U.S. patent application number 13/246544 was filed with the patent office on 2012-04-26 for pyrolytic carbon implants with porous fixation component and methods of making the same.
This patent application is currently assigned to Zimmer, Inc.. Invention is credited to Jeffrey Anderson, Oludele Popoola, Steven Seelman, Brian Thomas, Joseph Vargas.
Application Number | 20120101592 13/246544 |
Document ID | / |
Family ID | 44860506 |
Filed Date | 2012-04-26 |
United States Patent
Application |
20120101592 |
Kind Code |
A1 |
Thomas; Brian ; et
al. |
April 26, 2012 |
Pyrolytic Carbon Implants With Porous Fixation Component And
Methods Of Making The Same
Abstract
An orthopedic implant including an articulation portion having a
pyrolytic carbon bearing surface and a porous bone on- or in-growth
structure, and methods of making the same.
Inventors: |
Thomas; Brian; (LAKELAND,
FL) ; Popoola; Oludele; (Granger, IN) ;
Vargas; Joseph; (Garnerville, NY) ; Seelman;
Steven; (Montclair, NJ) ; Anderson; Jeffrey;
(Warsaw, IN) |
Assignee: |
Zimmer, Inc.
Warsaw
IN
|
Family ID: |
44860506 |
Appl. No.: |
13/246544 |
Filed: |
September 27, 2011 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
61387678 |
Sep 29, 2010 |
|
|
|
Current U.S.
Class: |
623/23.55 ;
156/308.2; 156/60; 228/194; 427/2.26 |
Current CPC
Class: |
A61F 2/3603 20130101;
A61F 2/30 20130101; A61F 2/30767 20130101; Y10T 156/10 20150115;
A61F 2002/30143 20130101; A61F 2/4003 20130101; A61F 2002/30011
20130101; A61F 2/32 20130101; A61F 2310/00395 20130101; A61F 2/3094
20130101; A61F 2002/30878 20130101; A61F 2002/30138 20130101; A61F
2310/00161 20130101; A61F 2310/00574 20130101; A61F 2002/3092
20130101; A61F 2/42 20130101; A61F 2002/3008 20130101; A61F 2/36
20130101; A61F 2/38 20130101; A61F 2/34 20130101; A61F 2/44
20130101; A61F 2/28 20130101 |
Class at
Publication: |
623/23.55 ;
427/2.26; 156/60; 156/308.2; 228/194 |
International
Class: |
A61F 2/30 20060101
A61F002/30; B23K 20/00 20060101 B23K020/00; B32B 37/14 20060101
B32B037/14; B05D 5/00 20060101 B05D005/00; B32B 38/08 20060101
B32B038/08 |
Claims
1. An orthopedic implant, comprising: an articulation portion
having a pyrolytic carbon bearing surface; and a bone-fixation
portion extending from the articulation portion and having a porous
structure configured for bone on-growth or bone in-growth.
2. The implant of claim 1 wherein the articulation portion further
includes a substrate and the bone-fixation portion is bonded to the
substrate.
3. The implant of claim 2 further including a metal interlayer
positioned at least partially between the bone-fixation portion and
the substrate.
4. The implant of claim 3 wherein the metal interlayer and the
bone-fixation portion are comprised of the same metal material.
5. The implant of claim 3 wherein the interlayer is comprised of a
first metal and the bone fixation portion is comprised of a second
metal, and the first metal is soluble with the second metal.
6. The implant of claim 3 further including a metal outer layer at
least partially covering the bone fixation portion and the
interlayer, wherein the interlayer and metal outer layer bond the
bone fixation portion to the substrate.
7. The implant of claim 1 wherein the bone fixation portion is
comprised of porous tantalum.
8. The implant of claim 2 wherein the substrate is comprised of
isotropic graphite.
9. A method of forming an orthopedic implant, comprising: providing
a carbon member having an articulation portion and a bone fixation
portion with a porous region; applying a layer of pyrolytic carbon
on an outer surface of the articulation portion; applying a metal
coating to the porous region of the bone fixation portion.
10. The method of claim 9 in which the metal coating is selected
from the group consisting of tantalum, titanium, niobium or alloys
or combinations thereof.
11. The method of claim 9 wherein the pyrolytic carbon is applied
by chemical vapor deposition.
12. A method of forming an orthopedic implant, comprising:
providing a substrate having a first surface and a second surface;
applying a layer of pyrolytic carbon to the first surface of the
substrate; placing an interlayer comprising a metal between the
second surface of the substrate and a porous metal structure; and
bonding the porous metal structure and the substrate together to
form the orthopedic implant.
13. The method of claim 12 wherein the bonding comprises applying
heat and pressure to the substrate, interlayer and porous metal
structure for sufficient time to achieve solid-state diffusion
between the interlayer and the porous metal structure.
