1. DISCUSSION
On the posterior view, the normal contour of the left deltoid bulges and hides the contour of the scapular spine. On the anterior view the normal contour of the anterior deltoid is depressed on the left. All this fits together as a posterior shoulder dislocation, which is rather uncommon but which is known to occur as a result of violent muscular contractions sustained during a seizure or electrical shock. During violent, simultaneous contraction of all the shoulder muscles, the large internal rotators (pec major, subscap, lat dorsi) overpower the relatively weak external rotators (teres minor and infraspinatus), and posterior dislocation ensues.
This injury can be easily missed on a quickie exam or x-ray evaluation. The patient’s main complaint is often inability to externally rotate the shoulder.