Mind-controlled prosthetic arm enables patients to feel the objects they grip
When electrician Rickard Normark lost his left arm after being electrocuted at work in 2011, he thought he had no other option than to endure the pain and discomfort of a conventional prosthesis. It would often slip off during his daily activities, and he scratched the irritated skin under the socket so much with his healthy hand that it began to lose sensation.
Then three years ago, Normark received a new kind of brain-controlled prosthetic that was surgically attached to the bone, muscles, and nerves of his upper arm, allowing him to not only grip objects intuitively with his hand but feel the sensation of touching them.
“You cannot even compare how things have changed for me,” Normark, 47, told STAT from his home in Sweden. “The socket prosthesis I previously had is a tool you can use for help in your daily life, but this … this is a part of you.”
This advanced prosthetic, described in a paper published Wednesday in the New England Journal of Medicine, represents an advance over other mind-controlled prosthetic limbs under development, the researchers said.
For one, all electronics are contained within the prosthesis, which removes the need for external equipment, such as wires, electrodes, or batteries. The prosthetic hand is controlled using electrodes implanted in the muscles of the upper arm, to which nerves involved in opening and closing the hand have been rerouted. Second, force sensors embedded in the thumb of the hand provide sensory feedback while grasping objects. Those signals are relayed through wires connected to nerves in the upper arm, and then to the brain, where they are perceived as pressure against the hand.
The scientists report on four Swedish patients who have lived with this new technology for between three and seven years. Normark is one of them. He’s been able to race and repair cars with the improved hand control afforded by the new prosthesis. The others reported being able to canoe, ice-fish, and ride a snowmobile.
“All patients reported having greater trust in their prosthesis since the intervention, referred to it as being part of themselves, and reported positive effects on their self-esteem, self-image, and social relations,” the authors wrote.
The implant system, called e-OPRA, was created by Integrum AB, a Swedish company that was the first to provide bone-anchored prostheses. Called osseointegration, this method anchors the prosthesis to the skeleton in the portion of the arm that remains after amputation, which allows for greater freedom of movement that feels more natural.
The device used in the four patients includes an embedded control system, developed by the researchers, which is small enough to fit inside the prosthesis but has the capability to process nerve signals, using artificial intelligence algorithms, and turning them into control signals for the prosthetic hand’s movements.
“We have focused on developing a prosthetic device which is reliable to be used every single day because 99% of the time, patients are unable to use them [conventional socket prostheses] reliably. … They go home and remove them because of how uncomfortable they are,” said lead author Max Ortiz-Catalan, an associate professor at Sweden’s Chalmers University of Technology, who developed the prostheses in collaboration with researchers at Gothenburg University, the Medical University of Vienna, and the Massachusetts Institute of Technology. He has worked as a consultant for Integrum.
Ortiz-Catalan said their device operates with much more precision than a conventional prosthetic hand. This makes it reliable, safe, and stable in the long term, he said.
“It is really wonderful that this group of researchers have worked on safely getting signals out of the nerves in the amputated limb,” said Cynthia Chestek, an associate professor of biomedical engineering at the University of Michigan whose research team reported last month on a way to capture signals from nerves in the arm to guide fine movements of a prosthetic hand. She was not involved in the new study.
Unlike technologies like pacemakers, she said, the Swedish scientists “have gotten around having any active electronics in the body, which clearly represents state-of-the-art.”
Ziv Williams, a neurosurgeon at Massachusetts General Hospital, said he’s an advocate of this technology because “it requires relatively limited training and much of it is intuitive to the patients, who are able to pick it up pretty quickly.”
However, Chestek said this system is taking longer to get approved in the U.S. because of the risk of infection — though no serious adverse events, including infection or bleeding, were reported by any of the four patients in the study.
“There’s a risk of infection because there is something permanently coming out of your body. It is remarkable how little infection they [the researchers] have seen, but it’s a trade-off that depends from person to person and how much risk they can tolerate,” she said.
Hugh Herr, associate professor and head of the biomechatronics group at the MIT Media Lab, disagreed that systems like the Swedish one carry a significant infection risk, though the approach is invasive. A neuromusculoskeletal prosthetic arm is “extremely advantageous compared to non-invasive prosthetics,” said Herr, whose lab is among a number of centers in the U.S. pioneering brain-controlled bionic limbs and new surgical approaches to better integrate human physiology with advanced robotic technology.
Among the challenges they’re working on is improving the sensations felt by people who use them. “This is just the beginning in the field,” he said.
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