were positive. Nostudies found statistically significant negativeassociations between forceful hand/wristexertions and CTS. One study reported ORsthat were less than one among the groups thatwere described as exposed to repetitive handmovements; chance and study limitationscannot be ruled out as possible explanations forthis finding. The other nonsignificant estimatesof RR were, with one exception, greater thanone.

Statistical significance can be a function ofpower (the ability of a study to detect anassociation when one does exist). In general,larger studies are necessary in order to havesufficient power to detect associations with rarediseases. CTS is a less frequently observeddisorder than tendinitis, for example, and solarger studies are required to detectassociations with confidence.

Coherence of Evidence, Force andCTS

Please refer to the Repetition and CTS Section.

Exposure-Response Relationship,Force and CTS

None of the studies reviewed demonstrated

that increasing levels of force alone resulted inincreased risk for CTS. The only evidence foran increasing risk for CTS that can beattributed to increasing levels of force alone isfrom a comparison across 2 studies that usedthe same methods. Chiang et al. [1993] andSilverstein et al. [1987] used the same methodsto measure hand/wrist force requirements andrepetitiveness of jobs. Chiang et al. [1993]used a lower cutoff point (3 kg compared to 4kg) in Silverstein et al.’s [1987] study forclassifying jobs as “high force”; theseinvestigators used identical definitions ofrepetitiveness. Therefore, a comparison of theRR estimates between the 2 studies providessome information about the level of riskassociated with different levels of force. Chianget al. [1993] reported an OR of 2.6 (95% CI1.0–7.3) for the high force and repetitive(HF/HR) (>3 kg) group (limited to females toavoid confounding) compared to the low forceand repetitive (LF/LR) group; whereasSilverstein et al. [1987] reported an OR of15.5 (95% CI 1.7–142) for the HF/HR group(in a statistical model that included gender, age,years on the job, plant and exposure level)compared to the LF/LR group. Thiscomparison provides limited evidence of anincreased RR for CTS with increasing level ofhand/wrist force.

There is more evidence of a dose-responserelationship for CTS with increasing levels offorce and repetition combined. Chiang et al.[1993] reported a statistically significant trendof increasing prevalence of CTS with increasingexposure level (8.2% [LF/LR], 15.3% [HF orHR], and 28.6% [HF/HR], p<0.01). Silversteinet al. [1987] suggested a multiplicative effectwhen exposure to high force and highrepetitiveness were combined (15.5),compared to high force (1.8) or highrepetitiveness (2.7) alone.

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Of the remaining nine studies, seven areconsistent with the combined effect of force andrepetition [Stetson et al. 1993; Moore andGarg 1994; Osorio et al. 1994; Armstrong andChaffin 1979; Nathan et al. 1988; Punnett et al.1985; Baron et al. 1991], one is not[McCormack et al. 1990]; and one is equivocal[Nathan et al. 1992a].

In conclusion, there is evidence that forcealone is associated with CTS. There is strongevidence that a combination of forcefulhand/wrist exertion and repetitiveness areassociated with CTS.

POSTURE AND CTSDefinition of Extreme Postures ForCTSWe selected those studies which addressedposture of the hand/wrist area including thoseaddressing pinch grip, ulnar deviation, wristflexion/extension. Posture is a difficult variableto examine in ergonomic epidemiologic studies.It is hypothesized that extreme or awkwardpostures increase the required force necessaryto complete a task. Posture may increase ordecrease forceful effort; its impact on MSDsmay not be accurately reflected in measurementof posture alone. Reasons that the variable“extreme posture” has not been measured oranalyzed in many epidemiologic studies are: 1)because of the extreme variability of posturesused in different jobs as well as the extremevariability of postures between workersperforming the same job tasks,2) because several studies have taken intoaccount the effects of posture when determiningother measured variables such as force[Silverstein et al. 1987; Moore and Garg1994]; and 3) stature often has a major impacton postures assumed by individual workersduring job activities.

Studies Meeting the Four Evaluation Criteria Two studies fulfilled the four criteria for postureand CTS: Moore and Garg [1994], Silversteinet al. [1987]. The overall study designs arementioned above; the following section willcover the posture assessment.

For the exposure assessment of the posturevariables in the Silverstein et al. [1987] study,three representative workers from eachselected job performing the jobs for at leastthree cycles were videotaped using twocameras. The authors then extrapolated theposture data to non-observed workers.

Moore and Garg [1994] used a wristclassification system similar to that used byStetson et al. [1993], classifying the wrist angleestimated from videotape as neutral, non-neutral or extreme if the flexion/extension anglewas 0° to 25°, 25° to 45° and greater than 45°,respectively; or if ulnar deviation was less than10°, 10° to 20°, and greater than 20°,respectively.

Strength of Association: Posture andCTSSilverstein found no significant associationbetween percentages of cycle time observed inextreme wrist postures or pinch grip and CTS.“CTS jobs” had slightly more ulnar deviationand pinching but these differences were notstatistically significant. The authors noted thatamong all the postural variables recorded, thevariability between individuals with similar oridentical jobs was probably the greatest forwrist postural variables. This individual variationwithin jobs was not taken into account in theanalysis, creating a potential formisclassification of individuals by using thevariable “job category” in the analysis. Theeffect of exposure misclassification is usually todecrease differences between exposure groups

5a-23

and decrease the magnitude of association.

Moore and Garg’s [1994] classification of jobsdid not separate the posture variables fromother work factors, and used posture alongwith other variables to classify jobs into“hazardous” and “safe” categories. The RR ofCTS occurring in hazardous jobs was 2.8 butnot statistically significant (p=0.44).

Studies Not Meeting All Four EvaluationCriteriadeKrom et al. [1990] compared certainexposure factors between 28 CTS cases froma community sample and 128 CTS cases froma hospital (a total of 156 CTS cases) to 473community “non-cases” (n=473). The authorsrelied on self-reported information aboutduration of exposure (hours per week) to CTSrisk factors (flexed wrist, extended wrist,extended and flexed wrists combined; pinchgrasp and typing), with respondents recallingexposure from the present to 5 years prior fromthe questionnaire date. Four groups of durationwere used in the analyses (0; 1–7; 8–19,20–40 hours/week). In this study, the selectionprocess of cases was not consistent. Initially, arandom population sample was used, thenhospital outpatients were used to supplementthe number of CTS cases when numbers werefound to be insufficient. This may be a problemwhen estimating the etiologic role of workload,as cases seeking medical care may cause areferral bias. However, the authors stated thatthey came up with the same relationshipbetween flexed and extended wrist using onlyCTS cases from the population-based data.The risk of CTS was found to increase with thereported duration of activities with flexed wrist(RRs from 1.5 to 8.7, with increasing hours) oractivities with extended wrist (RR from 1.4 to5.4 with increasing hours) over the past 5years, but not for working with a flexed orextended wrist in combination, or working with

a pinched grasp. Given the period of recall forself-reported exposure (0–5 years), and noindependent observation or attributes ofexposure, these results must be interpreted withcaution (meaning that within the limitations ofthe data and conclusions, when considered withother studies that have more stringent methods,the RRs seem consistent and supportive and donot offer alternate conclusions).

Armstrong and Chaffin’s [1979] pilot study offemale sewing machine operators withsymptoms and/or signs for CTS compared tocontrols found that pinch force exertion(exposure measurements estimated from EMG,film analysis) was significantly associated (OR2.0). Pinch force was a combination offactors—posture and forceful exertion. Theauthors reported that CTS-diagnosed subjectsused deviated wrist postures more frequentlythan nondiseased, particularly during forcefulexertions. What is unable to be answered dueto the study design, was whether the deviatedpostures were necessitated due to symptomsand signs of CTS, or the deviated posturescaused or exacerbated the symptoms and signs.

Stetson et al. [1993] found that “grippinggreater than 6 pounds” per hand was asignificant risk factor for median distal sensorydysfunction (an indicator of CTS) when thestudy population was divided into exposed andnon-exposed groups. “Gripping greater than 6pounds” is a variable which combines twowork-related variables, posture and forcefulexertion. As seen with other studies referencedabove, the single work-related variable was notfound to be associated with median nervedysfunction, but the combination of variableswas significant. Looking specifically at wristdeviation in the Stetson et al. [1993] study, themidpalm to wrist sensory amplitude was smallerin the group not exposed to wrist deviation

5a-24

(p=0.04) compared to those exposed to wristdeviation (contrary to what was expected).Also, no significant differences were found inthe mean measurements between nonexposedand exposed groups for use of pinch grip.

Tanaka et al. [1995] analysis of theOccupational Health Supplement of the NHISpopulation survey depended on self-reportedCTS, self-reported exposure factors, andoccupation of the respondent for analysis. Self-reported bending and twisting of the hand andwrist (OR 5.9) was found to be the strongestvariable associated with “medically-calledCTS” among recent workers, followed by race,gender, vibration and age (repetition and forcewere not included in the logistic models).Limitations of self-reported health outcome andexposure do not allow the conclusions of thisstudy to stand alone; however, when examinedwith the other studies, it suggests a relationshipbetween posture and CTS.

The two other studies which examined postureand its relationship to CTS did not focus on thehand and wrist. English et al. [1995] found arelationship between self-reported rotation ofthe shoulder and elevated arm and CTS, an ORof 1.8. Liss et al. [1995] found an OR of 3.7for self-reported CTS comparing risk factorsfrom dental hygienists to dental assistants, withself-reported percent of time the trunk was in arotated position relative to the lower body asone of the factors.

Given these limitations of categorizing posture,three studies [Stetson et al. 1993; Loslever andRanaivosoa 1993; Armstrong and Chaffin1979] using different methods to measureposture and estimate force, found that thecombination of significant force and posturewas significantly related to CTS. Marras andShoenmarklin [1993] also found posture to be

significantly associated with CTS whencomparing jobs where grip strength was threetimes greater than in the low risk jobs. In thosestudies which used self-reports for categorizingposture, the associations were also positive.

Temporal RelationshipThere were no longitudinal studies whichexamined the relationship between extremeposture and CTS. Two cross-sectional studiesthat met the evaluation criteria addressed theassociation between posture and CTS.Silverstein et al. [1987] did not find a significantrelationship between CTS and extremeposture, but exposure assessment was limitedto representative workers; inter-individualvariability limited the ability to identify actualrelationships between postures and CTS. In theStetson et al. [1993] study, the authorsmentioned the limitations of interpretation oftheir posture results due to misclassification ofworkers. They extrapolated exposure data tonon-observed workers, so individual variabilityin work methods and differing anthropometryare not accounted for. These limitations allinfluence outcome, and the conclusions must beinterpreted with caution, and considered alongwith biomechanical and laboratory studies.

Coherence of EvidenceFlexed wrist postures may reduce the area ofthe carpal tunnel thus potentially increasing thepressure in the tunnel with a concomitantincrease in the risk of CTS [Skie et al. 1990;Armstrong et al. 1991]. Marras andShoenmarklin [1993] found that the variables ofwrist flexion, extension, angular velocity, andwrist flexion, extension, angular accelerationdiscriminated between jobs with a high versus alow risk of having an upper extremityreportable injury (an OSHA recordabledisorder due to repetitive trauma). The authorssuggested that this result was due to high

5a-25

accelerations requiring high forces in tendons.Szabo and Chidgey [1989] showed thatrepetitive flexion and extension of the wristcreated elevated pressures in the carpal tunnelcompared to normal subjects, and that thesepressures took longer to dissipate than innormal subjects. Observed repetitive passiveflexion and extension appeared to “pump up”the carpal tunnel pressure; active motion of thewrist and fingers also had an effect over andabove that of the passive motions tested.Laboratory studies demonstrate that carpalcanal pressure is increased from less than5mmHg to more than 30 mmHg during wristflexion and extension [Gelberman et al. 1981].

Exposure-Response Relationship,CTS and PostureFew studies address exposure-responserelationship between CTS and extremeposture. deKrom et al. [1990] reported anincreased risk of CTS with workers reportingincreasing weekly hours of exposure to wristflexion or extension (but not a combination offlexion/extension). Laboratory studies alsosupport a dose-response relationship ofincreased carpal tunnel pressure due toincreasing wrist deviation from neutral [Weisset al. 1995] and pinch force [Rempel 1995].

In conclusion, there is insufficient evidence inthe current epidemiologic literature todemonstrate that awkward postures alone areassociated with CTS.

VIBRATION AND CTSDefinition of Vibration for CTSWe selected studies that addressed manualwork involving vibrating power tools and CTSspecifically.

Studies Meeting the Four Evaluation Criteria Two studies examining the association betweenvibration and CTS fulfilled the four criteria

[Chatterjee 1992; Silverstein et al. 1987].Chatterjee et al. [1982] performed independentexposure assessment of the vibrating tools, andfound the rock drillers to be exposed tovibration between the frequencies of 31.5 and62 Hertz.

Silverstein et al. [1987] is discussed above.Silverstein [1987] had no quantitative measuresof vibration, but observed exposure fromvideotapes and found all jobs with vibrationexposure to be highly repetitive and mostlyforceful jobs.

Studies Not Meeting the Evaluation CriteriaThere are seven studies on Table 5a–4 thatmeet at least one of the four criteria.

In addition, there are 2 clinical case studies ofvibration and CTS [Rothfleish and Sherman1978; Lukas 1970] that were not controlled forconfounders and not referenced in Table 5a–4.Rothfleisch and Sherman [1978] found anexcess of power hand tool users among CTSpatients. Lucas [1970] examined workers usingvibrating hand tools including stone cutters,tunnelers, coal miners, forest workers andgrinders (all with a mean of 14 years exposureto vibration) and found CTS in 21%. He foundthat the prevalence of CTS in some groups wasas high as 33% (neither study had a referentgroup.)

Cannon et al. [1981] found that the self-reported use of vibrating tools, in combinationwith reported forceful and repetitive handmotions, was associated with a greaterincidence of CTS than was repetitive motionalone.

Bovenzi’s study in 1994 compared stoneworkers (145 quarry drillers and 425 stonecarvers) exposed to hand-transmitted vibrationto 258 polishers and machine operators who

5a-26

performed manual activity only not exposed tohand-transmitted vibration. CTS was assessedby a physician, and exposure was assessedthrough direct observation to vibrating tools andby interview. Vibration was also measured in asample of tools.

Strength of Association: Vibrationand CTSChatterjee et al. [1982] found a significantdifference between rock drillers with symptomsand signs of CTS and the controls using thefollowing NCS measurements: median motorlatency, median sensory latency, mediansensory amplitude, and median sensoryduration, all at the p<0.05 level. Based onnerve conduction measurements, they alsofound an OR of 10.9 for rock drillers havingabnormal NCS amplitudes in the median andulnar nerves compared to controls. Bovenzi etal. [1991] found an OR of 21.3 for CTS basedon symptoms and physical exam comparingvibration-exposed forestry operators usingchain-saws to maintenance workers performingmanual tasks. Bovenzi’s study in 1994 found anOR of 0.43 for CTS defined by signs andsymptoms, controlling for several confounders.In the Silverstein et al. [1987] study the crudeOR for high force/high repetition jobs withvibration compared to high force/high repetitionwithout vibration was 1.9, but not statisticallysignificant. This suggested that there may havebeen confounding (the OR was not statisticallysignificant) between high force/high repetitionand vibration. Nilsson et al. [1990] found thatplaters operating tools such as grinders andchipping hammers had a CTS prevalence of14% compared to 1.7% among office workers.Nathan et al. [1988] found a PR of 2.0 (95%CI 1.3–3.4) for slowing of nerve conductionvelocity when grinders were compared toadministrative and clerical workers. Cannon etal. [1981] found an OR of 7.0 for CTS with theuse of vibrating hand tools, although there was

a strong potential for confounding by hand orwrist posture and forceful exertion.

Temporal RelationshipThere were no longitudinal studies whichexamined the relationship between vibrationand CTS.

Consistency in Association All studies on Table 5a–4 examining vibrationand CTS found a significantly positiverelationship between CTS and vibrationexposure. Most studies had ORs greater than3.0, so that results were less likely to be due toconfounding.

Coherence of Evidence and VibrationThe mechanism by which vibration contributesto CTS and tendinitis development is not wellunderstood, probably because vibrationexposure is usually accompanied by exposureto forceful and repetitive movements. Musclesexposed to vibration exhibit a tonic vibrationreflex that leads to increasing involuntarymuscle contraction. Vibration has also beenshown to produce short-term tactilityimpairments which can lead to an increase inthe amount of force exerted during manipulativetasks. Vibration can also lead to mechanicalabrasion of tendon sheaths. Neurological andcirculatory disturbances probably occur

independently by unrelated mechanisms.Vibration may directly injure the peripheralnerves, nerve endings, and mechanoreceptors,producing symptoms of numbness, tingling,pain, and loss of sensitivity. It has been found inrats that vibration has caused epineural edemain the sciatic nerve [Lundborg et al. 1987].Vibration may also have direct effects on thedigital arteries. The innermost layer of cells inthe blood vessel walls appears especiallysusceptible to mechanical injury by vibration. Ifdamaged, these vessels may become less

5a-27

sensitive to the actions of certain vasodilatorsthat require an intact endothelium. The NIOSHCriteria Document on exposure to hand-armvibration NIOSH [1989] quoted Taylor [1982]as follows: “ It is not known whether vibrationdirectly injures the peripheral nerves therebycausing numbness and subsequent sensory loss,or whether the para-anaesthesia of the hands issecondary to the vascular constriction of theblood vessels causing ischemia . . . in the nerveorgans.”

Exposure-Response Relationship,CTS and VibrationIn the studies examined, only dichotomouscategorizations were made, so conclusionsconcerning an exposure-response relationshipcannot be drawn. However, we can seesignificantly contrasting rates of CTS betweenhigh and low exposure groups. Wieslander etal. [1989] found that based on exposureinformation obtained from telephone interviews,CTS surgery was significantly associated withvibration exposure. Exposure for 1–20 yearsgave an OR of 2.7, more than 20 years gave anOR of 4.8.

ConclusionIn conclusion, there is evidence supporting

an association between exposure to vibrationand CTS.

CONFOUNDING AND CTSIt is clear that CTS has several non-occupational causes. When examining therelationship of occupational factors to CTS, it isimportant to take into account the effects ofthese individual factors; that is, to control fortheir confounding or modifying effects. Studiesthat fail to control for the influence of individualfactors may either mask or amplify the effectsof work-related factors. Most of the

epidemiologic studies of CTS that addresswork factors also take into account potentialconfounders.

Almost all of the studies reviewed controlled forthe effects of age in their analysis [Chiang et al.1990, 1993; Stetson et al. 1993; Silverstein etal. 1987; Wieslander et al. 1989; Baron et al.1991; Tanaka et al. 1995, In Press;McCormack et al. 1990]. Likewise, moststudies included gender in their analysis, eitherby stratifying [Schottland et al. 1991; Chiang etal. 1993], by selection of single gender studygroups [Morganstern et al. 1991; Punnett et al.1985] or by including the variable in the logisticregression model [Silverstein et al. 1987;Stetson et al. 1991; Baron et al. 1991].Through selection of the study population andexclusion of those with metabolic diseases,most studies were able to eliminate the effectsfrom these conditions. Other studies did controlfor systemic disease [Chiang et al. 1993; Baronet al. 1991]. Anthropometric factors have alsobeen addressed in several studies [Stetson et al.1993; Nathan et al. 1997; 1992b; Werner etal. 1997]. As more is learned aboutconfounding, more variables tend to beaddressed in more recent studies (smoking,caffeine, alcohol, hobbies). In those olderstudies which may not have controlled formultiple confounders, it is unlikely that they arehighly correlated with exposure, especiallythose with ORs above 3.0. When examiningthose studies that have good exposureassessment, widely contrasting levels ofexposure, and that control for multipleconfounders, the evidence supports a positiveassociation between occupational factors andCTS.

CONCLUSIONSThere are over 30 epidemiologic studies whichhave examined workplace factors and their

5a-28

relationship to CTS. These studies generallycompared workers in jobs with higher levels ofexposure to workers with lower levels ofexposure, following observation ormeasurement of job characteristics. Usingepidemiologic criteria to examine these studies,and taking into account issues of confounding,bias, and strengths and limitations of the studies,we conclude the following:

There is evidence for a positive associationbetween highly repetitive work and CTS.Studies that based exposure assessment onquantitative or semiquantitative data tended toshow a stronger relationship for CTS andrepetition. The higher estimates of RR werefound when contrasting highly repetitive jobs tolow repetitive jobs, and when repetition is incombination with high levels of forcefulexertion. There is evidence for a positiveassociation between force and CTS based oncurrently available epidemiologic data. There isinsufficient evidence for a positiveassociation between posture and CTS. There isevidence for a positive association between

jobs with exposure to vibration and CTS.There is strong evidence for a relationshipbetween exposure to a combination of riskfactors (e.g., force and repetition, force andposture) and CTS. Ten studies allowed acomparison of the effect of individual versuscombined work risk factors [Chiang et al.1990, 1993; Moore and Garg 1994; Nathan etal. 1988, 1992a; Silverstein et al. 1987;Schottland et al. 1991; McCormack et al.1990; Stetson et al. 1993; Tanaka et al. [InPress]. Nine of these studies demonstratedhigher estimates of RR when exposure was to acombination of risk factors, compared to theeffect of individual risk factors. Based on theepidemiologic studies reviewed above,especially those with quantitative evaluation ofthe risk factors, the evidence is clear thatexposure to a combination of job factorsstudied (repetition, force, posture, etc.)increases the risk for CTS. This is consistentwith the evidence that is found in thebiomechanical, physiologic, and psychosocialliterature.

Table 5a-1. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withrepetition

Study (first author andyear)

Risk indicator(OR, PRR, IR or

p-value)*,†Participation rate $$70%

Physicalexamination,and/or nerveconduction

studies

Investigatorblinded to

case and/orexposure

status Basis for assessing

hand exposure to repetition

Met all four criteria:

Chiang 1990 1.87† Yes Yes Yes Observation or measurements

Chiang 1993 1.1 Yes Yes Yes Observation or measurements

Moore 1994 2.8 Yes Yes Yes Observation or measurements

Osorio 1994 6.7 Yes Yes Yes Observation or measurements

Silverstein 1987 5.5† Yes Yes Yes Observation or measurements

Met at least onecriterion:

Barnhart 1991 1.9–4.0† No Yes Yes Observation or measurements

Baron 1991 3.7 No Yes Yes Observation or measurements

Cannon 1981 2.1 NR‡ Yes NR Job titles or self-reports

English 1995 0.4 Yes Yes Yes Job titles or self-reports

Feldman 1987 2.26† Yes No NR Observation or measurements

McCormack 1990 0.5 Yes Yes NR Job titles or self-reports

Morgenstern 1991 1.88 Yes No No Job titles or self-reports

Nathan 1988 1.0 NR Yes NR Observation or measurements

Nathan 1992a 1.0 No Yes NR Observation or measurements

Punnett 1985 2.7† No Yes NR Job titles or self-reports

Schottland 1991 2.86†,1.87

NR Yes NR Job titles or self-reports

Stetson 1993 NR Yes Yes NR Observation or measurements

Weislander 1989 2.7† Yes Yes No Job titles or self-reports

Met none of the criteria:

Liss 1995 5.2 3.7†

No No No Job titles or self-reports

*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. ‡Not reported.

