This study was

Biomedical Res

*Reprint req

Clinical Science

Coventry, CV2

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J Shoulder Elbow Surg (2014) 23, 1107-1112

1058-2746/$ - s

http://dx.doi.org

www.elsevier.com/locate/ymse

Ultrasound dimensions of the rotator cuffin young healthy adults

Shanmugam Karthikeyan, MRCSa,b,*, Santosh B. Rai, FRCRd, Helen Parsons, PhDa,Steve Drew, FRCS (Tr & Orth)b, Christopher D. Smith, FRCS (Tr & Orth)c,Damian R. Griffin, FRCS (Tr & Orth)a

aDepartment of Trauma and Orthopaedics, Warwick Medical School, University of Warwick, Coventry, UKbDepartment of Trauma and Orthopaedics, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, UKcDepartment of Trauma and Orthopaedics, Royal Devon and Exeter NHS Trust, Exeter, UKdDepartment of Radiology, University Hospitals Coventry and Warwickshire NHS Trust, Coventry, UK

Background: No studies have looked at the rotator cuff dimensions in the young healthy population usingultrasonography. Our aim is to define the ultrasound dimensions of the rotator cuff in the healthy youngadult population and explore correlations with other patient characteristics.Methods: Thirty male and 30 female healthy volunteers (aged 18-40 years), with no shoulder problems,underwent ultrasound assessment of both shoulders by a musculoskeletal radiologist. The dimensions ofthe rotator cuff, deltoid, and biceps were measured in a standardized manner.Results: A total of 120 shoulders were scanned. The mean maximum width of the supraspinatus footprintwas 14.9 mm in men and 13.5 mm in women (P < .001). The mean thickness of the supraspinatus tendonwas 4.9 mm in women and 5.6 mm in men. The mean thickness of the subscapularis was 4.4 in men and3.8 mm in women and for the infraspinatus was 4.9 mm in men and 4.4 mm in women. There was no cor-relation between height, weight, biceps, or deltoid thickness with any tendon measurements. Apart fromsupraspinatus tendon thickness, the difference between dominant and nondominant shoulders in thesame sex was not significant for any other tendon dimensions.Conclusion: This study has defined the dimensions of the rotator cuff in the young healthy adult, whichhas not been previously published. This is important for the documentation of normal ultrasound anatomyof the rotator cuff and also demonstrates that the asymptomatic contralateral shoulder can and should beused to estimate the expected dimensions.Level of evidence: Anatomic Study, Imaging.� 2014 Journal of Shoulder and Elbow Surgery Board of Trustees.

Keywords: Rotator cuff; dimensions; adults; normal; gender; ultrasound

reviewed and approved by the University of Warwick

earch Ethics Committee.

uests: Shanmugam Karthikeyan, MRCS, CSRL (1st Flr

s Building), University Hospitals, Clifford Bridge Rd,

2DX, UK.

ss: karthi@hotmail.co.uk (S. Karthikeyan).

ee front matter � 2014 Journal of Shoulder and Elbow Surgery

/10.1016/j.jse.2013.11.012

Shoulder pain is the second most prevalent cause ofmusculoskeletal pain in the community, behind only lowback pain.22 It has been estimated that every year approx-imately 1% of all adults consult their general practitionerwith new-onset shoulder pain.18,20 Rotator cuff pathology isreported to be the most common cause for painful shoulder

Board of Trustees.

Figure 1 Thickness of the subscapularis tendon on ultrasoundimaging.

