By using spinal cord stimulators designed to relieve chronic pain, American researchers have been able to restore the sensitivity of prosthetic arm wearers.
- Designed to relieve chronic pain, the electrodes implanted on the spinal cord allowed 4 volunteers to recover the sensations of their amputated limb.
- Participants felt natural and localized sensations in the hand, fingers and/or palm.
According to specialists, 70 to 90% of people with an amputated limb experience what is called phantom pain. Although their member (hand, arm, leg, etc.) is no longer there, they feel intense pain at the same time asa total lack of sensitivity, even when wearing a prosthesis. For example, they are able to tie their shoes or break an egg, but without any sensation in the hand.
Work carried out by the University of Pittsburgh (United States), could however help them to recover sensitivity in their amputated limb. In a statement published on the site of the medical center of the university of Pittsburgh, and in a study published on the site eLifethey explain that they used spinal cord stimulators commonly used to relieve chronic pain in order toprovide sensitivity to prosthetic arm wearers.
Natural and localized sensations
For the purposes of the study, four volunteers with amputated arms were fitted with stimulators which recreated the illusion of sensations in their missing limb. “What’s unique about this work is that we’re using devices that are already implanted in 50,000 people a year for pain relief. Doctors at all major medical centers in the country know how to perform these surgical procedures. And we get similar results to highly specialized devices and procedures.”said Lee Fisher, assistant professor of physical medicine and rehabilitation at the University of Pittsburgh School of Medicine and lead author of the study.
How do these stimulators work? Resembling “big spaghetti” according to the specialist, the electrodes run along the spinal cord, and are implanted at the top of the nerve roots which normally transmit the sensations of the arm. As it is a spinal cord implant, even a shoulder amputee can use this device. Electrical pulses were then sent to different locations on the electrodes, and participants had to report what they felt and where.
All reported feeling sensations in their missing arm or hand. Three of them reported localized sensations on a single finger or part of the palm. When asked to describe not only where but also how the stimulation felt, all four participants reported feeling natural sensations, such as touch and pressure, although these sensations were often mixed with unnatural sensations like tingling, buzzing, or tingling.
According to the researchers, the electrodes and the sensations they engender mostly remain in place for the entire month that the experiment lasts. “The stability of these devices is really essentialexplains Professor Fisher. If the electrodes move, it will change how a person feels when we stimulate them.”
The next big challenge for researchers now is to design spinal stimulators that are fully implanted rather than connected outside the body. They also want to demonstrate that sensory feedback can help improve control of a prosthetic hand during functional tasks, such as tying shoes or holding an egg without accidentally crushing it. Finally, they want to reduce the size of the contacts — the parts of the electrode where current exits — so users can experience even more localized sensations.