Posterior Glenohumeral Instability

Epidemiology

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

Classification

  • Divided into subgroups according to direction
    • Unidirectional – Posterior (smallest group)
    • Bidirectional – Posterior & Inferior
    • Multidirectional
  • Also divided into
    • Traumatic
    • Atraumatic
  • Acquired (Baseball pitching & swimming strokes)
  • Volitional groups
    • Voluntary
    • Involuntary

Acute Posterior Dislocation

  • 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