The shoulder joint is formed by the articulation of the glenoid cavity of the scapula and the head of the humerus. It is a synovial, polyaxial ball and socket joint. The glenoid fossa is too small and shallow to stably hold the humeral head, so the joint is inherently weak. Stability is provided by the joint capsule, glenohumeral ligaments, labrum, rotator cuff muscles, and other accessory ligaments. Injuries like dislocations or rotator cuff tears can compromise the stability of the shoulder joint.