U.S. patent application number 09/957971 was filed with the patent office on 2002-04-04 for prosthesis with resilient ankle block.
Invention is credited to Phillips, Van L..
Application Number | 20020040249 09/957971 |
Document ID | / |
Family ID | 23115548 |
Filed Date | 2002-04-04 |
United States Patent
Application |
20020040249 |
Kind Code |
A1 |
Phillips, Van L. |
April 4, 2002 |
Prosthesis with resilient ankle block
Abstract
An ankle block prosthesis is provided having a lower foot plate
and an upper ankle plate connected by a monolithic ankle block. The
foot plate, ankle plate and ankle block are generally sized to fit
within a surrounding cosmesis. The foot is configured such that
during a walking or running stride the wearer experiences a smooth
rollover or transition of compressive forces from a heel-strike
position to a toe-off position so as to provide a natural feeling
foot during walking or running activities.
Inventors: |
Phillips, Van L.; (Rancho
Santa Fe, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
620 NEWPORT CENTER DRIVE
SIXTEENTH FLOOR
NEWPORT BEACH
CA
92660
US
|
Family ID: |
23115548 |
Appl. No.: |
09/957971 |
Filed: |
September 20, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09957971 |
Sep 20, 2001 |
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09452032 |
Nov 30, 1999 |
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09452032 |
Nov 30, 1999 |
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09078450 |
May 13, 1998 |
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5993488 |
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09078450 |
May 13, 1998 |
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08515557 |
Aug 15, 1995 |
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5800569 |
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08515557 |
Aug 15, 1995 |
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08692340 |
Aug 5, 1996 |
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5728177 |
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08692340 |
Aug 5, 1996 |
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08290339 |
Aug 15, 1994 |
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Current U.S.
Class: |
623/52 ;
623/55 |
Current CPC
Class: |
A61F 2002/6657 20130101;
A61F 2230/0082 20130101; A61F 2002/30261 20130101; A61F 2002/5055
20130101; A61F 2002/6614 20130101; A61F 2002/30433 20130101; A61F
2002/5007 20130101; A61F 2/78 20130101; A61F 2220/0041 20130101;
A61F 2220/0075 20130101; A61F 2002/5001 20130101; A61F 2/66
20130101; A61F 2002/30462 20130101; A61F 2/6607 20130101 |
Class at
Publication: |
623/52 ;
623/55 |
International
Class: |
A61F 002/66 |
Claims
What is claimed is:
1. A prosthetic foot for providing resilient kinematic support to
an amputee, said prosthetic foot comprising: a lower foot plate
element having a length from toe to heel roughly equal to that of a
natural human foot being replaced, said foot plate element being
formed of a monolithic composite material having an area moment of
inertia about a first axis that is substantially smaller than the
area moment of inertia about a second axis perpendicular to said
first axis such that said foot plate element is capable of flexing
along its length in a fore-and-aft direction, but not substantially
in a side-to-side direction, said foot plate element defining toe
and heel portions of said prosthetic foot; an upper ankle plate
element having a length shorter than said foot plate element and
being separately formed of a monolithic composite material having
an area moment of inertia about a first axis that is substantially
smaller than the area moment of inertia about a second axis
perpendicular to said first axis such that said ankle plate element
is capable of flexing along its length in a fore-and-aft direction,
but not substantially in a side-to-side direction, said ankle plate
element and said foot plate element being spaced apart from one
another along their entire length; an ankle block comprising a
compressible material having a thickness of between about 0.83
inches and about 1.30 inches, said ankle block being positioned
between said ankle plate element and said foot plate element; and
an attachment member secured to said ankle plate element adapted to
attach said prosthetic foot to a pylon or socket, said attachment
member defining an attachment axis located posteriorly along a
longitudinal center line at a point approximately two-thirds of the
distance rearward along the length of said ankle plate element;
said foot plate element, said ankle plate element and said ankle
block cooperating such that as said amputee walks on said foot,
compression stress migrates substantially uniformly through said
ankle block such that substantially smooth rollover of said foot
prosthesis is achieved.
2. The prosthetic foot of claim 1, wherein said ankle block extends
roughly said length of said ankle plate element.
3. The prosthetic foot of claim 1, wherein said foot plate element
comprises a resilient plate formed from a plurality of laminae
embedded in a hardened flexible polymer material.
4. The prosthetic foot of claim 3, wherein said ankle plate element
comprises a resilient plate formed from a plurality of laminae
embedded in a hardened flexible polymer material.
5. The prosthetic foot of claim 1, wherein said ankle block
comprises a monolithic block formed of a relatively compliant
compressible material.
6. The prosthetic foot of claim 5, wherein said ankle block is
formed of a polyurethane material.
7. The prosthetic foot of claim 6, wherein said ankle block is
formed of a cellular polyurethane foam having a density of between
about 25-35 lbs/ft.sup.3.
8. The prosthetic foot of claim 1, wherein said ankle block
comprises a monolithic block formed of a natural or synthetic
rubber.
