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Rancho Los Amigos Develops Innovative Technology
By Miki Fairley Orthotics has taken a page from prosthetic
technology. A research team from Rancho Los Amigos, Downey,
California, has developed an AFO with dynamic dorsiflexion control
similar to what has been achieved by many devices in lower-limb
prosthetics.
 The research team, which included Roger Weber,
CPO, Ronan Reynolds, Samuel Landsberger, ScD, and Donald McNeal,
PhD, used biomechanics and analysis methods to create the posterior
strut AFO with controllable dorsiflexion resistance.
The research also has helped in developing a promising KAFO
design.
The Challenge
"Our challenge was to develop a dynamic orthosis that is light
in weight and cosmetically appealing, while allowing independent
control of plantarflexion and dorsiflexion resistance, with
dorsiflexion resistance being both dynamic and nonlinear," Weber
explained in a presentation during the 2005 Annual Meeting and
Scientific Symposium of the American Academy of Orthotists and
Prosthetists (the Academy).
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Hinged Vertebrace with progressive dorsistop and light shockcord dorsiflexion assist for patients with quadriceps weakness. |
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"Additionally, we wanted an orthosis that could be
custom-modified for an individual's height, weight, motor deficit,
and activity level. Prosthetics has handled these challenges
before, but with orthotics we have additional challenges such as
strict space and weight limitations, and limitations on a patient's
'gadget tolerance.'"
The team started with the question, "What does an energy-storing
'graphite' prosthetic system do?" The answer, they found, is:
generally two main functions. These functions are 1) to control
weight acceptance during initial heel contact, and 2) to
controllably deflect in dorsiflexion and store energy from
mid-stance to toe-off. Additionally, hybrid prosthetics generally
have some inversion, eversion, and rotary control.
The need for soft initial heel contact is even more important in
orthotics than it is in prosthetics, because many orthosis users
have proximal weakness. "If the ankle forces at initial contact are
not managed, a flexion moment may be generated at the knee, and at
the hip, which the wearer may not be able to control." Thus, there
must be a relatively soft heel or the ability to allow
plantarflexion during loading response to manage these forces.
The Solution
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Non-hinged Vertebrace with progressive dorsistop and stiff dorsiflexion assist for patients with strong quadriceps. |
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The Rancho team developed what they call "The
Vertebral Orthosis," which somewhat replicates the spine's
vertebral column. The orthosis has several distinct components.
First is the main support, which consists of a pre-manufactured
graphite strut that is selected based on patient requirements, such
as weight, activity, etc.
Ideally, this will conform to the proper plantar-resist/
dorsi-assist needed by the patient. However, if necessary, a
mechanical posterior articulation is incorporated with an
integrated dorsiflexion assist. Alternating graphite struts, with
some crossing the ankle joint and others not crossing, also can be
used to create plantarflexion and dorsiflexion resistances
independent of one another, Weber explained.
So how is the correct amount of dorsiflexion resistance for
specific dorsiflexion angles and input loads figured out and
achieved?
A quantitative process has been developed. Using this process,
the team can predict the required dorsiflexion resistance for a
particular patient and custom-engineer the orthosis to generate
this resistance.
 To achieve this, the orthosis utilizes segmented
sections between the foot shell and calf which replicate "vertebral
bodies." The graphite strut passes through the posterior area,
linking the segments together with a flexible structure. Along the
medial and lateral parameters a channel is created, which can be
used with elastic bands for increased dorsiflexion assist, as well
as aid in the alignment of the vertebral bodies during loading.
Based on the required dorsiflexion resistance, spacing between
vertebral bodies that sequentially close under load has been
calculated to allow for non-linear dorsiflexion resistance without
terminal collapse. This, therefore, creates a dynamic ground
reaction knee stabilizing orthosis.
 Several versions of the "Vertebral Orthosis" have
been developed, which allow each orthosis to have independent
plantar/dorsiflexion in a controlled and quantifiable manner, Weber
said. At the time of the Academy presentation, clinical trials had
been performed with five subjects and evaluated in a
pathokinesiology lab after two months of usage. The results are
currently being analyzed.
A grant from the National Institute on Disability and
Rehabilitation Research (NIDRR) of the US Department of Education
supported this research.
KAFO: Knee Stability
During gait, the normal human knee flexes during loading
response and during swing. However, the research team realized that
existing knee braces for patients with quadriceps weakness flex
only at loading response, only at swing, or not at all. They came
to the logical conclusion that a brace that flexes at both times
may improve the velocity and efficiency of gait.
During normal gait, the knee flexes to an angle of 17 degrees,
and during swing it flexes to an angle of 60 degrees, Ronan
Reynolds noted. This requires significant quadriceps strength;
however if a person's quadriceps are weakened below a grade 3, due
to such conditions as spina bifida, muscular dystrophy, polio, or
cerebral palsy, KAFOs are commonly prescribed.
Three types of knee joints are available for KAFOs, said
Reynolds. The first type does not bend at all during the gait
cycle, such as a drop lock. These have a sleeve that slides over
and locks a simple hinge. To sit down, the patient raises the
sleeve and the joint can then rotate.
The second type bends at loading response. One example bends at
loading response, and the knee is supported by a coil spring so it
doesn't collapse. During swing, this spring resists flexion and
locks the knee in extension. The third type is locked during
loading response but unlocks during swing.
None of these joints allow knee flexion during both loading
response and swing, as does the normal human knee, Reynolds pointed
out. Not allowing flexion at loading response may increase the
impact loads on hip and the knee, and delay tibial advancement and
foot flat, he explained. Not allowing flexion during swing usually
forces circumduction of the leg for toe clearance, which may cause
slower and less efficient gait. To solve these problems, the
Rehabilitation Engineering Program has developed a KAFO that stably
allows knee flexion at loading response and during swing.
 A normal knee is naturally unstable while flexed
and needs to be supported with muscles to prevent collapse. Thus,
if a person is weak or paralyzed, the muscles need to be replaced
with a mechanism. This mechanism should apply a moment across the
knee during loading response that varies nonlinearly with flexion
angle, Reynolds explained. Additionally, it must lock before
initial contact and unlock before swing.
The team used the vertebrace technology developed in the AFO
project described earlier in this article to provide a non-linear
spring for use as an extension assist and an extension stop on the
knee joint. This spring can provide a predictable non-linear
stiffness tailored to a particular patient's requirements,
according to Reynolds. The team has added to this spring a
locking/unlocking linkage driven by the dorsiflexion/plantarflexion
angle of the ankle. KAFOs using this design are currently being
developed and evaluated, Reynolds added. This work also was
supported by a grant from the NIDRR.
Table Of Contents - September 2005
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