On July 10, 2025, a team led by lead author Tony Shu and senior author Hugh Herr from the Massachusetts Institute of Technology published a study in the journal Science on a new prosthesis for people with above-knee amputation. Unlike a conventional socket prosthesis, the artificial leg sits on an implant that is surgically anchored in the bone and controlled via signals from surgically reconnected muscles. The researchers call the overall system an osseointegrated mechanoneural prosthesis, or OMP for short.
In the study, according to MIT News, two test subjects received the combined system of muscle surgery and bone implant, eight had the muscle surgery without implant, and seven had neither; all tested the same motorized knee prosthesis developed by the laboratory. The following look at the underlying surgical method shows how this control works in detail.
How muscles control the prosthesis and the bone implant provides stability
In a typical amputation, according to MIT News, muscle pairs that normally stretch and contract alternately are usually severed, making it difficult for the nervous system to perceive how the affected muscle moves. The procedure developed by Herr and his colleagues, called the Agonist-Antagonist Myoneuronal Interface or AMI for short, reconnects these muscle pairs during surgery so they communicate with each other again in the remaining limb and provide electrical signals to control the prosthesis. For above-knee amputations, the researchers supplemented this procedure with a titanium rod in the remaining thighbone that, according to their findings, provides better mechanical control and load-bearing than a conventional socket prosthesis. The implant contains 16 wires that receive signals from electrodes on the AMI muscles and relay them to a custom-developed robotic controller, which calculates the required torque for the desired knee movement from these signals.
Measurements included whether subjects could bend their knee to a specified angle, how they climbed stairs, and how they stepped over obstacles. On most of these tasks, the two users of the combined system performed better, according to the researchers, than the eight people with muscle surgery alone and significantly better than users of conventional prostheses. Additionally, the researchers asked participants whether they felt they had two legs, whether the prosthesis felt like part of their body, and whether they felt they could control it. The two people with the combined system reported significantly greater increases in this sense of control and body ownership over the course of the study compared to other participants.
What researchers and outsiders say about the results
Hugh Herr describes a prosthesis anchored in bone and directly controlled by the nervous system as an "integral part of self", not merely a tool that a person uses. Lead author Tony Shu explained to Smithsonian that part of the tissue-integrated prosthesis can only be removed through further surgery. The study authors themselves suggest in their abstract that such anatomical integration may be necessary to achieve and possibly exceed the movement capabilities of an intact limb. John Brinkmann, an orthotic technician not involved in the study from the Feinberg School of Medicine at Northwestern University, valued the results according to Smithsonian as progress in integrating a device with the patient and pointed out that such technologies are significantly rarer in lower extremity amputations. He also warned that costs could be a significant barrier to broader use, as patients have already experienced difficulties with insurance coverage for conventional prostheses; additionally, some patients may not be medically eligible for the procedure.
In comparison: what earlier tests with the procedure showed
The AMI procedure itself is not new: at Brigham and Women's Hospital, it has been used routinely for below-knee amputations, according to MIT News of July 10, 2025. As early as 2024, the MIT lab demonstrated that people with below-knee amputation had better control after this surgery than traditionally amputated individuals, though without the bone implant now additionally deployed. That AMI can enable faster walking and more natural obstacle avoidance was also already shown for below-knee amputations, according to MIT Technology Review. Conventional socket prostheses, in which the residual limb section sits in a shell, are often uncomfortable, can cause skin infections, and offer limited stability, as described in a review by ZME Science from July 14, 2025. The new study now extends the AMI approach to above-knee amputations and supplements it with bone anchoring.
Hurdles to possible approval and broader use
According to MIT Technology Review of October 21, 2025, the system first requires larger clinical trials to obtain FDA approval for commercial use; Herr estimates about five years for this. Second, according to Brinkmann, costs could be a barrier to broader use, as patients have already faced difficulties with insurance coverage for conventional prostheses. Third, according to Brinkmann's assessment, some patients may not be medically eligible for the procedure; according to Marasco, interested parties must also weigh for themselves whether the invasive procedure and adaptation time are worth the gain. For people with above-knee amputation, that means according to the 2025 reports: a system tested on a small scale that, according to the researchers, can provide more control and a stronger sense of body ownership; for FDA approval for commercial use, Herr estimated in October 2025 a timeframe of about five years.