Rheo Bionic Knee for Amputees
renardwc at ctrvax.Vanderbilt.Edu
Thu Jul 8 05:28:46 PDT 2004
>From one of our subscribers who prefers remaining in lurk mode:
Bionic Knee 'Learns' How to Walk New Prosthesis Is Designed To
Adapt to the Movements Of Users at Varying Speeds
By NICHOLAS ZAMISKA Staff Reporter of THE WALL STREET
JOURNAL July 6, 2004; Page D8
The human knee -- whose complexity is belied by its hinge-like
appearance -- has proved to be second only to the hand in difficulty
for doctors to replicate in the effort to help out amputees. Walking
involves a delicate pattern of shifting between bearing weight and
bending, doctors say, with the knee literally at the center. Enter the
Rheo Knee, a bionic body part that its maker, Ossur, touts as being
able to "learn" and adapt to a user's idiosyncratic movements.
"We can basically turn the knee on, have the person walk, and the
knee begins to learn how that person walks," said Scott B. Elliott, a
prosthetist with Ossur who has been testing the knee for the past
three years. "If they start to change their walking speed, Rheo will
A small group of prosthetists has been selected to receive the first
batch of Rheo Knees as part of what Ossur officials call "a soft
launch" of the new product. The knee will be available to the public
sometime early next year, according to officials of Ossur, which is
based in Iceland.
So how does a prosthetic knee learn? Electronic sensors on the
artificial joint measure both its angle and the loads it is bearing 1,
000 times per second while a computer chip, manufactured by
Motorola Inc., controls the viscosity of a magnetic fluid inside the
knee. Tiny metal particles suspended in the fluid form small chains
when the magnetic field is turned on, causing the fluid to become
thicker. That, in turn, affects the stiffness of the joint, which is
modified constantly while the knee is in use, allowing for a smooth
swing of the leg.
Doctors will be able to monitor the Rheo with Hewlett-Packard Co.
's handheld iPAQ computer, which can be plugged directly into the
knee, providing information about the internal settings, the battery
and other data.
It sounds expensive, and it is. The starting cost for the Rheo will be
around $18,000, although the final price tag for a knee, foot, socket
and labor of a prosthetist to fit the limb could be anywhere from $
40,000 to $50,000.
The completed design of the Rheo Knee has been tested in only 13
patients for one month, although 10 others have tested earlier
versions of the knee during development. Given the lack of
independent research on the Rheo Knee, it isn't yet clear whether the
technology will translate into improved functionality for amputees.
"I love it," says Julie Greder, one of the test subjects who has been
using the Rheo Knee for around a year. "It feels like it does the
walking for you."
While there's another "self-learning" knee on the market, made by
Daw Industries Inc. of San Diego, Calif., the Rheo Knee's main
competition, the C-Leg, made by Otto Bock HealthCare of
Germany, is now widely in use for wounded soldiers returning from
Iraq. World-wide, more than 5,000 people have been fitted for the
C-Leg, which costs around $16,000.
At Walter Reed Army Medical Center in Washington, Paul
Pasquina, chief of physical medicine and rehabilitation, says that
wounded soldiers he works with have been "extremely happy" with
the C-Leg, but he is eager to see the Rheo Knee come out of testing.
"We're still a long way off from recreating a leg as good as the one
you're born with," he says.
But Ossur's knee, which uses the same magnetic technology found
in the shock absorption systems installed in some new Corvettes,
may have an Achilles' heel, so to speak, according to competitors
familiar with the design. When its battery dies, the knee becomes a
"free swinging joint," leaving the user prone to a fall.
'Reviewed and Abandoned'
Indeed, Otto Bock is dismissive of Rheo. "The Rheo Knee, at its
heart, uses a very sexy technology, which we reviewed and
abandoned nine years ago," said Patrick Chelf, vice president of
marketing and business development for Otto Bock in the Americas.
Otto Bock says that its C-Leg is the most reliable knee in the
industry, helping users avoid falls.
Technicians at Ossur counter that with the Rheo Knee, warning
signals will give the user ample notice that the battery needs to be
charged before it shuts off.
Ossur CEO Jon Sigurdsson, a 48-year-old former Icelandic diplomat
who joined the company eight years ago, predicted that in coming
years, many artificial joints will have some sort of intelligence
similar to that found in the Rheo Knee.
Innovation in prosthetics has often been prodded along by wartime,
as wounded soldiers return home. Fighting in Iraq has produced
more than 800 U.S. deaths since the war began and at least 100
amputees, according to doctors at Walter Reed Army Medical
Anticipating where artificial-limb technology is headed, researchers
at the Defense Department are already looking at whether signals
from the brain can be captured and transmitted directly to the
The market for high-end prosthetics is a relatively narrow one,
given that a small fraction of the more than one million amputees in
the U.S. can afford the latest artificial limbs. Ossur expects to sell a
few hundred of its new knees next year, but hopes sales will grow
after word of the new technology has gotten out.
For an industry faced with such a small market, sinking money into
research and development is a risky business. Even after seven years
on the market, the C-Leg has still not made a profit for Otto Bock,
which estimates that total revenue among all prosthetics
manufacturers in the U.S. hovers around $300 million annually.
Health-insurance companies, meanwhile, can balk at paying for the
most expensive limbs.
"You can have this great technology out there, but the real concern
is how you can actually put it on patients," said David McGill,
chairman of the board of the Amputee Coalition of America, a
nonprofit advocacy group. "The reimbursement end of this thing is
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