14. The method of claim 12 wherein one of the porous metal
structure and the interlayer is comprised of tantalum and the other
is comprised of titanium.
15. The method of claim 12 wherein the interlayer is applied to the
second surface of the substrate by chemical vapor deposition.
16. The method of claim 12 wherein the pyrolytic carbon is applied
by chemical vapor deposition.
17. A method of forming an orthopedic implant, comprising: applying
a layer of pyrolytic carbon to a first surface of a substrate;
applying a metal interlayer to a second surface of the substrate;
contacting a porous metal structure with the metal interlayer; and
applying a second outer layer of metal to the substrate, interlayer
and porous metal structure.
18. The method of claim 17 in which the metal interlayer, metal
outer layer and porous metal structure all comprise the same
metal.
19. The method of claim 18 in which the metal is selected from the
group consisting of titanium, tantalum, niobium or alloys or
combination of the same.
20. The method of claim 17 in which the pyrolytic carbon is applied
to the substrate by chemical vapor deposition.
21. The method of claim 17 in which the metal interlayer is applied
to the substrate by chemical vapor deposition.
22. The method of claim 17 in which the metal outer layer is
applied by chemical vapor deposition.
23. A method of forming an orthopedic implant, comprising: applying
a layer of pyrolytic carbon to a first surface of a substrate;
applying an interlayer comprised of a metal to a second surface of
the substrate; providing a porous metal structure; placing a metal
foil between the interlayer and the porous metal structure; and
diffusion bonding the porous metal structure, the metal foil and
the interlayer.
Description
CROSS REFERENCE TO RELATED APPLICATION(S)
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 61/387,678, filed Sep. 29, 2010, which is
hereby incorporated by reference in its entirety.
FIELD OF THE DISCLOSURE
[0002] The present disclosure generally relates to prosthetic
orthopedic implants, and more particularly to prosthetic orthopedic
implants for use in bone joints and methods of making the same.
Even more particularly, the present disclosure relates to
prosthetic orthopedic implants that include a pyrolytic carbon
bearing or articulating surface and a porous bone fixation
structure.
BACKGROUND
[0003] Pyrolytic carbon has gained a lot of interest over the past
few years as a bearing material in orthopedic applications. The
material shows excellent wear characteristics, a modulus of
elasticity similar to bone, and high strength. Pyrolytic carbon
implants are commonly made by depositing a layer of pyrolytic
carbon on a graphite substrate or core. Typically, pyrolytic carbon
implants included a solid or non-porous bone fixation portion that
is implanted into the bone and relies on a press-fit interference
with surrounding bone tissue for fixation of the implant to the
bone.
[0004] Bone on-growth or in-growth porous structures, such as
porous tantalum and titanium structures, are sometimes used in
orthopedic implants as the bone fixation component of the implant.
Such porous structures are implanted into the bone and are designed
to foster osseointegration. Osseointegration is the integration of
living bone tissue within a man-made material. The porous structure
and the bone material become intermingled as the bone grows into
the pores. This intermingling of the bone tissue with the porous
structure can enhance fixation between the orthopedic implant and
the bone tissue. Because of the difficulties of bonding porous
on-growth and in-growth structures to pyrolytic carbon and graphite
surfaces, pyrolytic carbon implants have not included such porous
fixation surfaces.
SUMMARY
[0005] In one aspect, the present disclosure is directed to an
orthopedic implant including an articulation portion having a
pyrolytic carbon bearing surface. The implant also includes a bone
fixation portion extending from the articulation portion and having
a porous structure configured for bone on-growth or bone
in-growth.
[0006] In another aspect, a method of forming an orthopedic
implant. The method includes providing a member having a first
portion and a porous second portion. A layer of pyrolytic carbon is
applied to a surface of the first portion and a metal is applied to
the porous second portion.
[0007] In yet a further aspect, a method of forming an orthopedic
implant that includes applying a layer of pyrolytic carbon to a
first surface of a substrate and placing an interlayer comprising a
metal between a second surface of the substrate and a porous metal
structure. The porous metal layer, substrate and the interlayer are
bonded together.
[0008] In yet another aspect, a method of forming an orthopedic
implant including applying a layer of pyrolytic carbon to a first
surface of a substrate and applying a metal interlayer to a second
surface of the substrate. A porous metal structure is placed in
contact with the metal interlayer, and a second outer layer of
metal is applied to the substrate, interlayer and porous metal
structure to bond the porous metal structure to the substrate.
[0009] In yet a further aspect, a method of forming an orthopedic
implant includes applying a layer of pyrolytic carbon to a first
surface of a substrate and applying an interlayer comprised of a
metal to a second surface of the substrate. A metal sheet is then
placed between the interlayer and a porous metal structure, and
heat and pressure are applied to bond the metal structure, metal
sheet and interlayer together.
