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:
