U.S. patent application number 10/350834 was filed with the patent office on 2003-06-19 for conically shaped anterior fusion cage and method of implantation.
This patent application is currently assigned to Howmedica Osteonics Corp.. Invention is credited to Jayne, Kirk, Klyce, Henry A., Pavlov, Paul W., Winslow, Charles J..
Application Number | 20030114854 10/350834 |
Document ID | / |
Family ID | 23187276 |
Filed Date | 2003-06-19 |
United States Patent
Application |
20030114854 |
Kind Code |
A1 |
Pavlov, Paul W. ; et
al. |
June 19, 2003 |
Conically shaped anterior fusion cage and method of
implantation
Abstract
A fusion cage for promoting fusion with one or more bone
structures including a conically-shaped cage body including a
proximal end having a first diameter and a distal end having a
second diameter, wherein the first diameter of the proximal end is
greater than the second diameter of the distal end.
Inventors: |
Pavlov, Paul W.; (Nijmegen,
NL) ; Winslow, Charles J.; (Walnut Creek, CA)
; Jayne, Kirk; (Alameda, CA) ; Klyce, Henry
A.; (Piedmont, CA) |
Correspondence
Address: |
LERNER, DAVID, LITTENBERG,
KRUMHOLZ & MENTLIK
600 SOUTH AVENUE WEST
WESTFIELD
NJ
07090
US
|
Assignee: |
Howmedica Osteonics Corp.
Allendale
NJ
|
Family ID: |
23187276 |
Appl. No.: |
10/350834 |
Filed: |
January 24, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10350834 |
Jan 24, 2003 |
|
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|
09358188 |
Jul 20, 1999 |
|
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|
09358188 |
Jul 20, 1999 |
|
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|
08781525 |
Jan 9, 1997 |
|
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|
08781525 |
Jan 9, 1997 |
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08306879 |
Sep 15, 1994 |
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Current U.S.
Class: |
606/249 ;
606/86A; 606/907; 606/909; 623/17.11; 623/17.16 |
Current CPC
Class: |
A61F 2002/30593
20130101; A61F 2/4601 20130101; A61F 2002/30787 20130101; A61F
2002/30617 20130101; A61F 2002/30968 20130101; A61F 2002/448
20130101; A61F 2002/30797 20130101; A61F 2002/3085 20130101; A61F
2/442 20130101; A61F 2002/30785 20130101; A61F 2002/30154 20130101;
A61F 2250/0039 20130101; A61B 17/8883 20130101; A61F 2/4611
20130101; A61F 2310/00023 20130101; A61F 2002/30873 20130101; A61F
2002/30143 20130101; A61B 17/862 20130101; A61F 2002/3021 20130101;
A61F 2002/30813 20130101; A61F 2/30744 20130101; A61F 2002/30235
20130101; A61F 2220/0033 20130101; A61F 2250/0097 20130101; A61F
2230/0069 20130101; A61F 2/446 20130101; A61F 2002/30121 20130101;
A61F 2002/4627 20130101; A61F 2230/0006 20130101; A61F 2002/30863
20130101; A61F 2/4603 20130101; A61F 2220/0025 20130101; A61F
2002/30774 20130101; A61F 2230/0021 20130101; A61F 2002/2835
20130101; A61F 2002/30327 20130101; A61F 2002/30217 20130101; A61F
2/4637 20130101; A61F 2002/3082 20130101; A61F 2230/0067 20130101;
A61F 2002/30405 20130101; A61F 2002/30777 20130101; A61F 2002/30331
20130101; A61F 2230/0017 20130101 |
Class at
Publication: |
606/61 ;
623/17.11; 623/17.16 |
International
Class: |
A61B 017/70 |
Claims
1. A fusion cage for promoting fusion with one or more bone
structures comprising: a conically-shaped cage body including a
proximal end having a first diameter and a distal end having a
second diameter, wherein said first diameter of said proximal end
is greater than said second diameter of said distal end.
