A new bionic knee that connects directly to muscles and bones could improve movement and comfort for people with above-the-knee amputations, offering better performance than traditional prosthetics, according to research published in Science.
The advanced device attaches to the femur using a titanium rod and links to the nervous system through electrodes implanted in leg muscles. The system not only enhances physical function but also strengthens a user’s sense of control and ownership over the artificial limb, researchers said.
Surgical method reconnects key muscles
A team at the Massachusetts Institute of Technology led the study. Researchers combined two innovations: a surgical technique that reconnects opposing muscles, such as the hamstrings and quadriceps, and a direct connection between the prosthetic and the skeleton.
“A prosthesis that’s tissue-integrated—anchored to the bone and directly controlled by the nervous system—is not merely a lifeless, separate device,” said Hugh Herr, study co-author and professor at MIT. It becomes “a system that is carefully integrated into human physiology, offering a greater level of prosthetic embodiment.”
Herr, a double amputee, developed the surgical method with his team to improve how amputated limbs communicate with external devices. In typical amputations, opposing muscles are not rejoined, making it difficult for users to control prosthetics naturally.
The new approach restores that muscle pairing, allowing better signal transmission between the brain and the artificial limb.
The implant avoids socket-related problems
The bionic knee also avoids using traditional socket fittings, which are often uncomfortable and can cause skin infections. Instead, the implant anchors directly to the femur. This skeletal integration offers better load-bearing support and stability, researchers said.
“All parts work together to better get information into and out of the body and better interface mechanically with the device,” said Tony Shu, a biomechatronics researcher and co-author of the study. Shu researched while earning his graduate degree at MIT.
Participants show improved performance
To test the system, researchers studied three groups: two participants who received both the muscle-reconnection surgery and the bone implant, seven who had only the muscle surgery, and eight who had no interventions. All participants used the same powered prosthetic knee, but the connection methods varied.
The group with the full system consistently outperformed the others in mobility tests, including stair climbing, obstacle navigation, and controlled knee movements. These participants also reported a stronger sense of ownership—feeling the limb as part of their body—and a greater ability to control the device.
“No matter how sophisticated you make the AI systems of a robotic prosthesis, it’s still going to feel like a tool to the user,” Herr said. “But with this tissue-integrated approach, when you ask the human user what is their body, the more it’s integrated, the more they’re going to say the prosthesis is actually part of self.”
The device remains in the clinical trial phase
The bionic knee is not yet commercially available. Clinical trials for approval by the U.S. Food and Drug Administration could take up to five years.