Posterior Shoulder Dislocation

Posterior shoulder dislocation is far less common than anterior dislocation. But it is commonly missed with some sources stating 50% of posterior dislocations are missed in the ED.

Mechanism:

  • Trauma – Falls onto outstretched arm OR internal rotation while arm abducted
  • Microtrauma – Repetitive overhead activity, develop instability, onset can be insidious
  • Seizures/Shocks – The classical presentation with seizures or electrocution

X-Ray Imaging:

  • AP view 
    • Lightbulb sign – The head of the humerus in the same axis as the shaft producing a lightbulb shape
    • The ‘rim sign’ – Widening of the glenohumeral space
    • The ‘vacant glenoid sign‘ – Where the anterior glenoid fossa looks empty
    • The ‘trough sign‘ – a vertical line made by the impression fracture of the anterior humeral head
  • Lateral view – will normally be done with the AP, showing the head posterior
  • Modified Axillary views – can be more technically difficult but are often clearer (if you’re in any doubt),

 

Complications:

  • Osteonecrosis
  • Osteoarthritis
  • Loss of function
  • Instability

Reduction:

  • Orthopaedic Seniors – should be involved in any reduction attempts
  • Closed reduction – this can often be difficult and require deep sedation due to the impaction and the presence of fracture
    • 2 doing Traction-Countertraction technique, with a sheet
    • 3rd assistant pushing the humeral head forward
  • Open reduction  – the following may indicate the patient should go straight to open reduction in theatre
    • Reverse Hill Sachs deformity > 25% of humeral head
    • Bankart fracture
    • Chronic dislocation, >3 weeks

Resources:

 

 

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