U.S. patent application number 10/146426 was filed with the patent office on 2002-09-12 for lower leg prosthesis.
Invention is credited to Brueggemann, James R., Merlette, John B., Rubie, Eric W., Wall, David J..
Application Number | 20020128727 10/146426 |
Document ID | / |
Family ID | 23363723 |
Filed Date | 2002-09-12 |
United States Patent
Application |
20020128727 |
Kind Code |
A1 |
Merlette, John B. ; et
al. |
September 12, 2002 |
Lower leg prosthesis
Abstract
An improved lower leg prosthesis is disclosed that, during use,
provides an improved dynamic feel at heel strike and that provides
improved inversion/eversion compliance. The prosthesis includes an
elongated pylon having an upper, generally vertical section and a
lower, forwardly oriented foot section, and it further includes a
generally horizontally oriented foot plate disposed beneath the
pylon and including a heel section projecting a substantial
distance rearwardly of a vertical pylon axis. An elastomeric layer
is interposed between the pylon and the foot plate, extending along
substantially the entire length of the heel section of the foot
plate, for attaching the pylon and foot plate together. During use
of the prosthesis, at heel strike, upward deflection of the foot
plate's heel section is limited in substantial part both by the
stiffness of the heel section, itself, and by compression of the
portion of the elastomeric layer disposed rearwardly of the
vertical pylon axis.
Inventors: |
Merlette, John B.; (Wilson,
WY) ; Rubie, Eric W.; (Salt Lake City, UT) ;
Wall, David J.; (Sandy, UT) ; Brueggemann, James
R.; (Los Angeles, CA) |
Correspondence
Address: |
SHEPPARD, MULLIN, RICHTER & HAMPTON LLP
333 SOUTH HOPE STREET
48TH FLOOR
LOS ANGELES
CA
90071-1448
US
|
Family ID: |
23363723 |
Appl. No.: |
10/146426 |
Filed: |
May 15, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10146426 |
May 15, 2002 |
|
|
|
09347445 |
Jul 2, 1999 |
|
|
|
6398818 |
|
|
|
|
Current U.S.
Class: |
623/52 ;
623/55 |
Current CPC
Class: |
A61F 2002/607 20130101;
A61F 2/60 20130101; A61F 2002/6657 20130101; A61F 2002/6614
20130101; A61F 2/66 20130101 |
Class at
Publication: |
623/52 ;
623/55 |
International
Class: |
A61F 002/66 |
Claims
I claim:
1. A lower leg prosthesis comprising: an elongated pylon having an
upper, generally vertical section and a lower, forwardly oriented
forefoot section, wherein the upper section defines a vertical
pylon axis; a generally horizontally oriented foot plate disposed
beneath the pylon and including a heel section projecting a
substantial distance rearwardly of the vertical pylon axis; wherein
the pylon and the foot plate both are formed of a high-strength
composite material; and an elastomeric layer interposed between,
and attaching together, the pylon and the foot plate, wherein the
elastomeric layer extends along substantially the entire length of
the heel section of the foot plate; wherein during use of the
prosthesis, at heel strike, upward deflection of the heel section
of the foot plate is limited in substantial part both by the
stiffness of the heel section, itself, and by compression of the
portion of the elastomeric layer disposed rearwardly of the
vertical pylon axis.
2. A lower leg prosthesis as defined in claim 1, wherein: the
forward tip of the foot plate is disposed substantially beneath the
forward tip of the pylon's forefoot section; and the elastomeric
layer extends along substantially the entire length of the foot
plate, from its forward tip to the rearward tip.
3. A lower leg prosthesis as defined in claim 2, wherein the
elastomeric layer has a width that tapers from a minimum at the
foot plate's forward tip to a maximum at a mid-portion of the foot
plate to a minimum at the foot plate's rearward tip.
4. A lower leg prosthesis as defined in claim 3, wherein the
pylon's forefoot section has a width that tapers from a maximum at
a location substantially aligned with the maximum width of the
elastomeric layer to a minimum at the forefoot section's forward
tip.
5. A lower leg prosthesis as defined in claim 4, wherein the points
of maximum width of the pylon's forefoot section and the
elastomeric layer are located forward of the vertical pylon
axis.
6. A lower leg prosthesis as defined in claim 2, wherein the
portion of the elastomeric layer disposed on the heel section of
the foot plate has a concave upper surface.
