development of and recovery from short- and long-term low back pain in occupational settings: a...

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European Journal of Pain 11 (2007) 841–854

Development of and recovery from short- and long-term low backpain in occupational settings: A prospective cohort study

Els L.M. Gheldof a,*, Jan Vinck a, Johan W.S. Vlaeyen b,Alita Hidding c, Geert Crombez d

a Department of Health Psychology, Hasselt University, Agoralaan, Gebouw D, B-3590 Diepenbeek, Belgiumb Department of Medical, Clinical and Experimental Psychology, Maastricht University, P.O. Box 616, 6200 MD Maastricht, The Netherlands

c Atrium Medical Center, Department of Education and Research, P.O. Box 4446, 6401 CX Heerlen, The Netherlandsd Faculty of Psychology and Educational Sciences, Ghent University, Henri Dunantlaan 2, 9000 Ghent, Belgium

Received 27 January 2006; received in revised form 16 November 2006; accepted 22 December 2006Available online 20 February 2007

Abstract

Using the data of the EuroBack Unit prospective cohort study, this paper investigated the role of work-related physical factors andpsychological variables in predicting the development of and recovery from short-term and long-term LBP. At baseline, 1294 pre-dominantly male industrial workers from 10 companies in Belgium and the Netherlands filled in questionnaires. At follow-up, datafrom 812 employees were available. Odds ratios (ORs) were calculated using simple and multiple logistic regression analyses. Forthose workers reporting 0 days LBP in the year prior to baseline, negative affectivity (OR 1.06, 95% CI 1.01–1.11) was a risk factorfor the development of short-term LBP (=1–30 days total of LBP in the year prior to follow-up). For those who reported 1–30 daystotal of LBP in the year prior to baseline, only high fear of (re)injury due to movement (OR 1.07, 95% CI 1.02–1.12) increased the riskfor failure to recovery from short-term LBP. For the development of long-term LBP (=more than 30 days total of LBP in the year priorto follow-up), a significant increased risk was observed among workers with high pain severity (OR 1.19, 95% CI 1.01–1.40) and withpain referred to the ankles or feet (OR 2.92, 95% CI 1.09–7.83). The risk was reduced by social support of co-workers (OR 0.73, 95%CI 0.59–0.92) and by manual handling of materials (OR 0.63, 95% CI 0.46–0.85). For those who reported more than 30 days total ofLBP in the year prior to baseline, high pain severity (OR 1.18, 95% CI 1.04–1.34) increased the risk for failure to recovery from long-

term LBP. Results are compared to the baseline study (Gheldof et al., 2005) and discussed in relation with prospective studies.� 2007 European Federation of Chapters of the International Association for the Study of Pain. Published by Elsevier Ltd. Allrights reserved.

Keywords: Low back pain; Development of short- and long-term LBP; Recovery from short- and long-term LBP; Prospective cohort study design

1. Introduction

Low back pain (LBP) is a highly prevalent and costlysomatic complaint. There is a growing consensus thatthe problem of LBP is multi-dimensional, and is bestunderstood within a biopsychosocial perspective (Main,

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doi:10.1016/j.ejpain.2006.12.012

* Corresponding author. Tel.: +32 9 264 64 61.E-mail address: [email protected] (G. Crombez).

2002). First, various factors are involved in its aetiologyand further development (Van Tulder and Koes, 2002),ranging from mechanical (Hoogendoorn et al., 1999;Westgaard and Winkel, 2002) and work-related psycho-social (Bongers et al., 1993; Hoogendoorn et al., 2000;Linton, 2001, 2005) to generic or pain-specific psycho-logical factors (Linton, 2000; Linton et al., 2000; Turkand Okifuji, 2002). Second, the natural course of LBPis heterogeneous and several pathways are possible.One may experience a single episode of LBP, and may

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842 E.L.M. Gheldof et al. / European Journal of Pain 11 (2007) 841–854

quickly recover from it (Nachemson, 1985). However, inmany situations LBP becomes a recurrent problem (VonKorff and Saunders, 1996), and in a minority it becomesa severe chronic burden (Wahlgren et al., 1997; Croftet al., 1998). Third, the impact of LBP varies betweenpersons, both in extent and diversity. Outcomes maythen be related to individual suffering (Croft et al.,1998; Feyer et al., 2000; Waxman et al., 2000), socialand functional impairments (Burton et al., 1995; Wahl-gren et al., 1997; Williams et al., 1998) and socio-eco-nomic consequences (Goossens, 2002) such as short-or long-term sickness absences (Linton and Hallden,1998; Boersma and Linton, 2005).

Unsurprisingly, different variables are involved inexplaining different outcomes. During the last two dec-ades, research has been accumulating that a variety offactors are important in the onset of LBP and its furtherdevelopment. In a review of the available prospectivestudies investigating biomechanical factors, Hoogendo-orn et al. (1999) found that manual handling of materi-als, bending and twisting, and whole-body vibrationwere strongly related to the occurrence of LBP. Therewas only moderate evidence for handling of patientsand heavy physical work. The authors found no evi-dence for standing or walking, sitting, sports, and phys-ical activity during leisure-time as risk factors for backpain. Furthermore, not only biomechanical variablesproved to be important. Several studies identified a con-sistent relationship between work-related psychosocialfactors (such as low social support in the workplaceand low job satisfaction) and the occurrence of LBP(Hoogendoorn et al., 2000). Recently, evidence is accu-mulating that also specific pain-related variables suchas pain catastrophizing and pain-related fear areinvolved in LBP onset (Linton, 2005; Van Nie-uwenhuyse et al., 2006).

Various factors are also involved in the developmentof long-term or chronic LPB. In a sample of patientspresenting with an acute attack of LBP, Klenermanet al. (1995) found that fear-avoidance variables werethe most successful in predicting chronicity 12 monthslater. Picavet et al. (2002) found comparable results ina population-based cohort of the general Dutch popula-tion, in that pain catastrophizing and kinesiophobiawere predictive for several chronic LBP outcomes. Alsodistress or depressive mood, anxiety, cognitive function-ing, pain behaviour and – to a lesser extent – somatiza-tion have been found to be influential predictors forboth the onset of LBP and chronicity (Linton, 2000; Pin-cus et al., 2002).

It is yet unclear which variables are most important inpredicting the development of either short- or long-termLBP, nor which factors are most influential for recoveryfrom short- or long-term LBP. Most studies of LBPhave only investigated a part of the potentially relevantpredictors (for examples, see studies included in reviews

of Hoogendoorn et al., 1999; Hoogendoorn et al., 2000),or made use of outcome measures referring to merelypresence or absence of back pain (BP). Based on the factthat LBP episodes of one or two days are very commonamong employees and generally resolve quickly, it maybe of more interest to investigate risk factors for LBPof a more substantial and thus longer number of paindays, e.g., 30 days or more than 30 days over the courseof a year.

