A brain-controlled bionic leg has allowed amputees to walk faster and navigate stairs and obstacles more easily in a ground-breaking trial.
The device allows the user to bend, straighten and rotate the prosthetic leg using only their thoughts. This led to a more natural gait, improved stability on stairs and uneven terrain, and a 41% increase in speed compared to a traditional prosthesis. The bionic leg works by reading activity in the patient’s remaining leg muscles and uses these signals to control an ankle with electricity.
“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 robotic control algorithm,” said Prof Hugh Herr, a co-director of K Lisa Yang. Center for Bionics at the Massachusetts Institute of Technology (MIT) and senior author of the study.
“Not only will they be able to walk on a flat surface, but they will be able to 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 storm during a rock-climbing trip in 1982. Despite having his original amputations decades ago, he hopes to have a revision surgery to benefit from a pair of similar bionic legs in the future.
“I’m thinking of doing this for both my legs in the next few years,” he said.
In the test, published in Nature Medicine, seven patients were given bionic legs and compared with seven patients with traditional amputations. Patients reported less pain and less muscle atrophy after the pioneering surgery required for the bionic foot control, which preserves the natural connections between the leg muscles. 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 look at it as a tool, the way a carpenter would look at their hammer,” said Herr. “When the person can directly control and feel the movement of the prosthesis, it really becomes part of the anatomy of the person. This 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 ligaments, which, in a healthy leg, are used to bend and straighten the leg and to tilt the leg to the side.
During a conventional amputation these connections are severed, but in AMI surgery the remaining muscles are reattached. This means that even though the patient’s own leg is gone, their muscle contractions can be monitored and translated using an algorithm into electrically powered ankle movements.
The surgery may be done during a primary amputation, or the muscles may 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 a breakthrough in prosthetics that taps into the natural abilities of the body and brain rather than increasingly complex technology.
“The study shows impressive results for walking speed, but I think the results related to how people are able to cope with changes in terrain will have a more profound impact on people’s lives,” she said. “I look forward to seeing how this research develops and would like to see a wider application of this surgical approach.”
The MIT team hopes that a commercial version of the leg will be available within five years so that more patients can benefit. “It will lead to a step change in clinical care for so many patients around the world,” Herr said. “We are very passionate about getting this technology out to the patients who need it.”