U.S. patent application number 14/943262 was filed with the patent office on 2016-03-10 for highly lordosed fusion cage.
The applicant listed for this patent is DePuy Synthes Products, Inc.. Invention is credited to Michael Fisher, John Riley Hawkins, Michael J. O'Neil, Michael Andrew Slivka, Anwar M. Upal.
Application Number | 20160067055 14/943262 |
Document ID | / |
Family ID | 40161526 |
Filed Date | 2016-03-10 |
United States Patent
Application |
20160067055 |
Kind Code |
A1 |
Hawkins; John Riley ; et
al. |
March 10, 2016 |
HIGHLY LORDOSED FUSION CAGE
Abstract
A fusion cage has a first component that defines an outside
surface that is configured to engage a vertebral endplate, and an
interior surface. The fusion cage has a second component that
defines first and second opposed surfaces. One of the first and
second opposed surfaces can mate with the interior surface of the
first component. The fusion cage can include vertical and lateral
throughholes adapted to enhance fusion.
Inventors: |
Hawkins; John Riley;
(Cumberland, RI) ; Upal; Anwar M.; (Fall River,
MA) ; O'Neil; Michael J.; (West Barnstable, MA)
; Slivka; Michael Andrew; (Taunton, MA) ; Fisher;
Michael; (Lawrenceville, GA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DePuy Synthes Products, Inc. |
Raynham |
MA |
US |
|
|
Family ID: |
40161526 |
Appl. No.: |
14/943262 |
Filed: |
November 17, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14514700 |
Oct 15, 2014 |
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14943262 |
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11768636 |
Jun 26, 2007 |
8900307 |
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14514700 |
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Current U.S.
Class: |
623/17.16 |
Current CPC
Class: |
A61F 2002/30451
20130101; A61F 2250/0098 20130101; A61F 2/30771 20130101; A61F
2220/0033 20130101; A61F 2/30965 20130101; A61F 2002/30448
20130101; A61F 2310/00023 20130101; A61F 2220/0016 20130101; A61F
2/4611 20130101; A61F 2002/30593 20130101; A61F 2002/30062
20130101; A61F 2310/00059 20130101; A61F 2/442 20130101; A61F
2002/30481 20130101; A61F 2002/30904 20130101; A61F 2002/4627
20130101; A61F 2310/00017 20130101; A61F 2220/0025 20130101; A61F
2310/00239 20130101; A61F 2002/30331 20130101; A61F 2002/3008
20130101; A61F 2002/30685 20130101; A61F 2002/30604 20130101; A61F
2002/30579 20130101; A61F 2/447 20130101; A61F 2310/00029 20130101;
A61F 2/30744 20130101; A61F 2002/30387 20130101; A61F 2002/30841
20130101; A61F 2002/448 20130101; A61F 2002/30403 20130101; A61F
2002/30975 20130101; A61F 2002/30433 20130101; A61F 2002/3093
20130101; A61F 2/4455 20130101; A61F 2310/00203 20130101; A61F
2310/00161 20130101; A61F 2002/4629 20130101; A61F 2210/0004
20130101 |
International
Class: |
A61F 2/44 20060101
A61F002/44 |
Claims
1. (canceled)
2. An intervertebral fusion device comprising: a polymeric
component defining i) an upper outside surface configured to grip
an upper endplate, ii) a lower outside surface that is opposite the
upper outside surface and is configured to grip a lower endplate,
and iii) a throughhole that extends from the upper outside surface
to the lower outside surface, wherein each of the upper outside
surface and the lower outside surface is coated with a porous
titanium coating.
3. The intervertebral fusion device of claim 2, wherein each of the
upper and lower outside surfaces comprise teeth.
4. The intervertebral fusion device of claim 3, wherein the
polymeric component comprises PAEK.
5. The intervertebral fusion device of claim 4, wherein the PAEK is
selected from the group consisting of polyetherether ketone (PEEK),
polyether ketone ketone (PEKK) and polyether ketone (PEK).
6. The intervertebral fusion device of claim 4, wherein the PAEK is
PEEK.
7. The intervertebral fusion device of claim 6, wherein the porous
titanium coating is designed to promote bony affixation
thereto.
8. The intervertebral fusion device of claim 7, wherein the porous
titanium coating has an average pore size of 250 microns.
