Magnetic resonance imaging and scintigraphy of avascular necrosis of the femoral head. Prediction of subsequent segmental collapse.

For the purpose of an effective management of patients at high risk for nontraumatic avascular necrosis of the femoral head (ANFH), it is expedient to examine the femoral heads of patients most likely to undergo subsequent segmental collapse. The purpose of this study was to evaluate the ability of magnetic resonance imaging (MRI) and radionuclide bone scanning (RS) to predict segmental collapse of the femoral head at the roentgenographically normal stage. Fifty-five hips in 37 patients at risk for ANFH and having normal roentgenograms were included in this study. Magnetic resonance imaging was performed in all hips and RS in 29 hips. The patients were observed during a period of more than two years without any invasive intervention, and nine femoral heads manifested collapse during this period. Predictive values for subsequent segmental collapse of a positive test of MRI and RS were 31% and 13%, respectively, whereas those indicative of a negative test were 100% and 76%, respectively. Magnetic resonance imaging was more useful than RS in detecting patients in need of intensive follow-up examination. In particular, a bandlike area of low intensity that traversed the femoral head in midcoronal slices on MR images seemed to be a significant indicator of subsequent collapse.