U.S. patent application number 11/687862 was filed with the patent office on 2007-09-20 for prosthetic hip implants.
This patent application is currently assigned to ZIMMER TECHNOLOGY, INC.. Invention is credited to Lawrence D. Dorr, Wayne G. Paprosky, Aaron Rosenberg.
Application Number | 20070219641 11/687862 |
Document ID | / |
Family ID | 38421481 |
Filed Date | 2007-09-20 |
United States Patent
Application |
20070219641 |
Kind Code |
A1 |
Dorr; Lawrence D. ; et
al. |
September 20, 2007 |
PROSTHETIC HIP IMPLANTS
Abstract
Prosthetic hip stems and acetabular cups for use in prosthetic
hip joints. The hip stem may include a core having a stem portion
and a neck portion, a polymer matrix layer substantially covering
the stem portion of the core, and a porous metal layer
substantially covering the polymer matrix layer. The polymer matrix
layer connects the core and the porous metal layer and provides a
stiffness for the hip stem which more closely mimics the stiffness
of bone than do known hip stems. The hip stems and acetabular cups
additionally include a number of improvements adapted for more
optimized results with certain types of patient anatomy, such as
the anatomy of female patients, for example.
Inventors: |
Dorr; Lawrence D.; (La
Canada, CA) ; Rosenberg; Aaron; (Deerfield, IL)
; Paprosky; Wayne G.; (Winfield, IL) |
Correspondence
Address: |
ZIMMER TECHNOLOGY - BAKER & DANIELS
111 EAST WAYNE STREET, SUITE 800
FORT WAYNE
IN
46802
US
|
Assignee: |
ZIMMER TECHNOLOGY, INC.
Warsaw
IN
|
Family ID: |
38421481 |
Appl. No.: |
11/687862 |
Filed: |
March 19, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
60783880 |
Mar 20, 2006 |
|
|
|
Current U.S.
Class: |
623/22.42 ;
623/22.24; 623/23.26; 623/23.35; 623/23.36 |
Current CPC
Class: |
A61F 2/30907 20130101;
A61F 2/30767 20130101; A61F 2/3662 20130101; A61F 2002/30579
20130101; A61F 2/34 20130101; A61F 2/36 20130101; A61F 2250/0058
20130101; A61F 2002/30535 20130101 |
Class at
Publication: |
623/22.42 ;
623/23.35; 623/23.26; 623/22.24; 623/23.36 |
International
Class: |
A61F 2/36 20060101
A61F002/36; A61F 2/34 20060101 A61F002/34 |
Claims
1. A prosthetic hip stem, comprising: a stem portion having a
proximal end and a distal end, said stem portion defining a
medial/lateral plane; and a neck portion projecting from said
proximal end, said neck portion having a longitudinal axis
therealong which is oriented at a first angle between 13 degrees
and 25 degrees anteriorly with respect to said medial/lateral
plane.
2. The hip stem of claim 1, wherein said stem portion further
comprises: a core; a polymer matrix layer covering at least a
portion of said core; and a porous metal layer substantially
covering said polymer matrix layer.
3. The hip stem of claim 1, wherein said neck portion is integrally
formed with said stem portion.
4. The hip stem of claim 1, further comprising a head portion of
substantially spherical shape, said head portion integrally formed
with said neck portion.
5. The hip stem of claim 1, wherein said neck portion comprises a
modular component separate from said stem portion, said neck
portion selected from a plurality of neck portions having varying
first angles.
6. The hip stem of claim 1, further comprising a head portion of
substantially spherical shape and having a center disposed on said
longitudinal axis, said head portion connected to said neck portion
along a second axis which is disposed at a second angle of between
1 and 25 degrees anteriorly with respect to said longitudinal
axis.
7. The hip stem of claim 6, wherein said head portion comprises a
modular component separate from said neck portion, said head
portion selected from a plurality of head portions having varying
second angles.
8. A prosthetic hip stem, comprising: a stem portion having a
proximal end and a distal end, said stem portion defining a
medial/lateral plane therethrough; a neck portion projecting from
said proximal end of said stem portion and having a first,
longitudinal axis; and a head portion of substantially spherical
shape and connected to said neck portion along said first axis,
said head portion having a center disposed on second axis which is
disposed at a second angle of between 1 and 25 degrees anteriorly
with respect to said first axis.
9. The hip stem of claim 8, wherein said first, longitudinal axis
is disposed at a first angle of between 13 degrees and 25 degrees
anteriorly with respect to said medial/lateral plane.
10. The hip stem of claim 8, wherein said stem portion, said neck
portion, and said head portion are integrally formed with one
another.
11. The hip stem of claim 8, wherein said neck portion comprises a
modular component separate from said stem portion, said neck
portion selected from a plurality of neck portions of varying first
angles, and said head portion comprises a modular component
separate from said neck portion, said head portion selected from a
plurality of head portions having varying second angles.
12. The hip stem of claim 8, wherein said stem portion further
comprises: a core; a polymer matrix layer covering at least a
portion of said core; and a porous metal layer substantially
covering said polymer matrix layer.
13. A prosthetic hip stem, comprising: a stem portion having a
proximal end and a distal end, and a first, proximal/distal
longitudinal axis; and a neck portion projecting from said proximal
end, said neck portion having a second longitudinal axis therealong
which is oriented at a first angle of between 90 and 145 degrees
with respect to said first axis.
14. The hip stem of claim 13, wherein said neck portion is
integrally formed with said stem portion.
15. The hip stem of claim 13, wherein said neck portion is a
modular component separate from said stem portion, said neck
portion selected from a plurality of neck portions having varying
first angles.
16. A prosthetic hip stem, comprising: a stem portion having a
proximal end and a distal end; and a distal end fixation mechanism
operable between a first condition wherein said distal end of said
stem portion has a first width with respect to at least one of a
medial/lateral plane and an anterior/posterior plane of said stem
portion and a second condition wherein said distal end of said stem
portion has a second width with respect to at least one of said
medial/lateral plane and said anterior/posterior plane, said second
width greater than said first width.
17. The hip stem of claim 16, wherein said distal end fixation
mechanism comprises at least one expansion point in said stem
portion defining radially expandable portions of said stem portion,
wherein when said stem portion is in said first condition, said
radially expandable portions are substantially non-expanded and
when said stem portion is in said second condition, said radially
expandable portions are at least partially expanded.
18. The hip stem of claim 16, wherein said distal end fixation
mechanism comprises an expandable structure and at least one
passage in said stem portion, wherein upon insertion of a filler
substance through said at least one passage, said filler substance
expands said expandable structure, wherein when said stem portion
is in said first condition, said expandable structure is
substantially empty, and when said stem portion is in said second
condition, said expandable structure is at least partially expanded
by presence of said filler substance therewithin.
19. An acetabular cup, comprising: a substantially hemispherical
cup portion made of a relatively thin, flexible porous metal; and a
liner fitted within said cup portion, said liner including a
substantially hemispherical bearing surface.
20. An acetabular cup, comprising: a liner including a
substantially hemispherical bearing surface; a porous metal cup
portion; and an intermediate layer disposed between said liner and
said porous metal cup portion, said intermediate layer formed of a
polymer matrix.
21. An acetabular cup, comprising: a liner including a
substantially hemispherical bearing surface; and a cup portion
including an outer hemispherical portion including a substantially
annular loading rib.
22. A prosthetic hip stem, comprising: a proximal end including a
core, a polymer matrix layer covering at least a portion of said
core, and a porous metal layer substantially covering said polymer
matrix layer; and a distal end including a core and a porous metal
layer substantially covering said core.
23. A prosthetic hip stem, comprising: a proximal portion and a
distal portion; an inner core; a porous metal outer layer; and an
elongated cavity formed in said distal portion, wherein said distal
portion is flexible.
24. The hip stem of claim 23, wherein said proximal portion is
between 30 mm and 45 mm in length, and said distal portion is
between 100 mm and 135 mm in length.
25. The hip stem of claim 23, wherein said proximal portion
includes lateral and medial sides which are substantially
complementary radiused.
26. The hip stem of claim 23, wherein said proximal portion
includes anterior and posterior sides which each flare outwardly as
same approach a proximal end of said hip stem.