9. The intervertebral fusion device of claim 6, wherein the porous
titanium coating has a coefficient of friction of 0.8.
10. The intervertebral fusion device of claim 3, further comprising
a bone graft disposed in the polymeric component.
11. The intervertebral fusion device of claim 3, further comprising
a tapered front end configured for insertion into an intervertebral
space.
12. The intervertebral fusion device of claim 3, wherein each of
the upper and lower outside surfaces are perforated to promote bony
ingrowth.
13. The intervertebral fusion device of claim 3, wherein each of
the upper and lower outside surfaces are convex.
14. A method of fabricating an intervertebral fusion device, the
method comprising the steps of: providing a polymeric structure
having an upper toothed outside surface and a lower toothed outside
surface opposite the upper toothed outside surface; and coating
each of the upper and lower toothed outside surfaces with a porous
titanium coating.
15. The method as recited in claim 14, wherein the providing step
comprises defining an opening that extends from the upper toothed
outside surface to the lower toothed outside surface.
16. The method as recited in claim 14, further comprising the step
of inserting bone graft material into the polymeric structure.
17. The method of claim 14, wherein the polymeric structure
comprises PAEK.
18. The method of claim 17, wherein The PAEK comprises PEEK.
19. The method of claim 14, wherein the providing step comprises
providing the polymeric structure with a tapered leading end.
20. The method of claim 14, wherein the coating step comprises
coating each of the upper and lower toothed outside surfaces with
the porous titanium coating having an average pore size of 250
microns.
21. The method of claim 14, wherein the coating step comprises
coating each of the upper and lower toothed outside surfaces with
the porous titanium coating having a coefficient of friction of
0.8.
22. A method of restoring a disc height of an intervertebral disc
space defined between an upper vertebra and a lower vertebra, the
method comprising the steps of: inserting a polymeric
intervertebral fusion device into the intervertebral disc space,
wherein the inserting step comprises gripping the upper vertebra
with a toothed upper outside surface of the fusion device that is
coated with a porous titanium coating, and gripping the lower
vertebra with a toothed lower outside surface of the fusion device
that is coated with a porous titanium coating.
23. The method of claim 22, wherein the inserting step promotes
vertebral affixation to the porous titanium coating of each of the
upper and lower outside surfaces.
24. The method of claim 22, wherein the polymeric intervertebral
fusion device comprises PAEK.
25. The method of claim 24, wherein the PAEK is selected from the
group consisting of polyetherether ketone (PEEK), polyether ketone
ketone (PEKK) and polyether ketone (PEK).
26. The method of claim 24, wherein the PAEK is PEEK.
27. The method of claim 22, wherein the porous titanium coating has
an average pore size of 250 microns.
28. The method of claim 22, wherein the porous titanium coating has
a coefficient of friction of 0.8.
29. The method of claim 22, further comprising the step of
inserting bone graft in the polymeric component.
30. The method of claim 29, wherein the polymeric intervertebral
fusion device defines a throughhole that extends from the upper
outside surface to the lower outside surface.
31. The method of claim 22, wherein the inserting step comprises
inserting a tapered leading end of the polymeric intervertebral
fusion device into the intervertebral disc space.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This is a divisional application of U.S. patent application
Ser. No. 14/514,700 filed Oct. 15, 2014, which in turn is a
divisional application of U.S. patent application Ser. No.
11/768,636 filed Jun. 26, 2007, now issued as U.S. Pat. No.
8,900,307, the specification of each of which is incorporated by
reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] The natural intervertebral disc contains a jelly-like
nucleus pulposus surrounded by a fibrous annulus fibrosus. Under an
axial load, the nucleus pulposus compresses and radially transfers
that load to the annulus fibrosus. The laminated nature of the
annulus fibrosus provides it with a high tensile strength and so
allows it to expand radially in response to this transferred
load.
[0003] In a healthy intervertebral disc, cells within the nucleus
pulposus produce an extracellular matrix (ECM) containing a high
percentage of proteoglycans. These proteoglycans contain sulfated
functional groups that retain water, thereby providing the nucleus
pulposus within its cushioning qualities. These nucleus pulposus
cells may also secrete small amounts of cytokines such as
interleukin-1.beta. and TNF-.alpha. as well as matrix
metalloproteinases ("MMPs"). These cytokines and MMPs help regulate
the metabolism of the nucleus pulposus cells.
