Atypical spontaneous osteonecrosis of both knees. A case report.

One case of spontaneous osteonecrosis (S.O.N.) of the femoral condyles is described. Lesions were seen in both lateral femoral condyles; this implies a local, microtraumatic or circulatory factor. It is interesting that the patient was so young (a 14 year old girl). She presented with persistent pain in the right knee and at examination only a mild tenderness was noted. Radiography showed a radiolucent "halo" in the lateral condyles with a surrounding sclerotic reaction. Femoral condyles at arthroscopic examination appeared with a slight flattening over the articular cartilage. The diagnosis of S.O.N. was made by a bone scan that demonstrated an increased uptake of the tracer in the lateral femoral condyle bilaterally. A conservative therapy was successful after 18 months.