9. A prosthetic foot, comprising: a monolithic foot plate having
toe and heel portions and a length from toe to heel roughly equal
to that of a natural human foot being replaced, said foot plate
comprising a resilient multi-laminate material capable of flexing
substantially along its length; an ankle plate having a length
substantially shorter than said foot plate, said ankle plate being
disposed substantially above and roughly parallel to said foot
plate so as to define a space therebetween; a resilient ankle block
comprising a compressible material positioned between said ankle
plate and said foot plate in said space formed between said foot
plate and said ankle plate; and an attachment member secured to
said ankle plate adapted to attach said prosthetic foot to a pylon
or other intermediate prosthetic device, said attachment member
defining an attachment axis located posteriorly along a
longitudinal center line at a point such that more of said
resilient ankle block is disposed forward of the attachment axis
than is disposed to the rear of the attachment axis; said foot
plate, said ankle plate and said ankle block cooperating such that
as said amputee walks on said foot, compression stress migrates
substantially uniformly through said ankle block so as to provide
substantially smooth rollover of said prosthetic foot.
10. The prosthetic foot of claim 9, wherein said attachment member
defines an attachment axis located posteriorly along a longitudinal
center line at a point approximately two-thirds of the distance
rearward along the length of said ankle plate element.
11. The prosthetic foot of claim 9, wherein said ankle block
comprises a monolithic block formed of a relatively compliant
compressible material.
12. The prosthetic foot of claim 11, wherein said ankle block is
formed of a polyurethane material.
13. The prosthetic foot of claim 12, wherein said ankle block has a
thickness of between about 0.83 inches and about 1.30 inches.
14. The prosthetic foot of claim 12, wherein said ankle block is
formed of a cellular polyurethane foam having a density of between
about 25-35 lbs/ft.sup.3.
15. The prosthetic foot of claim 1, wherein said ankle block
comprises a monolithic block formed of a natural or synthetic
rubber.
16. A prosthetic foot, comprising: a lower foot plate having a
length and width approximately equal to that of a natural human
foot being replaced, said foot plate having anterior and posterior
ends and being constructed of a material capable of flexing along
its length; an upper ankle plate having a length shorter than said
length of said foot plate, said ankle plate having anterior and
posterior ends and being constructed of a material capable of
flexing along its length, said foot plate and said ankle plate
being disposed relative to one another so as to define a space
therebetween; an ankle block of compressible foam material bonded
to an upper surface of said foot plate and to a lower surface of
said ankle plate, said ankle plate being aligned with said ankle
block and both being positioned rearward from a center of said foot
plate; and an attachment member secured to said ankle plate adapted
to attach said prosthetic foot to a pylon or other intermediate
prosthetic member, said attachment member defining an attachment
axis located posteriorly along a longitudinal center line of said
ankle plate and wherein said attachment member further comprises
means for aligning said prosthetic foot relative to said pylon or
socket and for transmitting torsional forces from said prosthetic
foot to said pylon or socket.
17. The prosthetic foot of claim 16, wherein said attachment member
defines an attachment axis located posteriorly along a longitudinal
center line at a point approximately two-thirds of the distance
rearward along the length of said ankle plate element.
18. The prosthetic foot of claim 16, wherein said ankle block
comprises a monolithic block formed of a relatively compliant
compressible material.
19. The prosthetic foot of claim 18, wherein said ankle block is
formed of a polyurethane material.
20. The prosthetic foot of claim 19, wherein said ankle block has a
thickness of between about 0.83 inches and about 1.30 inches.
21. A prosthetic foot for replacing a natural human foot, said
prosthetic foot comprising: an elongated lower foot plate element
having a length and width roughly equal to that of said natural
human foot being replaced, said foot plate element having top and
bottom surfaces and being formed of a resilient material having an
area moment of inertia about a first axis that is substantially
smaller than the area moment of inertia about a second axis
perpendicular to said first axis such that said foot plate element
is capable of flexing along its length in a first direction but not
substantially in a second direction; an elongated upper ankle plate
element having a length shorter than said foot plate element, said
upper ankle plate element having top and bottom surfaces and being
formed of a resilient material having an area moment of inertia
about a first axis that is substantially smaller than the area
moment of inertia about a second axis perpendicular to said first
axis such that said ankle plate element is capable of flexing along
its length in a first direction, but not substantially in a second
direction; an elongated monolithic block of compressible material
having a top surface and a bottom surface, the bottom surface of
said monolithic block being bonded to the top surface of said foot
plate element such that they are substantially aligned along their
respective axes of elongation, the top surface of said monolithic
block being bonded to the bottom surface of said ankle plate
element such that they are substantially aligned along their
respective axes of elongation; and an attachment member secured to
said ankle plate element adapted to attach said prosthetic foot to
a pylon or other intermediate prosthetic member, said attachment
member defining an attachment axis located posteriorly along a
longitudinal center line at a point approximately two-thirds of the
distance rearward along the length of said ankle plate element.
22. The prosthetic foot of claim 21 further comprising a sole
cushion secured to said bottom surface of said foot plate
element.
23. The prosthetic foot of claim 21, wherein said ankle block
comprises a single monolithic block of material having sufficient
strength and resiliency such that it is capable of supporting
substantially the entire weight of an amputee wearing said
prosthetic foot while allowing substantially uniform migration of
stress through said ankle block in response to flexing of said
flexible plate members.
