ACCURACY OF ANATOMICAL HIP RECONSTRUCTION USING COMPUTERISED THREE-DIMENSIONAL PRE-OPERATIVE PLANNING AND A CEMENTLESS MODULAR-NECK PROSTHESIS

Abstract

The use of two-dimensional plain X-rays for preoperative planning in total hip arthroplasty is unreliable. For example, in the presence of rotational hip contracture the lateral femoral off set can be significantly under-estimated. Pre-operative planning is of particular importance when using uncemented prostheses. The aim of this study was to determine the precision of a novel 3D CT-based preoperative planning methodology with the use of a cementless modular-neck femoral stem.

Pre-operative computerised 3D planning was performed using HIP-PLAN® software for 223 patients undergoing THA with a cement-less cup and cement-less modular-neck stem. Components were chosen that best restored leg length and lateral off set. Postoperative anatomy was assessed by CT-scan and compared to the pre-operative plan.

The implanted component was the same as the planned one in 86% of cases for the cup and 94% for the stem. There was no significant difference between the mean planned femoral anteversion (26.1° +/− 11.8) and the mean postoperative anteversion (26.9° +/− 14.1) (p=0.18), with good correlation between the two (coefficient 0.8). There was poor correlation, however, between the planned values and the actual post-operative values of acetabular cup anteversion (coefficient 0.17). The rotational centre of the hip was restored with a precision of 0.73mm +/3.5 horizontally and 1.2mm +/− 2 laterally. Limb length was restored with a precision of 0.3mm +/− 3.3 and femoral off set with a precision of 0.8mm +/− 3.1. There was no significant alteration in femoral off set (0.07mm, p=0.4) which was restored in 98% of cases. Almost all of the operative difficulties encountered were predicted pre-operatively.

The precision of the three-dimensional pre-operative planning methodology investigated in this study is higher than that reported in the literature using two-dimensional X-ray templating. Cup navigation may be a useful adjunct to increase the accuracy of cup positioning.