U.S. patent application number 10/221127 was filed with the patent office on 2003-01-30 for synthetic reinforced interbody fusion implants.
Invention is credited to McKay, William F.
Application Number | 20030023305 10/221127 |
Document ID | / |
Family ID | 22692353 |
Filed Date | 2003-01-30 |
United States Patent
Application |
20030023305 |
Kind Code |
A1 |
McKay, William F |
January 30, 2003 |
Synthetic reinforced interbody fusion implants
Abstract
Interbody fusion implants that include a load bearing body
composed of a calcium phosphate material hardened around one or
more structural reinforcing members are provided. The reinforcing
members aid the load bearing body in resisting bending forces and,
in certain forms of the invention, aid in preventing expulsion of
the implant after implantation. Methods for promoting fusion bone
growth in the space between adjacent vertebrae and methods for
making the inventive implants are also provided.
Inventors: |
McKay, William F; (Memphis,
TN) |
Correspondence
Address: |
Woodard Emhardt Naughton Moriarty & Mcnett
Bank One Center Tower
Suite 3700
111 Monument Circle
Indianapolis
IN
46204
US
|
Family ID: |
22692353 |
Appl. No.: |
10/221127 |
Filed: |
September 9, 2002 |
PCT Filed: |
March 9, 2001 |
PCT NO: |
PCT/US01/07487 |
Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61L 27/425 20130101;
A61F 2310/00029 20130101; A61F 2002/2817 20130101; A61F 2002/30777
20130101; A61F 2/446 20130101; A61F 2310/00023 20130101; A61F
2002/30841 20130101; A61F 2310/00329 20130101; A61F 2/4611
20130101; A61F 2002/30909 20130101; A61F 2002/2835 20130101; A61F
2002/3085 20130101; A61L 27/04 20130101; A61F 2310/00365 20130101;
A61F 2310/00017 20130101; A61F 2310/00293 20130101; A61L 27/06
20130101; A61F 2002/30785 20130101; A61F 2/30965 20130101; A61L
27/042 20130101; A61F 2002/30593 20130101; A61F 2/3094 20130101;
A61F 2002/3082 20130101; A61F 2002/448 20130101 |
Class at
Publication: |
623/17.11 |
International
Class: |
A61F 002/44 |
Claims
What is claimed is:
1. An interbody fusion implant, comprising: a biocompatible load
bearing body, said body comprised of a synthetic calcium phosphate
material hardened around at least one structural reinforcing member
for resisting bending forces when implanted, said body sized and
configured for engagement between two vertebrae and having a
superior surface configured to contact one of said vertebrae, and
an inferior surface configured to contact the other of said
vertebrae, said structural reinforcing member disposed between said
superior surface and said inferior surface and extending along a
length of said body.
2. The interbody fusion implant of claim 1, wherein said calcium
phosphate ceramic is a calcium phosphate apatite.
3. The interbody fusion implant of claim 2, wherein said calcium
phosphate apatite is a low crystallinity apatite.
4. The interbody fusion implant of claim 1, wherein said
reinforcement member is comprised of a metal.
5. The interbody fusion implant of claim 4, wherein said metal is
titanium.
6. The interbody fusion implant of claim 5, wherein said titanium
is a titanium mesh.
7. The interbody fusion implant of claim 5, wherein said metal is
selected from the group consisting of titanium, stainless steel,
cobalt-chromium, tantalum, mixtures thereof and alloys thereof.
8. The interbody fusion implant of claim 1, wherein said implant
has a compressive strength of at least about 40 MPa.
9. The interbody fusion implant of claim 1, wherein said body
further comprises a tool engaging end defining a tool engaging hole
for receiving a driving tool for implanting the spacer.
10. The interbody fusion implant of claim 1, wherein said body has
an outer surface that defines threaded bone-engaging portions.
11. The interbody fusion implant of claim 1, wherein said implant
is a dowel.
12. The interbody fusion implant of claim 1, wherein said implant
is a wedge.
13. The interbody fusion implant of claim 1, wherein said body
further includes a wall connecting said superior surface and said
inferior surface.
14. The interbody fusion implant of claim 13, wherein said body is
elliptical.
15. The interbody fusion implant of claim 1, wherein said body
further defines at least one thru-hole.
16. The interbody fusion implant of claim 15, wherein said body has
a longitudinal axis and said thru-hole extends perpendicular to
said longitudinal axis.
17. The interbody fusion implant of claim 16, wherein said body
further includes an osteogenic material disposed within said
thru-hole.
18. The interbody fusion implant of claim 17, wherein said
osteogenic material comprises natural bone, demineralized bone, a
calcium phosphate material, a bioceramic, bioglass, an
osteoinductive factor and mixtures thereof.
19. The interbody fusion implant of claim 18, wherein said
osteoinductive factor comprises a bone morphogenetic protein.
20. The interbody fusion implant of claim 19, wherein said bone
morphogenetic protein comprises a recombinant protein.