[0004] In some instances of disc degeneration disease (DDD),
gradual degeneration of the intervetebral disc is caused by
mechanical instabilities in other portions of the spine. In these
instances, increased loads and pressures on the nucleus pulposus
cause the cells within the disc (or invading macrophases) to emit
larger than normal amounts of the above-mentioned cytokines In
other instances of DDD, genetic factors or apoptosis can also cause
the cells within the nucleus pulposus to emit toxic amounts of
these cytokines and MMPs. In some instances, the pumping action of
the disc may malfunction (due to, for example, a decrease in the
proteoglycan concentration within the nucleus pulposus), thereby
retarding the flow of nutrients into the disc as well as the flow
of waste products out of the disc. This reduced capacity to
eliminate waste may result in the accumulation of high levels of
toxins that may cause nerve irritation and pain.
[0005] As DDD progresses, toxic levels of the cytokines and MMPs
present in the nucleus pulposus begin to degrade the extracellular
matrix, in particular, the MMPs (as mediated by the cytokines)
begin cleaving the water-retaining portions of the proteoglycans,
thereby reducing its water-retaining capabilities. This degradation
leads to a less flexible nucleus pulposus, and so changes the
loading pattern within the disc, thereby possibly causing
delamination of the annulus fibrosus. These changes cause more
mechanical instability, thereby causing the cells to emit even more
cytokines, thereby upregulating MMPs. As this destructive cascade
continues and DDD further progresses, the disc begins to bulge ("a
herniated disc"), and then ultimately ruptures, causing the nucleus
pulposus to contact the spinal cord and produce pain.
[0006] One proposed method of managing these problems is to remove
the problematic disc and replace it with a porous device that
restores disc height and allows for bone growth therethrough for
the fusion of the adjacent vertebrae. These devices are commonly
called "fusion devices".
[0007] U.S. Pat. No. 5,865,848 ("Baker") discloses a two piece
intervertebral fusion cage having a ramp. Baker describes a
intervertebral spacer comprised of two components. The two portions
have opposed flanges connected by a screw to effect translation,
and complimentary slopes. The components are inserted together in a
collapsed condition. Post-insertion translation of one component
relative to the other creates an expanded condition and the desired
distraction. US Published Patent Application 2004/0230309 ("DePuy
Spine") discloses a two piece intervertebral fusion cage having a
ramp. See FIG. 14D.
[0008] US Published Patent Application Nos. US2003/0135275 and
2003/0139812 (collectively, "Garcia") disclose a two-piece implant
formed by upper and lower halves, wherein the inner surfaces of the
two halves form a dovetail joint that runs along a transverse axis
of the implant.
SUMMARY OF THE INVENTION
[0009] The present invention is directed to a two-piece
intervertebral fusion cage, comprising: [0010] a) an upper
component having a first outside surface adapted for gripping an
upper vertebral endplate and a first interior surface, [0011] b) a
lower component having a second outside surface adapted for
gripping a lower vertebral endplate and a second interior surface,
wherein the interior surfaces mate.
[0012] One advantage of such a cage is its easy insertion. In a
first step, the lower component is inserted into the disc space and
is held in place. The first step confirms placement of the implant
and its footprint. In a second step, the upper component is
inserted into the disc space by sliding its interior surface along
the opposed interior surface of the lower component. This two-step
method of insertion eliminates the need to provide an independent
distraction means, such as the use of an impaction hammer, and an
independent trialing means. It also provides mechanical leverage in
the cage to facilitate the creation of lordosis.
[0013] A second advantage of such a cage is its impact on patient
safety. The gradual nature of the distraction of the disc space
provided by this two-step insertion procedure should also reduce
the possibility of over-distraction, which can cause neural damage.
It also eliminates hammer-induced sudden impaction during cage
insertion, thereby reducing cage failures, over-insertion and
anterior damage. Lastly, the smaller height of the annular defect
produced during device insertion aids in preventing device
expulsion.
[0014] In a first aspect of the present invention, the outside
surface of at least one of the components is substantially parallel
to its corresponding interior surface. This provides the advantage
of ease of insertion through a small annular defect/incision.
Simply, one component can determine height and the other component
can determine lordosis.
