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Osteonecrosis of the Knee

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Topic updated on 02/01/16 1:31pm
Introduction
  • Two distinct entities including
    • secondary osteonecrosis of the knee (this topic)
    • spontaneous osteonecrosis of the knee (SONK)  
  • 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
    • 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
  • Pathophysiology
    • spontaneous osteonecrosis
      • appears to represent a subchondral insufficiency fracture
      • another hypothesis is an association with a meniscal root tear
  • Prognosis
    • self-limiting condition
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
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

 

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