U.S. patent application number 13/368688 was filed with the patent office on 2012-05-31 for hip prosthesis with monoblock ceramic acetabular cup.
This patent application is currently assigned to Amedica Corporation. Invention is credited to K. Scott Ely, Aaron A. Hofmann, Ashok C. Khandkar, Ramaswamy Lakshminarayanan.
Application Number | 20120136454 13/368688 |
Document ID | / |
Family ID | 37758203 |
Filed Date | 2012-05-31 |
United States Patent
Application |
20120136454 |
Kind Code |
A1 |
Ely; K. Scott ; et
al. |
May 31, 2012 |
Hip Prosthesis With Monoblock Ceramic Acetabular Cup
Abstract
An improved hlp prosthesis includes an acetabular cup bearing
component constructed from a relatively hard and high strength
ceramic material for articulation with a ball-shaped femoral head
component which may be constructed from a compatible ceramic or
metal material. In one form, the acetabular cup further includes a
ceramic porous bone ingrowth surface adhered thereto for secure
ingrowth attachment to natural patient bone.
Inventors: |
Ely; K. Scott; (Austin,
TX) ; Khandkar; Ashok C.; (Salt Lake City, UT)
; Lakshminarayanan; Ramaswamy; (Salt Lake City, UT)
; Hofmann; Aaron A.; (Salt Lake City, UT) |
Assignee: |
Amedica Corporation
Salt Lake City
UT
|
Family ID: |
37758203 |
Appl. No.: |
13/368688 |
Filed: |
February 8, 2012 |
Related U.S. Patent Documents
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Application
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Patent Number |
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12661991 |
Mar 26, 2010 |
8133284 |
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13368688 |
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11203047 |
Aug 12, 2005 |
7695521 |
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12661991 |
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10987415 |
Nov 12, 2004 |
7666229 |
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11203047 |
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10171376 |
Jun 13, 2002 |
6881229 |
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10987415 |
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11040477 |
Jan 20, 2005 |
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11203047 |
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10137106 |
Apr 30, 2002 |
6846327 |
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11040477 |
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60298669 |
Jun 14, 2001 |
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60287824 |
May 1, 2001 |
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Current U.S.
Class: |
623/22.15 ;
623/22.21 |
Current CPC
Class: |
A61F 2002/30324
20130101; A61F 2310/00317 20130101; A61F 2002/30685 20130101; A61F
2/32 20130101; A61F 2/34 20130101; A61F 2310/00011 20130101; A61F
2002/3611 20130101; A61F 2310/00029 20130101; A61F 2250/0036
20130101; A61F 2002/30332 20130101; A61F 2310/00203 20130101; A61F
2/30767 20130101; A61F 2/36 20130101; A61F 2002/365 20130101; A61F
2250/0023 20130101; A61F 2002/30934 20130101; A61F 2310/00239
20130101; A61F 2002/349 20130101; A61L 27/10 20130101; A61F
2002/3625 20130101; A61F 2002/30011 20130101; A61F 2220/0033
20130101; A61F 2310/00179 20130101; A61F 2/3662 20130101 |
Class at
Publication: |
623/22.15 ;
623/22.21 |
International
Class: |
A61F 2/32 20060101
A61F002/32; A61F 2/34 20060101 A61F002/34 |
Claims
1. A hip joint prosthesis, comprising: a generally shell-shaped
acetabular cup defining a convex upper side having a size and shape
adapted for seated engagement within a patient's natural
acetabulum, and a lower side defining a downwardly open and
generally part-spherical cavity lined by an articulation surface
having a size and shape for articulatory reception of a matingly
shaped femoral component; said acetabular cup being formed from
ceramic material having relatively high a relatively high flexural
strength and a relatively high fracture toughness for ultra-low
wear upon post-implantation articulation with said matingly shaped
femoral component.
2. The hip joint prosthesis of claim 1 wherein said ceramic
material has a relatively high flexural strength greater than about
500 Mega-Pascal (MPa) and a relatively high fracture toughness
greater than about 5 Mega-Pascal root meter (MPam.sup.0.5).
3. The hip joint prosthesis of claim 1 wherein said ceramic
material has a relatively high flexural strength greater than about
700 Mega-Pascal (MPa) and a relatively high fracture toughness
greater than about 7 Mega-Pascal root meter (MPam.sup.0.5).
4. The hip joint prosthesis of claim 3 wherein said ceramic
material comprises doped silicon nitride.