27. The hip stem of claim 23, wherein said distal portion includes
a distal end having a width of between 10 mm and 18 mm in the
posterior/anterior dimension and a width of between 11 mm and 19 mm
in the medial/lateral dimension.
Description
BACKGROUND
[0001] 1. Field of the Invention
[0002] The present invention relates to prosthetic hip implant
components, including a hip stem for implantation in the proximal
femur and an acetabular cup for implantation in the acetabulum. In
particular, the present invention relates to prosthetic hip stems
and acetabular cups which include improved features adapted to
achieve more optimized results with certain types of patient
anatomy, such as the anatomy of female patients.
[0003] 2. Description of the Related Art
[0004] Orthopedic implants are commonly used to replace some or all
of a patient's hip joint in order to restore the use of the hip
joint, or to increase the use of the hip joint, following
deterioration due to aging or illness, or injury due to trauma. In
a hip replacement, or hip arthroplasty procedure, a femoral
component is used to replace a portion of the patient's femur,
including the femoral neck and head. The femoral component is
typically a hip stem, which includes a stem portion positioned
within the prepared femoral canal of the patient's femur and
secured via bone cement, or by a press-fit followed by bony
ingrowth of the surrounding tissue into a porous coating of the
stem portion. The hip stem also includes a neck portion adapted to
receive a prosthetic femoral head. The femoral head is received
within a prosthetic acetabular component, such as an acetabular cup
received within the prepared recess of the patient's
acetabulum.
[0005] One known hip stem includes a core formed of either a
cobalt-chromium-molybdenum alloy or titanium, and a porous surface
layer in the form of a matrix of small metallic beads or a wire
mesh. Typically, the porous surface layer is sintered to the core
by heating the core and the porous surface layer to a high
temperature in order to cause the porous surface layer and core to
fuse, melt, or bond together along their interface. U.S. Pat. Nos.
6,395,327, 6,514,288, and 6,685,987, each assigned to the assignee
of the present invention and hereby incorporated by reference,
disclose various methods of enhancing the fatigue strength and the
connection between the core and the porous surface layer of the
foregoing types of hip stems.
SUMMARY
[0006] The present invention provides prosthetic hip stems and
acetabular cups for use in prosthetic hip joints. The hip stem may
include a core having a stem portion and a neck portion, a polymer
matrix layer substantially covering the stem portion of the core,
and a porous metal layer substantially covering the polymer matrix
layer. The polymer matrix layer connects the core and the porous
metal layer and provides a stiffness for the hip stem which more
closely mimics the stiffness of bone than do known hip stems. The
hip stems and acetabular cups additionally include a number of
improvements adapted for more optimized results with certain types
of patient anatomy, such as the anatomy of female patients, for
example.
[0007] In one form thereof, the present invention provides a
prosthetic hip stem, including a stem portion having a proximal end
and a distal end, the stem portion defining a medial/lateral plane;
and a neck portion projecting from the proximal end, the neck
portion having a longitudinal axis therealong which is oriented at
a first angle between 13 degrees and 25 degrees anteriorly with
respect to the medial/lateral plane.
[0008] In another form thereof, the present invention provides a
prosthetic hip stem, including a stem portion having a proximal end
and a distal end, the stem portion defining a medial/lateral plane
therethrough; a neck portion projecting from the proximal end of
the stem portion and having a first, longitudinal axis; and a head
portion of substantially spherical shape and connected to the neck
portion along the first axis, the head portion having a center
disposed on second axis which is disposed at a second angle of
between 1 and 25 degrees anteriorly with respect to the first
axis.
[0009] In a further form thereof, the present invention provides a
prosthetic hip stem, including a stem portion having a proximal end
and a distal end, and a first, proximal/distal longitudinal axis;
and a neck portion projecting from the proximal end, the neck
portion having a second longitudinal axis therealong which is
oriented at a first angle of between 90 and 145 degrees with
respect to the first axis.
[0010] In another form thereof, the present invention provides a
prosthetic hip stem, including a stem portion having a proximal end
and a distal end; and a distal end fixation mechanism operable
between a first condition wherein the distal end of the stem
portion has a first width with respect to at least one of a
medial/lateral plane and an anterior/posterior plane of the stem
portion and a second condition wherein the distal end of the stem
portion has a second width with respect to at least one of the
medial/lateral plane and the anterior/posterior plane, the second
width greater than the first width.
[0011] In another form thereof, the present invention provides an
acetabular cup, including a substantially hemispherical cup portion
made of a relatively thin, flexible porous metal; and a liner
fitted within the cup portion, the liner including a substantially
hemispherical bearing surface.
[0012] In another form thereof, the present invention provides an
acetabular cup, including a liner including a substantially
hemispherical bearing surface; a porous metal cup portion; and an
intermediate layer disposed between the liner and the porous metal
cup portion, the intermediate layer formed of a polymer matrix.
[0013] In another form thereof, the present invention provides an
acetabular cup, including a liner including a substantially
hemispherical bearing surface; and a cup portion including an outer
hemispherical portion including a substantially annular loading
rib.
[0014] In another form thereof, the present invention provides a
prosthetic hip stem, including a proximal end including a core, a
polymer matrix layer covering at least a portion of the core, and a
porous metal layer substantially covering the polymer matrix layer;
and a distal end including a core and a porous metal layer
substantially covering the core.
[0015] In a further form thereof, the present invention provides a
prosthetic hip stem, including a proximal end and a distal end; an
inner core; a porous metal outer layer; and an elongated cavity
formed in the distal end, wherein the distal end is flexible.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] The above-mentioned and other features of this disclosure,
and the manner of attaining them, will become more apparent and
will be better understood by reference to the following description
of embodiments taken in conjunction with the accompanying drawings,
wherein:
[0017] FIG. 1 is a first isometric view of a hip stem according to
the present invention;
[0018] FIG. 2 is a second isometric view of the hip stem of FIG.
1;
[0019] FIG. 3 is a first isometric view of the core of the hip stem
of FIGS. 1 and 2;
[0020] FIG. 4 is a second isometric view of the core of the hip
stem of FIGS. 1 and 2;
[0021] FIG. 5 is a sectional view through the hip stem, taken along
line 5-5 of FIG. 2;
[0022] FIG. 6 is a side view of the proximal end of the hip stem,
showing the contoured neck portion and the version indicator
feature;
[0023] FIG. 7 is an isometric view of the proximal end of the hip
stem, showing the contoured neck portion;
[0024] FIG. 8 is a side view of the proximal end of the hip stem,
shown with a femoral head thereof fitted within an acetabular cup
which is in turn positioned within an acetabulum, and illustrating
the relatively large degree of articulating movement possible
therebetween;
[0025] FIG. 9 is a schematic top view of the hip stem, showing
relative neutral and anteversion positions of the hip stem with
respect to a patient in solid and dashed lines, respectively;
[0026] FIG. 10 is an isometric view of the proximal end of the core
of the hip stem, showing the curved groove therein;
[0027] FIG. 11 is an isometric view of a portion of the distal end
of the core of the hip stem, showing the distal boss of the core,
including a plurality of dimples around the boss and a plurality of
ridges in the stem portion of the core;
[0028] FIG. 12 is a schematic proximal end view of several hip
stems each having an integral stem portion and neck portion and
showing a range of possible anteversion angles for the neck
portions;
[0029] FIG. 13 is a proximal end view of components of a modular
hip stem system, including a hip stem portion and a plurality of
anteverted modular neck portions which may be used with the hip
stem portion;
[0030] FIG. 14 is a proximal end view of components of a modular
hip stem system, including an integral stem portion and neck
portion, and a plurality of anteverted modular femoral heads which
may be used with the hip stem;
[0031] FIG. 15 is an end view of a modular femoral head taken along
line 15-15 of FIG. 14;
[0032] FIG. 16 is an exploded, partially sectioned proximal end
view of components of a modular hip stem system showing a hip stem
portion, an anteverted modular neck portion, and an anteverted
modular femoral head;
[0033] FIG. 17 is an assembled, partially sectioned proximal end
view of the components of the modular hip stem system of FIG.
