Functional alignment in robotic total knee arthroplasty achieves comparable outcomes in varus and valgus knees despite distinct intraoperative strategies: Analysis of 355 consecutive cases.

Abstract

Functional alignment (FA) optimises implant positioning based on patient-specific anatomy, but data on intraoperative adjustments in varus and valgus knees remain limited. This study evaluates the impact of preoperative coronal alignment on implant positioning, bone resections, functional outcomes, and revision rates in robotic-assisted total knee arthroplasty (TKA) under FA principles. A retrospective analysis of 355 robotic-assisted TKAs performed with FA was conducted. Patients were classified as varus (n = 294, HKA < 180°) or valgus (n = 61, HKA ≥ 180°). Intraoperative implant positioning, bone resections, and alignment parameters were recorded. Functional outcomes were assessed using the Knee Society Scores, Forgotten Joint Score, and Kujala score. Implant survivorship was analysed using the Kaplan-Meier method. Varus knees required greater tibial varus positioning (3.5° varus [interquartile range [IQR] 2-5] vs. 1° varus [IQR 0-2.5], p < 0.0001), while valgus knees required increased femoral valgus positioning (1.5° [IQR 0.38-2.5] vs. 0.7° [IQR -0.5 to 1.83], p = 0.0004). Bone resections also differed significantly between groups. Specifically, the valgus group had lower lateral tibial (p = 0.0001), distal lateral (p < 0.0001), and posterior lateral femoral resections (p < 0.0001), but higher distal medial femoral resections (p = 0.04). Postoperative functional outcomes were comparable across groups. Survival rates were 98.64% (varus) and 98.36% (valgus) (p = 0.86), with a hazard ratio of 1.23 (95% CI: 0.12-12.57) for valgus knees. This study systematically evaluates intraoperative modifications in FA-based robotic TKA for varus and valgus knees. Despite distinct balancing strategies, both groups achieved comparable outcomes and implant survivorship. Level III.