7. A lower leg prosthesis as defined in claim 6, wherein the
concave upper surface of the portion of the elastomeric layer
disposed on the heel section of the foot plate is a circular arc,
substantially tangent both to the pylon's upper, vertical section
and to the foot plate's rearward tip.
8. A lower leg prosthesis as defined in claim 1, wherein the pylon
and the foot plate each are of unitary construction.
9. A lower leg prosthesis as defined in claim 8, wherein: the
unitary pylon and the unitary foot plate each are formed of an
epoxy/carbon fiber composite material; the elastomeric layer is
formed of a high-density polyurethane material; and the elastomeric
layer non-removably attaches the foot plate to the pylon.
10. A lower leg prosthesis as defined in claim 1, wherein the
portion of the elastomeric layer disposed rearwardly of the
vertical pylon axis provides at least about one-third of the total
resistance to upward deflection of the foot plate's heel section at
heel strike.
11. A lower leg prosthesis as defined in claim 1, wherein the
elastomeric layer has a thickness of at least about one-half
centimeter along substantially its entire length.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates generally to lower leg prostheses
and, more particularly, to lower leg prostheses configured to
duplicate the dynamic performance characteristics of the human foot
and ankle.
[0002] Significant advancements in the field of lower leg
prostheses have been made in recent years, due largely to the
development of composite materials technology. Lower leg prostheses
incorporating fiberglass/epoxy and carbon fiber/epoxy composite
materials have been developed, which closely duplicate the dynamic
performance characteristics of the human foot and ankle.
[0003] One such lower leg prosthesis is disclosed in U.S. Pat. No.
4,959,073 issued to Merlette. The Merlette prosthesis incorporates
an elongated composite main member having a leg section and a
forwardly extending foot section, and it further incorporates a
heel member projecting rearwardly from the underside of the main
member's foot section. A high-density polyurethane elastomer is
disposed between the heel member and the main member's foot
section, to permanently attach the two members together and to
provide limited cushioning. The upper end of the main member's leg
section supports an amputation socket for receiving the amputee's
residual limb, and a crepe sole can be attached to the underside of
the heel member. A foam foot shell or cosmesis can be placed over
the composite members, to provide the prosthesis with an appearance
of a natural human foot.
[0004] The Merlette lower leg prosthesis described briefly above
has enjoyed substantial commercial success. Nevertheless, it is
believed that the Merlette prosthesis can be improved upon by
modifying the structure that resists upward deflection of its heel
section at heel strike and also by providing enhanced
inversion/eversion compliance.
[0005] It should therefore be appreciated that there exists a need
for a lower leg prosthesis that, during use, provides an improved
dynamic feel at heel strike and that provides improved
inversion/eversion compliance. The present invention fulfills this
need and provides further related advantages.
SUMMARY OF THE INVENTION
[0006] The present invention is embodied in an improved lower leg
prosthesis that, during use, provides an improved dynamic feel at
heel strike and that provides improved inversion/eversion
compliance. The prosthesis includes an elongated pylon having an
upper, generally vertical section and a lower, forwardly oriented
foot section, wherein the upper section defines a vertical pylon
axis, and it further includes a generally horizontally oriented
foot plate disposed beneath the pylon and including a heel section
projecting a substantial distance rearwardly of the vertical pylon
axis. The pylon and the foot plate both are formed of a
high-strength composite material, e.g., an epoxy/carbon fiber
composite material. Further, an elastomeric layer, e.g., formed of
a high-density polyurethane material, is interposed between the
pylon and the foot plate, extending along substantially the entire
length of the heel section of the foot plate, for attaching the
pylon and foot plate together. During use of the prosthesis, at
heel strike, upward deflection of the foot plate's heel section is
limited in substantial part both by the stiffness of the heel
section, itself, and by compression of the portion of the
elastomeric layer disposed rearwardly of the vertical pylon
axis.
[0007] In a more detailed feature of the invention, the forward tip
of the foot plate is disposed substantially beneath the forward tip
of the pylon's forwardly oriented foot section, and the elastomeric
layer extends along substantially the entire length of the foot
plate, from its forward tip to the rearward tip. The elastomeric
layer preferably has a width that tapers from a minimum at the foot
plate's forward tip to a maximum at a mid-portion of the foot plate
to a minimum at the foot plate's rearward tip. In addition, the
pylon's forwardly oriented foot section has a width that tapers
from a maximum at a location substantially aligned with the maximum
width of the elastomeric layer to a minimum at the foot section's
forward tip. The points of maximum width of the pylon's forwardly
oriented foot section and the elastomeric layer preferably are
located forward of the vertical pylon axis.
