Robot-assisted knee replacement surgery is more precise than a surgeon on their own, but does not currently lead to improvements in patient outcomes, according to the RACER-Knee trial, the world's largest clinical study of its kind.
This trial makes an important contribution to the evidence on robotics in health care and where future advances and research should focus. The trial, coordinated by the University of Warwick and University Hospitals Coventry and Warwickshire (UHCW) NHS Trust, is published in The Lancet, the world's oldest and best-known general medical journal.
Robotic assistance is increasingly used in knee replacement surgery worldwide, in six per cent of procedures in the UK, compared with 16 per cent in the US and 42 per cent in Australia, with the aim of helping surgeons place the knee replacement more precisely and tailoring surgery to a patient’s anatomy.
The National Institute for Health and Care Research (NIHR) funded the UK-wide RACER-Knee trial in partnership with Stryker, who make the robot that was tested. It was led by the Warwick Clinical Trials Unit, UHCW NHS Trust and the Royal Orthopaedic Hospital in Birmingham. It is the world's largest double-blinded randomised control trial comparing conventional total knee replacement to surgery assisted with the Stryker Mako robotic system, the most widely used system globally.
The trial found that one year after surgery, patients in both groups had similar recovery, mobility and pain levels. While robotic assistance was more precise, it did not translate into improvements in patient outcomes within the first year after knee replacement. The trial also found that robot-assisted knee replacement was not linked to an increased risk of serious adverse events, suggesting it was as safe as the usual approach to surgery.
The study was led between two Chief Investigators in the West Midlands, they said:
Professor Andrew Metcalfe, Warwick Medical School, University of Warwick, and Consultant Orthopaedic Surgeon at UHCW NHS Trust: “We are delighted to have completed this world-leading randomised trial of an exciting technology that is now being used globally and at scale. It is an important step in the process of innovation and will stimulate lots more high-quality studies. We are very grateful for the support of the many patients who took part which is so important, but also the NIHR and Stryker for working so well together to support this critical study. Technology such as this could really help the care we give for patients, but for robotic-assisted knee replacements, there is still work to do before we see benefits such as less pain or better movement.”
Professor Edward Davis, Consultant orthopaedic surgeon at The Royal Orthopaedic Hospital NHS Foundation Trust and Honorary Professor at University of Birmingham: “The trial demonstrates robotic-arm-assistance allows for higher precision, and in theory the system should allow surgeons to customise the procedure according to a patient’s anatomy. These results are by no means a condemnation of the robotic systems, but more understanding of the ideal position for a knee replacement and personalisation for each patient is needed. We’ll then be able to truly take advantage of the advanced precision of robotic systems. “
Professor Anthony Gordon, Director for the NIHR Health Technology Assessment (HTA) Programme, said: “Innovation in healthcare depends on evaluating promising technologies rigorously and at scale. While this study shows robotic-assisted knee replacement is not yet improving patient outcomes, it highlights opportunities to refine these technologies and harness their precision to deliver better care in the future. The NIHR continues to fund robust studies, such as RACER, ensuring we learn how to deliver the latest technologies most effectively within the NHS.”
Total knee replacement is one of the most common elective operations worldwide for treating knee arthritis. Conventionally, surgeons rely on their experience and a standard set of instruments to perform the procedure. Some surgeons now use a robotic arm, controlled by the surgeon, to assist in the operation. The system positions instruments with high precision and gives surgeons greater flexibility to vary cutting angles and depths, enabling personalised approaches tailored to individual patient’s anatomy in ways conventional surgery cannot achieve.
339 patients from 10 hospitals, under the care of 33 surgeons across the UK, took part in the trial. Despite the potential advantages of robotics, the trial found that there was no meaningful difference in the primary measure, the Forgotten Joint Score, 12 months after the operation. The score measures the extent to which patients are aware of their artificial joints during daily activities, and patients showed equal results with their artificial joints, whichever method was used for doing the replacement. Patients also showed comparable outcomes in their ability to walk, their experience of pain in the first three months and at 12 months, their pain in hospital, and the likelihood of a follow-up operation.
