Robotic TKR: distinguishing platform effects from alignment effects

Dear Editor
Mohammad et al. found no evidence of reduced early revision after robotic total knee replacement (TKR; hazard ratio 1.03, 95% confidence interval 0.86 to 1.26).[1] Their registry analysis provides valuable evidence about current practice, but the robotic interventions were heterogeneous: Mako accounted for 74.8% of robotic TKRs before matching. The pooled estimate does not isolate the contributions of robotic platform, alignment target, or soft-tissue balancing strategy, limiting inferences about specific surgical approaches.
Geng et al.’s multicentre randomised trial reported improved alignment accuracy but no significant differences in knee function or quality-of-life scores at 6 weeks.[2] In a separate trial using Mako in both groups, Wang et al. reported higher 6-month Forgotten Joint Scores and selected Knee injury and Osteoarthritis Outcome Score (KOOS) domain scores with functional versus mechanical alignment, but no significant differences in overall KOOS or satisfaction.[3] Neither trial compared different robotic platforms, and the within-platform comparison by Wang et al. cannot establish the incremental clinical benefit of robotic assistance. The subgroup findings reported by Wang et al. warrant cautious interpretation because formal interaction tests were not reported.
Larger trials provide further evidence on whether technical differences translate into patient benefit. RACER-Knee randomised 339 patients and found no clinically meaningful 12-month Forgotten Joint Score benefit with Mako-assisted versus conventional TKR (adjusted mean difference −1.5, 95% confidence interval −7.5 to 4.5); both groups initially targeted mechanical alignment, with surgeon-directed adjustments permitted.[4] RASKAL, a factorial trial including 303 patients in its modified intention-to-treat analysis, compared robotic-assisted with computer-assisted surgery and functional with mechanical alignment. Neither robotic assistance nor functional alignment showed a significant advantage in KOOS-12 outcomes over its respective comparator through 2 years, and no significant technology-by-alignment interaction was detected for this outcome, although functional alignment required fewer soft-tissue releases.[5]
Where event counts permit, comparing Mako-assisted TKR with a rematched conventional cohort could assess consistency with the pooled registry estimate, although alignment and implant effects would remain unresolved. Future registry-linked studies should link recorded platform and implant details with intended alignment targets, patient-reported outcomes, and revision surveillance. They should prespecify clinically justified subgroup hypotheses and be adequately powered for interaction testing. Mohammad et al. already matched on annual surgeon caseload and excluded each surgeon’s first 10 robotic procedures in sensitivity analyses; future analyses could additionally consider cumulative experience with each platform.[1] Building on RASKAL, future studies should evaluate whether these findings extend to other robotic platforms and implant systems, with longer-term assessment of patient-reported outcomes, revision risk, and cost effectiveness.

References
1. Mohammad HR, Judge A, Griffin XL, et al. Early national comparison of robotic versus conventional knee replacements for arthritis using National Joint Registry data: target trial emulation study. BMJ 2026;394:e100691. doi:10.1136/bmj-2026-100691.
2. Geng X, Zheng Y, Li Y, et al. Early radiographic and clinical outcomes of robotic-arm-assisted versus conventional total knee arthroplasty: a multicenter randomized controlled trial. Orthop Surg 2024;16(11):2732–2740. doi:10.1111/os.14196.
3. Wang Q, Yan Z, Wang Q, et al. The early outcome of robotic-assisted functional versus mechanical alignment in total knee arthroplasty: a prospective randomized control trial. J Arthroplasty 2025;40(11 Suppl 1):S36–S44. doi:10.1016/j.arth.2025.08.030.
4. Parsons H, Metcalfe A, Griffin J, et al. Robotic-arm-assisted versus conventional total knee replacement (RACER-Knee): a pragmatic, multicentre, participant-masked and assessor-masked, superiority, randomised controlled trial. Lancet 2026;408(10558):924–934. doi:10.1016/S0140-6736(26)00986-4.
5. MacDessi SJ, Wernecke GC, Ghadirinejad K, et al. Robotic-assisted surgery and functional alignment in total knee arthroplasty: the RASKAL registry-nested 2 × 2 factorial randomized trial. Bone Joint J 2026;108-B:622–633. doi:10.1302/0301-620X.108B.BJJ-2025-1472.R2.