BRIEF DESCRIPTION OF THE FIGURES
[0010] In the course of this description, reference will be made to
the accompanying drawings, wherein:
[0011] FIG. 1 is a perspective view of one embodiment of an implant
of the present disclosure;
[0012] FIG. 2 is a cross-sectional view of the implant of FIG.
1;
[0013] FIG. 3 is a cross-sectional view of another embodiment of an
implant of the present disclosure;
[0014] FIG. 4 is an elevation view of yet another embodiment of an
implant of the present disclosure;
[0015] FIG. 5 is a cross-sectional view of the implant of FIG.
4;
[0016] FIG. 6 is a cross-sectional view of another embodiment of an
implant of the present disclosure;
[0017] FIG. 7 is a cross-sectional view of still yet another
embodiment of an implant of the present disclosure;
[0018] FIG. 8 is a cross-sectional view of another embodiment of an
implant of the present disclosure;
[0019] FIG. 9a is a schematic illustration of one embodiment of a
method of making an implant of the present disclosure;
[0020] FIG. 9b is a flow-chart showing the method illustrated in
FIG. 7a;
[0021] FIG. 10a is a schematic illustration of another embodiment
of a method of making an implant of the present disclosure;
[0022] FIG. 10b is a flow-chart showing the method illustrated in
FIG. 8a;
[0023] FIG. 11a is a schematic illustration of yet another
embodiment of a method of making an implant of the present
disclosure;
[0024] FIG. 11b is a flow-chart showing the method illustrated in
FIG. 9a;
[0025] FIG. 12 is a flow-chart of one embodiment of a method of
making an implant of the present disclosure; and
[0026] FIG. 13 is a flow-chat of another embodiment of a method of
making an implant of the present disclosure.
DETAILED DESCRIPTION
[0027] As required, detailed embodiments of the present invention
are disclosed herein; however, it will be understood that the
disclosed embodiments are merely exemplary of the invention, which
may be embodied in various forms. Therefore, specific details
disclosed herein are not to be interpreted as limiting, but merely
as a basis for the claims and as a representative basis for
teaching one skilled in the art to variously employ the present
invention in virtually any appropriate manner.
[0028] Generally, the prosthetic implants disclosed herein include
an articulation portion having a pyrolytic carbon bearing or
articulating surface and a porous bone in-growth or on-growth
fixation structure or portion which is combined or otherwise
associated with the articulation portion. Pyrolytic carbon is a
brittle material that is biocompatible with bone and cartilage. It
has good wear and strength properties and has been found to be a
good bearing or articulating material for joint repair and
replacement applications. The bearing surface of implants may
articulate against, for example, natural body tissues, such as
bone, or may articulate against a surface of an adjacent prosthetic
component. Such implants are particularly useful in bone joint
repair and replacement and may be used to treat or repair defects
in, for example, the knee, hip, shoulder, fingers, elbow, toes or
ankle. However, it will be appreciated that the use of such
implants are not limited to joint repair or in connection with the
joints specifically identified.
[0029] Referring to FIGS. 1 and 2, implant 10a includes a first
portion or articulation portion 12a associated with a second
portion or bone fixation portion 14a. In the illustrated
embodiment, the bone fixation portion 14a is shaped to be received
into or implanted into a section of bone at the location of a joint
and includes a porous bone in-growth or on-growth structure or
region. The articulation portion 12a further includes a bearing
surface 16a that is comprised of pyrolytic carbon and that
functions as an articulating or bearing surface for the implant
10a. In the illustrated embodiment, the bearing surface 16a forms
an outer layer or cover of the articulation portion 12a, and more
specifically entirely covers an underlying body or substrate 24a
(see FIG. 2). However, it will be appreciated that the bearing
surface 16a may be sized to only cover a portion or multiple
portions of the substrate 24a depending on the desired articulation
points of the implant. Alternatively, the entire articulation
portion 12a could be formed of pyrolytic carbon.
[0030] In the embodiment illustrated in FIGS. 1 and 2 and other
figures contained herein, the articulation portion 12a is
hemisphericaly shaped or ball-shaped. In this configuration, the
articulation portion 12a may function, for example, as the
articulating head or ball of a ball and socket joint commonly found
in hip or shoulder. The articulation portion 12a of this and other
embodiments described herein may be, however, designed for other
joint functions, used in other types of joints, or even used for
other orthopedic applications. Accordingly, the articulation
portion 12a may take on any variety of suitable sizes and regular
and irregular geometric shapes, depending on the application. For
example, the articulation portion may be cubical, cylindrical,
cup-shaped, etc. In addition, depending on the desired application,
the bearing surface 16a may take on any variety of configurations,
for example, concave.
