The key to this bionic leg technology is a new surgical technique called agonist-antagonist myoneural interface (AMI).
A person wears a prosthetic leg while walking up stairs.
For many amputees, prosthetic legs offer a chance to regain mobility. But traditional prosthetics can feel clunky and unnatural.
Now, MIT researchers have tested a novel prosthesis that provides amputees with a more natural walking experience.
This brain-controlled bionic leg allows wearers to control the prosthetic foot using their thoughts alone. The study demonstrated the participants’ ability to walk more naturally, handle stairs, and easily maneuver around barriers.
“No one has been able to show this level of brain control that produces a natural gait, where the human’s nervous system is controlling the movement, not a robotic control algorithm,” said Hugh Herr, a co-director of the K. Lisa Yang Center for Bionics at MIT, and the senior author of the new study.
The key to this bionic leg technology is a new surgical technique called agonist-antagonist myoneural interface (AMI). This below-the-knee amputation surgery preserves and reconnects nerves and muscles in the residual limb.
Typically, amputation surgery severs the connections between muscles (agonists and antagonists) that normally work together. This disrupts the natural communication between these muscles and the nervous system.
AMI surgery reconnects the agonist and antagonist muscle pairs in the residual limb. The signals from rejoined muscles assist the bionic leg in determining how the user desires to use the prosthetic foot (flex, point, rotate).
“With the AMI amputation procedure, to the greatest extent possible, we attempt to connect native agonists to native antagonists in a physiological way so that after amputation, a person can move their full phantom limb with physiologic levels of proprioception and range of movement,” explained Herr.
The neuroprosthetic interface comes into action after the AMI surgery reconnects the muscles. It uses electrodes on the residual limb to detect and monitor these muscle contractions.
The interface doesn’t simply record muscle activity. It has an advanced algorithm that acts like a decoder. It analyzes the specific patterns of muscle contractions and translates them into the intended movements for the prosthetic foot.
For the study, all participants received a bionic leg with an electrically powered ankle joint. This usually picks signals from the gastrocnemius muscles, which control foot flexion and extension. The signals were then fed into a robotic controller, which determined the optimal ankle movement depending on variables such as bend angle, torque, and power supply.
As per the press release, the benefits of AMI surgery were evident in a study with seven patients. Moreover, they reported reduced pain and minimal muscle atrophy after surgery.
“This work represents yet another step in us demonstrating what is possible in terms of restoring function in patients who suffer from severe limb injury. It is through collaborative efforts such as this that we are able to make transformational progress in patient care,” said Matthew Carty, a surgeon at Brigham and Women’s Hospital and associate professor at Harvard Medical School.
MIT researchers are working to make this technology more widely available. They hope to have a commercial version of the bionic leg within five years.
The findings were published in the journal Nature Medicine.
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Mrigakshi Dixit Mrigakshi is a science journalist who enjoys writing about space exploration, biology, and technological innovations. Her professional experience encompasses both broadcast and digital media, enabling her to learn a variety of storytelling formats. Her work has been featured in well-known publications including Nature India, Supercluster, and Astronomy magazine. If you have pitches in mind, please do not hesitate to email her.
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