Biomechanical basis of common shoulder problems.

Balancing mobility and stability, the biomechanics of the shoulder provides optimal use of the thumb and hand. More than a glenohumeral joint, the shoulder complex consists of four joints and numerous muscles and ligaments. Injuries to the shoulder result from overuse, extremes of motion, and excessive forces. This review describes basic shoulder biomechanics, their role in impingement and instability, and how imaging can detail shoulder function and dysfunction.