U.S. patent application number 12/255731 was filed with the patent office on 2009-04-23 for method and spacer device for spanning a space formed upon removal of an intervertebral disc.
This patent application is currently assigned to SpinalMotion, Inc.. Invention is credited to Yves Arramon, David Hovda.
Application Number | 20090105833 12/255731 |
Document ID | / |
Family ID | 40564282 |
Filed Date | 2009-04-23 |
United States Patent
Application |
20090105833 |
Kind Code |
A1 |
Hovda; David ; et
al. |
April 23, 2009 |
Method and Spacer Device for Spanning a Space Formed upon Removal
of an Intervertebral Disc
Abstract
An intervertebral spacer is designed particularly for patients
who are not candidates for total disc replacement. The spacer
maintains disc height and prevents subsidence with a large
vertebral body contacting surface area while substantially reducing
recovery time by eliminating the need for bridging bone. The
intervertebral spacer or fusion spacer includes a rigid spacer body
sized and shaped to fit within an intervertebral space between two
vertebral bodies. In one embodiment, the spacer body has two
opposed metallic vertebral contacting surfaces, at least one fin
extending from each of the vertebral contacting surfaces and
configured to be positioned within slots cut into the two vertebral
bodies. Holes, if present, cover less than 40 percent of the entire
vertebral body contacting surfaces to provide increased bone
ongrowth surfaces and to prevent subsidence.
Inventors: |
Hovda; David; (Mountain
View, CA) ; Arramon; Yves; (Sunnyvale, CA) |
Correspondence
Address: |
TOWNSEND AND TOWNSEND AND CREW, LLP
TWO EMBARCADERO CENTER, EIGHTH FLOOR
SAN FRANCISCO
CA
94111-3834
US
|
Assignee: |
SpinalMotion, Inc.
Mountain View
CA
|
Family ID: |
40564282 |
Appl. No.: |
12/255731 |
Filed: |
October 22, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60981665 |
Oct 22, 2007 |
|
|
|
Current U.S.
Class: |
623/17.16 ;
128/898; 623/17.11 |
Current CPC
Class: |
A61F 2310/00179
20130101; A61F 2310/00796 20130101; A61F 2250/0032 20130101; A61F
2310/00017 20130101; A61F 2310/0088 20130101; A61F 2/4465 20130101;
A61F 2310/00407 20130101; A61F 2/30771 20130101; A61F 2310/00023
20130101; A61F 2310/00131 20130101; A61F 2002/30884 20130101; A61F
2002/30899 20130101; A61F 2310/00431 20130101; A61B 17/86 20130101;
A61F 2002/30056 20130101; A61F 2310/00029 20130101; A61F 2002/449
20130101; A61F 2002/30772 20130101; A61F 2310/00604 20130101; A61F
2002/30787 20130101; A61F 2310/00976 20130101; A61F 2310/00071
20130101; A61F 2002/30904 20130101 |
Class at
Publication: |
623/17.16 ;
128/898; 623/17.11 |
International
Class: |
A61F 2/44 20060101
A61F002/44; A61B 19/00 20060101 A61B019/00 |
Claims
1. A method of spanning a space formed by upon removal of an
intervertebral disc, the method comprising: performing a discectomy
to remove disc material between two adjacent vertebral bodies;
placing an intervertebral spacer between the two adjacent vertebral
bodies, the spacer comprising two end plates, each end plate having
a metallic vertebral body contacting surface and an inner surface,
and a connector interconnecting the inner surfaces of the two end
plates in a rigid manner which limits motion between the plates to
less than a total of 5 degrees, wherein the vertebral body
contacting surfaces of the end plates have no holes therein or have
holes which cover less than 40 percent of the vertebral body
contacting surfaces; and maintaining the disc space between the two
adjacent vertebral bodies with the intervertebral spacer without
the use of bone graft or bridging bone.
2. The method of claim 1, wherein the connector is a rigid
connector.
3. The method of claim 1, wherein the two end plates and connector
are formed of a single piece of metal.
4. The method of claim 1, wherein the intervertebral spacer is
selected, such that when the spacer is positioned between the two
vertebral bodies the spacer fills at least 50 percent of a
vertebral space formed between the vertebral bodies.
