Objective: Kinematic computer navigation technology has already shown improved alignment results in knee arthroplasty over the past years. But still all items and results are not perfect. The updated Orthopilot 4.0 navigation software is more sophisticated and gives the ability of additional navigation of soft tissue balancing. Together with the use of the new designed ultracongruent E-motion prosthesis, the Orthopilot 4.0 technology is very promising.

Material and Methods: In this combined study equal groups (n=100) of patients were prospectively operated using E-motion prostheses navigated by Orthopilot 4.0 technology including ligament tension balancing (group G1), and Search prostheses navigated by the older Orthopilot 3.0 technique (G3). Conventionally operated patients served as control using LCS prostheses (G2, n=100), and former implanted Search prostheses (G4, n=50). The results of all groups were compared retrospectively. The results were radiologically evaluated by measuring pre-, and postoperative mechanical leg axes, femoral and tibial angles in both the coronal and the sagittal plane. In each cohort all surgeries were consecutively performed. Patients suffered from primary or secondary osteoarthritis.

Results: Time of surgery did not differ significantly between group G1 and G2, but it was prolonged significantly for groups G3 and G4. In all patients of G1 a mechanical axis of 0 ± 5°, having 93% inside the excellent range of ± 3°, could be reached. Showing excellent ligament stability, full extension was possible much earlier than in the other groups. The mechanical axes in the control groups were more often different from optimum, with 63% inside an excellent range (G2), 76% (G3), and 57% (G4), respectively.

For the femoral axis in the coronal plane, excellent results, i.e. ± 2% off optimum, were found in 95% (G1), 91% (G2), 97% (G3), and 77% (G4). The corresponding results for the femoral axes in the sagittal plane were 81% (G1), 79% (G2), 71% (G3), and 67% (G4). For the tibial axes in both planes the results were similar.

All 5 axes in a perfect alignment at the same time were seen in 65% (G1), 40% (G2), 28% (G3), 22% (G4). In G1 femoral notching was inexistent.

Discussion and Conclusion: During surgery, the new Orthopilot 4.0 navigation technique allows precise determination of collateral ligament tension in full extension and in flexion up to 90 degrees. This leads to perfect intraoperative planning of the tibial and femoral cut with respect to the required soft tissue release. In comparison to the control groups, this new technique leads to a significant improvement in postoperative results towards the desired optimal criteria, as there are: straight mechanical leg axes, little deviations from optimum for each single femoral and tibial axis, perfect collateral ligament balancing, and optimal range of movement.