5. The hip joint prosthesis of claim 1 further including a bone
ingrowth surface on said convex upper side of said acetabular
cup.
6. The hip joint prosthesis of claim 1 wherein said bone ingrowth
surface comprises a ceramic bone ingrowth surface.
7. The hip joint prosthesis of claim 6 wherein said acetabular cup
comprises a ceramic material having a variable porosity gradient
defining a relatively low porosity first region forming a substrate
defining said articulation surface, and a comparatively higher
porosity second region defining said ceramic bone ingrowth surface,
said first and second regions being integrally formed.
8. The hip joint prosthesis of claim 7 wherein said ceramic
material has a porosity gradient ranging from about 2% to about 80%
by volume, with said higher porosity region having a porosity in
the range of from about 30% to about 80% by volume.
9. The hip joint prosthesis of claim 8 wherein said ceramic
material has pores formed therein with a pore size ranging from
about 100 microns to about 500 microns.
10. The hip joint prosthesis of claim 1 wherein said matingly
shaped femoral component comprises a ball-shaped femoral head.
11. The hip joint prosthesis of claim 10 wherein said femoral head
is formed from a ceramic material.
12. The hip joint prosthesis of claim 10 wherein said femoral head
is formed from a ceramic material substantially identical to the
acetabular cup ceramic material.
13. The hip joint prosthesis of claim 10 wherein said femoral head
is formed from a biocompatible metal.
14. The hip joint prosthesis of claim 10 further including a
retainer for movably retaining said acetabular cup on said femoral
head.
15. A hip joint prosthesis, comprising: a generally shell-shaped
acetabular cup defining a downwardly open and generally
part-spherical cavity lined by an articulation surface having a
size and shape for articulatory reception of a matingly shaped
femoral component; said articulation surface of said acetabular cup
being formed from ceramic material having relatively high a
relatively high flexural strength and a relatively high fracture
toughness for ultra-low wear upon post-implantation articulation
with said matingly shaped femoral component; said acetabular cup
further defining a convex upper side having a porous bone ingrowth
surface thereon and further defining a size and shape adapted for
seated engagement within a patients natural acetabulum.
16. The hip joint prosthesis of claim 15 wherein said acetabular
cup comprises a ceramic material having a variable porosity
gradient defining a relatively low porosity first region forming a
substrate defining said articulation surface, and a comparatively
higher porosity second region defining said bone ingrowth surface,
said first and second regions being integrally formed.
17. The hip joint prosthesis of claim 15 wherein said matingly
shaped femoral component comprises a ball-shaped femoral head.
18. The hip joint prosthesis of claim 17 wherein said femoral head
is formed from a ceramic material substantially identical to the
acetabular cup ceramic material.
19. The hip joint prosthesis of claim 17 wherein said femoral head
is formed from a biocompatible metal.
20. A hip joint prosthesis, comprising: a generally shell-shaped
acetabular cup defining a convex upper side and having a size and
shape adapted for seated engagement within a patient's natural
acetabulum, and a lower side defining a downwardly open and
generally part-spherical cavity lined by an articulation surface
having a size and shape for articulatory reception of a matingly
shaped femoral component; said acetabular cup being formed from
ceramic material having a relatively high flexural strength and a
relatively high fracture toughness for ultra-low wear upon
post-implantation with said matingly shaped femoral component; and
said acetabular cup having a rim with a recessed geometry for
increase range of motion.
21. The hip joint prosthesis of claim 20 wherein said rim includes
multiple recesses formed therein for enhanced range of motion.
22. The hip joint prosthesis of claim 20 wherein said rim includes
a pair of generally diametrically opposed recesses formed therein
for enhanced range of motion.
Description
[0001] This application is a continuation-in-part of copending U.S.
Ser. No. 10/987,415, filed Nov. 12, 2004, which is a division of
U.S. Ser. No. 10/171,376, filed Jun. 13, 2002, which in turn claims
the benefit of U.S. Provisional Application. 60/289,669, filed Jun.
14, 2001.
[0002] This application is also a continuation-in-part of copending
U.S. Ser. No. 11/040,477, filed Jan. 20, 2005, which is a
continuation-in-part of U.S. Ser. No. 10/137,106, filed Apr. 30,
2002, now U.S. Pat. No. 6,846,327, issued Jan. 25, 2005, which in
turn claims the benefit of U.S. Provisional Application 60/287,824,
filed May 1, 2001.
