[Posterior shoulder dislocation. An often overlooked injury].

Posterior dislocation of the shoulder is rare. Only 2% of dislocated shoulders are displaced posteriorly, and these are chiefly of the subacromial type. Over 60% of the cases are not diagnosed initially because the arm is held in the normal position of adduction and internal rotation. The most consistent findings on physical examination are: the fixed internal rotation of the arm and the characteristic movement of the scapula with abduction of the upper extremity. It is essential that appropriate radiographs are obtained to correctly diagnose the dislocation. While the routine anteroposterior shoulder film is often enough to diagnose various anterior dislocations, it is not sufficient to diagnose the subacromial type of posterior dislocation. We recommend an anteroposterior view and an axillary lateral or tangential scapula view.