Correlation of MRI images with histology in avascular necrosis in the hip. A preliminary study.

The role of MRI in identifying the tissue level changes in the femoral head was investigated in five patients diagnosed as having avascular necrosis by radiology, scintigraphy, and MRI (0.35 Telsa). Radiographic scoring by the Ficat and Arlet system showed one hip with stage I, one stage II, two stage III, and one stage IV changes. The histologic features of core biopsy specimens obtained during decompression of the femoral heads were compared to the preoperative T1 and mixed T1/T2-weighted MR images. The cores varied with respect to their distance from the subchondral bone (7-23 mm) and length (19-45 mm). At the subchondral end of the core tract, low T1-weighted images corresponded to marrow fibrosis (5 cases) and in three of five cases to increased trabecular bone volume (TBV = 44-50%). Subjacent areas of diffusely decreased MR signal corresponded to marrow fibrosis and necrosis, with a relatively normal TBV (17-28%). The distal ends of the core tracts showed normal fatty marrow and a normal MR signal. The observations affirm that the MR signal intensity is largely reduced as a function of marrow degeneration and loss of fat content, but the signal is not predictive of particular histotypic morphologic patterns.