U.S. patent application number 11/926569 was filed with the patent office on 2008-02-21 for intervertebral allograft spacer.
Invention is credited to Hansjuerg Emch, David C. Paul, Beat Schenk.
Application Number | 20080046090 11/926569 |
Document ID | / |
Family ID | 26789963 |
Filed Date | 2008-02-21 |
United States Patent
Application |
20080046090 |
Kind Code |
A1 |
Paul; David C. ; et
al. |
February 21, 2008 |
INTERVERTEBRAL ALLOGRAFT SPACER
Abstract
An allogenic intervertebral implant for fusing vertebrae is
disclosed. The implant is a piece of allogenic bone conforming in
size and shape with a portion of an end plate of a vertebra. The
implant has a wedge-shaped profile to restore disc height and the
natural curvature of the spine. The top and bottom surfaces of the
implant have a plurality of teeth to resist expulsion and provide
initial stability. The implant according to the present invention
provides initial stability need for fusion without stress
shielding.
Inventors: |
Paul; David C.;
(Phoenixville, PA) ; Emch; Hansjuerg;
(Philadelphia, PA) ; Schenk; Beat; (Nuglar,
CH) |
Correspondence
Address: |
STROOCK & STROOCK & LAVAN, LLP
180 MAIDEN LANE
NEW YORK
NY
10038
US
|
Family ID: |
26789963 |
Appl. No.: |
11/926569 |
Filed: |
October 29, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11150608 |
Jun 10, 2005 |
7300465 |
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11926569 |
Oct 29, 2007 |
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|
09828625 |
Apr 9, 2001 |
6986788 |
|
|
11150608 |
Jun 10, 2005 |
|
|
|
09363844 |
Jul 30, 1999 |
6258125 |
|
|
09828625 |
Apr 9, 2001 |
|
|
|
09219439 |
Dec 23, 1998 |
6143033 |
|
|
09363844 |
Jul 30, 1999 |
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60095425 |
Aug 5, 1998 |
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60095209 |
Aug 3, 1998 |
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60073271 |
Jan 30, 1998 |
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Current U.S.
Class: |
623/17.16 ;
606/86A; 606/99 |
Current CPC
Class: |
A61F 2002/30593
20130101; A61F 2002/30785 20130101; A61F 2/28 20130101; A61F
2002/30158 20130101; A61F 2002/30462 20130101; A61F 2002/30971
20130101; A61F 2002/30904 20130101; B29C 43/006 20130101; A61F
2/4455 20130101; A61F 2002/30153 20130101; A61F 2002/30433
20130101; A61F 2002/30843 20130101; A61F 2002/4635 20130101; A61F
2250/0039 20130101; B29C 33/26 20130101; A61F 2230/0019 20130101;
A61F 2002/30507 20130101; A61F 2310/00293 20130101; A61F 2/30724
20130101; A61F 2002/30782 20130101; A61F 2002/2835 20130101; A61F
2002/30228 20130101; A61F 2210/0004 20130101; A61F 2230/0026
20130101; A61F 2002/30237 20130101; A61F 2002/30733 20130101; A61F
2002/30481 20130101; A61F 2002/30772 20130101; A61F 2002/3028
20130101; A61F 2002/30909 20130101; A61F 2002/4649 20130101; A61F
2002/30387 20130101; A61F 2/30942 20130101; A61F 2310/00179
20130101; A61F 2/3094 20130101; A61F 2220/0033 20130101; A61F
2/30965 20130101; A61F 2310/00011 20130101; A61F 2002/2839
20130101; A61F 2002/30062 20130101; A61F 2002/302 20130101; A61F
2002/30324 20130101; A61F 2220/005 20130101; A61F 2002/30841
20130101; A61F 2002/30057 20130101; A61F 2250/0063 20130101; A61F
2250/0023 20130101; A61F 2002/3082 20130101; A61F 2002/30459
20130101; A61F 2002/30975 20130101; A61F 2230/0063 20130101; A61F
2002/30515 20130101; A61F 2002/30112 20130101; A61F 2002/30604
20130101; A61F 2002/30616 20130101; A61F 2002/30957 20130101; A61F
2220/0041 20130101; A61F 2230/0004 20130101; A61F 2002/30075
20130101; A61F 2002/30894 20130101; A61F 2002/30383 20130101; A61F
2210/0061 20130101; A61F 2310/00353 20130101; A61F 2002/30354
20130101; A61F 2002/30126 20130101; A61F 2002/30599 20130101; A61F