5a-29

Table 5a-2. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated with force

Study (first author and year)

Risk indicator(OR, PRR, IR,

or p-value)*,†Participation rate $$70%

Physicalexamination,and/or nerveconduction

studies

Investigator blinded tocase and/orexposure

status Basis for assessing

hand exposure to force

Met all four criteria:

Chiang 1993 1.8† Yes Yes Yes Observation or measurements

Moore 1994 2.8 Yes Yes Yes Observation or measurements

Osorio 1994 6.7 Yes Yes Yes Observation or measurements

Silverstein 1987 15.5† Yes Yes Yes Observation or measurements

Met at least one criterion:

Armstrong 1979 2.0† NR‡ No No Observation or measurements

Baron 1991 3.7 No Yes Yes Observation or measurements

McCormack 1990 0.4-0.9 Yes Yes NR Job titles or self-reports

Nathan 1988 1.7-2.0† NR Yes NR Observation or measurements

Nathan 1992a 1.0, 1.4†, 1.6 No Yes NR Observation or measurements

Punnett 1985 2.7† No Yes NR Job titles or self-reports

Stetson 1993 NR† Yes Yes NR Observation or measurements

*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.

5a-31

Table 5a-3. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withposture

Study (first author andyear)

Risk indicator(OR, PRR, IR,

or p-value)*,†Participato

n rate$$70%

Physicalexamination,and/or nerveconduction

studies

Investigator blinded to

case and/orexposure

status Basis for assessing

hand exposure to posture

Met all four criteria:

Moore 1994 2.8 Yes Yes Yes Observation or measurements

Silverstein 1987 NR‡ Yes Yes Yes Observation or measurements

Met at least one criterion:

Armstrong 1979 2.0† NR No No Observation or measurements

deKrom 1990 5.4† Yes Yes NR Job titles or self-reports

English 1995 1.8† Yes Yes Yes Job titles or self-reports

Stetson 1993 NR† Yes Yes NR Observation or measurements

Tanaka 1995 5.9† Yes No No Job titles or self-reports

Met none of the criteria:

Liss 1995 3.7† No No No Job titles or self-reports

*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus repetition, force, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.

5a-33

Table 5a-4. Epidemiologic criteria used to examine studies of carpal tunnel syndrome (CTS) associated withvibration

Study (first author andyear)

Risk indicator(OR, PRR, IR,

or p-value)*,†Participation

rate $$70%

Physicalexamination,and/or nerveconduction

studies

Investigator blinded tocase and/orexposure

status Basis for assessing hand

exposure to vibration

Met all four criteria:

Chatterjee 1992 10.9† Yes Yes Yes Observation or measurements

Silverstein 1987 5.3† Yes Yes Yes Observation or measurements

Met at least one criterion:

Bovenzi 1991 21.3† NR‡ Yes Yes Observation or measurements

Bovenzi 1994 3.4† Yes Yes No Observation or measurements

Cannon 1981 7.0† NR Yes NR Job titles or self-reports

Färkkilä 1988 NR† NR Yes NR Job titles or self-reports

Koskimies 1990 NR† NR Yes No Observation or measurements

Tanaka In Press 1.8† Yes No No Job titles or self-reports

Weislander 1989 3.3† Yes Yes No Job titles or self-reports

*Some risk indicators are based on a combination of risk factors—not on vibration alone (i.e., vibration plus repetition, posture,or force). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.

5a-35

(Continued)

Table 5a–5. Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

Armstrong and Chaffin1979

Case-control

18 female sewingmachine operators withCTS histories comparedto 18 female sewingmachine operatorswithout CTS histories.

Outcome: CTS defined ashistory of symptoms, surgicaldecompression of the mediannerve, positive Phalen’s test, orthenar atrophy.

Exposure: Hand/wristpostures and estimation offorearm flexor force in variouswrist and hand posturesassessed by film analysis andEMG.

Õ Õ For pinch forceexertion: 2.0

For handforce: 1.05

1.6-2.5

1.0-1.2

Participation rate: Not reported.

All cases of CTS diagnosed prior tostudy in working sewing machineoperators, may cause referral biasin estimating role of workload.

Subjects excluded if history offractures, metabolic or soft tissuedisease.

No association found betweenhand size or shape and CTS.

CTS diagnosed subjects useddeviated wrist more frequently thannon-diseased, particularly duringforceful exertions.

5a-37

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Barnhartet al. 1991

Cross-sectional

Ski manufacturingworkers: 106 withrepetitive jobs comparedto 67 with non-repetitivejobs.

Outcome: CTS determined by:(1) Case 1: Electro-diagnosisof median-ulnar difference(latency on response time);(2) Case 2: Either Tinel's orPhalen's test and electro-diagnosis; (3) Case 3: Everhaving symptoms of hand pain,tingling, numbness, ornocturnal hand pain and Tinel'sor Phalen's test and electro-diagnosis.

Exposure: Jobs classified asrepetitive and non-repetitive. Repetitive jobs entailedrepeated or sustained flexion,extension, or ulnar deviation ofthe wrist by 45E, radialdeviation by 30E, or pinch grip(determined by observation).

Case 1:34%

Case 2:15.4%

Case 3: 32.5%

19%

3.1%

18.2%

1.9

3.95

1.6

1.0-3.6

1.0-15.8

0.8-3.2

Participation rate: 70% (repetitivejobs), 64% (non-repetitive jobs).

Examiner blinded to subject’s jobstatus but clothing may have biasedobservations.

Controlled for age and gender.

Found for both right and left handof those with repetitive jobs; meandifference between distal sensorylatencies of median and ulnarnerves were primarily due to ashorter mean sensory latency ofthe ulnar nerve.

There was no difference in mediannerve distal sensory latenciesbetween groups.

Hormonal status, systemic diseaseincluded in questionnaire.

Diabetes significantly more frequentin those with CTS than without(p=0.01).

5a-38

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Baron et al.1991

Cross-sectional

119 female grocerycheckers vs. 56 otherfemale grocery storeemployees (comparisongroup).

Outcome: CTS case definedas having moderate to severesymptoms of pain, stiffness,numbness, tingling. Symptomsbegun after employment in thecurrent job; lasted > one weekor occurred > once a monthduring the past year; no historyof acute injury to part of bodyin question and a positivephysical exam of eitherPhalen's or Tinel's test.

Exposure: Based on jobcategory, estimates ofrepetitive, average, and peakforces based on observed andvideotaped postures, weight ofscanned items, and subjectiveassessment of exertion.

Exposure level in checkers:Average forces: LowPeak force: MediumRepetition: Medium

Exposure level in referents:Average force: MediumPeak force: Medium to lowRepetition: Medium.

11% 4% 3.7 0.7-16.7 Participation rate: 85% checkers;55% non-checkers in field study. Following telephone survey 91%checkers and 85% non-checkers.

Adjusted for duration of work.

Total repetitions/hr ranged from1,432 to 1,782 for right hand and882 to 1,260 for left hand.

Multiple awkward postures of allupper extremities recorded but notanalyzed in models.

Examiners blinded to worker’s joband health status.

Controlled for duration of work,hobbies.

5a-39

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Bovenziet al. 1991

Cross-sectional

65 vibration-exposedforestry operators usingchain-saws compared toreferents composed of31 maintenance workers(electricians, mechanics,and painters).

Outcome: CTS cases definedas having symptoms of pain,numbness, or tingling in themedian nerve distribution, andphysical exam findings ofTinel's or Phalen's test,diminished sensitivity to touchor pain in 3½ fingers on radialside, weakness in pinching orgripping.

Exposure: Direct observationof awkward postures, manualforces, and repetitivenessevaluated via checklist. Thefocus of the study was tocompare vibration-exposedworkers to controls doingmanual work. Vibrationmeasured from two chain-saws. Vibration exposure foreach worker assessed interms of 4-hr energy-equivalent frequency-weightedacceleration according to ISO5349.

38.4% 3.2% 21.3 (adjusted) p=0.002 Participation rate: Not reported.

Examiners blinded to case status.

Controlled for age and ponderalindex (height and weight variable). Metabolic disease also considered.

Controls also found to have severalrisk factors for MSDs atwork—static arm and handoverload, overhead work, stressfulpostures, non-vibrating hand-tooluse.

Controls had a greater proportion oftime in work cycles shorter than30 sec than forestry workers.

Chain saw operators workedoutdoors and were exposed tolower temperatures thanmaintenance workers.

5a-40

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Bovenzi andthe ItalianGroup 1994

Cross-sectional

Case group: Stoneworkers employed in9 districts in Northernand Central Italy;145 quarry drillers and425 stone carversexposed to vibration.

Referent group:Polishers and machineoperators (n=258) whoperformed manualactivity but were notexposed to hand-transmitted vibration.

All stone workersemployed in 6 districtsparticipated in the survey(n=578, 69.8%),whereas, in the threeother districts they wereselected on basis ofrandom sampling of thequarries and mills in thegeographic areas(n=250, 30.2%).

Outcome: CTS assessed byphysician assessment. CTSdefined as symptoms,(1) parathesias, numbness, orpain in median nervedistribution; (2) nocturnalexacerbation of symptoms andpositive Tinel's or Phalen's test.

Exposure: Direct observationof vibrating tools assessed byinterview. Vibration measuredin a sample of tools.

8.8% 2.3% 3.4 1.4-8.3 Participation rate: 100%. “All theactive stone workers participated inthe study, so self-selection wasnot a source of bias.”

Physician administeredquestionnaires containing workhistory and examinations, sounlikely to be blinded to casestatus.

Adjusted for age, smoking, alcoholconsumption, and upper limbinjuries.

Leisure activities and systemicdiseases included in questionnaire.

Univariate analysis showed noassociation between systemicdiseases and vibration so were notcriteria for exclusion.

Dose-response for CTS and lifetimevibration exposure not significant.

5a-41

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Cannon et al.1981

Case-control

Aircraft engine workersat 4 plants: 30 CTScases identified throughworker’s compensationclaims and medicaldepartment recordsduring a 2-year periodcompared to 90 controlsfrom the same plant,16 workers receivingcompensation benefitsfor treatment of CTS, and14 cases who had notreceived compensationbenefits.

Three controls randomlychosen from the sameplant for each CTS case.

Outcome: CTS cases identifiedthrough worker’scompensation claims andmedical department recordsduring a 2-year period.

Exposure: Based on jobcategory, years on the job,identified through recordreview and interviews.Exposure to vibrating tools,repetitive motion.

Buffing, grinding, and handtools were measured with anaccelerometer and found to bein the range of 10 to 60 Hz.

Õ Õ For vibratinghand tool use:7.0

For repetitivemotion tasks: 2.1

History ofgynecologicsurgery:3.7

Years on thejob:0.9

3.0-17

0.9-5.3

1.7-8.1

0.8-1.0

Participation rate: Participation rateunable to be calculated from datapresented. 30 cases identifiedthrough record review of 20,000workers.

Cases and controls on gender.

Controlled for gynecologic surgery,race, diabetic history, years on thejob, use of low-frequency vibratingtools.

Information obtained through self-administered questionnaires andpersonal interviews on cases andcontrols on age, sex, race, weight,occupation, years employed,worker compensation status,history of metabolic disease,hormonal status of females, historyof gynecologic surgery.

Number of years employedsignificantly different among cases(5.5 years) and controls(11.7 years). Range of yearsemployed among cases included0.1 year to 28 years.

5a-42

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Chatterjeeet al. 1982

Case-control

16 rock drillers comparedwith 15 controls.

Outcome: CTS wasdetermined by symptoms fromquestionnaire and interview bymedical investigator, clinicalexams carried out blindly, andnerve conduction studies. ForTable 5-7, CTS based solely onNCS results; Table 5-9 basedon symptoms and NCS.

Exposure: To vibration carriedout by measurement ofvibration spectra of the rockdrills and observation of jobs. Exposed group were thoseminers who regularly usedrock-drills in the fluorsparmines or other miners usingsimilar rock-drills. Exposurevaried from 18 months to25 years (mean 10 years). The rock drillers were exposedto vibration level in excess ofthe damage level criterionbetween the frequencies of31.5 and 62 Hz.

44% 7% Abnormalamplitudes ofdigital-actionpotentials fromfingerssupplied by themedian andulnar nerves;the OR invibrationexposed vs.controls:OR=10.89 1.02-524

Participation rate: 93%.

Examiners blinded to case status.

Groups standardized for age andgender.

Exclusionary criteria: History ofconstitutional white finger,secondary causes of Raynaud’sphenomenon, > one laceration orfracture in the hands or digits,severe or complicated injuryinvolving nerve or blood vessels orsignificant surgical operation,history of exposure to vibrationfrom tools other than rock drills.

Significant differences foundbetween controls and vibrationgroup for symptoms of numbnessand tingling: median motor latency;median sensory latency; mediansensory amplitude; median sensoryduration. All at the p< 0.05 level.

Skin temperature controlled for inNCVs.

5a-43

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Chiang et al.1990

Cross-sectional

207 active workers from2 frozen food plantsdivided into 3 groups: (1) low-cold, low-repetition (comparisongroup, mainly office staffand technicians, n=49),(2) low-cold, high-repetition (non-frozenfood packers, n=37),(3) high-cold, high-repetition (frozen foodpackers, n=121).

Outcome: CTS defined assymptoms of numbness, pain,tingling in the fingersinnervated by the mediannerve, onset since work incurrent job, no relationship tosystemic disease or injury andphysical exam of Tinel's test orPhalen's sign. Nerveconduction testing wasperformed on motor andsensory nerves of both upperlimbs. If subject had abnormalresults and symptoms andphysical exam findings, wasconsidered CTS. If nosymptoms, considered assubclinical CTS.

Exposure: Job analysesconducted by industrialhygienist, to cold and repetitionassessed by observation.

Highly repetitive jobs had cycletimes <30 sec. >50% of cycletime cold exposure wasdefined as whether the jobrequired hands to be locallyexposed to cold. The meanskin temperature of their handswas in the range of 26 to28EC, even with wearinggloves.

Group 2: 40.5%clinical plus8.1%sub-clinical

Group 3: 37.2%clinical plus22.3%sub-clinical

Group 1:4% clinicalplus 2%sub-clinical

Group 2 vs.Group 1:OR=8.28

Group 3 vs.Group 1:OR=11.66

LogisticRegressionModel:Cold:OR=1.85(p<0.22)

Repetitiveness:OR=1.87(p<0.018)

Cold xRepetitive-ness:OR=1.77(p<0.03)

1.18-58.3

2.92-46.6

Participation rate: Not specificallymentioned, however, paper statesthat “in order to prevent selectivebias, all of the employees in thefactories were observed initially.”

Examiners blinded to exposurestatus and medical history.

Controlled for age, sex, and lengthof employment. Interaction termstested.

Excluded subjects with diabetes,thyroid function disorders, historyof forearm fracture, unspecifiedpolyneuropathy, rheumatoidarthritis.

Workers in cold groups woregloves and exerted higher forcesthan workers in non-cold groups. Force was not evaluated in thisstudy. Confounding is possibleaccording to authors.

CTS was independent of age andlength of employment. Authorsconsidered this to be due to healthyworker effect.

OR for group 1 vs. group 2 is 8.3(1.2-58.3) when adjusted for sexbut 2.2 (0.2-21.1) when adjustedfor sex, age, and length ofemployment suggesting survivalbias.

5a-44

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Chiang et al.1993

Cross-sectional

207 fish processingworkers divided in3 groups: (1) low-force,low-repetition(comparison group,n=61); (2) high-force orhigh-repetition (n=118);(3) high-force and high-repetition (n=28).

Outcome: CTS defined ashaving symptoms ofnumbness, pain, or tingling inthe fingers innervated by themedian nerve, onset after jobbegan, and no evidence ofsystemic disease or injury andphysical exam findings ofpositive Tinel's sign or Phalen'stest.

Exposure: Assessed byobservation and recording oftasks and biomechanicalmovements of 3 workers, eachrepresenting 1 of 3 studygroups. Highly repetitive jobswith cycle time <30 sec or>50% of cycle time performingthe same fundamental cycles. Hand force from EMGrecordings of forearm flexormuscles. Classification ofworkers into 3 groupsaccording to the ergonomicrisks of the shoulders andupper limbs: Group 1: low-repetition and low-force; Group2: high-repetition and high-force; Group 3: high-repetitionor high-force.

Group 2 (Male): 6.9%

Group 2(Female):18.0%

Group 3 (Male): 0.0%

Group 3(Female): 36.4%

Group 1(Male):3.1%

Group 1(Female):13.8%

2 vs. 1 (male): OR= 2.2

2 vs. 1(female):OR=1.3

3 vs. 1 (male):Õ

3 vs. 1(female):OR=2.6

Repetition:OR=1.1

Force:OR=1.8

Repetition andforce:OR=1.1

Male vs.female:OR=2.6

0.2-22.0

0.5-3.5

Õ

1.0-7.3

0.7-1.8

1.1-2.9

0.7-1.8

1.3-5.2

Participation rate: Paper stated thatall of the workers who entered thefish-processing industry beforeJune 1990 and were employedthere full-time were part of thecohort.Workers examined in randomsequence to prevent observer bias;examiners blinded to case status.Analysis controlled for age,stratified by gender.Contraceptive use (females):significant (OR=2.0, 95% CI 1.2 to5.4); tubal ligation not significant.Workers with hypertension,diabetes, history of traumaticinjuries to upper limbs, arthritis,collagen diseases excluded fromstudy group.No significant age difference inexposure groups.Physician-observed cases about½ the prevalence of symptoms ofelbow pain (9.8 vs. 18.0; 15.3 vs.19.5; 35.7 vs. 17.9).Dose-response for symptoms bothin the hand and in the wrist(p<0.03) and physician-observedCTS (p<0.015).Age, gender, repetitiveness,forceful movement of upper limbsand interaction of repetitivenessand forceful movement calculatedin logistic regression.Significant trend for duration ofemployment in <12 months but not12 to 60 months or >60 months.

5a-45

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

deKrom et al.1990

Nestedcasecontrol

28 CTS cases from acommunity sample and128 CTS cases from ahospital (total n=156)compared to communitynon-cases (n=473).

Participants blinded toaim of study—told it wasabout “general health.”

Outcome: Tingling pain andnumbness in mediandistribution, frequency$2/week, awakened at nightand nerve conduction studies.Motor latency < 4.5 months,different median to ulnar DSL <4.0 months, controlled fortemperature.

CTS diagnosed by clinicalhistory and neurophysiologicaltests.

Exposure: Awkwardhand/finger postures and pinchgrasps assessed byquestionnaire: Self-reportedinformation about duration ofexposure (hr/wk) to flexedwrist, extended wrist,extended and flexed wristcombined, pinched grasp. Typing hr categorized as0, 1 to 7, 8 to 19, 20 to40 hr/wk of exposure 0 to 5years ago, responsestruncated at 40 hr/wk.

5.6%prevalencein thegeneralpopulation(28 casesfrom501 subjectcommunitysample)

Õ For work:20 to 40 hr/wkwith flexedwrist: OR=8.7

For work:20 to 40 hr/wkwith extendedwrist: OR= 5.4

3.1-24.1

1.1-27.4

Participation rate: 70% responserate obtained for both hospital andcommunity samples.Controlled for age, weight, slimmingcourses, gender, and checked forinteractions.Cases seeking medical care maycause referral bias in estimatingetiologic role of work-load. However, authors came up withsame relationship between flexedand extended wrist using only CTScases from population-based data.The associations from this studyare based on very small samplesizes. >64% of cases reported 0hr/wk to each of the exposures.In random sample, age, and sexstratified, included twice as manyfemales as males.No significant relationship betweenpinch grasp or typing.Dose-response found for durationof activities with flexed or extendedwrist statistically significant; dose-response relationship for bothpresent but not statisticallysignificant.Typing hr not significant but verysmall numbers (<5 in comparisongroups); may have been unable todetect a difference.Females with hysterectomy withoutoophorectomy significantlyincreased risk, PRR=2.0 (1 to 3.6),compared to females not operatedon; increase may be detection bias.Wrist fractures, thyroid disease,rheumatism, and diabetes notsignificant for CTS.Varicosis significant risk for males12.0 (3.6-40.1).Oral contraceptives not significantlyassociated with CTS.

5a-46

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

English et al.1995

Case-control

Cases: CTS patients(n=171) ages 16 to 65years from orthopedicclinics. Controls:(n=996) 558 males and438 females attendingthe same clinicsdiagnosed withconditions other thandiseases of the upperlimb, cervical, or thoracicspine; ages 16 to 65years.

Outcome: CTS based onagreed criteria diagnosed byorthopedic surgeons usingcommon diagnostic criteria (notspecified).

Exposure: Based on self-reported risk factors at work:questions addressed:awkward postures, grip types,wrist motions, lifting, shoulderpostures, static postures, etc.and job category.

Õ Õ Rotatingshoulder withelevated armand CTS: OR=1.8

Repeatedfinger tappingand CTS: OR=0.4

1.2-2.8

0.2-0.7

Participation rate: 96%.

Due to design of study (casesselected by diagnoses), blinding ofexaminers not an issue.

Adjusted for height, weight, andgender.

Significant negative associationwith height and presentation at theclinic as a result of an accident andCTS.

A significantly positive associationwith height.

Included “frequency of movements”in regression analysis.

5a-47

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Färkkiläet al. 1988

Cross-sectional

79 chain saw usersrandomly selected from186 forestry workerswith >500 hr ofsawing/year.

Outcome: CTS based on nerveconduction studies, motor andsensory conduction velocity,distal and proximal latencies,Tinel’s and Phalen's tests andsubjective symptoms.

Exposure: Chain saw vibrationnot measured. Duration ofchain saw use determined byinterview.

26% Õ Significantcorrelationbetweennumbness inthe hands(r=0.38,p<0.05) andCTS andmuscle fatigue(r=0.47,p<0.05) andCTS.

Õ Participation rate: 100% ofprofessional forestry workers.

Significant correlation between CTSand HAVs found.

Randomly selected from EMG out of186.

Alcohol consumption did notcorrelate with numbness in thehands or arms (r=0.14, p=NS) orsensory disturbances.

Only motor nerve recordings wereanalyzed for this study.

5a-48

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Feldmanet al. 1987

Cross-sectionalforsymptomsurvey

Pro-spectivefor nervecon-ductionstudies

586 electronics workersat a manufacturing firmwith 700 employees.

Outcome: Based onquestionnaire survey and insome an abbreviatedneurologic examination thatinvolved tests of handsensation, finger grip, andstrength of thenar muscles. Tinel’s and Phalen's done.“Standard nerve conduction” ofleft and right median nerves.

Exposure: Two subjectsrandomly selected forbiomechanical analyses fromeach of four high-risk areas,determined from questionnaireand walk-through observationsof tasks involving repetitiveflexion, extension, pinching,and deviated wrist postures. Videotaping andelectromyography done.

Highly repetitive job taskdefined as <30 sec cycle or>50% of cycle performing thefundamental cycle.

Wrist posture characterized interms of flexion and extension: >45 flexed, 15 to 45 flexion,neutral, 15 to 45 extension, and>45 extension and deviation. Hand posture characterized by6 types of grip.

