An innovative prosthetic system that mixes with muscle and bone may transform how amputees move and feel.

By Vraj Parikh | July 15, 2025

In a significant advancement that could change the landscape of prosthetic technology, researchers at MIT have introduced a novel bionic knee system that transcends traditional replacement limbs it integrates with the body. 

Unlike typical prosthetics that depend on uncomfortable sockets, this new design directly anchors into the bone and connects to surrounding muscles. The outcome? Amputees experience a more natural walking motion, are able to climb stairs effortlessly, and feel as if the prosthetic truly belongs to them.

“Rather than being a separate tool, this functions as an extension of the body,” stated Professor Hugh Herr, the leading author of the research and co-director of the K. Lisa Yang Center for Bionics. “It serves as a living link between human physiology and robotics.”

Transforming Muscle Signals into Fluid Motion

The innovation is a surgical method referred to as the agonist-antagonist myoneural interface (AMI), developed by Herr’s research team. Typically, amputation disrupts muscle pairs that collaboratively facilitate limb movement, complicating the nervous system’s ability to control a prosthetic. The AMI procedure reconnects these muscle pairs, restoring natural coordination and enabling the body to produce more precise movement signals.

The prosthetic system also incorporates a titanium rod implanted in the thigh bone, which is part of a technology known as e-OPRA. This rod secures the prosthetic leg more effectively and contains wires that capture signals from the AMI muscles within the body. These signals are interpreted by a robotic controller that understands the user’s intentions whether to walk, turn, or ascend stairs and adjusts the prosthetic movements accordingly.

Evaluated and Confirmed

In a limited clinical trial, two patients received both the AMI surgical procedure and the e-OPRA implant, resulting in what the researchers label an osseointegrated mechanoneural prosthesis (OMP). They were compared to eight participants who underwent only AMI and seven who had neither technology.

The findings were evident: users of the OMP performed considerably better on tasks such as bending the knee to designated angles, stepping over obstacles, and climbing stairs. Furthermore, they reported a significantly heightened sense of embodiment the perception that the prosthetic was an integral part of their body.

“This represents our closest approach to fusing machine and human elements,” noted Tony Shu PhD ’24, the lead author of the study published in Science.

Envisioning the Future of Prosthetics

For many amputees, a major obstacle isn’t solely physical movement it’s the psychological disconnection from their prosthetic limb. The research tackled this issue by querying patients about whether they perceived the prosthesis as part of their body, if it felt like they possessed two legs, and whether they felt in command. The two OMP users showed improvement in these indicators over time.

“This type of embodiment cannot be realized through AI alone,” Herr pointed out. “It necessitates a physical, neural, and mechanical integration.”

The AMI technique is currently being implemented for below-the-knee amputations at Brigham and Women’s Hospital, and Herr anticipates that it will soon become standard for above-the-knee cases as well. The complete OMP system still requires more extensive clinical trials before it can receive approval for broader application a process Herr estimates could take up to five years.

The research was funded by the Yang Tan Collective and DARPA, underscoring MIT’s commitment to enhancing lives through engineering and biomedical improvments.