Abstract
INTRODUCTION
Computer-aided systems have been developed recently in order to improve the precision of implantation of a total knee replacement (TKR). Several authors demonstrated that the accuracy of implantation of TKR was higher with the help of a navigation system in comparison to the conventional, manual technique. Theoretically, the clinical results and the survival rates should be improved. Our team was one of the first all over the world which decided to use routinely a navigation system for TKR.
Prostheses designed with a mobile bearing polyethylene component allow an increased congruence between femoral and tibial gliding surface, and should decrease the risk of long-term polyethylene wear. We designed a prosthetic system with one of the highest congruence on the current market. These prostheses might be technically more demanding than more conventional designs, and involve specific complications like bearing luxation. Navigation systems might be helpful in this was as well.
In the present study, we wanted to test clinically the theoretic advantages of these three specific points of our system (navigated implantation, mobile bearing and increased congruence) with a five-year clinical and radiological follow-up.
MATERIAL AND METHODS
128 patients were operated on at our Department with this TKR system between 2000, and were contacted for a five-year clinical and radiological follow-up. The clinical and functional results were evaluated according to the Knee Society Scoring System (KSS). The subjective results were analyzed with the Oxford Knee Score. The accuracy of implantation was assessed on post-operative long leg antero-posterior and lateral X-rays. The survival rate after 5 years was calculated according to the Kaplan-Meier technique.
RESULTS
The mean clinical score was 87 points (maximum of 100 points). The mean pain score was 43 points (maximum of 50 points). The mean flexion angle was 118°, and 33% oft he patients were able to reach 130° of knee flexion or more. The mean functional score was 70 points (maximum of 100). The mean Oxford Score was 23 points (best score = 12 points, worst score = 60 points).
An optimal correction of the coronal leg axis (less than 3° off the neutral axis) was obtained in 87% of the cases. 67% of the cases had an optimal implantation of both tibial and femoral implants on both coronal and sagittal planes.
The Kaplan-Meier survival rate was 97.4% after 5 years.
DISCUSSION
The present study confirmed the efficiency of the navigation system used on the accuracy of implantation. The clinical and functional results after 5 years were at least as good as those published after conventional implantation of uncongruent prostheses. The survival rate was comparable as well to the already accepted gold standards. We observed no complication directly related to the new prosthetic system. The mean flexion angle was better that the results we observed with the previously used fixed bearing system. The question of the polyethylene wear could not be assessed because of the too short follow-up period. An additional follow-up study is planned after 5 more years.
