Why true bionic limbs are out of reach . . . for nowS

Researchers continue to make remarkable headway on the path to developing next-generation prosthetic limbs, but when you get right down to it, there's still a monumental gap separating us from a truly bionic replacement for arms and legs.

Such an appendage would be capable of responding to mental commands with grace and fluidity, handling objects with incredible precision, and transmitting complex sensory information back to the brain; and while significant progress has certainly been made on these and other fronts, researchers say we still have quite a ways to go. And yet, according to this recently published feature by Wired's Michael Chorost (who is part machine, himself — he's deaf, but hears with two cochlear implants), the general outlook among researchers is one of "stubborn hopefulness"; a true bionic limb may be out of reach today, but it is definitely an achievable goal.

We've included the introduction to Chorost's feature on the present status of bionic limb research here. It's definitely an in-depth read, but trust us when we say this is a piece you'll be happy you set aside the time for.

Chorost begins:

On the night of November 1, 2008, Iraqi insurgents lobbed two RKG-3 armor-piercing hand grenades at an up-armored Humvee in Baghdad. The first grenade, a dud, bounced off the passenger-side door. But the second one detonated, sending a jet of molten copper through the door and through the right elbow of Sergeant First Class Glen Lehman. The liquid metal continued across Lehman's lap, burning his right thigh, and then sluiced across his left forearm.

The platoon medic was in the Humvee, too, but he couldn't extract Lehman through the shattered door. So the medic started treatment in the truck, in the dark, amid a mess of blood and smoke and debris, wriggling around Lehman's 6'4″ frame. Twenty minutes later Lehman was at a field hospital. Transferred by helicopter to Joint Base Balad, 40 miles north, Lehman received almost seven pints of blood, more than half his body's volume. Doctors in Germany had to amputate what remained of Lehman's right arm above the elbow and then transferred him to Walter Reed Army Medical Center in Washington, DC. The aftermath of all that surgery was excruciating. "Everybody asks, what was it like?" Lehman says. "The best answer I have is that it was like having your hand slammed in a car door continuously."

Usually a veteran like Lehman would get a prosthetic arm, and life, with luck, would go on. But Lehman's stump was the right shape for an experimental surgery called targeted muscle reinnervation. He was game to try it, in return for access to a remarkable new prosthetic arm.

Lehman's surgeons delicately pulled apart the nerves in his arm that would ordinarily control his elbow and hand and moved them. His distal radial nerve, which controls opening the hand, went to the lateral head of his triceps. His median nerve, which controls closing the hand, went to the medial head of the biceps.

It's a weird surgery with weird effects; Lehman's skin ripples when he thinks about moving his missing right arm, a physical reminder of the signals his brain is sending. When he tries to close his hand, his biceps contracts. The rerouted nerves are supposed to improve control of a new prosthesis, one that uses a computer to read the myoelectric impulses that are produced by the tiny neural zaps inside muscles. In short, when Lehman is wearing the new arm, he is a cyborg. But being a cyborg has not turned out the way science fiction promised.

Continue reading over on Wired.

Top photo by Andres Serrano via Wired