24. The prosthetic foot of claim 23, wherein said ankle block
comprises a monolithic block formed of a polyurethane material.
25. The prosthetic foot of claim 23, wherein said ankle block has a
thickness of between about 0.83 inches and about 1.30 inches.
26. The prosthetic foot of claim 23, wherein said ankle block is
formed of a cellular polyurethane foam having a density of between
about 25-35 lbs/ft.sup.3.
27. The prosthetic foot of claim 23, wherein said ankle block
comprises a monolithic block formed of a natural or synthetic
rubber.
28. A prosthetic foot for replacing a natural human foot, said
prosthetic foot comprising: a lower plate element having a length
and width roughly equal to that of said natural human foot being
replaced and having top and bottom surfaces, said lower plate
element being formed of a monolithic composite material capable of
flexing substantially along its length and having an area moment of
inertia about a first axis that is substantially smaller than the
area moment of inertia about a second axis perpendicular to said
first axis such that said lower plate element is capable of flexing
along its length in a first direction but not substantially in a
second direction; an upper plate element having a length shorter
than said lower plate element and having top and bottom surfaces,
said upper plate element being formed of a monolithic composite
material and having an area moment of inertia about a first axis
that is substantially smaller than the area moment of inertia about
a second axis perpendicular to said first axis such that said upper
plate element is capable of flexing along its length in a first
direction, but not substantially in a second direction; a resilient
ankle member composed of a compressible material sandwiched between
said lower plate element and said upper plate element, said ankle
member comprising a top surface and a bottom surface, the bottom
surface of said ankle member being matingly bonded to the top
surface of said lower plate element, the top surface of said ankle
member being matingly bonded to the bottom surface of said upper
plate element, such that said lower and upper plate elements and
said ankle member are thereby maintained in intimate cooperative
contact with one another along their respective mating surfaces;
and an attachment member secured to said upper plate element
adapted to attach said prosthetic foot to a pylon or other
intermediate prosthetic member, said attachment member defining an
attachment axis located along a longitudinal center line of said
prosthetic foot at a point such that more of said ankle member is
disposed forward of the attachment axis than is disposed rearward
of the attachment axis.
29. The prosthetic foot of claim 28, wherein said lower plate
element comprises a toe end and an uplifted heel end and an
intermediate region therebetween.
30. The prosthetic foot of claim 29, wherein said lower plate
element is tapered along at least a portion of its length so as to
provide desired bending and energy storage characteristics.
31. The prosthetic foot of claim 30, wherein said lower plate
element is tapered from a relatively thick portion proximal said
intermediate region to relatively thin portions proximal said heel
and toe ends.
32. The prosthetic foot of claim 28, wherein said attachment member
comprises a base plate adapted to be fastened to an upper surface
of the upper plate element and an upstanding coupling knob formed
integrally therewith for securing said prosthetic foot to a pylon
or other prosthetic member intermediate said prosthetic foot and
the stump of an amputee.
33. The prosthetic foot of claim 28, wherein said ankle member
comprises a single monolithic block of material having sufficient
strength and resiliency such that it is capable of supporting
substantially the entire weight of an amputee wearing said
prosthetic foot while allowing substantially uniform migration of
stress through said ankle member in response to flexing of said
upper and lower plate elements.
34. The prosthetic foot of claim 28, wherein said ankle member
comprises a monolithic block formed of a polyurethane material.
35. The prosthetic foot of claim 28, wherein said ankle member has
a thickness of between about 0.83 inches and about 1.30 inches.
36. The prosthetic foot of claim 28, wherein said ankle member
comprises a monolithic block formed of a natural or synthetic
rubber.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of application U.S. Ser.
No. 09/078,450 filed May 13, 1998, now U.S. Pat. No. 5,993,488,
which was a continuation of U.S. Ser. No. 08/515,557, filed Aug.
15, 1995, now U.S. Pat. No. 5,800,569, which was a
continuation-in-part of U.S. Ser. No. 08/692,340 filed Aug. 5,
1996, now U.S. Pat. No. 5,728,177, which was a file-wrapper
continuation of U.S. Ser. No. 08/290,339, filed Aug. 15, 1994,
abandoned.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to prosthetic feet and, more
particularly, to a simply constructed, low-profile prosthetic foot
having enhanced dynamic performance characteristics.
[0004] 2. Description of the Related Art
[0005] In the prosthetics market, the conventional SACH foot has
been the most widely prescribed artificial foot over the past 35
years. The SACH foot generally includes a solid ankle and cushioned
heel foot mounted to a limb along an approximate hinge axis taken
through the ankle. The SACH foot has been popular precisely for its
simplicity, and thus economy, but includes certain drawbacks in
terms of dynamic response characteristics. Specifically, the low
end SACH feet do not provide much energy storage and release, as do
more sophisticated prosthetic feet.
