Preoperative evaluation of femoral and tibial sagittal alignment in robotic-assisted and conventional total knee arthroplasty and consequences for practice

Abstract

PURPOSE: Robot-assisted total knee arthroplasty (TKA) was developed to improve the precision and accuracy of implant placement in conventional TKA. However, the angular differences between referenced axes in robot-assisted TKA and conventional TKA remain unclear. The aim of this study was to investigate the angular differences in sagittal alignment between robot-assisted TKA and conventional TKA for both the femur and the tibia and to discuss their clinical implications. METHODS: We conducted a retrospective analysis of data from 100 patients (97 patients) who underwent computed tomography (CT) for Mako TKA. We measured the angle between the robot femoral axis (RFA) and conventional femoral axis (CFA) in the sagittal plane and the angle between the robot tibial axis (RTA) and the conventional tibial axis (CTA). Angles were compared between the sexes. Correlation analysis was conducted between the angles and height. RESULTS: In the sagittal plane, the mean RFA-CFA angle was 2.2° ± 1.6°, and the mean RTA-CTA angle was 2.3° ± 1.6°. There were no significant differences between the two angles among males and females (p > 0.05). There was a correlation between the RFA-CFA angle and RTA-CTA angle (p < 0.001, r = 0.33), and there was a correlation between height and the combination of the RFA-CFA angle and RTA-CTA angle (p = 0.03, r = 0.22). CONCLUSION: There are angular differences between the axes referenced by robot-assisted TKA and those referenced by conventional TKA, which may be influenced by patient height. Correctly understanding these differences is crucial when evaluating the implant position and surgical outcomes after robot-assisted TKA. Furthermore, caution should be taken when assessing the flexion-extension angle of the knee since the angles displayed in the Mako system are different from the angles measured with intramedullary anatomical axes. After all, sagittal alignment principles differ between robot-assisted and conventional TKA; however, further studies are required to determine which principle is more appropriate or to modify these principles.