[0015] In a second aspect of the present invention, each component
has a throughhole extending from its outside surface to its
interior surface, and the interior surfaces of these components
mate to align the first and second throughholes. This alignment
provides a path for bone growth through the vertical dimension of
the device, thereby facilitating fusion between the vertebral
endplates.
[0016] In a third aspect of the present invention, each component
has opposed sidewalls and at least one of the components has a
lateral throughhole extending from a sidewall thereof to its
opposed sidewall. This lateral throughhole provides a path for
increased vascularization, increased diffusion, and bone growth
through the lateral dimension of the device, thereby facilitating
fusion between the vertebral endplates.
[0017] In a fourth aspect of the present invention, each component
has a dovetail feature extending along the longitudinal axis of its
interior surface and the dovetail features of the corresponding
components mate along the longitudinal axes. This mating of
dovetails provides for a locking of the mated upper and lower
components and increases the assurance that the mated components
will not disengage in vivo.
[0018] In a fifth aspect of the present invention, the upper
component has a tapered distal end, preferably a bulleted nose.
This tapered distal end allows for easy distraction of the opposed
vertebral endplates upon insertion of the upper component into the
disc space.
DESCRIPTION OF THE FIGURES
[0019] FIGS. 1a, 1b, 1c, and 1d disclose a cage of the present
invention having mating dovetail features and aligned vertical
throughholes.
[0020] FIGS. 1e, 1f, and 1g disclose the sequential insertion and
assembly of the components of the device into the disc space.
[0021] FIG. 2 discloses a cage of the present invention having a
lateral throughhole extending from a sidewall thereof to its
opposed sidewall, and an outside surfaces that is substantially
parallel to its corresponding interior surface.
[0022] FIG. 3 discloses an exploded cage of the present invention
having a bulleted distal nose, along with an assembled cage
attached to an insertion instrument.
[0023] FIG. 4 discloses an interior surface of the lower component
that is angled with respect to its corresponding outer surface,
thus creating lordosis.
[0024] FIG. 5a discloses a cage of the present invention wherein an
inside surface of the first component has a recess, and an inside
surface of the second component has an extension, wherein the
recess and extension mate to provide nesting of the components.
[0025] FIGS. 5b and 5c disclose a method of inserting the device of
FIG. 5a.
[0026] FIG. 6 discloses a cage of the present invention wherein one
of the components has extending side walls that create a housing
adapted to capture the other component.
[0027] FIGS. 7a and 7b disclose the device of the present invention
attached to an insertion instrument.
[0028] FIGS. 8a. 8b, and 8c disclose arcuate cages of the present
invention.
[0029] FIG. 8d discloses an arcuate cage inserted into a disc
space.
DETAILED DESCRIPTION OF THE FIGURES
[0030] For the purposes of the present invention, the terms "inner
surface", "inside surface" "interior surface are interchangeable,
as are the terms "exterior surface", "outer surface" and "outside
surface".
[0031] In general, the cage possesses a two-piece structure with
hard-endplates and a locking means that is compatible with MIS
techniques. Both the top and bottom portions have an interior and
exterior surface (FIG. 1), where the exterior surface interfaces
with the vertebra.
[0032] Now referring to FIGS. 1a-1d, there is provided an
intervertebral fusion cage, comprising: [0033] a) an upper
component 1 having a first outside surface 3 adapted for gripping
an upper vertebral endplate, a first interior surface 5 having a
first longitudinal axis, a first throughhole 7 extending from the
outside surface to the first interior surface, and a first dovetail
feature (not shown) extending along the first longitudinal axis,
and [0034] b) a lower component 11 having a second outside surface
13 adapted for gripping a lower vertebral endplate, a second
interior surface 15 having a second longitudinal axis, a second
throughhole 17 extending from the outside surface to the second
interior surface, and a second dovetail feature 19 extending along
the first longitudinal axis, wherein the interior surfaces mate to
align the first and second throughholes.
[0035] The device of FIGS. 1a-1d possesses mating dovetail features
on its interior surfaces. These features help maintain the device
in its assembled form. The device of FIGS. 1a-1d also possesses
aligned vertical throughholes through each component in its
assembled form. These aligned holes help provide desirable bone
growth through the device.
