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Spontaneous osteonecrosis of the medial femoral condyle

Osteonecrosis of the knee should be differentiated into two main categories: 1. Primary, spontaneous, or idiopathic osteonecrosis and 2. Secondary osteonecrosis (e.g., secondary to factors such as steroid therapy, systemic lupus erythematosus, alcoholism, Caisson decompression sickness, Gaucher's disease, hemoglobinopathies, and renal transplantation etc.).

Spontaneous osteonecrosis of the knee (SONK) usually affects the medial femoral condyle. It is three times more common in women than in men and presents with an acute knee pain in elderly patients. SONK may mimic other conditions such as meniscal tears and osteoarthritis. Typical radiographic findings include subchondral lucency in the medial femoral condyle, flattening of the medial femoral condyle, and a narrow zone of increased radiodensity adjacent to the depressed osseous surface.

Cor T1
Cor T1

Cor T2 Fat Sat
Cor T2 Fat Sat

Sag PD Fat Sat
Sag PD Fat Sat

Ax GRE
Ax GRE

46 yo with L knee pain

Osteonecrosis of the knee should be differentiated into two main categories:
1. Pprimary, spontaneous, or idiopathic osteonecrosis and
2. Secondary osteonecrosis (e.g., secondary to factors such as steroid therapy, systemic lupus erythematosus, alcoholism, Caisson decompression sickness, Gaucher's disease, hemoglobinopathies, and renal transplantation etc.).

Spontaneous osteonecrosis of the knee (SONK) usually affects the medial femoral condyle. It is three times more common in women than in men and presents with an acute knee pain in elderly patients. SONK may mimic other conditions such as meniscal tears and osteoarthritis. Typical radiographic findings include subchondral lucency in the medial femoral condyle, flattening of the medial femoral condyle, and a narrow zone of increased radiodensity adjacent to the depressed osseous surface.

Plain radiographs are often normal during the early course of the disease and, in such instances, nuclear medicine study (bone scan) and MRI may be helpful. MR images typically demonstrate low signal intensity at the affected area on T1-weighted spin echo and high signal intensity on T2-weighted images which is indicative of edema. MR also is helpful in determining the size of the lesion and in identifying associated findings such as meniscal tears/abnormalities, cystic lesions and bone collapse with buckling of the articular cartilage.

The other entities that enter into the differential diagnosis of the radiographic changes in spontaneous osteonecrosis of the knee are osteonecrosis from additional causes, osteochondritis dissecans, calcium pyrophosphate dihydrate crystal deposition disease, transient osteoporosis, stress fracture, and neuropathic osteoarthropathy.


Suggested Reading:

1. Ahlback S, Bauer GC, Bohne WH. Spontaneous osteonecrosis of the knee.
Arthritis Rheum 1968; 11:705-733.
2. Bjorkengren AG, Alrowaih A, Lindstrand A, et al: Spontaneous osteonecrosis of the knee: value of MR imaging in determining prognosis. AJR, 154(2): 331-6, Feb 1990.
3. Resnick D: Diagnosis of bone and joint disorders, 3rd edition, Volume 5, 3495-3542, 1995.
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