Most amputations sever the muscle pairs that control joints such as the elbow or ankle, disrupting the sensory feedback about the limb’s position in space that would help patients control a prosthesis. But a surgical technique developed by MIT researchers appears to leave amputees with both greater control and less pain than people who have had conventional amputations.
In agonist-antagonist myoneural interface (AMI) 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 still communicate within the residual limb: when one of the pair contracts, the other stretches, sending the familiar signals to the brain.
A study published in February of 15 patients who had AMI amputations performed below the knee found that they could control their muscles more precisely than patients with traditional amputations. Unexpectedly, the AMI patients also reported feeling more freedom of movement and less pain in their affected limb.
“It became increasingly apparent that restoring the 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, an MIT postdoc and lead author of the study.
The researchers have also developed a technique to reconnect the 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 to better control of a prosthetic leg while walking.
“We’re learning that this technique of rewiring the limb, and using spare parts to reconstruct that limb, is working, and it’s applicable to various parts of the body,” Herr says.