In order to study risk factors of back pain, disabilityand sick leave, the Euro Back Unit project was designed.A first study reported on cross-sectional findings regard-ing risk factors of short-term and long-term LBP (andsick leave) (Gheldof et al., 2005). To this end, study par-ticipants were divided into groups who reported no LBPin the past year, 1–30 days LBP in the past year, andmore than 30 days LBP in the past year. Building fur-ther on the results of this study (Gheldof et al., 2005),the aim of the present study is to examine the role ofbaseline variables in predicting number of days withLBP in the year prior to follow-up in an occupationalsetting. Outcome measures of interest are both the devel-opment of and recovery from short- and long-term LBPin an occupational setting. Variables included weresocio-demographics, health-related factors, back paincharacteristics, work characteristics, generic psychologi-cal variables (negative affectivity, psychological distress)and pain-specific psychological variables (fear-avoid-ance beliefs regarding work-related activities, fear of(re)injury due to movement).

2. Methods

2.1. Sample and methodology

The current study is a follow-up study using the dataof the Euro Back Unit project. Baseline data were col-lected in October 2000 using a mailed survey. Eighteenmonths later (May 2002), those participants whoresponded at baseline were sent again a survey. Partici-pants were recruited in 10 companies in Belgium (n = 7)and the Netherlands (n = 3). As most companies werepart of metallurgical or steel industry, the sample pre-dominantly included male industrial workers. Only aminority of the companies was involved in industrialcleaning, distribution and health care. This study hasbeen approved by the Advisory Committee on Ethicsof the Institute of Rehabilitation Research at Hoensb-roek (the Netherlands).

2.2. Participants

Procedures regarding study announcement, recruit-ment of participants, and inclusion criteria are reportedelsewhere (Gheldof et al., 2005; Gheldof et al., 2006),

E.L.M. Gheldof et al. / European Journal of Pain 11 (2007) 841–854 843

and will here only be briefly reviewed. Employees withan age between 18 and 65 years, having a lifetime work-ing contract, and working at least half time were consid-ered eligible. Using the company files, 11.960 employeeswere eligible, and were sent an invitation letter to takepart in the study. A total of 1325 workers responded,and gave a written informed consent. They also sentback the baseline questionnaire. Taking part in thestudy was not compensated.

The response rate at baseline was only 11% (1325/11.960). An independent sample t-test and a v2-testshowed that there was no significant difference in themean age between responders (M = 39.37, SD = 8.82)and non-responders [M = 38.99, SD = 8.83; t(11,951) =�1.40, p = 0.11]. The proportion of males in the baselineresponders was significantly lower than the proportion ofmales in the baseline non-responders (85.9% versus89.5%, respectively, v2 = 19.87, p < 0.001).

Of those who responded (N = 1325), 31 responderswere discarded due to missing information, resulting ina sample of 1294 participants with valid data at baseline.At follow-up, 902 employees responded by filling in andreturning the follow-up questionnaire. However, 90responders were excluded due to incomplete data(non-response on critical variables), or untraceable iden-tification number (which is necessary for linking baselinedata with outcomes at follow-up). The final sample withvalid data at both baseline and follow-up consisted of812 subjects. Mean (SD) age was 39.82 years (8.24)and 90% were male. About 50% was low-educated(=education no longer than the age of 18 years) and90% was cohabiting with a partner. At follow-up, about93% was at work. Almost 15% reported a job changeand 11% reported a job transfer in the past 12 months.The prevalence of baseline LBP (defined as ‘‘reportingone or more days of LBP in the year prior to the base-line assessment’’) in the follow-up sample (69%, amongn = 812) was comparable to the prevalence of LBP as inthe full sample of participants with valid data at baseline(69%, among n = 1294) (Gheldof et al., 2005). Sick leavedue to LBP was reported by 26%.

2.3. Measures

Participants completed a battery of questionnaires,covering individual and lifestyle characteristics and sev-eral areas of exposure, including work-related physicalburdens, work-related psychosocial factors and psycho-logical variables. Most factors were assessed with vali-dated questionnaires. All risk factors included in theanalyses were assessed at the beginning of the study(baseline) and are listed below.

Concurrent health and lifestyle characteristics. Self-reported health was assessed using a single item with fiveresponse categories (excellent health, very good health,good health, moderate health, poor health) which were

recoded into ‘1 = good to excellent health’ and‘2 = moderate to poor health’. The body mass index(BMI) was calculated using self-reported height andweight, and was dichotomized (625 and >25). Dailysmoking was measured with a dichotomous yes/no ques-tion. Frequency of sport activities was assessed with thequestion ‘‘How many times during your spare time doyou perform a physical exerting activity which takes atleast half an hour (such as doing sports, cycling, takingthe dog for a walk out)?’’ The response categories ‘morethan seven times a week’ and ‘2–7 times a week’ werecombined into one category, and compared to ‘neveror once a week at maximum’.

Current pain severity (due to LBP) and radiating pain.Current pain severity (‘‘How would you rate your backpain today on the subsequent scale?’’) was assessed byan 11-point numeric rating scale (NRS) anchored by‘0 = no pain’ and ‘10 = worst imaginable pain’ (VonKorff et al., 1992; Von Korff, 2001). The psychometricproperties of this scale are good (Jensen et al., 1989; Jen-sen and Karoly, 1992; Farrar et al., 2001; Closs et al.,2004). Radiating pain into knees or legs and radiatingpain into ankles or feet were assessed by two dichoto-mous yes/no items.

Work load. The perception of physical exertion atwork (range 1–15) was measured by the 15-point NRS(1 = no exertion at all, 15 = maximal exertion) of Borg(1990). In addition, there were 13 questions on work-related physical load. These items were based upon theshort version of the ‘‘Questionnaire on MusculoskeletalLoad and Health Complaints’’ (Hildebrandt and Dou-wes, 1991). Each item was scored on a 4-point Likertscale (1 = seldom or never, 4 = very frequently). Sub-scales scores were calculated for the following domains:(1) dynamic workload due to manual handling of mate-rials [=summation of lifting and carrying loads of morethan 25 kg each, lifting and carrying loads of more than50 kg each, press forcefully with arms or hands] (range3–12), (2) dynamic workload due to flexion and rotationof the trunk (range 1–4), (3) static workload due to long-lasting standing/sitting [=summation of long-lastingworking in a standing position, long-lasting working ina sitting position, long-lasting working in the same posi-tion] (range 3–12), (4) static workload due to long-last-ing kneeling, squatting, or working in an awkwardposture [=summation of long-lasting working in akneeling position, long-lasting working in a squattingposition, long-lasting working in an awkward position](range 3–12), (5) whole-body vibration [=summationof working with vibrating or bumping tools, drivingvehicles] (range 2–8), (6) repetitive movements manytimes per minute, with arms or hands (range 1–4).

Perceived job characteristics. The Dutch translationof the Job Content Questionnaire (JCQ) (Karasek,1986; Furda et al., 1994; Houtman, 1995; Karaseket al., 1998) assessed psychological job demands (five


items), decision latitude (nine items), supervisor support(four items) and co-worker support (four items). Eachitem was rated using a 4-point Likert scale (‘1 = fullydisagree’ and ‘4 = fully agree’). For each scale, highscores indicate high levels of psychological job demands(a = 0.64, range 12–48), decision latitude (a = 0.82,range 24–96), supervisor support (a = 0.86, range 4–16) or co-worker support (a = 0.71, range 4–16). TheJCQ has acceptable reliability and substantial validityin predicting stress-related diseases and illnesses (Kar-asek et al., 1998). Perceived job satisfaction and beingon shift work were assessed using dichotomous yes/noitems (Grundeman et al., 1993).

