Osteonecrosis of the knee. Diagnosis and outcome in 40 patients.

Clinically suspected primary osteonecrosis of the knee was studied in 40 patients with repeated plain radiography and scintimetry, and the patients were followed for 1-7 years. Thirty-three patients had typical scintimetric and radiographic signs of osteonecrosis of either one of the femoral condyles, whereas 7 patients had only typical scintimetric findings, but never developed an osteonecrosis based on plain radiography. Because the scintimetric findings were identical to the other 33 knees and because there is no other well-known localized disease in this region of the femoral condyle, we deemed that these 7 patients had probable osteonecrosis, but in an abortive form. The scintimetries were prognostic during the second half year after onset. Thirty knees had a poor outcome--29 because of development of arthrosis, of which eight were treated with a knee arthroplasty and four with a proximal osteotomy.