COMPUTERIZED CONTOL IS NEXT FOR ARTIFICIAL LIMBS
By IAN AUSTEN
New York Times
January 3, 2002
Among the many things that wearing an artificial leg
changed in Curtis Grimsley's life was the simple ritual of
going to the office.
Before Mr. Grimsley lost his left leg in a car accident
five years ago, he would step off a PATH train from New
Jersey and stroll across the concourse of the World Trade
Center before heading up to his office on the 70th floor of
the north tower, where he worked as a computer analyst for
the Port Authority.
After his accident, Mr. Grimsley, a former competitive
runner and a star of the Port Authority's basketball team,
was embarrassed to find himself suddenly unable to keep
pace with the thousands of other commuters in the vast
concourse. "I was kind of a little vain," Mr. Grimsley
acknowledged. "So I always came up the back way to get into
my office."
But last February Mr. Grimsley overcame his aversion to
using the concourse. He was fitted with a prosthetic leg
that uses microprocessors, strain gauges, angle detectors,
hydraulics and electronic valves to recreate the stability
and step of a normal leg. The C-Leg, made by the
German-based company Otto Bock, is widely seen as the most
advanced of a variety of artificial legs and knees. But Mr.
Grimsley said that his C- Leg did not just restore his
ability to walk more naturally: it saved his life.
On Sept. 11, Mr. Grimsley was talking to a co-worker on the
telephone when he felt his office floor shake. "I looked to
my right, and I saw a lot of paper flying right past the
window," Mr. Grimsley recalled. Running through his mind,
he said, along with thoughts of his wife and children, was
the prospect of fleeing on an artificial leg. "Was I was
going to make it down? You're talking about 70 floors. I
just immediately started walking to the stairwell."
With either of the two previous artificial legs Mr.
Grimsley had used before the C- Leg, stairs were a
potential trap: descending a slope or a staircase required
him to go through the exhausting and slow routine of
planting both the sound and artificial legs on every step.
The C-Leg allowed him to descend like everyone else,
placing only one foot on each stair tread while maintaining
the same speed as most of the people descending the
stairway.
"I saw other people, heavyset people, and it was very
exhausting for them," Mr. Grimsley said. "They had to go
off to the side. I was tired too. But I didn't have to
stop. It was like a workout for me. A steady, hard
workout."
When he reached the bottom of the tower, Mr. Grimsley made
one final trip across the concourse and out to Broadway to
have medical workers treat some minor abrasions where the
remains of his real leg and the C-Leg met. "The C-Leg made
a world of difference to me being dead or alive because it
allowed me to actually come down the steps normally," he
said.
The C-Leg is, in effect, a wearable computer, although Otto
Bock and other prosthetic-device makers avoid the phrase.
Beneath its carbon fiber composite shell are two
microprocessors that receive data from a string of sensors
at a rate of 50 times a second. The processors'
sophisticated software coordinates a mechanical and
hydraulic system that allows the leg to switch seamlessly
from a rigid position that supports the user's weight to a
relaxed position that allows the user to walk in a way that
closely imitates a natural gait.
Computerized prosthetic legs may not get the kind of
attention given to some prospective wearable devices - like
glasses that receive e-mail - but for patients like Mr.
Grimsley, they are undoubtedly more useful.
The C-Leg is not the first electronically controlled
artificial knee. Among the earlier innovators was the
Intelligent Prosthesis Plus made by a British-based
company, Chas. A. Blatchford & Sons, which is known in the
United States as Endolite North America. The Blatchford
limb had the advantage of not limiting the wearer to a
single walking speed as many previous artificial limbs had.
When the device detected that a user was picking up speed,
it adjusted the pneumatic piston that controlled the knee,
allowing the leg to swing more freely.
Early models had shortcomings. To start with, the only way
patients could support their weight on the Blatchford limb
was to lock it mechanically.
"That's totally the wrong approach for stability," said
Kelvin James, a biomechanical engineer at the University of
Alberta's division of neuroscience in Edmonton. "A locked
knee is too much."
In the mid-1980's, Mr. James began working on a system that
he hoped could overcome the problems of locking. He also
wanted to solve another problem with the leg's swing rate:
as he saw it, the Blatchford leg judged speed by counting
the number of steps taken within a given period of time.
But that also meant that it sometimes could not adjust
quickly enough to accommodate sudden obstacles.
"How often do you hit a curb in a time path that covers 10
feet?" Mr. James asked.
In his lab was a prototype of a leg developed by a local
prosthetist. He was intrigued by how the brake in the knee
was controlled with a switch in the heel that sensed when
the wearer was applying weight to the leg.