Fear of (re)injury due to movement was assessed withthe Dutch version of the Tampa Scale for Kinesiopho-bia (TSK, 17 items, 4-point scale) (Kori et al., 1990),which is reliable and valid in acute and in chronicLBP populations (Kole-Snijders et al., 1993; Vlaeyenet al., 1995). Results of a confirmatory factor analysis(Goubert et al., 2004c; Roelofs et al., 2004) resulted inthe exclusion of the four reversed key items (resultingin a 13-item TSK-AV, adapted version). Only employeeswho reported one or more days of LBP in the year priorto the baseline assessment completed this questionnaire(a = 0.83, range 13–52). Employees without LBP atbaseline were instructed to complete a modified versionof the TSK which has been developed specifically forpain free individuals in the ‘General Population’(TSK-G), (Houben et al., 2005). For this scale, it wasfound recently that the omission of the four inverseitems and one extra item (item 11) more adequately fit-ted the data than the original 17-item version. The TSK-G thus consists of 12 items measured on a 4-point scalewith scoring alternatives ranging from ‘strongly agree’to ‘strongly disagree’ (a = 0.75, range 12–48). A higherscore on the TSK-G reflects a higher degree of fear of(re)injury due to movement. This measure proved satis-factory reliability and validity (Houben et al., 2005).

Fear of work-related activities. The work-scale of theFear-Avoidance Beliefs Questionnaire (FABQ-work,seven items on a 7-point scale, range 7–49) (Waddellet al., 1993) was used to assess the beliefs of employeeswith back pain about how performance of work-relatedactivities impacts their pain. The FABQ-scale measuringfear-avoidance belief about physical activity was notincluded because of construct and content overlap withthe TSK-AV. The FABQ has proven to be internal con-sistent, to have a good test–retest reliability and a goodvalidity (Waddell et al., 1993; Crombez et al., 1999).Cronbach’s alpha in the current study was 0.88. Onlyworkers reporting LBP at baseline filled in thisquestionnaire.

Negative affectivity. To measure negative affectivity(during the past year), we used a subscale of the Positiveand Negative Affect Schedule (PANAS; 10 items scoredon a 5-points scale, range 10–50) (Tellegen, 1982; Wat-

son et al., 1988). Evidence has been found for an appro-priate test–retest reproducibility over a 2-month timeperiod as well as for convergent and discriminatoryvalidity (Watson et al., 1988). High scores denote higherlevels of negative affectivity. Cronbach’s alpha in thisstudy reached 0.89.

Psychological distress. Current mental health or psy-chological well-being was assessed with the GeneralHealth Questionnaire, short version (GHQ-12, 12 itemswith four response alternatives, range 12–48) (Gold-berg et al., 1997). Those with a total threshold scoreof 6 or more are considered as ‘cases’ having severepsychological distress. It has been established that theshorter GHQ is remarkably robust and works as wellas the longer instrument, if investigators wish to usea screening instrument as a case detector (Goldberget al., 1997). Internal consistency of the GHQ-12 hasbeen explored in different settings and amounted onaverage to 0.90 (Cronbach’s alpha in this study reached0.89).

Low back pain status and classification of workers in

groups as a function of number of pain days in the pastyear. Both at baseline and at follow-up, the number ofpain days in the past year was assessed by the NordicQuestionnaire on LBP, which is reliable and valid(Kuorinka et al., 1987). The corresponding multiplechoice answers were 0 days, 1–7 days, 8–30 days, >30days but not every day, and every day. Workers wereclassified in LBP groups as a function of pain daysin the year prior to baseline and of pain days in theyear prior to follow-up (see Fig. 1). Criteria for classi-fication were based upon the available response catego-ries of the Nordic Questionnaire (Kuorinka et al.,1987) and upon the criteria of previous studies (Ghel-dof et al., 2005).

Based on the number of pain days in the year prior tobaseline, three groups of workers were identified: (1)workers being pain free in the year prior to baseline,i.e. reporting 0 days of LBP in the previous year(N = 250), (2) workers who reported 1–30 days totalof LBP in the previous year (N = 309), and (3) workerswho reported more than 30 days total of LBP in the pastyear (N = 253). Next, number of pain days in the yearprior to follow-up was taken into account to identifythe four outcome categories of interest. Criteria andlabels for each of the outcome categories were identificalto the previous baseline study (Gheldof et al., 2005).

(1) Development of short-term LBP was investigatedby comparing the results of workers who reported0 days of LBP in the year prior to baseline andreported 0 days of LBP in the year prior to fol-low-up (coded as 0, N = 121) with the results ofworkers who had no back pain in the year priorto baseline but reported 1–30 days total LBP inthe year prior to follow-up (coded as 1, N = 85)

N=309

N=1.325

N=1.294

APPROACHED

BASELINE (BL)

FOLLOW-UP (FU) N=902

N=10.066 did not enroll in the study

N=31 discarded

N=90 discarded

N=812

N=250

DEVELOPMENT OF SHORT-TERM LBP [A versus B]

N=121

N=177

N=67N=65

0 days LBP year prior to baseline 1-30 days LBP year prior to baseline > 30 days LBP year prior to baseline

N=11.960

N=253

N=158N=44 N=19

N=76

RECOVERY FROM LONG-TERM LBP [A-B versus C]RECOVERY FROM SHORT-TERM LBP [A versus B-C]

DEVELOPMENT OF LONG-TERM LBP [A-B versus C]

N=85

0 days LBP year prior to FU

1-30 days LBP year prior to FU

> 30 days LBP year prior to FU







A BA

BC A

BC

Fig. 1. Sampling frame at baseline and at follow-up (FU), and response rates of different low backpain (LBP) groups.


(see Fig. 1). [Note that the LBP group referring tothose workers with 0 days LBP in the year prior tobaseline and more than 30 days total of LBP in theyear prior to follow-up was excluded from furtheranalysis. Due to small sample size, the statisticalpower of this group was assumed to be too low.]

(2) Failure of recovery from short-term LBP was inves-tigated by comparing the results of workers whoreported 1–30 days total of LBP in the year priorto baseline and reported 0 days LBP in the yearprior to follow-up (coded as 0, N = 65) with theresults of workers who reported 1–30 days totalof LBP in the year prior to baseline, but reportedan accumulated period of 1–30 days or more than30 days LBP in the year prior to follow-up (codedas 1, N = 244) (see Fig. 1).

(3) Development of long-term LBP was investigated bycomparing the results of workers reporting 1–30days total of LBP in the year prior to baselineand 0 days or 1–30 days total of LBP in the yearprior to follow-up (coded as 0, N = 242), withthe results of workers who reported 1–30 daystotal of LBP in the year prior to baseline and morethan 30 days total of LBP in the year prior to fol-low-up (coded as 1, N = 67) (see Fig. 1).

(4) Failure of recovery from long-term LBP was inves-tigated by comparing the results of workers whoreported >30 days total of LBP in the year priorto baseline and 0 days or 1–30 days total of LBPin the year prior to follow-up (coded as 0,N = 95) with the results of those reporting more

than 30 days total of LBP in the year prior to base-line and more than 30 days total of LBP in the yearprior to follow-up (coded as 1, N = 158).

