Imaging Case of the Week 482 Answer

The x-rays show a posteriorly dislocated left shoulder.

The frontal shoulder x-ray shows 3 signs of posterior shoulder dislocation.

  1. Light bulb sign secondary to internal rotation of the shoulder.
  2. Loss of half moon sign to to abnormal relation between glenoid and head of humerus.
  3. Reverse Hill Sach lesion which is due to impaction fracture involving the anteromedial head of humerus against the posterior glenoid.

The injury is seen in epileptics post seizure activity, after electrocution and trauma. Can be bilateral in up to 20%. It is one of the missable injuries both clinically and radiographically.