Magnetic Resonance Imaging in Legg-Calvé-Perthes Disease

Abstract: The aims of this study were: to compare the cartilaginous outline of the femoral head obtained on arthrograms with those on MR images and to correlate it to the bony head outlines on conventional radiograps; to study early, postoperative cartilaginous and bony remodeling of the femoral head, after proximal femoral varus derotation extension osteotomy, with MR imaging and conventional radiography; to describe signal abnormalities on MR images in the femoral epiphysis, their location, extent and restitution over time; to evaluate the degree and persistence of synovitis in the hip joint by MR imaging; to analyze the metaphyseal histology and to correlate it to the signal intensity on the MR images in the corresponding biopsy region. Results and conclusions: MR imaging and arthrography define the shape of the femoral head cartilage equally well. The bony head outlines on conventional radiographs do not adequately reflect the cartilaginous outlines of the femoral head obtained by MR imaging. There is an early, postoperative, continuous, spherical remodeling following proximal femoral varus derotation extension osteotomy. The cartilaginous remodeling as seen in MR images appears earlier than the bony remodeling seen on conventional radiographs. In the coronal plane on MR images, the pathological signal is lowest in the central portion of the necrotic epiphysis. In addition, hips with advanced disease show signal changes in the peripheral regions. Repair processes start from the periphery, slowly progressing towards the center of the necrotic epiphyseal region. Signal changes persist in the period 3-6 years after diagnosis. All diseased hips have synovitis initially. The degree of synovitis on MR images in the inferomedial aspect of the hip joint correlates to the extent of the epiphyseal necrosis seen in conventional radiography or MR imaging. Synovitis is most intense initially in the disease, slowly decreasing, but persisting for several years, in some hips for more than 5 years after diagnosis. There is no correlation between the uniform histological patterns of consistent morphologic changes of the metaphysis and MR imaging with a low-field unit.