A New Hope for Amputees: Nervous System-Driven Prosthesis
A groundbreaking prosthesis driven by the body’s nervous system now enables individuals with amputations to walk naturally. Researchers from MIT and Brigham and Women’s Hospital have developed a prosthetic leg that offers a natural gait by reconnecting muscles in the residual limb to receive proprioceptive feedback. This advancement promises to revolutionise mobility for amputees, improving their ability to navigate various terrains and perform daily activities with ease.
Restoring Natural Gait with a Neuroprosthetic Interface
Using a novel surgical intervention called the agonist-antagonist myoneural interface (AMI), the team successfully restored natural walking patterns in seven patients with below-the-knee amputations.
These individuals could walk faster, climb stairs, and avoid obstacles more naturally compared to those using traditional prostheses. “This is the first prosthetic study in history that shows a leg prosthesis under full neural modulation, where a biomimetic gait emerges,” says Hugh Herr, a senior author of the study.
Proprioceptive Feedback and Improved Control
Most limb movement is controlled by pairs of muscles that stretch and contract in opposition. During a traditional below-the-knee amputation, these muscle pairs are severed, disrupting the nervous system’s ability to accurately sense limb position and movement speed—critical information for coordinated movement. Without this sensory feedback, individuals with amputations often struggle to control their prosthetic limbs, relying instead on robotic sensors and predefined gait algorithms to guide movement.
The AMI procedure innovatively reconnects these muscle pairs within the residual limb, preserving their dynamic interactions. This reconnection allows patients to receive proprioceptive feedback, meaning they can sense where their prosthetic limb is in space and how it is moving. This feedback is crucial for adjusting their gait in real-time, enabling more natural and fluid movement.
In the study, patients with the AMI surgery demonstrated a significantly improved ability to sense and control their prosthetic limbs. They could feel the position and movement of their prosthetic legs, which allowed for more precise and adaptive control. This resulted in a smoother, more natural walking gait compared to those using traditional prosthetic technology. The ability to receive and respond to sensory feedback meant that AMI patients could navigate complex terrains and obstacles more effectively, enhancing their overall mobility and quality of life.
Comparative Study Shows Significant Improvements
The study involved seven patients who underwent the AMI surgery and seven who had traditional below-the-knee amputations. All participants were fitted with the same type of bionic limb, featuring a powered ankle and electrodes to sense electromyography (EMG) signals from key muscles. The results were striking: the AMI group performed significantly better in various walking tasks. They walked faster, navigated obstacles more easily, and climbed stairs with more natural movements compared to the control group.
In particular, the AMI group could point their toes upward while ascending stairs and better coordinate movements between their prosthetic and intact limbs. This coordination allowed them to push off the ground with the same amount of force as someone without an amputation, demonstrating a near-natural walking ability. The enhanced control and feedback from the AMI surgery translated into tangible improvements in everyday mobility, making it easier for patients to perform daily activities.
Less Pain, Less Muscle Atrophy
Patients who underwent the AMI surgery reported experiencing less pain and reduced muscle atrophy compared to those with traditional amputations. Traditional prostheses often lead to muscle atrophy due to disuse and lack of proper engagement. The AMI surgery, by reconnecting muscles in a physiological manner, allows patients to use their residual limb muscles more effectively. This not only preserves muscle mass but also improves overall limb health.
The procedure re-establishes the natural agonist-antagonist muscle dynamics, enabling patients to move their prosthetic limbs with physiological levels of proprioception and range of movement. This reduction in pain and muscle atrophy marks a significant improvement over traditional amputation methods, where patients struggle with discomfort and reduced muscle function. The improved muscle engagement and sensory feedback contribute to a more natural and effective use of the prosthetic limb, enhancing the overall quality of life for amputees.
Advancements in Sensory Feedback
The AMI procedure connects the ends of severed muscles in the residual limb to preserve their dynamic interaction. This innovative approach allows the nervous system to better sense limb position and movement speed, crucial for achieving a natural gait. Previous studies by Herr’s lab demonstrated that AMI patients could control their amputated limb muscles with greater precision, generating electrical signals similar to those from intact limbs.
The sensory feedback provided by the AMI surgery enables users to receive real-time information about their prosthetic limb’s position, which is vital for coordinated movement. This feedback allows patients to adjust their gait as needed, resulting in smoother and more natural walking patterns. By maintaining the natural muscle dynamics, the AMI procedure effectively integrates the prosthetic limb with the body’s own neural control mechanisms, significantly enhancing mobility and functionality for amputees.
Potential for Broad Application of the Nervous System-Driven Prosthesis
The current study focused on below-the-knee amputations. However, the AMI surgery has been performed on about 60 patients worldwide, including those with arm amputations. This broad applicability highlights the potential for this technology to benefit many amputees. By reconnecting muscle pairs and restoring natural proprioceptive feedback, the AMI procedure can improve mobility and quality of life for various types of limb loss.
The versatility of the AMI surgery means that it could be adapted to different amputation levels and limb types. It offers enhanced control and sensory feedback regardless of the specific prosthetic device used. This technology represents a significant step forward in prosthetic design. It moves beyond purely mechanical solutions to integrate the body’s own neural mechanisms for more effective and natural limb function.
The successful application of AMI in both leg and arm amputations demonstrates its potential to revolutionise prosthetic care. It provides a more holistic and integrated approach to limb loss rehabilitation.
Funding and Future Prospects
The research was funded by the MIT K. Lisa Yang Center for Bionics, the National Institute of Neurological Disorders and Stroke, and other organisations. It represents a significant leap towards integrating bionic limbs seamlessly with the human body. The successful demonstration of the AMI procedure’s benefits opens new avenues for future research and development.
Future studies aim to refine this technology further and explore its long-term benefits in everyday life for amputees. Researchers are particularly interested in understanding how continuous neural control of prosthetic limbs can improve users’ confidence. They also want to reduce cognitive load and enhance the feeling of the prosthetic as a part of the body. Additionally, they plan to investigate the potential for this technology to be applied to other types of prostheses. This includes upper-limb devices and more complex multijoint systems.
The ultimate goal of Herr’s lab is to develop prosthetic solutions that “rebuild human bodies” by fully integrating with the user’s nervous system. This approach moves away from reliance on sophisticated robotic controllers and sensors. Instead, it focuses on a more natural and intuitive use of prosthetic limbs. As the technology advances, it promises to transform prosthetic care. It will significantly improve the quality of life for amputees worldwide.
References
- A prosthesis driven by the nervous system helps people with amputation walk naturally. (2024, July 24). ScienceDaily. https://www.sciencedaily.com/releases/2024/07/240701162227.htm
- Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., Song, H., & Song, H. (2024). Continuous neural control of a bionic limb restores biomimetic gait after amputation. Nature Medicine. https://doi.org/10.1038/s41591-024-02994-9