21. The interbody fusion implant of claim 20, wherein said
recombinant bone morphogenetic protein comprises a human
protein.
22. The interbody fusion implant of claim 21, wherein said
recombinant human protein comprises BMP-2, BMP-4, BMP-7, or
heterodimers thereof.
23. The interbody fusion implant of claim 1, wherein said
reinforcing member extends parallel to said superior and inferior
surfaces.
24. An interbody fusion implant, comprising: a) a biocompatible
load bearing body, said body comprised of a hardened synthetic
calcium phosphate material, said body sized and configured for
engagement between two vertebrae and having a superior surface and
an inferior surface; and b) at least one structural reinforcing
member for resisting expulsion after implantation, said structural
reinforcing member at least partially embedded in said load bearing
body and configured to contact adjacent vertebrae.
25. An interbody fusion implant, comprising: a load bearing body
formed of a hardened synthetic calcium phosphate material, said
body containing at least one internal reinforcing member adapted to
resist bending or tensile forces along a length of said body, said
body sized and configured for engagement between two vertebrae and
having a first surface for contacting a first of said vertebrae and
a second surface for contacting another of said vertebrae.
26. A method of promoting fusion bone growth between adjacent
vertebrae, comprising: (a) providing an interbody fusion implant
comprising: (i) a porous, biocompatible load bearing body, said
body composed of a synthetic calcium phosphate material hardened
around at least one structural reinforcing member for resisting
bending forces when implanted, said body sized and configured for
engagement between two vertebrae and having a superior surface
configured to contact one of said vertebrae, and an inferior
surface configured to contact the other of said vertebrae, said
structural reinforcing member disposed between said superior
surface and said inferior surface and extending along a length of
said body. (b) preparing said adjacent vertebrae to receive the
implant in an intervertebral space between adjacent vertebrae; and
(c) placing the implant into the intervertebral space.
27. The method of claim 26, wherein said body defines a thru-hole
extending therethrough.
28. The method of claim 27, further comprising filling said
thru-hole with an osteogenic material prior to said placing the
implant into the intervertebral space.
29. A method of making an interbody fusion implant, said method
comprising: (a) providing a mold having positioned therein a
structural reinforcing member; (b) passing a hardenable synthetic
calcium phosphate material into the mold; and (c) causing said
material to harden to form a load bearing interbody fusion implant,
said implant sized and configured for engagement between two
vertebrae and having a superior surface configured to contact one
of said vertebrae, and an inferior surface configured to contact
the other of said vertebrae.
30. The method of claim 29, wherein said implant is a dowel.
31. The method of claim 29, wherein said implant is a wedge.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention broadly concerns medical implants.
More specifically, the invention provides reinforced interbody
fusion implants and methods for making and using the implants.
[0002] Intervertebral discs, located between the endplates of
adjacent vertebrae, stabilize the spine, distribute forces between
vertebrae and cushion vertebral bodies. A normal intervertebral
disc includes a semi-gelatinous component, the nucleus pulposus,
which is surrounded and confined by an outer, fibrous ring called
the annulus fibrosus. In a healthy, undamaged spine, the annulus
fibrosus prevents the nucleus pulposus from protruding outside the
disc space.
[0003] Spinal discs may be displaced or damaged due to trauma,
disease or aging. Disruption of the annulus fibrosus allows the
nucleus pulposus to protrude into the vertebral canal, a condition
commonly referred to as a herniated or ruptured disc. The extruded
nucleus pulposus may press on a spinal nerve, which may result in
nerve damage, pain, numbness, muscle weakness and paralysis.
Intervertebral discs may also deteriorate due to the normal aging
process or disease. As a disc dehydrates and hardens, the disc
space height will be reduced leading to instability of the spine,
decreased mobility and pain.
[0004] Sometimes the only relief from the symptoms of these
conditions is a discectomy, or surgical removal of a portion or all
of an intervertebral disc followed by fusion of the adjacent
vertebrae. The removal of the damaged or unhealthy disc will allow
the disc space to collapse. Collapse of the disc space can cause
instability of the spine, abnormal joint mechanics, premature
development of arthritis or nerve damage, in addition to severe
pain. Pain relief via discectomy and arthrodesis requires
preservation of the disc space and eventual fusion of the affected
motion segments.
[0005] Bone grafts are often used to fill the intervertebral space
to prevent disc space collapse and promote fusion of the adjacent
vertebrae across the disc space. In early techniques, bone material
was simply disposed between the adjacent vertebrae, typically at
the posterior aspect of the vertebra, and the spinal column was
stabilized by way of a plate or rod spanning the affected
vertebrae. Once fusion occurred, the hardware used to maintain the
stability of the segment became superfluous and was a permanent
foreign body. Moreover, the surgical procedures necessary to
implant a rod or plate to stabilize the level during fusion were
frequently lengthy and involved.