[0008] In other more detailed features of the invention, the
portion of the elastomeric layer disposed on the heel section of
the foot plate has a concave upper surface. This concave upper
surface preferably is a circular arc, substantially tangent both to
the pylon's upper, vertical section and to the foot plate's
rearward tip.
[0009] The portion of the elastomeric layer disposed rearwardly of
the vertical pylon axis preferably provides at least about
one-third of the total resistance to upward flexing of the foot
plate's heel section at heel strike. In addition, this layer has a
thickness of at least about one-half centimeter along substantially
its entire length.
[0010] Other features and advantages of the present invention
should become apparent from the following description of the
preferred embodiments, taken in conjunction with the exemplary
drawings, which illustrate the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a perspective view of a lower leg prosthesis in
accordance with he invention, the prosthesis including a pylon and
a foot plate that are permanently attached to each other by an
intermediate elastomeric layer.
[0012] FIG. 2 is a side elevational view of the lower leg
prosthesis of FIG. 1.
[0013] FIG. 3 is a top plan view of the lower leg prosthesis of
FIG. 1.
[0014] FIG. 4 is a rear elevational view of the lower leg
prosthesis of FIG. 1.
[0015] FIG. 5 is a graph depicting the heel tip deflection as a
function of load, both for the lower leg prosthesis of FIG. 1 and
for a similar prosthesis in which the portion of the elastomeric
layer disposed rearwardly of the vertical pylon axis has been
removed, normalized to have the same total deflection at maximum
load.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0016] With reference now to the illustrative drawings, and
particularly to FIGS. 1-4, there is shown a lower leg prosthesis 10
in accordance with the invention, the prosthesis incorporating an
elongated pylon 12 having an upper, vertically oriented ankle/shin
section 14 and a lower, forwardly oriented forefoot section 16, and
further incorporating an underlying foot plate 18. As best shown in
FIG. 2, the forward tip 20 of the foot plate is disposed
substantially beneath the forward tip 22 of the pylon's forefoot
section. In addition, the foot plate's rearward end defines a heel
section 24 that projects rearwardly of a vertical axis 26 defined
by the pylon's ankle/shin section. An elastomeric layer 28 extends
along substantially the entire length of the foot-plate, or
permanently attaching the foot plate to the pylon. The prosthesis
duplicates the dynamic performance characteristics of the normal
human foot, yet it is of simple construction and can be
manufactured relatively inexpensively.
[0017] The pylon 12 preferably is formed of a conventional
epoxy/carbon fiber material, and it has a rectangular cross-section
along its entire length. The pylon's ankle/shin section 14
transitions smoothly downwardly and forwardly to the forefoot
section 16. The pylon's width is substantially uniform along the
ankle/shin section, but increases to a maximum at the beginning of
the forefoot section and then tapers to a minimum at the forefoot
section's forward tip 22. The pylon's thickness, likewise, is
substantially uniform along the ankle/shin section, but increases
to a maximum where it transitions to the forefoot section, and then
decreases through the forefoot section to a minimum thickness at
the forward tip.
[0018] The foot plate 18, likewise, preferably is formed of a
conventional epoxy/carbon fiber material, and it has a rectangular
cross-section along its entire length. The foot plate's peripheral
shape generally matches that of a natural human foot, as best shown
in FIG. 3. In addition, the foot plate's thickness is generally
uniform, but tapers to minimum at the foot plate's toe tip 20 and
heel tip 30.
[0019] The elastomeric layer 28 is formed of a high-density
polyurethane material, and it is interposed between the foot plate
18 and the forefoot section 16 of the pylon 12 to permanently bond
the members together. This elastomeric layer extends along
substantially the entire length of the foot plate, from its toe tip
22 to its heel tip 30. In the region beneath the forefoot section,
the elastomeric layer has a substantially uniform thickness of
about one-half centimeter and a width that is slightly narrower
than that of the forefoot section, thus tapering to a minimum at
its forward tip.