16;
[0034] FIG. 18 is an anterior/posterior schematic view of several
hip stems each having an integral stem portion and neck portion and
showing a range of possible neck/shaft angles for the neck
portions;
[0035] FIG. 19 is a partially sectioned anterior/posterior view of
components of a modular hip stem system including a hip stem
portion and a plurality of modular neck components having various
neck/shaft angles which may be used with the modular hip stem
portion;
[0036] FIG. 20 is a cross-sectional view of a portion of a hip stem
within the diaphysis of a femur, further illustrating an embodiment
of a distal end fixation mechanism in a non-expanded condition;
[0037] FIG. 21 is a cross-sectional view of a portion of the hip
stem of FIG. 20, further illustrating the distal end fixation
mechanism in an expanded condition;
[0038] FIG. 22 is a cross-sectional view of a portion of a hip stem
within the diaphysis of a femur, further illustrating an
alternative embodiment of a distal end fixation mechanism in a
non-expanded condition;
[0039] FIG. 23 is a cross-sectional view of a portion of the hip
stem of FIG. 22, further illustrating the distal end fixation
mechanism in an expanded condition;
[0040] FIG. 24 is an exploded view of a flexible acetabular cup and
liner, and a pelvic region of a patient's anatomy;
[0041] FIG. 25 is a sectional view of an acetabular cup according
to another embodiment;
[0042] FIG. 26 is a partial sectional view of an acetabular cup
according to a further embodiment;
[0043] FIG. 27 is a sectional view of a hip stem according to a
further embodiment;
[0044] FIG. 28 is an anterior/posterior view of a hip stem
according to a further embodiment, showing portions of the
posterior femur in phantom; and
[0045] FIG. 29 is a medial/lateral view of the hip stem of FIG. 28,
showing portions of the posterior femur in phantom.
[0046] Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set out
herein illustrate embodiments of the disclosure, and such
exemplifications are not to be construed as limiting the scope of
the invention in any manner.
DETAILED DESCRIPTION
[0047] Referring to FIGS. 1-5, a prosthetic hip stem 20 according
to the present invention is shown, which generally includes stem
portion 22, and neck portion 24 extending at a generally obtuse
angle from stem portion 22 and including a tapered femoral head
fitting 26. Stem portion 22 of hip stem 20 is received within a
prepared femoral canal of a patient's femur to anchor hip stem 20
within the patient's femur. As discussed below, a femoral head
component is fitted on femoral head fitting 26, and is in turn
received within a prosthetic acetabular component, such as an
acetabular cup seated within a prepared recess in the patient's
acetabulum, to thereby provide an articulating, prosthetic hip
joint. Hip stem 20 further defines proximal end 28, distal end 30,
lateral side 32, medial side 34, as well as opposing anterior and
posterior sides depending upon whether hip stem 20 is used with a
patient's right or left femur.
[0048] Referring particularly to FIGS. 3-5, hip stem 20 generally
includes a substrate or core 36 generally defining stem portion 22
and neck portion 24 and, as best seen in FIG. 5, a polymer matrix
layer 38 substantially covering stem portion 22 of core 36, and a
porous metal layer 40 substantially covering polymer matrix layer
38. Polymer matrix layer 38 and porous metal layer 40 may cover
substantially all of stem portion 22 of core 36, or alternatively,
may cover only selected portions thereof, as desired. In one
embodiment, stem portion 22 has a length L (FIG. 1) extending
generally from proximal end 28 to distal end 30, and, in one
embodiment, stops slightly short of each end 28, 30 by
approximately 0.3 inches. Porous metal layer 40 extends along
length L from approximately 10, 20, 30% thereof or as much as 70,
80, 90, or 95% thereof. In one embodiment, porous metal layer 40
extends along stem portion 22 for approximately 33% of the length
thereof. In another embodiment, porous metal layer 40 covers
approximately 33% of proximal end 28 of stem portion 22, i.e., a
midcoat porous stem.
[0049] Core 36 may be made from a cobalt-chromium-molybdenum alloy
or a titanium alloy, for example, via a forging or casting process,
followed by machining to achieve a desired shape or profile.
Polymer matrix layer 38 may be formed of an inert
polyaryletherketone ("PAEK") polymer such as, for example,
polyetheretherketone ("PEEK"). Porous metal layer 40 may be a metal
wire mesh of titanium fibers, or alternatively, may also comprise a
metal bead matrix or other porous metal structures produced in
accordance with Trabecular Metal.TM. technology of Zimmer, Inc. of
Warsaw, Ind., for example.
[0050] Hip stem 20 may be manufactured as follows. First, core 36
is forged, followed by machining core 36 after forging to form a
desired shape or profile for core 36. Core 36 is then grit blasted
to sufficiently roughen its surface, and then is heat treated to
facilitate polymer flow across core 36 during the injection molding
process. Thereafter, core 36 is positioned within an injection
molding machine with stem portion 22 of core 36 positioned within
porous metal layer 40, with a gap provided therebetween.
Thereafter, polymer matrix layer 38 is injected into the space
between core 36 and porous metal layer 40 through suitable gates,
with polymer matrix layer 38 permeating into porous metal layer 40
and into the surface of stem portion 22 of core 36 via grooves 52,
dimples 56, ridges 58, and/or flats 60. Upon cooling of polymer
matrix layer 38, porous metal layer 40 is firmly bonded or secured
to stem portion 22 of core 36. Advantageously, core 36 is not
subjected to a sintering process to apply porous metal layer 40,
thereby maintaining the fatigue strength of core 36.
[0051] Referring to FIGS. 6-8, neck portion 24 of hip stem 20 is
contoured to allow for increased articulating movement of hip stem
20 with respect to an acetabular component in a prosthetic hip
joint, as illustrated in FIG. 8. As shown in FIGS. 6 and 7, neck
portion 24 of hip stem 20 includes a neck section 42 which extends
between stem portion 22 and femoral head fitting 26. Neck section
42 is shaped with a relatively thin or slender profile, having a
diameter along a substantial portion thereof which is less than the
maximum diameter of femoral head fitting 26. In particular, neck
section 42 may include a plurality of scalloped recesses 44
therearound which may be formed by removal of material from the
original forging of core 36 by machining. As shown in FIG. 8, the
thin or slender profile of neck section 42 allows for an increased
degree of angular, articulating movement of hip stem 20 with
respect to the acetabular component in a prosthetic hip joint when
a prosthetic femoral head 43 is fitted on fitting 26 of stem 20 and
received within the acetabular component, which is shown in FIG. 8
as an acetabular cup 46 positioned within a prepared recess in the
surrounding acetabulum. Also, as shown in FIGS. 2 and 4, neck
portion 24 of core 36 of hip stem 20 may include an instrument
engagement fitting 47 in proximal end 28 thereof within which an
instrument (not shown) may be engaged to aid in driving hip stem 20
into the prepared femoral canal of a patient's femur.
[0052] Referring to FIGS. 6 and 7, neck portion 24 of hip stem 20
also includes a version indicator feature 48, which is shown herein
as a bump or protrusion 50 projecting from medial side 34 of neck
portion 24 of hip stem 20. As explained below, version indicator
feature 48 is a tactile feature on hip stem 20 which may be felt by
a surgeon during implantation of hip stem 20 to aid the surgeon in
positioning hip stem 20 according to a desired version or
alignment. U.S. Pat. No. 6,676,706, assigned to the assignee of the
present invention and incorporated herein by reference, discloses a
method for performing a "non-open", or minimally invasive, total
hip arthroplasty. In the foregoing method, a small anterior
incision is made for preparing a recess or seat in the acetabulum
for receiving an acetabular cup, which is inserted and positioned
within the acetabulum through the anterior incision. A small
posterior incision is also made for preparing the femur and for
receiving a hip stem, such as hip stem 20, which is positioned
within the prepared femoral canal of the femur. During this and
other minimally invasive procedures, the insertion of the hip stem
into the prepared femoral canal may not be directly viewable by the
surgeon, or may be only partially viewable by the surgeon, such as
through the anterior incision.
