Spontaneous osteonecrosis of the knee: value of MR imaging in determining prognosis.

Sixteen patients with early and late stages of spontaneous osteonecrosis of the knee were studied to evaluate if MR imaging can be used to determine the prognosis of the disease. All patients had sequential conventional radiographs and clinical examinations, one or more 99mTc-methylene diphosphonate bone scintigrams, and an MR examination. The duration of the disease at the time of the MR examination ranged from 1 to 58 months (mean, 18 months). A relationship was identified between the pattern of bone marrow alteration noted on long TR/TE MR sequences and the scintigraphic stage and clinical course of the disease. The dimensions of the osteonecrotic region could be identified as well or better on the short TR/TE MR images than on the radiographs in all patients. MR imaging also afforded evaluation of the hyaline cartilage overlying the osteonecrotic lesion, revealing secondary osteoarthrosis in seven patients. We conclude that MR imaging in patients with spontaneous osteonecrosis of the knee may provide information of value for determining the prognosis of the disease.