Modified epiphyseal index for MRI in Legg-Calve-Perthes disease (LCPD)

On radiographs flattening of the femoral head is evaluated by the Epiphyseal Index (EI). Using the ability of MRI to show articular cartilage and the physis clearly, we wish to propose the use of an Epiphyseal Index for MRI (EIM) and demonstrate the value in LCPD. Fifteen patients were examined using 1.5T MR scanner and T1-weighted coronal images were obtained. EIM was calculated as a ratio of height and width of cartilaginous contour surrounding epiphysis, and was compared between normal and the three radiographic stages. EIM of normal hips were ranged from 0.39 to 0.60 and had a tendency to decrease with increasing age. All cases of Stage 1 (avascular necrosis) were within the normal range (n = 4, mean = 0.51, SD = 0.045). EIM of Stage 2 (fragmentation, n = 15, mean = 0.31, SD = 0.055) were smaller than that of Stage 1. Stag 2 and 3 (residual, n = 12, mean = 0.31, SD = 0.077) could not be distinguished by EIM. EIM was useful to show the flattening of epiphysis with growth and very important for differentiation between Stage 1 and 2 LCPD.