No quantitative measures ofvibration were obtained.

Wristtingling andnumbness:18%

Wristtingling andnumbness:8.7%

Numbness andtingling infingers:OR=2.26

High-risk vs.low-risk jobs:p<0.005

1.4-4.46

Participation rate: 84%.Examiners blinded to case andexposure status: Not stated.Analysis not controlled forconfounders.Questionnaire obtained data onpast medical history, exposure toneurotoxins, cigarettes, hobbies,and symptoms.For nerve conduction testing, thetemperature of limbs was monitoredand controlled for.More females were in high-riskareas and jobs than males. There were no workers >60 yearsold in high-risk group. There were34 workers >60 years incomparison groups.Rheumatoid arthritis more prominentin low-risk group (8.2%) than high-risk (2.4%) group.Nerve conduction in high-riskworkers performed year 1 andyear 2. Right sensory amplitudeabnormal (<8µV) in 22% ofworkers at year 1 and 35.5% atyear 2. Left sensory amplitudeabnormal in 16.7% and 29% atyear 2.Most apparent changes (increases)seen in bilateral sensory velocitiesand motor latencies (abnormal>4.5). Right motor latency abnormalin 8% at year 1 and 11% in year 2. Left motor latency abnormal in 2%in year 1 and 23% at year 2.Authors offered parameters forstaging CTS in high-risk subjects (0to 4 stages).

5a-49

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Franklinet al. 1991

Retro-spectivecohort: from1984 to1988

Workers in WashingtonState (n=1.3 million full-time workers in 1988).

Worker’s compensationdata for WashingtonState, usingcompensable (time loss)and non-compensableclaims for January 1984to December 1988.

Outcome: Assessed usingworkers’ compensation claimsfor CTS using ICD codes 354.0and 354.1. Incident claim wasthe first appearance of a paidbill for claimant with aphysician diagnosis. Algorithmwas developed to identifyunique claimants whichremoved multiple claims.

Exposure: Not measured. Workers in the same industrialclassification assumed toshare similar workplaceexposures.

25.7 claims/1,000 FTEs(oyster andcrabpackers)

23.9 claims/1,000 FTEs(meat andpoultryworkers)

1.74claims/1,000 FTEs(industrywide rate)

14.8 (oysterand crabpackers)

13.8 (meat andpoultryworkers)

11.2- 19.5

11.6- 16.4

Participation rate: This is a recordsreview so it does not apply.

Among claimants, the female-to-male ratio was 1.2:1.

Mean age of claimants was 37.4.

Diagnosis and data entry errorscomprised 25% of CTS surgeryclaims—cases were not coded asCTS.

82% of claims were true cases ofCTS.

5a-50

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Koskimieset al. 1990

Cross-sectional

217 forestry workerswho used chain saw>500 hr during previous3 years.

Outcome: 125 randomlyselected for EMG of sensoryand motor nerves both hands.

CTS diagnosis based onsymptoms, exclusion of otherconditions, results of Phalen’sand Tinel’s test, and findings insensory and motor nerve EMG.

Exposure: Number of years ofvibration exposure (onlyworkers who had 500 hrduring previous 3 years wereincluded.

Activevibration:5% whitefinger

CTS: 20%

Alcoholconsumptionand CTS casesr=0.15

Vibrationexposure timeand motor NCVin mediannerve of righthand: r=-0.27but not lefthand: r=-0.12

Exposure timewith bothmotor NCV inulnar nerve ofright handr=-0.26 and lefthand r=-0.39.

Distal latenciesin mediannerve andexposure inright handr=0.17; left handr=0.21.

Numbness andsensory NCSof mediannerve; righthand r=0.679; left handr=0.53.

p=NS

p=0.01

p=NS

p=0.05

p<0.001

p=0.05

p=0.05

p<0.001

p<0.01

Participation rate: Not reported.

Examiners may not have beenblinded to exposure status becauseof design of study.

No comparison group becausestudy was part of longitudinal studyof workers followed since 1972.

Most of 25 CTS workers had mildsymptoms at work despite severereduction of sensory NCS ofmedian nerve.

Males with primary Raynaud’sdisease, rheumatoid arthritis,diabetes, or positive urine glucoseslide test results excluded fromstudy.

12 (48%) of those with CTS hadbilateral diagnosis. The authorsstated that the left hand is thedominant working hand in sawing,the right hand acting more to directthe saw during the operation.

5a-51

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Liss et al.1995

Cross-sectional

1,066 of 2,142 dentalhygienists from OntarioCanada DentalHygienists Associationcompared to referentgroup, 154 of 305 dentalassistants.

Outcome: Mailed survey,2 CTS case definitions:(1) based on positive responseto "told by a physician that youhad CTS", (2) if during last 12months, for >7 daysexperienced numbness andtingling, pain, or burning indistribution of median nerve,night pain or numbness inhands, and no previouswrist/hand injury.

Exposure: Based on mailedsurvey: Length of practice,days/wk worked, patients/day,patients with heavy calculus,percent of time trunk in rotatedposition relative to lower body,instruments used, hr oftyping/wk, type of practice.

Respondertold thatthey hadCTS: 7%

Question-naire basedCTS: 11%

Respondertold thatthey hadCTS: 0.9%

Question-nairebasedCTS: 3.0%

OR=5.2

OR=3.7

0.9-32

1.1-11.9

Participation rate: 50% responserate from both groups.

Study population >99% female.

OR were age adjusted.

Confounders considered includedtyping, hobbies, and takingestrogens.

5a-52

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Loslever andRanaivosoa1993

Cross-sectional

17 selected jobs withfrequent and repeatedabsences of workersdueto CTS investigated atthe request ofoccupational doctors andmanagers. Biomechanical datarecorded on a number ofworkers from each job,ranging from 1 to4 workers. Involving961 workers.

Outcome: Occupationalphysician from each factoryinvolved in the study completedquestionnaire concerning eachjob and the number of CTScases. The prevalence of CTSwas then calculated from ratioof CTS cases and total numberof employees that worked atthat place.

Exposure: Videotaping ofmovements, use of vibratingtools, and two measurementtechniques used: (1) Flexion-extension measurements: Subjects recorded at severalpoints during the day for15 min. An angle meter used tomeasure flexion-extensionangles of the wrist: Rated highflexion, low flexion, lowextension, and high extensionusing fuzzy cutting functions. Each modality characterized byits arithmetic mean and itsrelative duration. (2) Force:Electromyography used; valuesunder 2 daN considered as lowforces. Calculated time spentover 2 daN, maximal force,number of peak exertions, andthe arithmetic mean of the nvalues during a period.

Meanprevalencerate amongjobs (jobschosen atworkplaceswhere CTShad beenreported):35% (range8 to 66%);prevalenceof CTS inboth hands:20%

High force withhigh flexionand CTS:r=0.62

High force andhigh extensionand CTS:r=0.29

Participation rate: Cases selected.

Occupational doctor suppliedinformation on gender, age, yearson the job, hand orientation, has orhas not contracted CTS.

Subjects spent 60 to 80% of theirtime in extension ranging from 13 to30E.

Vibratory tools more often used intasks with high prevalence of CTS(27%) than in ones with lowprevalence of CTS (13%).

92% of population were female.

Non-standard data analysisapproaches, no statistical testing.

Examiners not blinded.

Authors believe higher rate of CTSin both hands (20%) vs. dominanthand (100%) argue for non-occupational factors being moreimportant.

5a-53

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Marras andShoenmarklin1993

Cross-sectional

40 volunteers at a highlyrepetitive, hand-intensive industrial jobsin 8 different plants. Halfthe workers wereemployed in jobs that hadOSHA recordablerepetitive traumaincidents, half theworkers were in jobswith no history ofrecordable repetitivetrauma incidents. Twosubjects from 10repetitive, hand-intensive jobs wererandomly chosen toparticipate.

Outcome: CTS wasdetermined from evaluation ofOSHA illness and injury logsand medical records. Theindependent variable wasexposure to jobs in which CTShad occurred previously. Alow-risk job was defined ashaving a zero incidence rate; ahigh-risk job was defined ashaving an incidence rate ofeight or more recordablerepetitive trauma.

Exposure: Included number ofwrist motions/8-hr shift, weightof loads, handgrip types andforces, work heights, andmotion descriptions. Wristmotion monitors measured inthe radial/ulnar,flexion/extension, andpronation/supination planes:wrist angles, angular velocity,angular acceleration.

High-riskjob: 8incidents/200,000 hrexposure

Low-riskjob: 0incidents

Model forpredicting highvs. low job riskbased uponmotioncomponent:

PositionRadial/ulnarROM: OR=1.52Flexion/exten-sion ROM:OR=1.3Pronation/supinationROM:OR=1.2

VelocityRadialulnar vel:OR= 2.4Flexion/extension vel:OR=3.8Pronation/supination vel:OR=1.9

AccelerationRadial/ulnaraccel: OR=2.7Flexion/extensionaccel:OR=6.1Pronation/supinationaccel: OR=2.96

1.1-2.1

1.0-1.7

0.9-1.6

1.3-4.3

1.5-9.6

1.2-3.2

1.5-4.9

1.7-22

1.4-6.4

Participation rate: Not reported.

Examiners blinded: not stated.

Confounders controlled for: Age,gender, handedness, jobsatisfaction.

All the jobs required gloves excepttwo-one “low-risk” and one “high-risk.”

Significant difference betweengroups with regards to age, yearswith the company, and trunk depth.

No significant difference in jobsatisfaction, number of wristmovements, age, weight, stature,hand dimensions.

Turnover rate: High-risk jobs: 33%;low-risk jobs: 0.5%.

Grip forces were three times asgreat in the high-risk jobs than inthe low-risk jobs.

Variance between subjects withinjobs accounted for a substantialpercentage of total variance inwrist motion.

5a-54

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

McCormacket al. 1990

Cross-sectional

Textile workers: 4 broad job categoriesinvolving intensive upper extremity use.Workers randomlychosen: Sewing workers (n=562); boarding workers(n=296); packagingworkers (n=369); andknitting workers (n=352) compared toother non-office workers (n=468).

Outcome: Assessed byquestionnaire and screeningphysical examination initially bynurse. CTS diagnosed onclinical grounds of symptomsand positive Tinel's sign andPhalen's test. Physicianreassessed physical findingsby “standardized methods.”

Exposure: Assessment byobservation of jobs. Exposureto repetitive finger, wrist andelbow motions assumed fromjob title; no objectivemeasurements performed.

Prevalencesof CTS

Boarding:0.7%

Sewing: 1.2%

Packaging:0.5%

Knitting:0.9%

1.3% (non-office)

Boarding vs.non-officeOR=0.5

Sewing vs.non-officeOR=0.9

Packaging vs.non-officeOR=0.4

Knitting vs.non-officeOR=0.6

0.05-2.9

0.3-2.9

0.04-2.4

0.1-3.1

Participation rate: 91%.

Physician or nurse examiners notblinded to case or exposure status(personal communication).

Prevalence higher in workers with<3 years of employment. Race andage not related to outcome. Females found to have significantlymore CTS than males.

Job category not found to besignificant, however nomeasurement of force, repetition,posture analysis, etc.

Questionnaire asked types of jobs,length of time on job, productionrate, nature and type of upperextremity complaint, and generalhealth history.

11 physician examiners;interexaminer reliability potentialproblem acknowledged.

5a-55

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Moore andGarg 1994

Cross-sectional

32 jobs in which 230workers were employed. This study was more anevaluation of jobs than ofindividuals.

Outcome: CTS identified fromOSHA logs and medicalrecords. A case requiredelectrophysiologic testing,confirmed as abnormal byelectromyographer andpresence of suggestivesymptoms.

Exposure: Observation andvideotape analysis of jobs. Force, wrist posture, grasptype, high-speed work,localized mechanical stress,vibration, cold, and work timeassessed via observation ofvideotape. Jobs classified ashazardous or safe based ondata and judgement.

13.7% 4.9% 2.8 0.2-36.7 Participation rate: Study based onrecords.Investigators blinded to exposure,case outcome status, and personalidentifiers on medical records.Repetitiveness, “type of grasp”were not significant factorsbetween hazardous and safe jobcategories.No pattern of morbidity according todate of clinic visits.Strength demands significantlyincreased for hazardous jobcategories compared to safe jobcategories. IR based on full-time equivalentsand not individual workers, mayhave influenced overall results. Workers had a maximum of 32-months of exposure at plant–soduration of employment analysislimited.Average maximal strength derivedfrom population-based datastratified for age, gender, and handdominance. Using estimates of Silverstein’sclassification, association betweenforcefulness and overall observedmorbidity was statisticallysignificant; repetition was not.No control for confounders.

No information on work history,number of unaffected workers, orexposure duration.

5a-56

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Morgensternet al. 1991

Cross-sectional

1,058 female grocerycashiers from a singleunion.

Comparison group wasthose who reported nosymptoms.

Cashiers were alsocompared to results froma general populationstudy from Rochester,Minnesota (Stevens et al.1988).

Outcome: Defined CTS as self-reported hand/wrist pain,nocturnal pain, tingling in thehands or fingers, andnumbness.

Exposure: Duration, use oflaser scanner determined fromsurvey (no measurements).

12% 5.4%

For adifference of25 hr/wk: 1.88 0.9-3.8

Participation rate: 82%.

Controlled for age.

Information collected on age, sex,pregnancy status, work history asa checker, specific job-relatedtasks, use of selected drugs,history of wrist injury.

In logistic regression, “Use ofdiuretics” significantly associatedwith CTS, OR=2.66 (1.00-7.04);thought to be related to fluidretention by authors.

Laser scanning found not to besignificant factor.

5a-57

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Nathan et al.1988

Cross-sectional

471 industrial workersfrom 27 occupations in4 industries. Jobsgrouped into 5 classesbased on resistance andrepetition rate.

Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1-cmsegments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction. Case definition didnot deal with symptoms.

Exposure: Jobs grouped into27 occupations with similaritiesof characteristics as to type ofgrip, wrist position,handedness pattern,resistance, frequency, andduration of grasp andpresence of vibratory andballistic components. The27 occupations then groupedinto 5 classes. Resistance(Res.) rated from very light tovery heavy; repetition raterated from low to high.

Group I: very light resistanceand low repetitionGroup II: light resistance andvery high repetitionGroup III: moderate resistanceand moderately high repetitionGroup IV: heavy resistanceand moderate repetitionGroup V: very heavyresistance and high repetition.

Prevalenceof abnormalnerveconductionsensorylatency:

Group II: 27%

Group III: 47%

Group IV: 38%

Group V: 61%

Prevalenceofabnormalnerveconductionsensorylatency:

Group I: 28%

Group II vs. I:PR=1.0

Group I vs. III: PR=1.9

Group I vs. IV:PR=1.7

Group I vs. V:PR=2.0

0.5-2.0

1.3-2.7

1.3-2.7

1.1-3.4

Participation rate: Not reported.

Analysis controlled for age andgender.

No description of symptom statusfor defining CTS.

Method of categorization of jobsand occupations not described.

Classification system is based ononly repetition and not resistanceas listed.

Initially excluded cases of CTS instudy population, yet wassupposedly identifying prevalencesof CTS in exposure groups.

For nerve conduction analysis,wrongly assumed that each hand’snerve conduction study results inan individual were independent. The 2 hands in a single individualare not independent of each other.

5a-58

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Nathan 1992a Long-itudinal

315 workers using bothhands (each handanalyzed separately)from four industries. These represented 67%of original group ofworkers from 1988published studyrandomly selected fromfour industries (67% oforiginal subjects)

Group I: Very lightresistance and lowrepetition

Group II: Lightresistance and very highrepetition

Group III: Moderateresistance andmoderately highrepetition

Group IV: Heavyresistance and moderaterepetition

Group V: Very heavyresistance.

Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1-cmsegments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction.

Probable CTS: Presence ofany two primary symptoms(numbness, tingling, nocturnalawakening) or one primarysymptom and 2 secondarysymptoms (pain, tightness,clumsiness).

Exposure: For this article,previous exposureclassification was used from1988 Nathan article. Jobs hadbeen grouped into 27occupations with similarities ofcharacteristics as to type ofgrip, wrist position,handedness pattern,resistance, frequency, andduration of grasp andpresence of vibratory andballistic components. The 27occupations then grouped into5 classes. Resistance ratedfrom very light to very heavy;repetition rate rated from low tohigh.

Group II:19%

Group III:26%

Group IV: 24%

Group V:18%

Group 1:18%

Groups II vs.Group I:

PR=1.1

Group III vs.Group I:

PR=1.5

Group IV vs.Group I:

PR=1.4

Group V vsGroup I:

PR=1.0

0.6-1.9

1.0-2.2

0.9-2.1

0.5-2.2

Participation rate: Overall: 67%;Group 3 participation rate was59%.Examiners blinded: Not reported.Analyzed using gender, handdominance, occupational hand use,duration of employment, andindustry.76% of participants employed insame occupational hand-use classas in 1988. A lower percentage ofnovice workers returned (56%)than non-novice workers (69%) forfollow-up study.Analysis of “hands” instead ofindividual would cancel contributionof exposure effect if there wasunilateral slowing.Data in table two for 1984 subjectsis not the same data as presentedin previous article; numbers haveshifted to other groups. Thesignificant difference seenbetween nerve slowing betweenClass 1 and Class 5 in 1988 paperis no longer significantly different.Authors note that “130 handsexperienced a decrease inoccupational use.” No parametersgiven for decrease and assumptionis made that both hands in anindividual had similar decrease inuse. With one-third of cohort missingfrom 1984 study, there is no way todetermine if homogeneity insymptoms prevalence in 1984 and1989 reflects absence ofprogression or drop-out.

5a-59

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Nathan 1994b Long-itudinal

101 Japanese furniturefactory workers. Therewere 27 managers, 35clerical workers, 21assembly-line or foodservice workers and 18machine operators. TheirNCS results werecompared to 315workers using bothhands (each handanalyzed separately)from four industries.(These represented 67%of original group ofworkers from 1988published study randomly selected fromfour industries (67% oforiginal subjects) and arethe subject of a separatetable entry in thisdocument.

Group I: Very lightresistance and lowrepetition.

Group II: Lightresistance and very highrepetition.

Group III: Moderateresistance andmoderately highrepetition.

Group IV: Heavyresistance and moderaterepetition.

Group V: Very heavyresistance.

Outcome: Case defined asNCS-determined impairedsensory conduction (sensorylatency). Sensory latenciesassessed antidromically foreight consecutive 1 cm.segments of the nerve. Amaximum latency difference of0.4 ms or greater used todefine impaired sensoryconduction.Probable CTS: Presence ofany two primary symptoms(numbness, tingling, nocturnalawakening or one primarysymptom and 2 secondarysymptoms (pain, tightness,clumsiness).

Exposure: Exposure was notaddressed except is assumedto be self-reported byquestionnaire for the Japaneseworkers. The jobs weregrouped into 5 classes. Resistance rated from verylight to very heavy; repetitionrate rated from low to highrepetition.

8 cm.Sensorylatency:0.30

14 cm.Sensorylatency:0.36

ProbableCTS: 2.5%

DefiniteCTS:2.0

8 cm.Sensorylatency:0.31

14 cm.Sensorylatency:0.45

ProbableCTS:2.0%

DefiniteCTS:8.3

Participation rate: For JapaneseWorkers: 100%Americans: Overall: 67%; Group 3participation rate was 59%.

Examiners blinded: Not reported.

Analyzed using gender, handdominance, occupational hand use,duration of employment, andindustry.

Analysis of “hands” instead ofindividual would cancel contributionof exposure effect if there wasunilateral slowing.

Conducted step-wise regressionanalysis for Probable CTS andreported that repetitions andduration of employment wereprotective. Cigarettes and Agewere also retained in the model.

5a-60

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Osorio et al.1994

Cross-sectional

56 supermarket workers. Comparison wasbetween high and lowexposure groups.

Outcome: CTS assessed viamedical history, physical exam,median nerve conductionstudies, and vibratorythresholds.

A. CTS-like syndrome:Probable diagnosis: (1) Paintingling numbness in mediannerve distribution and(2) symptoms last >1 wk or $12 times in last year, no acutetrauma or systemic disease,onset or exacerbation sinceworking on current job.

B. Median neuropathy:Sensory median nerveconduction velocity 44 m/secor less.

Exposure: Observation of jobsby ergonomist and industrialhygienist. Analysis based oncategorization by job title afterobservation. Jobs divided into3 categories based on thelikelihood of exposure toforceful and repetitive wristmotions (low, moderate, high),years worked at this store,total years worked as checker,total years using laserscanners.

Symptoms: 63% inhigh-exposure;10% inmoderate-exposuregroup

PositiveNCS: 33%in high-exposure;7% inmoderate-exposuregroup

0% forlow-exposuregroup

0% forlow-exposuregroup

8.3(for CTS-symptoms highvs. lowexposuregroups)

6.7 (forabnormal NCS,high vs. lowexposuregroups)

2.6-26.4

0.8-52.9

Participation rate: 81%.

Adjusted for age, gender, alcoholconsumption, and high-risk medicalhistory.

Interview and testing proceduresperformed by personnel blinded tocase status.

Skin surface temperature notcontrolled.

Dose response for presumptive(symptoms of) exposure toforceful, repetitive wrist motion:CTS-prevalence 63% highexposure; 10% medium exposure;0% low exposure.

Dose response for prevalence ofabnormal median nerve velocity: 33% high; 7% medium; 0% low.

Linear regression showedsignificant relationship betweenyears worked and worsening ofnerve conduction (decreasednerve conduction velocity anddecreased nerve conductionamplitude) adjusted forconfounders (above), howeversmall sample size.

5a-61

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Punnett et al.1985

Cross-sectional

162 female garmentworkers; 85% wereemployed as sewingmachine operators whosewed and trimmed byhand.

Comparison: 76 of 190full- or part-time workerson day shift in a hospitalwho worked as nursesor aids; lab techniciansor therapists, or foodservice workers.

Employees typing >4hr/day excluded fromcomparison group. 162female garment workerscompared to 73 femalehospital workers.

Outcome: CTS assessed bysymptom questionnaire andphysical exam. Cases definedas the presence of persistentpain (lasted for most days forone month or more within thepast year); were notassociated with previousinjury; and, began after firstemployment in garmentmanufacturing or hospitalemployment. Key questionsbased on the arthritissupplement questionnaire ofthe National Health and NutritionExamination Survey (NHANES). Median nerve symptoms (pain,numbness, or tingling) ifpresent at night or early in themorning or met 2 of 3 criteria: (1) accompanied by weaknessin pinching or gripping;(2) alleviated by absence fromwork for >1 wk;(3) aggravated by houseworkor other non-occupationaltasks.

Exposure: Observation of jobtasks. Information on workhistory obtained byquestionnaire. Job title used asa proxy for exposure inanalyses.

18% 6% 2.7 1.2-7.6 Participation rate: 97% (garmentworkers), 40% (hospital workers).

Controlled for age, hormonal status,and native language.

Pain in the wrist and handsignificantly correlated (p<0.01;r=0.41).

Age distribution not significantlydifferent metabolic disease.

Symptoms of CTS showed trend byage (p<0.01).

