Avascular necrosis – osteonecrosis
- ‘Death’ of a (bony) structure secondary to insufficient blood supply.
- Primary pathology is of unknown aetiology, but secondary AVN is linked with a variety of pathologies – see below.
- Idiopathic avascular necrosis occurs in childhood in the proximal femoral epiphysis (‘Perthes’ = Legg–Calve–Perthes Disease); See Perthes’ disease. AVN is also seen in childhood hips following SCFE (or SUFE)
- Associated with steroid use, alcohol abuse, metabolic disease (e.g. Gaucher’s disease), vasculitis (SLE), sickle cell disease, malaria, occupational causes (e.g. deep-sea divers – caisson disease), venous thromboembolism and bone-marrow transplants.
- Certain bones in adulthood are particularly associated with AVN; the eponyms below are for idiopathic AVN.
- Femoral head – see separate section.
- Distal femur – usually medial femoral condyle – SONK (spontaneous osteonecrosis of the knee).
- Proximal humerus – idiopathic and post-traumatic.
- Lunate – Kienböck’s disease – see separate section.
- Metatarsal head – Freiburg’s disease for second MT head.
- Navicular – Köhler’s disease.
- Scaphoid – Preiser’s disease.
- Capitellum – Panner’s disease – associated with osteochondritis.
- Classically present with pain of insidious onset.
- Pain often worse at night.
- Pain is usually severe and often becomes more bearable after several weeks.
- Joint locking with loose bodies – separated osteochondral fragments.
- Reduced function of adjacent joints.
- The initial radiograph if taken early may be normal.
- The affected bone becomes sclerotic with later collapse and remodelling.
- Degenerative change within adjacent joints.
- MR – 90–100% sensitivity for symptomatic disease.
- Changes reflect the death of fatty marrow cells.
- Bone-marrow oedema is manifest as reduced signal on T1 weighted and increased signal on T2 weighted images.
- Early subchondral collapse is seen as crescentic low signal.
- In later disease, fibrosis results in low signal on both T1 and T2 weighted images.
- Pain relief with analgesics and immobilisation.
- Remove any precipitating factors, e.g. drugs, alcohol, occupation.
- Surgery, if indicated, is generally reparative or reconstructive in nature.
- Core decompression and vascularised bone graft aims to restore vascularity and prevent further collapse.
- In severe collapse, reconstructive surgery should be considered.
James R. D. M., Erskine J. H., Rakesh R. M. (2008). Musculoskeletal Radiology. A-Z Musculoskeletal and Trauma Radiology, 1st edition, Cambridge University Press, Cambridge, 1, 1-176.