The Posterior Shoulder Dislocation
The Posterior Shoulder Dislocation The posterior shoulder dislocation is a relatively uncommon but critical injury that involves the humeral head being displaced backward out of the glenoid cavity of the shoulder joint. Unlike the more prevalent anterior dislocations, posterior dislocations are often overlooked or misdiagnosed, which can lead to significant long-term complications if not promptly recognized and treated.
This type of dislocation typically results from high-energy trauma, such as motor vehicle accidents or falls onto an outstretched arm, especially when the arm is in a position of internal rotation and adduction. It can also occur during seizures or electrical shocks, where intense muscle contractions force the humeral head backward. The challenge with posterior dislocations lies in their subtle clinical presentation. Patients might report shoulder pain, weakness, or a sensation of instability, but the deformity is less obvious than with anterior dislocations. On physical examination, the classic signs include limited external rotation, a prominent coracoid process, and the arm held in a slightly adducted and internally rotated position.
Diagnosis begins with a thorough clinical assessment followed by imaging studies. Standard anteroposterior (AP) shoulder radiographs may not always clearly reveal the dislocation. However, specific radiographic signs can suggest a posterior dislocation, such as the “light bulb” appearance of the humeral head, due to internal rotation, or the “rim sign,” which indicates widening of the glenohumeral joint space. To confirm the diagnosis and assess associated injuries, such as fractures or Hill-Sachs lesions, an axillary lateral view or scapular Y view is highly valuable. In some cases, advanced imaging like MRI or CT scans may be necessary to evaluate soft tissue damage and the extent of bony injury.
Management of posterior shoulder dislocations depends on the duration since injury and the presence of associated injuries. Immediate reduction is critical, ideally performed within the first few hours to prevent complications such as soft tissue interposition or neurovascular compromise. Closed reduction techniques involve gentle maneuvers, often under sedation or anesthesia to relax the muscles. Post-reduction, the shoulder is typically immobilized in a sling or brace for a period to allow healing and prevent recurrence. Rehabilitation exercises focusing on restoring range of motion and strengthening the rotator cuff muscles are essential for functional recovery.
In cases where the dislocation is neglected or recurrent, surgical intervention might be necessary. Procedures can include open reduction, stabilization with sutures or anchors, or even shoulder arthroplasty in severe cases with substantial bony damage. The prognosis for posterior shoulder dislocation is generally favorable with prompt and appropriate treatment, but delays can lead to chronic instability, joint stiffness, or arthritis.
Preventing misdiagnosis requires heightened awareness among clinicians, especially in patients presenting with shoulder trauma without obvious deformity. Recognizing the subtle signs and utilizing appropriate imaging studies are vital steps in ensuring effective management. Overall, understanding the mechanics, presentation, and treatment strategies for posterior shoulder dislocation can significantly improve patient outcomes and minimize long-term disability.