Using the lower leg as a sensing point ultimately became
part of Mr. James's plan. He decided to use a combination
of sensors, measuring the heel strike rate and the
pressures being imposed on the leg with two piezoelectric
strain gauges on the lower part of the leg while, at the
same time, monitoring the angle of the knee with a magnetic
sensor in the knee. Two microprocessor chips in the upper
part of the leg analyzed the data from the sensors at a
rate of 50 times a second and used motors - initially ones
designed for the oil industry - to constantly adjust the
hydraulic pressure to reflect a user's walking pattern.
With their ability to change the properties of the device
almost instantly, the C- Leg's processors allow wearers to
change their pace rapidly or to shift weight naturally to
walk down stairs or slopes. The leg is powered by an
internal lithium ion battery that can operate for 30 to 35
hours before it needs recharging. (The C-Leg, however, does
not allow amputees to walk up stairs naturally. Dr. Hans
Dietl, chief executive of Otto Bock Austria, said that was
unlikely to change. To allow natural stair climbing, the
leg would have to lift its owner's weight, using a battery
and motors too heavy to be practical.)
The prosthetists' initial reaction to Mr. James's
development, which started to come together late in 1986,
was not encouraging. "They mostly said, `You're going to
tell an amputee to carry around a battery, take off his leg
and plug it into the wall at night?' " Mr. James recalled.
Still, a prosthetist in Edmonton, Stan Wlodarchzyk, agreed
to work with Mr. James at no charge, as did one of his
patients, a teacher named Tony Slemp who became the test
subject during the long software refinement period. Mr.
James eventually licensed the leg design to Otto Bock,
which refined the technology at its research center in
Vienna.
One of a small number of testers for Otto Bock was Adele
Fifield, who had lost a leg to cancer as a teenager. For
her, the most obvious difference after 22 years of wearing
artificial legs was that she stopped falling. But in some
ways that was the least of the improvements. Ms. Fifield,
who grew up in a fishing village in the Canadian province
of Newfoundland and Labrador felt she had been freed from a
mental drain.
"There wasn't a lot to do in small-town Newfoundland," Ms.
Fifield said, "so you tended to walk around the community.
I remember walking and trying to carry on a conversation
with my friends and finding it very difficult to do both
things at once. You had to be conscious of every step. And
that was on level ground." But with her C-Leg, Ms. Fifield
confidently strolled along a hilly path, crisscrossed by
roots, marked by mud and filled at points with loose rock
and uneven flagstones. "I didn't enjoy going for a walk the
way I do now."
Despite the early concerns of some prosthetists, Ms.
Fifield has not found it particularly troublesome that the
battery's charge lasts only about 30 hours. Only once in
the last four years has she forgotten to charge it. she
said. In that case, she revived the leg by plugging it in
under her desk for two hours the next morning. On another
occasion, the leg ran out of power and went stiff when she
was wilderness camping, forcing her to hobble around for
the rest of the trip.
But as the director of the National Amputee Center of the
War Amps, a Canadian charity that provides financial help
for people in need of artificial limbs, Ms. Fifield has one
concern about the C-Leg: its cost. "That's the only thing I
hate about the whole thing," she said.
The C-Leg, which was introduced to the United States market
in 1999, costs $40,000 to $50,000, compared with $15,000
for a nonelectronic hydraulic model. The company declined
to say how many units it had sold but acknowledged that the
number was quite small.
For some people, like Mr. Grimsley, insurers pick up the
entire cost, but Ms. Fifield believes that they are a
minority in North America. "Five years ago, I used to say
that my artificial leg cost as much as my car. Now my
artificial leg costs twice as much as my car."
Blatchford-Endolite is waiting for regulatory approval to
introduce a new combined hydraulic-pneumatic electronic leg
that a company official said would be considerably less
expensive (he declined to offer a price) than the C-Leg
while offering similar features, including the ability to
walk down stairs and over uneven terrain.
As for Mr. Grimsley, he was caught on Broadway with his
C-Leg partly removed by medical personnel when the towers
collapsed on Sept. 11. After taking shelter against a
building and then in a store, Mr. Grimsley got his C-Leg
back on and was able to walk away from the disaster scene
until he could flag down an ambulance, which took him to a
hospital for treatment of his irritated stump.
A few weeks after the disaster he had his C-Leg swapped for
a factory loaner because dirt had impaired the mechanical
performance of the leg, but it still worked. Mr. Grimsley's
office is now in a Port Authority data processing center on
Staten Island.
And while he is still coming to terms with that day's
attacks, he has no complaints about his leg. "It's really
beautiful technology," he said.
http://www.nytimes.com/2002/01/03/technology/circuits/03KNEE.html?ex=1011082332&ei=1&en=8f6372eafd520258
