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Updated: May 31 2021

Osteonecrosis of the Knee

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  • summary
    • Osteonecrosis of the knee represents a condition caused by reduced blood flow to bone secondary to a variety of risk factors such as sickle cell disease, steroid use, alcoholism, autoimmune disorders, and hypercoagulable states.
    • Diagnosis is radiographic for advanced disease but requires MRI for detection of early or subclinical disease.
    • Treatment is generally observation with management of the underlying systemic condition. Operative management is indicated for advanced disease with presence of severe subchondral collapse. 
  • Epidemiology
    • Demographic
      • women:men 3:1
      • more common in women <55 years with risk factors
      • reported to be found after knee arthroscopy in middle-aged women
    • Anatomic location
      • typically involves more than one compartment of the knee or even the metaphysis
      • 80% are bilateral
      • multifocal lesions are not uncommon
    • Risk factors
      • alcoholism
      • dysbaric disorders (decompression sickness, "the bends")
      • marrow-replacing diseases (e.g. Gaucher's disease)
      • sickle cell disease
      • hypercoagulable states
      • steroids (either endogenous or exogenous)
      • SLE
      • inflammatory bowel disease
      • transplant patient
      • virus (CMV, hepatitis, HIV, rubella, rubeola, varicella)
      • protease inhibitors (type of HIV medication)
      • trauma
  • Etiology
    • Pathophysiology
      • spontaneous osteonecrosis
        • appears to represent a subchondral insufficiency fracture
        • another hypothesis is an association with a meniscal root tear
  • Physical Exam
    • Symptoms
      • pain with weightbearing, especially sitting to standing
  • Imaging
    • Radiographs
      • first line imaging studies
        • AP knee
        • lateral knee
        • merchant view knee
      • findings
        • wedge-shaped lesion on imaging
    • MRI
      • most useful study
      • findings
        • highest sensitivity and specificity
        • T1: dark
        • T2: bright (marrow edema)
  • Differential
    • Osteochondritis dissecans (OCD)
      • more commonly found at lateral aspect of medial femoral condyle of 15 to 20-year-old males
    • Transient osteoporosis
      • more common in young to middle-aged men
      • multiple joint involvement found in 40% of patients (transient migratory osteoporosis)
    • Occult fractures and bone bruises
      • associated with trauma, weak bones, or overuse
    • Spontaneous osteonecrosis of the knee (SONK) 
  • Treatment
    • Nonoperative
      • NSAIDs, limited weightbearing, quadriceps strengthening, activity modification
        • indications
          • first-line of treatment
        • outcomes
          • favorable, but less so than nonoperative management for SONK
    • Operative
      • diagnostic arthroscopy
        • indications
          • remove small, unstable fragments from the joint
      • core decompression
        • indications
          • extra-articular lesions
      • osteochondral allograft
        • indications
          • large symptomatic lesions in younger patients that failed nonoperative management
      • total knee arthroplasty (TKA)
        • indications
          • large area of involvement
          • collapse
          • osteonecrosis in multiple compartments
  • Prognosis
    • Self-limiting condition
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