Which of the following is the most common cause of a posterior shoulder dislocation?

• A. Seizures or electrocution
• B. High-energy trauma
• C. Falling on the shoulder
• D. Sports injury

Answer: (A)

Seizure or electric shock events are the classic and most common cause of posterior shoulder dislocations. During a seizure or electrocution, the arm is driven into violent internal rotation and adduction, pushing the humeral head posteriorly out of the glenoid and tearing the posterior structures. While trauma can cause a posterior dislocation, it occurs far less often than those neurologic or electrical injuries. In contrast, falls on the outstretched hand or sports injuries typically produce anterior dislocations due to the force of abduction and external rotation. Because posterior dislocations can be subtle on standard X-rays, they’re often diagnosed with dedicated views such as an axillary or scapular-Y view.