[0036] In use, the component halves of the device of the present
invention are inserted into the disc space is a sequential fashion
and are assembled in situ. Now referring to FIG. 1e, the lower
component 11 is first inserted into the disc space, with the
tapered portion pointing posteriorly, so that it rests upon the
floor of the disc space. The reduced height of the lower component
allows it to be inserted without any need for distraction. Now
referring to FIG. 1f, the inside surface of the upper component is
mated to the inside surface of the lower component and advanced
into the disc space. Because the height of the combined components
is greater than the disc space, and because the nose of the upper
component is tapered, gradual insertion of the upper component into
the disc space in this manner provides a gradual distraction of the
disc space. Now referring to FIG. 1g, the assembled component is
located within the disc space.
[0037] In one embodiment, the interior surface of the top and/or
bottom portion is generally parallel to their exterior surface. Now
referring to FIG. 2, there is provided an intervertebral fusion
cage, comprising: [0038] a) an upper component 21 having a first
outside surface 23 adapted for gripping an upper vertebral endplate
and a first interior surface 25, a first sidewall 27 and a second
opposed sidewall (not shown), [0039] b) a lower component 31 having
a second outside surface 33 adapted for gripping a lower vertebral
endplate and a second interior surface 35, a third sidewall 37 and
a second fourth sidewall (not shown), wherein the interior surfaces
mate, wherein at least one of the components has a lateral
throughhole 39 extending from a sidewall thereof to its opposed
sidewall, and wherein at least one of the outside surfaces is
substantially parallel to its corresponding interior surface.
[0040] An alternative embodiment would have sloped sides and/or
non-parallel throughhole walls. These walls may be curved inwards
(concave) or bowed outward (convex). Such an embodiment would
increase the mechanical structural stability of the assembled
device. Additionally, increasing the devices' mating surface areas
would give additional room for the dovetail and locking features.
Simultaneously, increased mating surface areas would decrease
normal and shear load distributions at the mating surfaces, thereby
decreasing likelihood of mechanical failures and further minimizing
potential for the generation of particulate wear debris.
[0041] The device of FIG. 2 possesses a component that has parallel
outside and interior surface. The device of FIG. 2 also possesses
aligned lateral throughholes through at least one of its
components. These holes help in desirable bone growth through the
device.
[0042] Now referring to FIG. 3, there is provided the upper 41 and
lower 51 halves of the intervertebral fusion cage of the present
invention, along with an assembled cage 42 attached to an insertion
instrument 44. The intervertebral fusion cage comprises: [0043] a)
an upper component 41 having a first outside surface 43 adapted for
gripping an upper vertebral endplate, a first interior surface 45
having a recess 46, and a tapered distal end 47, [0044] b) a lower
component 51 having a second outside surface 53 adapted for
gripping a lower vertebral endplate and a second interior surface
55 having a projection 56 and a taper distal end 58, wherein the
interior surfaces mate so that the recess and projection form a
stop 57 and the tapered distal ends form a bullet nose 60.
[0045] The upper component of the device of FIG. 3 possesses a
bullet distal nose. This bullet nose helps the upper component
distract the disc space as it is inserted into the disc space. The
insertion instrument 44 includes a rail 48, a top pusher 50, and a
bottom rod 52 having a projection 54 that mates with a recess 38 in
the lower component of the cage.
[0046] In another embodiment, the interior surface 63 of the lower
component 61 creates a ramp having an angle a with respect to its
corresponding outer surface 65 (FIG. 4). The upper component 67 of
the implant translates along this ramp, creating lordosis.
[0047] Because the two pieces of the cage are inserted sequentially
into the disc space, the "insertion" height of the assembly and
thus the height of the annular defect required during the insertion
is approximately one half of the assembled device height.
[0048] Now referring to FIG. 5a, there is provided an
intervertebral fusion cage, comprising: [0049] a) a first component
71 having a first outside surface 73 adapted for gripping a first
vertebral endplate, a first interior surface 75, and a recess 77 in
the first interior surface extending toward the first outside
surface, [0050] b) a second component 81 having a second outside
surface 83 adapted for gripping a second vertebral endplate, a
second interior surface 85, and an extension 87 extending from the
second interior surface toward the first interior surface, wherein
the recess and extension of the interior surfaces mate to provide
nesting of the components.