5. The method of claim 1, wherein the vertebral body contacting
surface of the end plates has holes which cover less than 25
percent of the vertebral body contacting surfaces.
6. The method of claim 1, further comprising cutting at least one
slot in each of the adjacent vertebrae and placing a fin into the
at least one slot.
7. The method of claim 6, further comprising at least one
additional fixation means provided on the vertebral body contacting
surfaces the intervertebral spacer.
8. The method of claim 7, wherein the additional fixation means is
at least one of a screw, teeth, serrations or grooves.
9. The method of claim 1, wherein the metallic vertebral contacting
surface is formed of titanium or a titanium alloy.
10. An intervertebral spacer for spanning a space formed by upon
removal of an intervertebral disc, the spacer comprising: two end
plates sized and shaped to fit within an intervertebral space, each
end plate having a metallic vertebral contacting surface and an
inner surface; a connector interconnecting the inner surfaces of
the two end plates in a rigid manner which limits motion between
the plates to less than a total of 5 degrees; and wherein the
vertebral body contacting surfaces of the end plates have no holes
therein or have holes which cover less than 40 percent of the
vertebral body contacting surfaces.
11. The spacer of claim 10, wherein the connector is a rigid
connector.
12. The spacer of claim 10, wherein the two end plates and
connector are formed of a single piece of metal.
13. The spacer of claim 10, wherein the vertebral body contacting
surface of the end plates has holes which cover less than 25
percent of the vertebral body contacting surfaces.
14. The spacer of claim 10, further comprising at least one fin
extending from the vertebral contacting surfaces.
15. The spacer of claim 10, wherein the two end plates and
connector are formed of PEEK with metallic screens, layers or
coatings on the vertebral body contacting surfaces.
16. The spacer of claim 10, wherein the metallic vertebral
contacting surface is formed of titanium or a titanium alloy.
17. A method of performing an anterior/posterior fusion, the method
comprising: performing a discectomy to remove disc material between
two adjacent vertebral bodies; placing an intervertebral spacer
between the two adjacent discs, the spacer comprising two end
plates, each end plate having a metallic vertebral contacting
surface and an inner surface, and a rigid connector interconnecting
the inner surfaces of the two end plates, wherein the vertebral
body contacting surfaces of the end plates have no holes therein or
have holes which cover less than 40 percent of the vertebral body
contacting surfaces; maintaining the disc space between the two
adjacent discs with the intervertebral spacer; and posteriorly
placing a stabilization system to fix the angle between the
vertebral bodies.
18. The method of claim 17, wherein the intervertebral spacer is
placed anteriorly.
19. The method of claim 17, wherein the intervertebral spacer is
place posteriorly.
20. The method of claim 19, wherein the posteriorly placed
intervertebral spacer includes a two part spacer in which the two
parts together cover about 40 percent or more of the vertebral
surface.
21. The method of claim 19, wherein the posteriorly placed
stabilization system includes at least one screw placed into each
of the vertebral bodies and at least one connector
therebetween.
22. The method of claim 19, wherein the method is performed without
the use of bone graft.
23. The method of claim 19, wherein the vertebral body contacting
surfaces of the end plates have holes which cover less than 25
percent of the vertebral body contacting surfaces.
24. A fusion system, the system comprising: an intervertebral
spacer comprising: two end plates sized and shaped to fit within an
intervertebral space, each end plate having a vertebral contacting
surface an inner surface, wherein the vertebral body contacting
surfaces of the end plates have no holes therein or have holes
which cover less than 40 percent of the vertebral body contacting
surfaces; and a rigid connector interconnecting the inner surfaces
of the two end plates; and a posteriorly placed stabilization
system including at least two screws configured to be placed into
the vertebral bodies and at least one connector therebetween.
25. The system of claim 24, wherein the intervertebral spacer is a
unitary spacer sized to be placed anteriorly.
26. The system of claim 24, wherein the intervertebral spacer is a
two part spacer sized to be place posteriorly.
27. The system of claim 24, wherein the vertebral body contacting
surfaces of the end plates have holes which cover less than 25
percent of the vertebral body contacting surfaces.
