Signal variability in magnetic resonance imaging of femoral head osteonecrosis.

Abstract

The present study was designed to document the pattern and extent of magnetic resonance imaging (MRI) changes in femoral head osteonecrosis and also to correlate MRI findings with technetium bone scans and computed tomograms. Over a three-year period, MRI was performed on 26 patients who had clinical and roentgenographic evidence of femoral head necrosis in one or both hips. MRI abnormalities were present in all 41 hips with osteonecrosis, even when symptoms were absent and roentgenographic findings were nonspecific or not yet apparent. A single possible false-positive MRI was noted in a hip with mild degenerative change. There was considerable variation in the pattern and extent of MRI abnormalities. The most common findings were irregularity of the subchondral cortical outline (82.9%), an inhomogeneous pattern of signal loss (50%), focal increases in signal intensity with T2 weighting (35.5%), and effusion (33.3%). Regions of dense cancellous bone on computed tomograms correlated with bands of low-intensity MRI signal. In the diagnosis of asymptomatic hips, MRI was clearly more sensitive than technetium bone imaging. The role of MRI in defining prognosis and treatment selection remains to be established.