Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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PROSTHETIC FOOT
Technical Field of the Invention
The present invention relates generally
to prosthetic devices and in particular to
prosthetic feet.
Backqround of the Invention
Since the first peg leg, prosthetists
have been striving for a satisfactory sukstitute
for the human foot, which is an intricate structure
of over fifty bones and muscles. In an attempt to
imitate the functional dynamics of the human foot,
prosthetists designed artificial fe~t which
structurally were almost as complicated as the
human counterpart. These devices typically
' 15 comprised numerous wooden, rubber and metal
components, which made them cumbersome to wear.
! Moreover, because of their construction, they were
expensive to manufacture and required considerable
maintenance and repair.
It is only in recent years that those
i skilled in prostheticis have begun to use simpler
designs which achieve flexibility through the use
of resilient materials. These so-called "energy
storing" feet absorb some of the impact with each
step and then release this energy ~s the foot is
lifted.
Several "energy-storing" feet are known.
For example, U. S. Patent No. 4,721,510 describes
; a foot comprising a rigid keel clamped to the top
` 30 of a longer flexible stiffener supported inside a
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hollow cosmesis. The stiffener has a heel and a
toe portion, and the ]ceel also has a heel and a toe
portion, each of which is spaced a distance above
the corresponding portion of the stiffener. The
keel and stiffener are attached to a thickened
instep region in the cosmesis by means of an instep
reinforcement plate. In operation, when the toP
and heel portions of the stiffener are deflected,
they contact the overlying portions of the keel,
thereby transmitting the ground reaction to the
keel. Thus, the keel a~d stiffener components of
this foot interact as a lea spring.
A prosthetic foot with a monolithic
cantilever spring keel is shown in U. S. Patent No.
4,645,509. The keel is C-shaped, the back of the
"C" forming a heel transition portion and the
bottom of the "C" extending a length into a
forefoot portion. Shock absorption results from
the vertical compression of the curved heel
transition portion. In an alternate embodiment,
the keel is provided with an integral heel spur
which is short spike extending downwardly from the
back of the heel transition portion. The stated
purpose of the spur is to absorb energy and provide
rebound at heel strike.
A combination foot and leg prothesis is
the subject of U.S. Patent No. 4,547,913. The
forefoot portion and the leg portion are integrally
, formed of a single flat strip of flexible material
with a bend at the level of the ankle. A second
and separate strip is riveted to the posterior
aspect of the first portion to form the heel of the
prosthesis. In most of the embodiments shown, the
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heel portion is C-shaped with the back of the "C"
facing posteriorly. Thus, energy absorption occurs
by compression of the sharp bend in the heel member
and by flexion o~ the forefoot portion.
Finally, Russian Inventor's Certificate
No. 778,732 discloses a foot comprising an
integrally formed shock absorber housed in a shell
which is filled with foam. The shock absorber has
a lower branch, which repeats the curvature of the
arch of the human foot, and an upper branch which
slidably contacts the upper surface of the lower
branch in the area of the metatarsophalangeal
joints. The upper branch is supported over the
13wer branch by a curved transition portion in the
heel area. When a load is applied to the foot, the
transition portion is compressed verti-cally, and
the upper branch slides anteriorly upon the lower
~! branch. Thus, the upper and lower branches of the
shock absor~er function as a leaf spring.
These feet generally are lighter weight
and provide a more natural stride than the earlier
more complicated mechanical prostheses. However,
while thPse known devices represent advances in the
art, problems have remained with their use.
One disadvantage to most known prosthetic
feet results from the symmetrical thickness of the
forefoot porkions of the stxuctural components of
~ most of these devices. When walking casually on a
- foot with a symmetrical keel, an individual usually
-, 30 will toe the foot out slightly. This looks more
natural and gives lateral stability. However, when
walking vigorously and when running, an individual
wearing such a device will want to turn the foot su
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that a~ each toe-off the end of the forefoot is allgned with the
direction ln whlch he or she is runnlng. This is necessary to
achieYe a symmetrically reslstan~ toe-off and thus enjoy the
maximum spring from rebound of the forefoot. To turn the ~oot,
the wearer must internally rotate the hip. This manoeuvre must be
repeated with each stride and consumes a great deal of energy.