BACKGROUND OF THE INVENTION
[0003] This invention relates generally to improvements in hip
joint prostheses, particularly with respect to an improved
acetabular cup bearing component constructed from a relatively hard
and relatively high strength ceramic material. The ceramic
acetabular cup is designed for direct articulation against an
associated femoral head component formed from a compatible ceramic
or metal material, with minimal component wear to achieve
substantially optimal prosthesis service life. The present
invention thus permits elimination of a conventional polymer-based
bearing insert thereby also eliminating undesirable wear debris
associated therewith.
[0004] Hip prostheses generally comprise a femoral component
adapted for fixation to an upper end of the patient's femur, and
defining a generally ball-shaped head for articulation relative to
an acetabular cup component which is adapted in turn for seated
fixation within the patient's acetabulum. A polymer-based bearing
insert such as a cup-shaped component formed from a typically high
density or high molecular weight polyethylene (PE) or the like is
normally fitted between the femoral head and the acetabular cup to
accommodate smooth and relatively low-wear articulation between
these components.
[0005] However, clinical studies have shown that significant wear
debris can be generated and released by the polymeric bearing
insert over a period of time, and further that a principle
contributing factor to implant failure is osteolysis attributable
at least in part to the presence of such polymer-based wear debris.
More particularly, such studies have shown that PE wear debris
released into peri-implant tissues appears to elicit a deleterious
biological reaction, incorporating foreign body giant cell and
macrophage cell responses leading to undesirable bone resorption,
with eventual loosening and failure of the prosthetic implant. As a
result, alternative prosthesis constructions have proposed
improvements in and to the polymer-based bearing insert, such as
the use of heavily cross-linked polyethylene materials. Other
alternative prostheses have been proposed using rigid-on-rigid
components, such as ceramic-on-ceramic or metal-on-metal, thereby
eliminating the polymer-based bearing insert and wear debris
associated therewith.
[0006] In general, ceramic hip prosthesis components have shown
promise for use in a ceramic-on-ceramic or alternately in a
ceramic-on-metal articulating interface, thereby completely
eliminating the polymer-based bearing insert. Such prosthesis
constructions, when formed with a good surface finish and conformal
surface geometry, have demonstrated a relatively low coefficient of
friction and resultant substantial reduction in component wear in
comparison with ceramic-polymer or metal-polymer articulatory
interfaces. However, the major limitation on the use of ceramic
components particularly such as alumina-based ceramic materials has
been an unacceptably high rate of brittle fracture occurring within
a post-surgical follow-up period ranging from a few months to
several years. In this regard, ceramic materials generally exhibit
relatively low toughness and are thus prone to brittle
fracture.
[0007] U.S. Publication US 2003/0153984 discloses an improved
ceramic material for use in joint prostheses, such as hip
prostheses, wherein a ceramic-on-ceramic or a ceramic-on-metal
articulatory interface is defined. The improved ceramic material
comprises a doped silicon nitride (S.sub.3N.sub.4) having
relatively high hardness, tensile strength, elastic modulus,
lubricity, and fracture toughness. Specifically, the improved doped
silicon nitride ceramic has a flexural strength greater than about
700 Mega-Pascal (MPa) and a fracture toughness greater than about 7
Mega-Pascal root meter (MPam.sup.0.5). This high strength and high
toughness doped silicon nitride ceramic achieves ultra-low wear
over an extended service life, with dramatically reduced risk of
brittle fracture.
[0008] In addition, U.S. Pat. No. 6,846,327 discloses improved
ceramic materials for bone graft applications, wherein the ceramic
material is designed to mimic structural characteristics of natural
patient bone by including first and second regions of comparatively
lower and higher porosity to respectively mimic natural cortical
and cancellous bone structures. The preferred ceramic materials
disclosed exhibit a flexural strength greater than about 500
Mega-Pascal (MPa) and a fracture toughness greater than about 5
Mega-Pascal root meter (MPam.sup.0.5). In use, the relatively low
porosity region of the ceramic material provides high structural
strength and integrity, whereas the higher porosity region is
suitable for bone ingrowth to achieve secure and stable implant
affixation.
[0009] The present invention comprises an improved hip joint
prosthesis particularly wherein the acetabular cup component
thereof is constructed from an improved high strength and high
toughness ceramic material as disclosed, e.g., in U.S. Publi. US
2003/0153984 and/or U.S. Pat. No. 6,846,327.
