Comparative Analysis of Robotic-Assisted and Manual Total Knee Arthroplasty in Patients with Extra-Articular Deformities: A Propensity Score-Matched Prospective Cohort Study

Background: Total knee arthroplasty (TKA) in patients with extra-articular deformities (EAD) presents significant technical challenges. Robot-assisted TKA (RA-TKA) has the potential to provide more precise alignment and soft tissue balance. The primary aim of this study was to compare the rate of mechanical axis outliers (>3° deviation from target hip–knee–ankle angle) between RA-TKA and manual TKA in patients with EAD. Secondary aims included comparison of functional outcomes (KSS, FJS-12) at 12 months and exploratory subgroup analyses by deformity severity. Methods: This prospective, non-randomized, single-center cohort study included 80 patients with EAD undergoing primary TKA. Group allocation was based on the operating surgeon’s clinical judgment considering deformity complexity. To minimize selection bias, propensity score matching (1:1, nearest-neighbor algorithm) was performed, yielding two comparable groups of 30 patients: RA-TKA (CUVIS system) and manual TKA. The primary outcome was the frequency of mechanical axis deviations > 3° (outliers) at 12 months. Secondary outcomes included KSS and FJS-12 scores at 12 months. All subgroup analyses were designated as exploratory. Results: After propensity score matching, the groups were comparable in baseline deformity severity (standardized mean differences < 0.1 for all covariates). The outlier rate was 6.7% in the RA-TKA group versus 23.3% in the manual group (p = 0.03). KSS Functional (84 vs. 74, p = 0.008) and FJS-12 (70 vs. 60, p = 0.02) scores were significantly higher after RA-TKA. In exploratory subgroup analyses, the advantage of the robotic technique appeared more pronounced for deformities with HKA > 10° and multiplanar deformities, though these analyses were underpowered and should be interpreted with caution. Surgery time was longer in the RA-TKA group (148 min vs. 110 min, p < 0.001), but the complication rate did not differ significantly. Conclusions: RA-TKA was associated with a significantly lower rate of mechanical axis outliers and higher functional outcome scores at 12 months compared with manual TKA in patients with EAD. Exploratory subgroup analyses suggest that the advantage may be most pronounced in severe and multiplanar deformities, but adequately powered studies are needed to confirm these findings. The longer operative time and higher cost of RA-TKA should be weighed against potential alignment benefits. Multicenter studies with longer follow-up are needed to assess implant survival and refine indications.