In another aspect, most known prosthetic feet lack the
flexibillty in ~he heel required for balanced absorptlon of purely
vertical impacts, which occur frequently during athletic
activities. For shock absorp~ion, most of these devices primarily
on vertical compression of a sharp bend, such as a C-shaped heel
portion. The rebound resulting from this compression,
particularly in response to a substantially vertical lmpact, often
throws the wearer backwards. Moreover, a configuration which
depends for flexibility upon compression o~ a sharp bend is more
susceptible to breakage.
SummarY o~ the Invention
The present invention provides an energy storing
prosthetic foot comprlsing a keel formed of an energy storing
material, wherein the keel co~priseæ a heel portion characterized
by an elongate member, a forefoot portion characterlzed by an
- elongate me~ber and an ankle portion, wherein the inferior aspects
of the heel portlon, the ankle portion and tha fore~oot portlon
define a resillent arch in the keel, wherein the keel is supported
in the prosthetic ~oot so tha~ the apex of the resilient arch i5
generally under the ankle portion of the prosthetic foot, wherein
the keel is supported in the prosthetic foot so that tha resilient
arch iB capa~le of expandiny in xesponse to a load on the
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prosthetic foot for storing energy and capable of contractlng as
the load is lifted to release the stored energy, wherein the keel
is supported ln the prosthetic foot so that in the assembled
prosthetic foot the space under the resilient arch is
substantially unobstructed, and wherein substantially all the
energy ~toring capabillty of the prosthetic foot resides in such
expansion and contraction of the resilient arch ~f the keel.
In the preferred embodiment, the fore~oot portlon is
contoured 80 that the medial side is thicker than the lateral
side, and the toe end of the forefoot ls biased along the natural
toe break
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line. Also, the upper portion of the ankle portion
defines a platform, and the posterior aspect of the
ankle portion under the platform and the superior
aspect of the heel portion continuous therewith
define a concavity.
Tha ankle portion of the keel may be
provided with a vertical throughbore for connecting
the foot to any of several commercially available
leg assemblies in a known manner. Due to the
~ 10particular design of the present foot, the apex of
-~ the keel's arch is anterior to the central axis of
the pylon of most leg assemblies. To adjust for
, this, the central axis of the bore is posterior to
the apex of the arch of the keel.
15In most instances it will be desirable to
cover the keel with a flexible cosmetic covering.
The preferred covering of this foot is solid except
' ~or a cavity disposed under the ankle portion of
- the keel and ext~nding a distancQ under the heel
and forefoot portions as well. To prevent damage
to the inside of the cosmetic covering, the ends of
the forefoot and heel portions of the keel may be
provided with bumpers.
A prosthesis constructed in accordance
with the present invention overcomes the
aforementioned problems common in prior art
devices. The strength and dynamics of this
~, prosthesis are derived mainly from the basic arched
configuration of khe keel. The arch has long been
recognized as the strongest architectural shape.
The inherent strength of the arched design permits
the keel of the ~oot to be thinner, and thus
lighter and more flexible.
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The arch operating in concert with the
uniquely shaped heel and forefoot portions provides
pure balanced vertical shock absorption, most
appreciated in running and jumping and the more
strenuous athletic movements. Due to the
configuration of the ankle portion, with the
concavity formed at the point where the heel
portion joins the ankle portion, the length and
thus the flexibility of the heel portion is
increased. Yet, the entire keel fits nicely inside
a naturally shaped cosmesis.
The forefoot portion of a prosthesis
constructed in accordance with this invention will
flex as much as 40 to 60 degrees. This
co~figuration also increases the medio-lateral
flexibility contributing to eversion and inversion
of the foot.
