The morphology of residual acetabular deficiency in childhood hip dysplasia: three-dimensional computed tomographic analysis.

Seventy hips (in 48 patients) in children with residual dysplasia resulting from developmental dysplasia of the hip (DDH) were evaluated by using three-dimensional computed tomographic (3DCT) imaging to clarify the nature and degree of acetabular and femoral head deformity. We noted four types of dysplastic acetabulae: type I, subtle deficiency of the acetabulum with a mild break in Shenton's line (24%); type II, anterosuperior deficiency (29%); type III, midsuperior deficiency (38%); and type IV, global deficiency (9%). In untreated DDH with complete dislocation, the deficiency was predictably midsuperior (type III). Isolated posterosuperior deficiency, which is common in neuromuscular conditions, was not seen in these normal children with DDH. The 3DCT method used produced a topographic "contact map" that replicates the contact relation between the acetabulum and the femoral head. Analyzing the femoral head-acetabular contact relation and the type of acetabular deficiency allows the surgeon to plan better surgical correction of hip dysplasia in children.