Shoulder anatomy and biomechanics.

The evaluation of shoulder disorders is challenging because of anatomic and biomechanical complexities. The shoulder comprises three synovial joints and two movement interfaces. The following principles are important to establish an accurate anatomic diagnosis and to develop a treatment plan: (1) perform a careful history and physical examination; (2) determine whether or not the problem is mechanical; (3) for mechanical problems, establish pathophysiologic and mechanical diagnoses; and (4) use mechanical impairments as the basis for therapeutic interventions.