In addition to being more ~lexible, the
contoured forePoot with its biased toe end shifts
medially the longitudinal midline of the wearer's
wsight distribution. This allows th~ wearer to
walk vigorously and to run with ths foot in a more
natural toed-out position.
The unique design o~ the cosmetic
covering provides the prosthesis with a pleasing
appearance without obstructing the dynamic
movements of the keel or adding unnecessarily to
the weight of the foot.
Brief Descri~tion of the Drawinas
Figure 1 is a perspe~tive view of a
prosthetic foot constructed in accordance with the
present invention. The outer contours of the
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cosmetic covering are shown in phantom.
Figure 2 is an elevational view of the
medial side of the foot shown in Figure 1.
Figure 3 is an elevational view of the
lateral side of the ~oot shown in Figure 1.
Figure 4 is a plan view of the foot shown
in Figure 1.
Figure 5 is a sectional view of the foot
connected to a leg assembly.
10Figure 6 is a sectional view taken along
line 6-6 o~ Figure 5.
Figure 7 is a sectional view taken along
line 7-7 of Figure 5.
Figure 8 is a sectional view taken along
15line 8-8 of Figure 5.
Figure 9 is a ~ide elevational view of
another foot constructed in accordance with the
present inventio~. In this embodiment the ends o~
the heel and ~orefoot portions of the keel are
20covered by protective bumpers.
Figure 10 is a top plan view of the ~oot
shown in Figure 8.
Figures llA-llB illustrate schematically
the vertical or lift dynamics of the foot o~ this
25invention.
Figures 12A-12E illustrate schematically
the thrust dynamics of the foot during the stance
phase of the gait cycle.
Detailed Description Qf the Preferred Embodiments
30Referring now to the drawings in general
and to Figure 1 in particular, shown therein and
designated by the general reference numeral 10 is
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a prosthetic foot construc-ted in accordance with
the present invention. The foot 10 has as it
primary structural element a single arched keel 12
which preferably is contained within a cosmetic
covering 14 shown in dot-dash lines in Figures 1-4.
The keel 12 is integrally formed of a
sturdy but resilient material. The density of the
material and the degree of resiliency may vary and
should be selected according to the physique and
activity level of the intended wearer.
A preferred resilient material is a
hardened acetal copolymer, such as that marketed
under the brand name Celcon by the Celanese
Corporation (Westlake, Ohio). This material has
been found to be significantly more flexible than
other materials including acetal homopolymers. In
order to achieve the maximum flexibility afforded
by the unique configuration of the keel, the more
flexible copolymer composition should be used.
The method of forming the keel may vary
according to the resilient material selected.
Where a solid copol~mer acetal is used, the keel
may be formed by known milling techniques.
However, it will be appreciated that suitable
polymer compositions are available in liquid form,
and that these may be used to form the keel by
injection molding procedures.
The resilient material is formed to
provida a keel 12 having a forefoot portion 16 and
a heel portion 18 continuous with an ankle portion
20 ther~between. The inferior aspect of the ankle
portion 20 defines an arch 22. ~ost preferably,
the keel 12 is integrally formed, that is carved or
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molded from a single piece o~ flexible material.
The dimensions of the keel 12, including
the heel height, may be varied to suit the wearer.
Generally, a wider keel will provide better
stability for heavier persons and those who enjoy
strenuous physical activity. On the other hand, a
smaller and narrower keel is best for children, and
women may prefer an elevatad heel which permits
them to wear fashionable hi~h heeled shoes. The
arch 22 may be higher or lower to provide more or
less 1exibility. For example, an unusually heavy
individual requires a ~latter arch, a so-called
"low profile" version. It also will be appreciated
a low profile keel may be necessary where the lower
leg of the wearer is unusually lon~.
Attention now is directed to the shape of
the forefoot portion 16 of the keel 12. It is
known that in a normal gait cycle, the body moves
generally forward along a straight line which is
referred to in the art as the line of progression.
- However, with each stride the forefoot is turned
outwardly sightly, so that the longitudinal midline
of the foot is at angle to the line o~ progression.
