Lancet - 2026-08-20 - Journal Article
Robotic-arm-assisted versus conventional total knee replacement (RACER-Knee): a pragmatic, multicentre, participant-masked and assessor-masked, superiority, randomised controlled trial.
Parsons H, Metcalfe A, Griffin J, Khatri C, Bradley H, Blyth M, Clement N, Croft N, Deehan D, Ellard D, Frempong S, Grant N, Haddad F, Hutchinson C, Mason J, Mistry H, Naghdi S, Scott C, Smith T, Skinner J, Toms A, Rees S, Riemer B, Underwood M, Davis E, RACER-Knee trial team
Topics
Key Takeaway
Robotic-arm-assisted TKR (Mako) produced a mean Forgotten Joint Score of 49.2 versus 50.2 for conventional TKR at 12 months (adjusted difference -1.5, 95% CI -7.5 to 4.5; p=0.62), failing to reach the prespecified 12-point minimum clinically important difference.
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Summary
RACER-Knee asked whether Mako robotic-arm-assisted TKR improves patient-reported outcomes versus conventional TKR in routine practice across 10 UK hospitals and 33 surgeons. Participants were randomized 1:1 with participant and assessor masking achieved via sham incisions and masked operative notes. At 12 months, FJS was 49.2 (rTKR) versus 50.2 (cTKR), an adjusted difference of -1.5 points—far below the 12-point target difference—with equivalent serious adverse event rates (16 per group) and higher cost for the robotic arm.
Key Limitation
The 12-month primary endpoint may not capture the implant alignment and survivorship benefits most frequently cited to justify robotic systems, meaning the trial answers the short-term functional question but leaves the longevity question open.
Original Abstract
BACKGROUND
Robotic systems are being increasingly used to assist with total knee replacement (TKR). Whether robotic systems improve outcomes after TKR is uncertain. We aimed to ascertain the clinical efficacy and cost-effectiveness of the Mako robotic-arm system compared with conventional instruments for TKR.
METHODS
We conducted a participant-masked and assessor-masked pragmatic, superiority, randomised controlled trial at ten hospitals in Great Britain involving 33 surgeons. Patients with advanced knee osteoarthritis underwent TKR with conventional instruments (cTKR) or with the Mako robotic-arm-assisted system (rTKR). Key exclusion criteria were inflammatory arthropathy, previous fracture, or the need for complex implants. Participants were randomly assigned (1:1) through a remote computer system using minimisation by age, BMI, centre, surgeon, and primary knee compartment involved. Participants and assessors were masked through methods including using sham incisions, additional draping, and masked operation notes. The primary outcome was the Forgotten Joint Score (FJS) at 12 months after randomisation according to the intention-to-treat principle using a linear mixed-effects model. The prespecified target difference was 12 points. The trial is registered with ISRCTN (ISRCTN27624068), and long-term follow-up is ongoing.
FINDINGS
Between Dec 21, 2021, and Dec 13, 2023, 807 patients were screened and 339 were randomly assigned: 168 to rTKR and 171 to cTKR. The median age was 68·8 years (IQR 61·3-75·2), 167 (49%) were female, and 172 (51%) were male. At 12 months, the mean FJS was 49·2 (SD 28·4; n=154) in the rTKR group and 50·2 (29·9; n=158) in the cTKR group. The adjusted mean difference was -1·5 (95% CI -7·5 to 4·5; p=0·62,) favouring cTKR. 16 participants in each group had one serious adverse event.
INTERPRETATION
In this pragmatic trial, rTKR as delivered in routine practice was more costly than cTKR and did not provide a clinically meaningful patient benefit at 12 months after randomisation. The two groups had similar safety (ie, harms) profiles.
FUNDING
UK National Institute for Health and Care Research Health Technology Assessment Programme.