A new technique allows patients with a prosthetic arm to feel its movements as if it were a real limb, researchers say.

Currently, most prosthetics are not linked to muscles or connected to the nerves in the amputated area. Only a single motion can be controlled at a time, so movements of a prosthetic elbow, wrist and hand or hook have to be done in slow, awkward steps.

Claudia Mitchell, right, is able to control her artificial arm directly using her brain.
(CBC)

Todd Kuiken of the Neural Engineering Center for Artificial Limbs at the Rehabilitation Institute of Chicago and his colleagues developed a new method of nerve regrowth that they say improves control of a motorized prosthetic arm.

In Saturday's issue of the journal The Lancet, the team reports that a 26-year-old woman who lost her arm in a motorcycle accident is able to control her new prosthetic arm better than her conventional prosthesis. The technique has been tried on three others, twice successfully.

Faster, more efficient motion

The technique, called targeted muscle reinnervation, re-routes the end of the motor nerves that once controlled her real arm into the muscles of her chest and side.

Chest muscles are linked to sensors in the artificial limb, allowing the woman, Claudia Mitchell, to close her hand by thinking about it. Electrical signals are sent through surgically rerouted nerves to make the motion happen.

"The function of her prosthesis improved substantially, as shown by an increase in speed and efficiency of motion," the team wrote.

"In this study we showed that targeted sensory reinnervation can be purposefully implemented to provide … sensation of touch in the missing limb."

Ultimate compliment for developers

Psychologically, allowing patients to perceive that they are touching could help them to incorporate their prosthesis into their self-image and better connect with their environment, the researchers said.

The potential exists to provide meaningful light touch, graded pressure, texture, edge detection and thermal feedback to amputees intuitively, they added.

The system has other advantages, such as being relatively simple to implement, does not require hardware that can break and require extra surgery, and works with existing prosthetic technology.

"In the most important laboratory, the patient's home, she reported using her TMR prosthesis many hours a day — the ultimate compliment for a new technology and its developers," Dr. Leigh Hochberg, a neuroscientist at Brown University wrote in an accompanying editorial.

"Technologies developed for prosthetic limb applications will also benefit people with paralysis from injury or neurological disease, and will move the field closer to a neurotechnology-enabled restoration of movement and sensation."