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 an unicompartmental knee replacement (UKR) was also improved. Minimal invasive techniques have been developed to decrease the surgical trauma related to the prosthesis implantation. The benefits of minimal-incision surgery might include less surgical dissection, less blood loss and pain, an earlier return to function, a smaller scar, and subsequently lower costs. However, there might be a concern about the potential of minimal invasive techniques for a loss of accuracy. Navigation might help to compensate for these difficulties. Mobile bearing prostheses have been developed to decrease the risk of polyethylene wear. The benefits might be a better survival and less bone loss during revisions. However, these prosthesis are technically more demanding, and involve the specific risk of bearing luxation. Again, 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. 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.INTRODUCTION
MATERIAL AND METHODS
Revision total knee replacement (TKR) is a challenging procedure, especially because most of the standard bony and ligamentous landmarks used during primary TKR are lost due to the index implantation. However, as for primary TKR, restoration of the joint line, adequate limb axis correction and ligamentous stability are considered critical for the short- and long- term outcome of revision TKR. Navigation system might address this issue. We are using an image-free system (ORTHOPILOT TM, AESCULAP, FRG) for routine implantation of primary TKR. The standard software was used for revision TKR. Registration of anatomic and cinematic data was performed with the index implant left in place. The components were then removed. New bone cuts as necessary were performed under the control of the navigation system. The system did not allow navigation for intra-medullary stem extensions and any bone filling which may have been required. This technique was used for 37 patients. The accuracy of implantation was assessed by measuring following angles on the post-operative long-leg radiographs: mechanical femoro-tibial angle, coronal orientation of the femoral component in comparison to the mechanical femoral axis, coronal orientation of the tibial component in comparison to the mechanical tibial axis, sagittal orientation of the tibial component in comparison to the proximal posterior tibial cortex. Individual analysis was performed as follows: one point was given for each fulfilled item, giving a maximal accuracy note of 4 points. Prosthesis implantation was considered as satisfactory when the accuracy note was 4 (all fulfilled items). The rate of globally satisfactory implanted prostheses and the rate of prostheses implanted within the desired range for each criterion were recorded. The results of the 37 navigated revision TKR were compared to 26 cases of revision TKR performed with conventional intramedullary guiding systems.INTRODUCTION
MATERIAL AND METHODS