2. The fusion cage as claimed in claim 1, wherein said distal end
is rounded so as to facilitate insertion of said fusion cage
relative to one or more bone structures.
3. The fusion cage as claimed in claim 1, wherein said
conically-shaped cage body has a conically-shaped outer
surface.
4. The fusion cage as claimed in claim 3, wherein said
conically-shaped outer surface of said cage body has continuous
threads.
5. The fusion cage as claimed in claim 3, wherein said
conically-shaped outer surface has at least one flute formed
therein.
6. The fusion cage as claimed in claim 5, wherein said flute
extends from said distal end toward said proximal end of said cage
body.
7. The fusion cage as claimed in claim 6, wherein said flute is
formed in the rounded distal end of said cage body.
8. The fusion cage as claimed in claim 1, wherein said cage body
further comprises: an internal cavity surrounded by said
conically-shaped outer surface of said cage body; and a plurality
of apertures formed through said conically-shaped body for
providing communication between said conically-shaped outer surface
and said internal cavity.
9. The fusion cage as claimed in claim 8, wherein said apertures
increase in size from said distal end to said proximal end of said
cage body.
10. The fusion cage as claimed in claim 8, further comprising a
bone-growth inducing material disposed in said internal cavity of
said cage body.
11. The fusion cage as claimed in claim 10, wherein said
bone-growth inducing material includes bone.
12. The fusion cage as claimed in claim 10, wherein said proximal
end includes an opening in communication with said internal cavity
of said cage body so that said bone-growth inducing material may be
disposed in said internal cavity of said cage body.
13. The fusion cage as claimed in claim 12, further comprising an
end cap covering said opening for retaining said bone-growth
inducing material in said internal cavity.
14. The fusion cage as claimed in claim 13, wherein said opening at
the proximal end of said cage body includes internal threads and
said end cap includes external threads adapted for meshing with the
internal threads of said opening at said proximal end.
15. A fusion cage for promoting fusion with one or more bone
structures comprising: a conically-shaped cage body including a
proximal end having a first diameter and a distal end having a
second diameter, wherein said first diameter of said proximal end
is greater than said second diameter of said distal end; said cage
body defining a conically-shaped outer surface surrounding an
internal cavity of said cage body; and a bone-growth inducing
material disposed in said internal cavity of said cage body.
16. The fusion cage as claimed in claim 15, further comprising a
plurality of apertures formed through said conically-shaped body
for providing communication between said conically-shaped outer
surface and said internal cavity.
17. The fusion cage as claimed in claim 16, wherein said apertures
increase in size from said distal end to said proximal end of said
cage body.
18. The fusion cage as claimed in claim 17, wherein said
bone-growth inducing material includes bone.
19. The fusion cage as claimed in claim 15, wherein said proximal
end of said cage body includes an opening in communication with
said internal cavity of said cage body so that said bone-growth
inducing material may be disposed in said internal cavity of said
cage body.
20. The fusion cage as claimed in claim 19, wherein said opening at
the proximal end of said cage body includes internal threads and
said end cap includes external threads adapted for meshing with the
internal threads of said proximal end opening.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] The present invention is a continuation of application Ser.
No. 09/358,188, filed Jul. 20, 1999, which is a continuation of
application Ser. No. 08/781,525 filed Jan. 9, 1997, which is a file
wrapper continuation of application Ser. No. 08/306,879 filed Dec.
15, 1994 (now abandoned). The disclosures of the '188, '525 and
'879 applications are hereby incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] This invention is directed to devices and methods for
facilitating the fusing of bone structures and more particularly
the fusing together of adjacent vertebral bodies or bone
structures.
[0003] Technical literature and patent documents disclose a number
of devices and methods for fusing bones together. One such device
which has proven to be successful is disclosed in U.S. Pat. No.