[0053] Referring to FIG. 9, upon insertion of hip stem 20 into the
prepared femoral canal through a posterior incision, a surgeon may
feel protrusion 50 of version indicator element 48 by inserting the
surgeon's fingers through the anterior incision, for example, to
position hip stem 20 in an anteversion alignment, shown in dashed
lines in FIG. 9, in which neck portion 24 of hip stem 20 is rotated
approximately 12.degree. to 14.degree. anteriorly with respect to
stem portion 22 from the neutral version, or direct medial/lateral,
alignment shown in solid lines in FIG. 9. Optionally, according to
some surgical procedures, the surgeon may tactilely align
protrusion 50 of version indicator element 48 with respect to one
or more grooves which are cut in the medial calcar of the prepared
femur in order to position hip stem 20. Protrusion 50 of version
indicator element 48 may also be used by the surgeon to position
hip stem 20 in a position other than in an anteversion alignment if
needed. Thus, protrusion 50 of version indicator element 48
advantageously allows the surgeon to position hip stem 20 according
to a desired alignment during a minimally invasive hip arthroplasty
procedure without direct visualization of hip stem 20.
[0054] Although version indicator feature 48 is shown herein as
bump or protrusion 50, other tactile elements may be used, such as
a recess, a group of recesses, or a ridge or a group of ridges, for
example, in medial side 34 of neck portion 24 of hip stem 20, or at
another location or locations on neck portion 24 of hip stem
20.
[0055] Referring to FIGS. 10 and 11, core 36 includes a plurality
of features for enhancing the mechanical interconnection between
core 36 and polymer matrix layer 38. As shown in FIG. 10, proximal
end 28 of stem portion 22 of core 36 includes a curved, generally
"candy cane"-shaped or "number 7"-shaped groove 52 on one or both
of the anterior and posterior sides thereof. During manufacture of
hip stem 20, in which the material of polymer matrix layer 38 is
injected into the space between core 36 and porous metal layer 40,
the material of polymer matrix layer 38 flows into and
substantially fills grooves 52 to form a robust mechanical
interconnection between core 36 and polymer matrix layer 38 upon
curing of the material. The mechanical interconnection resists
relative movement between core 36 and polymer matrix layer 38, such
as rotational movement, responsive to torsional and/or other types
of loading which may be imposed upon core 36 when hip stem 20 is
used in a hip joint, and in particular, after porous metal layer 40
becomes substantially fused to the surrounding femoral bone
tissue.
[0056] Referring to FIG. 11, distal end 30 of core 36 includes a
boss 54 which provides a rigid leading surface for insertion of hip
stem 20 into a prepared femoral canal. Boss 54 also includes a
plurality of dimples 56 formed circumferentially therearound.
During manufacture of hip stem 20, in which the material of polymer
matrix layer 38 is injected into the space between core 36 and
porous metal layer 40, the material of polymer matrix layer 38
flows into and substantially fills dimples 56 to form a robust
mechanical interconnection between core 36 and polymer matrix layer
38 upon curing of the material. The mechanical interconnection also
resists relative movement, such as relative rotational movement,
between core 36 and polymer matrix layer 38 responsive to torsional
and/or other types of loading upon core 36 after hip stem 20 is
implanted.
[0057] Still referring to FIG. 11, stem portion 22 of core 36 may
additionally include further features to enhance the mechanical
interconnection between core 36 and polymer matrix layer 38, such
as ridges 58 and/or flats 60, or other projecting or recessed
features in core 36 such as grooves, cavities, bores, dimples,
bumps, protuberances, protrusions, or other features which may be
formed in core 36 by forging or post-forging machining, for
example. Ridges 58 and flats 60 extend longitudinally along core 36
and resist relative movement, such as relative rotational movement,
between core 36 and polymer matrix layer 38 responsive to torsional
and/or other types of loading which may be imposed upon core 36 as
described above.
[0058] As discussed in further detail below, the present inventors
have developed a number of improvements to hip stems and acetabular
cups in order to provide more optimized results with certain types
of patient anatomy, such as female anatomy.
[0059] The hip stems and acetabular cups described herein may be
implanted according to surgical techniques described in U.S. Pat.
No. 6,676,706, issued Jan. 13, 2004; U.S. Pat. No. 6,860,903,
issued Mar. 1, 2005; U.S. Pat. No. 6,953,480, issued Oct. 11, 2005;
U.S. Pat. No. 6,991,656, issued Jan. 31, 2006; abandoned U.S.
patent application Ser. No. 10/929,736, filed Aug. 30, 2004;
currently pending U.S. patent application Ser. No. 10/952,301,
filed Sep. 28, 2004; currently pending U.S. patent application Ser.
No. 11/235,286, filed Sep. 26, 2005; and currently pending U.S.
patent application Ser. No. 11/105,080, filed Apr. 13, 2005, all
titled METHOD AND APPARATUS FOR PERFORMING A MINIMALLY INVASIVE
TOTAL HIP ARTHROPLASTY and all assigned to the assignee of the
present application, the disclosures of which are hereby expressly
incorporated herein by reference.
[0060] Known hip stems typically have an anteversion angle between
the neck portion of the hip stem and the anatomical medial/lateral
plane of from 1 to 12 degrees, for example. The present inventors
have observed that for many patients, particularly certain female
patients, a greater anteversion angle between the neck portion of
the hip stem and the anatomical medial/lateral plane, and/or an
anteversion angle between the femoral head portion and the neck
portion of the hip stem, would provide more optimum anatomical
benefits.
[0061] Referring to FIG. 12, a top view of proximal end 28 of hip
stem 20 is shown including stem portion 22 and neck portion 24
integrally formed with one another. Typical known hip stems include
neck portion 24a with femoral head fitting 26, shown in dashed
lines in FIG. 12, whose central longitudinal axis 68c coincides and
is aligned with medial/lateral plane 61, i.e., neck portion 24a is
angled approximately 0.degree. anteriorly with respect to the
anatomical medial/lateral plane 61 and therefore has a neutral
version and lacks anteversion. Hip stem 20 also includes instrument
engagement fitting 47 in proximal end 28 thereof within which an
instrument (not shown) may be engaged to aid in driving hip stem 20
into the prepared femoral canal of a patient's femur. Although
illustrated throughout as the intersection point between
medial/lateral plane 61 and central longitudinal axis of the neck
portion, fitting 47 may be located at any location on hip stem 20
to aid in driving hip stem 20 into the prepared femoral canal. As
illustrated, however, fitting 47 provides a convenient location for
the intersection of plane 61 with the central longitudinal axis of
each neck portion.
[0062] In order to facilitate greater anteversion, hip stem 20 may
include a neck portion 24 which is angled with respect to the
anatomical medial/lateral plane 61. For example, hip stem 20 is
shown in an anteversion alignment in solid lines in FIG. 12, in
which neck portion 24c having femoral head fitting 26 is angled
approximately 25.degree. anteriorly with respect to stem portion 22
from the neutral version, or direct medial/lateral alignment.
Central longitudinal axis 68c of neck portion 24c defines a
25.degree. angle with medial/lateral plane 61. In another
embodiment, hip stem 20 may include neck portion 24b with femoral
head fitting 26, shown in dashed lines in FIG. 12, which is angled
approximately 20.degree. anteriorly with respect to stem portion 22
from the neutral version alignment, i.e., central longitudinal axis
68b of neck portion 24b defines a 20.degree. angle with plane 61.
Advantageously, the surgeon may choose a hip stem 20 from a
plurality of hip stems 20 in a system to have a desired anteversion
alignment corresponding to the patient-specific anatomy. The angle
of anteversion may be selected to have neck portion 24 angled with
respect to medial/lateral plane 61 between 0.degree. and 25.degree.
or more and, more particularly, the hip stem may be selected from a
plurality of hip stems in a system including hip stems having
respective anteversion angles of as little as 13.degree.,
14.degree., or 16.degree. or as great as 21.degree., 23.degree., or
25.degree. or more, for example, or any angle therebetween. In
particular, many female patients may require a larger degree of
anteversion alignment of neck portion 24 with respect to the
anatomical medial/lateral plane 61 than is provided by known hip
stem systems. As discussed above, a larger anteversion angle
between the neck portion and the medial/lateral plane may provide
more optimum anatomical benefits in certain patients, including
certain female patients.
[0063] Referring to FIG. 13, a top view of components of a modular
hip stem system are shown. Proximal end 78 of stem portion 72 of an
alternative hip stem 70 is shown wherein, except as described
below, hip stem 70 and stem portion 72 are substantially similar to
hip stem 20 and stem portion 22 of FIGS. 1-5 described above.
