The static rotator cuff does not affect inferior translation of the humerus at the glenohumeral joint

Background: The static contribution of the rotator cuff to the inferior sta bility of the shoulder is poorly understood. The purpose of this study was to determine the effect of static rotator cuff muscles on the inferior stab ility of the glenohumeral joint. Methods: The humeral head positions relative to the glenoid were obtained i n 12 shoulder specimens under the following conditions: with and without a 1.5-kg load; with the humerus adducted and abducted 90 degrees; and in thre e stages of dissection: (1) before release of any of the rotator cuff muscl es, (2) after release of the supraspinatus or the cuff muscles other than t he supraspinatus, and (3) after release of all of the cuff muscles. The ord er of release was changed in two ways: release of the supraspinatus followe d by the release of other muscles in one group, and the opposite order in t he other group. Results: In both adduction and abduction, there were no significant differe nces in the positions of the humeral head either among the three stages of release or between the two different orders of release. Conclusion: The static contribution of the cuff muscles to the inferior sta bility of the shoulder is insignificant.