[tt] Enhanced prosthetic is seven times faster

[Hughes, James J.]

http://technology.newscientist.com/article/dn12902-enhanced-prosthetic-i
s-seven-times-faster.html

Enhanced prosthetic is seven times faster

    * 09:00 12 November 2007
    * NewScientist.com news service
    * Bob Adler

Rewiring nerve fibres that once served a missing arm to the muscles in
an amputee's chest now offers a way to control prosthetic limbs more
intuitively and effectively.

In clinical trials, an improved interface for this type of prosthetic
arm allowed volunteers to use their limbs to perform a variety of tasks
up to seven times faster than before, after only minimal training.
Previous systems only allowed people to make a few movements, one after
the other, but the new one can be used to direct 16 distinct arm, hand
and finger movements.

The approach, called targeted muscle reinnervation (TMR), was first
proposed by Gerald Loeb, a professor of biomedical engineering at the
University of Southern California, in Los Angeles, US. He suggested in
1980 that it might be possible to detect and use signals from the motor
and sensory nerves that once served a severed limb to control a
prosthetic, by reconnecting them to nearby muscle and skin.

The idea was taken up by Todd Kuiken, then a medical student and now a
pioneering rehabilitation researcher at the Rehabilitation Institute of
Chicago (RIC), and Northwestern University, also in Chicago, US.

Surviving motor and sensory nerves are first surgically separated from
the stump of a patient's arm. Nerves serving chest muscles that once
helped support and move the missing limb, but that are no longer useful,
are also cut. The motor nerves once used to control the patient's arm
are then grafted to those connected to the chest muscles, while the
sensory nerves from the missing arm are redirected to tissue under the
skin of the chest.

"All the information is still contained in the nerves," because the
brain continues to send movement signals to the amputated limb, says
Ping Zhou, a biomedical engineer working with Kuiken at the RIC.

Once the reattached nerves become functional again, within four to six
months, patients can feel their chest muscles contract when they think
of moving their arm or hand. They can also feel pressure, heat, or
vibration in their chest as if it were coming from their missing arm or
hand.

The chest muscles act as a "biological amplifier" of the patient's
natural nerve impulses, says Kuiken, while the overlying skin can
receive tactile feedback from the prosthetic arm, hand, or fingers.

In a forthcoming article in the Journal of Neurophysiology Kuiken's
group describes how it has now refined the interface that detects and
interprets electrical signals from reinnervated chest muscles.

This lets the system determine what movement the patient wants to make
and command the artificial limb to make the desired movement more
effectively.

Previous versions of Kuiken's system were only able detect and use two
movements, opening or closing the hand and bending or extending the
elbow. The team expects that patients will be able to do far more with
this method, with 16 coordinated movements being possible.

Bernard Hudgins, Director of Biomedical Engineering at the University of
New Brunkswick, at Fredericton, New Brunswick, Canada, applauds Kuiken's
work. "Even given current limitations, TMR has proven its worth as a new
approach in treating individuals with high-level amputations," he says.
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Weblinks

    * Todd Kuiken
    * http://www.smpp.northwestern.edu/Kuiken.htm
    * Ping Zhou
    *
http://www.ric.org/aboutus/people/doctors/results.aspx?doctorID=121
    * Robotic limbs and TMR, Wikipedia
    * http://en.wikipedia.org/wiki/Artificial_limb#Robotic_Limbs