4,961,740, entitled "V-THREAD FUSION CAGE AND METHOD OF FUSING A
BONE JOINT," which patent has been assigned the present assignee
and which patent is incorporated herein by reference. The
referenced patent discloses a fusion cage which is preferably
cylindrical and has threads formed as part of the external
cylindrical surface. The fusion cage defines an internal cavity and
apertures through the wall of the cage which communicate the
external cylindrical surface with the internal cavity. The
apertures are formed in the valleys of the threads. Normally two
such cages are used to stabilized and fuse together adjacent
vertebral bodies or bone structures.
[0004] In practice, using a posterior approach, a patient's
vertebral bone structures are exposed and degenerate disk material
located between the vertebral bone structures is removed. A
threaded tap is used to tap complementary threads in the upper and
lower vertebral bone structures preparatory to the insertion of the
above fusion cage. Once such tapping has been accomplished, using
an introduction tool, the fusion cage is screwed into the space
between the adjacent vertebral bone structures. The threads bite
into the bone of the upper and lower vertebral bone structures,
stabilizing the bone structures, and preventing the fusion cage
from working out of this position due to patient movement.
Generally two such fusion cages are applied using this technique.
Once the two implants have been positioned, then bone growth
inducing substances, such as bone chips, are packed into the
internal cavity of-the fusion cages. These bone growth inducing
substances come into immediate contact with the bone from the
vertebral bone structures which project into the internal cavity
through the apertures. Such projection of bone is due to the fact
that the apertures are formed in the valleys of the external
threads of the fusion cage. Such immediate bone to bone contact
between the vertebral bone structures and the bone pack within the
fusion cages results in more rapid propagation of bone cells
between the adjacent vertebral bone structures and thus a more
rapid fusion of the adjacent vertebral bone structures.
SUMMARY OF THE INVENTION
[0005] The present invention is directed to a fusion cage which has
been designed to be implanted using an anterior approach to the
vertebral bone structures.
[0006] In a first embodiment of the present invention, the fusion
cage includes a conically-shaped cage body having a proximal end
and a distal end, said distal end having a diameter which is
smaller than the diameter of the proximal end. The distal end
further is rounded with for example a bull nose in order to
facilitate the insertion of the cage body relative to one or more
bone structures. The conically-shaped cage body is particularly
advantageous for use with an anterior approach to vertebral bone
structure fusion. This is due to the fact that the normal lordosis
of the vertebral bone structures defines a wedged-shape space for a
vertebral disk between, for example, lumbar vertebrae. Accordingly,
the conically-shaped body cage can be sized and selected in order
to maintain or enlarge upon the normal lordosis.
[0007] In a second embodiment of the present invention, a fusion
cage includes a conically-shaped cage body having a proximal end
and a distal end with the distal end having a diameter which is
smaller than the diameter of the proximal end. The conically-shaped
cage body has a conically-shaped outer surface and at least one
flute formed in the conically-shaped outer surface. The flute acts
as a relief much as the flute placed on self-tapping screws in
order to facilitate the insertion of the fusion cage using a
twisting motion between two vertebral bone structures.
[0008] In a third embodiment of the invention, a fusion cage
includes a conically-shaped cage body having a proximal end and a
distal end, the distal end having a diameter which is smaller than
the diameter of the proximal end. The conically-shaped cage body
has a conically-shaped outer surface and a plurality of threads
formed as part of the conically-shaped outer surface. The plurality
of threads allows the cage body to be inserted using an anterior
approach. Due to the fact that the cage body is conically-shaped,
the requirement for pretapping the vertebral bone structures to
receive the fusion cage is eliminated with the fusion cage being
self-tapping. Also the cage gradually spreads apart the vertebral
bone structures as the cage is inserted in order to regain or
enlarge the natural lordosis of the adjacent vertebral bone
structures. As with other embodiments of the present invention,
flutes can be provided through the plurality of threads in order to
allow for enhanced thread tapping by the cage and for a smoother
insertion of the fusion cage between the vertebral bone structures.