[0031] The second or bone fixation portion 14a preferably includes
a porous structure or region 26a in order to allow for bone
in-growth or on-growth. In one embodiment, the bone fixation
portion 14a may be made entirely or partially from a porous
material or made to contain pores and more specifically surface
pores 20a. Further, the bone fixation portion 14a includes a
projection or stem element 22a that is sized and shaped to be
implanted into bone. In the illustrated embodiment, the stem
element 22a has a polygonal cross-section and, more particularly a
hexagonal cross-section. In other embodiments, the stem element 22a
may have other polygonal shapes or may be cylindrical, spherical,
conical, or any other suitable configuration. In further
embodiments, multiple projections or stem elements 22a may be
incorporated to assist in limiting implant rotation or to provide
different bone fixation arrangements.
[0032] When implanted within bone, the porous structure or region
26a of the bone fixation portion 14a and in particular the stem
element 22a is receptive to bone cell and tissue on- and/or
in-growth which enhances fixation of the implant 10a to the bone.
The porous region 26a of the bone fixation portion 14a and the
porous regions of the bone fixation portions of other embodiments
described herein may have a pore size, pore interconnectivity,
and/or other features that facilitate bone tissue on- and/or
in-growth into the pores, as known in the art. Preferably, the bone
fixation portion 14a is formed entirely from a highly porous
material or a material adapted to be porous that may have a
porosity as low as about 55, 65, or 75 percent by volume or as high
as about 80, 85, or 90 percent by volume. However, it will be
appreciated that the bone fixation portion 14a may not be entirely
constructed of a porous material but includes region(s) comprised
of porous materials positioned thereon.
[0033] Referring to FIG. 2, in this embodiment, the implant 10a has
a core 18a that includes the body or substrate 24a of the
articulation portion 12a and the porous section or region 26a of
the bone fixation portion 14a. In one embodiment, the core 18a and
consequently the substrate 24a and porous region 26a may be
constructed out of a single material, for example, carbon, and more
particularly, a dense, isotropic graphite. As such, the substrate
24a and the porous stem element 22a may be of a one-piece or
unitary body or construction.
[0034] In order to enhance the visibility of the implant or
portions thereof under fluoroscopy or x-ray imaging, the carbon may
be doped with or otherwise include any suitable radiopacifiers,
such as tungsten, zirconia or barium sulphate. In the embodiment
illustrated in FIG. 2, the substrate 24a includes an exterior
surface 28a that has pyrolytic carbon layer 30a positioned at least
partially thereon. The pyrolytic carbon layer 30a helps form the
bearing surface 16a of articulation portion 12a. It shall be
appreciated that core 18a also may be constructed out of any other
suitable material that can have pyrolytic carbon applied thereto
and is suitable for use in orthopedic applications.
[0035] The pyrolytic carbon layer 30a may be applied to the
substrate 18a by any suitable method known in the art. For example,
the pyrolytic carbon layer 30a may be applied by chemical vapor
deposition (CVD) or physical vapor deposition (PVD). In the
embodiment shown in FIG. 2 and other embodiments described herein,
the pyrolytic carbon layer 30a has a uniform thickness. The
thickness of the pyrolytic carbon layer 30a, however, may vary to
accommodate particular applications of the implant. Preferably, the
pyrolytic carbon layer 30a has a thickness of at least about 50
.mu.m. In other embodiments, the pyrolytic carbon layer 30a has a
thickness of at least about 200 .mu.m, 300 .mu.m, 400 .mu.m or 500
.mu.m. In other embodiments, the pyrolytic carbon layer is between
about 500 .mu.m and 1000 .mu.m.
[0036] Referring back to bone fixation portion 14a, in this
embodiment, the bone fixation portion 14a comprises porous region
26a of the core 18a. As explained in more detail below, porous
region 26a of core 18a may be formed by drilling or machining holes
or pores 20a or a matrix of holes or pores into and/or through the
porous region 26a. The resultant holes or pores 20a of porous
region 26a may then be infiltrated and coated with a coating, such
as a metal coating, to promote bone in-growth or on-growth, as
described in more detail below. In one embodiment, the pores 20a
pass through the entire bone fixation portion 14a. In other
embodiments, the pores 20a are created to a porous region that
extends between about 500 um and 4000 um and preferably between
about 1000 um and 2000 um from the outer surface and into the bone
fixation portion 14a. Alternatively, as discussed below with
respect to FIGS. 7 and 8, the porous region 26a could be
constructed out of a material with the desired porosity and
attached or applied to the core.
