Posterior shoulder dislocations are infrequent (<5% of shoulder dislocations) but important types of shoulder dislocations.  These are frequently missed initially due to failure to suspect the injury combined with inadequate or misinterpreted radiographs.  The initial priorities are proper diagnosis and reduction.

     Posterior shoulder dislocations occur from severe internal rotation and adduction.  Because the internal rotator muscles are approx twice as powerful as the external rotator muscles, a sudden contraction (such as from a seizure or electrical shock) will cause the humeral head to dislocate posteriorly, sometimes bilaterally.  It can also occur from direct trauma or a fall on the outstretched hand.