Neglected congenital dislocation of the hip. Role of computed tomography and computer-aided design for total hip arthroplasty.

Computed tomography (CT) provides important three-dimensional anatomic details in congenital dislocation of the hip that are useful for total hip arthroplasty (THR) and are not obtainable with conventional radiographic evaluation. In this study, 84 patients (119 hips) with congenital dislocation of the hip were evaluated with CT before surgery. Specifically, both the acetabulum and the femur were analyzed to make the best selection of the prosthesis. The average anteversion of the acetabulum was 23 degrees, with an opening of 30.9 mm and a depth of 14.7 mm. The bone stock of the true acetabulum was calculated and the average available diameter for the acetabular implant was 44.9 mm. The CT topogram revealed the true leg-length discrepancy (average 0.5-1.9 cm), and the amount of a shortening osteotomy when necessary was determined. Finally, to determine the stem with optimum fit and fill, a three-dimensional reconstruction of the femoral canal using CT data and computer-aided design (CAD) was matched with a three-dimensional geometry of several stem designs and sizes obtained from a CAD system.