Targeted Muscle Reinnervation

Targeted muscle reinnervation is the process by which a prosthetic limb, controlled by the patient’s brain, is surgically implanted into an amputee. Doctors connect nerves that remain in the body after a limb is amputated to another muscle in the body (often the chest when the patient has lost an arm). They allow the nerves to grow into the muscles in the chest for a few months. Doctors then implant electrodes onto the reconnected nerves. When the patient wants to move the introduced prosthetic arm, the brain tells the muscles in the chest to contract by using electromyography. Electromyography (EMG) detects the electrical signals given off by muscle cells when the brain activates them. The contraction signals the prosthetic arm to move by EMG signals instead of the motor commands that once connected the brain directly to the muscles in the limb...

Prosthetic brain-controlled technologies are now advanced enough that implants can perform ten hand, wrist and elbow movements. When doctors reconnect sensory nerves into the chest muscle, some amputees can feel texture and sensations of hot and cold[1].

In the past, a prosthetic arm could perform very few movements—bending an elbow, twisting a wrist— but now, the limbs function more like real arms. Further, old models required that the patient think carefully about each movement they wanted to make. The most advanced models, though, function like normal arms. 

Research into prosthetics has concentrated on arms rather than legs because legs as prosthetic limbs, are much more simple to control. Hand and wrist movements are more difficult to manipulate and vital for use of human hands than toe and ankle movements.

The United States government and the armed forces have funded most brain-controlled prosthetic limb research. Americans have an increasing need for functioning prosthetic limbs due to higher rates of amputations from diabetes and military injuries.  Since the technology became available in 2001, thirty people in the United States, Canada and Europe have received brain-controlled prosthetic limbs. Doctors have had trouble applying this technology to people who suffered military injuries. Their wounds are more difficult to correct than with other amputees because often these injuries have extensive nerve, muscle and bone damage[2]

A movie demonstrates a woman using her prosthetic arm: http://video.nytimes.com/video/2009/02/10/health/research/1231547586164/new-artificial-arm-technology.html?scp=1&sq=prosthetic%20arm&st=cse

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[1] Singer, Emily. “Prosthetic Limbs That Can Feel.” MIT Technology Review. 27 November 2007. http://www.technologyreview.com/Biotech/19759/?nlid=689

[2]Belluck, Pam. “In New Procedure, Artificial Arm Listens to Brain.” The New York Times.  10 February 2009. http://www.nytimes.com/2009/02/11/health/research/11arm.html?pagewanted=2&_r=1