Proximal end 78 of stem portion 72 includes tapered recess 74 for
mating engagement with a selected one of a plurality of modular
neck portions 80. Each modular neck portion 80 includes tapered
fitting portion 82 for mating with recess 74 upon assembly. Each
modular neck portion 80 may also include an optional anti-rotation
feature, shown as key 81, for engagement with another anti-rotation
feature of hip stem 70, shown as groove 83 in recess 74 of stem
portion 72, to prevent rotational movement between neck portion 80
and stem portion 72. Alternatively, each modular neck portion 80
and stem portion 72 may be provided with an oval engagement profile
therebetween to provide anti-rotation. A substantially spherical
femoral head 43 may be integrally formed with each modular neck
portion 80 as shown in FIG. 13 or alternatively, each modular neck
portion 80 may be coupled with a modular femoral head separately
formed and attached to modular neck portion 80 via a tapered
bore/fitting connection, for example, as described below.
[0064] Each neck portion 80 is oriented in an alignment which is
anteriorly angled with respect to stem portion 72 from a neutral
version as defined by medial/lateral plane 76. For example, as
shown in FIG. 13, modular neck portion 80a may be angled
approximately 15.degree. anteriorly with respect to medial/lateral
plane 76, i.e., central longitudinal axis 79a of modular neck
portion 80a defines a 15.degree. angle with plane 76. In another
embodiment, modular neck portion 80b may be angled approximately
20.degree. anteriorly with respect to medial/lateral plane 76,
i.e., central longitudinal axis 79b of modular neck portion 80b
defines a 20.degree. angle with plane 76. In yet another
embodiment, modular neck portion 80c may be angled approximately
25.degree. anteriorly with respect to medial/lateral plane 76,
i.e., central longitudinal axis 79c of modular neck portion 80c
defines a 25.degree. angle with plane 76. In a modular system, a
plurality of neck portions 80 may be provided, wherein the
anteversion angle between central longitudinal axis 79 and
medial/lateral plane 76 for a given modular neck portion 80 may be
from approximately 0.degree. to 25.degree. or more, for example,
the anteversion angle may be as small as 13.degree., 14.degree., or
16.degree., and as large as 21.degree., 23.degree., or 25.degree.,
for example, or any angle therebetween.
[0065] Referring to FIG. 14, components of another modular system
are shown, wherein neck portion 24 of hip stem 20 is integrally
formed therewith, and is shown with a plurality of modular femoral
heads 84. In the manner described above, neck portion 24 may be
oriented in a desired anteversion alignment, for example, neck
portion may be angled approximately 15.degree. anteriorly with
respect to stem portion 22 from medial/lateral plane 61, similar to
neck portions 24a, 24b, 24c of FIG. 12, i.e., central longitudinal
axis 68 of neck portion 24 defines a 15.degree. angle with
medial/lateral plane 61. Each modular femoral head 84 includes
tapered recess 88 for mating engagement with femoral head fitting
26 of neck portion 24. Each modular femoral head 84 also includes
an optional anti-rotation feature, shown as groove 87, for
engagement with another anti-rotation feature of neck portion 24,
shown as key 85 on femoral head fitting 26, to prevent rotational
movement between neck portion 24 and each femoral head 84.
Alternatively, each modular femoral head 84 and neck portion 24 may
be provided with an oval engagement profile therebetween to provide
anti-rotation. As described below, each modular head 84 is itself
anteverted with respect to neck portion 24 of hip stem 20.
[0066] In particular, the recess 88 of each modular femoral head 84
defines a central axis 86 which is offset from the center of head
84 and from central axis 68 of neck portion 24 such that recess 88
of each head 84 is eccentric with respect to the center of the head
84. Central axis 86 may be angled anteriorly with respect to
central longitudinal axis 68 of neck portion 24 such that each
modular femoral head 84 is offset from central longitudinal axis 68
upon assembly. For example, modular femoral head 84a may be angled
approximately 5.degree. anteriorly with respect to longitudinal
axis 68, i.e., central axis 86a of femoral head 84a defines a
5.degree. angle with axis 68. In another embodiment, femoral head
84b may be angled approximately 10.degree. anteriorly with respect
to longitudinal axis 68, i.e., central axis 86b of femoral head 84b
defines a 10.degree. angle with axis 68. In yet another embodiment,
femoral head 84c may be angled approximately 15.degree. anteriorly
with respect to longitudinal axis 68, i.e., central axis 86c of
femoral head 84c defines a 15.degree. angle with axis 68. In a
modular system, a plurality of femoral heads 84 may be provided
wherein the angle between central longitudinal axis 68 and axis 86
of same may vary from approximately 1.degree. to 25.degree. or more
and, in particular, may be as small as 1.degree., 3.degree.,
5.degree., and as large as 21.degree., 23.degree., or 25.degree. or
more, for example, or any angle therebetween. As discussed above, a
larger anteversion angle between the femoral head and the neck
portion may provide more optimum anatomical benefits in certain
patient, including certain female patients.
[0067] Referring to FIG. 15, a view of modular femoral head 84a
taken along the line 15-15 in FIG. 14 is shown including central
longitudinal axis 68 of neck portion 24 (FIG. 14) and central axis
86a of recess 88 of femoral head 84a. As shown in FIG. 15, axis 86a
is offset from, i.e., not coaxial with, axis 68 to provide an
offset modular femoral head 84a to achieve an added amount of
anteversion alignment of hip stem 20. The offset of axes 86a and 68
provides a larger amount of mass of femoral head 84a on the right
side of FIG. 15 as compared to the left side, thereby providing the
added anteversion component to enhance the performance of the hip
stem. If no offset between femoral head 84 and neck portion 24 was
necessary, axis 68 would coincide with central axis 86 of a modular
femoral head 84.
[0068] As shown in FIGS. 16-17, exemplary components of a modular
hip stem system are shown which includes a modular neck portion and
a modular femoral head. In FIGS. 16 and 17, the proximal end 78 of
modular hip stem 90 is shown which, except as described below, is
substantially similar to hip stem 20 (FIGS. 1-5) and hip stem 70
(FIG. 13) described above. The modular hip system shown in FIGS.
16-17 combines the modularity of the systems shown in FIGS. 13 and
14 described above. Hip stem 90 may include modular femoral head 84
having tapered recess 88. Upon assembly, recess 74 of stem portion
72 engages with tapered fitting portion 82 of modular neck portion
80 and recess 88 of modular femoral head 84 engages with femoral
head fitting 26 of modular neck portion 80. Modular femoral head 84
includes an optional anti-rotation feature, shown as groove 87, for
engagement with another anti-rotation feature of neck portion 80,
shown as key 85 on femoral head fitting 26, to prevent rotational
movement between neck portion 80 and femoral head 84. Further, neck
portion 80 includes a further optional anti-rotation feature, shown
as key 81 on tapered fitting portion 82, for engagement with
another anti-rotation feature of stem portion 72, shown as groove
83 in recess 74, to prevent rotational movement between neck
portion 80 and stem portion 72. Alternatively, each of the
foregoing components may be provided with oval engagement profiles
therebetween to provide anti-rotation.
[0069] Stem portion 72 defines an anatomical medial/lateral plane
91, neck portion 80 defines central longitudinal axis 79, and
modular femoral head 84 defines central axis 86. Advantageously, a
surgeon may choose any combination of modular components to ensure
an adequate degree of anteversion is included in hip stem 90. For
example, as shown in FIGS. 16-17, modular femoral head 84 may be
angled at an angle .alpha. anteriorly with respect to longitudinal
axis 79, i.e., central axis 86 of femoral head 84 defines an angle
.alpha. with axis 79. Also, neck portion 80 may be angled at an
angle .beta. anteriorly with respect to medial/lateral plane 76,
similar to neck portions 80a, 80b, 80c described above, i.e.,
central axis 79 of neck portion 80 defines an angle .beta. with
axis 76. Angle .alpha. may be chosen to be between approximately
1.degree. and 25.degree. or more and, in particular, may be as
small as 13.degree., 14.degree., or 16.degree., and as large as
21.degree., 23.degree., or 25.degree., for example, or any angle
therebetween. Angle .beta. may be chosen to be between
approximately 1.degree. and 25.degree. or more and, in particular,
may be as small as 13.degree., 14.degree., or 16.degree., and as
large as 21.degree., 23.degree., or 25.degree., for example, or any
angle therebetween.