28. A fusion spacer comprising: a rigid spacer body sized and
shaped to fit within an intervertebral space between two vertebral
bodies, the body having two opposed metallic vertebral contacting
surfaces; at least one fin extending from each of the vertebral
contacting surfaces, the fins configured to be positioned within
slots cut into the two vertebral bodies; a plurality of serrations
on the vertebral contacting surfaces; and wherein holes cover less
than 40 percent of the entire vertebral body contacting
surfaces.
29. The spacer of claim 28, wherein holes cover less than 25
percent of the vertebral body contacting surfaces.
30. The spacer of claim 28, wherein the metallic vertebral
contacting surfaces are formed of titanium or a titanium alloy.
31. The spacer of claim 30, wherein the body is a unitary metallic
body.
32. The spacer of claim 30, wherein the body is formed of PEEK.
Description
CROSS-REFERENCES TO RELATED APPLICATIONS
[0001] The present application claims priority from U.S.
Provisional Patent Application No. 60/981,665 filed Oct. 22, 2007,
entitled "Method and Spacer Device for Spanning a Space Formed Upon
Removal of an Intervertebral Disc," the full disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to medical devices and
methods. More specifically, the invention relates to intervertebral
spacers and methods of spanning a space formed upon removal of an
intervertebral disc.
[0003] Back pain takes an enormous toll on the health and
productivity of people around the world. According to the American
Academy of Orthopedic Surgeons, approximately 80 percent of
Americans will experience back pain at some time in their life. In
the year 2000, approximately 26 million visits were made to
physicians' offices due to back problems in the United States. On
any one day, it is estimated that 5% of the working population in
America is disabled by back pain.
[0004] One common cause of back pain is injury, degeneration and/or
dysfunction of one or more intervertebral discs. Intervertebral
discs are the soft tissue structures located between each of the
thirty-three vertebral bones that make up the vertebral (spinal)
column. Essentially, the discs allow the vertebrae to move relative
to one another. The vertebral column and discs are vital anatomical
structures, in that they form a central axis that supports the head
and torso, allow for movement of the back, and protect the spinal
cord, which passes through the vertebrae in proximity to the
discs.
[0005] Discs often become damaged due to wear and tear or acute
injury. For example, discs may bulge (herniate), tear, rupture,
degenerate or the like. A bulging disc may press against the spinal
cord or a nerve exiting the spinal cord, causing "radicular" pain
(pain in one or more extremities caused by impingement of a nerve
root). Degeneration or other damage to a disc may cause a loss of
"disc height," meaning that the natural space between two vertebrae
decreases. Decreased disc height may cause a disc to bulge, facet
loads to increase, two vertebrae to rub together in an unnatural
way and/or increased pressure on certain parts of the vertebrae
and/or nerve roots, thus causing pain. In general, chronic and
acute damage to intervertebral discs is a common source of back
related pain and loss of mobility.
[0006] When one or more damaged intervertebral discs cause a
patient pain and discomfort, surgery is often required.
Traditionally, surgical procedures for treating intervertebral
discs have involved discectomy (partial or total removal of a
disc), with or without interbody fusion of the two vertebrae
adjacent to the disc. When the disc is partially or completely
removed, it is necessary to replace the excised material to prevent
direct contact between hard bony surfaces of adjacent vertebrae.
Oftentimes, pins, rods, screws, cages and/or the like are inserted
between the vertebrae to act as support structures to hold the
vertebrae and graft material in place while they permanently fuse
together.
[0007] One typical fusion procedure is achieved by inserting a
"cage" that maintains the space usually occupied by the disc to
prevent the vertebrae from collapsing and impinging the nerve
roots. The cage is used in combination with bone graft material
(either autograft or allograft) such that the two vertebrae and the
graft material will grow together over time forming bridging bone
between the two vertebrae. The fusion process typically takes 6-12
months after surgery. During in this time external bracing
(orthotics) may be required. External factors such as smoking,
osteoporosis, certain medications, and heavy activity can prolong
or even prevent the fusion process. If fusion does not occur,
patients may require reoperation.
[0008] One known fusion cage is described in U.S. Pat. No.
4,904,261 and includes a horseshoe shaped body. This type cage is
currently available in PEEK (polyetheretherketone). PEEK is used
because it does not distort MRI and CT images of the vertebrae.
However, PEEK is a material that does not allow bone to attach.
