[Growth plate in primary osteochondritis dissecans of the hip: a prospective study with MRI].

INTRODUCTION: In Perthes' disease, epiphyseal necrosis impairs the function of the growth plate and may result in growth disturbances of the femoral neck. The physeal changes during active disease were prospectively evaluated with magnetic resonance imaging (MRI). MATERIALS AND METHODS: MRI was performed and radiographs were obtained with six-month intervals from the time of diagnosis up to two years in nine hips (eight patients). RESULTS: Normal growth plate was seen in MRI as a stripe of low signal intensity between areas of high signal intensity from the epiphysis and the metaphysis. Distortion, widening and partial disappearance of the growth plate were noted in the hips classified into Catterall groups 3 and 4. The physeal distortion was seen as anterior curling, and, in some hips, as a W-shaped abnormality projecting down into the metaphysis. Delayed growth of the femoral neck, due to premature physeal closure, was noted in hips where the physeal deformation involved more than half of the growth plate. All pathological changes appeared on the MRI scans three to fifteen months after the first symptoms. The extent of the MRI changes did not correlate directly with Catterall's plain film staging. DISCUSSION: The distortion and widening of the growth plate seen in MRI probably reflect histological disarrangement of the physis due to an extensive epiphyseal necrosis. The physeal W-formation in MRI may represent a radiographic "metaphyseal cyst". Disappearance of the growth plate in MRI seems to indicate premature closure of the physis. CONCLUSION: It seems possible to predict premature closure with MRI even within fifteen months after the onset of Perthes' disease.