[0037] A schematic illustration and flowchart of one embodiment of
a method of making the implant 10a illustrated in FIGS. 1 and 2 are
shown in FIGS. 9a and 9b, respectively. It is understood that the
steps of the method may be carried out in any suitable order which
results in an implant fit for its desired orthopedic use. In one
step, a block of carbon 32a, preferably a dense, isotropic
graphite, is machined or otherwise processed into a desired shape
to form the core 18a of implant 10a. In the embodiment shown, the
block 32a is machined into a core 18a having a substrate 24a and a
bone fixation portion 14a. The substrate 24a at least partially
forms the articulation portion 12a. Holes or pores 20a or a matrix
of holes or pores are then created in the bone fixation portion 14a
of the core 18a, resulting in a porous region 26a of bone fixation
portion 14a. In one embodiment, the bone fixation portion 14a is
drilled or otherwise machined to create holes 20a in porous region
26a.
[0038] In another step, the bone fixation portion 14a is masked or
otherwise protected or covered leaving substrate 24a of core 18a
exposed and a pyrolytic carbon layer 30a is applied to the outer
surface 28a of substrate 24a. The pyrolytic carbon layer 30a may be
applied by any suitable process. In one embodiment, the pyrolytic
carbon layer 30a is applied by CVD. In yet another step, the
articulation portion 12a/substrate 24a is masked or otherwise
protected and covered leaving the bone fixation portion 14a and
more particularly the porous region 26a exposed and a coating is
applied to at least a portion of the porous region 26a so that the
coating infiltrates the holes 20a and coats the porous regions 26a
of second portion 14a. In one embodiment, the coating is a metal
such as but not limited to, tantalum, titanium, niobium, alloys of
the same or any other suitable metal or alloy. Further, the metal
may be applied to the porous regions 26a by, for example, CVD, PVD
or any other suitable process. Other examples of coatings include
bone on-growth or in-growth coatings such as hydroxyapatite or
forms of calcium phosphate.
[0039] The resulting implant 10a includes a articulation or first
portion 12a including a pyrolytic carbon bearing surface 16a and
second or bone fixation portion 14a having a porous structure or
region 26a that is suitable for bone cell and tissue on- and/or
in-growth.
[0040] FIG. 3 illustrates another embodiment of an implant 10b of
the present disclosure which includes an articulation or first
portion 12b and a second or bone fixation portion 14b with a porous
region 26b. Similar to the previous embodiment, the articulation
portion 12b includes a body or substrate 24b having a pyrolytic
carbon layer 30b thereon that forms the bearing surface 16b. The
substrate 24b may be made of any material or combination of
materials suitable for having pyrolytic carbon applied thereto and
in one embodiment the substrate 24b is carbon, preferably a dense,
isotropic graphite. Additionally, in order to enhance the
visibility of the implant or portions thereof under fluoroscopy or
x-ray imaging, the carbon may be doped with or otherwise include
any suitable radiopacifiers, such as tungsten, zirconia and barium
sulphate.
[0041] In this embodiment, the bone fixation portion 14b comprises
a porous structure preferably constructed out of metal. The bone
fixation portion 14b is separately formed and is not unitary with
the substrate 24b. The bone fixation portion 14b may be made of any
suitable porous bone on-or in-growth metal structure known in the
art. For example, the bone fixation portion 14b may be made of
Trabecular Metal.RTM., generally available from Zimmer, Inc. of
Warsaw, Ind. Such material may be formed from a reticulated
vitreous carbon foam substrate which is infiltrated and coated with
a metal, such as tantalum, titanium, niobium, alloys of the same or
any other suitable metal or alloy, by a CVD process in the manner
disclosed in U.S. Pat. No. 5,282,861. The porous metal structure
may have a pore size, pore interconnectivity, and/or other features
that facilitate bone tissue on-and/or in growth.
[0042] As described in more detail below, the bone fixation portion
14b is bonded or otherwise attached to the substrate 24b of the
articulation portion 12b by a metal interlayer 34b and/or a metal
outer layer 36b. The metal interlayer 34b may be a layer of metal
deposited or otherwise placed on a surface of substrate 24b or may
be a sheet or foil positioned between substrate 24b and bone
fixation portion 14b. Preferably, metal interlayer 34b and metal
outer layer 36b are constructed out of the same metal or alloy as
that of the bone fixation portion 14. It should be noted that the
thicknesses of metal interlayer 34b and metal outer layer 36b are
not drawn to scale in the figures, but have been exaggerated for
illustrative purposes. Such interlayer 34b may have a thickness of
between about 100 um and about 1 mm, and more preferably between
about 400 um and about 600 um. The outer layer 36b may have a
thickness of between about 50 um and about 400 um, and more
preferably between about 150 um and about 250 um. However, it will
be appreciated that the thicknesses may be altered in order to
obtain the desired implant properties.