2.4. Statistical analyses

The sum scores of all scales were calculated. When-ever there were no more than 20% missing values in ascale, a weighted sum score was calculated. When therewere more than 20% missing values in a scale, the sumscore was considered invalid (Gheldof et al., 2005).Then, data were analyzed in several steps, using SPSS(version 11.5). First, for each LBP group, reliabilityindices, overall means, standard deviations, and propor-tions of all independent variables were calculated. Sec-ond, single associations between each predictor andthe four outcome measures were calculated and repre-sented by crude odds ratios (ORs) along with the 95%confidence intervals (95% CI). The odds ratio for contin-uous variables measures the change in risk per unit orper point increase, while the odds ratio for categorizedpredictor variables estimates the risk per category.Third, for each of the outcome variables, a multiplelogistic regression model was performed in which all ofthe predictors with a p-value of at least 0.20 were enteredsimultaneously. In order to prevent multi-collinearity,the inter-correlations between the independent variableswere checked. Among variables with a spearman’s cor-relation of .50 or higher, it was decided to drop the vari-ables with the lowest p-value (as found in the bivariate


models) from the multiple regression model. Fear ofwork-related activities and fear of (re)injury due tomovement were never retained in the same model, irre-spective of their inter-correlation. In the multiple modelanalysis, missing data were handled by means of list-wise deletion. For each model, the final number of sub-jects on which the multiple odds was performed isreported in the last column heading of Tables 1–4.

Based upon previous research (Hurwitz and Morgen-stern, 1997; Kant et al., 2003), all of the models includedfollowing three independent variables, irrespective oflevel of significance: age (continuous), gender (dichoto-mous: 0 = male; 1 = female), and level of education(dichotomous: 0 = low education, shorter than age 18;1 = high education, longer than age 18).

Table 1Among workers with no LBP in the year prior to baseline: Means [Proportiogroups; crude and adjusted odds ratios for development of short-term LBP

Risk factors No low back pain yearprior to follow-up

Shorpainfollo

N Mean (SD) [Prop]a N

Socio-demographics and individual variables

Age 121 39.80 (9.70) 85Sex (maleb/female) 121 [0.96; 0.04] 85Education (highb/low education) 121 [0.48; 0.52] 85Body Mass Index (625b/>25) 120 25.38 (3.60) 81Self-rated health (goodb/poor) 121 [0.96; 0.04] 85Smoking daily (nob/yes) 121 [0.68; 0.32] 85Sports (>1xb/61x per week) 121 [0.61; 0.39] 85

Physical work and perceived job characteristics

Task exertion 120 7.80 (2.96) 84DWL due to manual materials handling 120 3.64 (1.00) 81DWL due to flexion and rotation trunk 119 2.34 (1.14) 85SWL due to long-lasting standing 120 6.82 (1.52) 85SWL due to long-lasting kneeling 120 4.83 (1.83) 85Whole-body vibration 119 3.30 (1.33) 83Repetitive movements 120 2.24 (1.18) 85Psychological job demands 118 31.34 (5.77) 85Decision latitude 118 65.11 (12.76) 83Supervisor social support 120 10.63 (2.57) 85Co-worker social support 120 11.69 (1.60) 85Job satisfaction (yesb/no) 121 [0.89; 0.11] 84Shift work (yesb/no) 119 [0.81; 0.19] 85

Psychological variables

Negative affectivity 119 17.15 (6.16) 84Psychological distress 121 1.22 (2.38) 85Fear of (re)injury due to movementc 78 28.39 (4.75) 49

OR = odds ratio; 95% CI = 95% confidence interval; high education = educlonger than the age of 18 years; DWL = Dynamic workload; SWL = Static

a Dichotomized variables (yes/no) are reported in terms of proportions (wb Reference category.c Fear of (re)injury due to movement was measured with the TSK-G.d Due to high inter-correlations with negative affectivity (r = 0.58, p < 0.00* p < 0.05.

3. Results

3.1. Response rate and general descriptives

In this study, 812 respondents were included for anal-ysis, resulting in a response rate at follow-up of 63%(=812/1294). About 45% (n = 349) of the participantsperformed technical work, 37% (n = 290) performedunskilled labour, and 16% (n = 128) fulfilled an execu-tive function, whereas the remaining 2% did ‘other’(not further specified) work.

For most of the predictor variables, no significant dif-ferences were found between the workers included in thisstudy (i.e., those who responded to the questionnaire bothat baseline and follow-up) and those who responded to

ns] and standard deviations (SD) of predictors at baseline for two LBPin the year prior to follow-up

t-term low backyear prior tow-up

Development of short-term low back pain yearprior to follow-up

Mean (SD) [Prop]a Crude OR (95% CI) Adjusted OR (95% CI),N = 195

40.25 (8.76) 1.01 (0.98–1.04) 1.03 (0.99–1.06)[0.95; 0.05] 1.15 (0.29–4.40) 1.01 (0.25–4.17)[0.51; 0.49] 0.90 (0.52–1.57) 0.79 (0.42–1.48)24.82 (3.49) 0.68 (0.38–1.20) 0.57 (0.31–1.07)[0.94; 0.06] 1.45 (0.41–5.17)[0.66; 0.34] 1.09 (0.60–1.96)[0.61; 0.39] 0.99 (0.57–1.77)

7.98 (2.88) 1.00 (0.91–1.10)3.72 (1.06) 1.07 (0.82–1.41)2.56 (1.12) 1.20 (0.93–1.53) 1.14 (0.85–1.53)7.23 (1.58) 1.19 (0.99–1.43) 1.18 (0.95–1.46)5.08 (1.98) 1.07 (0.93–1.24)3.41 (1.30) 1.06 (0.86–1.32)2.53 (1.27) 1.08 (0.86–1.35)

31.33 (5.61) 1.00 (0.95–1.05)66.72 (11.09) 1.01 (0.99–1.04)11.04 (2.59) 1.07 (0.95–1.19)12.01 (1.65) 1.13 (0.95–1.35) 1.19 (0.98–1.44)[0.94; 0.06] 0.51 (0.18–1.49)[0.84; 0.16] 1.22 (0.58–2.53)

19.07 (6.87) 1.05* (1.00–1.09) 1.06* (1.01–1.11)

1.78 (2.95) 1.08 (0.98–1.20) –d

28.88 (5.74) 1.02 (0.95–1.09)

ation longer than the age of 18 years; low education = education noworkload.hich equals percentage divided by 100).

1), psychological distress is dropped from the multivariate model.

