[Spontaneous osteonecrosis of the knee joint: MRT compared to CT, scintigraphy and histology]

We compared MR imaging with scintigraphy and CT in eight patients with spontaneous osteonecrosis of the knee. The histological changes accounting for the MR signal abnormalities were evaluated.

Eight patients with spontaneous osteonecrosis of the knee joint underwent MR imaging before and after i.v. administration of Gd-DTPA. Nuclear scintigraphy was performed in all 8 patients, three patients also had CT scans of the knee area. Histologic correlation was available in three patients.

Increased radionuclide uptake was observed in all patients. In one patient, however, scintigraphy showed increased radionuclide uptake consistent with osteonecrosis only in the medial femoral condyle, while MR imaging demonstrated osteonecrosis both in the medial as well as the lateral femoral condyles. MR demonstrated areas of low signal intensity on precontrast T1-weighted images in the femoral condyle in all patients. All these areas showed high signal intensity on T2-weighted images. On postcontrast T1-weighted images, signal intensity increase was either homogeneous throughout the lesion or it was seen at the periphery of the lesion in a band-like pattern. Histologically, the areas of high signal intensity on T2-weighted and on postcontrast T1-weighted images corresponded to granulation tissue.

MR imaging detects granulation tissue adjacent to the necrotic zone. Using morphological and signal intensity criteria, MR imaging can be utilised to differentiate spontaneous osteonecrosis of the knee from osteochondritis dissecans, degenerative osteoarthritis, and other conditions affecting the knee joint.