Bionic leg makes walking quicker and easier for amputees, trial shows

Patients reported less pain and less muscle atrophy following the pioneering surgery required for control of the bionic leg. Photograph: Herr Nature Medicine

A brain-controlled bionic leg has allowed people with amputations to walk more quickly and navigate stairs and obstacles more easily in a groundbreaking trial.

The device allows the wearer to flex, point and rotate the foot of the prosthetic using their thoughts alone. This led to a more natural gait, improved stability on stairs and uneven terrain and a 41% increase in speed compared with a traditional prosthetic. The bionic leg works by reading activity in the patient’s residual 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’s nervous system is controlling the movement, not a robotic 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’ll be able to go hiking or dancing because they’ll have full control over their movement,” he added.

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

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

In the trial, published in Nature Medicine, seven patients were given the bionic leg and compared with seven patients with traditional amputations. Patients reported less pain and less muscle atrophy following 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 not controlled by the brain, patients view it as a tool, like a carpenter would view their hammer,” said Herr. “When the person can directly control and feel the movement of the prosthesis it becomes truly part of the person’s anatomy. That can be quite emotional for the subjects that undergo 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 flex and point the foot and tilt the foot side to side.

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

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

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

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

The MIT team hopes a commercial version of the leg will be available within five years so more patients can benefit. “It’s going to lead to a step-change in clinical care for so many patients around the world,” said Herr. “We’re very passionate about getting this technology out to the patients who need it.”