[0051] Now referring to FIGS. 5b and 5c, there is provided a method
of inserting the nested cage of FIG. 5a: Place the baseplate 81 in
the interbody disc space. Position and slide the overrider plate 71
onto and over the baseplate 81. Initially, the overrider nose 78
will slide across the base plate's interior surface 87 thereby
creating a slight over-distraction of the disc space. As the
overrider's posterior aspect 75 approaches the baseplate's
posterior niche 85, the anterior overrider nose 78 will fall into
the anterior niche 88 thereby providing a positive stop and locking
mechanism to seat the overrider plate 71 onto the baseplate 81.
[0052] The preferred method for the order of insertion of the
two-piece cage of the present invention is now disclosed. The first
step can be placement of the first component of the device against
the inferior vertebral body. This is often followed by insertion
and eventual assembly of the second component onto and over the
first component. The first component should contain a lordosed or
angled component such that the surface over which the second
component is inserted is substantially parallel to the superior
vertebral endplate.
[0053] Alternatively, the method of inserting the first component
with substantially parallel bone contacting and interior surfaces
requires that the second component to contain a lordotic angle. As
this two-piece assembled cage is typically inserted from a
posterior approach, and the angle of the interbody cavity widens
anteriorly, insertion of the second component with a lordotic angle
requires over-distraction of the posterior aspect of the interbody
space to accommodate the larger/taller anterior aspect of the
second component. This over-distraction and the associated
increased insertion force is not associated with the preferred
method where the lordosed component is inserted first followed by
the height-restoring component with substantially parallel
sides.
[0054] Now referring to FIG. 6, there is provided an intervertebral
fusion cage, comprising: [0055] a) a first component 101 having a
first outside surface 103 adapted for gripping an upper vertebral
endplate and a first interior surface 105, a first sidewall 107
extending between the first outside surface and the first interior
surface and having an outer surface (not shown) and a second
opposed sidewall 109 extending between the first outside surface
and the first interior surface and having an outer surface (not
shown), [0056] b) a housing component 111 having a second outside
surface 113 adapted for gripping a lower vertebral endplate and a
second interior surface 115, a third sidewall 117 extending from
the second interior surface and away from the second outside
surface and having an inner surface 118, and a fourth sidewall 119
extending from the second interior surface and away from the second
outside surface and having an inner surface 120, wherein the
interior surfaces mate, and wherein the outer surfaces of the first
component mates with their respective inner surfaces of the housing
component.
[0057] In FIG. 6, one of the components has extending side walls
that create a housing adapted to capture the other component. The
advantage of this embodiment is that it possesses an enhanced
dovetail creating enhanced stability.
[0058] Now referring to FIGS. 7a-b, there is provided a device for
inserting the components of the present invention into the disc
space. FIG. 7a discloses the disposition of the instrument during
insertion of the inferior component into the disc space. FIG. 7b
discloses the disposition of the device when the upper component is
advanced into the disc space to the point where it rides on top of
the lower component and forms the assembly.
[0059] The endplates may have teeth to prevent migration and
perforations to allow bone growth.
[0060] Radiographic markers can be incorporated to allow intra- or
post-operative visualization.
[0061] Additionally, the outside surfaces of the superior and
inferior portions can be designed with varying geometries to allow
for their customization to the patient's anatomy, thereby
minimizing the risk of subsidence. For instance, the outside
surface of the superior half may have a convex dome while the
outside surfaces of the inferior half may be flat, convex, concave
or serpentine (concave posterior and convex anterior).
[0062] In an alternative embodiment, an arcuate sliding mating
pathway is contemplated. FIGS. 8a-8c disclose arcuate cages of the
present invention forming a lordotic angle 201 (FIG. 8a), no angle
203 (FIG. 8b) and a kyphotic angle 205 (FIG. 8c). FIG. 8d discloses
a lordotic arcuate cage 201 inserted into a disc space.
