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  • =  Death of bone from ischaemia. 
  • Osteocytes will survive 12 - 48 hours of ischaemia and marrow cells 6 hours


  • Age 20-50 years (average 38 years)
  • Slight male preponderance
  • Most commonly involves the femoral head, then in descending order, distal (medial) femoral condyle, humeral head, talus and less commonly the lunate, capitellum and metatarsal heads
  • Bilateral in 50% of idiopathic cases, and 80% of steroid induced cases
  • Insidious pain which starts initially with activity, then at rest and eventually at night
  • Pain may be severe for 6-8 weeks and then subside
  • Mild symptoms and effusion usually persists
  • Night pain may be an early feature
  • Pain may be present for many months before X-Ray changes are manifest
  • Earliest examination finding is decreased internal rotation
  • 5% of THR performed as a result of OA secondary to AVN


  1.  Idiopathic (40%)
  2. Arterial insufficiency
    1. Fracture
    2. Dislocation
    3. Infection
  3. Arteriolar occlusion
    1. Sickle cell disease and other haemoglobinopathies
    2. Caisson disease in divers and compressed air workers (e.g. miners)
    3. Vasculitis e.g. SLE, irradiation
  4. Capillary occlusion
    1. Fatty infiltration due to steroids, alcohol and other drugs e.g. chemotherapy
    2. Systemic steroid treatment (37%)
      • > 30 mg prednisolone for > 30 days
    3. High alcohol intake (20%)
      • > 400 ml/week or cumulative dose of 150 litres (equivalent to 375 litres of vodka!)
    4. Gaucher’s disease
    5. Hyperlipidaemia
  5. Venous occlusion
  6. Other
    1. Renal transplant patients (16% will develop ON)
    2. Pancreatitis
    3. Haematological malignancies e.g. lymphomas, leukaemias
    4. Diabetes mellitus
    5. Endotoxin reactions
    6. Toxic shock
    7. Inflammatory bowel disease
    8. Brain/spinal surgery
    9. Anticoagulant deficiencies
    10. Nephrotic syndrome


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