According to scientists, currently, a ground-breaking method of nerve re-growth makes it possible for a patient with a prosthetic arm to feel its movements.
The technique can considerably simplify the process of learning to use a new arm. Furthermore, combined with other innovations in prosthetic limbs, it could help arm amputees, especially injured soldiers coming back from Iraq and Afghanistan, improve the quality of their lives. "One of the greatest challenges with artificial limbs is how to tell a prosthesis what to do?" said the head of scientists, Dr Todd Kuiken, the director of the Neural Engineering Centre for Artificial Limbs at the Rehabilitation Institute of Chicago. "This paper describes one of our patients and demonstrates really amazing improvement in function. Our patients are seeing hundreds of per cent of improvement."
The patient mentioned in the report, a 24-year-old woman who lost her arm in a motorcycle accident, is "delighted" with the new technique, which is known as targeted muscle re-innervation, Kuiken explained.
An arm worth wearing
"She said to her healthcare professional: ‘Doc, my last arm wasn’t worth wearing, but this one is.’ Her previous arm was very difficult to use, and she gave up wearing it frequently," he added. The new system is effective due to the fact that sensation from the amputated limb remains in the nerves that used to go to the arm. Kuiken and his team took those nerves and transferred them to muscle and skin inside 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, however now a little piece of muscle on the chest contracts," Kuiken explained.
Hand nerves on chest
"Whenever a muscle contracts, there is a little electrical signal possible for us to pick up," he added. "And similarly, we have been able to get the hand-sensation nerves to grow into chest skin. As a result, when you touch that skin, the patient feels their hand being touched."
Currently, the patients need to look at their prosthesis in order to see when they have touched something and how hard they are squeezing it, Kuiken said.
By the use of the new method, that includes sensors in the prosthetic hand, the patient has a chance to feel how hard she is touching something or squeezing it or even how hot it is, Kuiken added. Then, information is sent to the chest skin, and the patient feels the pressure and temperature in the hand.
According to Kuiken, many amputees are unwilling to wear their prosthesis due to its weight and complexity of use. He hopes that newer, lighter limbs, combined with his technique, will simplify the process of learning how artificial limbs should be used.
A psychological boost
"Even more significant might be the psychological impact," Kuiken said. "The fact that you are touching something with your prosthetic hand and you feel your hand may be considered a great improvement in the emotional adjustment and acceptance of a prosthesis being a real thing as part of your body image."
This project was announced in the February 3 issue of The Lancet. It was funded by the US National Institutes of Health. "We hope to be doing the procedure in our servicemen and women this year," Kuiken said. Moreover, his colleagues are expanding their study to find out how they can adapt the technique to legs.
One of the specialists is convinced that the new technique is a crucial achievement in making better prosthetic limbs. "This is a significant 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.
More natural control on the way
According to Hochberg, this technique will shorten training time and increase control. "Using this, or any other technique, much more natural control of prosthetic limbs might be possible," he explained.
The technique, combined with newer limbs, may be an advance in prosthetic limbs in general, he said. "As engineers keep on creating better, lighter prosthetic limbs, there will be more effective ways to control that limb," Hochberg said.
