July 13, 2024

A brain-controlled bionic leg has enabled people with amputations to walk faster and navigate stairs and obstacles more easily in a ground-breaking trial.

The device allows the wearer to bend, point and rotate the foot of the prosthetic using their thoughts alone. This resulted in a more natural gait, improved stability on stairs and uneven terrain and a 41% increase in speed compared to a traditional prosthetic. The bionic leg works by reading activity in the patient’s remaining leg muscles and uses these signals to control an electrically powered ankle.

“No one has been able to show this level of brain control that produces a natural gait, where the human nervous system controls the movement, not a robot control algorithm,” said Prof Hugh Herr, a co-director of the K Lisa Yang. Center for Bionics at Massachusetts Institute of Technology (MIT) and the senior author of the study.

“Not only will they be able to walk on a flat surface, but they will be able to go for a walk or dance because they will have full control over their movement,” he added.

Herr is a double amputee himself, having lost both legs to severe frostbite after being caught in a blizzard during a rock-climbing trip in 1982. Despite his original amputations decades ago, he hopes to have revision surgery to benefit from a pair of similar bionic legs in the future.

“I’m thinking about doing it for both my legs in the coming years,” he said.

In the trial, published in Naturopathy, seven patients were given the bionic leg and compared with seven patients with traditional amputations. Patients reported less pain and less muscle atrophy after the pioneering surgery required for control of the bionic leg, which preserves natural connections between leg muscles. The patients were also more likely to feel that their prosthetic limb was part of their body.

“[With] a prosthesis that is not controlled by the brain, patients see it as a tool, as a carpenter would see their hammer,” said Mr. “When the person can directly control and feel the movement of the prosthesis, it truly becomes part of the person’s anatomy. It can be quite emotional for the subjects undergoing this procedure.”

The device requires patients to undergo a new form of below-the-knee amputation surgery called agonist-antagonist myoneural interface (AMI). The surgery aims to preserve two pairs of muscle connections, which in a healthy leg are used to bend and point the foot and tilt the foot from side to side.

During a conventional amputation, these connections are severed, but in AMI surgery, the remaining muscles are reconnected. This means even if the patient’s own leg is gone, their muscle contractions can be monitored and translated into movements of the electrically powered ankle with the help of an algorithm.

The surgery can be done during a primary amputation, or the muscles can be reattached after the initial amputation as part of a revision procedure.

Dr Sigrid Dupan, an expert in prosthetics at University College Dublin, who was not involved in the study, said it was exciting to see an advance in prosthetics that uses inherent capabilities of the body and brain rather than increasing complex technology.

“The study shows impressive results for walking speed, but I think the results related to how people are able to handle differences in terrain will have a bigger impact on people’s lives,” she said. “I look forward to seeing how this research develops, and would like to see a broader implementation of this surgical approach.”

The MIT team hopes that a commercial version of the bone will be available within five years so that more patients can benefit. “This is going to lead to a step change in clinical care for so many patients around the world,” said Mr. “We are very passionate about bringing this technology to the patients who need it.”

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