[0063] The benefit to assembling the two cage halves using an
arcuate assembly pathway is the potential to provide in situ
determination of lordotic angle. Also, the arcuate pathway would
embody a mechanism allowing a continuously variable lordotic angle
(as opposed to discrete lordotic angles represented by assembly of
different superior or inferior cage components). The arcuate mating
mechanism requires that one half of the cage contains a convex
mating surface while the other half contains a concave mating
surface with an arcuate geometry that exactly mimics the inverse of
the opposite curve. The assembled halves would represent a fixed
radial distance about some center of rotation (the geometric
centroid of the arcuate pathway). This fixed radial distance
represents the cage height. As the superior cage half slides along
the arcuate mating surface of the inferior cage half, the lordotic
angle of the assembly will vary continuously. Detents, stops, or
teeth can be inserted into the arcuate pathway to create discrete
increments of lordotic angles along the continuous arcuate pathway,
if this is a preferred further embodiment.
[0064] The arcuate pathway enables similar seating features
compared to the planar device mating pathway--dovetails, keyways,
detents, snap-fits, set screws, etc.
[0065] The two halves of the device may be secured together by
various means. For instance, a dovetail feature may be incorporated
into the interior surfaces of the top and bottom portions for ease
of insertion, as shown in FIGS. 1a-f, 2 and 3. The two components
may also be stacked and nested together without a dovetail, as
shown in FIGS. 5a-c, or the superior/inferior half may have side
walls creating a housing that captures the other portion, as shown
in FIG. 6. The two portions of the device may be locked together in
a variety of locking means including but not limited to Morse taper
locks, positive stop(s), ultrasonic welding, snap mechanism(s), a
set screw, a clip, a collet, cams, etc. Additional design features
can be included to aid in seating the two halves: mechanical keys,
a threaded nut can screw onto threaded features on the posterior
aspect of each half, and a mechanical channel can be incorporated
into the design for the use of curing compounds like adhesives and
grouts.
[0066] Both components of the device may also incorporate a variety
of holding means to assist during the insertion of the device.
These holding means may be located on the interior or exterior
surfaces as well as along the sidewalls. For example, the top
and/or bottom portion may have threaded holes, divots, or slots to
provide for secure holding and cage support during insertion,
placement and assembly.
[0067] After placing the inferior portion, the superior portion can
be inserted by several means to expand the overall device height
and provide appropriate lordosis or kyphosis.
[0068] The superior and inferior portions are generally hollow to
provide for filling with various osteogenic fillers and can be
porous to allow for graft filling, bony ingrowth and spinal fusion.
Lateral openings can also be incorporated to increase
vascularization of the osteogenic fillers as well as to provide
post-operative visualization of the bony fusion process. Filling
can be done preoperatively or intraoperatively, as a through hole
into the wedge can facilitate filling of the entire construct in
situ.
[0069] Unlike traditional single-piece cages, the two-piece
assembled cage requires sliding articulation of two half-cages
packed with bone. Bone packed within a cage is typically held in
place using friction forces. The sliding assembly mechanisms
described could potentially dislodge packed bone graft during cage
insertion and/or assembly. To mitigate the dislodgement of bone
chips or the potential for sliding-interference of the bone chips,
bonding a resorbable lamina of material between the two halfs is
proposed. Such a lamina could be placed on the interior surface 45
of the upper half 43 (see FIG. 3). Such a resorbable member could
be applied to all cage openings but is of particular utility to
prevent dislodgement or interference of the bone graft during
sliding assembly of the two halves.
[0070] The present invention also offers novel trialing methods.
The inferior or superior portion of the implant device can be
inserted alone to confirm disc space clearance and device
placement, and a trial of the superior component can be placed upon
the inserted component to confirm disc height, lordosis, and
placement.
[0071] Because these cages reduce the profile required for their
insertion, they allow for implantation through a cannula that may
be smaller than the conventional cannula.
[0072] The endplates can be made of any structural biocompatible
material including resorbable (PLA, PLGA, etc.), non-resorbable
polymers (CFRP, PEEK, UHMWPE, PDS), metallics (SS, Ti-6Al-4V, CoCr,
etc.), as well as materials that are designed to encourage bony
regeneration (allograft, bone substitute-loaded polymers, growth
factor-loaded polymers, ceramics, etc.). The materials for the
upper and lower components are biocompatible and generally similar
to those disclosed in the prior art. Examples of such materials are
metal, PEEK and ceramic.
[0073] In preferred embodiments, each of the upper and lower
components is manufactured from a material that possesses the
desirable strength and stiffness characteristics for use as a
fusion cage component.
[0074] These components of the present invention may be made from
any non-resorbable material appropriate for human surgical
implantation, including but not limited to, surgically appropriate
metals, and non-metallic materials, such as carbon fiber
composites, polymers and ceramics.