[0043] A schematic illustration and flowchart showing one
embodiment of a method of making implant 10b are shown in FIGS. 10a
and 10b, respectively. It is understood that the steps of the
method may be performed in any order that produces an implant
suitable for use in orthopedic applications. A block of carbon 32b,
preferably a dense, isotropic or fiber reinforced graphite, is
machined or otherwise processed to form the substrate 24b of
articulation portion 12b of the implant 10b. In order to form
bearing surface 16b, a pyrolytic carbon layer 30b is applied to an
outer surface 28b of substrate 24b by any suitable method known in
the art. For example, the pyrolytic carbon layer may be applied by
CVD.
[0044] An interlayer 34b, preferably metallic and more
specifically, a tantalum or titanium interlayer, is applied to
outer surface 38b of the substrate 24b. The metal interlayer 34b
may be applied by any suitable method known in the art, such as CVD
or PVD. Further, the metal interlayer 34b may be formed of a metal
foil or sheet. Undercuts, holes and/or other surface deviations may
be located or formed in substrate 24b, and particularly in outer
surface 38b, so that when the metal interlayer 34b is applied to
outer surface 38b, the metal enters and engages the undercuts,
holes, etc. to form a mechanical interlock between the interlayer
34b and substrate 24b.
[0045] The bone fixation portion 14b, which is comprised of a
porous metal structure and preferably a porous tantalum structure,
is placed against the metal interlayer 34b. A metal outer layer
36b, preferably a tantalum metal outer layer, is applied to the
bone fixation portion 14b, the metal interlayer 34b, and substrate
24b/articulation portion 12b. Again, the substrate 24b may include
undercuts, holes or other deviation so that when outer layer 36b is
applied, the metal may engage and enter such undercuts, holes or
other deviations in the surface to create a mechanical interlock.
Preferably, but not necessarily, the interlayer 34b, outer layer
36b and bone fixation portion 14b are all constructed of the same
metal. After the outer layer 36b has been applied, the metal
interlayer 34b, metal outer layer 36b and bone fixation portion 14b
are subjected to elevated temperatures to bond the bone fixation
portion 14b to substrate 24b and form the implant 10b.
[0046] FIGS. 4 and 5 illustrate another embodiment of an implant
10c of the present disclosure. Similar to the other embodiments,
the implant 10c includes a articulation or first portion 12c and a
bone fixation or second portion 14c. Referring to FIG. 5, the
articulation portion 12c includes a body or substrate 24c. The
substrate 24c includes a surface 28c having a pyrolytic carbon
layer 30c positioned thereon. The substrate 24c may be made of any
material or combination of materials suitable for having pyrolytic
carbon applied thereto and in one embodiment the substrate 24c is
carbon, preferably a dense, isotropic or fiber reinforced graphite.
Additionally, in order to enhance the visibility of the implant or
portions thereof under fluoroscopy or x-ray imaging, the carbon may
be doped with or otherwise include any suitable radiopacifiers,
such as tungsten, zirconia or barium sulphate.
[0047] Bone fixation portion 14c may be made of any suitable porous
bone on-or in-growth metal structure described herein or known in
the art. Alternatively, the bone fixation portion could be
constructed of a material that could be made porous through any
method known in the art. The porous bone fixation portion 14c is
bonded to the substrate 24c using interlayer 40c. Interlayer 40c is
preferably a metal that is readily soluble with the metal of the
porous stem 14c. As explained in more detail below, interlayer 40c
may be applied to surface 38c of the substrate 24c by any suitable
deposition process, such as CVD or PVD. Undercuts, holes and/or
other surface deviations may be located in substrate 24b, and
particularly in surface 38c, so that when the metal interlayer 40c
is applied to surface 38c, the metal enters and engages the
undercuts, holes, etc. to form a mechanical interlock between the
metal interlayer 40c and substrate 24c. In another embodiment, the
interlayer 40c may be a metal sheet or foil.
[0048] In a further embodiment, as shown in FIG. 6, the implant 10c
may include both a deposited interlayer 40c and a thin interlayer
such as a metal foil or sheet 42c located between bone fixation
portion 14c and substrate 24c to assist in the bonding process. It
should be noted that the thicknesses of metal interlayer 40c and
metal foil 42c are not drawn to scale in the figures, but have been
exaggerated for illustrative purposes. The interlayer 40c may have
a thickness of between about 100 um and about 1000 um, and more
preferably between about 400 um and about 600 um. The foil sheet
42c may have a thickness of between about 100 um and about 1000 um,
and more preferably between about 400 um and about 600 um.
[0049] A schematic illustration and flowchart showing one
embodiment of a method of making the implants 10c illustrated in
FIGS. 5 and 6 are shown in FIGS. 11a and 11b, respectively. The
steps of the method described herein may be performed in any order
that produces an implant suitable for use in orthopedic
applications. A block of carbon 32c, preferably a dense, isotropic
graphite, is machined or otherwise processed to form the substrate
24c of articulation portion 12c of the implant. A pyrolytic carbon
layer 30c is applied to an outer surface 28c of the substrate 24c.
