Posterior shoulder dislocation

Background

• Accounts for 2-4% of shoulder dislocations
• Mechanism of injury - forceful internal rotation/adduction (secondary to e.g. seizure, electric shock) or blow to ant shoulder
• Neurovascular and rotator cuff tears are less common than in ant dislocations

Clinical Features

• Prominence of posterior shoulder and ant flattening of normal shoulder contour
• Patient unable to rotate or abduct affected arm

Differential Diagnosis

Shoulder and Upper Arm Diagnoses

Traumatic/Acute:

• Shoulder Dislocation
  • Anterior shoulder dislocation
  • Posterior shoulder dislocation
  • Inferior shoulder dislocation
• Clavicle fracture
• Humerus fracture
• Scapula fracture
• Acromioclavicular injury
• Glenohumeral instability
• Rotator cuff tear
• Biceps tendon rupture
• Triceps tendon rupture
• Septic joint

Nontraumatic/Chronic:

• Rotator cuff tear
• Impingement syndrome
• Calcific tendinitis
• Adhesive capsulitis
• Biceps tendinitis
• Subacromial bursitis

Refered pain & non-orthopedic causes:

• Referred pain from
  • Neck
  • Diaphragm (e.g. gallbladder disease)
• Brachial plexus injury
• Axillary artery thrombosis
• Thoracic outlet syndrome
• Subclavian steal syndrome
• Pancoast tumor
• Myocardial infarction
• Pneumonia
• Pulmonary embolism

Evaluation

Light bulb sign (right picture) with post-reduction comparison (left picture)

• Plain film X-ray
  • Scapular "Y" view shows humeral head in posterior position
  • Lack of normal overlap of humeral head and glenoid fossa
  • "Light bulb sign" - fixed internal rotation makes for light bulb appearance of humeral head on AP
• Bedside ultrasound can be used to assess for both dislocation and successful reduction

Management

• Reduce
  • Consider procedural sedation
  • Traction applied to adducted arm in long axis of humerus
  • Assistant pushes humeral head anteriorly into glenoid fossa
• Post-reduction X-ray
• Apply sling

Disposition

• Discharge after reduction
• Ortho follow-up

See Also

• Shoulder dislocation

External Links

• https://youtu.be/KRCqVekNEKc

References

Authors

Ross Donaldson, Kevin Lu, Michael Holtz, Tianjiang Ye, Neil Young, Daniel Ostermayer