Comparison of Functional and Mechanical Alignment in Posterior-Stabilized Total Knee Arthroplasty: A Propensity-Matched Retrospective Cohort Study

Background: While mechanical alignment (MA) has long been the gold standard in total knee arthroplasty (TKA), functional alignment (FA) has recently emerged as a promising alternative, particularly with the advent of robotic-assisted techniques. The present study aims to compare MA and FA in terms of pain, functional outcomes, and perioperative outcomes. Methods: This single-center, retrospective cohort study included 172 patients undergoing primary TKA performed by the same surgeon between 2016 and 2024. Following a 1:1 propensity score matching, patients receiving MA-TKA with navigation (n = 86) were compared with those receiving FA-TKA with robotic assistance (n = 86). The primary outcome was the rate of chronic pain (VAS ≥ 4/10) at six months. Secondary outcomes included validated patient-reported outcomes (PROs: OKS, SF-12, WOMAC, FJS, SKV), Net Promoter Score (NPS), operative time, hospital stay, and complications. Results: At six months, the prevalence of chronic pain was comparable between groups (MA: 15.1%, FA: 19.8%; p = 0.55). At one-year, PROs were similar across all metrics (p > 0.05), although the FA group consistently demonstrated numerically superior scores. Two individual WOMAC items favored the FA group (pain and difficulty walking on flat surfaces; both p = 0.02). Operative time (101.7 ± 16.7 vs 119.6 ± 16.0 min; p < 0.01) and hospital stay (7.7 ± 2.0 vs 9.2 ± 3.8 days; p < 0.01) were significantly shorter in the FA group. Complication and revision rates were low and not significantly different between groups. Conclusion: Functional alignment in robotic-assisted TKA results in comparable pain and functional outcomes to mechanical alignment, while also demonstrating shorter operative time and hospital stay. These findings support the safety and clinical application of individualized alignment strategies in contemporary TKA. Level of evidence IV, retrospective cohort