Prevalence of pain not associatedwith years of employment ingarment workers.

Length of employment not predictorof risk.

Change in hormonal statussignificantly associated with CTSsymptoms but negativelyassociated with employment ingarment shop.

Logistic model found garment workand age significant for symptoms ofCTS.

Neither metabolic disease norchange in hormonal statusstatistically significant risk.

5a-62

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Schottlandet al. 1991

Cross-sectional

Poultry workers (27 males, 66 females)compared to jobapplicants (44 males,41 females).

Outcome: Defined asprolonged motor or sensorymedian latencies. Nosymptoms or physical examincluded in case definition.

Exposure: Based on currentemployment status at plant. Nomeasurements made. Repetitive tasks (15 to 50complex operations/min notrare), requiring firm grip, withwrists in flexion or extension,with internal deviations.

41%exceeding2.2 ms forsensorylatencyvalue ofmediannerve onNCS (right-hand,females,correctedfor age)

24%exceeding2.2 ms formediannervesensorylatencyvalue onNCS (left-hand,females,correctedfor age)

20%exceeding2.2 ms formediansensorylatencyvalue(right-hand,females,correctedfor age)

15%exceeding2.2 ms formediannervesensorylatencyvalue onNCS (left-hand,females,correctedfor age)

2.86

1.87

1.1-7.9

0.6-9.8

Participation rate: Not reported.

Not mentioned whether examinersblinded to case status or exposure.

Controlled for age and gender.

Referents not excluded if prioremployment at poultry plant;15 referents had previousemployment in poultry plant; thiswould result in poor selection ofcontrols, would tend to bias resultstowards the null.

Right-hand of female applicantswho never worked in a poultryplant had significantly longermedian palmar latency (MPS) onnerve conduction than referents(p<0.04).

Symptoms of CTS not inquired. Right hand of male workers hadlonger MPS on nerve conductionbut not significant (p<0.07).

From Table 5-2 in paper it showsthere is inadequate sample size fordetecting differences in female’sleft-hand and male’s left- and right-hand MPS.

Concluded there is an elevated riskof CTS, roughly equal to risk fromaging for the right hands of femaleworkers, less risk for male bothhands and female left hands.

5a-63

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Silversteinet al. 1987

Cross-sectional

652 industrial workers in4 groups: (1) low-force,low-repetition (comparison group,n=93 males, 64 females);(2) high-force, low-repetition (n=139 males,56 females); (3) low-force, high-repetition(n=43 males, 100females); (4) high-force,high-repetition (n=83males, 74 females).

Outcome: CTS determined bymedical examination andinterviews.

Symptoms of pain, numbnessor tingling in median nervedistribution.

Nocturnal exacerbation;symptoms >20 times or >1 wkin previous year; no history ofacute trauma; no history ofrheumatoid arthritis; onset ofsymptoms since current job;positive modified Phalen’s test(45 to 60 sec) or Tinel’s sign;rule out cervical root thoracicoutlet, pronator teressyndrome.

Exposure: To (1) forceful,(2) repetitive, and (3) awkwardhand movements assessed byEMG and video analysis ofjobs. Three workers in eachselected job videotaped for (atleast) 3 cycles. High-force job:A mean adjusted force >6 kg(mean adjusted force =[(variance/mean force)+ meanforce]); low-force job: A meanadjusted force <6 kg.

High repetition = work cycles<30 sec or work cyclesconstituting >50% of the workcycle.

1.0 (Group 2)

2.1 (Group 3)

5.6 (Group 4)

0.6 Group 2 vs.Group 1: OR=1.8

Group 3 vs.Group 1: OR=2.7

Group 4 vs.Group 1:OR=15.5

In separatelogistic models:

(1) Repetitive-ness: OR=5.5 (p<0.05)

(2) Force: OR=2.9 (non-significant)

0.2-21

0.3-28

1.7-142

Participation rate: 90% responserate obtained.

Controlled for age, gender, plant,years on the job. No interactionsfound.

Jobs evaluated by investigatorsblinded to worker health status.

Examiner blinded to medical historyand exposure.

Random sample of 12 to 20 activeworkers/job with 1 year’s seniority,stratified by age and gender.

Interview data included prior healthand injuries, chronic diseases,reproductive status of females,recreational activities, prior jobactivities.

No association found with wristposture, type of grasp, or use ofvibrating tool.

Positive associated with age butnot statistically significance.

No differences in health history orrecreational activities.

No association with gender, orindustrial plant.

Negatively associated with yearson the job but not statisticallyassociated.

Repetitiveness found to be strongerrisk factor than force.

No association with hormonalstatus.

5a-64

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Stetson et al.1993

Cross-sectional

Comparison of 137asymptomatic industrialworkers, 103 industrialworkers with hand/wristsymptoms, and 105control subjectsrandomly selected notexposed to highlyforceful or repetitivehand exertions.

Outcome: Symptomsconsistent with CTS defined asnumbness, tingling, or burninglocalized to median nerveanatomic area, not caused byacute injury, and occurred >20times in previous year. Nerveconduction studies conductedon the dominant hand; mediansensory and motor, ulnarsensory, distal amplitudes andlatencies were measured. Temperature monitored.

Exposure: Observation andworker interviews usingergonomic checklist. One ormore workers on each jobwere evaluated based onrepetitiveness, forcefulness,mechanical stress, pinch grip,and wrist deviation, then dataextrapolated to other workersperforming jobs. A 3-pointordinal scale used to estimateexposure (none, some,frequent or persistent).

Õ Õ Participation rate: 71% seen, 16%refused, others unavailablebecause of layoffs, transfers, orsick leave.

Industrial population randomlyselected.

Controlled for age, height, skintemperature, and dominant indexfinger circumference.

Comparing the means of the nerveconduction measures, the followingwere statistically significantlydifferent between: (1) theasymptomatic hand group and thecontrols: median sensory amplitudeand distal latency, and median toulnar comparison measures; (2) thesymptomatic hand group andcontrols: median sensory distallatency, and median to ulnarcomparison measures.

Median sensory amplitudes weresmaller and distal latencies longer insymptomatic compared toasymptomatic hand group.

Forceful hand and upper extremityexertions were significantlydifferent between exposed andnon-exposed groups. Repetitionnot significantly different, but littlestatistical power to detectdifference.

5a-65

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

(Continued)

Tanaka et al.In Press

Cross-sectionalinterviewsurvey

Data from the Occupational HealthSupplement of 1988National Health InterviewSurvey conducted by theNational Center forHealth Statistics. Households are selectedby multistage probabilitysampling strategy. Oneadult, 18 years or older,was randomly selectedfor interview. 44,233interviews completed.

Outcome: Outcomes includedthose “Recent Workers” whoworked anytime during the past12 months (excluding armedforces). Self-reported carpaltunnel syndrome= “yes” toquestion: During the past12 months, have you had acondition affecting the wristand hand called carpal tunnelsyndrome? Medically calledCTS = a response of “carpaltunnel syndrome” to thequestion: “What did the medicalperson call your handdiscomfort?”

Exposure: By questionnaire:Did the most recent job requireyou to bend or twist yourhands or wrists many times anhr? Did you work with hand-held or hand-operated tools ormachinery.

Prevalenceof self-reportedCTS amongrecentworkers:1.47%

Prevalenceof medicallycalled CTSamongrecentworkers:0.53%

Logistic modelfor medicallycalled CTSamong recentworkers

Bend/twist:OR=5.9

White race:OR=4.2

Female gender:OR=2.4

Vibration:OR=1.85

BMI $25: OR=2.1

Cigarette use:OR=1.6

Age $40: OR=1.3

Annual income$$20,000:OR=1.5

Education>12: OR=1.2

3.4-10.2

1.9-15.6

1.6-3.8

1.2-2.8

1.4-3.1

1-2.5

0.2-1.9

1-2.4

0.8-1.8

Participation rate: 91.5%.

Multiple logistic regression used toexamine age, gender, race,exposure to vibration, andbending/twisting of the hand/wriststo odds of reporting CTS. Interactions were checked for.

Self-reported CTS prevalenceamong recent workers higher inwhites compared to non-whites,highest in white females.

When vibration was not in themodel the bend/twist OR=5.99. When bend/twist is not in themodel, vibration OR=3.00.

Major limitation is CTS is based onself-reports without medicalvalidation.

No temporal relationship could befound between reported CTS andthe reported occupation/industry orexposure to bending/twisting of thehand/wrist.

5a-66

Table 5a–5 (Continued). Epidemiologic studies evaluating work-related carpal tunnel syndrome (CTS)

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposed workers

Referent group

RR, OR, or PRR 95% CI Comments

Weislanderet al. 1989

Case-control

34 male CTS patients,each matched to 2 otherhospital referents(drawn from amongothersurgical cases, onereferent had beenoperated on for gallbladder surgery and theother for varicose veins)and 2 populationreferents (from a generalpopulation register andtelephone directory)(total comparisongroup=143 males).

Outcome: CTS diagnosedclinically by a hand surgeon,confirmed by electro-diagnosticstudies.

Exposure: To vibrating tools,repetitive wrist movements,and loads on the wristassessed via telephoneinterview using a standardizedquestionnaire. The degree ofexposure was evaluated bothwith regard to the total numberof work years and the averagenumber of exposed hr a wk. Repetitive movementsclassified independently byphysician interviewer andoccupational hygienist. Exposure to repetitive wristmovements was considered toexist if they agreed.

Õ Õ Casescompared to allreferents(hospital- andpopulation-based):Vibrating tooluse: OR=3.3

Use of hand-held vibratingtools 1-20years: OR=2.7

Loads on thewrist: OR=1.8

Casescompared topopulationreferentsalone:Vibrating tooluse: OR=6.1

Repetitivewristmovement for>20 years:OR=4.6

Repetitivewristmovement:OR=2.7

Obesity:OR=3.4

1.6-6.8

1.1-6.7

1.0-3.5

2.4-15

1.8-11.9

1.3-5.4

1.2-9.8

Participation rate: 93%.

Referents matched for gender andage (±3 years.), hospital referentsfor year of operation.

Hospital referents and populationreferents statistically differentcomparing: use of vibrating tool,repetitive movements of wrist,workload on wrist, obesity.

Hospital-based population may notreflect industrial workplace.

Interviewers not blinded to casestatus.

Elevated OR for repetitivemovements of the wrist onlystatistically significant for thecategory ‘>20 years.’

Odds ratios (OR) for any of thethree diseases (thyroid disease,diabetes, rheumatoid arthritis)found to be statistically significantamong cases with CTS comparedto 143 referents; OR=2.8 (1.0-7.6).

ORs tended to increase withincreasing number of risk factorspresent. One factor, OR=1.7 (0.6-4.4); two factors, OR=3.3 (1.2-9.1);>two factors, OR=7.1 (2.2-22.7).

Obesity is >10% above referenceweight.

5a-67

5b-1

CHAPTER 5bHand/Wrist Tendinitis

SUMMARY Eight epidemiologic studies have examined physical workplace factors and their relationship to hand/wristtendinitis. Several studies fulfill the four epidemiologic criteria that were used in this review, andappropriately address important methodologic issues. The studies generally involved populations exposedto a combination of work factors; one study assessed single work factors such as repetitive motions of thehand. We examined each of these studies, whether the findings were positive, negative, or equivocal, toevaluate the strength of work-relatedness, using causal inference.

There is evidence of an association between any single factor (repetition, force, and posture) andhand/wrist tendinitis, based on currently available epidemiologic data. There is strong evidence that jobtasks that require a combination of risk factors (e.g., highly repetitious, forceful hand/wrist exertions)increase risk for hand/wrist tendinitis.

INTRODUCTION

Since the hand/wrist area may be affected bymore than one musculoskeletal disorder, onlythose studies that specifically addresshand/wrist tendinitis are considered here.Studies with outcomes described as hand/wristdisorders or symptoms in general, or those inwhich hand/wrist tendinitis was combined withepicondylitis, e.g., were excluded from thissection because it was not possible to evaluateevidence for work-related hand/wrist tendinitisfrom the data. The seven studies referenced inTable 5b-1 provided data specificallyaddressing hand/wrist tendinitis. In each ofthese studies the outcome was determined usingphysical examination criteria, although the casedefinitions varied among studies. Prevalence orincidence rates of hand/wrist tendinitis reportedin these exposed groups ranged from 4% to56%, and in unexposed groups from 0% to14%. Such wide ranges of prevalence ratesprobably reflect the variability in diagnosticcriteria as much as they do the range ofworkplace exposures in these studies. For

example, one study used very strict criteria[Byström et al. 1995]. The case definitionrequired observation of swelling along thetendon at the time of the physical examination.The only cases of tendinitis diagnosed weredeQuervain’s disease; no other cases oftenosynovitis or peritendinitis were diagnosedamong 199 automobile assembly line workers.In contrast, the studies with the highestprevalence rates either did not clearly statewhat diagnostic criteria were used to determinethe case definition, or the case definitionconsidered recurrences of tendinitis new cases.Whether case definitions were inclusive orexclusive would not affect the relative risk (RR)as long as they were applied non-differentiallybetween groups designated as exposed orunexposed.

Although several studies reported odds ratios,published data were reanalyzed and the resultspresented here and in Tables 5b1-3 as prevalence ratios (PRs). Thiswas done because odds ratios mayoverestimate RR when prevalence rates are

5b-2

high, and to make estimates of RR comparableacross studies. In studies that presented oddsratios in the original articles, the recalculation ofdata as PRs resulted in lower estimates of theRR. In the one prospective cohort study[Kurppa et al. 1991] incidence rates and riskratios are presented.

Except for a study reported by Armstrong et al.[1987a], risk estimates were not reportedseparately for single risk factors. Only theArmstrong et al. study used a formalquantitative exposure assessment as the basisfor determining exposure groups. Other studiesgrouped jobs with similar risk factors togetherand compared them to jobs without those riskfactors. Typically, the selection of jobs for theexposed and unexposed groups was based ongeneral knowledge of the jobs, previouslypublished literature, or questionnaire data.Repetition, force, and extreme postures wereconsidered in combination to determine whichworkers were exposed or unexposed. Formalexposure assessment (such as videotapeanalysis for cycle time, repetition, extremepostures, and estimates of force), was usuallyconducted on a sample of jobs and used asrationale in the grouping of jobs into exposedand unexposed categories, rather than to createquantitative measures of risk factors. In somecases (e.g., Luopajärvi et al. [1979]),investigators noted the difficulty in examiningrisk factors separately because of job rotation.For the purpose of this review, we havegrouped study findings according to the riskfactors present in the exposed job categories,based on the information in published articles.In Tables 5b1–3, studies are listed under singlerisk factors if there was evidence that theexposed and unexposed groups differed in thatrisk factor,

though the risk estimates mostly refer tocombined exposures.

REPETITION

Definition of Repetition forHand/Wrist Tendinitis

Armstrong et al. [1987a] analyzed videotapedjob tasks of a sample of workers, then dividedjob tasks according to level of repetitiveness:high repetition (cycle time <30 sec, or $50% ofthe cycle spent performing the samefundamental motions) or low repetition.Kuorinka and Koskinen [1979] created a“workload index” based on the number ofpieces handled per hour multiplied by thenumber of hours worked, for a dose-responseanalysis within the exposed group. Comparisongroups in the other studies were job categories;selection of the groups to be compared wasbased on observations, questionnaire data, orsurveillance data.

Studies Reporting on the Associationof Repetition and Hand/WristTendinitis

Seven studies addressed repetition: Amano etal. [1988]; Armstrong et al. [1987a]; Byströmet al. [1995]; Luopajärvi et al. [1979]; Rotoand Kivi [1984]; Kuorinka and Koskinen[1979]; and McCormack et al. [1990].

Studies Meeting the Four EvaluationCriteria

Two of the seven studies that addressedrepetition met all four of the evaluation criteria:Armstrong et al. [1987a], and Luopajärvi et al.[1979]. Armstrong et al. studied 652 industrialworkers at seven manufacturing plants(electronics, sewing, appliance, bearingfabrication, bearing assembly, and investment

5b-3

casting). Exposure assessment of jobs includedvideotape analysis and electromyography(EMG) of a sample of workers. Data from thisassessment were then used to categorize jobsaccording to level of repetitiveness and force.Health assessment of workers focused ondeQuervain’s disease, trigger finger, tendinitis,and tenosynovitis. The hand/wrist tendinitiscase definition required abnormal physicalexamination findings (increased pain withresisted but not passive motion or tendonlocking with a palpable nodule, or a positiveFinkelstein’s test) in addition to meetingsymptom criteria on standardized interviews.The PR for the high repetition/low force group(n=143) compared to the low repetition/lowforce group (n=157) was 5.5 (95% confidenceinterval [CI] 0.7–46.3). The PR for the highrepetition/high force group (n=157) comparedto the low repetition/low force group (n=157)was 17.0 (95% CI 2.3–126.2). The effect ofage, gender, years on the job, and plant wereanalyzed. A higher prevalence of tendinitis wasnoted among women but was not significantlyassociated with personal factors, whereassignificant differences in posture were observedbetween males and females.

Luopajärvi et al. [1979] compared theprevalence of hand/wrist tendinitis among 152female assembly line packers in a foodproduction factory to 133 female shopassistants in a department store. Exposure torepetitive work, awkward hand/arm postures,and static work was assessed by observationand videotape analysis of factory workers. Noformal exposure assessment was conducted onthe department store workers; their job taskswere described as variable. Cashiers wereexcluded, presumably because their work wasrepetitive. The health assessment consisted of

interviews and physical examinations conductedby a physiotherapist (active and passivemotions, grip-strength testing, observation, andpalpation). Diagnoses of tenosynovitis andperitendinitis were later determined by medicalspecialists using these findings andpredetermined criteria. The PR for tendinitisamong the assembly line packers compared tothe shop assistants was 4.13 (95% CI2.63–6.49). Age, hobbies and houseworkwere addressed and no associations withmusculoskeletal disorders were identified.

Studies Meeting at Least One Criteria

Amano et al. [1988] reported the prevalence ofcervicobrachial disorders, includingtenosynovitis, among 102 assembly lineworkers in an athletic shoe factory and 102age- and gender-matched non-assembly lineworkers (clerks, nurses, telephone operators,cooks, and key punchers). Exposureassessment was based on videotape analysis ofthe tasks of 29 workers on one assembly line.Assembly line workers produced about 3,400shoes a day. All but one task had cycle timesless than 30 seconds. No formal exposureassessment of the comparison group wasreported. Diagnoses were determined byphysical examination, including palpation fortenderness. The PRs for tenosynovitis of theright and left index finger flexors among theshoe factory workers were 3.67 (95% CI1.85–7.27) and 6.17 (95% CI 2.72–13.97)respectively, compared to the non-factoryworkers. Tenosynovitis of the other digits wasnot diagnosed in the comparison group. Shoeassembly workers held shoe lasts longer in theleft hand and had greater frequency ofsymptoms in the left hand. Comparison subjectswere matched to shoe factory workers ongender and age (within five years).

5b-4

Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure wasassessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and finger movements,wrist position, grip, and hand tool use[Fransson-Hall et al. 1995]. Videotape analysisand electromyograms were conducted on asubgroup [Hägg et al. 1996]. A diagnosis oftenosynovitis or peritendinitis required theobservation of swelling and pain during activemovement on physical examination. A diagnosisof deQuervain’s disease required a positiveFinkelstein’s test. No cases of tenosynovitis orperitendinitis, other than deQuervain’s disease,were found in this study, probably because ofstrict clinical criteria used for the case definition.The PR for deQuervain’s disease among theautomobile assembly line workers was 2.49(95% CI 1.00–6.23) compared to the generalpopulation group. Psychosocial variables andother potential confounders or effect modifierswere addressed by Fransson-Hall et al. [1995].A higher prevalence of deQuervain’s diseasewas noted among men than women.

Kuorinka and Koskinen [1979] studiedoccupational rheumatic diseases and upper limbstrain among 93 scissor makers and comparedthem to the same group of department storeassistants (n=143) that Luopajärvi used as acomparison group. Temporary workers andthose with recent trauma were excluded fromthe scissor

makers group. Exposure assessment includedvideotape analysis of scissor maker tasks. Thetime spent in deviated wrist postures per work

cycle was multiplied by the number of pieceshandled per hour and the number of hoursworked to create a workload index. Cycletimes ranged from 2 to 26 seconds; the numberof pieces handled per hour ranged from 150 to605. No formal exposure assessment wasconducted on the shop assistants. Healthassessment involved interview and physicalexamination by a physiotherapist following astandard protocol. Diagnoses of tenosynovitisand peritendinitis were later determined fromthese findings using predetermined criteria(localized tenderness and pain duringmovement, low-grip force, swelling of wristtendons [Waris et al. 1979]). In equivocalcases, orthopedic and physiatric teamsdetermined case status. The PR for muscle-tendon syndrome among the scissor makerswas 1.38 (95% CI 0.76–2.51) compared tothe department store assistants. Whether or notcashiers were excluded from the comparisongroup in this study, as they were in theLuopajärvi et al. [1979] study is unclear. Thestudy group was 99% female. No relationshipwas found between age- or body-mass indexand muscle-tendon syndrome. The number ofsymptoms increased with the number of partshandled per year. Analyses of subgroups ofscissor makers showed non-significantincreased prevalence of muscle-tendonsyndrome in short versus long cycle tasks andin manipulation versus inspection tasks. Theauthors noted a lack of contrast in exposuresbetween the subgroups. A non-significant trendof increasing prevalence of diagnosed muscle-tendon syndrome with increasing number ofpieces handled per year was noted in a nestedcase-controlanalysis (n=36).

McCormack et al. [1990] studied tendinitis andrelated disorders of the upper extremity among

5b-5

1,579 textile production workers compared to468 non-production textile workers, areference group that included machinemaintenance workers, transportation workers,cleaners, and sweepers. The textile productionworkers were reported as being exposed torepetitive finger, wrist and elbow motions basedon knowledge of jobs; no formal exposureassessment was conducted. Health assessmentincluded a questionnaire and screening physicalexamination followed by a diagnostic physicalexamination. The diagnosis of tendinitisrequired positive physical findings suggestive ofinflammation. The textile production workerswere divided into four broad job categories:boarding (n=296), which was noted to requireforceful work as well as the repetitive hand-intensive work of the other categories; sewing(n=562); packaging (n=369); and knitting(n=352). The PR for tendinitis among all textileproduction workers was 1.75 (95% CI0.9–3.39), compared to the reference groupnon-production textile workers. The PRs and95% CIs comparing tendinitis among eachbroad category of textile production workers tothe reference group are as follows:boarding—3.0 (1.4, 6.4); sewing—2.1 (1.0,4.3); packaging—1.5 (0.7, 3.5); andknitting—0.4 (0.1, 1.4). The authors noted thatthe knitting work was more automated than theother textile production job categories. Raceand age were not related to outcome, but theprevalence of tendinitis was higher in workerswith less than three years of employment.Female gender was a significant predictor of

tendinitis (p=0.01), but job category was astronger predictor (p=0.001).

