Movement occurs when the brain sends signals to the nerves, and the nerves automatically relay those signals to muscles. There’s no need to think about each step in the process of grasping a doorknob or lifting a cup to drink from it.
Amputees lose the intuitive communication among the brain, nerves and muscles, partly because prosthetics are limited in their movement. Current prosthetic arms can only bend at the elbow and rotate at the wrist, and the hands just open and close. Those limitations leave upper limb amputees like Sullivan able to regain only three percent of their natural arm function.
Now, thanks to the groundbreaking work of an international team of surgeons and scientists, including the University of New Brunswick's Kevin Englehart, a new generation of artificial limbs that restores the body’s intuitive communication is on the horizon.
Englehart specializes in using muscle signals to control prosthetics. He is involved in two projects to build advanced prosthetic limbs, financed by the U.S. military through its Defense Advanced Research Projects Agency (DARPA). The first project, which concluded in January 2008, involved working with the DEKA Research and Development Corporation in Manchester, New Hampshire, to build a prosthetic arm with a tiny computer embedded in the forearm. The computer acts as the control system, using algorithms to interpret the user’s muscle signals and relay those signals to an artificial limb capable of many movements.
“What we were able to do was control a shoulder, an elbow, a wrist, and a hand with pretty much unprecedented dexterity,” says Englehart, a professor of electrical and computer engineering, and associate director of the Institute of Biomedical Engineering at the university. “It's beautiful to watch.”
The second project, which is not yet complete, aims to access the motor cortex in the brain, where all movement originates, and the peripheral nerves that run down the limbs. Englehart is working with researchers at Johns Hopkins University in Baltimore, as well as the team at DARPA, to develop a prosthetic limb that has almost the same natural dexterity as a human arm, and can feel and interpret sensation such as texture and temperature. The team’s second prototype, known as Proto 2, included a hand with 22 motors at each joint that could make 27 movements. It won the Popular Mechanics 2007 Breakthrough Award.
These advancements have Sullivan, who lost his arms following a work accident that sent 7,200 volts of electricity through his body, ready to give prosthetics a second chance. Like most amputees, Sullivan often chose not to wear artificial limbs because they don't provide enough function to justify the effort. He previously had to use his shoulders to touch switches in his arm socket that opened and closed his artificial hands. It was a cumbersome process, he says.
“Sometimes you'd accidentally hit the button and you'd open the hand. Nothing about it was natural. It was frustrating.”
Restoring the connection between the brain and nerve signals would not be possible without the pioneering work of a team of surgeons at Northwestern University’s Rehabilitation Institute of Chicago. Led by Dr. Todd Kuiken, the surgeons transplant nerves left over from an amputated hand or arm, moving them to muscles and skin in the chest. By rerouting those nerves and attaching electrodes to them, Englehart's computer can access the neural information from the nerves that would have gone to the arm, had it not been amputated.
“When you think, 'Close hand,' that piece of muscle contracts, and we can use that signal to tell the [artificial] hand to close,” says Kuiken. “That's a huge advancement for prosthetics.”
Kuiken was the first to perform this surgery. A total of 25 transplants have been done around the world, including two at the University of Alberta earlier this year, and Kuiken has performed 18 of them. Surgeons and researchers hope this kind of surgery will one day become standard care for amputees.
“If people have a greater range of options for employment and leisure, it has an economic benefit and it would improve the quality of life for people,” says Englehart. He also points out the potential benefit of this technology for people with spinal cord injuries, strokes, or even neurological diseases that affect movement and mobility, like Parkinson's Disease.
Sullivan underwent the surgery in 2002, more than a year after his arms had been amputated. Afterwards, he worked with Englehart and Kuiken to train the computer to interpret his particular nerve and muscle patterns—much like calibrating an instrument. He made several movements, such as flexing and extending his elbow and wrist, rotating his wrist, and opening and closing his hand. The computer catalogued the muscle movements, then compiled and stored mathematical models of them. When Sullivan tried to move his arm in a new way, the computer interpreted the desired movement based on the stored patterns with 98 percent accuracy.
“That was one of those 'Hallelujah!' moments in science,” says Kuiken.
The new prototypes “give me a degree of freedom that I didn't have,” affirms Sullivan. “And I don't have to learn how to use this system—it learns how to use me! I think within the next five to 10 years, prosthetics will be much lighter, quicker, and easier.”
“I would love to have my arms back, but seeing as I have to wear prosthetics, being a part of this project has been an honour.”