Thus, fusion with a PEEK cage requires bridging bone to grow
through the holes in the cage to provide stabilization.
[0009] It would be desirable to achieve immobilization of the
vertebrae and maintain spacing between the adjacent vertebrae
without the associated patient discomfort and long recovery time of
traditional interbody fusion which may require immobilization for
several months.
[0010] Another problem associated with the typical fusion procedure
is the subsidence of the cage into the vertebral body. The typical
fusion cage is formed with a large percentage of open space to
allow the bone to grow through and form the bridging bone which
immobilizes the discs. However, the large amount of open space
means that the load on each segment of the cage is significantly
higher than if the cage surface area was larger. This results in
the cage subsiding or sinking into the bone over time causing the
disc space to collapse. In addition, the hard cortical bone on the
outer surface of the vertebral body that transfers load to the
interbody cage or spacer is often scraped, punctured or otherwise
damaged to provide blood to the interbody bone graft to facilitate
bone growth. This damage to the bone used to promote bone growth
can also lead to subsidence.
[0011] The U.S. Food and Drug Administration approved the use of a
genetically engineered protein, or rhBMP-2, for certain types of
spine fusion surgery. RhBMP-2 is a genetically engineered version
of a naturally occurring protein that helps to stimulate bone
growth, marketed by Medtronic Sofamor Danek, Inc. as InFUSE.TM.
Bone Graft. When InFUSE.TM. is used with the bone graft material it
eliminates the need for painful bone graft harvesting and improves
patients' recovery time. However, InFUSE.TM. adds significantly to
the cost of a typical fusion surgery. Additionally, even with the
bone graft and InFUSE.TM. bone may fail to grow completely between
the two vertebrae or the cage may subside into the vertebrae such
that the fusion fails to achieve its purpose of maintaining disc
height and preventing motion.
[0012] In an attempt to treat disc related pain without fusion and
to maintain motion, an alternative approach has been developed, in
which a movable, implantable, artificial intervertebral disc (or
"disc prosthesis") is inserted between two vertebrae. A number of
different artificial intervertebral discs are currently being
developed. For example, U.S. Patent Application Publication Nos.
2005/0021146, 2005/0021145, and 2006/0025862, which are hereby
incorporated by reference in their entirety, describe artificial
intervertebral discs. Other examples of intervertebral disc
prostheses are the LINK SB CHARITLE.TM. disc prosthesis (provided
by DePuy Spine, Inc.) the MOBIDISK.TM. disc prosthesis (provided by
LDR Medical), the BRYAN.TM. cervical disc prosthesis (provided by
Medtronic Sofamor Danek, Inc.), the PRODISC.TM. disc prosthesis or
PRODISC-C.TM. disc prosthesis (from Synthes Stratec, Inc.), the
PCM.TM. disc prosthesis (provided by Cervitech, Inc.), and the
MAVERICK.TM. disc prosthesis (provided by Medtronic Sofomor Danek).
Although existing disc prostheses provide advantages over
traditional treatment methods, many patients are not candidates for
an artificial disc due to facet degeneration, instability, poor
bone strength, previous surgery, multi-level disease, and pain
sources that are non-discogenic.
[0013] Therefore, a need exists for an improved spacer and method
for spanning a space and maintaining disc spacing between two
vertebrae after removal of an intervertebral disc. Ideally, such
improved method and spacer would avoid the need for growth of
bridging bone across the intervertebral space.
BRIEF SUMMARY OF THE INVENTION
[0014] Embodiments of the present invention provide a rigid
intervertebral spacer and methods of spanning a space formed upon
removal of an intervertebral disc.
[0015] In accordance with one aspect of the present invention, a
method of spanning a space formed by upon removal of an
intervertebral disc includes the steps of performing a discectomy
to remove disc material between two adjacent vertebral bodies;
placing an intervertebral spacer between the two adjacent vertebral
bodies; and maintaining the disc space between the two adjacent
vertebral bodies with the intervertebral spacer without the use of
bone graft or bridging bone. The spacer includes two end plates,
each end plate having a metallic vertebral body contacting surface
and an inner surface, and a connector interconnecting the inner
surfaces of the two end plates in a rigid manner which limits
motion between the plates to less than a total of 5 degrees. The
vertebral body contacting surfaces of the end plates have no holes
therein or have holes which cover less than 40 percent of the
vertebral body contacting surface.
