Vibrating muscles help arm amputees 'feel' their prosthetic hand movements, study suggests
Rob Anderson was fighting wildfires in Alberta when the helicopter he was in crashed into the side of a mountain. He survived, but lost his left arm and left leg.
More than 10 years after that accident, Anderson, now 39, says prosthetic limb technology has come a long way, and he feels fortunate to be using "top of the line stuff" to help him function as normally as possible. In fact, he continues to work for the Alberta government's wildfire fighting service.
His powered prosthetic hand can do basic functions like opening and closing, but he doesn't feel connected to it — and has limited ability to perform more intricate movements with it, such as shaking hands or holding a glass.
Anderson, who lives in Grande Prairie, Alta., compares its function to "doing things with a long pair of pliers."
"There's a disconnect between what you're physically touching and what your body is doing," he told CBC News.
Anderson is one of four Canadian participants in a study that suggests there's a way to change that. Researchers at the University of Alberta and the University of New Brunswick were co-authors of a study led by Ohio's Cleveland Clinic and published this week in the journal Science Translational Medicine.
Six people, all of whom had arm amputations from below the elbow or higher, took part in the research. It found that strategically placed vibrating "robots" made them "feel" the movements of their prosthetic hands, allowing them to grasp and grip objects with much more control and accuracy.
All of the participants had all previously undergone a specialized surgical procedure called "targeted re-innervation." The nerves that had connected to their hands before they were amputated were rewired to link instead to muscles (including the biceps and triceps) in their remaining upper arms and in their chests.
For the study, researchers placed the robotic devices on the skin over those re-innervated muscles and vibrated them as the participants opened, closed, grasped or pinched with their prosthetic hands.
While the vibration was turned on, the participants "felt" their artificial hands moving and could adjust their grip based on the sensation.
"It was kind of surreal," Anderson said. "I could visually see the hand go out, I would touch something, I would squeeze it and my phantom hand felt like it was being closed and squeezing on something and it was sending the message back to my brain.
"It was a very strange sensation to actually be able to feel that feedback because I hadn't in 10 years."
The feeling of movement in the prosthetic hand is an illusion, the researchers say, since the vibration is actually happening to a muscle elsewhere in the body. But the sensation appeared to have a real effect on the participants.
"They were able to control their grasp function and how much they were opening the hand, to the same degree that someone with an intact hand would," said study co-author Dr. Jacqueline Hebert, an associate professor in the Faculty of Rehabilitation Medicine at the University of Alberta.
"That ability to sort of tap into the system where their brain is just using the information without them even consciously realizing it, is what's really exciting," said Hebert, who is also a physician at Glenrose Rehabilitation Hospital in Edmonton, where she is Anderson's rehabilitation doctor.
A key part of the findings, the researchers say, is that while the vibrations were creating the sensation of hand movement, the participants didn't have to constantly watch their prosthetic device to control it — something they normally have to do because they can't feel what it is doing.
"Somebody with a prosthetic hand, since they can't feel the movement of their device, they essentially have to compensate [for] that with vision," said Paul Marasco, the study's lead author and an associate staff scientist in the Cleveland Clinic's department of biomedical engineering.
"It leaves someone with a prosthesis in a position of not being to do anything else other than watch their prosthesis. They can't have a normal conversation, they can't multi-task the way we do," he said.
"These are all things that we take for granted."
Although the researchers are encouraged by the study findings, they acknowledge that there was a small number of participants, who all had access to the specialized re-innervation surgery to redirect the nerves from their amputated hands to other parts of their body.
The next step, they say, is to see if they can also simulate the feeling of movement in a broader range of people who have had other types of amputations, including legs, and have not had the re-innervation surgery.
Anderson said he realizes this study is just a step toward real-life improvements for people like him — but he wants to help researchers make progress.
"Ultimately what it's going to do is allow you to know when you're touching something or holding something or carrying something," he said. "Just like a real hand."