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A Better Way to Amputate

Here’s some big news from Hugh Herr’s Biomechatronics Group at the MIT Media Lab. According to research published this spring in the Proceedings of the National Academy of Sciences (PNAS), amputation surgery that preserves agonist-antagonist myoneural interfaces (AMIs) can increase amputees’ ability to control neuroprosthetic devices while decreasing their phantom limb pain. 

The MIT study compared 15 below-knee amputees whose limbs were removed via AMI surgery to a control group of patients who underwent conventional amputations. By maintaining the relationships between paired muscles in the residual limb, the AMI procedure keeps natural patterns of sensory communication in place. An analysis of brain-scan data published last December in Science Translational Medicine showed that AMI amputees received more sensory feedback from their residual limb than patients in the control group. 

“Our study shows that persons with an AMI amputation experience a greater phantom joint range of motion, a reduced level of pain, and an increased fidelity of prosthetic limb controllability,” says Herr, the PNAS paper’s senior author and a leading innovator in bionic technology. 

“The AMI patients’ ability to control these muscles was a lot more intuitive than those with typical amputations,” adds co-author Shriya Srinivasan. “Restoring the muscles to their normal physiology had benefits not only for prosthetic control, but also for their day-to-day mental well-being.”

The best news? The MIT team has developed a modified version of AMI surgery that can be performed retroactively on existing amputees. They’re also working on adapting the concept for above-knee and above-elbow amputees. “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.

Larger clinical trials lie ahead before AMI becomes widely available. Stay tuned for updates.

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