Each year, new prosthetic devices enter the market and promise to offer
better function — or greater control, or a more lifelike appearance —
than devices currently on the market. None of these, however, has specifically
addressed the common amputee complaint of
phantom limb pain.
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| Thomas Weiss |
Until now. Thomas Weiss, PhD, professor in the department of biological
and clinical psychology at the Friedrich-Schiller-University of Jena in
Germany, and his research team collaborated with trauma surgeons from Jena
University Hospital, modifying prosthetic devices to achieve a reduction in
phantom pain for patients who have only one degree of freedom in thier current
prostheses.
Weiss explained to O&P Business News that his research
in this field began with studies on human cortical reorganization.
“Phantom limb pain was one of the fields where cortical
reorganization, which is usually useful for learning and memory, is
maladaptive,” he said.
When brain structures that were originally responsible for communicating
within the arm stop functioning after the loss of the limb, “these areas
take over the processing of sensory stimuli from other body parts, especially
the arm stump and the face,” Weiss stated in the release.
Building on his own prior research and that of Herta Flor, PhD, Weiss
and the team explored various possibilities to devise a way to reduce that
maladaptive process.
Weiss began with a standard prosthesis offering internal sensory
feedback. A stimulation unit inside the device connects pressure sensors to the
areas of the residual limb controlling what would be the thumb and index
finger. Originally, those areas were meant to regulate the strength of grip of
the artificial hand, tightening or loosening depending on whether the patient
wanted to pick up an object like a raw egg or a hammer.
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| The modified prosthesis reorganizes sensory stimuli in the brain to reduce phantom limb pain. |
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| Image: Sandra Preissler/FSU |
Researchers altered the device so that, instead of simply accepting
feedback from the residual limb, the modified device also sends electrocutanous
stimulation back to the residual limb. This two-way communication provides the
patient with information about what is happening in the prosthetic hand,
distracting the brain and reducing phantom limb pain.
“We have an engineer that thought about bringing together
biofeedback, radio transmission and low weight,” he said.
Although these factors already had been employed individually in this
capacity, previous research had yet to bring them together as a solution for
phantom pain.
Those who tested the device noticed the difference when compared to
other devices.
“Patients greatly appreciate the new prosthesis,” Weiss said.
“They are even more convinced about the functional improvement, [for
example, their ability to hold] a raw egg or a tangerine without breaking
it.”
Weiss said that researchers still must gain more experience before this
device is ready for patient use. He hopes to further develop the technology to
allow for additional options for both transradial and transhumeral patient
applications. The device also imposes approximately 600 g at the residual limb,
a feature that Weiss would like to lighten for prospective wearers.
Thus far, the system has been tested on just eight patients, but the end
result is quite promising, he said. It now seems possible to use detailed
feedback from the hand in a way that will reduce phantom limb pain.
“We designed a prosthesis that allows better motor performance and
— just as a side effect — reduction of phantom limb pain,” Weiss
said. — by Stephanie Z. Pavlou
What wonderful news — this will definitely be a win/win/win/win
situation for amputees, their families, physicians and prosthetists. The
implications are phenomenal. Almost every amputee experiences phantom pain at
some point in their lives. For the prosthetist who attempts to fit around
phantom pain, we have very few alternatives. Sometimes increased or decreased
pressure in specific areas will help. Sometimes different materials will help.
Sometimes simple mirror therapy helps.
The human body never ceases to amaze. Every amputee that I have seen
over the past 35 years thinks their missing limb is gone and wonders how it can
still feel? They do not understand that their limb exists everywhere the neural
track runs — that transfers information to the brain about that limb.
Ultimately, the limb exists in the brain, where it can never be amputated.
It seems to be such common sense that providing some form of adaptive
input for the disturbed neural function should alleviate the phantom limb pain
phenomenon, that this type of technology would already be available. We
prosthetists have always provided adaptive input for our patients, but it comes
in a variable form through the patient residual limb connection within the
prosthesis. That connection will allow greater and lesser levels of feedback in
a cyclical way as the prosthesis is used. For most amputees this is enough to
allow functional levels necessary for their lives.
For those individuals where this current prosthetic fit adaptive input
is not sufficient, there is now some viable light at the end of their tunnel.
This is truly much needed technology in prosthetics that could very well be
adapted to useful purpose for orthotics.
— Harry Layton, CPO,
LPO
Owner/practitioner, Lawton Brace & Limb Co.