[0006] It was therefore determined that a more optimal solution to
the stabilization of an excised disc space is to fuse the vertebrae
between their respective end plates, preferably without the need
for anterior or posterior plating. There have been an extensive
number of attempts to develop an acceptable intradiscal implant
that could be used to replace a damaged disc and maintain the
stability of the disc interspace between the adjacent vertebrae, at
least until complete arthrodesis is achieved. The implant must
provide temporary support and allow bone ingrowth. Success of the
discectomy and fusion procedure requires the development of a
contiguous growth of bone to create a solid mass because the
implant may not withstand the compressive loads on the spine for
the life of the patient.
[0007] There is a continuing need for interbody fusion implants
which have sufficient strength to support the vertebral column
until after the adjacent vertebrae are fused and which eliminate or
at least minimize any permanent foreign body after the fusion.
SUMMARY OF THE INVENTION
[0008] In accordance with one aspect of the present invention, an
implant includes a porous, biocompatible load bearing body composed
of a synthetic calcium phosphate material that is hardened around
at least one structural reinforcing member. The reinforcing member
advantageously helps the load bearing body resist bending forces
when implanted. The body is typically sized and configured for
engagement between two vertebrae and has a superior surface
configured to contact one vertebrae, and an inferior surface
configured to contact another vertebrae. The reinforcing member is
preferably an internal member and is disposed between the superior
surface and inferior surface, extending along a length of the
body.
[0009] In yet other embodiments, the implant includes a load
bearing body composed of a hardened synthetic calcium phosphate
material and at least one structural reinforcing member for
resisting expulsion after implantation. The structural reinforcing
member is at least partially embedded in the load bearing body and
configured to contact adjacent vertebrae. The body is sized and
configured for engagement between two vertebrae and has a superior
surface and an inferior surface.
[0010] In yet another aspect of the invention, methods of promoting
fusion bone growth between adjacent vertebrae are provided. In one
form of the invention, a method includes providing an interbody
fusion implant described above, preparing an adjacent vertebrae to
receive the implant in an intervertebral space between adjacent
vertebrae and placing the implant into the intervertebral
space.
[0011] Other aspects of the invention provide methods for making
the interbody fusion implants of the present invention. The
preferred methods include providing a mold having positioned
therein a structural reinforcing member, passing a hardenable
synthetic calcium phosphate material into the mold, and causing the
material to harden to form a load bearing implant.
[0012] These and other objects and advantages of the present
invention will be apparent from the descriptions herein.
BRIEF DESCRIPTION OF THE FIGURES
[0013] FIG. 1 depicts a perspective view of one embodiment of an
interbody fusion implant.
[0014] FIG. 2 depicts an end view of the implant of FIG. 1.
[0015] FIG. 3 depicts a perspective view of an alternative
embodiment of the interbody fusion implant of the present
invention.
[0016] FIG. 4 depicts an end view of the implant of FIG. 3.
[0017] FIG. 5 depicts a perspective view of a structural
reinforcing member used to reinforce the implant of FIG. 1.
[0018] FIG. 6 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0019] FIG. 7 depicts an end view of the reinforcing member of FIG.
7.
[0020] FIG. 8 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0021] FIG. 9 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0022] FIG. 10 depicts an end view of the reinforcing member of
FIG. 9.
[0023] FIG. 11 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0024] FIG. 12 depicts a perspective view of a helical-shaped
reinforcing member.
[0025] FIG. 13 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0026] FIG. 14 depicts an end view of the reinforcing member of
FIG. 13.
[0027] FIG. 15 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0028] FIG. 16 depicts an end view of the reinforcing member of
FIG. 15.
[0029] FIG. 17 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0030] FIG. 18 depicts an end view of the reinforcing member of
FIG. 17.
[0031] FIG. 19 depicts a perspective view of an alternative
embodiment of a reinforcing member.
[0032] FIG. 20 depicts an end view of the reinforcing member of
FIG. 19.
[0033] FIG. 21 depicts a perspective view of a wedge-shaped
interbody fusion implant.
[0034] FIG. 22 depicts an end view of the implant of FIG. 21.
[0035] FIG. 23 depicts a reinforcing member that may reinforce the
wedge-shaped implant of FIG. 25.
[0036] FIG. 24 depicts a perspective view of an elliptical-shaped
interbody fusion implant.
[0037] FIG. 25 depicts a perspective view of the reinforcing member
of the implant of FIG. 24.
[0038] FIG. 26 depicts a perspective view of an alternative
embodiment of the interbody fusion implant of the present
invention, having a score mark in one end.
[0039] FIG. 27 depicts a perspective view of an alternative
embodiment of an interbody fusion implant of the present invention,
showing a load bearing body reinforced with a spiral reinforcing
member that forms threads on the outer surface of the implant.
[0040] FIG. 28 depicts an end view of the implant of FIG. 27.
[0041] FIG. 29 depicts a perspective view of an alternative
embodiment of an interbody fusion implant of the present
invention.
