Computer assisted measurement of cup placement in total hip replacement.

The introduction of image guided systems in total hip replacement surgery provides the ability to plan precisely the alignment of the acetabular cup before surgery, and to perform the surgery according to the preoperative plan. Preoperative planners (interactive computer programs for surgical planning) based on three-dimensional medical images allow planning of optimal placement of implant components based on simulated implant performance. Exact measurement of the cup position during surgery allows precise placement of the cup and accurate measurement of the final position of the cup relative to the pelvis. This measurement is used to evaluate the radiographic techniques for postoperative measurement of cup alignment. Malposition of the acetabular component increases the occurrence of impingement, reduces the safe range of motion, and increases the risk of dislocation and wear. Dislocation of the implant after total hip replacement remains a significant clinical problem. Not fully understanding the interaction between pelvic orientation and final acetabular cup alignment may be one of the main contributing factors in the continued significant incidence of dislocations after total hip replacement. In this study an attempt was made to link the preoperative planning, intraoperative placement, and postoperative measurement of cup placement in total hip replacement using computer assisted techniques.