Spontaneous osteonecrosis of the knee. Scintigraphic findings.

: Three cases of spontaneous osteonecrosis (SON) of the knee, comprised of two cases involving the medial tibial plateau and one involving the medial femoral condyle, are reported. Because of the relatively normal x-rays early in the course of the disease, the differential diagnosis of a painful knee is markedly shortened with the typical scintigraphic findings in SON. The scintigraphic findings represent a focal area of increased activity at the affected site on a three-phase bone scan.