2002/30892 20130101; B29L 2031/3041 20130101; A61F 2002/30367
20130101; A61F 2220/0066 20130101; A61F 2002/30233 20130101; A61F
2002/30327 20130101; A61F 2250/0036 20130101; A61F 2230/0065
20130101; A61F 2002/30133 20130101; A61F 2002/30331 20130101; A61F
2/4644 20130101; A61F 2002/30477 20130101; A61F 2002/30492
20130101; A61F 2220/0075 20130101; Y10S 623/925 20130101; A61F
2230/0015 20130101; A61F 2/442 20130101; A61F 2250/0089 20130101;
A61F 2230/0069 20130101; A61F 2250/0097 20130101; A61F 2/4611
20130101; A61F 2230/0008 20130101; A61F 2002/2817 20130101; A61F
2002/3071 20130101; A61F 2002/30787 20130101; A61F 2002/30329
20130101; A61F 2/30744 20130101; A61F 2002/30011 20130101; A61F
2/4465 20130101; A61F 2002/30235 20130101; A61F 2002/30448
20130101; A61F 2002/30494 20130101; A61F 2002/30617 20130101; A61F
2220/0025 20130101 |
Class at
Publication: |
623/017.16 ;
606/072 |
International
Class: |
A61F 2/44 20060101
A61F002/44; A61B 17/56 20060101 A61B017/56 |
Claims
1. An intervertebral allograft implant for implantation between
adjacent first and second vertebrae, each of the first and second
vertebrae including an end-plate, the implant comprising: a
superior surface sized and configured to contact at least a portion
of the end-plate of the first vertebra, an inferior surface sized
and configured to contact at least a portion of the end-plate of
the second vertebrae, a front surface extending from the superior
surface to the inferior surface; a back surface extending from the
superior surface to the inferior surface, and a pair of lateral
surfaces extending from the superior surface to the inferior
surface and extending from the front surface to the back surface;
wherein the implant is formed from at least two pieces of bone
joined together to form a single body.
2. The implant of claim 1, wherein the plurality of bone pieces
have mating interlocking surfaces that aid in holding the pieces
together.
3. The implant of claim 1, further comprising at least one pin
extending through an opening formed in the plurality of bone pieces
to hold the pieces together.
4. The implant of claim 1, wherein the pin intersects the superior
and inferior surfaces at an oblique angle.
5. The implant of claim 1, wherein the implant includes a top piece
joined to a bottom piece, the top piece including the superior
surface for contacting the first vertebra and a first connecting
surface, the bottom piece including the inferior surface for
contacting the second vertebra and a second connecting surface, the
first connecting surface being sized and configured to contact the
second connecting surface so that the top and bottom pieces are
stacked one on top of the other.
6. The implant of claim 5, wherein the first and second connecting
surfaces include a plurality of interconnecting ridges and grooves
to interlock the top and bottom pieces.
7. The implant of claim 5, wherein the top and bottom pieces each
include at least one bore formed at least partially therein, the at
least one bore being sized and configured to receive at least one
pin for further securing the top piece to the bottom piece.
8. The implant of claim 1, wherein the implant includes a first
lateral piece and a second lateral piece, each of the first and
second lateral pieces including at least a portion of the superior
and inferior surfaces for contacting the first and second vertebra
respectively, the first lateral piece further including a first
connecting surface and the second lateral piece further including a
second connecting surface, the first connecting surface being sized
and configured to contact the second connecting surface so that the
first and second lateral pieces are arranged in a side by side
configuration.
