MRI in late sequelae of Perthes' disease: imaging findings and symptomatology in ten hips.

Five painful (group A) and five symptomless (group B) hips in nine patients with late sequelae of Perthes' disease were studied with plain radiography and magnetic resonance imaging (MRI) in order to correlate MRI findings with symptomatology. The unaffected hips were also studied. In group A hips, poor congruence of the articular cartilage surfaces was present in three of five cases, whereas good congruence was found in all group B hips. In one spherical but painful hip (group A), MRI revealed a protuberance in the anterolateral cartilage of the femoral head. The joint cartilage in group A and B hips was, on average, 0.5 and 1.5 mm thicker, respectively, than the cartilage in the unaffected hips. The lateral joint capsule was, on average, 3.0 mm thicker in group A hips than in the unaffected hips (P < 0.05), which possibly reflects reactive changes due to chronic irritation in the painful hips. The mean joint capsule thickness differed by only 0.5 mm between the unaffected and group B hips. Mean anterior acetabular coverage by MRI was 97 % in group A and 98 % in group B, while in the unaffected hips mean anterior coverage was 102 %. In an aspherical painful hip, MRI revealed a juxta-articular cyst not visible by radiography. A symptomless intra-articular fragment, due to osteochondritis dissecans, was well visualized with MRI. MRI is recommended for evaluation of pain in hips with late sequelae of Perthes' disease. It may show abnormalities in bony structures, as well as in joint capsule and cartilage.