Voluntary posterior dislocation may occur with the arm in flexion, adduction and internal rotation, or with the arm at the side. The association of voluntary dislocations of the shoulder with emotional instability and psychiatric problems has been noted by several authors. The desire to voluntarily dislocate the shoulder cannot be treated surgically. However, the fact that patients can voluntarily demonstrate their instability does not necessarily mean they are emotionally impaired. Neuromuscular causes of shoulder instability have been reported as well.
Stroke is another important neurological cause of instability.
Glenohumeral subluxation is defined as symptomatic translation of the humeral head on the glenoid without complete separation of the articular surfaces. Like dislocations, subluxations may be traumatic or atraumatic, anterior, posterior, or inferior, acute or recurrent, or they may occur after previous surgical repairs that did not achieve complete shoulder stability. Recurrent subluxations may coexist with or be initiated by glenohumeral dislocation. Apprehension refers to the fear that the shoulder will subluxate or dislocate. This fear may prevent the individual from participating fully in work or sports.