Roto and Kivi [1984] studied the prevalence oftenosynovitis among 92 male meatcutterscompared to 72 male construction foremen. Noformal exposure assessment was conducted.Meatcutters’ work entailed repetitive physicalexertion of upper extremities and shoulders.Construction foremen’s work did not involverepetitive movements of the upper extremities.Health assessment was by questionnaire andphysical examination. Tenosynovitis wasdefined as swelling, local pain, and fingerweakness during movement. The prevalence oftenosynovitis among the meatcutters was 4.5%.The PR for tenosynovitis as defined by physicalexamination could not be calculated becausethere were no cases among the comparisongroup. The PR of tendinitis-like symptomsreported on the questionnaire among themeatcutters was 3.09 (1.43, 6.67) comparedto the construction foremen. Serologic testingfor rheumatoid arthritis was done to control forpotential confounding, none was detected.Authors noted that tenosynovitis occurred inyounger age groups.

Strength of Association—Repetitionand Hand/Wrist TendinitisThe PRs for repetitive work and hand/wristtendinitis in the studies reviewed above rangedfrom 1.4 to 6.2:

5b-6

Repetition and Hand/Wrist Tendinitis

PR and 95% CI Authors Exposed/Unexposed Groups

5.5 (0.7–46.3)

17.0 (2.3–126.2)

Armstrong et al. [1987a]* HI REP & LO FORCE/LOREP & LO FORCEHI REP & HI FORCE/LOREP & LO FORCE

3.7 (1.9–7.3) to 6.2 (2.7–14.0)

Amano et al. [1988] Shoe assemblers/clerks, nurses,operators, cooks, keypunchers

2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation

1.4 (0.8–2.5) Kuorinka and Koskinen [1979] Scissor makers/departmentstore assistants

1.8 (0.9–3.4) McCormack et al. [1990] Textile production/ maintenanceworkers, etc.

3.1 (1.4–6.7) Roto and Kivi [1984] Meatcutters/constructionforemen

4.1 (2.6–6.5) Luopajärvi et al. [1979]* Food packers/department storeassistants excluding cashiers

*Study met all four criteria.

In evaluating these RR estimates, studylimitations should be considered in addition tostatistical significance. Statistical significanceaddresses the likelihood that the results are notdue to chance alone, whereas study limitationscan bias the RR estimates in either direction. Allof the PRs were greater than one, and four ofthe seven were statistically significant. Therange (1.4–6.2) might reflect the level ofcontrast in repetitiveness between the exposedand comparison groups. For example, inMcCormack et al. [1990], the comparisongroup consisted of machine maintenanceworkers, transportation workers, and

cleaners and sweepers, whose exposure torepetition was not measured. If there weresome exposure to repetitive work in thecomparison group, then this would tend todecrease the RR for hand/wrist tendinitis amongthe textile workers. Another concern with thisstudy is the possibility that the knitting workersmay not have been exposed to very repetitivework due to greater automation in the knittingprocess. The effect of this potentialmisclassification of exposure would also be todecrease the RR.

Note that Kuorinka and Koskinen andLuopajärvi et al. both used the same

comparison group, but the number of subjects

5b-7

in the department store assistant group was 143for Kuorinka and Koskinen, and 133 forLuopajärvi (who excluded cashiers from thecomparison group). If Kuorinka and Koskinendid not exclude cashiers, this might tend todecrease the RR.

The highest RR (6.2) reported for repetitivework was by Amano et al. [1988]. In this studyit is unclear whether the examiner was blindedto whether the subjects were shoe assemblersor in the comparison group of non-assemblyline workers that included clerks, nurses,telephone operators, cooks, and key punchers.Because the occupational groups wereexamined on separate dates blinding seemsunlikely. The lack of a clear case definitionleaves open the possibility of examiner bias,which might lead to an increased RR.Alternatively, if there were a significant numberof key punchers in the comparison group, whomay have been exposed to repetitive work, thatwould tend to decrease the contrast inexposure and might lead to a decrease in theRR.

In summary, the potential for underestimation ofthe RR has been noted in studies where the RRis at the low end of the range, and the potentialfor overestimation of the RR has been noted atthe high end of the range. Considering theseconcerns and statistical significance, the RR forhand/wrist tendinitis attributable torepetitiveness is probably more likely to be inthe middle range of the estimates, based on thestudies reviewed. The statistically significantestimates of RR in this middle group range from2.5 to 4.1.

Temporal Relationship—Repetitionand Hand/Wrist TendinitisAll of the studies reviewed for this section werecross-sectional, so proving that exposure torepetitive work occurred before hand/wristtendinitis is not possible. However, informationin several of the studies suggests the likelihoodthat exposure to repetitive work occurredbefore the diagnosis of tendinitis. For example,recently employed workers were excluded byKuorinka and Koskinen [1979]. In Luopajärviet al.’s [1979] study group, the minimum lengthof employment was3 years. In the McCormack et al. [1990] study,the minimum average length of employment inthe job categories was more than 7 years.Byström et al. [1995] noted that subjects wereselected for clinical examination 5 months aftercompletion of questionnaires on exposure. Rotoand Kivi’s [1984] subjects had all worked inthe food industry for more than one year.Armstrong and Chaffin [1979] required aminimum length of employment of one year.Case definitions generally required thatsymptoms began after starting the current jobor employment at the plant. This also suggeststhat exposure occurred before disease.

Consistency in Association forRepetition and Hand/Wrist Tendinitis

All of the studies reviewed showed positive RRestimates for hand/wrist tendinitis amongoccupational groups exposed to repetitivework, ranging from 1.4 to 6.2. Four of theseven studies resulted in statistically significantPRs. Considering only statistically significantestimates from studies not noted to have seriouslimitations (which might bias the RR), the rangenarrows to 2.5–4.1.

5b-8

Coherence of Evidence for Repetitionand Hand/Wrist TendinitisDeQuervain’s disease and othertenosynovitis of the hand, wrist, and forearmhave been associated for decades withrepetitive and forceful hand activities as one ofthe possible causal factors [Amadio 1995].DeQuervain’s disease is the entrapment of thetendons of the extensor pollicis brevis andabductor pollicis longus. Other similarconditions are trigger thumb and triggering ofthe middle and ring fingers, characterized bypain with motion of the affected tendon.Despite the fact that the tendon and its sheathmay be swollen and tender, the histopathologyshows peritendinous fibrosis withoutinflammation, and fibrocartilaginous metaplasiaof the tendon sheath tissue. The role ofinflammation early in the process is not clear[Hart et al. 1995]. As in carpal tunnelsyndrome or epicondylitis, acute classicalinflammation does not seem a criticalpathophysiological component of the clinicalcondition, at least once it becomes chronic.Despite the observations that too much forcefuland repetitive activity contributes to carpaltunnel syndrome and epicondylitis, the responseof the tendons and the muscles to repetitiveactivity is likely that of a U-shaped curve. Toolittle and too much activity may be harmful, butintermediate levels of activity are probablybeneficial. The studies of tendon and musclephysiology suggest that a certain amount ofactivity maintains the normal state of thesetissues and leads to adaptive changes. Thesetissues have the ability to repair significantamounts of damage from some overuse; thepoorly understood issue is when overuseexceeds the ability of the tissue to repair thedamage or triggers a more harmful type of

damage [Hart et al. 1995]. Marras and

Schoenmarklin [1991] reported that velocityand acceleration significantly predicted upperextremity musculoskeletal disorders (includingtendinitis) among industrial workers performinghand-intensive job tasks.

Dose-Response Relationship ForRepetition and Hand/Wrist TendinitisKuorinka and Koskinen [1979] reported thatwithin the group of scissor makers, increasedprevalence of muscle-tendon syndromeoccurred in short versus long cycle tasks and inmanipulation versus inspection tasks. Theseincreases were not statistically significant. Theauthors noted a lack of contrast in exposuresbetween the subgroups. A non-significant trendof increasing prevalence of diagnosed muscle-tendon syndrome with increasing number ofpieces handled per year was also noted in anested case-control analysis (n=36) in the samestudy.

The Armstrong et al. [1987a] data resulted in aPR of 17.0 (2.3, 126.2) for jobs that werehighly repetitious and required highly forcefulexertions. This suggests a synergistic effectwhen both risk factors are present because theestimate is greater than the sum of the RRestimate for force or repetition alone.

Conclusions on Repetition andHand/Wrist Tendinitis

There is strong evidence for a positiveassociation between highly repetitive work, incombination with other job risk factors, andhand/wrist tendinitis based on currentlyavailable epidemiologic data. All seven of thestudies reviewed reported positive RR

estimates. Four of these estimates werestatistically significant. Potential confounders

5b-9

(factors associated with both exposure andoutcome that may distort interpretation offindings) considered in the studies of hand/wristtendinitis included gender, age, other medicalconditions, and outside activities. There is noevidence that the associations reported herebetween repetitive work and hand/wristtendinitis are distorted by gender, age, or otherfactors.

FORCE

Definition of Force for Hand/WristTendinitisArmstrong et al. [1987a] based high and lowforce categories on electromyographs offorearm flexor muscles of representativeworkers. Comparison groups in the otherstudies were job categories; selection of thegroups to be compared was based onobservations, questionnaire data, orsurveillance data.

Studies Reporting on the Associationof Force and Hand/Wrist Tendinitis

Five studies addressed force: Armstrong et al.[1987a]; Byström et al. [1995]; Kurppa et al.[1991]; McCormack et al. [1990]; and Rotoand Kivi [1984].

Studies Meeting the Four Criteria

One of the studies that addressed force met allfour of the evaluation criteria: Armstrong et al.[1987a]. Armstrong et al. studied 652 industrialworkers at seven manufacturing plants(electronics, sewing, appliance, bearingfabrication, bearing assembly, and investmentmolding). Exposure assessment of jobsincluded videotape analysis and EMG of asample of workers. Data from this assessmentwere then used to categorize jobs

according to level of repetitiveness and force.Health assessment of workers focused ondeQuervain’s disease, trigger finger, tendinitis,and tenosynovitis. The hand/wrist tendinitiscase definition required abnormal physicalexamination findings (increased pain withresisted but not passive motion or tendonlocking with a palpable nodule, or a positiveFinkelstein’s test) in addition to meetingsymptom criteria on standardized interviews.The PR for the high force/low repetition group(n=195) compared to the low force/lowrepetition group (n=157) was 4.8 (95% CI0.6–39.7). The PR for the high repetition/highforce group (n=157) compared to the lowrepetition/low force group (n=157) was 17.0(95% CI 2.3–126.2). The effect of age,gender, years on the job and plant wereanalyzed. A higher prevalence of tendinitis wasnoted among women, but was not significantlyassociated with personal factors, whereassignificant differences in posture were observedbetween males and females.

Studies Meeting at Least One Criteria

Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure wasassessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and finger movements,wrist position, grip, and hand-tool use[Fransson-Hall et al. 1995]. Videotape analysisand electromyograms were conducted on asubgroup [Hägg et al. 1996]. A diagnosis oftenosynovitis or peritendinitis required theobservation of swelling and pain during activemovement on physical examination. A diagnosisof deQuervain’s disease required a positive

5b-10

Finkelstein’s test. No cases of tenosynovitis orperitendinitis, other than deQuervain’s disease,were found in this study, probably because ofstrict clinical criteria used for the case definition.The PR for deQuervain’s disease among theautomobile assembly line workers was 2.49(95% CI 1.00–6.23) compared to the generalpopulation group. Psychosocial variables andother potential confounders or effect modifierswere addressed by Fransson-Hall et al. [1995].A higher prevalence of deQuervain’s diseasewas noted among men than women.

Kurppa et al. [1991] conducted a prospectivecohort study of tenosynovitis or peritendinitis(and epicondylitis) in a meat processing factoryin Finland. Three hundred seventy-sevenmeatcutters, meatpackers, and sausage makerswere compared to 338 office workers,maintenance workers, and supervisors.Exposure assessment was based on previouslypublished literature and knowledge of jobs atthe plant. Job categories were selected basedon whether or not strenuous manual work wasrequired. The cohort was followed for 31months. Health assessment consisted ofphysical examinations by plant physicians whowere on-site daily, using predetermined criteriafor diagnosing tenosynovitis or peritendinitis(swelling or crepitation and tenderness topalpation along the tendon and pain at thetendon sheath, in the peritendinous area, or atthe muscle-tendon junction during activemovement) and deQuervain’s disease (positiveFinkelstein’s test). Incidence density rates (if arecurrence of tendinitis occurred after 60 days,it was considered a new case) for tendinitiswere compared between each of the strenuousjob categories and either the male or femalecomparison group of combined non-strenuousjob categories (office workers, maintenanceworkers and supervisors). The RR for tendinitis

among the meatcutters (100% males)compared to the male comparison group was14.0 (5.7, 34.4); the RR for tendinitis amongthe meatpackers (79% female) compared tothe female comparison group was 38.5 (11.7,56.1); and the risk ratio for tendinitis among thesausage makers (86% female) was 25.6 (19.2,77.5). A limitation of the study is the fact thatthe subjects were not actively evaluated formusculoskeletal disorders. Investigators reliedon workers to seek medical care. This couldresult in a difference in case ascertainmentbetween the exposed and unexposed groupsbecause workers in non-strenuous jobs maynot have sought medical care formusculoskeletal disorders since they might stillbe able to perform their jobs, whereas workerswith MSDs in strenuous jobs might not be ableto perform their jobs, and would be more likelyto seek medical care. If subjects sought medicalcare, investigators were very likely to capturethe information, even if medical care wasprovided outside the plant, plant nursesreceived and reimbursed the bills, and recordedthe diagnosis and sick leave. However, whendiagnoses were made by physicians outside theplant, diagnostic criteria were unknown; thisoccurred in 25% of the cases. Exposed andcomparison groups were similar in age andgender mix, although gender varied with job.

McCormack et al. [1990] studied tendinitis andrelated disorders of the upper extremity among1,579 textile production workers compared to468 referents that included machinemaintenance workers, transportation workers,cleaners, and sweepers. The textile productionworkers

were reported, based on knowledge of the jobsto be exposed to repetitive finger, wrist andelbow motions; no formal exposure assessment

5b-11

was conducted. Health assessment included aquestionnaire and screening physicalexamination followed by a diagnostic physicalexamination. The diagnosis of tendinitisrequired positive physical findings suggestive ofinflammation. The textile production workerswere divided into four broad job categories.Boarding (n=296), was the only category notedto require forceful work. The PR for tendinitisamong the boarding workers was 3.0 (95% CI1.4–6.4), compared to the reference group.Race and age were not related to outcome, butthe prevalence of tendinitis was higher inworkers with less than three years ofemployment. Female gender was a significantpredictor of tendinitis (p=0.01), but jobcategory was a stronger predictor (p=0.001).

Roto and Kivi [1984] studied the prevalence oftenosynovitis among 92 male meatcutterscompared to 72 male construction foremen. Noformal exposure assessment was conducted.Meatcutters’ work entailed repetitive physicalexertion of upper extremities and shoulders.Construction foremen’s work did not involverepetitive movements of the upper extremities.Health assessment was by questionnaire andphysical examination. Tenosynovitis wasdefined as swelling, local pain, and fingerweakness during movement. The prevalence oftenosynovitis among the meatcutters was 4.5%.The PR for tenosynovitis as defined by physicalexamination could not be calculated becausethere were no cases among the comparisongroup. The PR of tendinitis-like symptomsreported on the questionnaire among themeatcutters was 3.09 (1.43, 6.67) comparedto the construction foremen. Serologic testingfor rheumatoid arthritis was done to control forpotential confounding, none was detected.Authors noted that tenosynovitis occurred inyounger age groups.

Strength of Association—Force andHand/Wrist TendinitisEstimates of RR for hand/wrist tendinitis amongthose in jobs requiring forceful exertion rangefrom 2.5 to 38.5:

The very large risk ratios reported by Kurppaet al. [1991] could be biased upward becauseof the difference in case ascertainment betweenthe exposed and unexposed groups.Investigators did not actively evaluate subjectsfor MSDs, but relied on workers to seekmedical care. As the authors noted, workers innon-strenuous jobs may not have soughtmedical care for MSDs since they might still beable to perform their jobs, while workers instrenuous jobs may not have been able toperform their jobs and would be more likely toseek medical care. This potential for differentialcase ascertainment between the exposed andunexposed groups undermines the credibility ofthe magnitude of the risk estimate.

Statistically significant estimates of RR forhand/wrist tendinitis among workers whoperform strenuous tasks from the remainingstudies range from 2.5 to 3.1.

5b-12

Force and Hand/Wrist Tendinitis

PR and 95% CI Authors Exposed/Unexposed Groups

4.8 (0.6–39.7)

17.0 (2.1–26.2)

Armstrong et al. [1987a] HI FORCE & LO REP/LOFORCE & LO REPHI FORCE & HI REP/LO FORCE & LO REP

2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation

14.0 (5.7–34.4) to38.5 (11.7–56.1)

Kurppa et al. [1991] Meat processors/officeworkers, maintenance workers,supervisors

3.0 (1.4–6.4) McCormack et al. [1990] Textile boarding workers/maintenance workers, etc.

3.1 (1.4–6.7) Roto and Kivi [1984] Meatcutters/constructionforemen

* Study met all four criteria.

Temporal Relationship—Force andHand/Wrist TendinitisThe Kurppa et al. [1991] study determinedexposure status of 83% of the cohort onOctober 2, 1982, and followed their healthstatus until April 30, 1985. The remainingsubjects entered the study when they becamepermanent employees, and were also followeduntil April 30, 1985.

Although the remaining studies that addressedforce were cross-sectional, the followinginformation increases the likelihood thatexposure to forceful work occurred before theoccurrence of tendinitis; Byström et al. [1995]noted that subjects were selected for clinicalexamination5 months after completion of questionnaires onexposure. McCormack et al. [1990] reportedthat the minimum average length of employment

in the job categories studied was more than 7years. Roto and Kivi’s

[1984] subjects had all worked in the foodindustry for more than one year. Armstrong etal. [1987a] required a minimum of 1 year ofemployment to be included in the study.

Consistency of Association—Forceand Hand/Wrist TendinitisAll of the studies reviewed reported positiveRR estimates for hand/wrist tendinitis amongoccupational groups exposed to forcefulexertions, ranging from 1.8 to 38.5. Four of thefive studies reported statistically significantfindings. If only statistically significant estimatesfrom studies in which limitations were not notedare considered, RR estimates for force andhand/wrist tendinitis range from 2.5 to 3.1.

5b-13

Coherence of Evidence—Force andHand/Wrist TendinitisSee Repetition Section.

Evidence of a Dose-ResponseRelationship—Force and Hand/WristTendinitis

Armstrong et al. [1987a] demonstrated a dose-response relationship between jobs requiringforceful exertions and hand/wrist tendinitis. Theestimate of RR for hand/wrist tendinitis amongworkers with jobs that were classified as HIGHFORCE & LOW REPETITION was 4.8 (0.6,39.7), while the estimate for HIGH FORCE &HIGH REPETITION jobs was 17.0 (2.3,126.2), compared to the comparison group ofLOW FORCE & LOW REPETITION jobs.

Conclusions on Force andHand/Wrist Tendinitis

There is strong evidence for an associationbetween work that requires forceful exertions,in combination with other job risk factors, andhand/wrist tendinitis based on currentlyavailable epidemiologic data. All five of thestudies reviewed reported data that resulted inpositive RR estimates. Four of the fiveestimates were statistically significant.Eliminating one estimate of RR from a studywith noted limitations that might bias theestimate upward does not change thisconclusion. Potential confounders such as ageand gender were examined in these studies (seediscussion of potential confounders on page5b-16) and there was no evidence thatreported associations were distorted byconfounders.

POSTURE

Definition of Posture for Hand/Wrist

TendinitisKuorinka and Koskinen [1979] determined thetime spent in deviated wrist postures per workcycle as part of their “workload index” that wasused in a dose-response analysis

within the exposed group. Comparison groupsin the other studies were job categories;selection of the groups to be compared wasbased on observations, questionnaire data, orsurveillance data.

Studies Reporting on the Associationof Posture and Hand/Wrist Tendinitis

Four studies addressed posture: Amano et al.[1988]; Byström et al. [1995]; Luopajärvi et al.[1979]; and Kuorinka and Koskinen [1979].

Studies Meeting the Four Criteria

Luopajärvi et al. [1979] met all four evaluationcriteria. Luopajärvi et al. [1979] compared theprevalence of hand/wrist tendinitis among 152female assembly line packers in a foodproduction factory to 133 female shopassistants in a department store. Exposure torepetitive work, awkward hand/arm postures,and static work was assessed by observationand videotape analysis of factory workers. Noformal exposure assessment was conducted onthe department store workers; their job taskswere described as variable. Cashiers wereexcluded, presumably because their work wasrepetitive. The health assessment consisted ofinterviews and physical examinations conductedby a physiotherapist (active and passivemotions, grip-strength testing, observation, andpalpation); and diagnoses of tenosynovitis andperitendinitis were later determined by medicalspecialists using these findings andpredetermined criteria. The PR for tendinitisamong the assembly line packers compared tothe shop assistants was 4.13 (95% CI

5b-14

2.63–6.49). Age, hobbies, and houseworkwere addressed, and no associations withmusculoskeletal disorders were identified.

Studies Meeting at Least One CriteriaAmano et al. [1988] reported the prevalence ofcervicobrachial disorders, includingtenosynovitis, among 102 assembly lineworkers in an athletic shoe factory and 102age- and gender-matched non-assembly lineworkers (clerks, nurses, telephone operators,cooks, and key punchers). Exposureassessment was based on videotape analysis ofthe tasks of 29 workers on one assembly line.Characteristic basic postures were summarizedby the investigators as: holding a shoe or a tool,extending or bending the arms, and keeping thearms in a certain position. Assembly lineworkers produced about 3,400 shoes a day.All but one task had cycle times less than 30seconds. No formal exposure assessment of thecomparison group was reported. Diagnoseswere determined by physical examination,including palpation for tenderness. The PRs fortenosynovitis of the right and left index fingerflexors among the shoe factory workers were3.67 (95% CI 1.85–7.27) and 6.17 (95% CI2.72–13.97) respectively, compared to thenon-factory workers. Tenosynovitis of the otherdigits was not diagnosed in the comparisongroup. Shoe assembly workers held shoe lastslonger in the left hand and had greaterfrequency of symptoms in the left hand.Comparison subjects were matched to shoefactory workers on gender and age (within fiveyears).

Byström et al. [1995] studied forearm and handdisorders among 199 automobile assembly lineworkers and compared them to 186 randomlyselected subjects from the general Swedishpopulation. For both groups, exposure was

assessed using rating scales on nurse-administered questionnaires that addresseddaily duration of hand and

finger movements, wrist position, grip, andhand-tool use [Fransson-Hall et al. 1995].Videotape analysis and electromyograms wereconducted on a subgroup [Hägg et al. 1996]. Adiagnosis of tenosynovitis or peritendinitisrequired the observation of swelling and painduring active movement on physicalexamination. A diagnosis of deQuervain’sdisease required a positive Finkelstein’s test.No cases of tenosynovitis or peritendinitis,other than deQuervain’s disease, were found inthis study, probably because of strict clinicalcriteria used for the case definition. The PR fordeQuervain’s disease among the automobileassembly line workers was 2.49 (95% CI1.00–6.23) compared to the general populationgroup. Psychosocial variables and otherpotential confounders or effect modifiers wereaddressed by Fransson-Hall et al. [1995]. Ahigher prevalence of deQuervain’s disease wasnoted among men than women.