[0016] In accordance with another aspect of the present invention,
an intervertebral spacer for spanning a space formed by upon
removal of an intervertebral disc includes two end plates sized and
shaped to fit within an intervertebral space and a connector
interconnecting the inner surfaces of the two end plates in a rigid
manner which limits motion between the plates to less than a total
of 5 degrees. Each end plate has a metallic vertebral contacting
surface and an inner surface and the vertebral body contacting
surfaces of the end plates have no holes therein or have holes
which cover less than 40 percent of the vertebral body contacting
surfaces.
[0017] In accordance with a further aspect of the invention, a
method of performing an anterior/posterior fusion comprises
performing a discectomy to remove disc material between two
adjacent vertebral bodies; placing an intervertebral spacer between
the two adjacent discs; maintaining the disc space between the two
adjacent discs with the intervertebral spacer; and posteriorly
placing a stabilization system to fix the angle between the
vertebral bodies. The spacer includes two end plates each having a
metallic vertebral contacting surface and an inner surface, and a
rigid connector interconnecting the inner surfaces of the two end
plates. The vertebral body contacting surfaces of the end plates
have no holes therein or have holes which cover less than 40
percent of the vertebral body contacting surfaces.
[0018] In accordance with another aspect of the invention, a fusion
system includes an intervertebral spacer and a posteriorly placed
stabilization system including at least two screws configured to be
placed into the vertebral bodies and at least one connector there
between, The intervertebral spacer includes two end plates sized
and shaped to fit within an intervertebral space, each end plate
having a vertebral contacting surface an inner surface and a rigid
connector interconnecting the inner surfaces of the two end plates.
The vertebral body contacting surfaces of the end plates have no
holes therein or have holes which cover less than 40 percent of the
vertebral body contacting surfaces.
[0019] In accordance with an additional aspect of the invention, a
fusion spacer includes a rigid spacer body sized and shaped to fit
within an intervertebral space between two vertebral bodies, the
body having two opposed metallic vertebral contacting surfaces; at
least one fin extending from each of the vertebral contacting
surfaces, the fins configured to be positioned within slots cut
into the two vertebral bodies; and a plurality of serrations on the
vertebral contacting surfaces. Holes, if present, cover less than
40 percent of the entire vertebral body contacting surfaces.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a perspective view of an intervertebral spacer
according to one embodiment of the present invention;
[0021] FIG. 2 is a cross sectional side view of the intervertebral
spacer of FIG. 1;
[0022] FIG. 3 is a top view of the intervertebral spacer of FIG.
1;
[0023] FIG. 4 is a bottom view of the intervertebral spacer of FIG.
1;
[0024] FIG. 5 is a perspective view of an intervertebral spacer
according to another embodiment of the present invention;
[0025] FIG. 6 is a perspective view of an intervertebral spacer
according to an embodiment with added screw fixation; and
[0026] FIG. 7 is a perspective view of a further intervertebral
spacer with added screw fixation.
DETAILED DESCRIPTION OF THE INVENTION
[0027] Various embodiments of the present invention generally
provide for an intervertebral spacer having upper and lower plates
connected by a central connector which is substantially rigid. The
intervertebral spacer according to the present invention can
maintain disc height and prevent subsidence with a large vertebral
body contacting surface area while substantially reducing recovery
time by eliminating the need for bridging bone. The fusion spacer
described herein is designed particularly for patients who are not
candidates for total disc replacement.
[0028] One example of an intervertebral spacer 10 for maintaining
disc height between two adjacent vertebral discs is shown in FIG.
1. The spacer includes two end plates 20, 22, each end plate having
a vertebral contacting surface 24 and an inner surface 26, and a
connector 30 interconnecting the inner surfaces of the two end
plates in a substantially rigid manner. The intervertebral spacer
10 when implanted between two vertebral discs maintains a desirable
disc space between the two adjacent discs similar to that provided
by a natural disc and eliminates the long recovery time required to
grow bridging bone which is required in the traditional fusion
surgery.