[0075] In some embodiments, the cage material is selected from the
group consisting of PEEK, ceramic and metallic. The cage material
is preferably selected from the group consisting of metal and
composite (such as PEEK/carbon fiber).
[0076] If a metal is chosen as the material of construction for a
component, then the metal is preferably selected from the group
consisting of titanium, titanium alloys (such as Ti-6Al-4V), chrome
alloys (such as CrCo or Cr--Co--Mo) and stainless steel.
[0077] If a polymer is chosen as a material of construction for a
component, then the polymer is preferably selected from the group
consisting of polyesters, (particularly aromatic esters such as
polyalkylene terephthalates, polyamides; polyalkenes; poly(vinyl
fluoride); PTFE; polyarylethyl ketone PAEK; polyphenylene and
mixtures thereof.
[0078] If a ceramic is chosen as the material of construction for a
component, then the ceramic is preferably selected from the group
consisting of alumina, zirconia and mixtures thereof. It is
preferred to select an alumina-zirconia ceramic, such as BIOLOX
Delta.TM., available from CeramTec of Plochingen, Germany.
Depending on the material chosen, a smooth surface coating may be
provided thereon to improve performance and reduce particulate wear
debris.
[0079] In some embodiments, the cage member comprises PEEK. In
others, it is a ceramic.
[0080] In some embodiments, the first component consists
essentially of a metallic material, preferably a titanium alloy or
a chrome-cobalt alloy. In some embodiments, the second component
consists essentially of the same metallic material as the first
plate.
[0081] In some embodiments, the components are made of a stainless
steel alloy, preferably BioDur.RTM. CCM Plus.RTM. Alloy available
from Carpenter Specialty Alloys, Carpenter Technology Corporation
of Wyomissing, Pa. In some embodiments, the outer surfaces of the
components are coated with a sintered beadcoating, preferably
Porocoat.TM., available from DePuy Orthopaedics of Warsaw, Ind.
[0082] In some embodiments, the components are made from a
composite comprising carbon fiber. Composites comprising carbon
fiber are advantageous in that they typically have a strength and
stiffness that is superior to neat polymer materials such as a
polyarylethyl ketone PAEK. In some embodiments, each component is
made from a polymer composite such as a PEKK-carbon fiber
composite.
[0083] Preferably, the composite comprising carbon fiber further
comprises a polymer. Preferably, the polymer is a polyarylethyl
ketone (PAEK). More preferably, the PAEK is selected from the group
consisting of polyetherether ketone (PEEK), polyether ketone ketone
(PEKK) and polyether ketone (PEK). In preferred embodiments, the
PAEK is PEEK.
[0084] In some embodiments, the carbon fiber comprises between 1
vol % and 60 vol % (more preferably, between 10 vol % and 50 vol %)
of the composite. In some embodiments, the polymer and carbon
fibers are homogeneously mixed. In others, the material is a
laminate. In some embodiments, the carbon fiber is present in a
chopped state. Preferably, the chopped carbon fibers have a median
length of between 1 mm and 12 mm, more preferably between 4.5 mm
and 7.5 mm. In some embodiments, the carbon fiber is present as
continuous strands.
[0085] In especially preferred embodiments, the composite
comprises: [0086] a) 40-99% (more preferably, 60-80 vol %)
polyarylethyl ketone (PAEK), and [0087] b) 1-60% (more preferably,
20-40 vol %) carbon fiber, wherein the polyarylethyl ketone (PAEK)
is selected from the group consisting of polyetherether ketone
(PEEK), polyether ketone ketone (PEKK) and polyether ketone
(PEK).
[0088] In some embodiments, the composite consists essentially of
PAEK and carbon fiber. More preferably, the composite comprises
60-80 wt % PAEK and 20-40 wt % carbon fiber. Still more preferably
the composite comprises 65-75 wt % PAEK and 25-35 wt % carbon
fiber.
[0089] Although the present invention has been described with
reference to its preferred embodiments, those skillful in the art
will recognize changes that may be made in form and structure which
do not depart from the spirit of the invention.
[0090] Alternatively, combinations of cage materials could be
beneficial (i.e., --a ceramic bottom half with a PEEK top
half).
* * * * *