[0006] Some patients undergo what is known in the art as a Symes
amputation, where the foot is severed from the leg near the ankle
region. Because the Symes patient's calf and shin function as the
stump for prosthetic purposes, prosthetic devices utilized by the
patient must either be relatively compact, so as to be attachable
below the point of amputation, or must be configured to accommodate
the patient's shin and calf while attached thereto or higher up on
the wearer's leg. Prior art prostheses available to Symes patients
typically include an artificial foot bonded or bolted onto the
bottom end of a socket worn on a patient's stump. These compact
prosthetic feet can also attach below a downwardly depending pylon
secured to a socket higher up on the amputee's leg. For such
compact prostheses, it is difficult to provide the level of dynamic
response approximating the original ankle and foot due to the lack
of vertical space available. Some attempts at providing the
appropriate response characteristics of the original ankle and foot
in Symes foot prosthesis involve the use of rubber cushions, or
bumpers, between a lower leg and the foot. Many of these require a
pivotable bolt attachment between the leg and the foot.
Unfortunately, many of these rubber cushion devices have limited
durability due to the difficulty in bonding the rubber portions to
the solid leg or foot portions, or are relatively complex,
requiring several machined parts, which adds to the cost.
[0007] Consequently, there is a need for an inexpensive and durable
Symes foot prosthesis with improved performance
characteristics.
SUMMARY OF THE INVENTION
[0008] In response to problems with the prior art, the present
invention provides a simple, inexpensive prosthetic foot having a
curvilinear foot element, an ankle element, and an ankle block of
compressible material positioned between and connected to the foot
element and ankle element. Preferably, the foot element has a
length roughly equal to the length of a human foot, while the ankle
element is somewhat shorter. This foot element is constructed of a
resilient material capable of flexing along its length. The
prosthetic foot further has an attachment member connected to the
ankle element opposite the ankle block for coupling the foot to a
downwardly depending leg. In one preferred embodiment, the foot
element has a tapered thickness. Further, the foot element
comprises uplifted heel and toe ends and an arch region
therebetween.
[0009] In the preferred embodiments, the foot element and the ankle
element both comprise plates. In addition, the ankle block
preferably comprises a monolithic element constructed of foam.
Also, desirably, the ankle element is also capable of flexing along
its length.
[0010] In another form, the present invention provides a basic
prosthetic foot having enhanced performance characteristics
generally comprising a lower foot plate, an upper ankle plate, and
a monolithic foam ankle block joining the two plates. Both the foot
plate and the ankle plate are constructed of strong, flexible
material, preferably a vinyl ester based compound. The foot plate
is sized approximately equal to a human foot being replaced, while
the ankle plate has a similar width but has a shorter length than
the foot plate. The ankle block has a length and width
approximately equal to the ankle plate and is aligned therewith.
Preferably, an attachment member couples to a stump or lower-limb
pylon of the wearer via a bolt. During a walking stride, the
combination of the resilient ankle block and flexible plates
provides a smooth rollover from a heel-strike to a toe-off
position.
[0011] Desirably, the ankle block is constructed of a high density
polyurethane foam. During a walking stride, the majority of the
compressive forces imparted by the wearer is absorbed by the ankle
block, with a small portion being absorbed by the flexible plates
themselves.
[0012] Further advantages and applications will become apparent to
those skilled in the art from the following detailed description
and the drawings referenced herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a perspective view of a first preferred prosthetic
foot of the present invention within an outer foot cosmesis shown
in phantom;
[0014] FIG. 2 is a perspective exploded view of the prosthetic foot
of FIG. 1;
[0015] FIG. 3a is an elevational view of the prosthetic foot in a
heel-strike position of a walking stride;
[0016] FIG. 3b is an elevational view of the prosthetic foot in a
flat position of a walking stride;
[0017] FIG. 3c is an elevational view of the prosthetic foot in a
heel-off position of a walking stride;
[0018] FIG. 3d is an elevational view of the prosthetic foot in a
toe-off position of a walking stride;
[0019] FIG. 4 is a perspective view of an alternative preferred
embodiment of a prosthetic foot having features of the present
invention, the outer foot cosmesis being shown in phantom for
illustrative purposes only;
[0020] FIG. 5 is a perspective exploded view of the prosthetic foot
of FIG. 4;
[0021] FIG. 6 is a side elevational view of the prosthetic foot of
FIG. 4 more clearly showing a foot plate having a tapered thickness
along its length; and
[0022] FIG. 7 is a graph of load (F) vs. displacement (x) of a
prosthetic foot constructed in accordance with FIGS. 4-6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] Now with reference to FIGS. 1 and 2, a first embodiment of a
prosthetic foot 20 of the present invention is shown in assembled
and exploded perspective views, respectively. The prosthetic foot
20 generally comprises a lower foot plate 22, an upper, smaller
ankle plate 24, and a layer or block of resilient material 26
connecting the foot plate to the ankle plate. The foot plate 22 has
a length and width roughly equal to the approximate length and
width of the particular wearer's amputated foot and is sized to fit
within an outer flexible cosmesis 28, shown in phantom. The ankle
plate 24 and resilient block 26 have approximately the same
horizontal cross-sectional size. The ankle plate 24 and resilient
block 26 are centered transversely with respect to and are
generally positioned over the back half of the foot plate 22. The
ankle block 26 is sandwiched between the foot plate 22 and ankle
plate 24, and is preferably bonded to both plates. The foot plate
22 may also have a lower sole cushion 30 providing protection for
the inner surfaces of the cosmesis 28 from the corners of the foot
plate.