A metal interlayer 40c, preferably comprised of a metal that is
readily soluble with the metal of the porous metal second portion
14c, is applied to surface 38c of substrate 24c. In one embodiment,
the metal interlayer is comprised of titanium. The metal interlayer
40c may be applied by any suitable process know in the art, such as
CVD. Undercuts, holes or other surface deviations may be located in
the substrate 24c, and in particular surface 38c, so that when the
metal interlayer 40c is applied to the substrate 24c, the metal
enters and engages the undercuts, holes, etc. to form a mechanical
interlock between the metal interlayer 40c and substrate 24c. In
another embodiment, interlayer 40c is a metal foil or sheet.
[0050] A bone fixation portion 14c comprised of a porous metal
structure, such as any of the porous metal structures described
herein or known in the art, is placed against the metal interlayer
40c to form an assembly. In one embodiment, one of the porous bone
fixation portion 14c and the interlayer 40c is comprised of
tantalum and the other one is comprised of titanium. Optionally, an
interlayer such as a metal foil or sheet (not shown) may be placed
between the porous metal bone fixation portion 14c and a deposited
metal interlayer 34c so that the implant includes both a deposited
metal interlayer 40c and a metal foil or sheet. In one embodiment
the metal foil or sheet is constructed out of the same metal as the
interlayer 34c.
[0051] Heat and pressure are applied to the assembly for a period
of time sufficient to induce solid state diffusion between the
interlayer 40c and porous metal bone fixation portion 14c, and, if
used, the metal foil or sheet. As is known to those skilled in the
art, solid-state diffusion is the movement and transport of atoms
in solid phases. Solid-state diffusion bonding forms a joint
through the formation of bonds at an atomic level due to transport
of atoms between two or more metal surfaces. Heat and pressure may
be supplied to the assembly by a variety of methods known in the
art. For example, the assembly may be heated electrically,
radiantly, optically, by induction, by combustion, by microwave, or
any other suitable means known in the art. Pressure may be applied
mechanically by clamping the assembly together prior to insertion
of the assembly into a furnace, or pressure may be applied via a
hot pressing system capable of applying pressure once the assembly
reaches a target temperature, as is known in the art. Furthermore,
hot pressing may include hot isostatic pressing, also known in the
art. In one embodiment, the assembly is clamped and heated to at
least about 940.degree. C. for 4 hours in a vacuum or in another
sub-atmospheric pressure of an inert atmosphere.
[0052] Preferably, the clamped assembly is heated to less than the
melting temperature of the components. The time required to achieve
bonding may be as little as less than 1 hour and as long as about
48 hours, and will depend on the metals involved, the temperatures,
atmosphere and the pressures applied. After the diffusion process
has been completed, the implant is formed.
[0053] Yet another embodiment of an implant 10d of the present
disclosure is illustrated in FIG. 7. Implant 10d includes a core
18d that defines a substrate 24d for an articulation portion 12d
and a substrate 25d for a bone fixation portion 14d. Similar to
other embodiments disclosed herein, the substrate 24d of the
articulation portion 12d has a pyrolytic carbon layer 30d thereon
that forms the bearing surface 16d. The core 18d may be made of any
material or combination of materials suitable for having pyrolytic
carbon applied thereto and in one embodiment the substrate 24d is
carbon, preferably a dense, isotropic graphite. Additionally, in
order to enhance the visibility of the implant or portions thereof
under fluoroscopy or x-ray imaging, the carbon may be doped with or
otherwise include any suitable radiopacifiers, such as
tungsten.
[0054] The bone fixation portion 14d further includes a porous
exterior layer 46d overlaying at least a portion of substrate 25d
of core 18d to form porous region 26d. The exterior layer 46d may
be made of any suitable porous bone on- or in-growth material known
in the art. For example, the exterior layer 46d may be made of
metal structure such as but not limited to titanium or tantalum.
However, it will be appreciated that other materials may be used
depending upon the desired characteristics of the implant. The
porous region 26d may have a thickness, pore size, a pore
interconnectivity, and/or other features that facilitate bone
tissue on-and/or in growth. In one embodiment, the exterior layer
46d/porous region 26d may have a thickness of between about 5 .mu.m
and about 300 .mu.m. In order to facilitate the bonding of the
exterior layer 46d to the substrate 24d, the bone fixation portion
14d may include an intermediate layer 44d. In the embodiment
illustrated in FIG. 7, the intermediate layer 44d is formed from a
metal such as titanium that is applied via CVD or PVD onto the
substrate 25d of core 18d. The intermediate layer 44d may have a
thickness of up to about 1 mm.