Kuorinka and Koskinen [1979] studiedoccupational rheumatic diseases and upper limbstrain among 93 scissor makers and comparedthem to the same group of department storeassistants (n=143) that Luopajärvi used as acomparison group. Temporary workers andthose with recent trauma were excluded fromthe scissor makers group. Exposure assessmentincluded videotape analysis of scissor makertasks. The time spent in deviated wrist posturesper work cycle was multiplied by the number ofpieces handled per hour and the number ofhours worked to create a workload index.Cycle times ranged from 2 to 26 seconds; thenumber of pieces handled per hour ranged from150 to 605. No formal exposure assessment

5b-15

was conducted on the shop assistants. Healthassessment involved interview and physicalexamination by a

physiotherapist following a standard protocol.Diagnoses of tenosynovitis and peritendinitiswere later determined from these findings usingpredetermined criteria (localized tendernessand pain during movement, low-grip force,swelling of wrist tendons [Waris et al. 1979]).In equivocal cases, orthopedic and physiatricteams determined case status. The PR formuscle-tendon syndrome among the scissormakers as 1.38 (95% CI 0.76–2.51)compared to the department store assistants.Whether or not cashiers were excluded fromthe comparison group in this study, as theywere in the Luopajärvi et al. [1979] study isunclear. The study group was 99% female. Norelationship was found between age or bodymass index and muscle-tendon syndrome. Thenumber of symptoms increased with the numberof parts handled per year. Analyses ofsubgroups of scissor makers showed non-significant increased prevalence of muscle-tendon syndrome in short versus long cycletasks and in manipulation versus inspectiontasks. The authors noted a lack of contrast inexposures between the subgroups. A non-significant trend of increasing prevalence ofdiagnosed muscle-tendon syndrome withincreasing number of pieces handled per yearwas noted in a nested case-control analysis(n=36). Strength of Association—ExtremePosture and Hand/Wrist TendinitisThe PRs for extreme postures and hand/wristtendinitis ranged from 1.4 to 6.2. All of the PRswere greater than one and three of the fourstudies reported statistically

significant estimates. As noted in the RepetitionSection, the possibility of examiner bias mightexist in the study reported by Amano et al.[1988], potentially biasing the RR estimateupward. The middle of the range of statisticallysignificant estimates for RR for hand/wristtendinitis is 2.5 to 4.1.

Temporal Relationship

Although all of the studies reviewed in thissection were cross-sectional, at least two of thestudies addressed temporality by reporting aminimum length of employment (Luopajärvi etal. [1979]—5 years) or by evaluating exposurebefore health outcomes [Byström et al. 1995],as discussed in the previous sections onRepetition and Force.

Consistency

All of the studies reviewed showed positive RRestimates for hand/wrist tendinitis amongoccupational groups exposed to extremepostures, ranging from 1.4 to 6.2. Three of thefour studies reviewed resulted in statisticallysignificant PRs. Considering only statisticallysignificant estimates from studies not noted tohave design limitations that might bias the RR,narrows the range to 2.5 to 4.1.

Coherence of Evidence

See Repetition Section.

Dose-Response

See Repetition Section.

5b-16

Posture and Hand/Wrist Tendinitis

PR and 95% CI Authors Exposed/Unexposed Groups

4.1 (2.6–6.5) Luopajärvi et al. [1979] Food packers/department storeassistants

3.7 (1.9–7.3) to 6.2 (2.7–14.0)

Amano et al. [1988] Shoe assemblers/clerks, nurses,operators, cooks, keypunchers

2.5 (1.0–6.23) Byström et al. [1995] Auto assemblers/generalpopulation

1.4 (0.8–2.5) Kuorinka and Koskinen [1979] Scissor makers/department.store assistants

There is strong evidence for a positiveassociation between work that requiresextreme postures, in combination with other jobrisk factors, and hand/wrist tendinitis, based oncurrently available epidemiologic data. All ofthe studies reviewed reported data that resulted in positive RR estimates.Three of the four estimates from these studieswere statistically significant. Taking into accountthe effect of potential confounders (SeeRepetition Section) such as gender, age, andstudy limitations does not alter this conclusion.

Potential Confounders

GenderThe association between gender and tendinitisis not uniform. Byström et al. [1995] reported ahigher prevalence of deQuervain’s tendinitis inmen than in women, and proposed theexplanation that men in their study group usedhand tools more often than women. Ulnardeviation and static muscle loading werelikewise more often reported among men.Armstrong et al. [1987a] reported a higherprevalence of

tendinitis among women but found no significantassociations with other medical factors oractivities outside of work. However, significantdifferences in posture were observed betweenmales and females. Differences in postures maybe due to differences in height between menand women whose workstations have uniformdimensions. In McCormack et al.’s [1990]study of textile workers, three of the fourexposed groups were largely female(89%–95%), limiting the ability to separate theeffect of gender from job effect. However, in ananalysis that included gender and job as riskfactors, they reported that gender was asignificant predictor of tendinitis (p=0.01), butnot as significant a predictor as job category(p=0.001). The other studies reviewed did nothave both male and female subjects.

Age

Several investigators noted that tendinitisappears to be more prevalent in younger agegroups. Byström et al. [1995] reported thatmost of the cases of deQuervain’s tendinitisoccurred in the <40-yr age group.

McCormack et al. [1990] reported that age

5b-17

was not a significant predictor of tendinitis, butyears on the job was inverselyassociated—prevalence was higher if less than3 years on the job. Armstrong et al. [1987]noted that “a significant interaction betweensex, age, and years on the job suggested thatthe risk of hand/wrist tendinitis might actuallydecrease with an increased number of years onthe job, but the effect was too small to meritfurther discussion.” Roto and Kivi [1984] notedthat “The few cases of tenosynovitis occurred inyounger workers.” Kuorinka and Koskinen[1979] and Luopajärvi et al. [1979] found nosignificant association between age andtendinitis.

Other Potential Confounders

McCormack et al. [1990] reported that racewas not associated with tendinitis. Armstrong etal. [1987a] found no significant associationswith personal factors—birth control pills,hysterectomy, oophorectomy, recreationalactivities. No subjects with seropositiverheumatic diseases were included in theKuorinka and Koskinen [1979] study. Theyreported that their earlier unpublishedquestionnaire found no correlations betweenillness and extra work, work outside thefactory, work at home, or hobbies. Luopajärviet al. [1979] excluded subjects with previoustrauma, arthritis, and other pathologies.

There is no evidence in the studies reviewedhere that the associations reported betweenwork factors and hand/wrist tendinitis areexplained by gender, age, or other factors.

CONCLUSIONSEight epidemiologic studies have examinedphysical workplace factors and theirrelationship to hand/wrist tendinitis. Severalstudies fulfill the four epidemiologic criteria thatwere used in this review, and appropriatelyaddress important methodologic issues. Thestudies generally involved populations exposedto a combination of work factors; one studyassessed single work factors such as repetitivemotions of the hand. We examined each ofthese studies, whether the findings werepositive, negative, or equivocal, to evaluate thestrength of work-relatedness, using causalinference.

There is evidence of an association betweenany single factor (repetition, force, and posture)and hand/wrist tendinitis, based on currentlyavailable epidemiologic data. There is strongevidence that job tasks that require acombination of risk factors (e.g., highlyrepetitious, forceful hand/wrist exertions)increase risk for hand/wrist tendinitis.

Table 5b-1. Epidemiologic criteria used to examine studies of hand/wrist tendinitis associated with repetition

Study (first author andyear)

Riskindicators

(OR, PRR, IRor p-value)*,†

Participationrate $$70%

Physicalexamination

Investigatorblinded to

case and/orexposure

status

Basis for assessinghand/wrist exposure to

repetition

Met all four criteria:

Armstrong 1987a 5.5, 17.0†

Yes Yes Yes Observation or measurements

Luopajärvi 1979 4.1† Yes Yes Yes Observation or measurements

Met at least one criterion:

Amano 1988 3.7–6.2† NR‡ Yes NR Job titles or self-reports

Byström 1995 2.5† Yes Yes No Job titles or self-reports§

Kuorinka 1979 1.4 Yes Yes NR Observation or measurements

McCormack 1990 1.8 Yes Yes NR Job titles or self-reports

Roto 1984 3.1† Yes Yes Yes Job titles or self-reports

*Some risk indicators are based on a combination of risk factors—not on repetition alone (i.e., repetition plus force, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance.‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].

5b-18

Table 5b-2. Epidemiologic criteria used to examine studies of hand/wrist tendinitis MSDs associated with force

Study (first author andyear)

Riskindicator (OR,PRR, IR or p-

value)*,†

Participationrate $$70%

Physicalexamination

Investigatorblinded to

case and/orexposure

status

Basis for assessinghand/wrist exposure to

force

Met all four criteria:

Armstrong 1987a 17.0†,4.8

Yes Yes Yes Observation ormeasurements

Met at least one criterion:

Byström 1995 2.5† Yes Yes No Job titles or self-reports§

Kurppa 1991 14.0–38.5† Yes Yes NR‡ Observation ormeasurements

McCormack 1990 3.0† Yes Yes NR Job titles or self-reports

Roto 1984 3.1† Yes Yes Yes Job titles or self-reports

*Some risk indicators are based on a combination of risk factors—not on force alone (i.e., force plus repetition, posture,or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. ‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].

5b-20

Table 5b-3. Epidemiologic criteria used to examine studies of hand/wrist tendinitis MSDs associated with posture

Study (first author andyear)

Riskindicator (OR,PRR, IR or p-

value)*,†

Participationrate $$70%

Physicalexamination

Investigatorblinded to case

and/orexposure

status

Basis for assessinghand/wrist exposure to

posture

Met all four criteria:

Luopajärvi 1979 4.1† Yes Yes Yes Observation ormeasurements

Met at least one criterion:

Amano 1988 3.7–6.2† NR‡ Yes NR Job titles or self-reports

Byström 1995 2.5† Yes Yes No Job titles or self-reports§

Kuorinka 1979 1.4 Yes Yes NR Observation ormeasurements

*Some risk indicators are based on a combination of risk factors—not on posture alone (i.e., posture plus force, repetition, or vibration). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. ‡Not reported. §EMG and video analysis of subgroup reported in Hägg et al. [1996].

5b-22

(Continued)

Table 5b–4. Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR, or PRR 95% CI Comments

Amanoet al. 1988

Cross-sectional

102 assembly lineworkers in anathletic shoe factorycompared to 102age and gendermatched non-assembly lineworkers (clerks,nurses, telephoneoperators, cooks,and key punchers).

Outcome: Examinationby a physician: palpationfor tenosynovitis andtenderness.

Exposure: One line of29 shoe assemblyworkers was selectedfor job analysis.Videotapes wereevaluatedfor movements of theupper extremities andshoulders and cycleand holding times.

No formal exposureassessment ofcomparison group.

Tenosynovitis, right index fingerflexors: 32.35%

Tenosynovitis, left index fingerflexors: 36.27%

Tenosynovitisright indexfinger flexors:8.82%

Tenosynovitis left indexfinger flexors:5.88%

PRR=3.67

PRR=6.17

1.85-7.27

2.72-13.97

Participation rate: Not reported.

Unclear whether examiner was blindedto job category (occupational groupsexamined on separate dates). No clearcase definition provided. Potential forexaminer bias exists.

Comparison group was matched ingender and age (within 5 years).

Tenosynovitis of other digits was notdiagnosed in the comparison group.

Neurological exam and clinical tests of pinch strength, tapping, pressure, andvibration sensibility were also done. No significant differences betweengroups in finger-pinch strength. Shoeworkers failed the tapping test moreoften, had lower pressure-sensibility in1 of 10 fingers tested, and had lowervibration-sensibility in 2 of 10 fingers. One of 3 neurological maneuvers(Morley’s test) was more often positivein shoe workers. Exposure to tolueneis noted and is a potential confounderfor neurological findings.

Assembly line workers produced about3,400 shoes a day. All but one taskhad cycle times <30 sec.

Assembly workers held shoe lastslonger in the left hand and had greaterfrequency of symptoms in left hand vs. non-assembly workers, who wereassumed to use right hand (dominanthand) more frequently.

5b-24

(Continued)

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

Armstrong1987a

Cross-sectional

652 industrialworkers divided into4 groups: (1) lowforce, low repetition(comparison group,n=157), (2) highforce, low repetition(n=195), (3) lowforce and highrepetition (n=143),and (4) high forceand high repetition(n=157).

Outcome: Positivefindings on interviewand physical exam wererequired for casedefinition. Tendinitis/teno-synovitis: localized pain orswelling lasting > aweek, and increasedpain with resisted butnot passive motion. Trigger finger: locking inextension or flexion anda palpable nodule atbase of finger.

DeQuervain’s: positiveFinkelstein test withlocalized pain score of>=4 (range 1 to 8).

Exposure: To force andrepetition assessed byEMG and video analysisof jobs performed by a sample of workers.

3.1% (Group 2)

3.5% (Group 3)

10.8% (Group 4)

0.6% PRR=4.8

PRR=5.5

PRR=17.0

0.6-39.7

0.7-46.3

2.3-126.2

Participation rate: 90% of workersoriginally selected for inclusion actuallyparticipated.

The effect of age, gender, years on thejob, and plant were analyzed. Higherprevalence of tendinitis among women,but not significantly associated withpersonal factors. Significantdifferences in posture were observedbetween males and females.

Examiners were blinded to exposurestatus of study participants.

5b-25

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Byströmet al. 1995

Cross-sectional

199 automobileassembly lineworkers, comparedto 186 generalpopulation.

Outcome: Tenosynovitisor peri-tendinitis werediagnosed based onphysical examinationobservations: swellingand pain at the tendonsheath, peritendinousarea or muscle-tendonjunction during activemovement of the tendon. deQuervain’s tendinitis:Positive Finkelstein’stest.

Exposure: Dailyduration of hand andfinger movements,manual handling, wristposition, grip type, andhand-tool use wererated by workers on6-point scales inquestionnaires[Fransson-Hall et al.1995]. Forearmmuscular-load and wristangle were evaluatedby EMG and videotapeanalysis for a subgroup[Hägg et al. 1996].

8.04%(deQuervain’stendinitis)

3.23% PRR=2.49 1.00-6.23 Participation rate: 96%. Study grouprandomly selected from assemblydivision of a plant. Comparison group isfrom the MUSIC study [Hagberg andHogstedt 1991].

Examiners blinded to exposure status:no, everyone examined by the authorswas in the exposed group.

Results are reported separately formales and females, and for age <40years. Psychosocial variables andother potential confounders or effectmodifiers were addressed byFransson-Hall et al. [1995].

Higher prevalence of deQuervain’stendinitis in males than infemales—possibly related to greateruse of hand tools, ulnar deviation,and/or static muscle loading.

No cases of tenosynovitis orperitendinitis were found in this study,probably because of strict clinicalcriteria (required observation ofswelling).

5b-26

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

KuorinkaandKoskinen1979

Cross-sectional

93 scissor makerscompared to 143shop assistants.

Phase One: physicalexamination andinterview. Phase Two: workanalysis. 10-monthinterval betweenphases.

Comparison groupwas from anotherstudy that used thesame method[Luopajärvi et al.1979].

Outcome: Tenosynovitisand peritendinitisdiagnosed by interviewand physical exam.Physiotherapistexamined workers,diagnoses were frompredetermined criteria[Waris 1979] (localizedtenderness and painduring movement andlow grip-force andswelling of wristtendons). In problemcases orthopedic andphysiatric teamsdetermined case status.

Exposure: Work history,hr, and production ratesfor the previous yearwere taken fromcompany records. Aworkload index wasbased on videotapeanalysis of scissormaker workstations: time spent in deviatedwrist-posture(>20E)/work cycle;multiplied by numberpieces handled multipliedby hr worked. Noexposure assessmentof shop assistants.

18.3% 13.5% PRR=1.38 0.76-2.51 Participation rate: 81%.

Examiner was not blinded to casestatus, but diagnosis was madeseparately, using predetermined criteria[Waris et al. 1979].

Study group was 99% female. Norelationship found between age orbody mass index and “muscle-tendonsyndrome.”

The number of symptoms increasedwith the number of parts handled/year. Workers were paid by piece rate.

Within the group of scissor makers,non-significant increased prevalencesof muscle-tendon syndrome in shortvs. long cycle tasks and in manipulationvs. inspection tasks was reported. The authors noted a lack of contrast inexposures between the subgroups. Anon-significant trend of increasingprevalence of diagnosed muscle-tendon syndrome with increasingnumber of pieces handled/year wasnoted in a nested case-control analysis(n=36).

5b-27

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Kurppaet al. 1991

Cohort: 31-monthfollow-up

377 meatcutters,meatpackers andsausage makerscompared to388 office workers,maintenanceworkers, andsupervisors.

Outcome: Defined asphysician-diagnosedtenosynovitis orperitendinitis of the handor forearm. Criteriawere swelling orcrepitation andtenderness to palpationalong the tendon andpain at the tendonsheath, in theperitendinous area, or atthe muscle-tendonjunction during activemovement of the tendon. deQuervain’s tendinitis: positive Finkelstein’stest (if not positive,included in tendinitisgroup). 25% ofdiagnoses made byphysicians outside plant,criteria unknown.

Exposure: Jobcategories selectedbased on whether ornot strenuous manualwork was required. Exposure data obtainedfrom previous publishedliterature and plant walk-throughs.

12.5/100 personyears(meatcutters)

25.3/100 personyears (meat-packers)

16.8/100 personyears (sausagemakers)

0.9/100person years(males)

0.7/100person years(females)

14 (meat-cutters)

38.5 (meat-packers)

25.6(sausagemakers)

5.7-34.4

11.7-56.1

19.2-77.5

Participation rate: >70%. Job transfersand employee termination followed upwith questionnaire. Questionnaireresponse rate over 70%.

Exposed and comparison groups weresimilar in age and gender mix, althoughgender varied with job.

If same diagnosis occurred at samesite in worker after 60 days, it wasconsidered new episode. Therefore,separate episodes may berecurrences, and thus influenceresults. Median interval of 233 daysbetween episodes.

Packers worked in temperatures 8E to10EC; sausage makers worked intemperatures 8E to 20EC.

Examiners were not blinded tooccupation of subjects.

Plant selected because of high numberof reports of musculoskeletaldisorders. All permanent workers inmeat cutting, sausage making andpacking departments were included,after 3 months of work. Case ascertainment: Workers in non-strenuous jobs may not have soughtmedical care for MSDs since they mightstill be able to perform their jobs.

5b-28

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Luopajärviet al. 1979

Cross-sectional

152 femaleassembly linepackers in a foodproduction factorywere compared to133 female shopassistants in adepartment store. Cashiers wereexcluded fromcomparison group.

Outcome: Tenosynovitisand peritendinitisdiagnosed by interviewand physical exam.Physiotherapistperformed active andpassive motions, gripstrength tests,observation andpalpation. Medicalspecialists used thesefindings later todiagnose disordersusing predeterminedcriteria [Waris 1979].

Exposure: Exposure torepetitive work,awkward hand/armpostures, and staticwork assessed byobservation and videoanalysis of factoryworkers. No formalexposure assessmentof shop assistants.

55.9% 13.5% PRR= 4.13 2.63-6.49 Participation rate: 84%. Workersexcluded from participation forprevious trauma, arthritis and otherpathologies.

Examiner blinded to case status: Notstated in article.

No association between age and MSDsor length of employment and MSDs. Factory opened only short time. Hobbies and housework were notsignificantly associated with outcome.

Unable to examine effect of job-specific risk factors because of jobrotation.

5b-29

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

McCormacket al. 1990

Cross-sectional

Textile workers: 4broad job categoriesinvolving intensiveupper extremityuse—sewing (n=562), boarding(n=296), packaging(n=369), and knitting(n=352); comparedto other non-officeworkers (n=468),including machinemaintenanceworkers,transportationworkers, andcleaners andsweepers.

Outcome: Assessed byquestionnaire andscreening physicalexam, followed bydiagnostic physicalexamination.

Tendinitis: Positivephysical findingssuggestive ofinflammation.

Severity reported asmild, moderate orsevere.

Exposure: To repetitivefinger, wrist and elbowmotions based onknowledge of jobs; noformal exposureassessment performed.

Boarding: 6.4%

Sewing: 4.4%

Packaging: 3.3%

Knitting: 0.9%

Overall exposedgroup: 3.75%

Other non-office: 2.1%

PRR=3.0

PRR=2.1

PRR=1.5

PRR=0.4

PRR=1.75

1.4-6.4

1.0-4.3

0.7-3.5

0.1-1.4

0.9-3.39

Participation rate: 90.5% for screening;93.6% of those screened went on tocomplete physical examination.

Stratified random sampling withinoccupational groups.

Not mentioned whether examinersblinded to exposure status (jobcategory).

Prevalence higher in workers with<3 years of employment. Race andage not related to outcome. Femalegender was a significant predictor oftendinitis (p=0.01), but job categorywas a stronger predictor (p=0.001).

10/12 physician examiners recordeddiagnoses within 12% of the mean forthe group.

47.9% of workers who had eitherpositive screening physical exams orreported symptoms on questionnairewere diagnosed with tendinitis ortendinitis-related syndromes.

5b-30

Table 5b–4 (Continued). Epidemiologic studies evaluating work-related hand/wrist tendinitis

MSD prevalence

StudyStudydesign Study population

Outcome andexposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

Roto andKivi 1984

Cross-sectional

90 meatcutterscompared toreference group of72 constructionforemen who hadnot been exposed torepetitivemovements of theupper extremities intheir work. Allparticipants weremale.

Outcome: Tenosynovitisdefined as swelling,local pain and fingerweakness duringmovement (determinedby questionnaire andphysical exam).

Exposure: Based on jobtitle. Study groups wereselected based ongeneral knowledge ofjob tasks: meatcutters’work entailed physicalexertion of upperextremities andshoulders. Constructionforemen’s work did notinvolve repetitivemovements of the upperextremities. No formalexposure assessment.

4.5%

Symptomprevalence rate:30.0%

0.0%

Symptomprevalencerate: 10.0%

Indetermin-ate

PRR=3.09

Õ

1.43-6.67

Participation rate: 100% formeatcutters, 94% for comparisongroup.

Authors state that examiners wereblinded to occupation of subjectsbecause part of larger group of meatprocessing workers examined, but it isunclear whether construction foremen(referents) were examined separately.

Serologic testing for rheumatoidarthritis was done to control forpotential confounding (none detected).

Relatively strict diagnostic criteria usedto avoid false positive cases. Authorsnote that tenosynovitis occurred inyounger age groups.

Although the only diagnosed cases oftenosynovitis occurred in themeatcutters (none in the referents), theauthors were reluctant to inferassociation with meatcutting becauseof the relatively low prevalence rate(4.5%).

