Posterior Shoulder Dislocations

Posterior Shoulder Dislocations is an uncommon but clinically important shoulder injury. Despite its rarity, it carries a high risk of missed diagnosis, particularly in acute care settings. This condition demands a high index of suspicion and careful radiographic evaluation to avoid missed diagnosis and long-term morbidity.

Incidence

Posterior Shoulder Dislocations:

• Account for 2%–4% of all shoulder dislocations
• Represent about 2% of shoulder injuries overall
• Are missed in 60%–80% of initial evaluations, making them one of the most frequently overlooked joint dislocations

Mechanism of Injury

Indirect Trauma (Most Common)

• Posterior Shoulder Dislocation Occurs when the shoulder is positioned in:
  • Adduction
  • Flexion
  • Internal rotation
• Common scenarios:
  • Seizures
  • Electrical shock
• Pathophysiology:
  • Powerful contraction of internal rotators (latissimus dorsi, pectoralis major, subscapularis)
  • These overpower weaker external rotators (infraspinatus, teres minor), forcing the humeral head posteriorly

Direct Trauma

• Force applied to the anterior shoulder
• Results in posterior translation of the humeral head

See Also: Anterior Glenohumeral Dislocation

Clinical Evaluation

Posterior shoulder dislocations are often subtle in presentation:

Typical Findings

• Arm held in:
  • Adduction
  • Internal rotation
• Limited external rotation (often < 0°)
• Limited forward elevation (often < 90°)

Physical Examination Signs

• Flattened anterior shoulder contour
• Prominent coracoid process
• Palpable posterior mass (displaced humeral head)

Neurovascular Assessment

• Essential to evaluate:
  • Axillary nerve function
• Neurovascular injuries are less common than in anterior dislocations but still possible

Radiographic Evaluation

A complete trauma series is mandatory:

• AP view
• Scapular-Y view
• Axillary view (most diagnostic)

If standard axillary view is not feasible:

• Use Velpeau axillary view

Key Radiographic Signs (AP View)

• Loss of normal humeral head–glenoid overlap
• Vacant glenoid sign (>6 mm space)
• Trough sign (reverse Hill-Sachs lesion; seen in ~75%)
• Internal rotation appearance (“light bulb sign”)
• Loss of humeral neck profile

Advanced Imaging

• CT scan:
  • Essential for evaluating humeral head impaction defects
  • Determines percentage of articular surface involvement

See Also: Shoulder X-ray Views

Classification

Etiologic Classification

• Traumatic: sprain, subluxation, dislocation (acute or recurrent)
• Atraumatic:
  • Voluntary
  • Congenital
  • Acquired (microtrauma)

Anatomic Classification

• Subacromial (98%):
  • Humeral head displaced posteriorly without gross displacement
  • Often associated with reverse Hill-Sachs lesion
• Subglenoid (rare):
  • Humeral head posterior and inferior to glenoid
• Subspinous (rare):
  • Humeral head medial to acromion and below scapular spine

Posterior Shoulder Dislocation Treatment

Nonoperative Management

Closed Reduction

• Requires:
  • Adequate sedation and analgesia
  • Often general anesthesia
• Technique:
  • Traction applied to adducted arm
  • Gentle anterior repositioning of humeral head

⚠️ Important Precaution

• Avoid forced external rotation → risk of fracture if humeral head is locked

Special Consideration

• If impaction fracture is locked:
  • Combine axial traction + lateral traction

Post-reduction Care

• Immobilization:
  • Sling and swathe
  • External rotation positioning for large defects
• Early rehab:
  • Deltoid isometrics
  • Gradual strengthening of rotator cuff

See Also: Shoulder Reduction Techniques

Operative Management

Indications

• Irreducible posterior shoulder dislocation
• Large humeral head defect (reverse Hill-Sachs lesion)
• Significant fractures:
  • Lesser tuberosity
  • Posterior glenoid rim
• Recurrent instability
• Open dislocation

Surgical Options

• Modified McLaughlin procedure (20%–40% defect)
• Hemiarthroplasty (>40% defect)
• Open reduction and stabilization
• Tendon transfers:
  • Subscapularis
  • Biceps (Boyd-Sisk procedure)
• Capsulorrhaphy or osteotomies

Special Case

• Voluntary dislocators:
  • Managed nonoperatively with rehabilitation and counseling

Complications

Fractures

• Posterior glenoid rim
• Humeral head
• Tuberosities
• Humeral shaft

Recurrent Instability

• More common in:
  • Atraumatic cases
  • Large humeral head defects
  • Glenoid fractures

Neurovascular Injury

• Less frequent than anterior dislocation
• Possible injuries:
  • Axillary nerve
  • Suprascapular nerve (infraspinatus branch)

Iatrogenic Anterior Subluxation

• Caused by overtightening posterior structures
• Leads to:
  • Limited flexion
  • Restricted internal rotation

Key Clinical Pearls

• Always suspect posterior shoulder dislocation in:
  • Seizure patients
  • Electrical injuries
• Do not rely on AP X-ray alone
• Loss of external rotation is a critical clinical clue
• Early diagnosis prevents chronic instability and joint damage

References & More

1. Kammel KR, El Bitar Y, Leber EH. Posterior Shoulder Dislocations. [Updated 2022 Sep 12]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2026 Jan-. Available from: Pubmed
2. Egol KA. Handbook of fractures. 6th ed. Philadelphia: Lippincott Williams & Wilkins; 2019.