What is the appropriate treatment for a patient with a possible posterior dislocation of the shoulder?

Posterior Shoulder Dislocation: Diagnostic and Treatment Approach

Immediate Diagnostic Priority

Obtain a complete radiographic trauma series immediately, including anteroposterior (AP) views in internal and external rotation PLUS an axillary or scapula-Y view—AP views alone will miss the diagnosis in over 60% of cases. 1, 2, 3

Why Posterior Dislocations Are Frequently Missed

• Posterior dislocations are misdiagnosed initially in more than 60% of cases because they can appear deceptively normal on standard AP radiographs alone 1, 2, 3
• The arm is held in the normal position of adduction and internal rotation, unlike anterior dislocations where deformity is obvious 3
• Axillary or scapula-Y views are absolutely vital as glenohumeral dislocations are routinely misclassified on AP views 4, 1, 5

Clinical Examination Findings to Identify

• Fixed internal rotation of the arm with inability to externally rotate or abduct 2
• Subtle posterior fullness and anterior flatness of the shoulder compared to the unaffected side 2
• Characteristic abnormal scapular movement with attempted abduction 3
• History of seizure, electroshock therapy, or fall onto a flexed, adducted arm should immediately raise suspicion 2

Radiographic Confirmation

Standard Initial Imaging

• Radiographs are the preferred initial diagnostic modality and must include three views minimum: AP in internal rotation, AP in external rotation, and axillary or scapula-Y view 4, 1, 5
• The axillary or scapula-Y view will definitively show the humeral head displaced posteriorly relative to the glenoid 1

When to Obtain CT

• If symptoms persist or radiographs are equivocal, obtain CT without contrast to definitively identify the posterior dislocation and characterize any associated fracture patterns 1
• CT is superior to radiography for identifying the reverse Hill-Sachs defect (anteromedial humeral head compression fracture) that occurs with posterior dislocations 4, 6

Treatment Algorithm Based on Timing and Reducibility

Acute Reducible Dislocations (Diagnosed Early)

• Attempt closed reduction if diagnosed within days to weeks 7, 8
• Post-reduction radiographs are mandatory to confirm successful reduction and evaluate for fractures 1
• If closed reduction is successful and the shoulder remains stable, conservative treatment with immobilization in neutral position for 6 weeks followed by rehabilitation is appropriate 7, 6

Locked/Irreducible Dislocations or Late Diagnosis

The treatment depends critically on the size of the reverse Hill-Sachs defect and duration of dislocation 7, 8:

For defects <25% of humeral head:

• Closed reduction may still be attempted if diagnosed within 6 months 7, 8
• If successful, immobilize and rehabilitate 7

For defects 25-50% of humeral head:

• McLaughlin procedure (subscapularis tendon transfer into the defect) or Neer modification (lesser tuberosity transfer) is the preferred surgical approach 8, 6
• This provides excellent functional outcomes with mean Constant scores of 86.2 points and avoids arthroplasty in younger patients 6

For defects >50% of humeral head:

• Shoulder arthroplasty is necessary 6
• Reverse total shoulder replacement is most often indicated due to frequently associated rotator cuff injuries 6
• Hemiarthroplasty can be considered in select cases 8

Chronic Locked Dislocations (>1 year)

• The average interval from injury to diagnosis in missed cases is one year 8
• There is a high correlation between time to correct diagnosis and outcome—early diagnosis is essential 7
• Surgical options include subscapularis transfer, lesser tuberosity transfer, bone grafting, rotational osteotomy, or arthroplasty depending on defect size and chronicity 7, 8

Critical Pitfalls to Avoid

• Never rely on AP views alone—dislocations will be missed 1, 5
• Never attempt reduction without radiographic confirmation—you could worsen an associated fracture-dislocation 1
• Delaying reduction increases risk of neurovascular compromise 1
• Assess for axillary nerve injury and vascular compromise following any reduction attempt 1
• Older patients commonly have associated rotator cuff tears that must be evaluated 4, 9

Post-Reduction Management

• Immobilization in neutral position (not internal rotation) for 6 weeks 6
• Assess for neurovascular compromise immediately after reduction 1
• Consider MRI without contrast if soft tissue injuries (rotator cuff tears, labral injuries) need assessment after reduction 1
• Younger patients have higher recurrence rates due to labroligamentous injury 9