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One Step Closer to Fully Functional Prosthetics May 14, 2009

Posted by Matt Brown in Bionics.
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Technology Review has a very interesting article about a new surgical technique that is giving arm amputees a chance to regain most of their lost mobility.

The technique, called targeted muscle re-innervation and developed by Todd Kuiken of the Rehabilitation Institute of Chicago’s Center for Bionic Medicine, involves transplanting surviving arm motor nerves into other parts of the body, most commonly the chest.  These nerves then function much as they would were they still in the arm, flexing the muscle they are innervating whenever the person thinks of say, performing a high five or opening a jar.  Electrodes placed on the muscle detect contractions that a motorized prosthetic arm translates into the appropriate movement.  This gives the amputee intuitive control of the arm and the ability to perform fine motor movements that have typically not been possible, such as “[slicing] hot peppers, [opening] a bag of flour, [and putting] on a belt.”

As I mentioned in my post on the Open Prosthetics Project, prosthetic devices have until recently been nowhere near as efficient as a regular biological arm.  They’ve been cumbersome and with only a few degrees of freedom have been unable to perform anywhere near the level of biological arms.  Partly this is due to the primitive technology of the arms themselves (which in many cases are no more than a claw and a hook) but it is also due to the primitive technology controlling them.  As stated in the article, “prosthetic arms have been controlled in a rudimentary way, by transforming residual shoulder movements or muscle signals in to the simplest of movement commands.”This new technique gives amputees the ability to perform activities of daily living that had previously been impossible.

What is even more incredible is the possibility that this technology can give back to amputees not only motion, but sensation.  Currently no prosthetics possess tactile abilities.  They cannot feel texture, heat, pressure and so on.  But while most research into muscle re-innervation has focused on motor nerves, “it appears that sensory nerves, which carry signals from the skin to the brain, are affected as well.  Patients, including Mitchell, have reported that when certain areas of their rewired chest muscles are touched, they feel as if their missing hand is being touched.”

If a prosthetic arm can be developed to detect the sensations we feel through our skin, it appears that the nerve wiring would already be in place to make it work.

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