Table 2Among workers reporting 1–30 days LBP in the year prior to baseline: Means [Proportions] and Standard Deviations (SD) of predictors at baselinefor two LBP groups; crude and adjusted odds ratios for failure of recovery from short-term LBP in year prior to follow-up

Risk factors No low back pain yearprior to follow-up

P 1 day low back painyear prior to follow-up

Failure of recovery from short-term lowback pain year prior to follow-up

N Mean (SD) [Prop]a N Mean (SD) [Prop]a Crude OR (95% CI) Adjusted OR (95% CI),N = 305


Age 65 37.62 (7.38) 244 39.85 (7.83) 1.04* (1.01–1.08) 1.03 (0.99–1.07)Sex (maleb/female) 65 [0.91; 0.09] 244 [0.89; 0.11] 1.22 (0.48–3.10) 1.98 (0.67–5.69)Education (highb/low education) 65 [0.59; 0.41] 244 [0.50; 0.50] 1.39 (0.80–2.41) 1.10 (0.60–2.02)Body Mass Index (625b/>25) 62 25.38 (3.52) 240 25.35 (3.34) 0.99 (0.92–1.08)Self-rated health (goodb/poor) 65 [0.97; 0.03] 244 [0.92; 0.08] 2.81 (0.64–12.36) 2.89 (0.36–23.13)Smoking daily (nob/yes) 65 [0.65; 0.35] 244 [0.64; 0.36] 1.05 (0.59–1.86)Sports (>1xb/61x per week) 64 [0.64; 0.36] 244 [0.66; 0.34] 0.92 (0.52–1.63)

Pain characteristics

Current pain severity 65 1.35 (1.93) 244 1.79 (1.91) 1.14 (0.97–1.34) 1.01 (0.85–1.20)Radiating pain into knee-leg (nob/yes) 65 [0.83; 0.17] 244 [0.78; 0.22] 1.34 (0.68–2.85)Radiating pain into ankle–feet (nob/yes) 65 [0.92; 0.08] 244 [0.93; 0.07] 0.96 (0.34–2.68)


Task exertion 65 8.49 (2.99) 244 8.97 (2.77) 1.06 (0.96–1.17)DWL due to manual materials handling 65 3.85 (1.03) 242 4.05 (1.38) 1.14 (0.91–1.43)DWL due to flexion and rotation trunk 65 2.69 (1.13) 244 2.70 (1.07) 1.01 (0.78–1.30)SWL due to long-lasting standing 65 7.18 (1.51) 244 7.12 (1.45) 0.97 (0.80–1.17)SWL due to long-lasting kneeling 65 5.77 (2.35) 244 5.64 (2.04) 0.97 (0.85–1.11)Whole-body vibration 63 4.00 (1.63) 241 3.87 (1.53) 0.95 (0.79–1.13)Repetitive movements 65 2.46 (1.12) 244 2.49 (1.17) 1.02 (0.81–1.30)Psychological job demands 65 31.71 (5.91) 244 31.90 (6.26) 1.01 (0.96–1.05)Decision latitude 65 65.96 (13.30) 242 63.83 (11.58) 0.99 (0.96–1.01)Supervisor social support 65 10.54 (2.50) 242 10.20 (2.51) 0.95 (0.85–1.06)Co-worker social support 65 11.81 (1.47) 241 11.49 (1.64) 0.88 (0.74–1.05) 0.88 (0.72–1.07)Job satisfaction (yesb/no) 64 [0.83; 0.17] 238 [0.87; 0.13] 0.71 (0.34–1.51)Shift work (yesb/no) 65 [0.85; 0.15] 244 [0.82; 0.18] 0.80 (0.38–1.70)


Negative affectivity 65 17.71 (7.50) 244 20.34 (7.67) 1.05*(1.01–1.10) 1.03 (0.98–1.08)Psychological distress 65 1.85 (3.21) 244 2.09 (3.00) 1.03 (0.94–1.13)Fear of work-related activities 64 9.75 (7.74) 244 13.27 (6.83) 1.05*(1.02–1.09) –d

Fear of (re)injury due to movement c 64 24.59 (6.92) 244 28.35 (6.83) 1.08*** (1.04–1.13) 1.07** (1.02–1.12)

OR = odds ratio; 95% CI = 95% confidence interval; high education = education longer than the age of 18 years; low education = education nolonger than the age of 18 years; DWL = Dynamic workload; SWL = Static workload.

a Dichotomized variables (yes/no) are reported in terms of proportions (which equals percentage divided by 100).b Reference category.c Fear of (re)injury due to movement was measured with the TSK-AV.d Due to high inter-correlations with fear of (re)injury due to movement (r = 0.47, p < 0.001), fear-avoidance beliefs regarding work is dropped from

the multivariate model.* p < 0.05.

** p < 0.01.*** p < 0.001.


the baseline questionnaire only. However, the current fol-low-up sample differed significantly from study partici-pants who did not complete the follow-up questionnaireregarding static work load due to long-lasting standing,sitting or working in the same posture [M = 7.24,SD = 1.53 versus M = 7.44, SD = 1.63; t(1293) = 4.99,p < 0.05], repetitive movements [M = 2.52, SD = 1.19versus M = 2.71, SD = 1.18; t(1293) = 8.32, p < 0.01],negative affectivity [M = 19.83, SD = 7.38 versusM = 20.83, SD = 7.81; t(1293) = 5.43, p < 0.05], and fear

of work-related activities [M = 15.09, SD = 9.75 versusM = 16.94, SD = 11.27; t(889) = 7.53, p < 0.01]. Crosstabulation further showed that more follow-up complet-ers (as compared to non-completers) reported a good toexcellent health at baseline (88.5% versus 82%,v2 = 10.84, p < 0.01).

For each of the LBP groups, overall means (or propor-tions) and standard deviations for the baseline predictorsused in this study are presented in the first two columns ofthe corresponding table (see Tables 1–4).

Table 3Among workers reporting 1–30 days LBP in the year prior to baseline: Means [Proportions] and Standard Deviations (SD) of predictors at baselinefor two LBP groups; crude and adjusted odds ratios for development of long-term LBP in the year prior to follow-up

Risk factors 0–30 days low back painyear prior to follow-up

Long-term low backpain year prior tofollow-up

Development of long-term low back painyear prior to follow-up



Age 242 39.54 (7.79) 67 38.81 (7.81) 0.99 (0.95–1.02) 0.97 (0.93–1.02)Sex (maleb/female) 242 [0.91; 0.09] 67 [0.84; 0.16] 1.96 (0.90–4.29) 2.24 (0.92–5.42)Education (highb/low education) 242 [0.54; 0.46] 67 [0.46; 0.54] 1.35 (0.78–2.32) 1.31 (0.71–2.43)Body Mass Index (625b/>25) 236 25.44 (3.42) 66 25.06 (3.18) 0.97 (0.89–1.05)Self-rated health (goodb/poor) 242 [0.93; 0.07] 67 [0.91; 0.09] 1.39 (0.52–3.70)Smoking daily (nob/yes) 242 [0.65; 0.35] 67 [0.58; 0.42] 1.35 (0.78–2.35)Sports (>1xb/61x per week) 241 [0.33; 0.67] 67 [0.61; 0.39] 1.28 (0.73–2.23)


Current pain severity 242 1.50 (1.78) 67 2.43 (2.22) 1.26**(1.10–1.44) 1.19* (1.01–1.40)

Radiating pain into knee-leg (nob/yes) 242 [0.80; 0.20] 67 [0.75; 0.25] 1.37 (0.73–2.59)Radiating pain into ankle–feet (nob/yes) 242 [0.95; 0.05] 67 [0.85; 0.15] 3.09**(1.29–7.41) 2.92*(1.09–7.83)


