Accuracy of reconstruction of the hip using computerised three-dimensional pre-operative planning and a cementless modular neck.

Pre-operative computerised three-dimensional planning was carried out in 223 patients undergoing total hip replacement with a cementless acetabular component and a cementless modular-neck femoral stem. Components were chosen which best restored leg length and femoral offset. The post-operative restoration of the anatomy was assessed by CT and compared with the pre-operative plan. The component implanted was the same as that planned in 86% of the hips for the acetabular implant, 94% for the stem, and 93% for the neck-shaft angle. The rotational centre of the hip was restored with a mean accuracy of 0.73 mm (SD 3.5) craniocaudally and 1.2 mm (SD 2) laterally. Limb length was restored with a mean accuracy of 0.3 mm (SD 3.3) and femoral offset with a mean accuracy of 0.8 mm (SD 3.1). This method appears to offer high accuracy in hip reconstruction as the difficulties likely to be encountered when restoring the anatomy can be anticipated and solved pre-operatively by optimising the selection of implants. Modularity of the femoral neck helped to restore the femoral offset and limb length.