SUMMARY OF THE INVENTION
[0010] In accordance with the invention, an improved hip prosthesis
includes an acetabular cup bearing component constructed from a
relatively high strength and high toughness ceramic material for
ultra-low wear articulation with a ball-shaped femoral head
component which may be constructed from a compatible ceramic or
metal material. In one form, the acetabular cup further includes a
ceramic porous bone ingrowth surface for secure ingrowth affixation
to natural patient bone.
[0011] In one preferred form of the invention, a unipolar hip joint
prosthesis includes the ceramic acetabular cup having a generally
shell-shaped or cup-shaped geometry defining a relatively low
porosity substrate in combination with a comparatively higher
porosity bone ingrowth surface. The low porosity ceramic substrate
defines a downwardly open, part-spherical cavity for receiving and
articulating with a ball-shaped femoral head of a femoral
component, wherein the femoral head may be constructed from a
compatible and preferably identical high strength and high
toughness ceramic material, or alternately from a compatible metal
material such as biocompatible cobalt chrome alloy or the like. The
higher porosity ceramic bone ingrowth surface extends over an upper
surface of the acetabular cup for suitable seated contact within a
prepared patient acetabulum, for secure affixation thereto by bone
ingrowth.
[0012] The ceramic acetabular cup of the hip prosthesis may
incorporate a lower free circumferential edge or margin defined by
a pair of shallow relief segments formed at diametrically opposed
positions corresponding with the flexion/extension plane. The
inclusion of these relief segments beneficially provides the
patient with an enhanced range-of-motion (ROM).
[0013] The relief segments may be in the form of cutouts or
recesses. Alternatively, the acetabular cup may employ a single
cutout or relief, or multiple cutouts or reliefs may be used.
Further the cutouts or reliefs can be symmetrically configured or
asymmetrically configured. For example, the cutouts or reliefs can
be diametrically oppositely disposed, spaced adjacent to each
other, or spaced in other circumferential orientations.
[0014] Other features and advantages of the present invention will
become apparent from the following more detailed description; taken
in conjunction with the accompanying drawings, which illustrate, by
way of example, the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings illustrate the invention. In such
drawings:
[0016] FIG. 1 is a fragmented perspective view illustrating an
exemplary hip prosthesis in an installed position affixed to a
patient's femur and acetabulum;
[0017] FIG. 2 is an enlarged and exploded perspective view showing
components of an improved hip prosthesis embodying the novel
features of the invention;
[0018] FIG. 3 is a further enlarged and fragmented sectional view
depicting details of an acetabular cup used in the hip prosthesis
of FIG. 2;
[0019] FIG. 4 is an exploded perspective view showing one
alternative preferred form of a hip prosthesis;
[0020] FIG. 5 is a perspective view illustrating an alternative
preferred geometry for an acetabular cup component for use in the
invention;
[0021] FIG. 6 is a side elevation view of the acetabular cup of
FIG. 5; and
[0022] FIG. 7 is a sectional view taken generally on the line 7-7
of FIG. 6.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0023] As shown in the exemplary drawings, an improved hip
prosthesis referred to generally in one preferred form by the
reference numeral 10 in FIGS. 2-3 includes an acetabular cup 12
constructed from a relatively hard and high strength ceramic
material which may also incorporate a relatively porous ceramic
bone ingrowth surface 14 for secure affixation to patient bone. The
cup 12 is designed for articulation with other prosthesis
components such as a ball-shaped femoral head component 16 which
may be constructed from a hard and high strength material such as a
compatible and preferably identical ceramic material, or a
biocompatible metal material (FIG. 4). The resultant
ceramic-on-ceramic or ceramic-on-metal articulatory interface
beneficially exhibits ultra-low wear over an extended service life,
while additionally permitting elimination of traditional
polymer-based bearing inserts and wear debris problems associated
therewith.
[0024] FIG. 1 illustrates a traditional hip prosthesis construction
for repairing or replacing the natural anatomical ball-and-socket
human hip joint. More specifically, FIG. 1 shows an acetabular cup
12 seated and/or affixed within the patient's natural acetabulum or
socket 17, in combination with a femoral component 18 including an
elongated stern 20 (FIG. 2) seated within a resected upper end of
the patient's femur bone 22, an upwardly protruding femoral neck
24, and the ball-shaped femoral head 16 mounted or otherwise formed
on an upper end of the neck 24. Accordingly, a generally cup-shaped
bearing insert 26 formed typically from a polymer-based material
such as a high density or high molecular weight polyethylene (PE)
or the like is normally fitted between the acetabular cup 12 and
the femoral head 16 to accommodate smooth articulation between
these components. However, as previously noted herein, premature
prosthesis failure has been attributed to the generation and
accumulation of polymer-based wear debris associated with the
bearing insert 26. A further drawback to the use of polymer-based
inserts is the higher thickness of the construct, restricting its
application to larger bone patients capable of receiving the larger
sizes, and thus preventing the use of larger diameter heads in
smaller bone patients.
