Functional alignment preserves the native Coronal Plane Alignment of the Knee phenotype while improving early clinical outcomes after robotic-assisted total knee arthroplasty.

BACKGROUND: Functional alignment (FA) has emerged as a personalized strategy for robotic-assisted total knee arthroplasty (ra-TKA), aiming to preserve constitutional knee anatomy and native soft-tissue balance. However, evidence directly comparing robotic-assisted FA and mechanical alignment (MA) using the same robotic platform remains limited. THE AIM OF THE STUDY: To compare the early clinical, radiographic, and constitutional phenotype outcomes of ra-TKA performed using FA and MA. METHODS: In this prospective randomized single-center study, 100 patients with primary varus knee osteoarthritis underwent primary ra-TKA using the CORI Surgical System and were randomized to the FA (n=50) or MA (n=50) group. Clinical outcomes (KSS, FJS-12, VAS), radiographic alignment (HKA, LDFA, MPTA), soft-tissue release, and postoperative CPAK phenotype preservation were evaluated over 12 months. RESULTS: Both groups demonstrated significant postoperative improvement. At 3 months, the FA group achieved significantly higher KSS Knee, KSS Function, and FJS-12 scores together with lower VAS pain scores than the MA group (all p<0.05). These differences were no longer significant at 12 months. FA required fewer soft-tissue releases while maintaining radiographic accuracy comparable to MA. Constitutional CPAK phenotype was preserved in 82% of FA patients, whereas all mechanically aligned knees were converted to CPAK phenotype V. Native joint-line orientation and constitutional varus alignment were preserved in all FA cases. CONCLUSION: Robotic-assisted functional alignment provides accurate and reproducible component positioning while preserving constitutional knee phenotype and reducing soft-tissue release. Although long-term clinical outcomes were comparable, FA resulted in superior early functional recovery and represents a safe personalized alignment strategy.