On July 10, 2025, a team led by principal 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 limb sits on an implant anchored surgically in bone and controlled by signals from surgically reconnected muscles. The researchers call the complete system an osseointegrated mechanoneural prosthesis, or OMP.
In the study, two individuals received the combined system of muscle surgery and bone implant, eight had the muscle surgery without the implant, and seven had neither. All tested the same motorized knee prosthesis developed by the laboratory. How this control works in detail emerges from examining the underlying surgical method.
How muscles control the prosthesis and the bone implant provides support
In a typical amputation, muscle pairs that normally stretch and contract alternately are severed, leaving the nervous system with limited ability to sense how the affected muscle moves. The procedure developed by Herr and colleagues, called Agonist-Antagonist Myoneural Interface or AMI, reconnects these muscle pairs during surgery so they communicate again in the residual limb and provide electrical signals to control the prosthesis. For above-knee amputations, researchers supplemented this procedure with a titanium rod in the remaining thighbone, which according to their findings provides better mechanical control and load distribution than a conventional socket prosthesis. The implant contains 16 wires that pick up signals from electrodes on the AMI muscles and relay them to custom-developed robotic control that calculates the necessary torque for the desired knee movement.
Measurements included whether participants could bend the knee to a specified angle, how they climbed stairs, and how they navigated obstacles. On most of these tasks, the two users of the combined system outperformed the eight individuals with muscle surgery without bone implant and significantly outperformed users of conventional prostheses. Additionally, 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 individuals with the combined system reported substantially greater increases in this sense of control and bodily integration throughout the study compared to other participants.
What researchers and others say about the results
Hugh Herr describes a bone-anchored and directly nervous-system-controlled prosthesis as an "integral part of self," not merely a tool the person uses. Principal author Tony Shu explained to Smithsonian that part of the tissue-integrated prosthesis can only be removed through additional 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. Orthopedic technician John Brinkmann of Northwestern University's Feinberg School of Medicine, not involved in the study, valued the results as progress in integrating a device with the patient. He also warned that cost could be a significant barrier to broader use, as patients have faced problems with insurance coverage for conventional prostheses. Some patients may not be medically eligible for the procedure.
In context: what earlier tests with the procedure showed
The AMI procedure itself is not new. It has been routinely applied at Brigham and Women's Hospital for below-knee amputations. In 2024, MIT's laboratory demonstrated that people with below-knee amputation using this procedure had better control than traditionally amputated individuals, though without the bone implant now additionally employed. That AMI can enable faster walking and more natural obstacle negotiation was already shown for below-knee amputations. Conventional socket prostheses, in which the residual limb section sits in a shell, are often uncomfortable, can cause skin infections, and offer limited stability. The new study extends the AMI approach to above-knee amputations and supplements it with bone anchoring.
Hurdles to potential FDA approval and broader use
According to MIT Technology Review of October 21, 2025, the system first needs larger clinical trials to obtain FDA approval for commercial use. Herr estimates about five years for this. Cost could be a barrier to broader use, as patients have experienced difficulties with insurance coverage for conventional prostheses. Some patients may not be medically eligible for the procedure. Interested individuals must also weigh whether the invasive intervention and adjustment period justify the gain. For people with above-knee amputation, the current state in 2025 means a small-scale tested system that, according to researchers, can provide greater control and a stronger sense of embodiment. Herr estimated in October 2025 that FDA approval for commercial use would take about five years.