Through use of a direct interface connected to the residual peripheral nerve in upper extremity amputees, investigators at the Advanced Platform Technology Center in the Department of Veterans Affairs are pursuing a system that attempts to provide sensory feedback for the hand.
“For a long time prosthetics have been limited mechanically and recently there has been this big push in adding new mechanics to the hand, but what is actually probably more significant is the sense of touch or feel,” Dustin Tyler, PhD, research scientist of the Department of Rehabilitation, Research and Development at the Louis Stokes Cleveland VA Medical Center, told O&P Business News. “By placing an electrode on the residual peripheral nerve, we are able to excite that nerve and send impulses back to the brain. The brain interprets [the impulse] as coming from the hand and in that manner the amputee will actually feel their hand.”
Although Tyler and colleagues have been working on the neural interface system since the 1990s, it was not until 2012 that the first electrodes were implanted, setting their research apart from previous studies.
“Skin is the largest sensory organ we have and provides tactile information. It is one of the predominant ways in which we explore and understand the world around us. With that missing it is a pretty big hole and by adding sensation back into the equation this will serve the idea that makes the prosthesis now a replacement hand,” Tyler, who is also associate professor at the Department of Biomedical Engineering at Case Western Reserve University, said. “People have tried electrical stimulation on the surface of the skin… but all of that is just exciting the sensory nerve endings on the skin where the device itself is. The difference is by going directly on the nerve, we are actually stimulating or turning on the fibers that used to go to part of the hand. So now, the user perceives it directly as the hand [and] they actually feel their finger applying pressure.”
During the past year, two amputees have had experience with the interface and have felt 10 to 19 individual sensations on their hand, either individually or together. After the system was turned on, the amputees became immediately aware of the prosthetic hand. Their ability to grasp, hold and move small objects without looking at them also has improved with the system.
“We found their performance significantly increases when they do tasks blindfolded, [which] means the attention a person will have to pay to the hand will be significantly reduced and ultimately can be used much more like the normal hand would be,” Tyler said. “For example, they could be looking at the computer screen and grabbing a cup or something else and get a feel for that without actually having to turn and look at the hand and make sure they are not crushing the cup or make sure they have the cup in their grasp, all those types of things that are problematic now.”
Through their research, Tyler and colleagues also found both amputees have experienced long-term, stable sensations in their hand with use of the interface.
“I think we have been able to collect some pretty good evidence to show that we think this method of providing sensation is in fact robust and long term,” Tyler said.
Importance of sense
For Tyler, continued research on electrical stimulation is important so amputees can continue to regain the sense of touch they lost with their limb no matter what prosthesis they use.
“While there has been improvement in mechanics and multi-articulate fingers, without the addition of sensation I think the gains that those are going to bring will be fairly limited,” Tyler said. “We feel that sensation is probably the most important, and by adding sensation, I think we are going to significantly enhance the function of the currently existing prostheses as well as the new ones. We are going to allow them to achieve the full capabilities of the advanced mechanics.”
According to Tyler, one of the biggest limitations with the system is that it is designed to be used in research, not for commercial use. To create something more user friendly, the researchers plan to invest in the development of an implanted system where the prosthetic arm connects to a pacemaker that will provide sensation, as well as record muscle activity.
“We are excited for the future, and where this is going to take us,” Tyler said. “We think this is going to move the prosthesis beyond just a tool to being a replacement hand. We think sensation is probably one of the most important parts of restoring and reconnecting to the environment. We are headed to not just restoring lost function, which is what a lot of people think when they think of a prosthetic [limb], but actually restoring the lost limb.” — by Casey Tingle
Natural Sensations for Amputees. Available at: www.aptcenter.research.va.gov/programs/ortho/natural-sensation-for-amputees/. Accessed Sept. 2, 2014.
Disclosure: Tyler has no relevant financial disclosures.