Wed. Oct 27th, 2021


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In 2005, US Army Sergeant Jerry Majetich was seriously injured in a bomb and gun attack by insurgents in Iraq. Two colleagues who were traveling in the same vehicle were killed. He underwent more than 80 surgeries for serious burns, spinal fractures, internal injuries and limbs.

Last year, he presented himself as a pioneer surgeon: an experimental form of amputation that makes prosthesis replacements feel like part of the body. Majetich agreed to remove his hand, which had limited movement but gave him constant pain. A video posted by health news site Stat shows his replacement robot hand and fingers moving at will – with the pain largely gone.

The operation seems to restore proprioception, the feeling of knowing where our limbs are, even if we can not see them. The technique can change the way amputation has long been viewed: not as a last resort pulled from the body, but as an act of rejuvenation with the potential to restore a sense of completeness.

The research on the agonist-antagonistic myonal interface (AMI) operation was led by Hugh Herr and colleagues in the biomechatronics group at the MIT Media Lab in Cambridge, Massachusetts. While amputations traditionally involve simply cutting and clearing nerves and muscles, AMI surgery re-connects the muscle pairs that normally control joints. These pairs, like biceps and triceps, work in a push-pull way: when one contracts, the other stretches. It causes elbows and knees to bend, while the movements also provide sensory information to the brain so that they can keep track of what limbs are doing and where they are in space.

Patients with reconnected muscle pairs after leg amputations were better able to control their prosthetic limbs – and had less pain in the ghost. The latter was unexpected, but is now attributed to the brain being less confused by incoming signals.

Majetich was the first patient to undergo surgery on an upper limb, with his hand placed just above the wrist. He can now feel his individual fingers; as he tries to move each one, pulls the corresponding muscles in his arm visibly under the skin. The muscle activation is taken up by electrodes in the prosthetic hand and converted into motion.

It feels like a significant development in a branch of surgery that has been applied for thousands of years, but can still seem a bit rude, especially in contrast to advances in prosthetic technology and design. The earliest confirmed proof of amputation in Europe goes back to the Neolithic period: the remains of a male dated around 4800 BC, found near Paris in 2007, contain a partially healed severed bone.

Amputations later became a mainstay of military surgery. But the procedures were still very risky, as acknowledged by John Woodall, a naval surgeon from the East India Company. In his manual for seemedici from 1617, The Surgions Partner, Woodall advises to encourage the unhappy patient to ‘prepare his soul as a ready sacrifice to the Lord through sincere worshipers, longing for grace and help impartial. . . It is no small suspicion to deny the image of God. ”

AMI surgery joins several other refinements that promise to improve the outlook for amputees, according to Stephen Cruse, who lost both his legs in a car accident in 2008 and later founded the British charity Amputation Foundation. Oxenointegration allows replacement limbs to be surgically anchored to the bone so that the bone grows around it; purposeful muscle restoration shifts nerve points to the remaining muscle to allow for more intuitive control of prosthesis.

“AMI can be fantastic for amputees to be able to feel where they are in space, without having to stare at their limbs all the time,” says Cruse, who is fully active but suffers from intermittent ghost pain. The seam between man and machine becomes smoother; it can still become invisible.



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