This story is from the category Augmenting Organics
Date posted: 21/03/2007
Some months ago, we looked at the case of ex-Marine Claudia Mitchell, who lost her arm in a motorcycle accident and became the first woman to be fitted with a bionic arm.
Now, the art of prosthetics has moved forwards once more, and Claudia has now become the first woman to be fitted with an artificial arm ? same arm ? that returns a sense of touch to her nervous system.
Surgeons have re-routed the ends of the motor nerves ? which once controlled her arm?s movement ? into the muscles in her chest and side. And the ends of the sensory nerves, which fed signals responding to heat and touch from her now-amputated arm to her brain, have been transferred to the skin on her chest.
To make the process more intuitive, Todd Kuiken and colleagues at the Rehabilitation Institute of Chicago developed a technique called "targeted muscle reinnervation". Motor nerves that once controlled the arm are transferred to nearby muscles, which are then fitted with myoelectric sensors to detect contraction.
"When the person imagines closing their hand, the signal goes down the nerve. Then we use that signal to control the prosthetic hand," explains prostheticist Laura Miller.
Three amputees have previously had their motor nerves redirected in this way, and are able to control their prosthetic arms much more effectively than conventional devices.
With Claudia, touching certain points on her upper chest produces the same sensations she would if someone touched her finger, her palm, or the back of her hand. She can even distinguish a range of pressures, temperatures and vibrations.
"Anybody who's ever tried to button their shirt when their hands are cold will know how important sensory-motor integration is," says Greg Clark, a bioengineer at the University of Utah in Salt Lake City, US, who is working to develop a similar system that uses electrodes to tap signals from nerves directly.
Before the senses can be used to provide feedback, a prosthetic arm must be built to pick up sensory input and transmit it to the portion of the chest that feels like the hand.
Kuiken's team is now working on a prototype device that transfers the feeling of pressure to the chest using a plunger-like mechanism, which they hope to begin testing in three to six months. Systems for transmitting vibrations and temperature are also in development.
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