1108 S. Karthikeyan et al.

episodes, accounting for up to 70% of cases.20 Accuratediagnosis of shoulder conditions is difficult because theclinical findings are often shown to have poor correlationwith the actual pathology.8,10

Magnetic resonance (MR) arthrography is the mostsensitive and specific technique for diagnosing rotator cufftears.7 Ultrasound is accurate and the most cost-effectivemethod to identify full-thickness tears and, to a lesserextent, partial-thickness tears, comparable to MR imaging(MRI) in sensitivity and specificity.7,21 According to recentsystematic reviews,7,25 ultrasound had a sensitivity of 92%to 96% and a specificity of 93% to 94.4% for diagnosingfull-thickness tears. For partial-thickness tears, the sensi-tivity was 66% to 84% and specificity was 89% to 93.5%.One of the criteria used to diagnose a rotator cuff tear isthinning of the tendon.5,11,24,30,31 It is based on knowing thenormal dimensions of the rotator cuff and trying to visu-alize a decrease in tendon thickness.

Although there is an abundance of literature on thepathologic appearances and frequencies of rotator cuff pa-thology, a detailed literature review has revealed no previ-ous studies looking at the cuff dimensions in a younghealthy population using ultrasonography. Specifically,there is no evidence of correlation with sex, hand domi-nance, weight, height, and other ultrasound measurements.Defining the normal parameters for the rotator cuff willhelp clinicians make a comparison between normal andpathologic conditions.

The aim of this study is to define the dimensions of thesupraspinatus tendon and other rotator cuff muscles in ahealthy young adult population and compare them with thecontralateral shoulder. Correlations with sex, height,weight, dominance of hand, and other muscle dimensionswill also be established.

Materials and methods

Inclusion and exclusion criteria

All healthy adults aged between 18 and 40 years, who had nosignificant medical conditions and had no shoulder problems,were considered eligible to participate in the study. Anyonewith significant comorbidities or who had undergone previousshoulder surgery was excluded. Volunteers who had or hadexperienced pain in their shoulder or who were limited in theirdaily activities due to shoulder problems in the preceding4 weeks were also considered ineligible to participate in thestudy.

Recruitment

The first 60 volunteers (30 men and 30 women) from among thestaff and students of our institution who met the eligibility criteriaformed the study population. Each volunteer included in the studyunderwent an ultrasound assessment of both shoulders in a privateconsultation room by a musculoskeletal radiologist (S.B.R.).

Data collection

Demographic details, including age, height, weight, hand domi-nance, sports activities, comorbidities, and smoking and drinkinghabits were collected for each individual.

One experienced consultant musculoskeletal radiologist (S.B.R.)who routinely performs ultrasound assessment of shoulders did allof the measurements. Both shoulders were scanned in each indi-vidual sequentially. A GE Logiq E9 (GE Healthcare, Chalfont St.Giles, UK) ultrasound scanner with a 10- to 15-MHz linear arraytransducer was used for all assessments. The scan was performedwith the individual sitting on a couch and facing the examiner.

The following structures were visualized in sequence, andmeasurements were taken as described for each structure. Tominimize bias, all measurements were taken with reference tobony landmarks.

1. Tendon of long head of biceps2. Subscapularis3. Supraspinatus4. Subacromial bursa5. Infraspinatus6. Deltoid

The biceps tendon was identified first, and its maximal thicknesswas measured in the transverse view at the highest point of the groovewith the forearm resting supine on the lap. With the arm in externalrotation, the thickness of subscapularis tendon was measured justmedial to the attachment at the lesser tuberosity (Fig. 1).

The maximal mediolateral width of the supraspinatus footprintat its insertion was measured in the coronal view of the tendon,with the arm in internal rotation. Two further measurements weremade to assess the thickness of supraspinatus tendon in the sameview. The first was made at the medial edge of footprint and thesecond was at the midpoint of the footprint (Fig. 2). In addition,the thickness of supraspinatus tendon on the sagittal view wasdone at a fixed point 15 mm posterior to the biceps tendon (Fig. 3).

The thickness of the subacromial bursa was measured on thecoronal view in the same plane as the thickness of the supraspinatustendon. Infraspinatus tendon thickness was measured at the level ofthe posterior border of the acromion, and thickness of deltoidmuscle was measured at the anterolateral edge of acromion.

Figure 3 Thickness of the supraspinatus tendon (2) at a fixedpoint 1.5 cm (1) posterior to the biceps tendon in the sagittal planeon ultrasound imaging.