Typically, the foot turns out about 7 to 12 degrees
from the line of progression. The structure of the
human foot, with the heavier, larger bones on the
medial side and the slanted toe break line ~ormed
by the toe joints, is consistent with the toed-out
position of the fsot durin~ walking.
As mentioned previously, in prior art
prostheses the symmetrical shape of the internal
components which form the forefoot of the device
causes the ~oot to ~all in an unnaturally straight
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forward position at midstance. The prosthetic foot
of this invention overcomes this problem by
providing the forefoot 16 of the keel 12 with an
asymmetrical contour.
Specifically, referring still to Figure
1 and now also to Figures 2 through 4, the forefoot
portion 16 preferably is contoured so that the
medial side 24 (Figure 2) is thicker than the
lateral side 26 (Figure 3). The effect of this
contouring of the forefoot is illustrated in Figure
4. The solid arrow 30 designates the lon~itudinal
midline of weight distribution across the forefoot
16 at midstance. The broken arrow 32 designates
the true longitudinal centerline of the forefoot
16. Thus, the load is shifted to the medial side
of the forefoot 16.
During the gait cycle, the midline of
weight distribution 30 remains generally parallel
to the line of progression, while the true
longitudinal midline 32 of the foot is at a slight
- angle to the line of progression in a normal
fashion. Thus, this prosthesis not only mimic~ the
slightly toed-out position of the human ~oot during
the stance phase, but in effect duplicates the
biomechanics of weight distribution in the human
foot as well.
With continuing reference to Figures 1
through 4, the toe end 28 preferably is biased so
that the medial side 24 is longer than the lateral
side 26. In this way, the toe end conforms to the
line along which the toes in the natural foot flex
relative to the forefoot, referred to as the toe
break line. This enhances the toeing out effect
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caused by the contoured shape of the forefoot 16,
described previously.
The toe end 28 also may be upturned
slightly. This will prevent tearing of the
cosmetic covering 14, and also will provide a
smoother toe-off.
All prosthetic feet must be attached in
some manner to the end of the wearer's affected
limb. This may be accomplished by using a variety
of known leg components, including pylons ~these
form the lower leg), ankle and knee joints and
socXets. The components which combine to serve as
the lower leg portion are referred to herein simply
as a "leg assembly". A prosthetic foot in
combination with a leg assembly is referred to
herein as a "lower limb prosthesis".
Turning now to Figures 5 and 6, the foot
10 of the present invention is shown attached to a
leg assembly 36, which comprises a pylon 38 inside
a cosmetic covering 40, to form a complete lower
limb prosthesis 42. It will be understood that the
foot 10 could be adapted ~or use with virtually any
commercially available leg assembly.
The upper portion of the ankle portion 20
preferably defines a platform 44 (see also Figure
1), which engages the inferior aspect of the leg
assembly 36. The periphery of the plat~orm 44,
best seen in Figure 4, may be shaped to fit within
the ankle portion of the cosmetic covering 14.
For connecting the foot 10 to the leg
assembly 36, the ankle portion 20 has a bore 46
through ~hich a bolt 48 extends. The threaded end
50 of the bolt 48 threadedly engages the threaded
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bore 52 in the lower end of the pylon 38. As best
seen in Figure 5, the bore 46 should be positioned
in the ankle portion 20 so that the central axis of
the bore is disposed slightly posterior to the apex
of the arch 22 in the keel 12.
Returning now to Figures 2 and 3, the
posterior aspect 54 of the ankle portion 20 defines
a concavity 56 which i~ continuous with the
inferior aspeçt 58 of the platform 44 and the
superior aspect 60 of the heel portion 18. This
configuration increases extends the Iength of the
heel 18 and permits tha heel to have a slender
shape. Thus, the heel portion 18 is deformable
along almost its entire length. It will be
appreciated that in some instances the throughbore
46 may intersect the concavity 56.
With a heel portion formed in this
manner, the keel can absorb a vertical shock and
balanc the impact therefrom between the heel 18
and forefoot 16. In other words, in response to a
vertical load, the arch 22 expands evenly and
without throwing or tipping the wearer anteriorly
or posteriorly.