Preferably two or three flutes would be formed spaced about the
fusion cage in order that one flute would be engaging with or
adjacent to an upper vertebral bone structures with another flute
being engaging with or adjacent to a lower vertebral bone
structure. Such a relationship maintains alignment of the fusion
cage and prevent wandering as the fusion cage is introduced between
the two vertebral bone structures. Without two or more flutes,
wandering might occur due to the fact that the threads are only
substantially engaged with the vertebral bone structures and not
with the disk material between the vertebral bone structures, which
disk material does not provide support to the threads.
[0009] In a further aspect of the invention, any of the above
embodiments can be provided with a plurality of apertures through
the fusion cage and an internal cavity with the apertures
communicating between the internal cavity and the external surface
of the fusion cage. Bone growth inducing substances, such as bone
chips, can be packed into the internal cavity either before the
fusion cage is inserted or after the fusion cage has reached a
final insertion position. The bone chips come in contact with the
vertebral bone structures through the apertures in order to
facilitate fusion between the adjacent vertebral bone
structures.
[0010] In another aspect of the invention which can be included in
any of the above embodiments, the cage body can have a round or
bull nose distal end with one or more flutes formed in the round or
bull nose distal end in order to enhance the self-tapping nature of
the fusion cage.
[0011] In yet another aspect of the invention, introduction tools
allow the fusion cage to be accurately positioned between the
vertebral bone structures.
[0012] The method of the present invention affords access to
adjacent vertebral bone structures using an anterior approach and
procedure. Such anterior approach and procedure can be preferably
performed laparoscopically using an introduction set including a
cannula. A laparoscopic procedure is minimally invasive as the
abdomen muscle tissue can be spread using a set of cannula of
increasing size and a small opening thereby developed through which
a fusion cage can be inserted. Such a procedure is less traumatic
to the tissue than an alternate anterior approach and procedure,
also known as an anterior lumbar interbody fusion, where an
incision, perhaps up to five inches long is made, through the
abdomen muscle tissue. It is to be understood however that either
anterior approach and procedure can be used with the fusion cage
and fall within the scope of the invention.
[0013] After such access, using preferably a laparoscopic
technique, degenerate disk material can be removed and, using a
cannula and insertion tool, an appropriately shaped fusion cage can
be screwed into place between the vertebral bone structures in
order to stabilize the vertebral bone structures and allow for
fusion. Either preparatory to insertion of the fusion cage or after
it has been inserted, bone chips or other bone growth inducing
substances can be inserted into the fusion cage to promote bone to
bone contact and subsequent fusion.
[0014] It is to be understood that although the above embodiments
have been described with respect to the fusion of adjacent
vertebral bodies or bone structures, that the present invention can
be used to fuse together a variety of bone structures, in addition
to being fused to one bone structure and used as, for example, a
base for an implant.
[0015] Other objects and advantages of the invention can be
obtained through a review of the specification and the figures.
BRIEF DESCIPTION OF THE FIGURE
[0016] FIG. 1 is a partially sectional side view of an embodiment
of the fusion cage of the invention.
[0017] FIG. 2 depicts a left end (distal end) view of the fusion
cage of FIG. 1.
[0018] FIG. 3 depicts a right end (proximal end) view of the fusion
cage of FIG. 1.
[0019] FIG. 4 depicts a view through line 4-4 of the fusion cage of
FIG. 1.
[0020] FIG. 5 depicts fusion cage of FIG. 1 in conjunction with an
introduction tool.
[0021] FIG. 6 depicts an alternative embodiment of the introduction
tool.
[0022] FIGS. 7, 8, and 9 depict progressive stages in the method of
inserting the fusion cage between adjacent vertebral bone
structures.
[0023] FIG. 10 depicts a side view of an alternative embodiment of
the fusion cage of the invention.
[0024] FIG. 11 depicts the left end (distal end) view of the fusion
cage of FIG. 10.
[0025] FIG. 12 depicts the right end (proximal end) view of the
fusion cage of FIG. 10.
[0026] FIG. 13 depicts a side view of yet another embodiment of the
fusion cage of the present invention.
