New Surgery Helps Preserve Better Control And Feeling After Amputation – Forbes

Silhouette of amputee man with prosthetic leg on bridge with sunset sky
Researchers at the Massachusetts Institute of Technology have made major headway towards helping people with amputations retain a richer awareness over their residual limb. This restored sense of awareness should make it easier for amputees to use artificial limbs, allowing them to more fully feel like an extension of their body. 
Published in Science Translational Medicine, the report by Shriya Srinivasan et al. discusses a novel amputation technique that successfully preserves the muscle dynamics we rely on for an understanding of where our bodies are. 
Close your eyes and touch the tips of your two index fingers together. Did you manage? Probably. This is because we have a kind of intuitive awareness, known as proprioception, of where our bodies and our limbs are in space. When we move a certain body part, we know where it is in relation to the rest of our body, we know how quickly it’s moving, and we know what direction it’s moving in. 
For many amputees, however, the loss of a limb is accompanied by a loss of proprioception. They may maintain a “phantom awareness,” the feeling that a missing limb is still attached, but generally this awareness is unwieldy and doesn’t extend onto their artificial limb. In practice, people who have had an amputation often end up needing to rely on sight in order to gather information about the location of their artificial limb. 
Even with the latest technology, which allows artificial limbs to be controlled via thought, amputees still can’t feel the exact location or speed when they move them. Thinking can bring about movement in the bionic limb, but movement in the bionic limb doesn’t return any direct sensory feedback.
A big reason for this diminished awareness is the way that traditional amputation methods break the dynamic relationship between muscles. 
Take a moment to focus your attention onto your ankle. First, flex your ankle so that your toes point towards your knee. Notice how you feel a tightness in the front of the shin, that’s your shin muscles contracting. Next, extend your ankle so that your foot, and toes, point away from you. Notice again a kind of tightness, this time at the back of your leg, that’s your calf muscles contracting. The shin muscles and the calf muscles work together dynamically; when the one set of muscles contracts, the other set stretches, and vice versa. 
It is these kinds of muscular contractions and relaxations that let us know where a particular limb is, even when we’re not actively looking or thinking about it. Unfortunately, it is also these exact cues that are lost after traditional amputations. 
First implemented back in 2018, the Biomechatronics group at MIT developed a surgical technique that keeps the aforementioned muscle dynamics intact. During amputation, the surgeon directly connects the oppositional muscles, like those of the calf and the shin, to each other. In so doing, they reestablish the muscle dynamics needed for a sense of proprioception, giving amputees a much fuller awareness of their residual and “phantom” limbs. 

“Amputation architecture and efferent-afferent signaling mechanism.” SCIENCE TRANSLATIONAL MEDICINE, SRINIVASAN, S. ET AL. 
When looking at brain scans of amputees who underwent this new operation, called agonist-antagonist myoneural interface (AMI) amputation, Shriya Srinivasan et al. found that the area of the brain in charge of proprioception was a lot more active than in those who had undergone a traditional amputation. In fact, AMI amputees had similar levels of activation as those individuals with no amputation of any kind. 
This difference in brain activity was reflected in practice. When asked to move their phantom joint to specific locations, up and to the left, for example, AMI amputees displayed greater control and accuracy than did traditional amputees. 
“Both our study and previous studies show that the better patients can dynamically move their muscles, the more control they’re going to have. The better a person can actuate muscles that move their phantom ankle, for example, the better they’re actually able to use their prostheses,” says Shriya Srinivasan.

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