Effects of glenohumeral rotations and translations on supraspinatus tendon morphology

Objective. The purpose of this study was to evaluate the effects of glenohumeral rotations and humeral head translations on supraspinatus tendon morphology. Design. A convenience sample of cadaver shoulders was used to measure supraspinatus tendon shape and dimensions from MRI images. Background. Epidemiological evidence has indicated that shoulder elevation and external rotation may be risk factors for rotator cuff tendon pathology, but little is known about how these postures affect tendon morphology. Methods. Measurements of supraspinatus tendon morphology were made from three-dimensional reconstructions based on T2-weighted fast spin-echo magnetic resonance images. Seven cadaver arms were imaged at neutral, 45° external and 45° internal rotations at 0°, 30°, and 60° of glenohumeral abduction. Measurements of the anterior, middle, and posterior portions of the tendon were made using analyze TM software. Results. The supraspinatus tendon was twisted at the muscle–tendon junction of the middle and posterior portions in 45° external and 45° internal axial rotations of the humerus, especially over 30° of abduction. Abduction over 30° shortened the entire supraspinatus tendon. External and internal rotation motions elongated the anterior and posterior portions, respectively. Conclusions. Arm posture affects morphology of the supraspinatus tendon. Relevance The results support the epidemiologic evidence linking external rotation and abduction to supraspinatus tendon disorders.