Femoral remodelling after subtrochanteric osteotomy for developmental dysplasia of the hip.

Children who present late with hip dislocation may require femoral osteotomy after reduction, to correct valgus and anteversion deformity of the femoral neck. After these procedures proximal femoral growth is unpredictable. We have studied proximal femoral growth in 40 children who had been treated by femoral osteotomy. Preoperatively, the mean femoral neck-shaft angle was 5 degrees greater on the affected side than on the contralateral side. Postoperatively, it was 28 degrees less. There was progressive recorrection; after five years the angle was not significantly different from that on the contralateral side. In our series 70% of the capital epiphyses became abnormally shaped, taking the appearance of a 'jockey's cap'. All the growth plates became angulated but this corrected with time. Correction of the neck-shaft angle probably results from the more normal mechanical environment provided by reduction. The abnormal radiographic appearance of the epiphysis and growth plate is probably due to the rotation produced by the osteotomy.