Although the cosmetic covering 14, shown
best in FIgures 5 through 8, is not necessary to
the function of this prosthesis, in most instances
it will be desirable. The covering 14 preferably
consists of self-skinning polyurethane foam
composition which when cured retains a soft, flesh-
like consistency and color.
When fo~med in accordance with the
present invention, the covering 14 is solid with an
outer sh~pe resembling a natural foot and an upper
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surface 62 at the level of the ankle and ~lush with
the platform 44 of the keel 12 for close engagement
with the inferior aspect of the leg assembly 36.
on the inside of the foot 10, the
covering 14 conforms closely to the keel 12 except
for a ca~ity 64 immediately beneath the arch 22 of
the ankle portion 20. The cavity 48 extends a
distance under the forefoot and heel portions 16
and 18 of the keel 12. The cavity 64 reduces the
weight of the foot 10 and prevents the covering 14
from interfering with the flexibility of the Xeel
12.
The cavity 64 may be formed at th~ time
the cosmetic covering 14 is formed by employing the
so-called "void wax" technique. A wedge of wax in
the shape of the desired cavity is applied to the
underside of the arch of the keel before the foam
is applied. After the foam is applied and has set
sufficiently, a bore 66 is drilled through the
foot~ Next, the wax is melted and drained out of
the ~oot 10 through the bore 66. The bore 66 then
permits the bolt 48 to be inserted into the keel
12, as described above.
With continuing reference to Figures 5
and 8, friction patches 68 and 70 may be placed
immediately beneath the pressure points between the
keel 12 and the cosmetic covering 14, namely under
the toe end 28 of the forefoot portion 16 and
beneath the heel portion 18. These patches most
conveniently can be applied, by gluing or the like,
prior to application of the cosmetic covering 14.
The patches preferably are made of a sturdy fabric,
such as polyethylene terephthalate cloth, laminated
~3~81~
with a resin, such as urethane. The patches 68 and
will reduce wear on the covering and thus
prolong the life of the foot 10.
Shown in Figures 9 and 10 is another
embodiment of the present invention. In this
embodiment, the foot 72 comprises a keel 74 with a
cosmetic covering 76 provided as described above.
However, here each of the toe end 78 of the
forefoot portion 80 and the heel portion 82 is
provided with a flexible, bulbous tip or bumper 84
and 86, respectively. The bumpers 84 and 86
preferably are formed of a foam of greater density
than the covering 76. By blunting the edges on the
keel 12, the bumpers ~4 and 86 reduce wear on the
inside the covering 76 without substantially
affecting the flexibility or weight of the foot 72.
The lift or rebound characteristics of
the foot of this invention during midstance are
depicted schematically in Figures llA and llB.
Figure llA depicts the keel in a relaxed or static
- position. In response to a load or sudden impact,
the arch of the keel expands as shown in Figure
llB, and absorbs the ~hock of impact. As the load
is lifted, the arch of the keel springs back
returning the keel to the shape shown in Figure
llA. Because of the flexibility of the heel and
the forefoot portion, the keel remains relatively
level during this motion.
The balanced expansion of the keel in
response to a sudden vertical impact, such as that
caused by jumping and running, will be appreciated
most by those who engage in strenuous sports and
athletic activities. ~t this point, another
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important advantage of the construction of this
foot will be apparent. ~his is the lateral to
medial flexibility of the keel 12, which permits
inversion and eversion of the prosthesis. This
feature is most pronounced in the forefoot portion.
Again, while this feature generally makes the
prosthesis more comfortable for any wearer, it
proves most advantageous to the athlete~
Figures 12A through 12E depict the
forward motion or thrust dynamics of the prosthetic
foot of this invention during the stance phase of
the gait cycle. Figure 12A depicts heel strike,
the first of the stance phases. This is the point
immediately following the swing phase (not shown)
at which tha heel touches down and just prior to
weight being shifted from the othPr foot to the
prosthesis. As weight shifts to the prosthesis,
the heel portion of the keel flexes, ~s shown in
Figure 12B. By flexing at this point, the heel
provides controlled movement of the ~oot from heel
strike to midstance and eliminates the slapping
e~fect sometimes experi nced in prosthsses with
less resilience in the heel. Accordingly, the
flexibility of the heel portion in this foot
substitutes for the anterior muscles of the lower
leg.