[0070] The angle between the neck and the shaft of the femur in
certain patients, including many female patients, is typically more
varus than the angle between the neck and the shaft of the male
femur which is relatively more valgus. Known hip stems are not
shaped with a sufficiently varus neck/shaft angle which would
provide optimum results in certain female patients. Also, in order
to accommodate a hip stem having a more varus neck/shaft angle
without the need to lengthen leg length, it is typically necessary
to osteotomize a greater portion of the metaphysis of the femur in
female patients than in male patients. Specifically, in certain
females, the femur is osteotomized at a location near the lesser
trochanter. This results in less of the metaphysis being available
for hip stem fixation in many female patients as compared to male
patients, thereby increasing the importance of diaphyseal fixation
of the hip stem in female patients.
[0071] Referring to FIG. 18, several embodiments of hip stem 100
are shown which, except as described below, are substantially
similar to hip stem 20 (FIGS. 1-5), described above. Each hip stem
100 includes integral stem portion 22 and neck portion 104. Hip
stem 100 defines central longitudinal axis 106 extending through
stem portion 22 and includes a neck portion 104 having a central
longitudinal axis 102. Central longitudinal axis 106 and each
central longitudinal axis 102 define an angle therebetween which
may be chosen depending on the anatomy of the patient. For example,
neck portion 104a, shown in solid lines in FIG. 18, may have
central longitudinal axis 102a which defines an angle of
approximately 110.degree. with axis 106. If more valgus neck/shaft
angle is desired, a surgeon may choose hip stem 10b, shown in
dashed lines in FIG. 18, including neck portion 104b having central
longitudinal axis 102b which defines an angle of approximately
120.degree. with axis 106. Alternatively, if less valgus (more
varus) neck/shaft angle is desired, a surgeon may choose hip stem
100c, shown in dashed lines in FIG. 18, including neck portion 104c
having central longitudinal axis 102c which defines an angle of
approximately 90.degree. with axis 106. In a system of hip stems
100 having various neck/shaft angles, a particular hip stem may be
selected having a neck/shaft angle corresponding to the anatomy of
a particular patient. In this system, the neck/shaft angle may
range from approximately 90.degree. to approximately 145.degree.,
and in particular, may be as small as 90.degree., 110.degree., or
120.degree. or any increments therebetween, for example.
Advantageously, hip stem 100 may be chosen to have more varus
orientation without increasing the leg length of the hip implant
system. Hip stem 100 may allow a surgeon to select from a
sufficient variation of hip stems having various neck/shaft angles
to optimize results in certain female patients.
[0072] Referring to FIG. 19, a modular hip stem system includes hip
stem 110 which, except as described below, is substantially similar
to hip stem 20 (FIGS. 1-5), described above. Hip stem 110 may
include stem portion 112 and a plurality of modular neck portions
120 each having tapered fitting portion 122 for mating engagement
in tapered recess 114 in proximal end 118 of stem portion 112 and
femoral head fitting 26 for acceptance of a modular femoral head.
Each neck portion 120 includes an optional anti-rotation feature,
shown as key 121 on tapered fitting portion 122, for engagement
with another anti-rotation feature of stem portion 112, shown as
groove 119 in recess 114, to prevent rotational movement between
each neck portion 120 and stem portion 112. Alternatively, each
neck portion 120 and stem portion 112 may be provided with oval
engagement profiles to provide anti-rotation. Each modular neck
portion 120 defines a central longitudinal axis 116 forming an
angle with central longitudinal axis 111 of stem portion 112. In
one embodiment, modular neck portion 120a may have central
longitudinal axis 116a which forms an angle of approximately
110.degree. with axis 111.
[0073] If a surgeon desires a larger neck/shaft angle, modular neck
portion 120b may be chosen which defines central longitudinal axis
116b which forms an angle of approximately 120.degree. with axis
111 and an angle of approximately 10.degree. with central
longitudinal axis 116a, i.e., a +10.degree. change in neck/shaft
angle from modular neck portion 120a. If a surgeon desires a
smaller neck/shaft angle, modular neck portion 120c may be chosen
which defines central longitudinal axis 116c which forms an angle
of approximately 90.degree. with axis 111 and an angle of
approximately 20.degree. with central longitudinal axis 116a, i.e.,
a -20.degree. change in neck/shaft angle from modular neck portion
120a. Various values for the neck/shaft angle may be chosen
depending on the varus/valgus anatomy of a particular patient. For
example, the neck/shaft angle may range from approximately
90.degree. to approximately 145.degree., and in particular, may be
90.degree., 110.degree., or 120.degree., or any increment
therebetween. Hip stem 110 advantageously allows a surgeon to
select from a variety of modular neck portions to vary the
neck/shaft angle to optimize results in certain female
patients.
[0074] The present inventors have also observed that as certain
patients age, particularly females, the cortex of bone in the
metaphysis and in the diaphysis of the proximal femur typically
becomes thinner, particularly from the level of the lesser
trochanter downwardly. The thinning cortex of the metaphysis and
diaphysis results in a "stovepipe" shape of the cortex in the
metaphysis and a pronounced widening of the intramedullary canal in
the diaphysis, respectively. These effects are more pronounced with
women who have osteoporosis, which results in further thinning of
the cortex and consequent widening of the intramedullary canal, and
in particular, a reduction of bone stock in the proximal
diaphysis.
[0075] When cementless prostheses are used, the widened
intramedullary canal of certain patients, particularly aging
females, promotes a tendency for using a wider hip stem to more
completely fill the intramedullary canal and achieve initial
fixation. In many existing hip stems, stiffness increases with
increasing width, such that use of wider hip stems of increased
stiffness could result in stress shielding around the hip stem.
Advantageously, the hip stems described herein which include a
core, a polymer matrix intermediate layer, and porous metal outer
layer, have a stiffness modulus which more closely approximates the
stiffness modulus of cortical bone. This allows relative motion
between the hip stem and the femur to be minimized, and allows more
loading to be distributed to the cortical bone to reduce the
potential for stress shielding as opposed to known, more stiff hip
stems which have only a core and a porous metal coating.
[0076] Additionally, the inventors have observed that in females,
the intramedullary canal tends to widen relatively more in the
anterior/posterior plane, as viewed with a lateral x-ray, for
example, than in the medial/lateral plane, particularly in females
with osteoporosis, which commonly causes thinning of the posterior
cortex of the diaphysis. Thus, when the anterior/posterior and
medial/lateral diameters of the intramedullary canal are typically
not equal, known hip stems which have a substantially cylindrical
shape may not achieve optimal fixation in the diaphysis.
[0077] Referring to FIG. 20, a portion of hip stem 130 is shown
which, except as described below, is substantially similar to hip
stem 20 shown in FIGS. 1-5 and described above. Hip stem 130 may
include stem portion 135 with core 36, polymer matrix layer 38, and
porous metal layer 40. Stem portion 135 may further include a
distal end fixation mechanism operable between a first,
non-expanded condition and a second, expanded condition. The distal
end fixation mechanism may include a plurality of expansion points
140 in porous metal layer 40, such as slits, hinges, or weakened
areas, for example, which define a plurality of radially expandable
portions 138. The distal end fixation mechanism may also include
activation member 148 having a threaded aperture 149 for mating
engagement with threaded end 146 of shaft 134. Shaft 134 may be a
permanent part of hip stem 130 and may be rotatably positioned
within throughbore 132 in core 36. Shaft 134 includes proximal end
137 having suitable instrument engagement structure, such as a hex
fitting, for example, for engagement with an actuator device 139
(FIG. 21) for imparting rotational motion to shaft 134.
[0078] In operation and referring to FIG. 21, after hip stem 130 is
initially implanted in intramedullary canal 145 of the prepared
femur 144, shaft 134 may be rotated by actuator device 39 in the
general direction of Arrow A to thread threaded end 146 of shaft
134 into threaded aperture 149 of activation member 148. Rotation
of shaft 134, and the threading of end 146 thereof into threaded
aperture 149 of activation member 148, causes movement of
activation member 148 towards distal end 133 of hip stem 130 in the
general direction of Arrow B towards distal end 133 of hip stem
130. Movement of activation member 148 along the direction of Arrow
B causes activation member 148 to compress expandable portions 138
of porous metal layer 40 against a fixed reaction surface provided
by abutting portion 136 of core 36, thereby causing expansion
points 140 in porous metal layer 40 to deform and expand radially
expandable portions 138 from a first, non-expanded condition to a
second, expanded condition. The plurality of radially expandable
portions 138 cause hip stem 130 to widen and substantially fill
intramedullary canal gaps 142 (FIG. 20), thereby enhancing distal
fixation of hip stem 130 in the diaphysis of femur 144.