[0024] The prosthetic foot 20 is connected to a stump or lower leg
pylon (not shown) of a wearer via an attachment member 32. The
attachment member 32 is adapted to be fastened to an upper surface
of the ankle plate 24 and includes a coupling knob 34 for mating
with a coupling member on the pylon. In the illustrated embodiment,
the attachment member 32 comprises a base plate 36, having the
upstanding coupling knob 34 formed integrally therewith. The
attachment member further may include a pair of upstanding location
pins 48, which help transmit torsional forces between the pylon and
the foot prosthesis 20.
[0025] A central threaded bore 38 in the knob 34 receives a
fastening bolt 40 extending upwardly through an aperture 42 in the
ankle plate 24. The resilient block 26 is preferably formed with a
cavity 44 in its upper surface to receive the downwardly protruding
bolt head 46. Of course, other attachment members can be attached
via the upwardly directed fastening bolt 40, as will be readily
apparent to those of skill in the art. The center of the bolt 40
defines an attachment axis 47 which is generally aligned with the
vertical centerline of an imaginary ankle so as to more faithfully
simulate the location at which forces are transmitted between leg
and foot. This centerline is positioned rearwardly from the
longitudinal center of the ankle plate 24 and block 26 and,
preferably, approximately two-thirds of the way from the front end
of the ankle plate 24 and ankle block 26. Thus, there is
substantially more resilient material forward of the centerline 47,
as well as the attachment member 32, than to the rear.
[0026] Both the foot plate 22 and the ankle plate 24 are preferably
constructed of fiberglass, which provides strength and flexibility.
Alternatively, the plates 22 and 24 may be formed by a plurality of
lamina embedded in a hardened, flexible polymer. In other
arrangements the plates 22 and 24 may be formed of other materials,
such as carbon fibers, as may be apparent to one skilled in the
art. The desirable properties of the plates 22, 24 are that they
are relatively resilient so as to withstand cracking upon
application of repeated bending stresses, yet have sufficient
flexibility to enhance the performance characteristics felt by the
wearer, in conjunction with the properties of the resilient ankle
block 26.
[0027] To more fully explain the improved performance
characteristics of the present prosthetic foot 20, FIGS. 3a-3d show
"snapshots" of a prosthetic foot in several positions of a walking
stride. More particularly, FIG. 3a shows a heel-strike position,
FIG. 3b shows a generally flat position, FIG. 3c shows a heel-off
position, and FIG. 3d shows a toe-off position. Throughout the
various positions shown for a walking stride, the present
prosthetic foot 20 provides a smooth and generally life-like
response to the wearer. During a walking stride, the ankle block 26
transmits the forces imparted thereon by the foot plate 22 and
ankle plate 24, and experiences a gradual rollover, or migration of
the compressed region, from rear to front.
[0028] With specific reference to FIG. 3a, a first position of a
walking stride generally entails a heel strike, wherein the wearer
transfers all of his or her weight to the heel of the leading foot.
In this case, a rear portion 50 of the foot plate 22 comes in
contact with a ground surface 52, albeit through the sole cushion
30 and cosmesis 28. The flexible nature of the foot plate 22 allows
it to bend slightly in the rear portion 50, but most of the
compressive stresses from the weight of the wearer through the
prosthetic foot 20 to the foot plate 22 are absorbed by a rear
region 54 of the ankle block 26. Further, a slight amount of
bending may occur in a rear region 56 of the ankle plate 24,
although this bending is limited by the short lever arm between the
axis of attachment 47 and effective center of application of
resisting force by the walking surface on the foot 20.
Additionally, the ankle block 26 reinforces all but a small portion
of the rear portion 50 of the foot portion against bending. A front
portion 58 of the ankle block 26 experiences a stretching, or
tension, due to the attachment along the entire lower edge of the
ankle block with the foot plate 22.
[0029] Next, in FIG. 3b, the wearer reaches a generally flat-footed
position, whereby the foot plate 22 contacts the ground 52 along
substantially its entire length, again through the sole cushion 30
and cosmesis 28. In this position the weight of the wearer is
directed substantially downwardly, so that the compression along
the length of the ankle block 26 is only slightly greater in the
rear portion 54 due to the off-center application of force.
Although this view freezes the compressive stress distribution as
such, in reality the weight of the wearer is continually shifting
from behind the centerline 47 of the attachment member 32 to
forward thereof. Thus, as the wearer continues through the stride,
the compression of the ankle block 26 travels from the rear portion
54 toward the front portion 58. This migration of the compressed
region can be termed "rollover."
