Innovative Tissue-Integrated Bionic Knee Restores Natural Leg Movement

Researchers at the Massachusetts Institute of Technology (MIT) have developed a groundbreaking bionic knee system that seamlessly integrates with human tissue, offering a significantly more natural movement experience for individuals with above-the-knee amputations. Published in the journal Science, this advanced prosthesis enhances stability, control, and embodiment, allowing users to walk faster, climb stairs more easily, and navigate obstacles with higher precision.

Unlike traditional prosthetic devices that rely on residual limbs fitting into sockets, this new system establishes direct integration with the user's muscles and bone tissue. This direct engagement results in improved stability and allows for more intuitive control of limb movements. Clinical studies suggest that users experience a heightened sense of connection with their prosthesis, feeling more like the limb is an extension of their body rather than an external tool.

Professor Hugh Herr, co-director of MIT's Bionics Center, explained that by creating a prosthesis that is integrated into the body’s physiology, patients achieve a greater sense of embodiment. This integration involves a surgical technique called agonist-antagonist myoneuronal interface (AMI), which reconnects muscle pairs after amputation to restore dynamic muscle communication. This allows the nervous system to send more precise signals to control the prosthesis.

The research further pushes boundaries with the development of an implant called e-OPRA, a titanium rod inserted into the residual femur, which enhances mechanical stability and load-bearing capacity. The implant contains a network of wires connecting to electrodes on the AMI muscles, transmitting electrical signals to a custom robotic controller. This system accurately interprets muscle signals to produce smooth, natural movements.

In a recent clinical trial, participants with above-the-knee amputations used this system—referred to as an osseointegrated mechanoneural prosthesis (OMP). These users demonstrated improved performance in tasks such as knee bending, stair climbing, and obstacle crossing compared to traditional prostheses. Additionally, they reported increased feelings of control and belongingness to the prosthetic limb.

The study highlights the significance of body ownership and agency in prosthetic technology. Participants with the OMP system reported a stronger sense that the prosthesis was part of their body, indicating a profound psychological benefit alongside physical improvements.

The AMI surgical approach is now routinely performed for below-the-knee amputations at Brigham and Women’s Hospital. MIT researchers intend for the combined OMP system to undergo larger clinical trials to gain FDA approval, which is expected within approximately five years. The continuous development of such tissue-integrated prostheses promises a future where artificial limbs can be virtually indistinguishable from natural limbs in both function and sensation.