Functional alignment with robotic-assisted total knee arthroplasty is associated with reduced early postoperative pain and alignment outliers compared to mechanical alignment with conventional total knee arthroplasty: a prospective cohort study

Abstract

Introduction: Robotic-assisted total knee arthroplasty (RATKA) has been introduced to enhance surgical precision, alignment, and soft-tissue balancing, thus enabling the advent of numerous alignment philosophies including functional alignment (FA). This study aimed to compare early clinical outcomes, patient-reported outcome measures (PROMs), and radiographic accuracy brought about by RATKA using FA principles against the current reference standard of conventional total knee arthroplasty (TKA) and mechanical alignment (MA). Methods: This prospective, non-randomized cohort study included 45 patients undergoing primary unilateral TKA (30 RATKA, 15 conventional). Outcomes assessed were Visual Analogue Scale (VAS), Knee Society Score (KSS), and Knee injury and Osteoarthritis Outcome Score (KOOS) preoperatively and up to 1 year postoperatively. Forgotten Joint Score-12 (FJS-12) was evaluated at 1 year. Radiographic parameters included hip-knee-ankle angle (HKA), medial proximal tibial angle (MPTA), lateral distal femoral angle (LDFA), and femoral component rotation. Alignment outliers were defined as a deviation of > ±3° from the target. Statistical significance was set at p < 0.05. Results: RATKA resulted in significantly lower VAS pain scores at 2 weeks and 3 months (p < 0.05), with a consistent trend toward reduced pain at other timepoints. PROMs demonstrated improvements favoring RATKA across several KSS and KOOS subdomains at selected intervals. FJS-12 was higher in the RATKA group but did not reach statistical significance (p = 0.12). Radiographic alignment was comparable between groups except for femoral component rotation, which showed greater external rotation in the conventional cohort (p = 0.009). RATKA significantly reduced alignment outliers (10.0% vs 40.0%, p = 0.042). No complications were observed. Conclusion: The adoption of RATKA and functional alignment is associated with reduced early postoperative pain, modest improvements in PROMs, and improved consistency in achieving target alignment, without increased complications.