Task exertion 242 8.76 (2.84) 67 9.24 (2.72) 1.06 (0.96–1.18)DWL due to manual materials handling 242 4.10 (1.34) 66 3.70 (1.18) 0.76*(0.60–0.98) 0.63**(0.46–0.85)

DWL due to flexion and rotation trunk 242 2.67 (1.11) 67 2.80 (0.99) 1.13 (0.87–1.45)SWL due to long-lasting standing 242 7.11 (1.47) 67 7.23 (1.42) 1.06 (0.88–1.28)SWL due to long-lasting kneeling 242 5.65 (2.09) 67 5.73 (2.15) 1.02 (0.90–1.18)Whole-body vibration 238 3.91 (1.59) 66 3.85 (1.39) 0.98 (0.82–1.17)Repetitive movements 242 2.41 (1.16) 67 2.76 (1.13) 1.31*(1.03–1.66) 0.97 (0.70–1.34)Psychological job demands 242 31.74 (6.17) 67 32.27 (6.27) 1.01 (0.97–1.06)Decision latitude 241 65.34 (12.09) 66 60.39 (10.77) 0.97**(0.95–0.99) 0.99 (0.96–1.02)Supervisor social support 241 10.31 (2.54) 66 10.15 (2.40) 0.97 (0.87–1.09)Co-worker social support 241 11.72 (1.53) 65 10.95 (1.74) 0.73**(0.61–0.88) 0.73**(0.59–0.92)

Job satisfaction (yesb/no) 238 [0.87; 0.13] 64 [0.81; 0.19] 1.54 (0.74–3.21)Shift work (yesb/no) 242 [0.81; 0.19] 67 [0.87; 0.13] 1.51 (0.70–3.27)


Negative affectivity 242 19.27 (7.17) 67 21.66 (9.20) 1.04* (1.01–1.07) 1.00 (0.97–1.04)Psychological distress 242 1.93 (2.91) 67 2.42 (3.46) 1.05 (0.97–1.14)Fear of work-related activities 242 11.76 (7.91) 67 15.33 (10.32) 1.05**(1.02–1.08) 1.04* (1.00–1.08)

Fear of (re)injury due to movementc 242 27.27 (7.16) 67 28.64 (6.38) 1.03 (0.99–1.07)


a Dichotomized variables (yes/no) are reported in terms of proportions (which equals percentage divided by 100).b Reference category.c Fear of (re)injury due to movement was measured with the TSK-AV.* p < 0.05.

** p < 0.01.


3.2. Development of short-term LBP

The crude and adjusted odds ratio’s (ORs) and corre-sponding confidence intervals (CI) for the developmentof short-term LBP are presented in Table 1 (in the thirdand fourth column, respectively). The only significantunivariate association which was found was for workersscoring high on negative affectivity (OR 1.05, 95% CI1.00–1.09). Results of the multiple model analysisshowed an adjusted odds for negative affectivity (OR1.06, 95% CI 1.01–1.11) as risk factor for the develop-ment of short-term LBP. That is, for every one point

increase on the negative affectivity scale, the odds ofdeveloping 1–30 days total of LBP is increased by about6%. Regarding model fit, results showed that the fit of themodel was better than the fit of a model containing nopredictors (null model: v2(8) = 15.28, p = 0.05). We fur-ther evaluated the fit of the model using two additionalstatistics. First, the Hosmer–Lemeshow statistic wasnot significant (p = 0.16), indicating that the model hadan acceptable fit. Second, we also calculated the Nage-lkerke R2 statistic, which is an approximation of theexplained variance (R2) concept for the ordinary regres-sion model. This statistic showed that the likelihood rises

Table 4Among workers reporting > 30 days LBP in the year prior to baseline: Means [Proportions] and Standard Deviations (SD) of predictors at baselinefor two LBP groups; crude and adjusted odds ratios for failure of recovery from long-term LBP in the year prior to follow-up

Risk factors No or short-term lowback pain year prior tofollow-up

Long-term low back painyear prior to follow-up

Failure of recovery from long-term lowback pain year prior to follow-up



Age 95 39.96 (7.89) 158 40.31 (7.85) 1.01 (0.97–1.04) 1.02 (0.99–1.06)Sex (maleb/female) 95 [0.92; 0.08] 158 [0.87; 0.13] 1.67 (0.71–3.93) 1.99 (0.79–5.03)Education (highb/low education) 95 [0.51; 0.49] 158 [0.45; 0.55] 1.25 (0.75–2.08) 1.16 (0.67–2.04)Body Mass Index (625b/>25) 94 25.36 (3.63) 153 25.96 (3.47) 1.39 (0.83–2.33)Self-rated health (goodb/poor) 95 [0.83; 0.17] 158 [0.75; 0.25] 1.67 (0.88–3.19) 1.30 (0.64–2.65)Smoking daily (nob/yes) 95 [0.72; 0.28] 158 [0.63; 0.37] 1.50 (0.87–2.60) 1.44 (0.80–2.61)Sports (>1xb/61x per week) 95 [0.62; 0.38] 156 [0.61; 0.39] 1.02 (0.61–1.73)


Current pain severity 95 3.67 (2.20) 158 4.61 (2.34) 1.20** (1.07–1.35) 1.18* (1.04–1.34)

Radiating pain into knee-leg (nob/yes) 95 [0.65; 0.35] 158 [0.58; 0.42] 1.35 (0.80–2.28)Radiating pain into ankle–feet (nob/yes) 95 [0.76; 0.24] 158 [0.76; 0.24] 0.99 (0.55–1.80)


Task exertion 94 9.49 (2.65) 157 9.65 (2.63) 1.02 (0.93–1.13)DWL due to manual materials handling 92 4.13 (1.54) 153 4.09 (1.59) 0.98 (0.83–1.16)DWL due to flexion and rotation trunk 95 3.02 (1.04) 158 3.13 (0.99) 1.11 (0.86–1.42)SWL due to long-lasting standing 94 7.53 (1.51) 158 7.57 (1.54) 1.02 (0.86–1.20)SWL due to long-lasting kneeling 95 5.75 (2.09) 158 6.16 (2.10) 1.10 (0.97–1.25) 1.04 (0.90–1.20)Whole-body vibration 92 3.68 (1.37) 153 3.73 (1.47) 1.02 (0.85–1.22)Repetitive movements 95 2.59 (1.13) 158 2.79 (1.21) 1.15 (0.93–1.43)Psychological job demands 95 32.49 (5.29) 158 33.92 (6.43) 1.04 (0.99–1.09) 1.02 (0.97–1.08)Decision latitude 95 61.84 (13.25) 157 58.95 (13.37) 0.98 (0.96–1.00) 0.99 (0.97–1.02)Supervisor social support 95 10.04 (2.63) 158 9.80(2.59) 0.97 (0.87–1.07)Co-worker social support 95 11.51 (1.79) 158 11.30 (1.66) 0.93 (0.80–1.08)Job satisfaction (yesb/no) 92 [0.74; 0.26] 154 [0.71; 0.29] 1.14 (0.64–2.04)Shift work (yesb/no) 95 [0.79; 0.21] 158 [0.89; 0.11] 2.07*(1.03–4.16) 1.84 (0.86–3.96)


Negative affectivity 95 20.36 (7.67) 158 21.74 (6.92) 1.03 (0.99–1.07) 1.01 (0.97–1.05)Psychological distress 94 2.72 (3.45) 158 2.54 (3.13) 0.98 (0.91–1.06)Fear of work-related activities 95 17.37 (10.71) 158 20.21 (11.01) 1.02*(1.00–1.05) 0.99 (0.97–1.03)Fear of (re)injury due to movementc 95 30.75 (7.23) 158 31.55 (6.55) 1.02 (0.98–1.06)


a Dichotomized variables (yes/no) are reported in terms of proportions (which equals percentage divided by 100).b Reference category.c Fear of (re)injury due to movement was measured with the TSK-AV.* p < 0.05.

