The often overlooked posterior dislocation of the shoulder.

Unlike most shoulder dislocations, the posterior dislocation is truly a diagnostic challenge to the treating physician because it may be missed more often than it is recognized. In fact, more than 60% of posterior dislocations are misdiagnosed initially by the treating orthopedic surgeon, and the correct diagnosis is often delayed for months or years. A history of seizures, electroshock, or a fall onto a flexed, adducted arm should alert the physician to the possibility of posterior dislocation. A careful physical examination with comparison to the unaffected arm must be performed with particular attention given to subtle posterior fullness and anterior flatness of the shoulder, along with a lack of external rotation and abduction. A radiographic trauma series made in the scapular plane must always be obtained in cases of shoulder trauma to rule out posterior dislocation. A computed tomographic scan may also be necessary. The correct diagnosis of this injury will facilitate proper orthopedic evaluation and treatment and will reduce the incidence of missed posterior shoulder dislocation and its associated morbidity.