DYNAMIC ANTERIOR STABILIZERS OF THE SHOULDER WITH THE ARM IN ABDUCTION

The stabilising effects on the glenohumeral joint of each of the rotat or-cuff muscles and of the biceps were studied with the arm in abducti on and external rotation in 13 cadaver shoulders. The muscles were loa ded one at a time with forces proportional to their cross-sectional ar eas. We recorded the positions of the humeral head before and after th e application to the humerus of an anterior force of 1.5 kg. When the capsule was intact, the anterior displacement with the subscapularis l oaded was significantly larger than with the other muscles loaded (p = 0.0009). With the capsule vented, the displacement with the biceps lo aded was significantly smaller than that with the subscapularis loaded (p = 0.0052). After creating an imitation Bankart lesion, the displac ement with the biceps loaded was significantly less than with any of t he rotator-cuff muscles loaded (p = 0.0132). We conclude that in the i ntact shoulder, the subscapularis is the least important anterior stab iliser, and that the biceps becomes more important than the rotator-cu ff muscles as stability from the capsuloligamentous structure decrease s. Strengthening of the biceps as well as the rotator-cuff muscles sho uld be part of the rehabilitation programme for anterior shoulder inst ability.