[0025] Accordingly, the present invention is particularly directed
to the provision of an improved hip joint prosthesis 10 constructed
in any one of a plurality of alternative preferred forms, to
include improved implantable and biocompatible materials designed
for achieving ultra-lowwear as a consequence of component
articulation over an extended service life or duty cycle, using a
ceramic-on-ceramic or a ceramic-on-metal articulatory interface,
and omitting use of the traditional polymer-based bearing
insert.
[0026] The present invention is also particularly directed to the
provision of an improved hip joint prosthesis 10 constructed in any
one of a plurality of alternative preferred forms, to include
improved implantable and biocompatible materials designed for
achieving a thinner overall acetabular cup diameter, and as a
consequence, providing the ability to use larger diameter heads on
smaller bone patients than otherwise possible, using a
ceramic-on-ceramic or a ceramic-on-metal articulatory interface,
and omitting the use of traditional polymer-based bearing
inserts.
[0027] FIGS. 2-3 illustrate the improved hip prosthesis 10 in one
preferred unipolar form. As shown, the acetabular cup 12 has a
generally cup-shaped or shell-shaped geometry defining a downwardly
open part-spherical and substantially hemispherical cavity 28. This
shell-shaped acetabular cup 12 has a size selected for
substantially conformal seated reception into the generally
matingly shaped acetabulum or socket 17 (FIG. 1) which may be
surgically prepared as by removal of accumulated calcium deposits
or other procedures known in the art. Importantly, in accordance
with a primary aspect of the invention, the acetabular cup 12 is
formed from a relatively high strength and high toughness or high
hardness ceramic material defining a part-spherical substrate 30
lining the cavity 28 to define an articulation surface for
receiving and articulating against the ball-shaped femoral head
16.
[0028] More specifically, the preferred ceramic material used for
constructing the ceramic acetabular cup 12 of the present invention
comprises a high flexural strength and high fracture toughness
ceramic material particularly such as a doped silicon nitride
(S.sub.3N.sub.4) having relatively high hardness, tensile strength,
elastic modulus, lubricity, and fracture toughness properties, as
described in detail in U.S. Publi. 2003/0153984 which is
incorporated by reference herein. This doped silicon nitride
ceramic material has a relatively high flexural strength greater
than about 700 Mega-Pascal (MPa) and a relatively high fracture
toughness greater than about 7 Mega-Pascal root meter
(MPam.sup.0.5). This high strength and high toughness doped silicon
nitride ceramic achieves ultra-low wear over an extended service
life, with dramatically reduced risk of brittle fracture.
[0029] In the preferred form as shown best in FIG. 3, this high
strength and high toughness ceramic material is used to form the
substrate 30 of the ceramic acetabular cup 12. In this regard, the
substrate 30 of the ceramic cup 12 has a relatively low porosity,
and thus exhibits high density and high structural integrity
generally consistent with and generally mimicking the
characteristics of natural cortical bone lined with smooth
lubricious articular cartilage. FIG. 3 further shows a surface
coating or lining 14 formed on the part-spherical upwardly
presented surface or convex upper side of the cup 12, wherein this
coating or lining exhibits a comparatively greater or higher
porosity that is generally consistent with and generally mimics the
characteristics of natural cancellous bone. As a result, this
higher porosity surface coating or lining 14 provides an effective
bone ingrowth surface for achieving secure and stable bone ingrowth
affixation of the ceramic acetabular cup 12 within the patient's
acetabulum.