The researchers will continue to follow-up patients for ten years to find out if there are any long-term differences between the two approaches. Importantly this might find out if there is a difference in number or patients needing more surgery for their knee.
Robotic TKRs took longer to perform (on average 10.5 minutes) and were around £950 more expensive on average, but were more precise and were not associated with an increased risk of serious adverse events, suggesting the robotic procedure was as safe as conventional surgery. Under current NHS cost limits, the robotic system tested in this trial was not cost-effective over the first year after surgery.
In the future, if the use of robotic assistance could help surgeons to better tailor to each patient's individual anatomy, then the robotic system's better precision could become worthwhile. This would need more development and further research but is an exciting area for future studies.
The results of the RACER-Knee trial have published in The Lancet. DOI: 10.1016/S0140-6736(26)00986-4
Notes to Editors
For more information please contact:
Matt Higgs, PhD | Media & Communications Manager (Warwick Press Office): Email: This email address is being protected from spambots. You need JavaScript enabled to view it. | Phone: +44(0)7880 175403
About the Trial
This research has been organised by University Hospitals Coventry and Warwickshire NHS Trust, and the University of Warwick. It has been funded by the UK NHS research body, the National Institute for Health Research, through its Health Technology Assessment Programme (NIHR128768)
Stryker, the manufacturers of the robotic system, met the additional costs of doing robotic surgery within this study. They were not involved in the analysis or interpretation of the study findings.
About the University of Warwick
Founded in 1965, the University of Warwick is a world-leading institution known for its commitment to era-defining innovation across research and education. A connected ecosystem of staff, students and alumni, the University fosters transformative learning, interdisciplinary collaboration, and bold industry partnerships across state-of-the-art facilities in the UK and global satellite hubs. Here, spirited thinkers push boundaries, experiment, and challenge convention to create a better world.
About University Hospitals Coventry and Warwickshire NHS Trust
University Hospitals Coventry and Warwickshire NHS Trust (UHCW) are one of the largest acute teaching Trusts in the UK, comprising University Hospital in Coventry and the Hospital of St Cross in Rugby and working in partnership with Warwick University Medical School and Coventry University. It has more than 11,000 staff and delivers services across the West Midlands region. This includes hosting region-wide services such as the Coventry and Warwickshire Pathology Network and Bowel Cancer Screening programme. The Trust works closely with its partners in health and social care in Coventry and Warwickshire to develop patient-focused services that meet the needs of our communities.
About the Royal Orthopaedic Hospital NHS Foundation Trust
The Royal Orthopaedic Hospital NHS Foundation Trust is one of the largest specialist orthopaedic units in Europe, offering planned orthopaedic surgery to people locally, nationally, and internationally. The Trust is an accredited Veteran Aware organisation and a Disability Confident Leader. A national centre for bone cancer and musculoskeletal medicine, the Royal Orthopaedic Hospital has a vibrant research portfolio of clinical trials, observational studies and laboratory studies exploring new treatment options, new approaches in rehabilitation and therapy, and new medical devices. This research is delivered by our researchers and clinicians spread across the Knowledge Hub, our home for education and research, and the Dubrowsky Regenerative Medicine Laboratory.
About NIHR
The mission of the National Institute for Health and Care Research (NIHR) is to improve the health and wealth of the nation through research. The mission of the National Institute for Health and Care Research (NIHR) is to improve the health and wealth of the nation through research.
We do this by:
- funding high quality, timely research that benefits the NHS, public health and social care
- investing in world-class expertise, facilities and a skilled delivery workforce to translate discoveries into improved treatments and services
- partnering with patients, service users, carers and communities, improving the relevance, quality and impact of our research
- attracting, training and supporting the best researchers to tackle complex health and social care challenges
- collaborating with other public funders, charities and industry to help shape a cohesive and globally competitive research system
- funding applied global health research and training to meet the needs of the poorest people in low- and middle-income countries
NIHR is funded by the Department of Health and Social Care. Our work in low- and middle-income countries is principally funded through UK international development funding from the UK government.
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Image credit to University Hospitals Coventry and Warwickshire NHS Trust
