Functional alignment robotic-assisted TKA improves clinical outcomes compared with conventional mechanical alignment TKA: A single-surgeon randomised controlled non-inferiority trial with 2-year follow-up.

Abstract

Purpose: Functional alignment (FA) has emerged as an alternative to mechanical alignment (MA) in total knee arthroplasty (TKA), supported by robotic assistance to enhance precision and soft‑tissue preservation. Evidence comparing FA performed with robotic assistance to conventional MA‑TKA across mid‑term patient‑reported outcomes measures (PROMs) remains limited. This randomised controlled trial evaluated differences in recovery trajectories and 2‑year knee‑specific outcomes between FA‑RATKA and MA‑CTKA.

Methods: This study reports the predefined primary 2-year outcomes of a prospective randomised controlled non-inferiority trial including 180 patients (FA-RATKA, n = 81; MA-CTKA, n = 82), of whom 163 completed follow-up. Assessments were performed preoperatively and at 3-months, 1- and 2-years using validated PROMs: Knee Society Score (KSS) subdomains, Oxford Knee Score (OKS), Forgotten Joint Score (FJS-12), VAS pain, EQ-5D-5L (index and VAS), Lower Extremity Activity Scale (LEAS), and overall satisfaction. Mixed-effects models evaluated group, time, and Group × Time interactions, adjusting for age, BMI, and soft-tissue release. Effect sizes (r) were calculated to contextualise clinical relevance.

Results: FA-RATKA demonstrated more favourable knee-specific outcomes across follow-up, with significant Group × Time interactions for KSS Function (F(3,679) = 6.970, p < 0.001; r = 0.173), KSS Satisfaction (F(3,679) = 10.892, p < 0.001; r = 0.214) and KSS Symptoms (F(3,679) = 4.425, p = 0.004; r = 0.138). FA-RATKA also showed more favourable OKS trajectories (F(3,679) = 8.053, p < 0.001; r = 0.185), lower VAS pain (F(3,679) = 8.339, p < 0.001; r = 0.188), and higher EQ-5D index scores (F(2,515) = 5.227, p = 0.006; r = 0.141). Categorical satisfaction favoured FA-RATKA at early follow-up (F(2,503) = 3.491, p = 0.031; r = 0.117). Effect sizes ranged from r = 0.117 to 0.214, corresponding to small to small-medium magnitudes.

Conclusions: In this prospective, randomised, single-surgeon study, several knee-specific patient-reported outcomes demonstrated modest but statistically supported differences at 2-year follow-up, with consistently higher values in the FA-RATKA group.

Level of evidence: Level I, randomised controlled trials with adequate statistical power to detect differences (narrow confidence intervals) and follow up >80%, as per the KSSTA guidelines.