[0042] FIG. 30 depicts an end view of the implant of FIG. 29.
[0043] FIG. 31 depicts a perspective view of reinforcing member
270, with radially extending plates 260, that may be used to
reinforce the implant of FIG. 30.
[0044] FIG. 32 depicts a top view of two implants of the present
invention bilaterally implanted within an intervertebral space.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0045] For the purposes of promoting an understanding of the
principles of the invention, reference will now be made to
preferred embodiments and specific language will be used to
describe the same. It will nevertheless be understood that no
limitation of the scope of the invention is thereby intended, such
alterations and further modifications of the invention, and such
further applications of the principles of the invention as
illustrated herein, being contemplated as would normally occur to
one skilled in the art to which the invention relates.
[0046] As disclosed above, the present invention relates generally
to synthetic reinforced medical implants. One specific aspect of
the invention provides interbody fusion implants that include a
porous, biocompatible load bearing body formed of a synthetic
calcium phosphate material hardened around at least one internal
reinforcing member for resisting bending or tensile forces when
implanted. The implant may include a low crystallinity calcium
phosphate material that is self-hardening, and requires no
externally applied heat or pressure to harden, formed around a
metallic reinforcing member, such as a metallic mesh. In
alternative embodiments, the material is hardenable upon exposure
to pressure and/or a temperature of about 5.degree. C. to about
50.degree. C., typically about 20.degree. C. to 40.degree. C.
[0047] Such implants are advantageous, for example, in minimizing
the metal artifact in computer tomography (CT) or magnetic
resonance imaging (MRI) which makes post-operative complications
diagnosis easier. It is also easier to assess the fusion
radiographically. Moreover, the above calcium phosphate materials
may degrade over time and be replaced by bone. In addition, such
implants may be constructed to provide for the relative absence of
stress shielding, and make it easier to assess the fusion after the
ceramic has degraded. Additionally, direct bone apposition to the
calcium phosphate instead of possible fibrous tissue interfaces
with metal devices is advantageous.
[0048] Referring now to FIGS. 1-5, an implant 10 may include a load
bearing body 20 having disposed therein structural reinforcing
members 30. Load bearing body 20 has a first end 21, a second end
22, and a wall 23 connecting first end 21 and second end 22. Wall
23 defines a first, superior surface 24 and a second, inferior
surface 25 that are configured to contact adjacent vertebrae. Load
bearing body 20 may optionally include a thru-hole 26 that may be
filled with osteogenic material as further described below. Other
configurations will be apparent to the skilled artisan. For
example, in other embodiments, the hole may not extend completely
through the load bearing body. The load bearing body may define a
cavity, or other discontinuity on the superior and/or inferior
surface that may also be advantageously filled with osteogenic
material. The load bearing body may further include a
tool-engagement end 27 that defines a tool engaging, or instrument
attachment hole 28 as seen in FIGS. 3 and 4, wherein body 20' also
includes a second end 22', a wall 23', a superior surface 24' and
an inferior surface 25'. The body may further include a score 29,
as seen in FIGS. 3 and 4, for indicating the orientation of other
components of the implant 10, for example the hole 26 and/or the
reinforcing members 30, as well as external threads 190.
[0049] Load bearing body 20 is preferably formed of a hardenable
calcium phosphate material. A wide variety of calcium phosphate
materials may be used including hydroxyapatite, tricalcium
phosphate and mixtures thereof. The calcium phosphate material of
which the load bearing body is composed preferably has a
composition substantially similar to natural bone. Furthermore, a
preferred synthetic calcium phosphate material is one that is
flowable at a low temperature, such as below about 50.degree. C.,
especially room temperature (about 25.degree. C.), and is
hardenable at such temperatures. More preferred materials will be
flowable at room temperature (about 25.degree. C.) and hardenable
at about body temperature (about 37.degree. C.). Such synthetic
calcium phosphate materials include a poorly or low crystalline
calcium phosphate, such as a low or poorly crystalline apatite,
including hydroxyapatite, available from Etex Corporation and as
described in U.S. Pat. Nos. 5,783,217; 5,676,976; 5,683,461; and
5,650,176, and PCT International Publication Nos. WO 98/16268, WO
96/39202 and WO 98/16209, all to Lee et al. As defined in the
recited patents and herein, by "poorly or low crystalline" calcium
phosphate material is meant a material that is amorphous, having
little or no long range order and/or a material that is
nanocrystalline exhibiting crystalline domains on the order of
nanometers or Angstroms. The calcium:phosphate ratio of the load
bearing body is typically in the range of about 1.3 to 1.7, more
typically about 1.5 to 1.7.
[0050] Other additives may be included in the compositions that
form the load bearing bodies of the present invention to adjust
their properties, including supporting or strengthening filler
materials, pore forming agents and osteoinductive factors as
described below.
