Most amputations cut pairs of muscles that control joints such as the elbow or ankle, disrupting sensory feedback about the limb’s position in space that would help patients control a prosthesis. But a surgical technique developed by researchers at MIT appears to give amputees both better control and less pain than people who have had conventional amputations.
In myoneural agonist-antagonist (MAI) surgery, which the Biomechatronics group led by Hugh Herr, SM ’93, at the MIT Media Lab invented a few years ago, the two ends of the muscle are reconnected so that they always communicate in the residual limb: when one of the two contracts, the other stretches, sending the familiar signals to the brain.
A study published in February on 15 patients with AMI amputations below the knee, found that they could control their muscles more precisely than patients with traditional amputations. Unexpectedly, AMI patients also reported feeling more freedom of movement and less pain in their affected limb.
“It became increasingly clear that restoring muscles to their normal physiology had benefits not only for prosthetic control, but also for their day-to-day mental well-being,” says Shriya Srinivasan, PhD ’20, postdoc at MIT and lead author of the study.
Researchers have also developed a technique to reconnect muscle pairs in people who have had a traditional amputation. They are working on developing the AMI procedure for amputations at other points, including above the knee and above and below the elbow, and measuring whether the benefits translate into better control of a prosthetic leg while walking.
“We’re learning that this technique of rewiring the limb and using spare parts to rebuild that limb works and applies to various parts of the body,” Herr says.