New bionic ankle debuts at Providence VA
The first powered ankle-foot prosthesis, an important advance for lowerlimb
amputees, was unveiled July 23 at the Providence VA Medical
Center. Garth Stewart, a 24-year-old Army veteran who lost his left leg below
the knee following an injury in Iraq, demonstrated the new prosthesis.
Stewart walked in the prosthesis, which, unlike any other, propels users
forward using tendon-like springs and an electric motor. The prototype device
reduces fatigue, improves balance, and provides amputees with a more fluid
gait. It could become commercially available as early as the summer of 2008.
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MIT Media Lab Professor Hugh Herr, a VA-affiliated investigator since
2004, led the group that developed the ankle-foot. He is also a double amputee
who tested his invention. "This design releases three times the power of a
conventional prosthesis to propel you forward and, for the first time, provides
amputees with a truly humanlike gait," Herr said. He compared using the
device to walking on a moving walkway at an airport.
Stewart said that when he first began using the prototype, "One of the first
things I noticed was a huge relief in back pressure."
Herr created the device through the Center for Restorative and Regenerative
Medicine, a collaborative research initiative that includes the Providence
VA Medical Center, Brown University and MIT. The center was
initially funded in 2004 with $7.2 million from VA, and an additional
$6.9 million from the agency is now funding construction of
a new state-of-the-art research building to house the center on the
Providence VA campus.
Goal of center is 'biohybrid limb'
The center boasts a team of researchers with expertise in tissue
engineering, orthopedics, neurotechnology, prosthetic design and
rehabilitation. Their aim is to eventually create "biohybrid" limbs
that integrate biological and manmade materials and function almost
like natural limbs. Part of the effort involves research led by John
Donoghue, PhD, on a system called BrainGate that allows movement
signals from the brain to be picked up by a tiny implanted
sensor and decoded into commands for prosthetics or other robotic
and electronic devices. Other research is aimed at promoting osseointegration,
an innovative surgical technique that allows prostheses
to be anchored directly into the bone of the residual limb.
'This design releases three times the power of a
—Dr. Hugh Herr
Stewart, the veteran who demonstrated the new bionic ankle on
July 23, said he is looking forward to seeing more research-driven
advances: "What’s really exciting is that they want, within a couple
of years, to be able to graft this device to a human skeleton and then
run interfaces between the brain and the nerves, so you can feel it
and move it by thinking."
'Creativity, ingenuity on behalf of amputees'
Joel Kupersmith, MD, chief research and development officer
for VA, remarked how the new ankle is a prime example of how VA
research is advancing prosthetics care for veterans—especially those
returning from Iraq and Afghanistan.
"Up to now, prosthetic devices have not been able to duplicate
the complex functions of our feet and ankles as we walk and run,"
he said. "The ingenious computerized design of this new prosthesis
changes all of this, as it constantly 'thinks' and responds, allowing
the person to walk or run in a more natural and comfortable way."
Michael E. Selzer, MD, PhD, director of Rehabilitation Research
and Development for VA, added: "Hugh Herr and his Media Lab
group are well-known for their scientific ingenuity and creativity on
behalf of amputees. This new technology represents rehabilitation
research at its finest, and is yet another milestone in VA’s long history
of outstanding achievements in this area."
How does the new ankle-foot benefit amputees?
The device being developed by Herr’s group is the first
powered ankle-foot prosthesis. It propels the wearer forward, thanks to a unidirectional
spring and force-controllable actuator. It also varies its stiffness as users walk over irregular
terrain. These two properties enable the device to mimic the action of a biological ankle.
Conventional ankle-foot prostheses, on the other hand, are passive. This causes users to
expend up to 30 percent more energy during walking than non-amputees. As a result, they
typically walk at speeds that are 30 to 40 percent slower.
Herr’s team recorded improvements from 7 to 20 percent in the "metabolic economy" of
research volunteers who wore the device—even though it is two times heavier than conventional
The new foot-ankle prosthesis is also expected to alleviate problems
of abnormal gait that are common among below-the-knee
amputees. These problems include greater-than-normal hip
extension, knee flexion and ankle dorsiflexion—a movement that
decreases the angle between the foot and leg—on the unaffected
side, and less-than-normal flexion of the hip and knee on
the affected side. Studies have associated these
problems with long-term complications such
as low back pain and osteoarthritis.