[0027] FIG. 14 depicts a left distal end (distal end) view of the
fusion cage of the invention of FIG. 13.
[0028] FIG. 15 depicts a right end (proximal end) view of the
fusion cage of the invention of FIG. 13.
[0029] FIG. 16 depicts a sectional view taken through line 16-16 of
FIG. 13.
DETAILED DESCRIPTION
[0030] With respect to the figures in a particular FIG. 1, a side
view of the preferred embodiment of the fusion cage 20 is depicted.
Fusion cage 20 includes a fusion cage body 22 which in this
preferred embodiment is provided in the shape of a cone. Fusion
cage 20 includes a distal end 24 and a proximal end 26. The distal
end 24 in a preferred embodiment is rounded or bull nosed in order
to facilitate the insertion of the fusion cage 20 relative to one
or more bone structures. The proximal end 26 includes an opening 28
which communicates with an internal cavity 30 defined by the fusion
cage 20. The opening 28 in a preferred embodiment is threaded so
that it can receive an end cap or plug 32 (FIG. 5). End cap 32 is
used to close off the proximal end 26 and retain bone growth
inducing substances packed therein as described hereinbelow. As can
be seen in FIG. 5, end cap 32 includes a threaded bore 34 which is
designed to receive an insertion tool. The threaded bore 34 has an
initial unthreaded, hex-shaped section 35 which can be used with a
socket wrench to tightly position end cap 32 in opening 28. The
proximal end 26 further define first and second peripheral
indentations 36, 38. These peripheral indentations 36, 38 receive
tangs from an insertion tool as described hereinbelow for
facilitating the insertion of the fusion cage 20.
[0031] A plurality of threads 40 is defined as part of the outer
cylindrical surface 42 of the body 22. It is to be understood that
the plurality of threads can be replaced with a plurality of
interrupted or discrete threads or a plurality of projections,
ridges, protrusions, barbs, or spurs and be within the spirit and
scope of the invention.
[0032] The rounded distal end 24, and at least some of threads 40
defined flutes or relief grooves 42, 44, and 46. (FIGS. 1, 2.) In a
preferred embodiment, flutes 42, 44, and 46 meet at a central point
48 of the distal end 24 on the longitudinal axis 50 of the fusion
cage 20. In other embodiments the flutes can be smaller and not
extend all the way to the central point 48 on the longitude axis
50. Still in other embodiments, the flutes can be eliminated from
the distal end 24 and such embodiments are still within the spirit
and scope of the invention.he flutes extend from the distal end 24
toward the proximal end 26 as shown in FIG. 1 with respect to flute
42. These flutes are defined by the sections 52 which are removed
from the threads. In a preferred embodiment, the flutes become
narrower as they approach the proximal end 26 due to the fact that
thread relief for purposes of self-tapping becomes less important
as the cage reaches a final resting position. As shown in other
embodiments, the flutes can be deeper and extend from the distal
end completely to the proximal end. Still further in other
embodiments the flutes can be confined to the first several threads
adjacent to the distal end and/or to just the distal end.
[0033] As can be seen in FIGS. 1, 4, a plurality of apertures 54
are provided through wall 56 of the fusion cage 20. In a preferred
embodiment, these apertures 54 are formed by broaching grooves 58
in the internal surface 60 of the internal cavity 30. The effect of
such broaching is to remove material from the valleys between the
threads 40, thus defining the aperture 54. The advantages of such
an arrangement are taught by the above-referenced U.S. Pat. No.
4,961,740, which patent is incorporated herein by reference and
allows for immediate bone to bone contact between the vertebral
bodies or bone structures and the bone packed within the internal
cavity 30 of the fusion cage 20.
[0034] The apertures 54 in a preferred embodiment increase in size
from smaller apertures closer to the distal end 24 to a larger
aperture closer to the proximal end 26. This increase in size
allows for more bone to bone contact. Alternatively in the
embodiment as shown in FIG. 1, all the apertures are of the same
size.