[0029] Although the connector 30 has been shown as circular in
cross section, other shapes may be used including oval, elliptical,
or rectangular. Although the connector has been shown as a solid
member connecting the plates 20, 22 in the center of the plates one
or more connectors may be provided in other configurations and at
other locations. By way of example, a connector may be the same or
substantially the same diameter and shape as the plate, as in FIGS.
6 and 7. Alternatively, multiple connectors can be arranged in a
pattern, such as a rectangular pattern, or a hollow cylindrical
connector can be used.
[0030] In some embodiments, the outer surface 24 is planar.
Oftentimes, the outer surface 24 will include one or more surface
features and/or materials to enhance attachment of the spacer 10 to
vertebral bone. For example, as shown in FIG. 2, the outer surface
24 may be machined to have serrations 40 or other surface features
for promoting adhesion of the plates 20, 22 to a vertebra. In the
embodiments shown, the serrations 40 are pyramid shaped serrations
extending in mutually orthogonal directions and arranged on
opposite sides of a fin 50. The serrations 40 may also be disposed
in a region between fins 52 when the outer surface 24 has two fins.
Other geometries such as teeth, grooves, ridges, pins, barbs or the
like would also be useful in increasing fixation of the spacer 10
to the adjacent vertebral bodies. When the bone integration
structures are ridges, teeth, barbs or similar structures, they may
be angled to ease insertion and prevent migration. These bone
integration structures can be used to precisely cut the bone during
implantation to cause bleeding bone and encourage bone integration.
Additionally, the outer surface 24 may be provided with a rough
microfinish formed by blasting with aluminum oxide microparticles
or the like to improve bone integration. In some embodiments, the
outer surface may also be titanium plasma sprayed or HA coated to
further enhance attachment of the outer surface 24 to vertebral
bone.
[0031] The outer surface 24 may also carry one or more upstanding
fins 50, 52 extending in an anterior-posterior direction. The fins
50, 52 are configured to be placed in slots cut into the vertebral
bodies. Preferably, the fins 50, 52 each have a height greater than
a width and have a length greater than the height. In one
embodiment, the fins 50, 52 are pierced by transverse holes 54 for
bone ingrowth. The transverse holes 54 may be formed in any shape
and may extend partially or all the way through the fins 50, 52. In
alternative embodiments, the fins 50, 52 may be rotated away from
the anterior-posterior axis, such as in a lateral-lateral
orientation, a posterolateral-anterolateral orientation, or the
like to accommodate alternate implantation approaches.
[0032] The fins 50, 52 provide improved attachment to the bone and
prevent rotation of the plates 20, 22 in the bone. In some
embodiments, the fins 50, 52 may extend from the surface 24 at an
angle other than 90.degree.. For example on one or more of the
plates 20, 22 where multiple fins 52 are attached to the surface 24
the fins may be canted away from one another with the bases
slightly closer together than their edges at an angle such as about
80-88 degrees. The fins 50, 52 may have any other suitable
configuration including various numbers, angles and curvatures, in
various embodiments. In some embodiments, the fins 50, 52 may be
omitted altogether. The embodiment of FIG. 1 illustrates a
combination of a first plate 20 with a single fin 50 and a second
plate 22 with a double fin 52. This arrangement is useful for
double level disc replacements and utilizes offset slots in the
vertebral body to prevent the rare occurrence of vertebral body
splitting by avoiding cuts to the vertebral body in the same plane
for multi-level implants.
[0033] The spacer 10 has been shown with the fins 50, 52 as the
primary fixation feature, however, the fins may also be augmented
or replaced with one or more screws extending through the plates
and into the bone. For example in the spacer 10 of FIG. 1 the upper
fin 50 may be replaced with a screw while the two lower fins 52
remain. The plates 20, 22 can be provided with one or a series of
holes to allow screws to be inserted at different locations at the
option of the surgeon. However, the holes should not be of such
size or number that the coverage of the plate 20, 22 is decreased
to such an extent that subsidence occurs. When one or more screws
are provided, they may incorporate a locking feature to prevent the
screws from backing out. The screws may also be provided with a
bone integration coating.
[0034] The upper and lower plates 20, 22 and connector 30 may be
constructed from any suitable metal, alloy or combination of metals
or alloys, such as but not limited to cobalt chrome alloys,
titanium (such as grade 5 titanium), titanium based alloys,
tantalum, nickel titanium alloys, stainless steel, and/or the like.
