EMBARGOED
FOR RELEASE UNTIL
November 11, 2007
APS Contact
Christine Guilfoy
Office: (301) 634-7253
cguilfoy@the-aps.org
www.The-APS.org
Thinking Makes It So: Science
Extends Reach of Prosthetic Arms
BETHESDA, Md. − Motorized prosthetic arms can
help amputees regain some function, but these devices take time to learn to
use and are limited in the number of movements they provide.
Todd A. Kuiken, M.D., Ph.D., a physiatrist at the
Rehabilitation Institute of Chicago and professor at Northwestern
University, has pioneered a technique known as targeted muscle reinnervation
(TMR), which allows a prosthetic arm to respond directly to the brain’s
signals, making it much easier to use than traditional motorized
prosthetics. This technique, still under development, allows wearers to open
and close their artificial hands and bend and straighten their artificial
elbows nearly as naturally as their own arms.
“The idea is that when you lose your arm, you
lose the motors, the muscles and the structural elements of the bones,”
Kuiken explained. “But the control information should still be there in the
residual nerves.” He decided to take the residual nerves, which once carried
the commands from the brain to produce arm, wrist and hand movements, and
connect them to the chest muscles so that the signals can be used to move
the artificial limb.
Nearly a dozen patients who have undergone TMR so far
have motorized prosthetic arms that produce two arm movements: open and
close hand and bend and straighten elbow. But in a new study from the
Journal of Neurophysiology, published by
The American Physiological Society, Kuiken and his colleagues
demonstrate that TMR has the potential to provide an even greater number of
arm and hand movements, beyond the four they’ve already achieved. The
researchers have begun work with two U.S. Army medical centers to help
soldiers who have lost limbs.
The study, entitled “Decoding a new neural-machine
interface for control of artificial limbs,” was conducted by Ping Zhou,
Madeleine M. Lowery, Kevin B. Englehart, He Huang, Guanglin Li, Levi
Hargrove, Julius P.A. Dewald and Kuiken, all of Northwestern University and
the Rehabilitation Institute of Chicago. Hargrove is also affiliated with
the University of New Brunswick, Canada and Lowery is also affiliated with
University College Dublin, Ireland.
Redirects nerves
Kuiken first got the idea for TMR when he was a
graduate student during the 1980s. In his first patient, Kuiken took four
nerves that had gone to the amputated arm and redirected them to the
patient’s chest muscles. As a result, when the patient wants to close his
hand – a hand that is no longer there – the impulse travels down the nerve,
into his chest and causes the chest muscle to contract.
The next step was to use the muscle contraction in the
chest to move the prosthetic arm. This was accomplished with the help of an
electromyogram (EMG), which picks up the electrical signal that the muscle
emits when it contracts.
The signal is directed to a microprocessor in the
artificial arm which decodes the signal and tells the arm what to do. In
their work thus far, Kuiken and his colleagues have programmed the processor
in the prosthetic arm to recognize four signals to produce two arm
movements: open and close hand and bend and straighten elbow.
The result? When the patient thinks ‘close hand’ the
hand closes. Contrast this with current motorized prosthetic arm technology:
The patient has to learn to use new muscle groups to move the prosthetic
arm; can perform only one movement at a time; and must contract two muscles
at once to achieve a new movement.
“It’s not very common to flex your chest muscle to
close your hand or bend your wrist,” said Kuiken. “Quite frankly, most
people with a unilateral shoulder disarticulation amputation don’t wear a
prosthesis at all: It’s just too cumbersome.”
More moves
While TMR is more intuitive and natural, Kuiken and his
team wanted to see if they could extract more of the wealth of information
from the electrical signals produced by the nerves and chest muscles and
harness it to provide a greater number of hand and arm movements.
In the study published in the Journal of
Neurophysiology, they placed between 79-128 electrodes from the EMG onto
the chest muscles of five patients to see if they could identify the unique
EMG patterns emitted with 16 different elbow, wrist, hand, thumb and finger
movements they asked the patients to perform. The EMG signals from each of
the 16 movements were analyzed using advanced signal processing techniques.
The study found that the researchers could recognize the signals associated
with the different arm movements with 95% accuracy.
The next step is to use this information to program
these new moves into the microprocessor of the artificial arm, so that
instead of just opening and closing a hand and bending and straightening an
elbow, now the signals can produce various hand grasp patterns, such as the
one needed to hold a baseball, pick up a pen or grasp a tool.
May benefit soldiers
Kuiken and his colleagues have begun to work with the
military at Brooke Army Medical Center at Fort Sam Houston in Texas and the
Walter Reed Army Hospital in Washington, D.C. to apply this technology to
soldiers who have lost limbs.
“We’re excited to move forward in doing this
surgery with our soldiers some day,” he said. “We’ve been able to
demonstrate remarkable control of artificial limbs and it’s an exciting
neural machine interface that provides a lot of hope.”
There are a couple of additional things to note in the
work of Kuiken and his colleagues: They performed nerve transfer surgery
9-15 months after the injury that led to amputation, showing that these
neural pathways remain intact, even when they have not been used for awhile.
Also, when the researchers touch these patients on
their chests, the patients say it feels like they are being touched
somewhere on their arm or hand -- the arm or hand that is no longer there.
That’s not really surprising, because the brain receives an impulse from a
nerve that used to go to the arm. The brain doesn’t know the nerve is now
embedded in a different muscle, and interprets this touch as it always has.
Editor’s Notes: An audio version of this story
will appear on Life Lines, the podcast of The American Physiological
Society. You can find it on Nov. 12 at
www.lifelines.tv.
The best time to interview Dr. Kuiken and Dr. Zhou
will be Nov. 6 and Nov. 7. To arrange an interview, please contact Christine
Guilfoy at
cguilfoy@the-aps.org or (301) 634-7253. Interviews on other days may
also be arranged.
Physiology
is the study of how molecules, cells, tissues and organs function to create
health or disease. The American Physiological Society (APS) has been an
integral part of this scientific discovery process since it was established
in 1887.
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