5b-31

5c-1

CHAPTER 5c Hand-Arm Vibration Syndrome

SUMMARYIn general, the studies listed in Table 5c–1 show strong evidence of a positive association between highlevel exposure to hand-arm vibration (HAV) and vascular symptoms of hand-arm vibration syndrome(HAVS). These studies are of workers with high levels of exposures such as forestry workers, stone drillers,stone cutters or carvers, shipyard workers, or platers. These workers were typically exposed to HAVacceleration levels of 5 to 36 m/s². These studies typically were cross sectional studies which examinedthe relationship between workers with high levels of exposures to HAV with a non-exposed control group.There is substantial evidence that as intensity and duration of exposure to vibrating tools increase, the riskof developing HAVS increases. There also is evidence that an increase in symptom severity is associatedwith increased exposure. As intensity and duration of exposure are increased, the time from exposureonset and beginning of symptoms is shortened.

As described above, the relationship between vibration exposure and HAVS was evaluated favorably withregard to other epidemiological causality criteria, including consistency and coherency of availableinformation and evidence describing the temporal sequence of exposure and outcome.

INTRODUCTION

The 20 epidemiologic studies discussed in thisreview were selected according to criteria thatappear in the introduction of this document. Inour review, we evaluated the studies accordingto criteria that enabled us to assess theresearch. These criteria, including adequateparticipation rate, definition of health outcomeby both symptoms and medical exam criteria,blinding of investigators to exposure/outcomestatus, and independent/objective measure ofexposure, also are described in detail in theIntroduction.

In reviewing the studies, we gave greatestqualitative weight to those which fulfilled all fourof the above criteria. Table 5c-1 (all tables arepresented at the end of the chapter)characterizes the 20 reviewed Hand-ArmVibration studies according to the fourevaluation criteria. Full summary descriptions ofall the studies appear at the end of the chapter.

In addition to the four criteria we used toevaluate the studies, we determined whetherstudies demonstrated statistically significantassociations between exposure attributes andhealth outcomes. We also examined whetherthe observed associations were likely to becaused or substantially influenced by majorstudy flaws, including confounding and selectionbias. Some of these limitations are shown in thedescriptions of individual studies (Table 5c–2).

We then reviewed and summarized the studieswith regard to standard criteria used byepidemiologists to evaluate the causalrelationship between a health outcome and anexposure of interest. These criteria includedstrength of association, temporal relationship,consistency of association, coherence ofassociation, and exposure-responserelationships.

In this review, results of each of the studies

5c-2

examined, whether negative, positive, orequivocal, contributed to the pool of data usedto make our decision regarding the strength ofthe causal relationship between HAVS andworkplace risk factors. Greater or lesserconfidence in the findings reflected theevaluation criteria described above.

Definition of HAV for HAVSHand-Arm Vibration is defined as the transferof vibration from a tool to a worker’s hand andarm. The amount of HAV is characterized bythe acceleration level of the tool when graspedby the worker and in use. The vibration istypically measured on the handle of tool whilein use to determine the acceleration levelstransferred to the worker.

EVIDENCE FOR THE WORK-RELATEDNESS OF HAVS

The hazardous effects of occupational exposureto HAV have been discussed in hundreds ofstudies dating to the work of Loriga in 1911.The composite of vibration-induced signs andsymptoms referred to as hand-arm vibrationsyndrome includes episodic numbness; tinglingand blanching of the fingers, with pain inresponse to cold exposure; and reduction ingrip strength and finger dexterity. These signsand symptoms are known to increase inseverity as exposure to vibration increases inintensity and duration.

A review of pertinent epidemiologic studies ofHAVS has been previously presented [NIOSH1989]; therefore, Table 5c–2 includes onlythose studies completed after 1989. Except fora few longitudinal studies of chain sawyers inthe United Kingdom, Finland, and Japan, theliterature comprises largely cross-sectionalstudies carried out within an industry. Cross-

sectional studies are limited in their ability toascertain temporal relationships betweenexposure and outcome. Because results areobtained at only one point in time, the cross-sectional study design also is subject tounderassessment of the health outcome(particularly in groups with longer durations ofemployment and higher participant attrition).

The studies included in this review varied indesign and quality of information. Sixteen werecross-sectional in design, and three wereprospective cohort in design. One study wasboth cross-sectional and prospective, including10 cross-sectional follow-ups over time and acohort group [Koskimies et al. 1992]. Thirteenof the 20 studies reported assessing case statususing physical exams, while other studies usedonly a questionnaire to determine outcomes. Ofthe studies in which the subjects underwent aphysical exam, five performed a coldprovocation test [Bovenzi et al. 1988; Bovenziet al. 1995; Brubaker et al. 1983; Brubaker etal. 1987; McKenna et al. 1993], threeperformed a nail compression test [Mirbod etal. 1992b; Nagata et al. 1993; Saito 1987],one performed a nerve conduction test[Virokannas 1995], one performedsensorineural physician testing [Bovenzi andBetta 1994], one performed a neurologicalexam [Shinev et al. 1992], one performed anAllan test [Nilsson et al. 1989] and one usedphysician judgement based on workers’complaints and history [Koskimies et al. 1992].

Twelve of the 20 studies conducted anexposure assessment of the tools subjects wereusing; an additional study used exposureassessment information the authors hadcollected in a previous investigation. Theremaining studies estimated exposures by self-

5c-3

report or job title.

The one study that met all four criteria and thefour studies which met the three criteria arediscussed in the following section. Detaileddescriptions for all 20 investigations can befound at the end of the chapter.

Comments Related to SpecificStudies of HAVSThe Bovenzi et al. [1995] cross-sectionalinvestigation of forestry workers comparedvibration white finger (VWF) in this group withshipyard worker referents. VWF wasdiagnosed by symptom report and coldprovocation test; vibration exposures wereestimated by questionnaire report on frequencyof chain saw work and types of saws used,along with direct measurement of vibrationproduced by 27 antivibration and 3 non-antivibration saws. Daily exposure to sawvibration was estimated by linking the twoassessments. The prevalence rates for VWFwere 23.4% in forestry workers and 2.6% inshipyard referents [Odds ratio (OR) 11.8, 95%Confidence Interval (CI) 4.5–31.1]. Forworkers using only antivibration saws, the ORwas 6.2 (95% CI 2.3–17.1); for those usingnon-antivibration saws, the OR was 32.3 (95%CI 11.2–93). A dose-response was observedfor VWF and lifetime vibration dose (OR 34.3,95% CI 11.9–99, for the highest category).Although participation rates were not stated forreferents, the participation appeared to be100% for forestry workers. Authors included10 retired workers to lessen the problems withselection out of the workforce. Resultsdemonstrated that antivibration saw use wasassociated with a lower prevalence of VWF.

Koskimies et al. [1992] examined vibrationsyndrome in a group of forestry workersemployed by the National Board of Forestry inFinland. All those employed in one parishparticipated in a series of 10 cross-sectionalstudies from 1972 to 1990. Results also werereported for a cohort of 57 individuals whoremained in the study from 1972 to 1986.HAVS symptoms were assessed byquestionnaire and physical exam criteria.Exposure to chain saw vibration wasdetermined by measurement of front handleacceleration. Cross-sectional analysis resultsshowed a monotonic decrease in prevalence ofVWF from 40% in 1972 to 5% in 1990. In thecohort of 57, VWF increased from 30% in1972 to 35% in 1975. VWF decreasedmonotonically to approximately 6% in 1986.Over the same time period, modifications ofchain saws used by the workers resulted in adecrease in saw vibration acceleration from 14m/s2 to 2 m/s2. The authors attributed the reduction inVWF to saw changes, although exposures andoutcomes were never linked for individualworkers. Strengths of the study includedobservation of similar results from the series ofcross-sectional analyses and full participationon the part of the 57 subjects. Limitationsincluded failure to assess chain saw exposuremeasures at the individual level. The studydemonstrated the potential for symptomimprovement after exposure reduction.

In the Nilsson et al. [1989] cross-sectionalstudy of male pulp mill machine manufacturingemployees, VWF was examined in a group of89 platers and 61 office workers. VWF wasascertained by physical exam and interview.For platers, vibration exposure was assessedby measuring acceleration intensity on a sample

5c-4

of tools and linking results to subjective ratingsof exposure time. Current and past exposureswere estimated for both platers and officeworkers (some office workers had experiencedexposures in the past). Prevalence for platerswith current exposure was 42%, in comparisonto 2.3% for office workers with no exposures(OR 85, 95% CI 15–486). When thoseexposed to vibration (platers plus officeworkers with previous vibration exposure)were compared to unexposed office workers,prevalences were 40.0% and 2.3%respectively (OR 56, 95% CI 12–269). Adose-response was observed for VWF andyears of exposure. The relationships betweenoutcome and exposure, after adjustment forage, were strong. Representativeness of thereferent group of office workers could not bedetermined.

Bovenzi [1994] examined HAVS cross-sectionally in 570 quarry drillers and stonecarvers, along with a referent group of polishersand machine operators who were not exposedto hand-transmitted vibration. HAVS wasassessed by physician interview, andsensorineural symptoms were staged andgraded. Exposure to vibrating tools wasassessed by interview and linked to vibrationmeasurements obtained from assessment of asample of tools. Prevalences of HAVS were30.2% in the exposed and 4.3% in theunexposed groups (OR 9.33, 95% CI4.9–17.8). Symptoms of VWF increased withlifetime vibration dose (OR 10.2, 95% CI4.8–21.6, for the highest category). Studystrengths included detailed exposureassessment and modeling of relationships,100% participation, and a very stable workpopulation. Because of the work populationstability, results were unlikely to be influenced

by participant attrition.

The Bovenzi et al. [1988] cross-sectionalinvestigation examined VWF in vibration-exposed stone drillers and stonecutters/chippers and a reference group ofquarry and mill workers. VWF was assessedby questionnaire and physical exam. Exposurewas assessed by measuring accelerationintensity on a sample of tools and linking it withself-reported exposure time. VWF prevalencerates were 35.5% in exposed and 8.3% inunexposed groups (OR 6.06, 95% CI2.0–19.6; OR 4.26, 95% CI 1.8–10.4). Asignificant association was observed betweenvibration acceleration level and severity ofVWF symptoms (0% and 18.4% in the lowestand highest categories, respectively).

Strength of Association One of the studies examined met all four of theevaluation criteria [Bovenzi et al. 1995]. Fiveinvestigations met three of the criteria [Bovenziet al. 1988, 1994; Kivekäs et al. 1994;Koskimies et al. 1992; and Nilsson et al.1989]. The criterion that was not met (or notreported) by four of the studies was blinding ofthe physician with regard to worker job status.However, most studies used objectivemeasures for determining case status: coldprovocation [Bovenzi et al. 1988, 1995],sensorineural physician grading [Bovenzi andthe Italian Study Group 1994], and the Allantest [Nilsson et al. 1989]. Use of objectivemeasures lessens the likelihood that case statuswas influenced by knowledge of participants’exposures.

In the Bovenzi et al. [1988] cross-sectionalinvestigation, vibration-exposed stone drillers

5c-5

and stone cutters/chippers showed a 6.06-fold(95% CI 2.0–19.6) increase in risk of VWF incomparison to unexposed quarry and millworkers. Similar results were observed inanother study of stone workers conducted byBovenzi in 1994. Quarry drillers and stonecarvers exposed to vibration showed an OR forVWF of 9.33 (95% CI 4.9–17.8) whencompared to a reference group of polishers andmachine operators. A dose-responserelationship was observed for VWF andlifetime vibration dose, with an OR of 10.2(95% CI 4.8–21.6) for the highest exposurecategory. A study of forestry workers [Bovenziet al. 1995] demonstrated an OR of 11.8 (95%CI 4.5–31.1) for VWF when comparingforestry workers with exposure to chain sawvibration to an unexposed group of shipyardworkers. A lower risk of VWF (OR 6.2, 95%CI 2.3–17.1) was observed for those using onlyantivibration saws. A dose-response betweenVWF and vibration exposure also was observedin this investigation, with an OR of 34.3 (95%CI 11.9–99) for the highest exposure category.Nilsson et al. [1989] observed very strongrelationships between VWF and exposure tovibration in machine manufacturing platers. Incomparison to office workers with noexposure, platers had an OR of 85 (95% CI15–486). Kivekäs et al. [1994] found asignificantly increased OR in the cumulativeincidence of HAVs in a 7-year cohort study(OR 6.5, 95% CI 2.4–17.5). Koskimies et al.[1992] examined a dynamic cohort of forestryworkers at 10 intervals from 1972 to 1990during which time saws were being modified inweight, vibration frequency, and vibrationacceleration. Over the 18-year period, amonotonic decrease in VWF was observed inthe 10 cross-sectional examinations, with anoverall eight-fold reduction in prevalence. Asubset of workers followed

from 1972 to 1986 showed a decrease inVWF from 30% to 6%. The reductions wereattributed to modifications in chain saws duringthe same time period.

The remaining, less rigorous, studies showedvarying relationships between HAVS andexposure. The majority of the studiesdemonstrated moderate to strong positiveassociations. Most compared exposed tounexposed groups with little or no detailedanalysis by exposure level. Two investigationsexamined HAVS in exposed groups and foundan increase in risk by years of employment,with ORs of 8.4 and 8.9 (95% CI 2.9–28.9)when comparing the highest and lowestcategories [Mirbod et al. 1992b; Kivekäs et al.1994]. Another study that examined HAVSprevalence in power tool users found noassociation with duration of employment (with aparticipation rate of only 38%) [Musson et al.1989]. For other investigations, exposed andunexposed groups were defined by job titles.ORs for these studies ranged from 3.2 to 40.6(relative risk [RRs] from 3.2 to 16) [Brubakeret al. 1983; Dimberg and Oden 1991; Letz etal. 1992; McKenna et al. 1993; Mirbod et al.1992a; Mirbod et al. 1994; Nagata et al.1993]. Three studies demonstrated varyingHAVS rates for exposed groups, but includedno referents [Shinev et al. 1992; Starck et al.1990; Virokannas and Tolonen 1995].

Two investigations produced conflictingevidence related to the effects of chain sawmodifications on HAVS in forestry workers.The Brubaker et al. [1987] study, observed a28% increase in prevalence of VWF in acohort of tree fellers over a 5-year period andclaimed that saw modifications were ineffective.Saito [1987] found no new HAVS symptom

5c-6

development over 6 years in a cohort of chainsawyers in reducing symptoms.

Comparing construction workers to officeworkers, one study demonstrated an OR of 0.5(95% CI 0.1–11.8) for HAVS. This study metnone of our four criteria [Miyashita et al. 1992].

In general, the studies in Table 5c-1 showstrong evidence of a positive associationbetween exposure to HAV and vascularsymptoms of HAVS.

TemporalityThe temporal relationship between HAVexposure and symptoms of HAVS is wellestablished by studies which have determinedthe latency between exposure and symptomonset. Of 52 studies reviewed by NIOSH in1989, 44 included some information about thelatency period for the development of vascularHAVS symptoms following initial exposure.Latency ranged from 0.7 to 17 years, with amean of 6.3 years. Unfortunately, because mostof these studies were cross-sectional (i.e.,latency was determined retrospectively) andbecause HAVS develop slowly, the possibilityof recall bias is strong [Gemne et al. 1993].However, longitudinal studies provide supportfor the temporal nature of the association.Kivekäs et al. [1994], in a 7-year follow-up ofFinnish lumberjacks, found a cumulativeincidence rate (IR) of 14.7%, compared to acumulative IR of only 2.3% among referents.The cumulative IR of lumberjacks who hadmore than 25 years of exposure at the end ofthe follow-up period was 30.6%. Other studiesof Finnish forestry workers also showed amarked decrease in HAVS prevalencefollowing the introduction of improved chain

saws [Pyykkö and Starak 1986; Koskimies etal. 1992].

ConsistencyThe literature consistently shows that workersexposed to HAV develop HAVS at asubstantially higher rate than workers notexposed to vibration. Although there isconsiderable variation in the occurrence ofHAVS among different groups using similartypes of vibrating tools, the lack of consistencyprobably is explained by methodologicaldifferences between studies (i.e., someresearchers did not account for exposurevariation over time in the summary estimate ofexposure) or by differences in work methods,work processes, and work organization[Gemne et al. 1993]. Important also is thedifference in the intensity and duration ofexposure.

Coherence of Evidence

The mechanisms by which HAV producesneurological, vascular, and musculoskeletaldamage are supported by some experimentalevidence [Armstrong et al. 1987b; Lundborg etal. 1990; Necking et al. 1992]. Neurologicaland circulatory disturbances probably occurindependently and by unrelated mechanisms.Vibration may directly injure the peripheralnerves, nerve endings, and mechanoreceptors,producing symptoms of numbness, tingling,pain, and loss of sensitivity. Vibration also mayhave direct effects on the digital arteries. Theinnermost layer of cells in the blood vessel wallsappears especially susceptible to mechanicalinjury by vibration. If these vessels aredamaged, they may become less sensitive to theactions of

5c-7

certain vasodilators that require an intactendothelium. Experiments involvinglumberjacks exposed to chain saw vibrationsupport this hypothesis [Gemne et al. 1993].There also is evidence that the walls of thedigital blood vessels are thickened in personswith HAVS [Takeuchi et al. 1986]. Duringcold exposure, vessels with these changes willbecome abnormally narrow and may closeentirely [Gemne 1982]. Symptoms of numbnessand tingling which characterize HAVS may besecondary to vascular constriction of the bloodvessels, resulting in ischemia in the nerve-endorgans.

Other evidence concerning the coherence ofinformation regarding the association betweenvibration exposure and HAVS relates tobackground prevalence of similar disorders inthe general population. One estimate placed theprevalence of Raynaud's phenomenon at 4.6%for females and 2.5% for males in the generalpopulation [Iwata and Makimo 1987]. Only 7of the studies examined in this review foundprevalence rates less than 20% among workersexposed to HAV. In the 1989 NIOSH review,only 9 of 52 cross-sectional studies reported aprevalence rate of less than 20% amongworkers exposed to HAV. This providesstrong evidence that individuals working invibration-exposed occupations are at muchhigher risk of these disorders than those in thegeneral population.

Exposure-Response RelationshipExposure-response relationships involvingHAV have been postulated, including: (1) arelationship between the prevalence of HAVSand vibration acceleration (and cumulativeexposure time), (2) a relationship between thedose and symptom severity, and/or (3) a

relationship between the dose and the latencyof symptom onset.

Support for the first relationship is provided bya few longitudinal studies of workers exposedto HAV. In general, all show strong evidencethat decreasing the acceleration level of a hand-held vibrating tool has a positive relationshipwith prevalence of HAVS. In a study of Finnishforestry workers using chain saws, Koskimieset al. [1992] found that the prevalence ofHAVS symptoms declined from a peak of 40%to 5% after the introduction of light-weight,low-vibration chain saws with reducedacceleration from 14 to 2 m/s2. Likewise, astudy of similar workers in Japan found that theprevalence of vascular symptoms among chainsaw operators who began their jobs before theintroduction of various engineering andadministrative controls peaked at 63%.(Vibration acceleration levels for chain sawsused during this period ranged from 111 to 304m/s2.) In contrast, the peak prevalence forchain saw operators who began working afterthe introduction of antivibration chain saws(acceleration level: 10-33 m/s2) and exposureduration limits (2 hrs/day) was only 2%[Futatsuka and Uneno 1985, 1986].

NIOSH authors ranked 23 cross-sectionalstudies that measured HAV acceleration levelsand estimated a prevalence rate for vascularsymptoms [NIOSH 1989]. To test whether alinear relationship existed between the HAVlevel and the prevalence of vascular symptoms,a correlation coefficient was calculated. Thecorrelation analysis found a statisticallysignificant linear relationship between HAVacceleration level and prevalence of vascularsymptoms (R 0.67, p<0.01), indicating thatprevalence of vascular symptoms tendsto increase as the HAV acceleration level

5c-8

increases. However, the absorption of vibrationenergy by the hand is influenced by thevibration intensity, as well as by frequency,transmission direction, grip and feed forces,hand-arm postures, and anthropometric factors[Gemne et al. 1993].

Several studies reviewed for the currentdocument found relationships betweenprevalence of HAVS and duration of vibration-exposed work [Bovenzi 1994; Bovenzi et al.1995; Letz et al. 1992; Nilsson et al. 1989].One cross-sectional study with a very poorresponse rate found no association withduration of exposure [Musson et al. 1989].

Justification for a relationship between dose andHAVS prevalence and symptom severity isprovided by Bovenzi et al. [1988] and Mirbodet al. [1992b]. In a study of stone-cutters usingrock drills and chisel hammers, Bovenzi foundthat HAVS prevalence increased linearly withthe total number of working hours, from about18% for persons with 6,000 hrs of exposure, tomore than 50% among persons with more than26,000 hrs of exposure. Likewise, in a study of447 workers using chain saws, Mirbod et al.[1992b] found that the prevalence of HAVSincreased from 2.5% among workers with lessthan 14 years of exposure to 11.7% amongworkers with 20–24 years exposure, to 20.9%among workers exposed 30 years or more.Both studies found a statistically significantcorrelation between the severity of symptoms(graded according to the Taylor-Pelmear scale)and a dose measure based on total exposuretime.

Support for a relationship between dose and

latency of symptom onset is provided by Britishstudies conducted in the 1970s among variousoccupational groups, including chain sawyers,grinders, chiselers and swagers [Gemne et al.1993]. Exposure to 10-25 m/s2 chainsawvibration correlated with a latency of about 3years. Pedestal grinders using machines withzirconium wheels were exposed to vibrationlevels of 50 m/s2 and demonstrated a meanlatency of 1.8 years, whereas grinders whoused softer wheels with accelerations of 10-20m/s2 had a mean latency of 14 years. Exposureto 70 m/s2 vibration during swaging correlatedwith a mean latency of about 7 months,although some swagers developed symptoms inas few as 6 weeks.

Confounding and HAVSAge and metabolic disease are the primarypotential confounders for HAVS.

It is important that epidemiologic studiesexamine non-occupational factors, and controlfor them. Most of the studies were able toaddress “age” by stratification in their analyses,or through use of multiple logistic regression.[Bovenzi and Betta 1994; Bovenzi et al. 1995;Brubaker et al. 1983, 1987; Kivekäs et al.1994; Letz et al. 1992; McKenna et al. 1993;Mirbod et al. [1994]. Several authorscontrolled for metabolic disease [Bovenzi andBetta 1994; Bovenzi et al. 1995; Letz et al.1992; McKenna et al. 1993]. This is importantbecause of the effects that some disorders haveon peripheral circulation which may havesymptoms similar to HAVS.

Nonoccupational Raynaud’s phenomena - a

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rare disorder which mimics HAVS has beenknown to occur in individuals with metabolicdisorders, peripheral neuropathy, alcohol-related illness, as well as other conditions.

In reviewing the methods and results of thesestudies, taking into account substantiallyelevated ORs and evidence of dose-responserelationships, it appears that potentialconfounders do not account for the consistentrelationships seen.

Review of the 20 studies, leads us to theconclusion that there is substantial evidence thatas intensity and duration of exposure tovibrating tools increase, the risk of developing

HAVS increases. Most of the studies showed apositive association between high levelexposure to HAV and vascular symptoms ofHAVS. For many of the studies there is astrong association between HAVS andexposure to vibrating tools in the workplace.The temporal relationships and consistencybetween exposure and symptoms of HAVS arewell established in these studies. Themechanisms by which HAV producesneurological, vascular, and musculoskeletaldamage are supported by some experimentalevidence. Many of the studies showed anexposure-response relationship between doseof HAV and the HAVS prevalence andsymptom severity.

