What is the appropriate management of an acute versus chronic posterior shoulder dislocation?

Treatment of Posterior Shoulder Dislocation

Acute posterior shoulder dislocations with <25% reverse Hill-Sachs defects and <3 weeks duration should undergo closed reduction followed by immobilization in 15° external rotation, while chronic locked dislocations or those with >25% humeral head involvement require open reduction with subscapularis transfer (McLaughlin or Neer procedure). 1, 2

Initial Diagnostic Imaging

Obtain three-view radiographs immediately: anteroposterior (AP) in internal rotation, AP in external rotation, and axillary or scapula-Y view—the axillary/scapula-Y view is mandatory because posterior dislocations are frequently missed on AP views alone. 3, 4

• Perform radiographs with the patient upright, as supine positioning underrepresents shoulder malalignment and can lead to missed pathology 4
• Posterior dislocations account for only 4% of all shoulder dislocations and are misdiagnosed in two-thirds of cases, often presenting as "locked" shoulders 5
• The diagnosis is frequently delayed by an average of 66 days, with delays ranging from 3 weeks to 14 months 2, 6

Acute Posterior Dislocation Management (<3 Weeks)

Closed Reduction Attempt

Attempt closed reduction first for all acute posterior dislocations, which succeeds in approximately 25-40% of cases. 2, 6

• Closed reduction is most effective when performed within 3 weeks of injury 1
• After successful closed reduction, immobilize the shoulder in 15° of external rotation 1
• Obtain post-reduction radiographs (same three views) to confirm successful reduction and rule out iatrogenic fractures 4

Conservative Management Criteria

If closed reduction is successful and the reverse Hill-Sachs defect (Malgaigne lesion) involves <25% of the humeral head articular surface, proceed with conservative treatment. 1, 2

• Conservative treatment yields excellent long-term results with mean Constant scores of 85-87 points at 5+ years follow-up 1, 6
• No recurrent instability or need for revision surgery occurs in properly selected cases 1
• This approach is contraindicated if the defect exceeds 25% or if reduction is unstable 1, 2

Surgical Indications for Acute Cases

Proceed directly to open reduction with subscapularis transfer if:

• Closed reduction fails 5, 2
• The reverse Hill-Sachs defect involves >25-33% of the humeral head articular surface 2, 1
• Reduction is unstable after closed manipulation 2
• Associated greater tuberosity fracture requires fixation to prevent redislocation 2

Chronic/Locked Posterior Dislocation Management (>3 Weeks)

Classification-Based Treatment Algorithm

For chronic posterior dislocations, treatment depends on three factors: humeral head bone loss percentage, greater tuberosity malunion, and proximal humeral metaphyseal malunion. 7

Type A: Intact Greater Tuberosity

• Type A1 (<50% bone loss): Modified McLaughlin procedure (subscapularis transfer into defect) 7
• Type A2 (>50% bone loss): Hemiarthroplasty 7

Type B: Severe Greater Tuberosity Malunion

• Type B1 (<50% bone loss): Modified McLaughlin procedure + corrective osteotomy of greater tuberosity 7
• Type B2 (>50% bone loss): Reverse shoulder arthroplasty 7

Type C: Metaphyseal Malunion

• Type C1 (<50% bone loss): Modified McLaughlin procedure + osteotomy of proximal humeral metaphysis 7
• Type C2 (>50% bone loss): Hemiarthroplasty 7

Surgical Technique Selection

The McLaughlin or Neer subscapularis transfer procedure is the workhorse operation for chronic locked posterior dislocations with <50% humeral head involvement. 5, 2, 7

• This procedure yields good results in 9 out of 14 chronic cases (64% success rate) 2
• Functional outcomes are significantly better in acute cases (71% satisfactory) versus chronic unreduced dislocations (43% satisfactory) 2
• The procedure is indicated regardless of patient age when the defect does not exceed one-third of the humeral head articular surface 2

Critical Pitfalls to Avoid

The most common error is missing the diagnosis entirely—posterior dislocations are misdiagnosed in 66% of initial presentations because clinicians rely solely on AP radiographs without obtaining axillary or scapula-Y views. 5, 6

• High-risk mechanisms include electrocution, epileptic seizures, and severe direct trauma—maintain heightened suspicion in these scenarios 5, 2
• Motor vehicle accidents account for 44% of cases, while convulsive fits cause 56% 2
• Time to correct diagnosis directly correlates with worse outcomes—delays beyond 3 weeks significantly compromise results 6, 1
• Post-traumatic osteoarthritis develops in chronic cases, particularly when diagnosis is delayed beyond several months 5, 2

Advanced Imaging for Surgical Planning

Obtain CT scan for all chronic posterior dislocations to quantify humeral head bone loss, assess greater tuberosity position, and evaluate metaphyseal alignment—this imaging guides the specific surgical approach. 7

• CT is superior to radiography for characterizing fracture patterns and bone loss percentage 3
• MRI or MR arthrography is not typically necessary for posterior dislocation management, as the primary concern is bony anatomy rather than soft tissue 3