Three men with severe nerve damage have voluntarily had their hands amputated and replaced with prothetic versions that they're able to control with their minds.

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The procedure—performed by Oskar Aszmann at the Medical University of Vienna, Austria, and now published in The Lancet—has been called "bionic reconstruction." Each of the patients involved has suffered damage to the brachial plexus, a bundle of nerves between the spine and hand. They had all undergone surgery to try and repair the damage—in each there are still some nerves remaining, just not many—but their hands had remained paralyzed.

Instead, they volunteered to try Aszmann's alternative. Prior to any surgery, their bodies and brains were 'trained,' reports New Scientist. A section of leg muscle was transplanted into their arms, intended to amplify the small signal sent through the few existing nerves. That was left for three months for the nerves to grow into the muscle, and then the patients began to practice controlling the muscle—first using an armband to detect activity, then using the signal to control a virtual arm.

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Then came the big moment: Aszmann amputated their hands and replaced them with a prosthesis. The new bionic hand is independently powered, so it only require small nervous input signals from the grafted muscle to control it, unlike a real hand. And it's worked, as you can see inn the video above: each patient can now pick up a ball, pour from a jug and do up clothes fasteners. That's more than each was able to do before the operation. Their general limb control improved, too.

There are other approaches to bionic control of hands and arms—some of which use direct brain activity to control them. But this particular case is special because of the fact that the patients chose to have their hands amputated. While that was no doubt a big decision for those involved, it also makes it easier for the doctors: unlike a patient who long since lost their hand, it allows them to plan exactly where and how cuts should be made, providing the best possible fit and control for the device.

Still, there are features that the prosthetic hand can't yet deliver—in particular a sense of touch. Delivering signals to sensory fibres is a rather more complex problem—though not impossible to solve—with the vast majority of of nerves in the hand being related to touch not motion. But it's one that, unsurprisingly, Aszmann and his team is working on. [The Lancet]