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Prosthetic Knees: What’s Currently New and Impressive?
By Judith Otto Everyone agrees that there is no perfect prosthetic
knee--if there were, the knee researchers and design engineers
could all quit and go home. What makes the continuing search for
that perfect knee so interesting is the myriad widely divergent
approaches designers are now exploring--hydraulic, mechanical, and
computerized--as reflected in the variety of available knee designs
currently regarded as state-of-the-art.
Space and other limitations make it impossible to showcase every
recently marketed prosthetic knee, but here's a representative
sample:
Otto Bock C-Leg
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Otto Bock C-Leg |
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The Otto Bock C-Leg® tends to jump to the
forefront in any listing of state-of-the-art knees, largely because
it appeared first on the US scene (about four years ago) with such
dramatically different technology, and its successes achieved
widespread coverage--any marketer's dream! Former knee designs
traditionally locked between swings in order to support the
patient's weight--which necessarily slowed them down and made them
hazardous for walking on anything but a level surface. The C-Leg's
microprocessors adapt and compensate for stairs, slopes, and
irregular terrain, allowing the wearer to walk naturally without
thinking about it or compensating.
The C-Leg's multiple sensors, which relay data at a rate of 50
times per second, provide the feedback used to operate its
mechanical and hydraulic systems. Two strain gauges measure
pressures on the leg and note how often the heel strikes; magnetic
sensors report changes in knee angle. Greg Schneider, CP, clinical
specialist in prosthetics for Otto Bock Health Care, Minneapolis,
Minnesota, estimates that more than 5,000 C-Legs have been sold
worldwide in over 20 countries since 1997. "As C-Leg technology
becomes more and more accepted as a standard' type of prosthesis,
then it becomes more accepted in the field as far as payment goes,
too," he points out. "Sometimes insurance companies declare that
they will only pay for a standard' prosthesis. When they talk about
"standard" prostheses, they might be talking about technology that
was developed and patented back in the 60's!
Schneider continues, "Definitely microprocessors in every aspect
of our lives are becoming more prevalent--more standardized. Forty
years ago you'd use a typewriter, engineers would use a slide rule,
and if we wanted to communicate with someone we would do so by mail
rather than e-mail. Times change. Microprocessors are obviously
becoming the standard in everything--prosthetics is no different in
that respect."
Ohio Willow Wood GeoLite Knee
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Ohio Willow Wood GeoLite Knee |
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Ohio Willow Wood's GeoLite" Knee, an evolution of
its earlier GeoFlex" Knee, was introduced in March 2002, and offers
significant advances, according to Mark Ford, director of marketing
for the company, based in Mount Sterling, Ohio. "The new GeoLite
knee has taken the benefits of the polycentric, variable-friction
design and made it shorter, lighter, and less expensive." The knee
still provides outstanding stability to amputees, but now takes up
less room on the prosthesis.
Both the GeoLite and GeoFlex Knee enable low-activity amputees
to manage all types of terrain with confidence that the knee will
support them in the event of a stumble, with up to 20 degrees of
flexion adding stability. No locking mechanism is required; a
sliding crank design and variable friction controls provide a
stable knee without manually locking and unlocking it. The design
also helps amputees to better manage hip flexion contracture by
providing stability despite the contracted limb. The GeoLite is
available with two different proximal connection options; the
GeoFlex offers four different connection combinations.
Fillauer Swing Phase Lock (SPL)
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Fillauer Stance Control Lock with remote |
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The Swing Phase Lock (SPL) stance control knee is
Fillauer's current star, says Gerry Stark, BSME, CP, FAAOP,
director of education and technical support for Fillauer Inc.,
Chattanooga, Tennessee. "It's position-dependent rather than
load-dependent," Stark explains. "In orthotics, that's a great
application because there's not a lot of axial load that passes
through the knee itself. In prosthetics, we can utilize that load
to engage the knee."
Benefits listed on the Fillauer website note that it
automatically locks prior to stance phase, closely mimics normal
gait patterns, allows free flexion during swing phase, minimizes
energy consumption, eliminates circumduction vaulting, allows toe
clearance during swing phase, offers three modes of control,
eliminates cables and special heel connections, fabricates easily,
and lets the patient feel secure.
Endolite Adaptive Knee
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Endolite Adaptive Knee |
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The Adaptive Knee, the newest offering from
UK-based Chas. A. Blatchford & Sons Ltd, is described by Alan
Kercher, technical service and education manager for Endolite North
America, Centerville, Ohio, Blatchford's US company. The knee is
the third generation of microprocessor control in Endolite's
history. "It's a hydraulic and pneumatic hybrid cylinder which is
controlled by microprocessors through time, force, and swing
sensors," Kercher explains. "It detects various things happening in
the gait cycle at 62.5 times a second and adjusts accordingly. It
creates an electronic image of what's being used in the terrain the
patient is walking on, and adjusts to the necessary support modes.