[0051] As discussed above, and as seen in FIGS. 1-5, implant 10
includes at least one structural reinforcing member 30 disposed
therein. FIGS. 1-4 depict two structural reinforcing members 30
disposed along the length of implant 10. The calcium phosphate
material is preferably hardened around structural reinforcing
members 30, such that the reinforcing members are contained within
the load bearing body. Although the members shown in FIGS. 1-4 are
completely surrounded by the load bearing body, they may, in
alternative embodiments, be partially exposed.
[0052] The reinforcing members may be disposed between the superior
surface and the inferior surface, and may extend along a length, of
the load bearing body, including extending non-parallel, such as
obliquely or transverse, or parallel to the superior and inferior
surfaces of the body. Additionally, the reinforcing members may
extend non-parallel, including obliquely or transverse, and in
other forms may extend parallel, to the central longitudinal axis
of the load bearing body of the implants.
[0053] Structural reinforcing members 30 may assume a wide variety
of shapes. For example, member 30 may be cylindrical-shaped as best
seen in FIG. 5. Member 30 may assume other shapes known in the art,
including spherical, pyramidal, rectangular and other polygonal
shapes. FIGS. 6-16 depict a variety of other ways in which the
structural members may be configured.
[0054] FIGS. 6 and 7 depict a structural member 50 having two
longitudinal members 51 connected at either end 52 to end members
53. Each end 52 of longitudinal members 51 is attached to an
internal surface 54 of end members 53. Longitudinal members 51 are
preferably elongated members, such as cylindrical-shaped members,
and are further preferably positioned generally parallel to each
other. Longitudinal members 51 and end members 53 may be
constructed independently and then joined by methods known to the
art, or may be made as a single, integral unit or by any other
variation known to the skilled artisan.
[0055] Referring now to FIG. 8, a reinforcing band member 60 is
shown that is preferably a length of material that has been formed
into a substantially ovate shape with rounded ends 61, sides 63 and
defining a gap 62. The dimensions of reinforcing member 60, as with
all the reinforcing members described herein, are such that will
reinforce the load bearing body against bending forces. Such
bending forces imposed upon the implant in situ include, for
example, tensile forces and compressive forces. Referring now to
FIG. 9, a reinforcing member 70 may include a reinforcing band 71
and attached intermediate members 72 to form reinforcing member 70.
Intermediate members 72 span the area, or gap 73 defined by
reinforcing band 71 to form reinforcing member 70, and are
positioned preferably such that a longitudinal axis AG of the
intermediate members 72 is perpendicular to the longitudinal axis
A.sub.R of reinforcing member 71 as seen in FIGS. 9 and 10. Two
intermediate members 72 are seen in FIG. 9, although less than or
more than this number may be present in order to affect the
structural integrity of the load bearing body into which it is
incorporated. Intermediate members 72 shown in FIGS. 9 and 10 are
ring-shaped structures, but may also assume other shapes known in
the art as described above.
[0056] Referring now to FIG. 11, reinforcing member 80 is shown.
Reinforcing member 80 is an elongated plate 81 having an outer
surface 82. Plate 81 may further include thru-holes 83 disposed
along the length of plate 81. One or more of reinforcing member 80
may be disposed within a particular load bearing body.
[0057] Referring now to FIG. 12, a reinforcing member 90 shaped in
a spiral, or helical configuration is shown. This particular
configuration is advantageous in that, in one preferred form of the
invention, reinforcing member 90 may be only partially embedded in
the load bearing body such that it forms threads on the outer
surface of the body as more fully described below.
[0058] The reinforcing members, or scaffolds, described herein may
be made of a wide variety of materials that resist bending or
tensile loads. Such materials will therefore increase the
structural integrity of the load bearing bodies described herein.
The reinforcing member is preferably formed of a metallic material,
including titanium, stainless steel, tantalum and alloys thereof,
as well as cobalt-chromium, cobalt-chromium-nickel and
cobalt-chromium-molybdenum alloys. The reinforcing member may also
be formed of other materials, for example, carbon fiber, carbon
fiber composites, collagen strands (e.g. fibers or woven ropes), or
plastics such as polyethylene, Dacron.RTM., and degradable
polymers. The reinforcing member will advantageously be combined
with the load-bearing body to form an implant able to withstand
compressive forces of at least about 40 MPa.
[0059] In one preferred embodiment of the present invention, the
reinforcing members described above are composed of a mesh, such as
a titanium mesh. The mesh may be formed into a reinforcing member
that will form the shaped members described above. For example,
metallic mesh may be shaped into several configurations that will
form the cylindrical-shaped reinforcing members described in FIGS.
5 and 6. Still further alternative reinforcing members are shown in
FIGS. 17-24, discussed more fully below.
[0060] Referring now to FIGS. 13 and 14, reinforcing member 100
includes three generally ovate rings 101, 102 and 103 which are
attached at their ends to form an overall, generally cylindrical
shape. Reinforcing member 100 also includes end rings 104 and 105
to which ovate rings 101, 102 and 103 are attached at points of
intersection to provide additional stability to the reinforcement
member 100.
