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Surgery Improves Use of Artificial Arms

Study Shows Surgery Called TMR Allows Amputees to Have Better Control of Prostheses
By Caroline Wilbert
WebMD Health News
Reviewed by Louise Chang, MD

Feb. 9, 2009 -- A new surgery may give people with an amputated arm better control of a new artificial limb.

advanced hand control of the DEKA Research arm
The surgery, called targeted muscle reinnervation (TRM), allows amputees to control multiple parts of an artificial limb at the same time.

Current prostheses do not restore adequate function of the arm and hand. Most prostheses are body-powered; they capture remaining shoulder motion with a harness and transfer that movement through a cable to operate the hand, wrist, or elbow. This allows just one joint to be moved at a time.

Access to nerve-control information is lost during amputation. The TMR procedure transfers remaining arm nerves to chest or upper-arm muscles. Once nerve function has been restored through the surgery, these muscles provide correct electrical signals to control the elbow, wrist, and hand.

To test the effectiveness, researchers led by 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," the researchers write. "Additional research and development need to be conducted before field trials can be performed."

In an accompanying editorial, Gerald Loeb, MD, chief executive of SynTouch, a start-up company developing tactile sensor technology, said the speed and accuracy of the TMR patients' movements "represent substantial improvements over previous myoelectric systems."

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