Abstract
INTRODUCTION
Computer-aided systems have been developed recently in order to improve the precision of implantation of unicompartmental knee replacement (UKR).
Minimal invasive techniques may decrease the surgical trauma related to the prosthesis implantation, but there might be a concern about the potential for a loss of accuracy. Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear, but are technically more demanding. Navigation might help to compensate for these difficulties.
We wanted to combine the theoretical advantages of the three different techniques by developing a navigated, minimal invasive, mobile bearing unicompartmental knee prosthesis.
MATERIAL AND METHODS
160 patients have been operated on at our institution with this system. The 81 patients with more than 2 year follow-up have been re-examined. Complications have been recorded. The clinical results have been analyzed according to the Knee Society Scoring System. The subjective results have been analyzed with the Oxford Knee Questionnaire. The accuracy of implantation has been analyzed on post-operative antero-posterior and lateral long leg X-rays. The 2-year survival rate has been calculated.
RESULTS
We observed 8 complications related to the implant or the operative technique: 2 cases of meniscus instability (1 revision to TKR, 1 bearing exchange); 2 cases of tibia loosening (revised to TKR), 2 cases of femoral loosening (revised to TKR), 1 case of lateral disease progression (revised to TKR), 1 case of unexplained pain syndrome (revised to TKR).
The mean Knee Score was 93 points, 44% had the maximum of 100 points, and only 10% have less than 85 points. The mean pain score was 48 points/50. The mean flexion angle was 128°, and 60% had at least 130° of knee flexion. The mean Function Score was 97 points, 84% have the maximum of 100 points, and only 5% had less than 85 points. The mean Oxford Knee Questionnaire score was 19 points (best result: 12 points, worst result: 60 points).
Expected limb axis correction was obtained in 77% of the cases. 62% of the cases had an optimally implanted prosthesis for all studied criteria. The 2-year survival rate was 97%.
DISCUSSION
Most of the revision cases were related to technical difficulties during the development phase. Fixation of the implant has been improved, and some imprecise steps of the software have been corrected. Since these changes occurred, no severe early complication related to implant or software has been observed. The current implant is considered reliable, and the current minimal invasive navigated technique is considered reliable as well.