[0055] FIG. 12 is a flowchart showing one embodiment of a method of
making the implant 10d illustrated in FIG. 7. The steps of the
method described herein may be performed in any order that produces
an implant illustrated in FIG. 7. In one step, a block of carbon,
preferably a dense, isotropic graphite, is machined or otherwise
processed to form core 18d with substrate 24d and substrate 25d. In
another step, a pyrolytic carbon layer 30d is applied to the outer
surface 28d of substrate 24d of the articulation portion 12d. An
intermediate layer 44d, preferably comprised of a metal that can
adhere to the graphite substrate 24e is applied, preferably via CVD
or PVD, to an outer surface of the substrate 25d of the bone
fixation portion 14d. The exterior porous layer 46d is applied to
the intermediate layer 44d, preferably via plasma spraying.
However, it will be appreciated that any other suitable method of
attaching the exterior layer 46d to the intermediate layer 44d or
directly to the substrate 25d if the intermediate layer is omitted
may be used. The bearing surface 16d of the pyrolytic carbon layer
30d may be polished or otherwise treated or conditioned in order to
obtain a generally smooth articulating surface.
[0056] Turning to FIG. 8, implant 10e is another embodiment of an
orthopedic device of the present disclosure and is similar to the
other implants disclosed herein. Implant 10e includes a metallic
core 18d, such as but not limited to titanium or tungsten, that
partially defines an articulation portion 12e and bone fixation
portion 14e. The articulation portion 12e has a pyrolytic carbon
layer 30e thereon that forms the bearing surface 16e. An
intermediate layer 19e is positioned between the pyrolytic carbon
layer 30e and the core 18. The intermediate layer 19e is preferably
constructed out of a material, such as carbon, preferably a dense,
isotropic graphite, that can bond or otherwise adhere to the metal
core 18e and pyrolytic carbon layer 30e. The core 18e also forms
the interior portion of the bone fixation portion 14e and is at
least partially surrounded by a porous exterior layer 46e that
forms the porous region 26e. In the illustrated embodiment, the
exterior layer 46e is made of a metal such as but not limited to
porous titanium or tantalum metal structures. In one embodiment,
the exterior layer 46e is Trabecular Metal.RTM., generally
available from Zimmer, Inc. of Warsaw, Ind. It will be appreciated,
however, that other materials for the exterior layer 46e may be
used depending upon the desired characteristics of the implant. The
exterior layer 46e/porous region 26e preferably have a thickness,
pore size, a pore continuity, and/or other features that facilitate
bone tissue on-and/or in growth.
[0057] FIG. 13 is a flowchart showing one embodiment of a method of
making the implant 10e illustrated in FIG. 8. The steps of the
method described herein may be performed in any order that produces
an implant illustrated in FIG. 8. In one step, the metallic core is
formed to the desired shape using a metal such as but not limited
to titanium or tungsten. In another step, a block of carbon,
preferably a dense, isotropic graphite, is machined or otherwise
processed to form the intermediate layer 19e. The core 18e and
intermediate layer 19e are positioned adjacent one another. Heat
and pressure are applied to the assembly for a period of time
sufficient to induce solid state diffusion between the core 18e and
intermediate layer 19e. In another step, a pyrolytic carbon layer
30e is applied to the outer surface 28e of the intermediate layer
19e. The bearing surface 16e of the pyrolytic carbon layer 30e may
be polished or otherwise treated or conditioned in order to obtain
a generally smooth articulating surface. An exterior layer 46e is
applied to the core 18e of the bone fixation portion 14e to form
the porous region 26e. The exterior layer 46e is preferably
comprised of a metal that can adhere to the material of the core
18e. in one embodiment, the exterior layer 46e comprised of a metal
such as titanium is applied to the core 18e, preferably via plasma
spaying. Alternatively, the exterior layer 46e may be comprised of
a porous tantalum metal structure such as Trabecular Metal.RTM.,
generally available from Zimmer, Inc. of Warsaw, Ind. In this
embodiment, the metal exterior layer 46e may be positioned adjacent
the core 18e. Heat and pressure are applied to the assembly for a
period of time sufficient to induce solid state diffusion between
the metal exterior layer 46e and the core 18e. It will be
appreciated that bonding of the core 18e and intermediate layer 19e
to one another and the exterior layer 46e to the core 18e could be
formed in either a single step or two step process.
[0058] It will be understood that the methods, compositions,
devices and embodiments described above are illustrative of the
applications of the principles of the subject matter disclosed
herein. It will also be understood that certain modifications may
be made by those skilled in the art without departing from the
spirit and scope of the subject mater disclosed and/or claimed
herein. Thus, the scope of the invention is not limited to the
above description, but is set forth in the following claims and/or
any future claims made in any application that claims the benefit
of this application.
* * * * *