[0030] In a next snapshot of the walking stride, FIG. 3c shows the
prosthetic foot 20 in a "heel-off" position. This is the instant
when the wearer is pushing off using ball 60 and toe 62 regions of
the foot. Thus, a large compressive force is generated in the front
region 58 of the ankle block 26, causing the rear region 54 to
experience a large amount of separation or tension. The front tip
64 of the foot plate 22 may bend substantially to absorb some of
the compressive stresses. Likewise, the front tip 66 of the ankle
plate 24 may bend somewhat at this point. It is important to note
that although the ankle block 26 absorbs a majority of the
compression generated by the wearer, the foot plate 64 and ankle
plate 66 are designed to work in conjunction with the resilient
ankle block and provide enhanced dynamic performance. Further, the
flexing of the foot plate 64 and ankle plate 66 relieves some of
the extreme sheer stresses applied to the interfaces between the
ankle block 26 and plates, thus increasing the life of the bonds
formed therebetween.
[0031] In FIG. 3d, a final position of the walking stride is shown,
wherein the prosthetic foot 20 remains in contact with the ground
52, but some of the weight of the wearer is being transferred to
the opposite foot, which has now moved forward. In this position,
there is less bending of the front tip 64 of the foot plate 22 and
less compression of the front portion 58 of the ankle block 26.
Likewise, the front tip 66 of the ankle plate 24 may flex a slight
amount, depending on the material and thickness utilized. The
region of highest compression of the ankle block 26 remains at the
farthest forward region 58, but it is reduced from the compression
level of the heel-off position of FIG. 3c. Thus, the rear portion
54 of the ankle block 26 experiences a small amount of tension or
spreading.
[0032] Although the foot plate 22 is shown as substantially flat in
the illustrations for the first preferred embodiment, it may
alternatively be constructed with a slight arch in the center
region, with the toe and heel regions being slightly upwardly
curved to simulate the natural curve of the sole of a human foot as
illustrated in FIGS. 4-6. However, even with a flat foot plate 22,
the foot 20 still performs substantially better than other SACH
feet.
[0033] Referring now in detail to FIGS. 4 and 5, an alternative
preferred embodiment of a prosthetic foot 100 of the present
invention is illustrated. The prosthetic foot 100, as shown in the
assembled view of FIG. 4, generally comprises a lower foot plate
110, an upper, smaller ankle plate 112 and a resilient ankle block
114. The resilient ankle block 114 is located intermediate the
ankle plate 112 and the foot plate 110. The foot plate 110 has a
length and width roughly equal to the approximate length and width
of the particular wearer's amputated foot and is sized to fit
within the outer flexible cosmesis 28, shown in phantom. The ankle
plate 112 and ankle block 114 are centered transversely with
respect to and are generally positioned over the back portion of
the foot plate 110. The ankle plate 112 and ankle block 114 extend
substantially more forwardly of the attachment axis 47 than
rearwardly.
[0034] The ankle block 114 is sandwiched between the foot plate 110
and the ankle plate 112, as shown, and is preferably bonded to both
plates. A limit strap 116 further secures the foot plate 110,
resilient ankle block 114 and ankle plate 112. An attachment plate
118 is positioned over the limit strap 116 and is generally aligned
with the rear end of the ankle plate 112. From FIG. 5, it can be
seen that the attachment plate 118 preferably includes a cutaway
portion 120 to accommodate the thickness of the limit strap
116.
[0035] The prosthetic foot 100 is attached to a socket or lower leg
pylon via a bolt (not shown) which extends through a corresponding
hole 122 in the foot plate 110 and coaligned holes 124, 128, 130
formed in the ankle block 114, the ankle plate 112 and the
attachment plate 118, respectively. A stainless steel washer 126 is
received in a recess 132 formed on the top of the ankle block 114
in order to provide a flush interface between the block 114 and the
ankle plate 112. Other attachment means, as may be apparent to
those of skill in the art, may alternately be utilized with the
prosthetic foot of the present invention.
[0036] As illustrated in FIG. 6, the foot plate 110 is preferably
of curvilinear shape. The thickness t along its length is tapered,
and the tapered profile corresponds approximately to the weight of
the amputee. That is, for a heavier amputee, the thicknesses along
the length would be greater than for a lighter weight amputee.
Generally, the weight groups may be classified as light, medium, or
heavy.
[0037] Table I below presents preferred groupings, as module sizes
C/D/E, of cosmesis sizes corresponding to a male "A" width shoe
last. The sizes are presented by length L, width B at the forefoot
and width H at the heel of the cosmesis.
1TABLE I Cosmesis Sizes for Male "A" Width Shoe Last WIDTH B WIDTH
H MODULE LENGTH L (cm) (cm) (cm) C 22 2.88 2.19 23 3.00 2.25 24
3.12 2.31 D 25 3.25 2.44 26 3.38 2.50 27 3.50 2.56 E 28 3.62 2.69
29 3.75 2.75 30 3.88 2.81
[0038] Table II below presents preferred module sizes for various
weight groups of amputees.
2TABLE II Modules vs. Weight Groups WEIGHT GROUP MODULE LIGHT
MEDIUM HEAVY C CL CM -- D DL DM DH E -- EM EH
[0039] Table III below presents preferred taper thicknesses (t) for
an average or "DM" size foot plate 110, taken at positions spaced
by distance x=1 inch (2.54 cm).
