Spontaneous osteonecrosis of the knee (SONK)

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SONK

  • Similar appearances to osteochondritis dissecans of the knee but is found in an older age group.
  • SONK is not thought to be caused by bone death but may be caused by osteoporosis and insufficiency fractures.
  • It is almost always unilateral, usually affects the medial femoral condyle
  • Often associated with meniscal tear
  • MRI is the best imaging modality: a focal subchondral area of low signal intensity adjacent to the subchondral bone plate and representing local ischaemia, this area does not enhance due to lack of blood flow.

  • Late complication: secondary OA, secondary osteonecrosis
  • Treatment:
    – Conservative treatment is favored – early treatment reduces risk of progression to subchondral collapse and osteonecrosis.: limitation of weight-bearing of the affected limb, NSAIDs for symptoms
    – Surgery for refractory/progressed cases: total knee arthroplasty, osteochondral allografts

Reference: radiopaedia.org

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