** p < 0.01.


to 10.2% when introducing the explanatory variables inour model.

3.3. Recovery from short-term low back pain

Crude and adjusted odds ratios regarding recoveryfrom short-term LBP are presented in Table 2. Age(OR 1.04, 95% CI 1.01–1.08) and negative affectivity(OR 1.05, 95% CI 1.01–1.10) showed a significant unad-justed odds for recovery from short-term LBP. Further,also high fear of (re)injury due to movement (OR 1.08,95% CI 1.04–1.13) and high fear-avoidance beliefs

regarding work (OR 1.05, 95% CI 1.02–1.09) showedsignificant associations with this outcome. Resultsrevealed that only high fear of (re)injury due to move-ment increased the risk for failure to recovery fromshort-term LBP (OR 1.07, 95% CI 1.02–1.12). That is,for every one point increase on the TSK-AV, the oddsof failure to recovery from short-term LBP is increasedby 7%. This model proved to be parsimonious androbust. First, the fit of the model was better than thefit of a model containing no predictors (null model:v2(8) = 25.76, p < 0.01). Second, the Hosmer–Leme-show statistic was not significant (p = 0.14), indicating


that the model had an acceptable fit. Third, the Nage-lkerke R2 statistic showed that the likelihood rises to12.6% when introducing the explanatory variables inour model.

3.4. Development of long-term low back pain

As can be seen from Table 3, a broad range of univar-iate risks was associated with the development of long-term LBP. An increased crude odds was noted for work-ers reporting high baseline pain severity (OR 1.26, 95%CI 1.10–1.44), pain radiation into ankles or feet (OR3.09, 95% CI 1.29–7.41), high fear of work-related activ-ities (OR 1.05, 95% CI 1.02–1.08) and high negativeaffectivity (OR 1.04, 95% CI 1.01–1.07). A high levelof decision latitude (OR 0.97, 95% CI 0.95–0.99) or ahigh level of co-worker social support (OR 0.73, 95%CI 0.61–0.88) were protective for long-term LBP.Regarding the physical loading factors, repetitive move-ments (OR 1.31, 95% CI 1.03–1.66) substantially height-ened the risk of developing long-term LBP, whereasdynamic work load due to manual materials handling(OR 0.76, 95% CI 0.60–0.98) reduced the risk of long-term LBP. The multiple regression model revealed thatthe risk of developing long-term LBP is significantlyheightened by high pain severity (OR 1.19, 95% CI1.01–1.40), the presence of pain radiation into anklesor feet (OR 2.92, 95% CI 1.09–7.83), and high fear ofwork-related activities (OR 1.04, 95% CI 1.00–1.08).The risk of developing long-term LBP is reduced by ahigh level of social support from colleagues (OR 0.73,95% CI 0.59–0.92) or a high level of manual materialshandling (OR 0.63, 95% CI 0.46–0.85). The fit of themodel was better than the fit of a model containing nopredictors (null model: v2(11) = 45.49, p < 0.001). TheNagelkerke R2 statistic showed that the likelihood risedto 21.7% when introducing the explanatory variables inour model. However, the Hosmer–Lemeshow statisticwas significant (p = 0.02), indicating that the modelhad an inadequate fit. Further analyses indicated thatthe inadequate model fit was predominantly owing tothe radiating pain variable (the Hosmer–Lemeshow sta-tistic of the same model in which radiating pain wasexcluded was not longer significant, p = 0.09).

3.5. Recovery from long-term low back pain

The crude and adjusted odds ratio’s for recoveryfrom long-term LBP are presented in Table 4. Currentpain severity (OR 1.20, 95% CI 1.07–1.35), performingshift work (OR 2.07, 95% CI 1.03–4.16) and fear ofwork-related activities (OR 1.02, 95% CI 1.00–1.05)were significant risks limiting recovery from long-termLBP. The multiple model analysis revealed that only ahigh level of pain severity (OR 1.18, 95% CI 1.04–1.34) significantly increased the risk for failure to recov-

ery from long-term LBP. This model proved to be par-simonious and robust. First, the fit of the model wasbetter than the fit of a model containing no predictors(null model: v2(12) = 22.73, p < 0.05). Second, the Hos-mer–Lemeshow statistic was not significant (p = 0.35),indicating that the model had an acceptable fit. Third,the Nagelkerke R2 statistic showed that the likelihoodrised to 11.7% when introducing the explanatory vari-ables in our model.

4. Discussion

The aim of the present prospective cohort study wasto assess the relative importance of socio-demographics,pain characteristics, work-related physical and psycho-social factors, and psychological factors, in explainingdevelopment of and recovery from short-term andlong-term LBP. Although several predictors were identi-fied in our study, the effect sizes were small, indicatingthat one should be careful when translating and imple-menting these results into practice. We discuss theresults of our study as a function of the outcomecategories.

4.1. Development of short-term LBP

The actual development of short-term LBP over theyear preceding follow-up proved difficult to predict. Ofthe 23 variables examined, only negative affectivity hadan effect, and just passed our 0.05 criterion of signifi-cance. Despite its small effect size, the effect of negativeaffectivity extends and replicates the effects of negativeaffectivity in our cross-sectional study (Gheldof et al.,2005). Also Linton (2000) concluded in his review thatpsychological factors such as emotional distress, moodand emotions play a significant role in the etiology ofacute pain, and possibly in the transition to chronicpain. As yet it is unclear how the effect of general dis-tress variables, such as the disposition to experience neg-ative affect, upon the occurrence of back pain isexplained. There are several possibilities. First, it is pos-sible that those with a disposition to experience negativeaffect have a response bias to endorse somatic symptoms(Vervoort et al., 2006). Second, negative affectivitymight be considered as a vulnerability factor that makesindividuals more likely to attend and to notice bodilysymptoms such as back pain (Goubert et al., 2004b;Waddell, 2004).

Several reviews (Hoogendoorn et al., 1999; Van Tul-der et al., 2002) reported evidence for an effect of heavyphysical work load, such as the often reported role ofmanual materials handling, bending and twisting (trunkflexion), and whole-body vibration as a risk factor forback pain. For just an example, in a prospective cohortstudy of Linton (2005) a sample of randomly selected


workers from the general population with no pain atbaseline were followed for one year. It was found thatpsychological distress, pain catastrophizing, and per-ceived physical work load were risk factors for the devel-opment of back pain (Linton, 2005). To our surprise, wedid not find any effect for physical load variables.Although the care for ergonomics undoubtedly remainsimportant, inconclusive evidence regarding the influenceof physical burden in the development of short-termLBP might remind us of the inability to prevent an ill-ness which natural history is to recur, irrespective ofits preceding cause (Waddell, 2004).

