Posterior Shoulder Dislocation: Reduction Technique, Clinical Features, Imaging & Complications

Posterior shoulder dislocation is Complete posterior displacement of the humeral head out of the glenoid

Posterior shoulder dislocations are rare, accounting for < 4 % of all dislocations around the shoulder

Mechanism of action

At risk position for posterior shoulder dislocation is adduction and internal rotation of the arm and indirect force aggravating this position may lead to posterior dislocation

Most common causes are:

• During a seizure (most common cause)
• Due to an electric shock
• After a fall on the flexed, adducted arm
• Due to a direct anterior blow to the shoulder
• After a fall on the outstretched hand

Clinical features

• Patient present with shoulder pain and muscle spasm
• Arm is held adducted and internally rotated and patient often comfortable in this position
• The front of shoulder looks flat (normal is rounded) with prominent coracoid process, sometimes swelling will obscure the coracoid but generally speaking, deformity is less dramatic than in anterior shoulder dislocation
• The patient will not be able to externally rotate their arm, and they also can’t abduct their arm beyond 80 degrees
• Enquire about mechanism of injury (to assess severity) and look for other injuries
• Neurovascular examination is done looking for vascular and nerve injuries

Imaging

• AP shoulder X-ray (unreliable): shows the light bulb sign (the humeral head looks like a light bulb because the arm is in full internal rotation and greater tuberosity contour is sitting in front now so it is lost)
• You also see that the humeral head is located away from the glenoid (empty glenoid sign)
• Lateral or axillary views (diagnostic) will show posterior displacement of the humeral head (very obvious); Reverse Hill Sachs lesion (anterior impaction fracture maybe obvious on the lateral view)
• CT scan is indicated if the patient uncomfortable to do the main imaging techniques and to look for other injuries

Posterior shoulder dislocation AP shoulder X-ray on the left vs normal shoulder X-ray on the right; by Hellerhoff, via Wikimedia Commons

Light bulb sign of posterior shoulder dislocation on AP shoulder X-ray on the left image vs normal shoulder AP X-ray on the Right; by Hellerhoff, via Wikimedia Commons

Axillary view shoulder X-ray showing posterior shoulder dislocation, by Doc James, via Wikimedia Commons

Notes

• Posterior shoulder dislocation is often a missed diagnosis in Emergency department
• Unique features of posterior shoulder dislocation include:
  • Loss of external rotation of the affected arm
  • Posterior displacement on the axillary or lateral shoulder views
  • A high index of suspicion is important to decrease missed diagnoses

Treatment

Closed reduction

Closed reduction is done with sedation and sometimes GA is used, patient is supine then:

• Pulling on the arm with the shoulder adducted for few minutes to allow the humeral head to disengage
• Then shoulder is flexed and adducted and further internal rotation is added
• Direct pressure to the humeral head from behind maybe added to facilitate reduction
• Once the humeral head reduces, the arm is gently rotated externally
• Neurovascular examination is done after reduction to check for vascular and nerve injuries
• X-ray is taken to confirm reduction and exclude fractues
• If reduction feels stable then the arm is immobilized in a sling or a collar and cuff but if reduction feels unstable then the shoulder is held widely abducted and laterally rotated in an airplane type splint for 3-6 weeks to allow the posterior capsule to heal in the shortest position
• Active shoulder exercises are done to regain function

Open reduction

• Open reduction indications:
  • Irreducible acute dislocation
  • Fracture – dislocation
• Surgery indications:
  • In some cases of acute neurovascular compromise
  • In persisting acute instability
  • Unreduced dislocation
  • If the patient is young and missed dislocation is fairly recent then open reduction is indicated
• Open reduction is done through deltopectoral approach, the shoulder is reduced and the defect in the humeral head is treated by transferring the subscapularis tendon into the defect (McLaughlin procedure) or it can be bone grafted or lesser tuberosity is transferred with the subscapularis tendon
• Late dislocations in elderly are best left untreated but movement is encouraged

Complications

• Fractures of humeral neck, posterior glenoid rim or lesser tuberosity associated with the dislocation
• Recurrence
• Stiffness
• Osteoarthritis
• Nerve injury
• Adhesive capsulitis

Course Menu

This article is a part of the Shoulder and Arm Trauma Free Course, this course also contains:

• Course Introduction
• Clavicle Bone Fractures
• Scapula Bone Fractures
• Acromioclavicular Joint Injuries
• Sternoclavicular Joint Injuries
• Anterior Shoulder Dislocation
• Posterior Shoulder Dislocation
• Inferior Shoulder Dislocation
• Proximal Humerus Fractures
• Humeral Shaft fractures
• Shoulder X-ray Interpretation