Abstract
INTRODUCTION
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.
MATERIAL AND METHODS
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.
RESULTS
We observed a significant improvement of all radiological items by navigated cases. Limb alignment was restored in 82% of the navigated cases and 74% of the conventional cases. The coronal orientation of the femoral component was acceptable in 85% of the navigated cases and 76% of the conventional cases. The coronal orientation of the tibial component was acceptable in 95% of the navigated cases and 89% of the conventional cases. The sagittal orientation of the tibial component was acceptable in 77% of the navigated cases and 66% of the conventional cases. Overall, 50% of the implants were oriented satisfactorily for the four criteria for navigated cases, and only 40% for conventional cases.
DISCUSSION
The navigation system enables reaching the implantation goals for implant position in the large majority of cases, with a rate similar to that obtained for primary TKA. The rate of optimally implanted prosthesis was significantly higher with navigation than with conventional technique. The navigation system is a useful aid for these often difficult operations, where the visual information is often misleading.