Table I Study participant characteristics by sex

Participantcharacteristics)

Females(n ¼ 30)

Males(n ¼ 30)

Age, y 26.7 (21-39) 29.9 (23-39)Height, m 1.63 (1.50-1.78) 1.80 (1.70-1.95)Weight, kg 60.6 (45-77) 81.4 (67-100)Body mass index, kg/m2 24.96 (17-31) 22.73 (22-33)Hand dominanceRight-handed 28 27Left-handed 2 3

) Continuous data are shown as the mean (range) and categoric data

as the number of participants.

Figure 2 Maximum width of footplate (1) and thickness ofsupraspinatus at the medial edge of the footplate (2) and at themiddle of the footplate (3).

Figure 4 Box-and-whisker plot shows the mean maximum di-mensions of the supraspinatus footplate. The horizontal line in themiddle of each box indicates the median, the top and bottomborders of the box mark the 75th and 25th percentiles, respec-tively, and the whiskers represent 1.5 times the interquartile rangefrom the box borders.

Ultrasound dimensions of normal rotator cuff 1109

Interobserver and intraobserver agreement

For a subset of 10 participants (5 men and 5 women), repeatmeasurements were taken by the initial observer at 4 weeks afterthe first measurement and by a second observer who was also anexperienced consultant musculoskeletal radiologist (R.W.).

Statistical analysis

Differences in measurements between men and women and handdominance were determined by performing t tests. Paired t testswere used to compare dominant and nondominant arms for eachparticipant. For comparisons of dominant arms between men andwomen a 2-sample t test was conducted. The Pearson correlationcoefficient was calculated to measure the strength of associationbetween the tendon measurements and the height and weight ofthe individuals. Differences were considered significant at the 5%level if the P values were <.05. Bland-Altman plots were con-structed to measure intraobserver and interobserver agreement. Allanalyses were performed using R software (The R Foundation forStatistical Computing, http://www.r-project.org/).

Results

Scans were done of 120 shoulders from 60 participants(30 men and 30 women); of these, 55 were right hand-dominant and 5 were left hand-dominant. Participants’age, height, weight, and hand dominance are reported inTable I.

The mean maximum mediolateral width of the supra-spinatus insertion onto the humerus in the coronal plane(footprint) was 14.9 mm in men and 13.5 mm in women(Fig. 4). The mean thickness of the supraspinatus tendonvaried from 4.9 mm in women to 5.6 mm in men at themedial edge of its insertion and between 3.6 and 4.2 mm,respectively, at the midpoint of its insertion.

Table II presents the mean � standard deviation (SD)and range for each muscle measurement, separately formale and female participants by hand dominance.

The supraspinatus footprint measurements were signifi-cantly different between men and women for dominant and

Table II Descriptive statistics for the average measurements for male and female participants in the study)

Variable Female (n ¼ 30) Male (n ¼ 30)

Dominant arm Nondominant arm Dominant arm Nondominant arm

Rotator cuffSubscapularis 3.8 � 0.5 (2.8-4.7) 3.8 � 0.5 (2.9-4.9) 4.4 � 0.8 (2.8-6.1) 4.4 � 0.7 (2.9-6.1)SupraspinatusCoronal viewMedial edge of FP 5.0 � 0.6 (3.9-6.4) 4.8 � 0.7 (3.3-6.3) 5.8 � 0.9 (4.6-8.2) 5.3 � 0.8 (4.2-7.6)Middle of FP 3.7 � 0.5 (2.6-4.8) 3.5 � 0.5 (2.4-4.4) 4.3 � 0.7 (3.1-6.0) 4.0 � 0.8 (2.7-6.4)Max width of FP 13.4 � 1.2 (11.3-16.6) 13.5 � 1.3 (11.6-15.4) 14.9 � 1.5 (12.1-18.8) 14.9 � 1.5 (11.5-18.3)