[0079] The degree of expansion of expandable portions 138 may be
controlled by the amount of rotation of shaft 134. For example, in
one embodiment, a half turn, or 1800 turn, of shaft 134 with the
actuator device provides a limited degree of expansion of
expandable portions 138 to provide initial fixation if the
intramedullary canal of femur 144 is only slightly wider than hip
stem 130. In one embodiment, two complete turns, or a 720.degree.
turn, of shaft 134 provides maximum expansion of expandable
portions 138 to provide initial fixation if the intramedullary
canal of femur 144 is substantially wider than hip stem 130,
wherein shaft 134 is rotated until surface 143 of activation member
148 abuts distal end 133 of hip stem 130 to limit the travel of
activation member 148. In this manner, the amount of rotation
imparted to shaft 134 may advantageously allow the surgeon to
provide the appropriate amount of expansion of expandable portions
138 to ensure adequate diaphyseal fixation of hip stem 130, which
may be verified by X-ray or other imaging. In one embodiment,
expansion points 140 may include a sliding-enhancement element, for
example, a plastic sheet, to facilitate movement of porous metal
layer 40 radially outward instead of a potential collapse of porous
metal layer 40 in the direction of Arrow B with no radial
expansion. Advantageously, portions 138 in the first, non-expanded
condition define the original cross-sectional shape of the hip
stem. After implantation, deformation of portions 138
advantageously allows the hip stem to have a larger cross-sectional
shape in the distal portion thereof to enhance diaphyseal fixation
of the hip stem in the femur.
[0080] Referring to FIGS. 22-23, a portion of hip stem 150 is shown
which, except as described below, is substantially similar to hip
stem 20, shown in FIGS. 1-5, and hip stem 130, shown in FIGS.
20-21. Hip stem 150 may include a distal end fixation mechanism
having expandable structure 155 which facilitates widening of hip
stem 150 near distal end 152 to enhance distal fixation of hip stem
150 in the diaphysis of femur 144. Core 36 may be provided with
central throughbore 154. Core 36, polymer matrix layer 38 and
porous metal layer 40 may include a plurality of passages 153
providing for travel of a filler material within throughbore 154
into expandable structure 155. Although illustrated as horizontally
oriented, passages 153 may be oriented diagonally or any other
orientation to facilitate flow of the filler material into
expandable structure 155 from throughbore 154. Any number of
passages 153 may be provided and the width of passages 153 may be
varied to regulate the flow of filler material 156 (FIG. 23) into
expandable structure 155. As shown in FIG. 22, prior to expansion
within intramedullary canal 145 of femur 144, expandable structure
155 remains substantially flat and non-expanded and does not
significantly increase the overall diameter of hip stem 150.
Alternatively, expandable structure 155 may be disposed within a
recessed area of porous metal coating 40 of hip stem 150 such that
expandable structure 155 does not increase the overall diameter of
hip stem 150.
[0081] As shown in FIG. 23, upon introduction of filler material
156, e.g., bone cement or polymethylmethacrylate (PMMA), into
throughbore 154 by a tube or other suitable delivery device in the
general direction of Arrow C, filler material 156 migrates into
passages 153 and fills expandable structure 155. Expansion of
expandable structure 155 widens distal end 152 of hip stem 150 to
substantially fill any gaps 142 between hip stem 150 and the
intramedullary canal of femur 144. The filler supply device is
gradually proximally removed from central throughbore 154 while
simultaneously distally filling central throughbore 154 and,
consequently, passages 153 and expandable structure 155 to ensure
complete filling of expandable structure 155 to the desired
expansion state. Expandable structure 155 may be formed of any
suitable biocompatible material, such as the materials used for the
prosthetic implant described in U.S. patent application Ser. No.
11/250,927, filed Oct. 14, 2005, titled METHOD AND APPARATUS FOR
REDUCING FEMORAL FRACTURES, assigned to the assignee of the present
application, the disclosure of which is hereby expressly
incorporated herein by reference.
[0082] In some embodiments, expandable structure 155 may be
expanded non-uniformly around the circumference of hip stem 150,
for example, by varying the number, relative locations, and
relative cross sections of passages 153 in hip stem 150. This may
allow hip stem 150 to more optimally achieve fixation in the
diaphysis because hip stem 150 may expand further in the
anterior/posterior plane than in the medial/lateral plane, for
example, to provide optimal fixation in females with osteoporosis
wherein the width of the anterior/posterior plane of the
intramedullary canal may exceed that in the medial/lateral plane.
As discussed above, osteoporosis in females commonly causes
thinning of the posterior cortex of the diaphysis. The ability to
expand in a non-uniform manner, particularly expanding further
posteriorly than either medially, laterally, or anteriorly, allows
hip stem 150 to achieve optimum fixation.
[0083] In a total hip arthroplasty, a prosthetic acetabular cup
component is seated within a patient's acetabulum anteriorly of the
medial wall of the pelvis. In certain patients, loading from the
femoral prosthesis may be transmitted to the pelvis primarily
around the rim of the acetabular cup, as opposed to being
distributed more evenly around the hemispherical portion of the
acetabular cup, which could potentially result in stress shielding
around the hemispherical portion of the acetabular cup. Stress
shielding of bone around the hemispherical portion of the
acetabulum may cause resorption of bone in the medial wall of the
pelvis posteriorly of the acetabulum, potentially resulting in
migration of the acetabular cup into the medial wall of the pelvis.
The present inventors have observed that in female patients, the
medial wall of the pelvis is often thinner than in most men.
[0084] Referring to FIG. 24, a flexible acetabular cup 160 is
shown, which generally includes a liner 166 made of ultra high
molecular weight polyethylene, for example, including a
hemispherical articulating surface 168. Liner 166 is fitted within
a porous metal cup portion 170 which may be made from a metal wire
mesh of titanium fibers, a metal bead matrix, or may be a porous
metal layer produced in accordance with Trabecular Metal.TM.
technology available from Zimmer, Inc. of Warsaw, Ind. Cup portion
170 may be formed relatively thin, or may include relief slits
therein such that cup portion 170 is generally flexible, as
represented by dashed lines 172 in FIG. 24, to more evenly
distribute acetabular loading around both the rim and the
hemispherical portions of cup portion 170 to reduce the potential
for stress shielding and, in turn, to reduce the potential for
migration of acetabular cup 160 into the medial wall 163 of the
pelvis 162.
[0085] Referring to FIG. 25, acetabular cup 180 according to
another embodiment is shown, which generally includes liner 182
made of ultra high molecular weight polyethylene, for example,
intermediate layer 184 of a polymer matrix similar to that of hip
stem 20 described above, which may be formed of an inert
polyaryletherketone ("PAEK") polymer such as for example,
polyetheretherketone ("PEEK"), and porous metal layer 186 which may
be made from a metal wire mesh of titanium fibers, a metal bead
matrix, or may be a porous metal layer produced in accordance with
Trabecular Metal.TM. technology available from Zimmer, Inc. of
Warsaw, Ind., for example. Liner 182 includes a hemispherical
bearing surface 188 for articulating receipt of the femoral head
component of a hip stem, such as the various hip stems described
herein. Porous metal layer 186 allows osseointegration of
acetabular cup 180 into the surrounding bone of the acetabulum.
Advantageously, polymer matrix layer 184 allows flexing movement
between liner 182 and porous metal layer 186 to provide a stiffness
for acetabular cup 180 which more closely approximates that of bone
than the stiffness of known acetabular cups. In this manner, loads
from the femoral head component of the hip stem are distributed
more evenly about the hemispherical portion of the cup to the
surrounding bone of the acetabulum, thereby reducing the potential
for stress shielding and resulting migration of the cup into the
medial wall of the pelvis.
