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

A surgical technique to reattach nerves in amputees may help them to gain better control of artificial arms.

In Wednesday's issue of the medical journal JAMA, Dr. Todd Kuiken of the Rehabilitation Institute of Chicago and his colleagues compared artificial elbow and wrist movements of five arm-amputees with the movements of five people whose arms were intact.

Most bionic arms are not linked to muscles or connected to the nerves in the amputated area. Only one motion can be controlled at a time, so movements of a prosthetic elbow, wrist, hand or hook are cumbersome and slow.

In contrast, Kuiken's team has develop a new method of nerve regrowth aimed at improving control of a motorized prosthetic arm.

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

Muscles are linked to sensors in the artificial limb. Electrical signals are sent through surgically rerouted nerves to make the motion happen.

In the study, all participants were told to move their arm in various ways while researchers measured the subjects' ability to control the prosthetic arm.

Three of surgical patients were able to control prostheses — including motorized shoulders, elbows, wrists and hands — for tasks such as gripping a key or holding a cup.

The average accuracy among surgical patients was 88 per cent, compared with 97 per cent among the control group.

"The prosthetic arms tested in this study performed very well as early prototypes," the researchers concluded.

"Further improvements are needed and have been planned, including reducing the size and weight and increasing the robustness of these advanced prostheses.”

'Effects tend to be profound'

Writing in an editorial accompanying the study, Dr. Gerald Loeb of the University of Southern California, Los Angeles, called the finding exciting and promising.

"Such revolutions develop slowly at best, but their effects tend to be profound," Loeb said.

"With increasing functional capabilities, patients with upper-extremity amputations may derive exceptional benefit from prosthetic arms, just as legions of patients with lower-extremity amputations now lead remarkably normal and even athletic lives."

This study was supported by the Defense Advanced Research Projects Agency, DEKA Integrated Solution Corp., and the National Institute of Child Health and Human Development. Loeb has patents pending on tactile sensors and programs that might be used with advanced prosthetic hands.