Aims: The latest software 3.0 and 4.0 of the OrthoPilot knee navigation system use a new mathematical algorithm to reconstruct mechanical axis. The purpose of the study is to evaluate the alignment of prosthetic components with this software and compare it with the results from older software as well as with manual technique. Method: Thirty navigated SEARCH knees with software 3.0 of an uninterrupted series were evaluated versus thirty navigated knees with older software and a similar series of conventionally instrumented knees of a different type. Results: The results, concerning the five parameters mechanical axis a.p., femoral axis a.p., femoral axis lateral, tibial axis a.p. and tibial axis lateral, are clearly superior to the old navigation group and the manual group. For example, the number of cases with a good mechanical axis, 0,1or 2° of deviation from optimum, was reached in 17 of the manual, 19 of the old navigation and 27 of the new navigation cases. The additional time for operation is 8.7 minutes. No specific complications occurred. Conclusions: The OrthoPilot-Software 3.0 and 4.0 are clearly superior to the old generations. More features, as for example resection-height of the distal femur and the orientation of the femoral component are solved in a convincing manor. The numbers of outliers is again diminished. Navigation in knee arthroplasty with the OrthoPilot has become more sure and intelligent.

Background: The aim of introduction of navigation in knee arthroplasty was to further contribute to precision of endoprosthetic alignment.

Methods and material: A multicentre comparative study was conducted including 821 patients. The SEARCH knee system was used throughout the series. 555 TKA’s were implanted with the use of a navigation system (OrthoPilot) and 266 cases were operated using manual instrumentation. Alignment was radiographically evaluated at the three months follow-up with respect to mechanical axis and femoral and tibial axes using one-leg stance x-rays and standardized lateral radiographs.

Results: The summarized results of the series are shown in the table below. The chi-square test was applied for the statistical analysis.

Conclusions: Endoprosthetic alignment using the navigation system was superior to manual implantation technique on the average with respect to all parameters. Results were more consistent on the tibial side. The navigation system proved to be reliable. The overall results justify the further use and development of navigation tools in knee arthroplasty.