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

Clinical Snapshot

Key Findings

• P Value: Robotic p = 0.137; Functional alignment p = 0.867

• Effect Size: KOOS-12 difference: robotic vs computer-assisted -2.8 points; functional vs mechanical alignment 0.3 points

• Primary Outcome: No difference in KOOS-12 scores between robotic vs computer-assisted surgery or functional vs mechanical alignment

• Nnt Or Sensitivity: No clinically meaningful benefit demonstrated; NNT not applicable as no significant benefit shown

• Confidence Interval: Robotic: 95% CI -6.4 to 0.9; Functional alignment: 95% CI -3.4 to 4.0

Clinical Application

Robotic systems require significant capital investment and training; computer-assisted surgery more widely available Results directly applicable to Australian practice; may inform PBS funding decisions and hospital technology investments; aligns with AOANJRR data collection Patients undergoing primary total knee arthroplasty for osteoarthritis in Australian public and private healthcare settings

Abstract

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.

References

1. 1.MacDessi, S. J., Wernecke, G. C., Ghadirinejad, K., Wood, J. A., Holder, C., Lorimer, M., Harris, I. A., Bastiras, D., Boyle, R., Chen, D. B., Du, P., Fritsch, B., Guzman, M., Kirsh, G., Limbers, J., McEwen, P., McMahon, S., Mulford, J., Oakey, H., Penn, D., & Yu, J. (2026). Robotic-assisted surgery and functional alignment in total knee arthroplasty: the RASKAL registry-nested 2 × 2 factorial randomized trial. The Bone & Joint Journal, 108B. https://doi.org/10.1302/0301-620X.108B.BJJ-2025-1472.R2