For many amputees, prosthetic legs offer a crucial opportunity to regain mobility, but traditional prosthetics often feel cumbersome and unnatural. However, researchers at MIT have developed a brain-controlled bionic leg that promises a more natural walking experience for amputees.
Hugh Herr, co-director of the K. Lisa Yang Center for Bionics at MIT and senior author of the study, emphasized the breakthrough nature of this technology. “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,” Herr stated.
The foundation of this bionic leg technology is a new surgical technique known as agonist-antagonist myoneural interface (AMI). This below-the-knee amputation surgery preserves and reconnects nerves and muscles in the residual limb, maintaining the natural communication between muscles and the nervous system. Typically, amputation surgery severs the connections between muscle pairs (agonists and antagonists) that normally work together, disrupting their natural interaction.
AMI surgery, however, reconnects these muscle pairs in the residual limb. Rejoined muscles send signals that help the bionic leg determine the user’s intended movements for the prosthetic foot, such as flexing, pointing, and rotating.
“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,” Herr elaborated.
After the AMI surgery, the neuroprosthetic interface comes into play. This interface uses electrodes on the residual limb to detect and monitor muscle contractions. Beyond simply recording muscle activity, it employs an advanced algorithm to decode these contractions and translate them into the intended movements of the prosthetic foot. During the study, participants received a bionic leg with an electrically powered ankle joint, which picked up signals from the gastrocnemius muscles responsible for foot flexion and extension. These signals were fed into a robotic controller that determined the optimal ankle movement based on factors such as bend angle, torque, and power supply.
The benefits of AMI surgery were apparent in a study involving seven patients, who reported decreased pain and minimal muscle atrophy post-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 now focusing on making this technology more widely available, aiming to have a commercial version of the bionic leg ready within five years.
The findings of this study were published in the journal Nature Medicine.