The limits of precision in conventionally instrumented computer-navigated total knee arthroplasty

Computer-navigated total knee arthroplasty (TKA) improves the accuracy of component implantation. However, the final implant alignment may not match planned alignment. The hypothesis of this study is that although computer navigation improves alignment, imprecision may not be completely eliminated. The aim of the study was to establish the incidence and sources of imprecision during TKA using computer navigation to measure deviations from planned alignment.

Computer navigation was used to quantify changes in planned alignment at four steps during 136 TKA's: application of cutting blocks, addition of definitive pin fixation, bone cuts and after prosthesis application. Mean changes in alignment deviation at each step in each plane were measured and the number of significant outliers (>3° from the planned resection plane) were assessed in each plane.

Overall changes in planned alignment were small and non-cumulative between steps but the incidence of outliers (cuts measured as >3° from planned alignment at each step) increased through the steps, with 21.3 % (n = 29) of final implants outlying in the tibial sagittal plane, which was the least precise plane. The highest number of outliers occurred after bone resection and the addition of pins to cutting blocks was also identified as a source of imprecision.

Despite improved accuracy of bone resection with computer-navigated TKA, the precision of bone cuts may be affected at several steps of the procedure. Cutting block application, bone resection and prosthesis application may all affect accuracy. Bone cuts should be made with meticulous care, whether navigated or not, and navigated cuts should be checked and corrected, particularly in the tibial sagittal plane.

IV.