Sagittal view 4.7 � 0.6 (3.6-6.1) 4.5 � 0.6 (3.7-5.9) 5.2 � 1.0 (3.8-8.1) 5.0 � 0.9 (3.8-7.0)Infraspinatus 4.4 � 0.4 (3.6-5.2) 4.3 � 0.5 (3.5-5.5) 4.9 � 0.6 (3.8-6.2) 4.9 � 0.7 (3.4-6.4)

OtherBiceps tendon 2.9 � 0.4 (2.2-3.9) 2.9 � 0.4 (2.3-4.2) 3.4 � 0.4 (2.6-4.2) 3.3 � 0.6 (2.2-4.6)Deltoid muscle 6.1 � 0.8 (4.6-8.0) 5.9 � 0.9 (4.8-8.8) 7.1 � 0.8 (5.4-8.8) 7.1 � 1.0 (5.4-9.8)SASD bursa 1.0 � 0.2 (6.0-1.5) 0.9 � 0.2 (.06-1.3) 1.2 � 0.3 (0.8-1.7) 1.1 � 0.3 (0.7-1.8)

FP, Footprint; SASD, subacromial-subdeltoid.) Data are shown as the mean � standard deviation, and the range for each measurement is shown in parentheses. All measurements are in millimeters.

Figure 5 A Bland-Altman plot shows the intraobserver agree-ment. The dashed lines show 95% confidence intervals around thehypothesis of no difference between observations. S Sagittal,supraspinatus sagittal view; SC Medial, supraspinatus coronalview medial edge of footprint; SC Middle, supraspinatus coronalview middle of footprint.

1110 S. Karthikeyan et al.

nondominant shoulders. The footprint for the dominant armwas measured at 13.4 mm in women compared with 14.9 mmin men (P < .001; t test). For the nondominant arm, womenhad a footprint dimension of 13.5 mm compared with14.9 mm in men (P < .001; t test). However, the differencebetween the dominant and nondominant arm among men andwomen was not significant. The mean difference in supra-spinatus footprint dimensions between the dominant andnondominant arms was 0.03 mm in men (P ¼ .867; paired ttest) and 0.09 mm (P ¼ .607; paired t test) in women.

The thickness of the supraspinatus tendon was signifi-cantly different between the dominant and nondominantarms in men and women. The difference in thickness was0.5 mm (P ¼ .003; paired t test) in men and 0.3 mm(P ¼ .005; paired t test) in women at the medial edge of thefootprint and was 0.3 mm (P ¼ .022; paired t test) in menand 0.27 mm (P ¼ .007; paired t test) in women at themiddle of the footprint.

For all other tendon measurements, a significant differ-ence was found between men and women for dominant andnondominant sides, but no significant difference betweenthe dominant and nondominant sides was found among thesame sex (Table II).

Correlation

Bland-Altman plots2,3 were constructed for measuring theintraobserver (Fig. 5) and interobserver (Fig. 6) agreement.Agreement was analyzed by plotting the differences in the2 sets of measurements against the mean values of thesemeasurements. The Bland-Altman plots are consistent withthe hypothesis that 95% of the differences between theassessments were within �1.96 standard deviations of themean of the differences (‘‘limits of agreement’’), denotinggood agreement between the 2 sets of measurements.2,3

No significant correlation was found between theheight or weight of the individual and any of the tendonmeasurements (P > .05 for all tests). Deltoid muscledimension and biceps dimensions did not have any cor-relation to the thickness of the rotator cuff tendons(P > .05 for all tests).

Discussion

This study has demonstrated for the first time the mean andrange of dimensions of the rotator cuff in the young healthyadult. Although a statistical difference was found between

Figure 6 A Bland-Altman plot shows the interobserver agree-ment. The dashed lines show 95% confidence intervals around thehypothesis of no difference between observations. S Sagittal,supraspinatus sagittal view; SC Medial, supraspinatus coronalview medial edge of footprint; SC Middle, supraspinatus coronalview middle of footprint.

Ultrasound dimensions of normal rotator cuff 1111

the dimensions of women and men, it has demonstrated thatexcept for thickness of the supraspinatus tendon at the foot-print, the dimensions between dominant and nondominanthands are not statistically significantly different. This isimportant, because it means that an asymptomatic contralat-eral shoulder can be used as a guide to estimate normal di-mensions of the affected shoulder.

Partial-thickness tears are classified arthroscopically usingthe Ellman grading,9 which is based on a supraspinatusthickness of 10 to 12 mm just proximal to its insertion on tothe humerus. However, there is no evidence for using this as areference range. Although the gross anatomy of the supra-spinatus has been documented,27 and the tendon thickness hasbeen reported as 3 � 0.07 mm (range, 0.2-0.4 mm) in elderlycadaveric specimens,16,23 that the integrity of the rotator cuffdecreases with age has been well established.17 Milgromet al17 showed that there is a very significant difference in theincidence of rotator cuff tears in individuals aged older than50 years compared with someone aged between 30 and39 years for both dominant and nondominant arms (P< .001).Besides, another study showed that themuscle volume and thecross-sectional area of the rotator cuff muscles were 1.6 timeshigher in living humans, primarily due to age and dehydrationeffects.13 Therefore, these data are unlikely to reflect whatwould be found in young healthy adults.

Ultrasound has been used to measure the thickness of thesupraspinatus tendon in asymptomatic adults1,4,6,12,19,28,29

and also to calculate the cross-sectional area of the supra-spinatus within its fossa in the asymptomatic patient.14,15

The mean diameter of the supraspinatus tendon has beenrecorded by ultrasound in these studies as between 4.0 and6.25 mm.1,6,19,28,29 It was approximately 5.2 to 5.6 mm inthe elite baseball athlete29 and was increased in patients

with diabetes1 and amyloidosis.12 However, these studiesassessed the tendon at different points and none of them atthe point referred to by Ellman,9 which is most critical tothe surgeon as the point where rotator cuff tears occur.

Our study has documented the width of the supraspinatusfootprint in a younger population that is most likely to sus-tain a partial-thickness tear. This information will be helpfulin determining the percentage of the tendon involved in apartial-thickness tear at arthroscopy. Although there is awide range in the data, our study has shown that thecontralateral shoulder can and should be used as a control inalmost all circumstances, supporting the argument for al-ways performing bilateral shoulder ultrasound assessments.

Our study has some limitations. All of the volunteers forour study were chosen from our institution; however, thereare no reasons to believe they are any different from thegeneral population.

Ultrasound is highly user-dependent.5,25,26 Previousstudies using ultrasound to measure the thickness of ten-dons have shown that even with well-defined protocols,substantial interobserver and, to a lesser extent, intrasubjectintervisit variation exists.19 In our study, the Bland-Altmanplots show good agreement for interobserver and intra-observer measurements, supporting the use of ultrasound toimage the shoulder.

All of themeasurementsweremade in a younger age groupthat is unlikely to have rotator cuff pathology, and because therotator cuff is known to display thinning with advancing age,these data cannot be extrapolated to other age categories.6

Conclusion

This study has shown the normal dimensions of the rotatorcuff for subscapularis, supraspinatus, and infraspinatus inyoung adults. However, there is a wide range in the di-mensions, which makes using classifications based on anaverage size difficult. This has not previously beenpublishedand aids clinicians and radiologists in the evaluation of theshoulder. It reassures us of the reliability of shoulder ultra-sound measurements and emphasizes the utility and appro-priateness of routine screening of the other shoulder as acontrol.

Acknowledgments

We thank Dr RichardWellings for his help with ultrasoundmeasurements and Dr Nick Parsons for help with statistics.

Disclaimer

None of the authors, their immediate families, and anyresearch foundations with which they are affiliated

1112 S. Karthikeyan et al.

received any financial payments or other benefits fromany commercial entity related to the subject of thisarticle.

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