A trial testing a brain-controlled bionic leg has shown that it allows people with amputations to walk faster and navigate stairs and obstacles more easily.
The device allows the person wearing it to move the foot of the prosthetic by simply thinking about it. This results in a more natural walking pattern, better stability on stairs and uneven ground, and a 41% increase in speed compared to a traditional prosthetic.
The bionic leg operates by reading the activity in the patient’s remaining leg muscles and using these signals to control an electronically powered ankle.
Prof Hugh Herr, a co-director of the K Lisa Yang Center for Bionics at Massachusetts Institute of Technology (MIT) and the study’s senior author, stated that no one has been able to demonstrate this level of brain control that produces a natural gait. In this case, the human nervous system controls the movement, not a robotic control algorithm.
“They will not only be able to walk on a flat surface, but they’ll also be able to go hiking or dancing because they’ll have full control over their movement,” he said.
Herr is a double amputee. He lost both legs due to severe frostbite during a rock climbing trip in 1982. Despite the amputations being done decades ago, he hopes to have revision surgery in the future to benefit from a pair of bionic legs.
“I plan to have both legs done in the coming years,” he said.
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In a study published in Nature Medicine, seven patients received a bionic leg. They were compared to seven patients with traditional amputations.
Patients who underwent the groundbreaking surgery for the bionic leg experienced reduced pain and muscle atrophy. This surgery preserves natural connections between leg muscles. As a result, patients also felt that their prosthetic limb was a more integrated part of their body.
“When a prosthesis is not controlled by the brain, patients see it as a tool, like a carpenter sees their hammer,” explained Herr.
“When a person can directly control and feel the movement of the prosthesis, it truly becomes a part of their anatomy. This can be a very emotional experience for the individuals who undergo this procedure.”
The device needs patients to have a new type of amputation surgery below the knee, known as agonist-antagonist myoneural interface (AMI).
The surgery is intended to save two pairs of muscle connections. In a healthy leg, these muscles are used for flexing and pointing the foot and tilting the foot from side to side.
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In AMI surgery, the residual muscles are reconnected instead of completely severing the connections. This allows the patient’s muscle contractions to be monitored and translated into movements of the electrically powered ankle, even though the patient’s leg is gone.
The surgery can be done when the limb is first removed, or the muscles can be reconnected later to improve the amputation.
Dr Sigrid Dupan, a prosthetics expert at University College Dublin who was not part of the study, finds it exciting to see advancements in prosthetics that leverage the body and brain’s natural abilities instead of relying on increasingly complex technology.
She said, “The study’s results for walking speed are impressive, but I believe the impact of how people cope with differences in terrain will be more significant in their lives.”
“I’m eager to see how this research progresses and would like to see this surgical approach used more widely.”
The MIT team expects a commercial leg version to be available within five years so more patients can benefit. Herr said, “It will significantly improve clinical care for many patients worldwide. We are very dedicated to making this technology available to patients who need it.”
