A novel surgical technique may give people with an amputated arm better control of a new artificial limb, say researchers.
The surgery, called targeted muscle reinnervation (TRM), allows amputees to control multiple parts of an artificial limb at the same time.
Currently available prostheses following upper-limb amputation do not adequately restore the function of an individual's arm and hand.
The most commonly used prostheses are body-powered, which capture remaining shoulder motion with a harness and transfer this movement through a cable to operate the hand, wrist, or elbow. With this control method, only one joint can be operated at a time.
Improving the function of prosthetic arms remains a challenge, because access to the nerve-control information for the arm is lost during amputation.
With the surgical procedure, targeted muscle reinnervation (TMR), remaining arm nerves are transferred to chest or upper-arm muscles that are no longer biomechanically functional due to loss of the limb.
The goal of this procedure is to improve control of prostheses that use electromyogram (EMG) signals (the electrical signals generated during muscle contraction) from residual limb muscles to control motorized arm joints.
Once reinnervated (restore nerve function), these muscles provide physiologically appropriate EMG signals for control of the elbow, wrist, and hand.
To test the effectiveness, Todd Kuiken, MD, PhD, from the Rehabilitation Institute of Chicago, and colleagues tested five amputees who had had the surgery.
A comparison group included five participants who had not had amputations.
For the study, conducted between January 2007 and January 2008, participants performed various arm movements. Researchers tested their ability to control a virtual prosthetic arm.
While non-amputees were faster than TMR patients, the times were close.
For instance, TMR patients were able to complete elbow and wrist movements in an average of 1.29 seconds, compared to 1.08 seconds for the non-amputee participants.
"These early trials demonstrate the feasibility of using TMR to control complex multifunction prostheses. Additional research and development need to be conducted before field trials can be performed," the authors said.
"The prosthetic arms tested in this study performed very well as early prototypes. Further improvements are needed and have been planned, including reducing the size and weight and increasing the robustness of these advanced prostheses," they added.
The study is published in the February 11 issue of JAMA.