Spontaneous Osteonecrosis of the Knee (SONK)

Topic updated on 11/17/15 11:00am
  • Two distinct entities including
    • Secondary osteonecrosis of the knee 
    • Spontaneous osteonecrosis of the knee (this topic)
  • Epidemiology
    • demographics
      • most common in middle age and elderly
      • affects females (>55yo) more frequently than males
    • location
      • 99% of patients have only one joint involved
      • usually epiphysis of medial femoral condyle
  • Pathophysiology
    • may represent a subchondral insufficiency fracture
    • also believed to be caused by a meniscal root tear
  • Symptoms
    • sudden onset of severe knee pain
    • effusion
    • limited range of motion secondary to pain
    • tenderness over medial femoral condyle
  • Radiographs
    • recommended views
      • standing AP and lateral of hip, knee and ankle
  • MRI
    • most useful study
    • is helpful to confirm the diagnosis and assist in determining the extent of disease helping guide treatment considerations
    • lesion is crescent shaped 
  • Must differentiate from 
    • osteochondritis dissecans
      • more common on lateral aspect of medial femoral condyle in adolescent males
    • transient osteoporosis
      • more common in young to middle age men
    • bone bruises and occult fractures
      • associated trauma, bone fragility or overuse
    • idiopathic osteonecrosis of the knee
      • lesion is not crescent shaped
  • Nonoperative
    • NSAIDs, narcotics, protected weight bearing
      • indications
        • mainstay of treatment as most cases resolve
      • technique
        • physical therapy directed at quadriceps strengthening
      • outcomes
        • initial conservative measure and has shown good results
  • Operative
    • arthroplasty
      • indications
        • when symptoms fail to respond to conservative treatment
      • outcomes
        • successful results reported with TKA (larger lesions or bone collapse) and UKA (smaller lesions) when properly indicated
    • high tibial osteotomy
      • indications
        • when angular malalignment present


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Qbank (1 Questions)

(OBQ08.99) A 59-year-old female librarian complains of progressively worsening left knee pain over the last 4 months. She does not recall any traumatic injury to the knee. Physical exam is noteable for tenderness isolated to the medial joint line. She has full ROM and no instability of the knee. Radiographs and MRI image are provided in figures A,B, and C. Which of the following is the best management? Topic Review Topic
FIGURES: A   B   C      

1. Open biopsy
2. Chest CT and bone scan
3. Osteochondral autograft transfer
4. Unicompartmental knee arthroplasty
5. Valgus-producing high tibial osteotomy


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