A 42 yo male presents to the ED after he was assaulted.  He reports that his right shoulder was stomped on and now he has right shoulder pain and limited range of motion.  An x-ray is shown below.  What's the diagnosis?  Scroll down for answer

Answer:  Posterior shoulder dislocation

• Rare, only 2-4% shoulder dislocations
• Can be bilateral
• Common mechanisms are seizure and electrocution
• Patient will have limited range of motion on exam; roughly half will be missed on initial presentation
• On plain x-ray - the light bulb sign on AP view (with forced internal rotation, the humeral head looks like a light bulb), or the rim sign (widening of the glenohumeral joint space)
• Closed reduction is performed wiht the Depalma method: medial upper arm is pushed laterally while maintaining caudal traction, adduction and internal rotation of the affected arm
• Chronic postieror dislocations or those accompanied by fracture may require orthopedic consultation
• Complications:  osteonecrosis of the humeral head, functional deficits, nerve injury, recurrence, chronic arthritis