Joint · Shoulders

Glenohumeral joint

Articulatio humeri

The main shoulder joint — the ball of the humerus against the shallow socket of the shoulder blade. It is the most mobile joint in the body, and it pays for that mobility with stability: the socket is small and flat relative to the ball, deepened only slightly by a fibrocartilaginous rim called the labrum. The bones do not hold this joint together; the rotator cuff, the capsule and the ligaments do. That trade-off is the reason so many shoulder problems are muscular control problems rather than bone problems.