Knee Replacement Robot: Mako, ROSA and ABB's Role

A knee replacement robot is now routine kit in many hospitals, and in 2026 it also got its hardest test so far. Two large British studies, published in August and September, found that robots cut bone more precisely but did not yet give patients better results. This post follows knee replacement from the first ivory implants and Frank Gunston's polycentric knee to ROBODOC, Mako, ROSA and VELYS, looks at what the new evidence says, and asks where ABB robots could fit. For now that is in the factories that make implants, since ABB has no robot in the operating room.

A patient's leg after knee replacement surgery, with the stitched incision over the knee, 2025. Photo: Plazadelcamino / Wikimedia Commons (CC BY-SA 4.0)

How surgeons replaced knees by hand, from ivory to the total condylar knee

The first documented artificial knee was reported in 1890: ivory components fixed together with plaster of Paris. In the 1950s surgeons tried hinged knees made of cobalt chrome, and these failed often because a hinge cannot follow the small rotation a real knee makes as it bends. In all of these operations the surgeon worked by hand and by eye, shaping the bone with saws and cutting guides and judging the alignment of the leg on the table.

The Hospital for the Ruptured and Crippled on East 42nd Street, New York, in 1912; it later became the Hospital for Special Surgery. Photo: Irving Underhill via Wikimedia Commons (public domain)

The design that led toward the modern knee came from Frank Gunston, a surgeon from Winnipeg who was a fellow at John Charnley's hip centre in Wrightington, England, in the late 1960s. His polycentric knee used metal half discs set into the femur that ran on plastic runners in the tibia, and he published his results in 1971. It went into thousands of patients, many of them at the Mayo Clinic. In 1974 surgeons at the Hospital for Special Surgery in New York performed the first successful total condylar knee replacement, which covered the femur, the tibia and the kneecap.

A knee prosthesis photographed in 1976. Photo: National Archives and Records Administration via Wikimedia Commons (public domain)

Robots came to the knee by way of the hip. ROBODOC was developed by IBM's Thomas J. Watson research lab and the University of California, Davis, with veterinarian Howard Paul and surgeon William Bargar, and its use later widened to knees. In 2001 a team at Imperial College London published the first paper on partial knee replacement with its Acrobot. Mako Surgical, founded in Florida in 2004, implanted its first partial knees with the RIO robotic arm in 2006, and Stryker bought the company in 2013. The FDA cleared Zimmer Biomet's ROSA knee robot in 2019 and DePuy Synthes' VELYS in January 2021.

A total knee implant fitted to a model of the femur and tibia. Photo: Rama / Wikimedia Commons (CC BY-SA 2.0 FR)

What the 2026 knee robot trials found

On 21 August 2026 the University of Warwick and University Hospitals Coventry and Warwickshire published the RACER-Knee trial in The Lancet. It is the largest double blinded randomised trial comparing conventional knee replacement with surgery using the Stryker Mako system, and it followed 339 patients treated by 33 surgeons in 10 hospitals. The robot placed implants more precisely, yet a year later both groups had similar pain, mobility and recovery. Robotic operations took 10.5 minutes longer and cost about £950 more. Robots are used in 6% of UK procedures, compared with 16% in the US and 42% in Australia.

A full leg X-ray with a knee prosthesis and the hip, knee and ankle alignment line drawn on it. Photo: Hiroshi Inui, Shuji Taketomi et al. / Wikimedia Commons (CC BY 2.0)

On 30 September The BMJ published registry studies covering 697,145 UK knee replacements done between 2018 and 2024, of which 22,111 were robotic. The robotic knees had no lower early risk of repeat surgery. The authors put the cost of a system at about £1 million up front plus £1,000 to £2,500 per patient, and questioned NHS plans for wide adoption. Hospitals are still buying. On 6 October Stryker launched its Mako 4 system in India, and US hospitals keep announcing their 2,000th and 3,000th robotic joint operations.

The Hospital for Special Surgery's main campus in New York, 2023. Photo: Holstenc / Wikimedia Commons (CC BY-SA 4.0)

ABB does not make a surgical robot, so its place in this story is on the factory side. Knee implants are precise metal and plastic parts that have to be machined, ground and polished, and ABB arms already do that kind of work in other industries. The new generation IRB 1200, launched in 2025, is a compact arm for machine tending and small parts, and GoFa CRB 15000 cobots load parts into machine tools. Cobots like these already work on medical device lines, where parts are small and tolerances tight.

The new generation ABB IRB 1200, launched in 2025, a compact arm for machine tending and small parts. Photo: ABB

Where robotic knee surgery goes from here, in theatres and factories

Surgeons now need evidence that precision pays off. The RACER-Knee team found that it had not done so in the first year, and Professor Andrew Metcalfe, one of the trial's leaders, said: "Technology such as this could really help care we give for patients, but there is still work to do." Longer follow up will show whether better alignment matters after many years of wear. Until then hospitals have to set a large up front cost against benefits nobody has measured yet, which our wider look at surgical robots also found.

An ABB GoFa cobot loading parts into a machine at a small factory. Photo: ABB

In factories, more knee surgery means more implants to make and finish. Grinding cells such as Teqram's EasyGrinder, which uses an ABB IRB 6700 to grind steel parts at Ancofer, show a robot taking over a dirty manual finishing job. A smaller ABB arm doing the same on implants is only a possibility today, and ABB does not sell such a cell. Cells like this are usually built and tested first in RobotStudio, so the path of every part can be checked before any metal is cut.

An ABB IRB 6700 grinding a steel part in Teqram's EasyGrinder cell at Ancofer. Photo: ABB

For patients, the 2026 studies make the decision easier to think about. A robot can make the bone cuts more precise, but the trial found no better recovery in the first year and the registry found no lower risk of early revision, so the surgeon's own experience still counts for a lot. Recovery happens at home with exercise, and the robots most likely to help there are the ones used in rehabilitation therapy. How fast the share of robotic knees grows will depend on cost, training and the long term data still to come.

Hip, spine and knee implants on bones at the Deutsches Hygiene-Museum in Dresden, 2024. Photo: Dguendel / Wikimedia Commons (CC BY 4.0)

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