Likewise, none of the occupational psychosocial vari-ables like psychological job demands and decision lati-tude were predictive of short-term LBP in our study.We concur with the conclusion of Hoogendoorn et al.(2000) who stated that the role of specific work-relatedpsychosocial factors in the occurrence of LBP has notbeen established yet.

4.2. Recovery from short-term LBP

With respect to risks for failure to recovery fromshort-term LBP, a high score on fear of (re)injury dueto movement appeared to be important both in theunadjusted and the adjusted model. According to ourresults, a fearful – as opposed to a confronting – attitudeimpedes recovery from short-term LBP. This finding isin support of the fear-avoidance model (Vlaeyen andLinton, 2000) and strengthens the thesis that the efficacyof interventions with individuals experiencing short-term LBP might improve by including efforts to changepatients’ fear-avoidance beliefs about work and physicalactivity (Goubert et al., 2004a; Woby et al., 2004). Ourfindings support the idea that fear-avoidance beliefsmay not play a critical role in initiation of LBP, buthas a role once it is experienced (e.g., Sieben et al.,2005).

4.3. Development of long-term LBP

A number of significant predictors for the develop-ment of long-term LBP were found, albeit of small effectsize. First, our results show that a high level of decisionlatitude (only univariate) and sufficient co-worker socialsupport were significant protectors in the course towardslong-term LBP. According to previous reviews (Bongerset al., 1993; Hoogendoorn et al., 2000) evidence existsfor an effect of work-related psychosocial factors (suchas co-workers social support), but most studies exam-ined these factors in relation to the mere occurrence ofback pain, and not in relation to long-term LBP.Although our cross-sectional study (Gheldof et al.,2005) reveals inconclusive results with regard to the roleof decision latitude, some evidence was shown regardingthe role of psychological job demands and a lack of

supervisor social support as risks for long-term LBP.All in all, the current findings are in line with the ideathat work-related psychosocial risks become increas-ingly important when LBP becomes more chronic.

Further, a significant univariate risk is found for ahigh level of repetitive movements. This is in line withthe findings of our cross-sectional study (Gheldof et al.,2005), revealing physical work load (which includedrepetitive movements) and high task exertion as (univar-iate) risks of long-term LBP. However, at odds seems tobe the finding that a high level of manual materials han-dling reduced the risk of the development of long-termLBP. Although the reason for this effect is not yet clear,it may be that the found ‘protective’ effect of dynamicwork load due to manual materials handling is simplythe result of an (un)healthy worker effect: Those whoexperienced more pain during handling of manual mate-rials, changed to other jobs or functions. Further posthoc analyses were in line with this idea. More employeesof the long-term LBP group changed work or functiondue to BP (17.2% as compared to 1.6–14.3% for the othergroups, v2 = 16.50, p < 0.05).

Of further interest in this model are the findingsregarding fear-avoidance beliefs. Fear-avoidance beliefshave been found to predict the inception of an episodeof LBP (Linton et al., 2000), LBP chronicity (Klenermanet al., 1995; Picavet et al., 2002) and prolonged workrestrictions (Linton and Hallden, 1998; Fritz and George,2002), whereas others failed to find such an effect (Burtonet al., 1995; Burton et al., 2004). Indeed, Werneke andHart (2001) for instance found fear of work-related activ-ities to be univariately but not multivariately associatedto developing chronic pain (and to return-to-work sta-tus). As a result, several authors concluded that prospec-tive evidence regarding the role of pain-related fear uponthe development of chronic LBP (Vlaeyen and Linton,2000; Asmundson et al., 2004) remains inconclusive orat best weak in occupational settings (Linton, 2000; Pin-cus et al., 2002). The present study, which is in line withour baseline study (Gheldof et al., 2005) showed a signif-icant effect for high fear of work-related activities in thedevelopment of long-term LBP.

Finally, as expected based on our cross-sectionalstudy (Gheldof et al., 2005), important predictors forlong-term LBP concern high pain severity and radiatingpain into ankles or feet. It is generally known thatpatients with pain radiating below the knee have slowerclinical progress, poorer response to rehabilitation, andmore risk of long-term disability (Waddell and Burton,2001) than patients with back pain alone or with painreferred to the buttock/thigh region (Bolton and Chris-tensen, 1994). However, despite the risk for adverse clin-ical outcomes, there is moderate evidence that – in theabsence of other neurological findings – these patientsare best treated with conservative treatment (Atlas andNardin, 2003).


4.4. Recovery from long-term LBP

A high level of current pain severity not only seems toincrease the risk of developing long-term LBP, but alsoheightens the risk for failure to recover from long-termLBP. van der Giezen et al. (2000) found high pain severityto be one of the main obstacles to return to work (next tothe role of poor self-rated health). Adequate pain man-agement may not be overlooked when developing returnto work programs for individuals with long-term pain.

Our study has a number of strengths. First, this is aprospective study that includes many variables that wereidentified as potentially important predictors of LBP.Predictors belonged to one of five relevant areas (i.e.,individual, pain, physical work, work-related psychoso-cial or psychological factors), and were measured by val-idated instruments. Our study therefore allowsinvestigating the unique predictive value of variables.Second, the natural course of LBP is heterogeneous,and probably several subgroups of individuals withLBP may be identified. As such we classified our partic-ipants into subgroups, assuming that the timing andduration of interventions need to be carefully chosenand tailored to the selection of appropriate subjects.However, more research is needed to validate our classi-fication system, or to unravel different categories.

There are also a number of limitations. First, the lowenrolment rate (11%) and the high LBP prevalence atbaseline (69%) might have biased the initial sampleselection (Gheldof et al., 2005). It is conceivable thatespecially workers with LBP have participated at base-line. In addition, also the response rate at follow-upwas not high (63%). As a result, the possibility of biasdue to selective loss to follow-up cannot be excluded.Therefore, conclusions regarding the prevalence ofLBP in occupational settings are inappropriate. Second,as our results are from a cohort of mainly male indus-trial workers, one should be careful in generalizing theresults to other samples, for example white-collar orfemale workers. Third, all variables have been assessedby self-reports. The use of a retrospective measure ofthe number of days of LBP over the course of the pastyear, might have been influenced by a recall bias (seeVan Tulder et al., 2002). Fourth, in some analyses (i.e.the model predicting development of long-term LBP)there may have been too few outcome events relativeto the number of independent variables {Concatoet al., 1993, #4834}. There is then a danger of overfittingthe data. However, we are confident that our results arerobust, as the results from the crude and the adjustedOR analyses do not dramatically differ, and the confi-dence intervals of most variables of interest were small.Fifth, one should be mindful that the effect sizes of ourpredictors are small, still providing no clear-cut answeras to which factors are most important for developmentof or recovery from LBP.

Acknowledgements

This study was supported by an EU Interreg II grant:EMR. INT2.97.10.V.061. We also would like toacknowledge Helma Van den Heuvel, Marielle E.J.B.Goossens, Sandra Beurskens, Philippe Mairiaux andAnnette Leclerc for their helpful suggestions throughoutthe design and realization of the study.

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