3TABLE III Taper Thickness t for DM Foot Plate POSITION (x = 2.54
cm) THICKNESS t (cm) a 0.16 b 0.16 c 0.32 d 0.52 e 0.69 f 0.78 g
0.71 h 0.60 i 0.48 j 0.28
[0040] The foot plate 110 has a heel end 134, toward the left in
FIG. 6, is concave-upward or slightly uplifted from a horizontal
plane P.sub.1 tangential to the heel end 134 of the foot plate 110.
Similarly, a toe end 136, to the right of FIG. 6, is concave upward
or somewhat uplifted from a horizontal plane P.sub.2 tangential to
the front portion of the foot plate 110. An arch section 138 is
formed between the heel and toe ends and is preferably
concave-downward, as shown.
[0041] It is understood that within the cosmesis 28 (FIG. 4), the
tangent plane P.sub.1 of the heel end 134 is slightly raised a
distance y relative to the tangent plane P.sub.2 of the toe end
136, as shown. The DM-sized foot plate of Table III, for example,
has y=0.5 inches (1.27 cm). The foot plate 110 is preferably 0.25
inches (0.63 cm) from the bottom or sole of the cosmesis 28. The
cosmesis 28 may be insert molded using an anatomically sculpted
foot shape, with details and sizing based on a master pattern
and/or digitized data representing typical foot sizes.
[0042] An intermediate region 138 comprising the arch portion of
the foot plate 110 has the greatest thickness of the foot plate
110. The curvature of the arch region 138 is defined by the
cosmesis or shoe sole profile, and generally corresponds to
selected ranges of human foot lengths.
[0043] The ankle plate 112 is preferably shorter in length than the
foot plate 110 and has a thickness also defined by the weight group
of the wearer. The ankle plate 112 is also preferably formed of a
flexible material so that flexing of the foot plate 110 and ankle
plate 112 tends to relieve extreme sheer stresses applied to the
interfaces between the ankle block 114 and the plates 110, 112. The
preferred material for the ankle plate 24,112 and the foot plate
22,110 is a vinyl ester based sheet molding compound, such as
Quantum #QC-8800, available from Quantum Composites of Midland,
Mich.
[0044] The ankle block 114 is generally sized such that its upper
surface 140 is planar and corresponds to the length and width of
the ankle plate 112. A lower surface 142 of the ankle block 114 is
longer than its upper surface 140 and generally corresponds to the
contour and size of the arch region 138 of the foot plate 110. A
downwardly sloping front section 144 of the ankle block 114 forms a
face 146 connecting the upper and lower surfaces 140, 142 of the
ankle block 114. The face 146 forms an angle .theta. of
approximately 15.degree. to the vertical or to the attachment axis
47, extending downwardly from the ankle plate 112 to the foot plate
110. Alternatively, other angles .theta. ranging from about
5.degree. to about 45.degree. may be used to achieve the benefits
taught herein. The particular shape of the ankle block 114 causes
it to distribute and transfer compression stress uniformly. The
shorter length of the ankle plate 112 and the sloping front section
144 of the ankle block 114 tend to reduce shear stresses occurring
near the front tip of the ankle plate 112, which could otherwise
cause undesirable delamination of the foot 100.
[0045] For the example given in Table III for a DM-sized foot plate
110, the length of the plate 110 is approximately 9.05 inches
(22.81 cm) and its width is about 2.0 inches (5.04 cm). The hole
122 is centered about 2.31 inches (5.82 cm) from the rear edge
(position a), and the diameter is preferably 0.75 inches (1.89 cm).
The corresponding ankle block 114 for this example has a width of
about 1.85 inches (4.66 cm), and the length of a top surface 140 is
about 4.75 inches (11.97 cm). The recess 132 is preferably 1 inch
(2.54 cm) in diameter, and the hole 124 is 0.63 inches (1.59 cm) in
diameter. The hole 124 and recess 132 are desirably centered 1.31
inches (3.30 cm) from the rear edge of the ankle block 114.
[0046] In the present example, the block 114 has a preferred
maximum thickness, at its front, of about 1.30 inches (3.28 cm),
and its thickness tapers to a minimum of about 0.83 inches (2.09
cm). The rear of the block 114 is preferably about 1.06 inches
(2.67 cm), which is less than the front of the block 114 due to the
raised heel end 134 of the foot plate 110. The corresponding ankle
plate 112 in the present example is preferably about 0.22 inches
(0.55 cm) thick, and approximately 4.75.times.1.85 inches
(11.97.times.4.66 cm). The hole 128 is preferably about 0.41 inches
(1.03 cm) in diameter.
[0047] The attachment plate 118 is sized to about 2.62.times.1.85
inches (6.60.times.4.66 cm), and has a thickness of about 0.12
inches (0.30 cm) at the front and about 0.06 inches (0.15 cm) at
the rear to accommodate the strap 116. The cutaway portion 120
extends about 0.80 inches (2.02 cm) from the rear end of the plate
118. The plate hole 130 is also about 0.41 inches (1.03 cm) in
diameter.