Table 5c-1. Epidemiologic criteria used to examine studies of hand/wrist and hand/arm MSDs associated withvibration

Study (first author andyear)

Riskindicator

(OR, PRR, IRor p-

value)*,†Participation

rate $$70%

Physicalexamination

or coldprovocation

Investigatorblinded to

case and/orexposure

status

Basis for assessinghand/wrist or hand/armexposure to vibration

Met all four criteria:

Bovenzi 1995 6.2–32.3† Yes Yes Yes Observation or measurements

Met at least one criterion:

Bovenzi 1988 6.06† NR‡ Yes NR Observation or measurements

Bovenzi 1994 9.33† Yes Yes No Observation or measurements

Brubaker 1983 NR Yes Yes NR Job titles or self-reports

Brubaker 1987 NR No Yes NR Observation or measurements

Dimberg 1991 NR† Yes No NR Job titles or self-reports

Kivekäs 1994 3.4–6.5† Yes Yes Yes Job titles or self-reports

Koskimies 1992 NR Yes Yes NR Observation or measurements

Letz 1992 5.0–40.6† Yes No No Job titles or self-reports—previous study results used

McKenna 1993 24.0† NR Yes No Job titles or self-reports

Mirbod 1992a, 1994 3.77† NR No NR Observation or measurements

Mirbod 1992b NR NR Yes No Observation or measurements

Musson 1989 NR No No NR Observation or measurements

Nagata 1993 7.1† NR Yes No Job titles or self-reports

Nilsson 1989 14–85† Yes Yes NR Observation or measurements

Saito 1987 NR No Yes NR Job titles or self-reports

Shinev 1992 NR NR Yes NR Observation or measurements

Starck 1990 NR NR No No Observation or measurements

Virokannas 1995 NR† NR Yes NR Observation or measurements

Met none of the criteria:

Miyashita 1992 0.5 NR No No Job titles or self-reports

*Some risk indicators are based on a combination of risk factors–not on vibration alone (i.e., vibration plus force, posture,or repetition). Odds ratio (OR), prevalence rate ratio (PRR), or incidence ratio (IR).

†Indicates statistical significance. If combined with NR, a significant association was reported without a numerical value.‡Not reported.

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(Continued)

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

Bovenzi etal. 1988

Cross-sectional

Vibration-exposed stonedrillers (n=32) and stonecutters/chippers (n=44);quarry and mill workersnot exposed to vibration(control group, n=60).

Outcome: Assessed byphysical examination andquestionnaire. VWFsymptoms staged using theTaylor-Pelmear scale.

Exposure: Vibrationexposure assessed bymeasuring the accelerationintensity on a sample of tools,together with subjectiveratings of exposure time.

35.5% 8.3% 6.06 2.01-19.6 Participation rate: Participationrate cannot be determined fromdata in the study.

Significant associationbetween vibration accelerationlevel and severity of VWFsymptoms.

Mean latency period tosymptom onset =12.3 yr.

Frequency-weightedacceleration levels ranged from19.7 to 36.4 m/s2 (rock drillsand chipping hammers) andfrom 2.4 to 4.1 m/s2 (grindersand hand cutters).

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Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Bovenziand theItalianGroup 1994

Cross-sectional

Case group: Stoneworkers employed in ninedistricts in Northern andCentral Italy: 145 quarrydrillers and 425 stonecarvers exposed tovibration. Referent group: polishers and machineoperators (n=258) whoperformed manual activityonly not exposed tohand-transmittedvibration.

Outcome: HAVs assessedby physician-administeredinterview; sensineuralsymptoms staged accordingto Brammer [1992]. Gradedaccording to the Stockholmscale [Gemne 1987].

Exposure: To vibrating toolsassessed by interview. Vibration measured in asample of tools used.

30.2% 4.3% 9.33 4.9-17.8 Participation rate: 100% “Allthe active stone workersparticipated in the study, soself-selection was not asource of bias.”Physician administered thequestionnaires containing workhistory and examinations, sounlikely to be blinded to casestatus.Adjusted for age, smoking,alcohol consumption, andupper limb injuries.Leisure activities, systemicdiseases included inquestionnaire. Univariateanalysis showed noassociation between systemicdiseases and vibration so wasnot criteria for exclusion.Univariate analysis showed noassociation between systemicdiseases and vibration so wasnot criteria for exclusion.Dose–response for CTS andlifetime vibration exposure notsignificant.Frequency-weightedacceleration levels = 15 m/s2

(stone drills), 21.8 m/s2 (stonehammers), 2.84 m/s2 (rotarygrinding tools).

Percent of workers affectedwith HAVs increased inproportion to the square root ofthe exposure duration.

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Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Bovenzi etal. 1995

Cross-sectional

222 active forestryworkers and 10 retiredforestry workers with>400 hr of sawingcompared with 195randomly chosenshipyard workers neverexposed to handvibration. Controlsexcluded forcardiovascular andmetabolic disease.

Outcome: (1) History ofepisodes of cold provokedwell–demarcated blanching inone or more fingers and(2) occurrence afteremployment and exposure tohand vibration and vibrationwhite finger (VWF) attacks inlast 2 years and (3) abnormaldigital arterial response tocold provocation. Clinically,VWF graded using Stockholmscale.Exposure: Vibrationmeasured on front and rearof 27 antivibration (AV) chainsaws used in the forest; forprevious exposureassessment, 3 non-AV chainsaws were measured. Vibration measurementswere made in the field duringcross-cutting operations byskilled workers according toISO 7505.

Forestry workers gavedetailed list of chain sawsused.Workplace questionnairesvalidated by direct interviewswith employers andemployees, employmentrecords, and amount of fuelused by chain sawsDaily exposure to sawvibration assessed in termsof 8-hr energy–equivalentfrequency–weightedacceleration.

All Forestryworkers:23.4%

Workers usingonly AV chainsaws: 13.4%

Workers usingchain sawswithoutvibrationisolationsystems:51.7%

Shipyardworkers:2.6%

(adjustedOR’s)11.8

6.2

32.3

VWFoperators ofnon-AV andAV saws vs.Operators ofantivibrationsaws only:OR=4.0

Lifetimevibrationdosein 9m(m2S-4 hd)<19: OR=4.119-20: OR=4.720-21: OR=9.4>21: OR=34.3

4.5-31.1

2.3-17.1

11.2-93

1.1-16.4

1.3-16.1

3.1-28.4

11.9-99

Participation rate: 95% vibratingtool users, not reported forcontrol.Analysis controlled for age,smoking, drinking habits.Physicians blinded to casestatus–since cold provocationtest was used, it was not anissue.Smoking, alcohol, metabolic,cardiovascular, neurologic,previous musculoskeletalinjuries, use of medicinesincluded in questionnaire andaccounted for in logisticregression model.Cold provocation testingperformed on both forestryworkers and controls.Exposure–responserelationship found betweenVWF and vibration exposure:the expected prevalence ofVWF increased almost linearlyto either the 8-hrenergy–equivalentfrequency–weightedacceleration or the number ofyears of exposure (withequivalent accelerationunchanged).

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Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Brubaker etal. 1983

Cross-sectional

146 tree fellers in 7camps employed for $1year compared to 142workers not exposed tovibration matched forlocation.

Outcome: VWF symptomsstaged using Taylor-Pelmearscale.

Ischemic water bath testingfor VWF completed on allsubjects.

Exposure was based onquestionnaire data.

Withsymptoms:51%

Stage 3: 22%

Excludingother vibrationexposure andmedicalhistory: 54%

Stage 3: 25%

Withsymptoms:5%

Stage 3: 2%

2%

Stage 3: 1%

Õ Õ Participation rate: 100%.

Smoking, no significantdifferences.

Age was significantly differentbetween cases and controls.

Height and weight notsignificantly different.

Mean latency period betweenwork and symptoms 8.6 years.

Records of duration ofexposure.

5c-15

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Brubaker etal. 1987

Cohort: 5-yearfollow-upofexposedgroup.

Fellers at Canadianlumber camps (n=71)who hadbeen interviewedand tested in 1979 to1980 then again in1984 to 1985.

Outcome: Defined as HAVssymptoms, assessed byquestionnaire and digitsystolic blood pressure.

VWF symptoms staged usingTaylor-Pelmear scale.

Ischemic water bath testingfor VWF completed on allsubjects.

Exposure: Vibrationmeasurements recorded froma representative sample ofchain saws used in thelogging camp.

Raynaud’ssymptoms:53% (1984 to 1985)

Tingling,numbness:56% (1984 to 1985)

Raynaud’ssymptoms:51% (1979 to1980)

Tinglingnumbness:65% (1979 to1980)

Õ Õ Participation rate: 53%.

Original group (1979 to 1980)included 146 fellers.

16 fellers excluded because ofpotential confounders.

Author concluded antivibrationsaws not effective atpreventing HAVs.

15% of fellers reported newsymptoms of VWF over 5-yearperiod.

28% increase in prevalence ofVWF in workers usingantivibration chain-saws.

Correlation between objectivetest and symptoms poor: 54%reporting symptoms withpositive findings on objectivetests.

5c-16

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Dimbergand Oden1991

Cross-sectional

2,814 Aircraft engineworkers.

68 Sheet metal workers.26 Polishers/grinders.20 Cleaners.40 Forklift-truck drivers.46 Engine testers.146 Fitters.49 Storemen38 Electric welders.

No control group used.

Outcome: Exposure tovibrating hand-toolsassessed by questionnaire. White fingers as a spasm inblood vessels occurring inone or more fingers inconnection with coolingleading to reversible pallorfollowed by redness.

Exposure: Vibrationassessed by questionnaire:working with vibrating tools,time in present job, leisureactivities.

23%(polishers/grinders)

19% (sheetmetalworkers)

15%(cleaners)

Õ Multivariateanalysisshowedincreasedsymptomswithincreasingage, workwith vibratinghand toolsand weightloss

Õ Participation rate: 96%questionnaire.

Vibrating tool use significantlycorrelated with HAVs symptomprevalence.

Analysis was stratified bygender, age, and employmentcategory.

5c-17

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Kivekäs etal. 1994

Cohortwith7-yearfollow-up(1978 to1985)

213 lumberjacks and140 referents.

Outcome: HAVs assessedby questionnaire, clinicalexamination, andradiographs.

Exposure: Not measured. Exposure history determinedvia questionnaire.

Prevalence(HAVs)

1978: 16.9%

1985: 24.9%

Cumulativeincidence,HAVs (7years): 14.7%

Prevalence(HAVs):

1978: 5.0%

1985: 5.7%

CumulativeincidenceHAVs (7years): 2.3%

For 1978:OR= 3.4

For 1985:OR= 4.4

OR=6.5

1.7-6.9

2.3-8.1

2.4-17.5

Participation rate: 76% amongexposed workers, 78% amongcontrol.

Follow-up group included 76%of lumberjacks and 78% ofreferents from original group.

Adjusted for age.

X-ray films read by radiologistsblinded to case status

After adjusting for age, nodifference in lumberjacks with<15-years exposure andreferents, but risk increasedwith increasing duration ofexposure. For those exposedRR=8.9 (2.9-28.9).

No X-ray differences inprevalence of detectabletranslucencies or osteoarthriticchanges in wrists or hands.

5c-18

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Koskimieset al. 1992

Cohort(18-yearfollow-up)

Finnish forest workers(n=118-124).

Outcome: HAVs assessedby questionnaire andphysical examination.

Exposure: Vibrationacceleration of the fronthandle of chain sawsanalyzed.

Prevalence ofHAVs amongforestryworkers in1990: 5%

Prevalenceof HAVsamongforestryworkers in1972: 40%

Õ Õ Participation rate: 100% ofthose who had a yearlyphysical exam.

Decrease in prevalenceattributed to reduction in weightof saws, increase in vibrationfrequency, and reduction invibration acceleration (from 14to 2 m/s2).

5c-19

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Letz et al.1992

Cross-sectional

Shipyard workers withfull-time vibrationexposure (n=103); part-time vibration exposure(n=115), and no vibrationexposure (n=53,comparison group).

Outcome: HAVs assessedby self-administeredquestionnaire; gradedaccording to the Stockholmscale.

Vibration measurements from51 pneumatic tools made in 3studies. Extreme variabilityprecluded direct comparisonof tools. Number of hours perweek and years using toolsasked.

Vascularsymptomsamong part-time vibration-exposedworkers: 33%

Vascularsymptomsamong full-time vibration-exposedworkers:70.9%;

Sensorineuralsymptomsamong part-time vibration-exposedworkers:50.4%

Sensorineuralsymptomsamong full-time vibration-exposedworkers:83.5%

Vascularsymptoms:5.7%

Sensori-neuralsymptoms:17%

Part-timevibration-exposedworkers vs.controls:OR=8.23

Full-timevibration-exposedworkers vs.controls:OR=40.6

Part-timevibration-exposedworkers vs.controls:OR= 5.0

Full-timevibration-exposedworkers vs.controls:OR=24.7

2.3-35.4

11-177

2.1-12.1

9.5-67

Participation rate: 79%.

Participants randomly selectedwithin departments.

Significant exposure–responserelationship found afteradjustment for smoking, notage or race.

Average latency to symptomonset <5 years.

Alcohol consumption, pastmedical conditions consideredin analysis.

Exposure–responserelationship found regardingself-reported cumulativeexposure to vibratory tools,sensorineural stages, andcorresponding vascularclassifications but no furtherincreases in workers with >17,000 hr of exposure.

Median latency for appearanceof symptoms of white fingerwas 8,400 hr of vibratorytool/use and 8,200 hr fornumbness.

Participants not blinded topurpose of questionnaire mayhave been over-reporting.

5c-20

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

McKennaet al. 1993

Cross-sectional

46 pairs of riveters andmatched control subjects(machine operators whohad never used vibratingtools).

Outcome: Defined as cold-induced digital vasospasm.

Exposure: To specific toolsassessed via questionnaire.

35% 2% 24 3.1-510 Participation rate: Not reported.

Matched on age and smokinghabits.

Only males studied.

Excluded those with injury toneck, trunk, upper limbs.

44% of riveters had <2.5 yearsof vibration exposure.

Did not of blind examinersbecause they tested the mostsymptomatic finger.

No differences in resting fingersystolic pressure, vibrationperception, or fingertemperature between casesand controls.

17% of riveters reportedsymptoms of VWF.

5c-21

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Mirbod etal. 1992b

Cross-sectional

Forestry workers(n=447)

No control group used.

Outcome: HAVs assessedby interview and physicalexamination. Symptomsgraded using theStockholm scale.

Frequency-weightedvibration-accelerationmeasurements made on thehands of chainsaw operators duringdifferent job processes.

9.6% overall

20.9% amongworkers with30 or moreyearsexperience

2.5% amongworkers <14years

11.7% 20 to24 years

Õ Õ Õ Participation rate: Not reported.

HAVs symptom severitypositively correlated withexposure duration.

Chain saw vibration levelsranged from 2.7 to 5.1 m/s2. Low prevalence attributed torecent improvements inworking conditions.

5c-22

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Mirbod etal. 1994;Mirbod etal. 1992a

Cross-sectional

(A) 164 male dentaltechnicians, (B) 54 maleorthopedists, (C) 256male aircraft technicians,(D) 79 male laborers,(E) 27 male grinders,(F) 46 female sewing-machine operators,(G) 23 male tea-harvesting-machineoperators, (H) 272 malechain-saw operators;compared with 1,027males and 1,301 femalesnot exposed to vibration.

Outcome: HAVs assessedby questionnaire, interviews,field visits, or annual healthexaminations.

Exposure: To vibratingtools assessed byquestionnaire andinterviews. Hand-transmitted vibrationmeasured among a sampleof workers usingrepresentative tools in actualwork activities.

(See firstcolumn for jobcategories)

A: 4.8%B: 3.7%C: 2.3%D: 2.5%E: 3.7%F: 4.3%G: 0.0%H: 9.6%

Males: 2.7%Females: 3.4%

H vs.unexposedMales: 3.77

2.1-6.8 Participation restricted toworkers age 30 to 59 years. Subjects stratified by age inanalysis.

Hand-transmitted vibrationlevels in groups A to G rangedfrom 1.1 to 2.5 m/s2. Hand-transmitted vibration levels ingroup H ranged from 2.7 to 5.1m/s2.

5c-23

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Miyashitaet al. 1992

Cross-sectional

355 Male constructionworkers (machineoperators) comparedwith 44 male officeworkers. (A) 184 power shoveloperators.(B) 127 bulldozeroperators.(C) 44 forklift operators.

Outcome: HAVs assessedby self-administeredquestionnaire.

Exposure: Status assumedfrom job title (no objectivemeasurements performed).

1.1% 2.3% 0.5 0.1-11.8 Participation rate: Not reported.

Participation restricted to maleworkers age 30 to 49.

Vibration due to construction-machinery operation.

5c-24

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Musson etal. 1989

Cross-sectional

Impact power-tool usersin The Netherlands(n=169).

No control group used.

Outcome: HAVs based onsymptoms, assessed viapostal questionnaire.

Exposure: Vibration intensitymeasured using fiverepresentative tools. Duration of vibrationexposure assessed viaquestionnaire.

17% Õ Õ Õ Participation rate: 38%questionnaire.

Adjusted for age.

Exposure duration not relatedto HAV symptoms.

5c-25

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Nagata etal. 1993

Cross-sectional

179 chain-saw workersand 205 local inhabitantswho had never usedvibrating tools (controlgroup).

Outcome: HAVs assessedby dermatological tests andphysical examination.

Exposure: Vibration notmeasured directly; exposureduration expressed as yearssince commencement ofoccupation.

>20-yearsexposure:16%

< 20-yearsexposure:2.4%

2.9% 7.1 for >20-yearsvibrationexposure

2.5-19.9 Participation rate: Not reported.

Adjusted for age.

Examiners not blinded toexposure status.

5c-26

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Nilssonet al.1989

Cross-sectional

Platers (n=89) and officeworkers (n=61) dividedinto 4 groups accordingto current and pastvibration exposure.

Outcome: Assessed byphysical examinationand interview. VWFsymptoms staged usingthe Taylor-Pelmear scale.

Exposure: Vibrationexposure assessed bymeasuring theacceleration intensity ona sample of tools,subjective ratings, andobjective measures ofexposure time.

Platers withcurrentexposure:42%

Platers withcurrent andformerexposure.

Platers andofficeworkers withcurrent orformerexposure.

Officeworkerswith noexposure:2%

Officeworkerswith novibrationexposureand formerexposure.

Officeworkerswith novibrationexperience.

85

14

56

15- 486

5-38

12-269

Participation rate: 79% amongplaters, not reported amongcontrol.

Controlled for age.

Vibration acceleration levels=5.5 m/s2 (grinders), 10.3 m/s2

(hammers), 1.5 m/s2 (diegrinders).

Mean latency to symptom onset= 9.8 years.

Odds ratio increased by 11%for each year of exposure. Nocorrelation between the Taylor-Pelmear stage and years ofexposure.

5c-27

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Saito 1987 Cohort: 6-yearfollow-upprospect-ive

Chain sawers withoutHAV symptoms in 1978(n=155) followed up in1983.

Outcome: Assessed bysymptoms, skin temperature,vibration threshold, nailcompression, pain sense,and cold provocation.

Exposure: Chain sawoperating time determined byquestionnaire.

0% in 1983 0% in 1978 Õ Õ Participation: Follow-up ofcohort.

Improvements in chain sawdesign, age restrictions, and adecrease in weekly operatingtime credited for preventingHAV.

Recovery rates of skintemperature after 10-minprovocation test significantlybetter in 1982 and 1983compared to 1978.

Vibratory sense thresholds at5th minute after coldprovocation significantly betterin 1980, 1982, and 1983compared with 1978.

Age significance correlated torecovery rates from 1978 to1983.

5c-28

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Shinev etal. 1992

Cross-sectional

77 male fettlers; 59 malemolders; 85 malepolishers.

No control group used.

Outcome: HAV assessed byneurological examination.

Exposure: Vibrationcharacteristics of chippingand caulking hammers, airtampers, and polishingmachines measured.

22.1%(fettlers)6.8%(molders)25%(polishers)

Õ Õ Õ Participation rate: Not reported.

Percussive vibration hadgreater effect on muscle andbone pathology than constanthigh-frequency vibration.

5c-29

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

(Continued)

Starck etal. 1990

Cross-sectional

Forest workers (n=200),pedestal grinders (n=12),shipyard workers(n=171), stone workers(n=16), and platers (n=5).

No control group used.

Outcome: HAV based onsymptoms, assessed viaquestionnaire.

Exposure: Vibrationmeasurements taken on asample of tools during normaloperation at the workplace.

40% (forestworkers using1st generationchain saw)

16% (forestworkers using2ndgenerationchain saw)

<7% (forestworkers using3rd generationchain saw)

100% (forpedestalgrinders withzirconiumwheels)

5% (shipyardworkers)

75% (stoneworkers usingpneumatichammers)

50% (stoneworkers usingchisel heads)

40% (platers)

Õ Õ Õ Participation rate: Not reported.

No demographic data aboutstudy participants provided.

Poor correlation betweenvibration exposure and HAVwhen tools were highlyimpulsive.

5c-30

Table 5c–2. Epidemiologic studies evaluating work-related hand-arm vibration syndrome

MSD prevalence

StudyStudydesign Study population Outcome and exposure

Exposedworkers

Referentgroup

RR, OR,or PRR 95% CI Comments

VirokannasandTolonen1995

Cross-sectional

Railway workers (n=31)and lumberjacks (n=32)exposed to HAV. Nocontrols used. Articleevaluates the vibrationperception threshold(VPT) among exposedworkers and tries todetermine a dose-response relationshipbetween exposure toHAV and the VPTs.

Outcome: “History of attack”of white finger reported bysubjects.

VPT and electroneuro-myography used asindicators of sensory nervedamage (outcome measure).

Exposure: To vibrating toolsassessed by interview. (Nomeasurements performed). Groups asked aboutexposure time with self-estimated annual use ofvibrating tools and vehicles(hr) and number of years ofexposure to vibration. Mean(SD) duration of exposure tovibration was 8,050 (3,500)among railway workers and21,250 (10, 950) hrs amonglumberjacks.

Railwayworkers: 45%VWF

Lumberjacks:38% VWF

Õ Õ Õ Participation rate: Not reported.

Total exposure to HAV hadsignificant correlation with VPTin railway workers (r=0.55-0.47; p=0.017) and lumberjacks(r=0.77-0.59; p=0.003).

Increase in VPT approximately2 times greater in railwayworkers.

7 workers excluded—2railway workers withpolyneuropathy; 4 railwayworkers with CTS;1 lumberjack with CTS. Thesemay have been related tovibration exposure.

Lumberjacks used chain sawsdaily >1,000 hr per year. Railway workers used hand-held tamping machines -500hrs per year.

Found peak value differencesfor hand-held tampingmachines (40 to 60 Hz) andchain saws (120 to 150 Hz).

Nerve-conductionmeasurements adjusted forskin temperature.

5c-31