Beyond the coronal plane in robotic total knee arthroplasty-Part 1: Variations in tibial slope and distal femoral flexion do not affect outcomes.

Purpose: Robotic-assisted total knee arthroplasty (TKA) and new alignment principles are transforming traditional implant positioning, not only in the coronal plane but also in the sagittal and axial planes. The impact of differences between a patient's native tibial slope (TS) and distal femoral flexion (DFF) compared to the final implant positioning remains unclear. This study aims to evaluate whether variations in TS (ΔTS) and DFF (ΔDFF) play a role in clinical outcomes and implant survival.

Methods: This retrospective study analysed patients who underwent robotic-assisted TKA following functional alignment (FA) principles between March 2021 and January 2023. A total of 310 patients were included. Preoperative and postoperative data, including radiographic and robotic measurements, were collected. Clinical outcomes (KSS, FJS-12 and AKPS), range of motion (ROM), complication rates, and implant survival were compared between groups at a minimum of 2 years follow-up.

Results: At the final follow-up (mean 2.93 ± 0.62 years), no significant differences were found in clinical scores or ROM between groups with different ΔTS or ΔDFF values. Complication rates and implant survival (99%) were also similar. However, patients with ΔTS > 5° had a slightly increased femoral valgus alignment, while those with ΔDFF ≤ 5° had lower preoperative ROM, with the femoral implant positioned in varus.

Conclusions: Variations between native and implant TS and DFF in robotic-assisted TKA do not negatively impact functional outcomes or implant survival. A personalised sagittal alignment approach within the concept of FA represents a progression to a functional knee positioning based on three dimensions. Further research is needed to explore the long-term effects of sagittal alignment on TKA performance.

Level of evidence: Level III.