Reproducibility of intra-operative measurement of the mechanical axes of the lower limb during total knee replacement with a non-image-based navigation system

Abstract

Objective: The restoration of a normal mechanical axis of the lower limb following total knee prosthesis (TKP) depends on the accuracy of the intra-operative measurement of the femoro-tibial angle. We have studied the reproducibility of intra-operative measurement of the coronal mechanical femoro-tibial axis with the OrthoPilot® (Aesculap, Tuttlingen, Germany) non-image-based navigation system.Material and Methods: A consecutive series of 20 TKP (Aesculap SEARCH Evolution® prosthesis) implanted by the same surgical team of two senior orthopedic surgeons was analyzed. They used a non-image-based navigation system that allows the mechanical axes of the femur and tibia to be defined with a kinematic analysis. The operating surgeon and assistant surgeon performed the kinematic analysis twice and once, respectively, and measured coronal mechanical femoro-tibial angles in maximal extension and at 90° flexion without varus or valgus stress.Results: The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1° (SD=0.7°). The mean intra-observer variation in the measurement of the coronal mechanical femoro-tibial angle at 90° of knee flexion was 0.2° (SD=0.6°). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.1° (SD=0.7°). The mean inter-observer variation in the measurement of the coronal mechanical femoro-tibial angle in maximal extension was 0.0° (SD=0.6°). There were no significant differences and a high correlation between all paired intra- and inter-observer measurements.Conclusion: This system allows high reproducibility of the intra-operative measurement of the mechanical axes of the lower limb by a non-image-based kinematic registration of the hip, knee and ankle centers.