Robotic-assisted surgery and functional alignment in total knee arthroplasty: the RASKAL registry-nested 2 × 2 factorial randomized trial.

Aims: Robotic-assisted surgery and functional alignment are increasingly being adopted in total knee arthroplasty (TKA). This study assessed the individual and combined effectiveness of robotic-assisted surgery and functional alignment in improving outcomes in TKA, compared with computer-assisted surgery and mechanical alignment, respectively. Methods: A registry-nested, multicentre, blinded, 2 × 2 factorial, randomized trial was performed with 303 TKA patients randomized to robotic-assisted or computer-assisted surgery, and functional or mechanical alignment. The primary outcome was the between-group differences in postoperative change over two years in the mean Knee Injury and Osteoarthritis Outcome Score (KOOS-12). Secondary outcomes included knee-specific and general patient-reported outcome measures (PROMs), operative and functional outcomes, and adverse events. Primary modified intention-to-treat and secondary per-protocol analyses were performed. Results: There were no differences comparing robotic-assisted with computer-assisted surgery in KOOS-12 at three months, six months, one year, and two years (mean two-year difference -2.8; 95% CI -6.4 to 0.9; p = 0.137), and no differences comparing functional with mechanical alignment at three months, six months, one year, and two years (mean two-year difference 0.3 (95% CI -3.4 to 4.0); p = 0.867). No differences were found in Oxford Knee Score, Forgotten Joint Score, EuroQol five-dimension five-level visual analogue scale, patient satisfaction, joint-related improvement, and pain comparing technology or alignment groups at three months, six months, one year, and two years. Robotic-assisted surgery had a shorter mean operating time by 11.5 minutes (95% CI 7.3 to 15.9; p < 0.001) and better mean posterior cruciate ligament macroscopic soft-tissue injury score (mean difference 0.7 (95% CI 0.3 to 1.1); p = 0.001) compared with computer-assisted surgery. Mechanical alignment had a higher soft-tissue release rate compared with functional alignment (44.8% vs 8.1%; OR 9.2 (95% CI 4.6 to 18.3); p < 0.001). In most cases, surgeons preferred the use of robotics and functional alignment. Conclusion: Robotic-assisted surgery and functional alignment were not superior to computer-assisted surgery and mechanical alignment, respectively, in improving clinical and functional outcomes up to two years post-TKA.