They may also be formed of ceramics, biologically compatible
polymers including PEEK, UHMWPE (ultra high molecular weight
polyethlyne) or fiber reinforced polymers. However, the vertebral
contacting surfaces 24 are formed of a metal or other material with
good bone integration properties. The metallic vertebral body
contacting surfaces 24 may be coated or otherwise covered with the
metal for fixation. The plates 20, 22 and the connector 20 may be
formed of a one piece construction or may be formed of more than
one piece, such as different materials coupled together. When the
spacer 10 is formed of multiple materials these materials are fixed
together to form a unitary one piece spacer structure without
separately moving parts.
[0035] Different materials may be used for different parts of the
spacer 10 to optimize imaging characteristics. For example, the
plates may be formed of titanium while the connector is formed of
cobalt chromium alloy for improved imaging of the plates. Cobalt
chrome molybdenum alloys when used for the plates 20, 22 may be
treated with aluminum oxide blasting followed by a titanium plasma
spray to improve bone integration. Other materials and coatings can
also be used such as titanium coated with titanium nitride,
aluminum oxide blasting, HA (hydroxylapatite) coating, micro HA
coating, and/or bone integration promoting coatings. Any other
suitable metals or combinations of metals may be used as well as
ceramic or polymer materials, and combinations thereof. Any
suitable technique may be used to couple materials together, such
as snap fitting, slip fitting, lamination, interference fitting,
use of adhesives, welding and/or the like.
[0036] As shown in FIG. 5, some limited holes 60 may also be
provided in the plates 20, 22 to allow bone in growth. Holes
provided in a typical fusion spacer provide a spacer with little
structural support and maximum area for bone growth. Thus, the load
transferred across the disc space per unit area of spacer is quite
high resulting in possible subsidence of the typical spacer. In the
spacer 10 of the present invention, the load transfer is spread
across a larger area. If the outer surfaces 24 have holes 60
therein, the holes will cover less than 40 percent of the outer
surface 24 which contacts the bone to prevent subsidence of the
plates into the vertebral bodies. Preferably the holes will cover
less than 25 percent, and more preferably less than 10 percent of
the outer bone contacting surfaces. At the option of the surgeon,
when the small holes 60 are present in the plates 20, 22, bone
graft can be placed in the space between the inner surfaces 26 of
the plates to encourage bone to grow through the plates. The holes
60, when present can take on a variety of shapes including
circular, as shown, rectangular, polygonal or other irregular
shapes. The holes 60 may extend through the various parts of the
spacer including through the connector or through the fins. The
holes 60 may change shape or size as they pass through portions of
the spacer, for example, holes through the plates and the connector
may taper to a smaller interior diameter.
[0037] The typical fusion spacer requires bleeding bone to
stimulate the growth of bridging bone. In this typical method, the
cortical endplates are damaged purposefully to obtain bleeding by
rasping or cutting the bone. This damage weakens the bone and can
cause subsidence of the spacer. The spacer 10 described herein does
not rely on bridging bone and does not require damaging the bone to
cause bleeding. The spacer 10 can be implanted after simply
cleaning the disc space and cutting slots into the vertebral
endplates configured to receive the fins 50, 52. The rest of the
endplates remain undamaged, providing better support and disc
height maintenance.
[0038] FIG. 6 shows another embodiment of a spacer 100 having a
single fin 50 on the top and bottom and two fixation screws 70
extending at an angle of about 30 to about 60 degrees with respect
to the vertebral body contacting surfaces 24 of the spacer. The
spacer 100 also includes a connector 30 between the vertebral body
contacting surfaces 24 which is formed in one piece with the upper
and lower plates. The fixation screws 70 can include a locking
mechanism, such as a locking thread or a separate locking member
which is inserted into the screw holes 80 after the screws are
inserted to prevent backing out of the screws.
[0039] FIG. 7 illustrates an alternative embodiment of a spacer 110
having a single superior fin 50, two inferior fins 52, and three
alternating holes 80 for receiving bone screws (not shown). The
spacer 110 has multiple fixation structures to provide the patient
near immediate mobility after the fusion procedure. As an
alternative to the alternating angled holes 80, the spacer 110 can
be formed with an anterior flange extending from the top and the
bottom at the anterior side of the plate. This optional flange can
include one or more holes for receiving bone screws placed
laterally. The laterally placed bone screws can prevent
interference in the event of multilevel fusions and are
particularly useful for a cervical fusion where space is more
limited.