[0030] While persons skilled in the art will recognize and
appreciate that the specific material used for the bone ingrowth
surface coating or lining 14 may vary, a preferred porous material
comprises a ceramic porous ingrowth surface material. In this
regard, U.S. Pat. No. 6,846,327 which is incorporated by reference
herein discloses a ceramic bone graft component having relatively
high flexural strength and relatively high toughness properties yet
defining first and second regions of comparatively lower and higher
porosity to respectively mimic natural cortical and cancellous bone
structures. These regions of different porosity may be unitarily
constructed or otherwise integrated into a common or monolithic
ceramic component having a variable porosity gradient. In a
preferred form, the ceramic cup 12 has a porosity gradient ranging
from, about 2% to about 80% by volume, with the higher porosity
region having a porosity in the range of from about 30% to about
80% by volume, and with overall pore sizes ranging from about 100
microns to about 500 microns. In use, the relatively low porosity
region of the ceramic material provides a dense and hard structure
with high structural strength and integrity, whereas the higher
porosity or less dense region is suitable for bone ingrowth to
achieve secure and stable implant affixation.
[0031] U.S. Pat. No. 6,846,327 discloses a preferred
alumina-zirconia ceramic material having a zirconia composition of
about 10% to about 20% by volume, with either yttria stabilized
zirconia (about 2.5 to about 5 mol % yttria in zirconia) or ceria
stabilized zirconia (about 2.5 to about 15 mol % ceria in zirconia)
for the zirconia phase. The resultant ceramic material exhibits a
highly desirable combination of high flexural strength (greater
than about 500 MPa) and high fracture toughness (greater than about
5 MPam.sup.0.5). Such alumina-zirconia based ceramic material may
be employed in the present invention for the ceramic acetabular cup
12, although the harder and tougher silicon nitride
(S.sub.3N.sub.4) ceramic as described in U.S. Publi. 2003/0153984
is preferred.
[0032] FIG. 3 shows the ceramic acetabular cup 12 to include the
substrate 30 formed from relatively low porosity ceramic material
having the desired high strength and high toughness properties,
such as the doped silicon nitride (S.sub.3N.sub.4) material
described in the above-referenced U.S. Publi. 2003/1053984, wherein
this low porosity ceramic material lines and defines the concave
part-spherical cavity 28. FIG. 3 further shows the comparatively
higher porosity bone ingrowth surface 14, formed preferably from a
higher porosity ceramic material as described in the
above-referenced U.S. Pat. No. 6,846,327, extending over a
substantial area of the convex upper side of the acetabular cup 12.
As noted, this bone ingrowth surface 14 may be formed integrally
with or otherwise applied to the substrate 30.
[0033] The femoral head 16 is sized and shaped for articulatory
reception within the acetabular cup cavity 28. In a preferred form
as viewed in FIG. 2, the femoral head 16 is constructed from a
ceramic material that is compatible with the ceramic cup material.
In this regard, a preferred material for the femoral head 16
comprises a matching or identical high strength and high toughness
ceramic material corresponding with the acetabular cup material, as
disclosed in U.S. Publi. 2003/1053984. Alternately, as viewed in
one preferred alternative unipolar embodiment of the invention
depicted in FIG. 4, a modified femoral head 16' may be constructed
from a biocompatible metal material, preferably such as a cobalt
chrome alloy as disclosed in the above-referenced 2003/1053984.
[0034] FIGS. 5-7 depict a modified ceramic acetabular cup 12' which
may be incorporated into any one of the foregoing embodiments of
the invention as shown in FIGS. 2-4 and previously described
herein. In this regard, FIGS. 5-7 show the modified acetabular cup
12' to include the relatively low porosity substrate 30 defining
the downwardly presented part-spherical cavity 28, in combination
with the bone ingrowth coating or surface 14 on the upwardly
presented or convex side thereof. Persons skilled in the art will
appreciate that the bone ingrowth coating or surface may be
omitted, as previously described herein. Importantly, the
circumferential free edge or margin 60 of the ceramic cup 12'
incorporates a pair of smoothly contoured, shallow relief segments
62' and 64 formed generally at diametrically opposed positions
corresponding with the flexion/extension plane during normal
patient movements. The inclusion of these shallow relief segments
62 and 64 beneficially provides the hip prosthesis and thus the
patient with an enhanced range-of-motion (ROM).
[0035] A variety of further modifications and improvements in and
to the hip prosthesis of the present invention will be apparent to
persons skilled in the art. For example, it wilt be understood that
the ceramic acetabular cup component as shown and described herein
may be used for articulatory engagement with the natural
ball-shaped femoral head at the upper end of the patient's femur,
or with an appropriately capped natural femoral head, in lieu of a
prosthetic femoral head. Accordingly, no limitation on the
invention is intended by way of the foregoing description and
accompanying drawings, except as set forth in the appended
claims.
* * * * *