[0020] The portion of the elastomeric layer 28 that is disposed
rearwardly of the pylon's vertical axis 26, which portion is
identified by the reference numeral 32, interconnects the foot
plate's heel section 24 to the portion of the pylon 12 that
transitions between its ankle/shin section 14 and forefoot section
16. The width of this elastomeric layer portion 32 tapers smoothly
to a minimum at the heel tip 30. In addition, the thickness of this
elastomeric layer portion has a concave curvature, with a
substantially uniform radius of about six centimeters. This
curvature has tangent points substantially at the heel tip 30 and
at the ankle/shin section 14. It will be appreciated that
alternative shapes for this elastomeric layer portion 32 also could
be used.
[0021] The elastomeric layer portion 32 disposed rearwardly of the
pylon's vertical axis 26 functions not only to assist in
permanently attaching the foot plate 18 to the pylon 12, but also
to enhance the performance of the prosthesis 10 during its use,
particularly at heel strike. During the heel strike phase of the
amputee's gait, the heel section 24 of the foot plate 18 deflects
upwardly, to cushion the prosthesis' impact on the ground.
Resistance to this upward deflection is provided not only by the
inherent stiffness of the heel section, itself, but also by
compression of the elastomeric layer portion 32. This contrasts
with many prior composite lower leg prostheses incorporating
projecting heel sections, which resist upward deflection of the
heel section solely by the heel section's inherent stiffness.
[0022] At the point of maximum deflection, the compression of the
elastomeric layer portion 32 is believed to contribute about
one-third of the prosthesis' total resistance to deflection of the
heel section 24 of the foot plate 18. Thus, if a prosthesis were to
be constructed without the elastomeric layer portion, a similar
amount of upward deflection of the heel section would occur for an
impact force about one-third less in magnitude.
[0023] Moreover, the inherent stiffness of the heel section 24 of
the foot plate 18 and compression of the elastomeric layer portion
32 contribute in different ways to resisting upward deflection of
the heel section. In particular, the contribution of the
elastomeric layer portion to upward deflection tends to be greatest
when impact forces are low, while the contribution of the inherent
stiffness of the heel section tends to be greatest when impact
forces are high.
[0024] The different dynamic performance characteristics of the
heel section 24 and the elastomeric layer portion 32 in resisting
the heel section's upward deflection can be appreciated with
reference to FIG. 5, which depicts a graph of the heel section's
load/deflection curve. Actually, two curves for the load/deflection
relationship are presented, including one showing the deflection as
the load is being applied and the other showing the deflection as
the load is being removed. Slightly greater deflection occurs in
the latter case, for a given load.
[0025] Also depicted in FIG. 5 is a graph of the load/deflection
curves for a prosthesis constructed without an elastomeric layer
portion located rearwardly of the prosthesis' vertical pylon axis,
normalized to have a total deflection the same as that of the
prosthesis 10. It will be noted that the prosthesis 10 experiences
less deflection of its heel section at non-maximum loads. This
difference is believed to provide an improved dynamic feel for the
amputee.
[0026] Another performance benefit provided by the elastomeric
layer 28 results from its substantial thickness along its entire
length. As mentioned above, the layer has a substantially uniform
thickness of about one-half centimeter along its entire length
beneath the pylon's forefoot section 16. This thickness facilitates
limited articulation, including inversion and eversion movement, of
the pylon 12 relative to the foot plate 18. The prosthesis 10
thereby better duplicates the motion of the natural human foot.
[0027] It should be appreciated from the foregoing description that
the present invention provides an improved lower leg prosthesis
that, during use, provides an improved dynamic feel at heel strike
and that provides improved inversion/eversion compliance. The
prosthesis includes an elongated pylon having an upper, generally
vertical section and a lower, forwardly oriented foot section, and
it further includes a generally horizontally oriented foot plate
disposed beneath the pylon and including a heel section projecting
a substantial distance rearwardly of a vertical pylon axis. An
elastomeric layer is interposed between the pylon and the foot
plate, extending along substantially the entire length of the heel
section of the foot plate, for attaching the pylon and foot plate
together. During use of the prosthesis, at heel strike, upward
deflection of the foot plate's heel section is limited in
substantial part both by the stiffness of the heel section, itself,
and by compression of the portion of the elastomeric layer disposed
rearwardly of the vertical pylon axis.
[0028] Although the invention has been described in detail with
reference to the presently preferred embodiment, those of ordinary
skill in the art will appreciate that various modifications can be
made without departing from the invention. Accordingly, the
invention is defined only by the following claims.
* * * * *