[0061] Referring now to FIGS. 15 and 16, reinforcing member 110 is
shown and is identical to reinforcing member 100 except for the
presence of attached intermediate rings 111 and 112 along the
length of the ovate rings to provide still further stability.
[0062] Referring now to FIGS. 17 and 18, reinforcing member 120
includes a central wire 121a having an ovate shape with rounded
ends 122, sides 124a and 124b and defining a gap, or area 123.
Three additional ovate wire members, identified as upper wire 121b,
medial wire 121c and lower wire 121d are disposed along the length
of central wire 121a, and may be positioned one on top of each
other, between sides 124a and 124b, such that a longitudinal plane
passing independently through of each of the upper, medial and
lower wires is non-parallel, e.g. perpendicular, to a similar
longitudinal plane passing through central wire 121a, although
other configurations are also envisioned. Reinforcing member 120
further includes wire stabilizer rings 125 connected to wires
121a121d at intersecting locations.
[0063] Referring now to FIGS. 19 and 20, reinforcing member 130 is
shown that includes upper, medial and lower wires 131a, 131b and
131c, respectively, disposed in the same configuration as shown for
reinforcing member 120. Reinforcing member 130 includes end
stabilizers 135 disposed about and connected at intersecting points
to wires 131a-131c. End stabilizers 135 are preferably formed from
a ring-shaped wire that is bent such that the profile of the
ring-shaped wire is arcuate as best seen in the end view of
reinforcing member 130 shown in FIG. 20.
[0064] Referring now to FIGS. 21 and 22, implant 40 includes a load
bearing body 41 that is substantially rectangular in shape, and
includes a first, superior surface 42, a second, inferior surface
43, and a wall 44 connecting the two surfaces. Wall 44 is
preferably of a height approximating that of an intervertebral disc
space of a mammal, such as a human. Load bearing body 41 may
further define a thru-hole 45 into which osteogenic material may be
disposed. In alternative embodiments, load bearing body may define
a cavity or other discontinuity on superior surface 42 and/or
inferior surface 43 into which osteogenic material may be disposed.
Reinforcing member 140 is disposed within load bearing body 40.
[0065] Reinforcing member 140 for load bearing body 40 is depicted
separately in FIG. 23. Reinforcing member 140 includes a body 141
that is also substantially rectangular-shaped and defines a gap 143
to provide an opening corresponding to the location of thru-hole 45
of implant 40 (see FIG. 21).
[0066] Yet another example of an implant configuration of the
present invention is shown in FIGS. 24 and 25. Implant 150 is shown
including load bearing body 151 that is substantially elliptical in
shape, and includes a first, superior surface 152, a second,
inferior surface 153 and a wall 154 connecting first surface 152
and second surface 153. Load bearing body 151 may also include a
thru-hole 155 or other area which may be used for containing
osteogenic material therein as discussed above. Internal structural
reinforcing member 160 is disposed within load bearing body 151. As
seen in FIG. 25, reinforcing member 160 includes a body 161 that is
substantially elliptical in shape and defines a gap 163 to provide
an opening corresponding to the location of thru-hole 155 of
implant 150.
[0067] As mentioned above, the thru-holes or other apertures or
discontinuities may be filled with an osteogenic material. Any
suitable osteogenic material or composition is contemplated,
including autograft, allograft, xenograft, demineralized bone,
synthetic and natural bone graft substitutes, such as bioceramics,
polymers, and osteoinductive factors. The terms osteogenic material
or osteogenic composition as used herein mean virtually any
material that promotes bone growth or healing including autograft,
allograft, xenograft, bone graft substitutes and natural, synthetic
and recombinant proteins, nucleotide sequences (e.g. genes such as
growth factor genes), hormones and the like.
[0068] Autograft can be harvested from locations such as the iliac
crest using drills, gouges, curettes, trephines and other tools and
methods which are well known to surgeons in this field. Preferably,
autograft is harvested from the iliac crest with minimally invasive
surgery. The osteogenic material may also include bone reamed away
by the surgeon while preparing the end plates for the implant.
[0069] Advantageously, where autograft is chosen as the osteogenic
material, only a very small amount of bone material is needed to
pack the thru-hole. The autograft itself is not required to provide
structural support as this is provided by the implant. The donor
surgery for such a small amount of bone is less invasive and better
tolerated by the patient. There is usually little need for muscle
dissection in obtaining such small amounts of bone. The present
invention therefore eliminates or minimizes many of the
disadvantages of employing autograft.
[0070] Natural and synthetic graft substitutes which replace the
structure or function of bone are also contemplated for the
osteogenic composition. Any such graft substitute is contemplated,
including for example, demineralized bone matrix, mineral
compositions and bioceramics. As is evident from a review of An
Introduction to Bioceramics, edited by Larry L. Hench and June
Wilson (World Scientific Publishing Co. Ptd. Ltd, 1993, volume 1),
there is a vast array of bioceramic materials, including
BIOGLASS.RTM., hydroxyapatite and calcium phosphate compositions
known in the art which can be used to advantage for this purpose.
