Coracoacromial Ligament

The capsule of the glenohumeral joint is loose and pleated. The ligaments, which are merely thickenings in the capsule, provide little support. The major support of the humerus into the fossa is provided by the rotator cuff muscles, which hold the head into the fossa. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis. Abduction-adduction and axial and horizontal rotations are coupled in that angular motions are accompanied by translatory slides. The caudal slide of the humeral head with abduction confers increased freedom of motion on the supraspinatus tendon beneath the coracoacromial ligament. 

The two functional joints in the shoulder girdle are the suprahumeral joint and the scapulothoracic joint. As mentioned, both figure prominently in shoulder biomechanics and pathology. The suprahumeral joint is formed by the articulation of the head of the humerus with the coracoacromial arch, composed of the acromion, the coracoid process, and the ligament between them. Articulation occurs during abduction. 

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