Comparison of MRI with subchondral fracture in the evaluation of extent ofepiphyseal necrosis in the early stage of Legg-Calve-Perthes disease

We reviewed 20 patients in the early stage of Legg-Calve-Perthes disease wh o showed a subchondral fracture line in radiographs. All 20 patients underw ent magnetic resonance imaging (MRI) within 2 months after the first sympto ms. Follow-up MRT after treatment was performed in 10 patients. The subchon dral fracture line in radiographs and serial T-1-weighted image was used to measure the extent of the epiphyseal necrosis volumetrically. These extent s in the early stage were compared with those in the late stage for determi nation of prognostic significance. The intensities of coronal MRIs under th e subchondral fracture were not homogeneous. The uninvolved epiphysis also showed nonhomogeneous intensities because the posterior column revealed hig her intensity compared with the anterior column. The extent of the subchond ral fracture line is more accurate in predicting the amount of eventual nec rosis than is the extent of necrosis in MRI, which does not have a consiste nt correlation.