June 2, 2009

Spontaneous Osteonecrosis of the Knee (SPONK)

Author: Aasis Unnanantana, M.D.

Figure 1 and 2: AP and lateral radiographs of the left knee show subchondral sclerosis and lucency at the medial femoral condyle with narrowing of the joint space and osteophytes. Note that the lateral and patellofemoral compartments are normal.

SPontaneous OsteoNecrosis of the Knee (SPONK)
  • Well-recognized cause of spontaneous, sudden onset of knee pain
  • Common in woman during their 50s and 60s
  • Pain typically locates around medial joint line
  • Almost all cases are unilateral, one condylar involvement and epiphyseal to subchondral surface
Differential Diagnosis and Diagnosis
  • Once SPONK is suspected, other DDx should be considered including osteochondritis dissecans (OCD), secondary osteonecrosis, meniscal tears, etc.
  • Diagnosis made in patients with typical clinical symptoms and radiographic findings (as in this case, subchondral lucency in the medial femoral condyle, flattening of the condyle, narrow zone of increased sclerosis adjacent to the depressed osseous surface).
Barrack RL, Booth Jr RE, Lonner JH, et al (eds). Orthopedic Knowledge Update: Hip and Knee Reconstruction 3. 2006

About Guest Author:
Dr. Aasis Unnanantana is a clinical fellow in orthopedics (Metabolic Bone Diseases Service) at the Hospital of Special Surgery, Cornell University, New York, NY. He is a member of orthopedic instructor at Siriraj Hospital, Mahidol University, Bangkok, Thailand.

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