Anterior stability of the glenohumeral joint. A dynamic model

This study defines the interaction of the rotator cuff musculature and the glenohumeral ligaments in providing anterior stability to the glenohumeral joint. Eight cadaveric shoulders were studied using a testing frame that individually simulated the forces of the subscapularis, the supraspinatus, and the infraspinatus/teres minor musculature. The application of these forces abducted the humerus to approximately 90 degrees. The cocking phase of throwing was then simulated through the use of an Instron. With random variation of the rotator cuff forces, we investigated the effects that each force had on the rotation of the humerus and the strain of the inferior glenohumeral ligament. Our results demonstrate that the infraspinatus/teres minor muscle group was the most effective in controlling external rotation of the humerus and in reducing ligamentous strain. These observations are pertinent in the treatment of anterior instability syndromes of the shoulder.