[0035] As can be seen in FIG. 4, the apertures are clustered about
a transverse axis 51, both at the upper and lower end of the axis.
This is so that in position, the apertures come into contact with
the upper and lower vertebral bone structures (FIG. 9) to encourage
bone growth through the fusion cage from the vertebral bone
structures. The lateral section of the fusion cage found along the
other transverse access 53 do not have apertures in order to
prevent growth of disk material which might interfere with the bone
fusing process.
[0036] A preferred embodiment of the conically-shaped fusion cage
20 includes a fusion cage which is 23 millimeters in length having
a distal end 24 with a diameter of 14 millimeters and a proximal
end 26 with a diameter of 18 millimeters. The cage body is a right
circular cone. The threads have a pitch of 300 and there are ten
threads per inch with a thread depth of 0.053 inches. Further the
cage is made of a titanium material. Preferably this and the other
disclosed fusion cages disclosed are machined. However, the
processes such as molding can be used to accomplished formation of
the fusion cages.
[0037] The cage is inserted between vertebral bodies using an
insertion tool 62 (FIG. 5). Insertion tool 62 includes an inner
handle 64 and an outer handle 66. The outer handle includes a bore
68 for receiving the inner handle 64. Handles 64, 66 include knobs
70, 72 respectively. The distal end of inner handle 64 defines a
threaded shaft 74, having a reverse thread to facilitate easy
removal, and the distal end of handle 66 define a cylindrical disk
76 which has first and second tangs 78, 80, projecting from the
peripheral edge of the cylindrical disk 76. These tangs 78, 80 are
designed to mate with the peripheral indentation 36, 38 of the
fusion cage 20. For purposes of inserting the fusion cage between
the vertebral bodies, the end cap 32 is inserted into the fusion
cage 20 as shown in FIG. 5. Then the threaded shaft 74 of the inner
handle is introduced into the threaded bore 34 of the end cap 32.
After this is accomplished, the outer handle 66 is slid over the
inner handle 64 and the tangs 78, 80 are positioned into engagement
with the indentations 36, 38. In this arrangement, the fusion cage
20 can be anteriorly inserted into the space between the vertebral
body structure using the insertion tool 62.
[0038] An alternative embodiment of the insertion tool is shown in
FIG. 6. In this figure, insertion tool 82 includes a handle 84 with
a knob 86. At the end of the insertion tool 82 distal from the knob
86 is a cylindrical disk 88 which has first and second tangs 90,
92, which have the same function as the above tangs 78, 80.
Extending from the center of the cylindrical disk 88 along the
centerline of the insertion tool 82 is a shaft 94 which has a ball
detent 96. For use with insertion tool 82, the -threaded bore 34 of
the end cap 32 would be replaced with a bore having a lip which
could engage with the ball detent 96 of the insertion tool 82.
[0039] The method for inserting the fusion cage 20 of FIG. 1 using
an anterior approach and procedure to the vertebral bodies is as
follows. It is to be understood that although the focus of this
discussion is on a laparoscopic procedure, that the anterior
approach and procedure can also include a more invasive procedure
where a long incision is made in the abdomen wall.
