ACCURACY OF SIDE-CUTTING IMPLANTATION INSTRUMENTS FOR TOTAL KNEE ARTHROPLASTY

Abstract

Introduction: Based on the benefits of less postoperative pain and accelerated rehabilitation associated with minimally invasive implanted unicompartmental knee joint replacement new surgical approaches have been developed for total knee replacement. New side-cutting implantation instruments were proposed for the minimally invasive surgical technique. Different randomized studies have shown improved component position in association with the use of navigation systems for TKA as compared with standard implantation instruments. There is a lack of randomized studies showing whether the same level of accuracy provided by computer-assistance is possible when using a minimally invasive approach and the side-cutting jigs. We hypothesized an imageless navigation system leads to improved component positioning in the coronal and sagittal plane when compared with a non-navigated study group. Both cohorts were operated on with a mini-subvastus surgical approach using side-cutting instruments. We questioned whether clinical outcomes were affected by the application of the navigation system at 3 months followup.

Methods: 100 patients were randomized to undergo computer-assisted TKA or non-navigated TKA using a mini-subvastus surgical approach and side-cutting implant instrumentation. The radiographic parameters, clinical outcomes and knee scores were evaluated 3 months postoperative.

Results: The mechanical axis of the limb was within 3° varus/valgus in 76 % of the patients who had navigated procedures versus 66 % of patients who had conventional surgery. The tibial slope showed a rate of inaccuracy of 3° or less for 78 % of the patients in the navigated total knee arthroplasty group versus 66 % of the patients in the conventional group. Clinical outcomes and knee scores were similar in both groups.

Conclusion: The navigated study group showed a trend to a higher implantation accuracy but the differences were not significant. We think the reasons were the cutting direction from medial to lateral – longer cutting distance – and the insufficient cutting-jig fixation. We cannot recommend the use of the MIS Quad-Sparing™ instrumentation without a navigation system. With computer-assistance the implantation accuracy could duplicate the findings in the literature for non-navigated cohorts using a standard surgical approach. Using a navigation system for minimal invasive subvastus TKA did not influence the 3-month clinical outcome.