This disclosure is herein incorporated by reference for this
purpose. Preferred compositions include bioactive glasses,
tricalcium phosphates and hydroxyapatites. In one embodiment, the
graft substitute is a biphasic calcium phosphate ceramic including
tricalcium phosphate and hydroxyapatite.
[0071] In some embodiments, the osteogenic compositions used in
this invention comprise a therapeutically effective amount to
stimulate or induce bone growth of a substantially pure bone
inductive or growth factor or protein in a pharmaceutically
acceptable carrier. The preferred osteoinductive factors are the
recombinant human bone morphogenetic proteins (rhBMPs) because they
are available in unlimited supply and do not transmit infectious
diseases. Most preferably, the bone morphogenetic protein is a
rhBMP-2, rhBMP-4, rhBMP-7, or heterodimers thereof.
[0072] Recombinant BMP-2 can be used at a concentration of about
0.4 mg/ml to about 1.5 mg/ml, preferably near 1.5 mg/ml. However,
any bone morphogenetic protein is contemplated including bone
morphogenetic proteins designated as BMP-1 through BMP-18. BMPs are
available from Genetics Institute, Inc., Cambridge, Mass. and the
BMPs and genes encoding them may also be prepared by one skilled in
the art as described in U.S. Pat. No. 5,187,076 to Wozney et al.;
U.S. Pat. No. 5,366,875 to Wozney et al.; U.S. Pat. No. 4,877,864
to Wang et al.; U.S. Pat. No. 5,108,922 to Wang et al.; U.S. Pat.
No. 5,116,738 to Wang et al.; U.S. Pat. No. 5,013,649 to Wang et
al.; U.S. Pat. No. 5,106,748 to Wozney et al.; and PCT Patent Nos.
WO93/00432 to Wozney et al.; WO94/26893 to Celeste et al.; and
WO94/26892 to Celeste et al. All osteoinductive factors are
contemplated whether obtained as above or isolated from bone.
Methods for isolating bone morphogenetic protein from bone are
described, for example, in U.S. Pat. No. 4,294,753 to Urist and
Urist et al., 81 PNAS 371, 1984.
[0073] The choice of carrier material for the osteogenic
composition is based on biocompatibility, biodegradability,
mechanical properties and interface properties as well as the
structure of the load bearing member. The particular application of
the compositions of the invention will define the appropriate
formulation. Potential carriers include calcium sulphates,
polylactic acids, polyanhydrides, collagen, calcium phosphates,
hyaluronic acid, polymeric acrylic esters and demineralized bone.
The carrier may be any suitable carrier capable of delivering the
proteins, nucleotide sequences, or the like. Most preferably, the
carrier is capable of being eventually resorbed into the body. One
preferred carrier is an absorbable collagen sponge marketed by
Integra LifeSciences Corporation under the trade name Helistat.RTM.
Absorbable Collagen Hemostatic Agent. Another preferred carrier is
a biphasic calcium phosphate ceramic. Ceramic blocks and granules
are commercially available from Sofamor Danek Group, B. P. 4-62180
Rang-du-Fliers, France and Bioland, 132 Rou d Espangne, 31100
Toulouse, France. The osteoinductive factor is introduced into the
carrier in any suitable manner. For example, the carrier may be
soaked in a solution containing the factor.
[0074] In many cases, the osteoinductive factor may be included in
the calcium phosphate material prior to its hardening around the
reinforcing member to form the interbody fusion implant as the
hardening typically is performed at or below 37.degree. C.
Alternatively, the factor, such as a bone morphogenetic protein in
a suitable liquid carrier, may be applied onto and/or into the
hardened, porous load bearing body after hardening, for instance by
soaking, dripping, etc.
[0075] The interbody fusion implants of the invention may be
provided with surface features defined in their outer surfaces. In
one form of the invention, for example, at least one of the ends of
the implant is a tool engagement end 27 that defines a tool
engaging or instrument attachment hole 28 as seen in FIGS. 3 and 4.
In a preferred embodiment, hole 28 is threaded but any suitable
attachment configuration is contemplated.
[0076] Interbody fusion implants of the present invention may
further include a tool-engaging slot 29 for receiving an
implantation tool. The slot is typically perpendicular to the
central longitudinal axis AL of the implant, as shown, for example,
in FIG. 3. In yet other embodiments, the slot 29 may serve as an
alignment score mark or groove 29' defined in tool engagement end
27' of implant 10" seen in FIG. 26, thus making the opposite end
the insertion end. Implant 10" is identical in all respects to
implant 10', except for the difference in the feature present on an
end of the implant and the absence of external threads. Thus,
components of spacer 10" are numbered correspondingly to those of
spacer 10', except with a denoting prime """ symbol.
