Should external rotation of the arm be performed when reducing a posterior shoulder dislocation in the ED?

Posterior Shoulder Dislocation Reduction Technique: Internal Rotation, Not External Rotation

When reducing a posterior shoulder dislocation in the ED, internal rotation of the arm should be performed, not external rotation. 1, 2

Anatomical Rationale and Technique

Posterior shoulder dislocations differ fundamentally from anterior dislocations in their mechanism and reduction technique:

• For posterior dislocations: The humeral head is locked posterior to the glenoid
  • Internal rotation is required to disengage the humeral head 2
  • External rotation would further lock the humeral head posteriorly

Proper Posterior Dislocation Reduction Technique:

1. Apply constant traction on the injured arm
2. Internally rotate the arm to disengage the locked humeral head
3. Lateralize the shoulder (using physician's second arm as lever)
4. Ventralize the humeral head to guide it around the glenoid
5. Steps 3 and 4 are performed simultaneously 2

Diagnostic Considerations

Proper diagnosis is critical as posterior dislocations are frequently missed:

• Radiographic evaluation should include at least 3 views:

  • AP views in internal and external rotation
  • Axillary lateral view or scapular Y view 1

• The axillary or scapular Y views are vital as posterior dislocations can be misclassified on AP views alone 1

Common Pitfalls to Avoid

1. Misdiagnosis: Posterior dislocations are often initially missed due to lack of clear clinical signs compared to anterior dislocations 3

2. Inappropriate technique: Using external rotation (which is appropriate for anterior dislocations) would worsen a posterior dislocation

3. Delayed diagnosis: There is high correlation between time to correct diagnosis and clinical outcome - early diagnosis is essential 3

4. Inadequate imaging: Failure to obtain proper orthogonal views (axillary or scapular Y) can lead to missed diagnosis 1

Post-Reduction Management

After successful reduction:

• Assess stability
• Consider conservative treatment if the shoulder remains stable after reduction 3
• Protect the hemiplegic limb from trauma and injuries to reduce complications 1
• Avoid overhead pulleys which encourage uncontrolled abduction 1

Evidence Quality and Limitations

The evidence clearly distinguishes between reduction techniques for anterior versus posterior dislocations:

• External rotation is appropriate for anterior dislocations 4, 5
• Internal rotation is required for posterior dislocations 2

The technique described by Unfallchirurg (2012) provides a simple, gentle reduction method for posterior locked shoulder dislocations that can be performed by one person with good outcomes 2.