[0086] Referring to FIG. 26, acetabular cup 190 according to a
further embodiment is shown which generally includes liner 192 made
of ultra high molecular weight polyethylene, for example, and
porous metal layer 194 which may be a metal wire mesh of titanium
fibers, or alternatively, may be a metal bead matrix or other
porous metal structure produced in accordance with Trabecular
Metal.TM. technology available from Zimmer, Inc. of Warsaw, Ind.,
for example. Liner 192 includes a hemispherical bearing surface 196
for articulating receipt of the femoral head component of a hip
stem, such as the various hip stems described herein. Porous metal
layer 194 allows osseointegration of acetabular cup 190 into the
surrounding bone of the acetabulum, and advantageously, further
includes a loading rib 198 disposed around the outer hemispherical
portion of porous metal layer 194 which contacts the surrounding
bone of the acetabulum to transfer loads thereto, such that loads
from the femoral head component of the hip stem are distributed
more evenly about the hemispherical portion of the cup to the
surrounding bone of the acetabulum, thereby reducing the potential
for stress shielding and resulting migration of the cup into the
medial wall of the pelvis.
[0087] Referring to FIG. 27, hip stem 200 according to a further
embodiment of the present invention is shown which, except as
described below, is similar to hip stem 20 shown in FIGS. 1-5 and
described above. Hip stem 20 generally includes proximal end 28 and
distal end 30, wherein proximal end 28 is configured similarly to
that of hip stem 20 in that proximal end 28 of hip stem 200
includes core 36, polymer matrix layer 38, and porous metal layer
40 as described above with respect to hip stem 20. However, distal
end 30 of hip stem 200 includes only core 36 and porous metal layer
40, and lacks polymer matrix layer 38. In this manner, distal end
30 of hip stem 200 has a higher stiffness than proximal end 28 of
hip stem 200 to facilitate initial fixation of distal end 30 of hip
stem 200 in the diaphysis of the femur, wherein proximal end 28 of
hip stem 200 has a stiffness which more closely mimics that of
natural bone than known hip stems to thereby transfer loading to
the surrounding bone of the metaphysis around proximal end 28 of
hip stem 200 to reduce the potential for stress shielding. As
discussed above, in certain patients, such as in certain female
patients, not only does the cortex of the metaphysis thin, but a
greater extent of the metaphysis of the femur must be osteotomized
during a total hip arthroplasty, which results in less of the
remaining metaphysis being available for fixation. Thus, for these
types of procedures, hip stem 200 advantageously includes a
relatively stiff distal end 30 for enhanced initial fixation in the
diaphysis of the femur, and a relatively more flexible proximal end
28 to prevent stress shielding and bone resorption in the
metaphysis of the femur.
[0088] Referring to FIGS. 28 and 29, anterior and lateral views of
a hip stem 210 according to a further embodiment are shown,
respectively. In FIGS. 28 and 29, hip stem 210 is shown
superimposed on proximal femur "F", shown in ghost lines, to
illustrate features of hip stem 210 in relation to the proximal
femur. Hip stem 210 is particularly useful in patients, such as
older female patients, for example, whose proximal femur is
characterized by thinned cortices "C" in the metaphysis and
diaphysis as shown in FIG. 28, perhaps with complete loss of the
medial and posterior cortices in the metaphysis resulting in the
"stovepipe" shape of the intramedullary canal seen in FIG. 28, as
well as a thinned intramedullary canal in the diaphysis. Although
anatomical features of the proximal femur, including the greater
trochanter "GT", lesser trochanter "LT", femoral neck "FN", and
femoral head "FH" are shown in ghost lines in FIGS. 28 and 29 in
order to illustrate features of hip stem 210 in relation thereto,
it is to be understood that the femoral neck and head, as well as
portions of the greater trochanter, are osteotomized during a total
hip arthroplasty to accommodate insertion of femoral stem 210 into
the prepared intramedullary canal of the femur.
[0089] Hip stem 210 generally includes a proximal, or metaphyseal,
portion 212 and a distal, or diaphyseal, portion 214. Hip stem 210
may be constructed in a similar manner as hip stem 20 described
above with respect to FIGS. 1-5, wherein hip stem 210 may include a
core 36, a polymer matrix layer (not shown) disposed over at least
a portion of core 36, and a porous metal layer 40, such as those
described above or a grit-blasted layer, disposed over the polymer
matrix layer. Proximal portion 212 of stem 210 has a length
dimension D.sub.1 measured from stage line 216, which is typically
15 mm from the top of the lesser trochanter, to line 220 at the
base of the lesser trochanter which may be as small as 30 mm or 35
mm to as large as 40 mm or 45 mm for example, or any length
therebetween. As may be seen from FIG. 28, proximal portion 212 of
stem 210 is not trapezoidally shaped as are many known hip stems
when viewed in the anterior/posterior view of FIG. 28, but rather
has a "goose neck" profile, including medially curved,
complementary radiused lateral and medial sides 222 and 224. In
particular, lateral side 222 is curved medially in order to clear
the greater trochanter and prevent loading on any portion of the
greater trochanter which remains after the osteotomy. When viewed
in the lateral view of FIG. 29, proximal portion 212 of hip stem
210 has a flared shape including anterior and posterior sides 226
and 228 which flare slightly outwardly, such as between 1 and 2 mm,
for example, in the anterior and posterior directions as same
approach the proximal end of hip stem 210.
[0090] The neck portion and the femoral head (not shown) of
proximal portion 212 of hip stem 210 may be integrally formed with
hip stem 210 and may be aligned in desired anteversion/retroversion
and varus/valgus angles in the same manner as the other hip stems
described above with reference to FIGS. 12 and 18. Alternatively,
the neck portion and the femoral head of hip stem 210 may be
configured as one or more modular components to provide the desired
anteversion/retroversion and varus/valgus angles in the manner
described above with reference to FIGS. 13-17 and 19.
[0091] Distal portion 214 of hip stem 210 may have a circular or
trapezoidal cross section, and is elongated with respect to known
hip stems to allow the distal portion 214 to engage the cortex of
the diaphyseal isthmus, having a length dimension D.sub.2 measured
from the from the mid lesser trochanter line 221 to the distal end
230 of the hip stem 210 which may be as small as 100 mm, 105 mm, or
110 mm and as large as 125 mm, 130 mm, or 135 mm, for example, or
any length therebetween. Near the distal end 230, the width of hip
stem 210 at dimension D.sub.3 measured laterally-medially may vary
from 10 mm to 18 mm and, as shown in FIG. 29, the width of hip stem
210 at dimension D.sub.4 measured anteriorly-posteriorly may be 1
mm or more greater than dimension D.sub.3, i.e., may vary between
11 mm and 19 mm, in order to optimally fit within the
intramedullary canal of certain patients, particularly in older
female patients, wherein the intramedullary canal is slightly wider
in the anterior/posterior dimension and in the medial/lateral
dimension.
[0092] Additionally, distal portion 214 of hip stem 210 may have a
substantially hollow construction, including an elongated blind
cavity 232 extending inwardly from distal end 230 toward proximal
portion 212 of hip stem 210, optionally extending to line 220 at
the base of the lesser trochanter. Cavity 232 allows distal portion
214 of hip stem 210 to flex, such that the stiffness modulus of
distal portion 214 of hip stem 210 more closely approximates the
stiffness modulus of the femoral bone surrounding hip stem 210 to
aid in prevention of stress shielding around distal portion 214 of
hip stem 210. Alternatively, distal portion 214 of hip stem 210 may
be formed to include a core/polymer matrix/porous outer layer
construction similar to the other hip stems disclosed herein to
provide a stiffness modulus which more closely approximates the
stiffness modulus of the femoral bone around distal portion 214 of
hip stem 210. In a still further embodiment, distal portion 214 of
hip stem 210 may include a plurality of grooves, slopes, or other
enervations or weakenings therein to reduce the stiffness modulus
thereof.
[0093] While this disclosure has been described as having exemplary
designs, the present disclosure can be further modified within the
spirit and scope of this disclosure. This application is therefore
intended to cover any variations, uses, or adaptations of the
disclosure using its general principles. Further, this application
is intended to cover such departures from the present disclosure as
come within known or customary practice in the art to which this
disclosure pertains and which fall within the limits of the
appended claims.
* * * * *