Comparison of Functional and Mechanical Alignment in Robotic- and Computer-Assisted Posterior-Stabilized Total Knee Arthroplasty: Clinical and Patient-Reported Outcomes from a Propensity-Matched Cohort Study.

INTRODUCTION: 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. Despite its growing adoption in clinical practice, comparative evidence between functional and mechanical alignment remains limited, especially for postero-stabilized (PS) TKA. The present study means to compare mechanical and functional alignment in TKA in terms of patient-reported and functional outcomes at a minimum of one year follow-up. HYPOTHESIS: Functional alignment would result in superior functional outcomes compared to mechanical alignment in total knee arthroplasty, without compromising perioperative safety. 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 persistent pain (VAS ≥ 4/10) at six months. Secondary outcomes included validated patient-reported outcomes (PROs), operative time, hospital stay, and complications. RESULTS: At six months, the prevalence of persistent 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 isolated WOMAC items (pain and difficulty walking on a flat surface; both p = 0.02) favored the FA group. 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. As the two cohorts also differed in surgical technology and treatment era, these perioperative findings should be interpreted as exploratory and not necessarily attributable to alignment strategy alone. CONCLUSION: Functional alignment in robotic-assisted TKA resulted in pain and functional outcomes comparable to mechanical alignment with computer navigation, without demonstrating clinical superiority. Perioperative differences (operative time and hospital stay) were observed but may reflect differences in technology and treatment era rather than alignment strategy alone. These findings support the safety of functional alignment as an individualized alternative to mechanical alignment in contemporary TKA. LEVEL OF EVIDENCE: III; comparative retrospective investigation.