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Stabilizers of the Shoulder

- Discussion:
    - muscular stabilizers
    - static stabilizers
    - stabilizers include: glenoid, glenoid labrum, negative intraarticular pressure, glenohumeral capsular ligaments, rotator cuff and scapular muscles;
    - stabilizers include glenohumeral size, posteriorly angulated glenoid & humeral head, & functional muscle control (most important);
    - structure that is most responsible for preventing anterior glenohumeral dislocation varies with the position of the arm.
    - 0 deg: at 0 degrees of abduction, subscapularis muscle stabilizes the joint to a large extent.
    - 45 deg: at 45 degrees of abduction subscapularis, middle glenohumeral ligament, and the anterior superior fibers of inferior glenohumeral ligament provide shoulder stability; (greatest strain in the inferior and middle ligaments);
    - 90 deg: in abduction with external rotation, the inferior glenohumeral ligament prevents dislocation;
               - when arm is in a position of anterior instability (90 deg abduction & 90 degrees external rotation), role of dynamic stabilizers changes.
               - in this position, pectoral, short head of biceps, coracobrachial, anterior deltoid, & subscapularis  resist anterior dislocation

Stabilizing mechanisms preventing anterior dislocation of the glenohumeral joint.