Acetabular hypertrophy in Legg-Calvé-Perthes disease.

Measurements from the radiographs of 65 children with unilateral Legg-Calvé-Perthes disease showed that in 61 cases, the acetabulum was larger on the affected side by a mean of 4.0 mm. The mean femoral head size was increased in 60 of 65 cases by 6.8 mm. Acetabular and femoral head overgrowth occurred in a parallel fashion with onset early in the course of the disease. Hyperemia is the most likely explanation for this joint overgrowth. Acetabular contour was evaluated in 83 hips. Nineteen of these hips exhibited the sign of acetabular bicompartmentalization. This appears to be the result of maximally active cartilage hypertrophy and lateral placement of the femoral head. Bicompartmentalization can be seen 3 months after the onset of symptoms and is a poor prognostic sign.