New advances in prosthetic devices are allowing people with artificial hands to tell when they’re holding something without even looking, and pluck a stem from a cherry without bursting it, two studies have shown.
Different groups in the U.S. and Europe reported key breakthroughs in connecting healthy nerves to a prosthesis, giving patients whose hands or arms have been amputated better control of the devices and, for the first time, returning at least some of the sensation of touch.
In one study, U.S. surgeons connected electrodes to nerves in a man’s forearm that were stimulated when someone placed something in his bionic hand. The procedure allowed the patient to tell when he was touching something without having to see it. In the other report, Swedish scientists surgically connected a titanium rod to existing bone, nerves and muscles in an undamaged part of the arm, then ran wires through the prosthesis helping the patient control its use more precisely.
“What is fascinating about this is the perception of touch actually occurs in the brain, not in the hand itself,” said Dustin Tyler, an associate professor of biomedical engineering at Case Western Research University in Cleveland, who led the U.S. effort. “Losing the limb is just losing the switch that turns that sensation on or off.”
Both results were reported yesterday in the journal Science Translational Medicine.
Igor Spetic, 48, said he vividly remembers the first time he felt his right hand again, two years after it was amputated following an industrial accident. Researchers working to craft his prosthetic pulled a curtain to limit his view and then placed a large, hard block into his palm.
“I hadn’t felt anything other than pain for two years,” he said by telephone. The new sense of feeling “was amazing. It felt like my hand was actually working, that I didn’t have a prosthetic. That’s how close to reality it was for me.”
The new hand allows Spetic to perform routine tasks in a laboratory without serious thought or concentration, he said, including picking up and drinking from a flimsy water bottle without squirting it all over or plucking stems from a cherry without bursting it.
There are currently 19 spots on the prosthetic that Spetic can feel. That’s likely to double or triple within a year, Tyler said in a telephone interview.
“The thing we like is that we can get that refined of sensation,” Tyler said. “There was skepticism before we did this work that we could get that kind of control. Now we know this has the potential for a true restoration of sensation for people when they are missing their hand.”
Spetic said the most unexpected benefit was the end of his phantom pain, which he often felt as if he was fiercely clenching his fist. “That was a bonus they didn’t anticipate,” he said.
When researchers vary the intensity, frequency and location of the stimulation, it allows Spetic to pick up the signals for different fabrics such as burlap and cotton, textures like sandpaper, and motion such as a pulse or water running across his hand. There remain several steps ahead.
For now, the sensors on his prosthetic arm are taped to the outside of the device, making it impossible to use at home. The researchers are working on an integrated system that would be sturdy enough for routine use. The sensors also can’t yet distinguish between textures, so Spetic only feels unique sensations beyond a tingling or pressure when the researchers deliver the stimulation.
The Swedish scientists, meanwhile, developed a fully integrated robotic arm. Their patient, identified only as Magnus, has used the device at home and work for the past year, even sleeping with it attached.
The tight connections allow Magnus, a truck driver, to have more precise, natural control over the arm. He can tie his children’s shoes, catch a ball out of the air and even crack an egg on command, according to their report in the journal. Using his old electric prosthesis, an egg or ball would fly out of his hand if he moved too quickly or extended his arm too far.
“The major contribution of our work is we have this interface that allows implanted electrodes to become clinically viable,” said Max Ortiz Catalan, a research scientist at Chalmers University of Technology in Gothenburg, Sweden. “Patients can take them home and use their prosthesis for their activities of daily living. We know it’s reliable and long-term,” he said in a telephone interview.
Ortiz Catalan is planning a larger study of the devices, currently used only for Magnus, next year. The Cleveland researchers already are working with another amputee and companies to try to devise a prosthetic that incorporates the sensors into the device itself.
(An earlier version of this story misspelled Spetic’s last name.)