New Technique Allows 'Feeling' in Artificial Arm

By Steven Reinberg
HealthDay Reporter
Thursday, February 1, 2007; 12:00 AM

THURSDAY, Feb. 1 (HealthDay News) -- An innovative method of nerve regrowth now allows a patient with a prosthetic arm to feel its movements, researchers reported late Thursday.

The technique can make learning to use a new arm easier, and combined with other breakthroughs in prosthetic limbs, it could help arm amputees, particularly injured soldiers returning from Iraq and Afghanistan, improve the quality of their lives.

"One of the biggest challenges with artificial limbs is, how do you tell a prosthesis what to do," said lead researcher Dr. Todd Kuiken, the director of the Neural Engineering Center for Artificial Limbs at the Rehabilitation Institute of Chicago. "This paper describes one of our patients and shows really remarkable improvement in function. Our patients are seeing hundreds of percent of improvement."

The patient in the report, a 24-year-old woman who lost her arm in a motorcycle accident, is "delighted" with the new technique, which is called targeted muscle reinnervation, Kuiken said.

"She said, 'Doc, my last arm wasn't worth wearing; this one is.' Her previous arm was just too hard to use, and she quit wearing it very often," he added.

This new system works because sensation from the amputated limb remains in the nerves that used to go to the arm. Kuiken and colleagues took those nerves and transferred them to muscle and skin in the patient's chest.

"So now, when our patient thinks 'close hand,' the signal goes from the brain through the spinal cord out through the hand nerve, but now a little piece of muscle on the chest contracts," Kuiken said.

"Every time a muscle contracts, there is a little electrical signal that we can pick up," he added. "In the same way, we have been able to get the hand-sensation nerves to grow into chest skin, so that when you touch that skin, the patient feels their hand being touched."

Right now, patients have to look at their prosthesis to see when they have touched something and how hard they are squeezing it, Kuiken said.

Using the new method, which includes sensors in the prosthetic hand, the patient can feel how hard she is touching something or squeezing it or even how hot it is, Kuiken said. The sensors send information to the chest skin, and the patient feels the pressure and temperature in the hand.

Many amputees are reluctant to wear their prosthesis because of its weight and difficulty of use, Kuiken said. He hopes that newer, lighter limbs, coupled with his technique, will make it easier to learn how to use artificial limbs.

"Even more important might be the psychological impact," Kuiken added. "The fact that you touch something with your prosthetic hand, and you feel your hand, may be a profound improvement in the emotional adjustment and acceptance of a prosthesis being a real thing as part of your body image."

This project, which is reported in the Feb. 3 issue ofThe Lancet, was funded by the U.S. National Institutes of Health.

"We hope to be doing the procedure in our servicemen and women this year," Kuiken said. In addition, his team is expanding its research to see how they can adapt the technique to legs.

"This is an important step in more intuitive control systems for prosthetic limbs," said Dr. Leigh R Hochberg, a neuroscience investigator at Brown University and the author of an accompanying editorial in the journal.

This technique will cut the training time and increase the control, Hochberg added. "Using this, or other techniques, much more natural control of prosthetic limbs might be possible," he said.

The technique, combined with newer limbs, may be an advance in prosthetic limbs in general, he added. "As engineers continue to create better, lighter prosthetic limbs, there will be better ways to control that limb," Hochberg said.

More information

The U.S. Department of Veterans Affairs can tell you more about artificial limbs.

SOURCES: Todd Kuiken, M.D., Ph.D., director, Neural Engineering Center for Artificial Limbs, Rehabilitation Institute of Chicago; Leigh R. Hochberg, M.D., Ph.D., investigator in neuroscience, Department of Neuroscience and Brain Science Program, Brown University, Providence, R.I.; Feb. 3, 2007,The Lancet