[0077] Alternatively, a projection may be formed on the end walls
instead of a slot. Such a projection may form a straight,
flat-sided shape (such as a mirror image of the slot depicted in
FIG. 3), an elliptical eminence, a bi-concave eminence, a square
eminence, or any other protruding shape which provides sufficient
end-cap or tool engaging end strength and drive purchase to allow
transmission of insertional torque without breaking or otherwise
damaging the eminence.
[0078] Yet other surface features can be defined along the length L
of the spacer. As mentioned above with respect to FIGS. 3 and 4,
the outer surface of the implant may define threads 190 or other
expulsion-resistant configurations such as teeth, grooves, waffle
patterns, etc. The threads or other surface features may also
stabilize the bone-spacer interface and reduce micromotion to
facilitate fusion. The implants of the present invention may be
provided with threads by methods well known to the skilled artisan
such as incorporation of threaded features in a mold in which the
load bearing body is hardened, and/or by machining the piece after
hardening.
[0079] In certain embodiments, the threads or other
expulsion-resistant surface features may be formed from the
reinforcing members, as illustrated in FIGS. 27 and 28. Implant 200
includes a load bearing body 201 having disposed therein structural
reinforcing member 90 which includes a body 91 which has a helical,
or spiral, configuration. Load bearing body 201 further has a first
end 202, a second end 203, and a wall 204 connecting first end 202
and second end 203. Wall 23 also defines a first, superior surface
205 and a second, inferior surface 206. Reinforcing member 90 is
disposed in load bearing body 201 so that at least a portion of
reinforcing member 90 is exposed from the outer surface of body 91
to form threads on outer surface 208 of implant 200. A substantial
portion of reinforcing member 90 is embedded in load bearing body
201 to provide fixation of the member 90 within body 201 and
preferably also to improve the resistance of implant 200 against
bending forces.
[0080] Referring now to FIGS. 29 and 30, an implant 250 is shown
that includes plates that may provide reinforcement and further aid
in preventing expulsion of the implant after implantation. Implant
250 includes a load bearing body 256 that has a first end 251,
second end 252 and a wall 253 connecting first end 251 and second
end 252. The illustrated implant includes an elongate reinforcing
member 270 that is disposed, and preferably partially embedded, in
load bearing body 256. Reinforcing member 270 includes body 271,
extending along the central longitudinal axis of implant 250.
Plates 260 extend radially from body 271 of reinforcing member 270,
and are partially exposed on superior surface 254 and inferior
surface 255 of implant 250 or are otherwise partially embedded in
load bearing body 256. The plates 260 may be configured and
positioned to resist expulsion of the implant after implantation.
Reinforcing member 270, with radially extending plates 260, is best
seen in FIG. 31.
[0081] In yet another aspect of the present invention, methods of
promoting fusion bone growth between adjacent vertebrae are
provided. In one form of the invention, a method includes providing
a first interbody fusion implant described herein, such as one
having a load bearing body with a reinforcing member disposed
therein. The implant selected is of the appropriate dimensions,
based on the size of the cavity created and the needs of the
particular patient undergoing the fusion. The adjacent vertebrae
are prepared to receive the spacer in an intervertebral space
between adjacent vertebrae according to conventional procedures.
The spacer is mounted on an instrument known to the art, preferably
via an instrument attachment hole. An osteogenic material may
optionally be placed within a thru-hole, or gap, of the implant
should one be present. The implant is then inserted into the cavity
created between the adjacent vertebrae to be fused. Once the
implant is properly oriented within the intervertebral space, the
implant may be disengaged from the instrument. In a preferred form
of the invention, a second implant is inserted into the
intervertebral space after the first implant is properly positioned
near vertebral body V, resulting in bilateral placement of the
spacers as seen in FIG. 32. Osteogenic material may also optionally
be placed within those implants having thru-holes.
[0082] In a further aspect of the present invention, methods of
making an interbody fusion implant are provided. In one form of the
invention, a method of making an interbody fusion implant includes
providing a mold having positioned therein a structural reinforcing
member. The mold will be shaped as desired to form an implant
having the desired shape. The reinforcing member may include at
least one of the reinforcing members, or similar members, described
herein. A hardenable, flowable synthetic calcium phosphate
material, for example selected from materials described above, is
then poured or otherwise passed into the mold. The material is then
caused to harden, by, for example, exposing the material to
temperatures of 37.degree. C. or below, and/or exposing the
material to pressure.
[0083] While the invention has been illustrated and described in
detail in the drawings and foregoing description, the same is to be
considered as illustrative and not restrictive in character, it
being understood that only the preferred embodiment has been shown
and described and that all changes and modifications that come
within the spirit of the invention are desired to be protected. In
addition, all references cited herein are indicative of the level
of skill in the art and are hereby incorporated by reference in
their entirety.
* * * * *