Recurrent Posterior Instability, radiograph showing the lightbulb sign of a posterior shoulder dislocation — Radiograph showing the lightbulb sign of a posterior shoulder dislocation. Image by Hellerhoff, Wikimedia Commons, CC BY-SA 3.0.

Epidemiology

Much less common than anterior
< 5% of shoulder dislocations in most series

Classification

Basis	Groups
Direction	Unidirectional, posterior (smallest group) Bidirectional, posterior & inferior Multidirectional
Cause	Traumatic Atraumatic Acquired (baseball pitching & swimming strokes)
Volition	Voluntary Involuntary

Acute Posterior Dislocation

Name: Posterior Glenohumeral Instability - Glenohumeral Instability - Orthofracs
Published: 2020-09-23T05:23:58+00:00

Epidemiology
- Rare
- 2% of acute dislocations
- Often missed
Aetiology
- Usually major trauma
  - MVA
  - Seizures
  - ECT
  - Electrocution
  - Alcohol-related injuries
History
- History of injury
- Pain
- Stiffness
Examination
- Loss of ER
- Internally rotated 40°
- Hold arm across chest
- Beware of young patient with arm across chest & limited ROM
- Don’t think frozen shoulder only
Investigations
- X-ray
  - AP
    - Light bulb sign
    - Globular head due to internal rotation
    - Fracture of Lesser Tuberosity
  - Axillary view
    - Diagnostic
    - May see reverse Hill-Sach’s
- CT Scan
  - Confirms
  - Quantifies humeral head defect
  - Very important to decide management if locked
Treatment
- Depends on
  - Duration of dislocation
  - Size of humeral head defect
- 1. Reduction
  - Indications
    - Duration < 6 weeks
    - Reverse Hill-Sach’s defect < 25%
  - Technique
    - GA
    - Traction with arm in extension & rotating to neutral position & then lifting the humeral head anteriorly into the glenoid
    - May require open reduction
    - Immobilise with Donjoy shoulder immobiliser in the Gunslinger Position (15° of ER)
- 2. Stabilisation
  - Indications
    - Duration < 1 year
    - Head defect 25-50%
  - Technique
    - McLaughlin procedure
      - Delto-Pectoral approach
      - Lesser tuberosity with attached subscapularis transferred into Reverse Hill-Sach’s lesion
      - Renders defect an extra-articular problem
      - If > 40% & young maybe use osteochondral allograft to fill defect
- 3.Hemiarthroplasty
  - Indications
    - Duration > 1 year
    - Defect > 50%
    - Ie. too big to stabilise but should avoid in the young
  - Technique
    - Neutral version rather than normal retroversion
    - More stable to posterior instability

Reviewed by Professor Phong Tran, Head of Orthopaedic Surgery, Western Health. Last updated 10 October 2026.