Investigating the multifactorial etiology of supraspinatus tendon tears

Abstract

The purpose of this study was to develop a multivariable model to determine the extent to which a combination of etiological factors is associated with supraspinatus tendon tears. Fifty-four asymptomatic individuals (55 ± 4 years) underwent testing of their dominant shoulder. Diagnostic ultrasound was used to assess for a supraspinatus tendon tear. The etiological factors investigated included demographics (age and sex), tendon impingement during shoulder motion (via biplane videoradiography), glenohumeral morphology (via computed tomography imaging), family history of a tear (via self-report), occupational shoulder exposure (via shoulder job exposure matrix), and athletic exposure (via self-report). Univariate relationships between etiological predictors and supraspinatus tears were assessed using logistic regression and odds ratios (ORs), while multivariable relationships were assessed using classification and regression tree analysis. Thirteen participants (24.1%) had evidence of a supraspinatus tear. Individuals with a tear had a higher critical shoulder angle (OR 1.2, p = 0.028) and acromial index (OR 1.2, p = 0.016) than individuals without a tear. The multivariable model suggested that a tear in this cohort can be explained with acceptable accuracy (AUROC = 0.731) by the interaction between acromial index and shoulder occupational exposure: a tear is more likely in individuals with a high acromial index (p < 0.001), and in individuals with a low acromial index and high occupational exposure (p < 0.001). The combination of an individual's glenohumeral morphology (acromial index) and occupational shoulder exposure may be important in the development of supraspinatus tears.

Keywords: etiology; morphology; occupational shoulder exposure; rotator cuff tear; supraspinatus.

Figure 1:

CONSORT diagram illustrating the flow of participant screening, enrollment, and testing during the study.

Figure 2:

Estimation of rotator cuff tendon impingement during in vivo shoulder motion. A) Subacromial impingement was assessed by calculating the distance between the acromion and rotator cuff footprint, with contact assumed to occur when the minimum distance at the humeral articular margin was less than the rotator cuff tendon thickness measured during the ultrasound examination. B) Internal impingement was assessed by calculating the proximity between the glenoid and rotator cuff footprint, with contact assumed to occur when the minimum distance was less than an estimated labral thickness.

Figure 3:

Measurement of glenohumeral morphology variables. A) Posterolateral view showing the scapular reference coordinate system (dashed axes) and glenoid-based coordinate system (solid axes) involved in the morphology calculations. B) Glenoid inclination. C) Glenoid version. D) Critical shoulder angle. E) The acromial index (GA/GH×100%). Note that the full humerus model includes the epicondyles but was cropped for visualization.

Figure 4:

The results of the multivariable classification and regression tree analysis. Of all the etiological predictor variables included in the analysis (subacromial impingement, internal impingement, glenoid inclination, glenoid version, critical shoulder angle, acromial index, family history of rotator cuff tear, occupational shoulder exposure, athletic exposure), the final model included two variables: acromial index and age-normalized occupational shoulder exposure. A supraspinatus tendon tear is 11.0 times more likely in someone predicted to have a tear based on this model than someone who was not (p<0.001). Within each node (i.e., predicted tear classification), counts and percentages are provided based on actual tear classification, which were used to calculate relative risks and odds ratios.