NAVIGATED CONTROL OF THE CUP ORIENTATION DURING TOTAL HIP REPLACEMENT

Abstract

Introduction: The accurate positioning of the cup implant is a relevant prognostic factor for both short- and long-term results after total hip replacement. Conventional, manual control has proved to be less than optimal. Navigation systems might improve the accuracy. We designed this study to validate the accuracy of a non image based navigation system for cup orientation during total hip replacement, with post-operative 3D CT-scan analysis.

Material and methods: 60 cases of navigated total hip replacement have been analysed. Navigation was performed with the OrthoPilot® system (Aesculap, Tuttlingen, FRG), a non image based system. A localizer was implanted on a screw on the anterior iliac crest. Three relevant landmarks (both antero-superior iliac spines and pubis) were palpated with a navigated stylus, defining the anterior pelvic plane (Lewinnek plane). Acetabular preparation and cup implantation were performed under navigation control. Safe zone for acetabular implantation was defined pre-operatively: 40 to 50° of abduction, 10 to 20° of flexion in comparision to the anterior pelvic plane. The final orientation of the cup was registered intra-operatively by the navigation system, and compared to the 3D CT-scan measurement of the cup positioning with the same reference frame.

Results: There was no significant difference between the intra-operative and post-operative measurements of the cup abduction. There was a significant difference between the intra-operative and post-operative measurements of the cup flexion, mainly ±5°. 50 implants were positioned within the safe zone (83%).

Discussion: The navigation system used allowed an accurate positioning of the cup in abduction. The flexion positioning was less accurate, but the differences observed (mainly less than 5°) are probably clinically irrelevant. Furthermore, the accuracy was higher than that observed with conventional, manual implantation.

Conclusion: The navigation system used allows improving the accuracy of cup placement in comparison to conventional, manual techniques.