As the forefoot portion is brought down
into midstanc~, shown in Figure l~C, the tension in
the heel is expressed as a thrust force propelling
the foot forward towards midstance. Much of the
impact of each stride is absorbed during midstance,
which also is depicted in Figures llA and llB
described previously.
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At the end of midstance and as the body
of the wearer moves forward (Figure 12D), the
weight is lifted off the prosthesis. As the arch
recoils, the wearer experiences a bounce or lift.
As the body continues to move forward and
the opposite foot swings towards its next heel
strike, the ~orefoot portion flexes, as shown in
Figure 12E. As the forefoot continues to flex,
resistance increases preventing the wearer from
moving forward too quickly. The release o~ the
tension at push-off urges the foot up and away from
the ground and propels the foot towards the next
swing phase. ThP power~ul spring action of the
forefoot simulates the action of the posterior
muscles in the lower leg.
Now it will be appreciated that the
present invention provides a prosthetic foot having
uni~ue shock a~sorbing characteristics. Because of
its shape and flexibility, all of the directional
components of a single stride, from heel strike to
. toe-off are progressively absorbed by this foot ~s
each portion of the keel is deformed and then
rebounds to its original shape in a single,
sustained and ~luid movement. Similarly, purely
vertical shocks are absorbed by balanced expansion
of the arch. The positive energy produced by the
rebound action actively participates in the
mechanic~ of walking and running throughout the
stance phase. Further, because of its simple
construction, this lightweight and sturdy
prosthesis can be produced economically and
requires virtually no mainkenance or repair.
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-17-
SUPPLEMENTAL DISCLOSURE
In another embodiment depicted in Figures
13 and 14, the prosthetic foot 90 is provided with
a horizontal slot 92. The slct 92 is formed in the
ankle portion 94 of the keel 96. The slot 92 is
continuous with the concavity 98 of the posterior
aspect of the ankle portion 94 and extends
anteriorly therefrom towards the anterior aspect
100 of the ankle portion 94. The slot 92 generally
is below and parallel to the plat~orm 102 and above
the arch 104 and intersects the throughbore 106
which receives the bolt 108.
The anterior end portion 110 o~ the slot
92 preferably is substantially circular in
longitudinal cross-section and has a diameter
greater than the width o~ the slot 92. The enlarged
rounded end 110 of the slot stunts any tendency of
the ankle portion 94 anterior to the slot to cracX
or break.
The slot 92 extends the entire width of
the ankle portion 94. Thus, the slot 92 divides
approximately the rear half of the ankle portion 94
into an upper segment 112 and a lower segment 114.
The portion of the throughbore 106 which extends
through the lower segment 114 is slightly larger
than the portion which extends through the upper
segment 112. In this way the head 116 of the bolt
108 engages the upper segment 112. When thus
arranged, the bolt 108 will not interfere with the
compression of the slot 92.
It will be appreciated that when weight
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is placed on the foot 90, the slot 92 in the ankle
portion 94 compresses at the same time that the
arch 104 expands. Thus, the slot 92 in effect
extends the length of the heel portion 118 and even
further enhances the flexibility and the shock
absorption capacity of the keel 96. This movement
in the ankle portion 94 i5 similar to a slight
dorsiflexion and plantar flexion and contributes to
the anterior-posterior spring in the keel 96. In
effect, the compression and release of the slot 92
mimic the natural movement of the ankle bones in
the human foot.
Changes can be made in the nature,
composition, operation and arrangement of the
various elements, steps and procedures described
herein without departing from the spirit and scope
of the invention as defined in the following
claims.
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