Functional versus mechanical alignment in robot-assisted total knee arthroplasty: a prospective randomized single-center trial

Abstract

Background. Despite substantial advances in total knee arthroplasty (TKA), a considerable proportion of patients remain dissatisfied with surgical outcomes. One possible explanation is the discrepancy between restored joint biomechanics and the patient’s native anatomy. Functional alignment has recently emerged as a promising personalized alignment strategy facilitated by robotic-assisted technologies. The aim of the study. To compare the early clinical, functional, and radiographic outcomes of robotic-assisted total knee arthroplasty performed using functional alignment versus mechanical alignment. Methods. A prospective randomized single-center study was conducted including 103 patients with Kellgren–Lawrence grade III–IV knee osteoarthritis. Patients were allocated to robotic-assisted functional alignment (n=52) or robotic-assisted mechanical alignment (n=51). All procedures were performed using the CORI Surgical System and Anthem Total Knee System. Clinical outcomes were assessed using the Knee Society Score (KSS), Forgotten Joint Score-12 (FJS-12), and Visual Analogue Scale (VAS). Soft-tissue release requirements and radiographic parameters including HKA, LDFA, and MPTA were also evaluated. Results. At 3 months postoperatively, the functional alignment group demonstrated significantly higher KSS Knee, KSS Function, and FJS-12 scores, as well as lower VAS pain scores compared with the mechanical alignment group (p0.05). Functional alignment was associated with a reduced need for additional soft-tissue releases and a lower mean number of released structures per knee. Both groups demonstrated excellent accuracy of surgical plan execution with comparable deviations from planned alignment parameters. By 12 months, clinical outcomes became comparable between groups. Discussion. The findings suggest that functional alignment may facilitate faster early recovery by preserving native soft-tissue balance and constitutional anatomy. However, the magnitude of intergroup differences decreased over time, indicating convergence of outcomes during later stages of recovery. Conclusion. Robotic-assisted functional alignment is a safe and reproducible TKA strategy associated with improved early functional outcomes and reduced soft-tissue release requirements compared with mechanical alignment. Further multicenter studies with longer follow-up are required to determine its long-term advantages.