The end result is a lot more natural gait than most knees
offer--and it also gives the wearer the freedom to control a
prosthesis that will work with them rather than for them."
"The C-Leg is a great invention, but is a different concept than
the Adaptive," Kercher continues. "Voluntary control is what we
advocate, using the muscles to control the prosthesis. The Adaptive
walks with the wearer and they're in control of it. With the
Adaptive, we're also after symmetry: muscles in the socket are
encouraged to work as they would on the sound side, resulting in
amputees having a healthier residual limb. In walking a ramp, for
example, the leg detects extra force and increases the resistance
to provide the extra needed support--resulting in a more natural
walk, operating just as the sound side does." The improved symmetry
and more natural style of walking have encouraged patients to free
up their shoulders and swing both arms as they walk, Kercher
adds.
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Ossur Hydraulic Knee |
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The Adaptive's rechargeable batteries last from
three to ten days, dependent on settings. An optional shock and
torsion pylon is also available to take away much of the shear and
stress forces through the residual limb, providing a more natural
function. The warranty is for three years, and every anniversary of
the fitting date, Endolite provides an exchange unit updated with
any newer software and improvements.
About 50-60 patients have been fitted with an Adaptive Knee
since its introduction late last year, Kercher believes. "We rolled
it out slowly--didn't want to get caught with hundreds of people
phoning up, because we haven't got hundreds of staff to go and fit
them!"
Kercher points out that one novel aspect of the Adaptive Knee is
that experts from Endolite attend the first fitting when a
prosthetist purchases one of these knees. The next day, Endolite
representatives are again there to follow up as needed: to
fine-tune the knee, to make sure everything is functioning properly
and that the prosthetist is aware of how the knee is
performing.
Ossur Improved Total Knee 2000
Ossur's improved "Total Knee 2000"" was recently reengineered
(May 2003) by adding needle bearings, retaining rings, and an
improved extension assist, all of which contribute to enhanced
durability, according to Ossur North America, Aliso, Viejo,
California. A two-year warranty is standard with the Total Knee
2000, which also includes geometric locking to provide for maximum
security and natural walking motion; three-phase hydraulics, which
help the user to alter walking speed smoothly and swiftly; stance
flex, which acts as a shock absorber to simulate the natural
flexing action of the normal knee; and a unique seven-axis design,
which imitates true knee motion and facilitates a more natural
gait, the company notes.
Ossur Mauch XG
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Ossur Mauch Knee |
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Ossur's Mauch XG" carbon frame knee, introduced in
2002, combines high performance with a sleek new design. The frame
is made of ultra-lightweight carbon fiber wound with Kevlar®,
a fabric used in bulletproof vests. "The Mauch XG" package is
targeted to the high-activity above-the-knee amputee requiring
strength and performance, in order to pursue an extreme lifestyle
during both work and play," says Michelle Hamilton, director of
marketing and public relations for Ossur. "This is the strongest
carbon frame on the market and has a weight limit of 285 lbs."
Prolite Smart Magnetix
The Prolite" Smart Magnetix" AK Prosthetic is a product of
German-based Biedermann OT Vertrieb, which utilized Rheonetic"
(magnetorheological) technology from the Lord Corporation, Cary,
North Carolina, to create the device.
Lord Corporation's website describes it: "The prosthesis, which
uses a modified Lord RD-1005 MR fluid damper, enables
above-the-knee amputees to walk with a more natural gait and makes
climbing up and down stairs and inclines much easier than
before--at a fraction of the cost of other high-end knee products.
The unique characteristics of Lord Rheonetic MR fluid dampers--high
controllability, millisecond response time, and
velocity-independent force--make this product possible."
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Lord Corp. - MR Damper Knee 2003 Lord Corp - All rights reserved. |
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"In addition to the great improvement in function
over passive damper systems, the Prolite Smart Magnetix Knee&is
less costly, less complex, and more dependable than
state-of-the-art motor-controlled active damper systems. The
Prolite Knee includes a powerful two-day battery derived from cell
phone battery technology and includes sensor and control technology
developed by Biedermann. The system senses and adapts to all
possible movement changes in milliseconds, allowing the wearer to
walk naturally up and down stairs and inclines, ride a bicycle,
carry heavy objects, and walk or run with varying gaits.
Prosthetics specialists are now being trained to fit amputees in
Germany with the new knee."
Lord's Lynn Yanyo, PhD, sales and marketing manager, reports a
continuing increase in interest regarding the MR process and
methods of adapting it for other prosthetic uses, such as ankles
and elbows; a resistance element for exercise during
rehabilitation; calibrating how well a joint is doing during
therapy by allowing comparison with measurements from the sound
joint, etc.
We've considered just some examples of what's happening now.
What will the future see in high-tech prosthetic knees to benefit
amputees? Stay tuned.
Judith Otto is a freelance writer based in Holly Springs, Mississippi. 
Table Of Contents - October 2003
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