[0040] With an anterior approach, using an introduction set such as
described by way of example only, in U.S. Pat. No. 4,863,430,
entitled "INTRODUCTION SET WITH FLEXIBLE TROCAR WITH CURVED
CANNULA," which is incorporated by reference, but however with
larger diameter instruments, an amount of disk material is removed
between the two vertebral bodies or bone structures which are to be
fused together. This procedure is accomplished through a cannula
position adjacent to the vertebral bone structures. With the same
or a larger diameter cannula, the fusion cage 20 can be introduced
adjacent to the vertebral bone structures. In a first procedure,
the fusion cage is packed with bone growth substances and the end
cap 32 is affixed to the fusion cage 20. Insertion tool 62 is then
secured to the fusion cage 20 and the fusion cage is guided through
the cannula to a location adjacent to the upper and lower vertebral
body such as presented schematically in FIGS. 7, 8, 9, by upper
body 98 and lower body 100. In the initial position as shown in
FIG. 7, the fusion cage 20 is adjacent to the anterior surfaces
102, 104 of the vertebral bodies 98, 100. As the introduction tool
is turned, the threads 40 of the fusion cage 20 bite into the
vertebral bodies 98, 100. Further turning of the introduction tool
causes the fusion cage to move through the position shown in FIG. 8
to the final resting position shown in FIG. 9, where the distal end
24 is moved adjacent to the posterior sections 106, 108 of the
vertebral bone structures 98, 100. As this occurs, the fusion cage
20 increases the lordosis or spacing between the vertebral bodies,
basically distracting the vertebral bodies and causing the
vertebral bodies to pivot about the posterior sections 106, 108,
with such posterior sections acting like a hinge. It is noted that
most of the distraction occurs adjacent to the anterior sections,
but that distractions also occur at the posterior sections where
the hinged effect is exhibited. Preferably, the lordosis. is
increased over the normal lordosis in order to stabilize the
vertebral bone structures prior to fusion occurring. Stabilization
occurs due to the fact that increased lordosis places additional
stress on the anterior longitudinal ligaments which are part of the
anatomy holding the vertebral bodies in place.
[0041] Once the fusion cage 20 is appropriately positioned, the
handle 64 of the insertion tool 62 is unscrewed from the cap 32 and
the fusion handle 62 is pulled away from the fusion cage.
[0042] An alternative embodiment of a fusion cage 200 is shown in
FIGS. 10, 11, and 12. Fusion cage 200 includes a distal end 202 and
an a proximal end 204. Fusion cage 200 includes an internal cavity
206. End caps not shown can be used to close the ports 208, 210 of
distal and proximal ends 202, 204. A plurality of threads 212 are
defined on the external conical surface 214 of the fusion cage 200.
Defined by the threads 212 are first and second flutes 216, 218,
which in this embodiment extend from the distal end 202 to the
proximal end 204. These flutes provide thread relief allowing the
fusion cage 200 to be self-tapping.
[0043] The fusion cage 200 includes a plurality of elongated
apertures 220 which are formed through the side walls of a fusion
cage 200. The elongated apertures 202 are formed in such a way that
the internal conical surface 214 is spaced away from the internal
surface 224 of the internal cavity 206 by the thickness of the
sidewall 222.
[0044] A further embodiment of the invention is shown in FIGS. 13,
14, 15 and 16. In FIG. 16 the fusion cage 300 has distal and
proximal ends 302 and 304 respectively. The fusion cage 300 defines
an internal cavity 306, and ports 308 and 310 defined through the
distal and proximal ends 302 and 304 respectfully. A plurality of
thread 312 is defined as part of the external conical surface 314
of the fusion cage 200. First, second and third flutes 316, 318,
and 320, are defined in the threads 312 from the distal end 302 to
the proximal end 304. These flutes give the fusion cage 300 an
enhanced self-tapping advantage. These flutes are equally spaced
about the fusion cage 300 in a manner similar to the flutes of the
fusion cage embodiment 20 in FIG. 1.
[0045] A plurality of aperture 322 is provided through the external
conical surface 314 of the fusion cage 300 and through the side
wall 324 opening into the internal cavity 306. Accordingly, at the
location of the aperture 322 the external surface 314 is held away
from the internal surface 326 by the thickness of the side wall
324.
[0046] The present invention affords the advantages of a fusion
cage which can be introduced through an anterior approach in order
to maintain or increase lordosis between adjacent vertebral bodies.
The fusion cage has the advantage of being conically-shaped and
self-tapping through the use of external flutes. The flutes
additionally assist in keeping the fusion cage aligned and centered
as the cage is being inserted between the vertebral bone
structures.
[0047] Other advantages, aspects, and objects of the invention can
be obtained through a review of the claims and the appended
figures.
[0048] It is to be understood that additional embodiments of the
invention can be constructed and fall within the spirit and scope
of the claims.
* * * * *