[0040] The intervertebral spacer 10 shown herein is configured for
placement in a lumbar intervertebral space from an anterior
approach. It should be understood that all approaches can be used
including PLIF (posterior lumbar interbody fusion), TLIF
(transverse lumbar interbody fusion), XLIF (Lateral extracavitary
interbody fusion), ALIF (anterior lumbar interbody fusion),
trans-sacral, and other approaches. The shape of the intervertebral
spacer would be modified depending on the approach. For example,
for a posterior approach, the spacer may include two separate
smaller spacers which are either positioned separately side-by-side
in the intervertebral space or two spacers which are joined
together once inside the intervertebral space. For a lateral
approach, the intervertebral spacer may be formed in a more
elongated, kidney bean or banana shape with a transversely oriented
fin.
[0041] The spacers 10, 100 can be provided in different sizes, with
different plate sizes, angles between plates, lordosis angles, and
heights for different patients or applications. The spacers 10, 100
are primarily designed for use in the lumbar spine, however the
spacers may also be used for fusions of the cervical spine. In one
variation, the height of the spacer can be adjustable, such as by
rotating an adjustment screw in the connector 30 before or after
implantation. The spacers preferably are sized to provide
substantial coverage of the vertebral surfaces. For example in an
anterior procedure, the plates are sized to cover at least 50
percent of the vertebral surface, and preferably cover at least 70
percent of the vertebral surface. In posterior or lateral
procedures the coverage of the vertebral surface may be somewhat
smaller due to the small size of the access area, i.e. the
posterior or lateral spacers may cover about 40 percent or more of
the vertebral surface with a one or two part spacer, and preferably
at least 50 percent of the vertebral surface.
[0042] The size of the intervertebral spacers 10, 100, 110 can also
be described in terms of the amount of the volume of the
intervertebral space occupied by the spacer. According to a
preferred embodiment, the total volume of the intervertebral spacer
selected for a particular intervertebral space fills at least 50
percent of the volume of the space available between the adjacent
vertebrae. More preferably, the volume of the spacer is at least 70
percent of the volume of the intervertebral space. The volume of
the intervertebral space is defined as the volume of the space
between the vertebrae when the vertebrae are distracted to a normal
physiologic position for the particular patient without over or
under distracting. The size of the intervertebral spacers 10, 100,
110 can also be determined by the amount of the support provided to
the ring of cortical bone surrounding each vertebrae. The cortical
bone surrounds a more spongy cancellous. Preferably, the
intervertebral spacer is selected to support at least 75 percent of
the diameter of the ring of cortical bone.
[0043] One common fusion procedure, referred to as an
anterior/posterior fusion, uses of one or more fusion cages to
maintain the disc space while bridging bone grows and also uses a
system of posterior screws and rods for further stabilization.
Fusing both the front and back provides a high degree of stability
for the spine and a large surface area for the bone fusion to
occur. Also, approaching both sides of the spine often allows for a
more aggressive reduction of motion for patients who have deformity
in the lower back (e.g. isthmic spondylolisthesis).
[0044] According to a method of the present invention, the anterior
approach is performed first by removing the disc material and
cutting the anterior longitudinal ligament (which lays on the front
of the disc space). The spacer is positioned anteriorly and then
the patient is turned over for the implantation of a posterior
stabilization system. The intervertebral spacers of the present
invention may be used in combination with a posterior stabilization
system, dynamic rod stabilization system, or interspinous spacer to
achieve the anterior/posterior fusion.
[0045] In another example, a posterior intervertebral spacer formed
in two parts can be used with a posterior stabilization system
including screws and rods. This system provides the advantage of
maintenance of disc height and stabilization with an entirely
posterior approach.
[0046] While the exemplary embodiments have been described in some
detail, by way of example and for clarity of understanding, those
of skill in the art will recognize that a variety of modifications,
adaptations, and changes may be employed. Hence, the scope of the
present invention should be limited solely by the appended
claims.
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