[0048] The washer 126 is preferably about 0.125 inches (0.32 cm)
thick and has an outer diameter of about 0.938 inches (2.36 cm) and
an inner diameter of 0.406 inches (1.02 cm). The limit strap 116 is
preferably about 0.75 inches (1.89 cm) wide and forms an inner
circumference of about 6.40 inches (16.13 cm) in the present
example for a DM-sized foot plate 110. The strap 116 is desirably
about 0.06 inches (0.15 cm) thick.
[0049] A preferred material for the ankle block 26, 114 is expanded
polyurethane such as Cellular Vulkolka.RTM. Pur-Cell #15-50, with a
density approximately 500 kg/m.sup.3, as available from Pleiger
Plastics Company of Washington, Pa. Alternatively, the ankle block
may be molded or fabricated from a wide variety of other resilient
materials, as desired, such as natural or synthetic rubber,
plastics, honeycomb structures or other materials. Cellular foam,
however, provides a desirable viscoelastic springiness for a more
natural feeling stride without the drawback of limited compression
associated with solid elastomeric materials. Furthermore, the
cellular nature of the block 26, 114 makes it lighter than solid
elastomers. Foam densities between about 150 and 1500 kg/m.sup.3
may be used to obtain the benefits of the invention taught
herein.
[0050] The ankle block 26, 114 may be provided in varying heights
or thicknesses, as desired, but is most effective with a thickness
of between about 1 and 3 inches (2.54 and 7.56 cm). The ankle block
thus provides a relatively stiff, yet flexible ankle region which
can be customized for various wearers. Heavier wearers may require
a denser resilient material for the ankle block, while lighter
wearers may require a less dense material or less thickness.
[0051] The limit strap 116 serves to contain or control the
separation or delamination of the rear portions of the foot plate
110, ankle block 114 and ankle plate 112 during the heel-off
portion of the amputee's stride, when the rear of the foot 100
undergoes maximum tension. The strap 116 preferably forms a snug
fit around this sandwiched assembly. The strap 116 desirably has an
overlap 148 of approximately 1 inch (2.54 cm) which is sewn using a
cross-stitch of heavy nylon thread. The strap 116 may be formed of
any durable material; although, woven nylon is preferred. Although
the strap 116 is shown with the overlapped portion 148 beneath the
attachment plate 118, it is understood that the overlap 148 may be
positioned otherwise, such as on the outside of the foot contacting
neither the attachment plate 118 or the foot plate 110.
[0052] The attachment plate 118 is preferably shorter in length
than the ankle plate 112, as shown, and is connected to the top
surface of the ankle plate 112 at its rearward portion. The top
surface of the attachment plate 118 forms a mating surface for
receiving a socket or the pylon of a prosthetic lower limb. A
preferred material for the attachment plate 118 is a urethane
elastomer; although, any similar durable material may be utilized,
as desired.
[0053] The thicknesses of the foot plate 110 and ankle plate 112
may be customized for the wearer according to his/her foot size as
well as the approximate weight group of the wearer. Likewise, the
material choice and size for the ankle block 114, limit strap 116
and attachment plate 118 may be varied according to the wearer's
foot size and weight.
[0054] The preferred embodiment of FIGS. 4-6 provides a
particularly smooth and life-like response during normal walking or
running activities. The uniquely curved and sloped ankle block 114
transmits the forces imparted thereon by the foot plate 110 and
ankle plate 112 such that the rollover or migration of the
compressed region is even more gradual and natural as felt by the
amputee. During heel strike the weight of the amputee is initially
transmitted to the heel of the leading foot, and the compressive
stresses are absorbed by a rear region of the ankle block 114. As
the amputee continues through his stride, the compression of the
ankle block 114 travels smoothly and continuously toward the front
portion, giving the foot a natural feel.
[0055] FIG. 7 is a graph of load (F) vs. displacement (x) of a
prosthetic foot constructed in accordance with FIGS. 4-6. The test
specimen was subjected to various toe-loads applied with the foot
prosthesis mounted at an angle .phi. of 20 degrees from vertical,
as illustrated in the accompanying schematic drawing.
[0056] Although not illustrated, the prosthetic foot of the present
invention also provides enhanced performance for the wearer in
inversion or eversion. Prior SACH feet were often relegated to
pivoting about a horizontal axis through the ankle and had
relatively little flexibility from side to side. The present
invention allows the wearer to walk transversely upon sloped
surfaces, for example, with the foot plate generally conforming to
the terrain while the ankle plate remains relatively horizontal due
to the sideways compression of the ankle block. Again, as the
wearer lifts his or her foot, the ankle block resumes its original
shape, thus helping the wearer as energy is stored and then
released.
[0057] It can now be appreciated that the "feel" of the present
prosthetic foot is greatly enhanced by the cooperation between the
foot plate, ankle plate, and ankle block. As the wearer continues
through the walking stride, the dynamic response from the
prosthetic foot is smooth as the ankle block compresses in
different regions. Further, the flexing of the ankle and foot
plates assists in smoothly transmitting the various bumps and jars
found in uneven walking surfaces.
[0058] The embodiments illustrated and described above are provided
merely as examples of certain preferred embodiments of the present
invention. Other changes and modifications can be made from the
embodiments presented herein by those skilled in the art without
departure from the spirit and scope of the invention, as defined by
the appended claims.
* * * * *