9. The implant of claim 1, wherein the implant comprises a first
lateral piece joined to a second lateral piece, wherein the first
and second lateral pieces are substantially C-shaped so that when
joined side by side they define a central bore.
10. The implant of claim 1, wherein the implant is formed by at
least three pieces of bone.
11. The implant of claim 1, wherein the pair of lateral surfaces
each have a length extending from the front surface to the back
surface and wherein the front and back surfaces each have a length
extending between the pair of lateral surfaces, the length of the
lateral surfaces being at least approximately twice as long as the
length of the front and back surfaces.
12. The implant of claim 1, wherein the pair of lateral surfaces
each have a length extending from the front surface to the back
surface and wherein the front and back surfaces each have a length
extending between the pair of lateral surfaces, the length of the
lateral surfaces being at least approximately half as long as the
length of the front and back surfaces.
13. The implant of claim 1, wherein the superior and inferior
surfaces include a plurality of teeth.
14. The implant of claim 13, wherein the teeth have a
pyramidal-shape.
15. The implant of claim 13, wherein the teeth have a saw tooth
shape.
16. The implant of claim 1, wherein each of the lateral surfaces
includes a channel for engaging a surgical instrument.
17. The implant of claim 1, further comprising a threaded hole
formed in one of the front, back or lateral surfaces for receiving
a surgical instrument.
18. The implant of claim 1, wherein the superior and inferior
surfaces include a wedge-shaped profile so that the body has a
gradual decreasing height.
19. The implant of claim 1, wherein the superior and inferior
surfaces are curved to substantially match the contours of the
end-plates.
20. The implant of claim 1, wherein the implant includes at least
one rounded edge along a perimeter of the superior and inferior
faces for facilitating insertion of the implant in-between the
first and second vertebrae.
21. The implant of claim 1, wherein the implant includes a hollow
bore extending from the superior surface to the inferior
surface.
22. An intervertebral allograft implant for implantation between
adjacent first and second vertebrae, each of the first and second
vertebrae including an end-plate, the implant comprising: a
superior surface sized and configured to contact at least a portion
of the end-plate of the first vertebra, an inferior surface sized
and configured to contact at least a portion of the end-plate of
the second vertebrae, a front surface extending from the superior
surface to the inferior surface; a back surface extending from the
superior surface to the inferior surface, and a pair of lateral
surfaces extending from the superior surface to the inferior
surface and extending from the front surface to the back surface;
wherein the implant is formed from at least a first lateral piece
joined to a second lateral piece to form a single body, the first
and second lateral pieces being sized and configured so that when
joined side by side they define a central bore, the central bore
extending from the superior surface to the inferior surface.
23. An intervertebral allograft implant for implantation between
adjacent first and second vertebrae, each of the first and second
vertebrae including an end-plate, the implant comprising: a
superior surface sized and configured to contact at least a portion
of the end-plate of the first vertebra, an inferior surface sized
and configured to contact at least a portion of the end-plate of
the second vertebrae, a front surface extending from the superior
surface to the inferior surface; a back surface extending from the
superior surface to the inferior surface, and a pair of lateral
surfaces extending from the superior surface to the inferior
surface and extending from the front surface to the back surface;
wherein the implant is formed from at least a top piece joined to a
bottom piece to form a single body, the top piece including the
superior surface for contacting the first vertebra and a first
connecting surface, the bottom piece including the inferior surface
for contacting the second vertebra and a second connecting surface,
the first connecting surface being sized and configured to contact
the second connecting surface so that the top and bottom pieces are
stacked one on top of the other.
24. An intervertebral allograft implant for implantation between
adjacent first and second vertebrae, each of the first and second
vertebrae including an end-plate, the implant comprising: a
superior surface sized and configured to contact at least a portion
of the end-plate of the first vertebra, an inferior surface sized
and configured to contact at least a portion of the end-plate of
the second vertebrae, a front surface extending from the superior
surface to the inferior surface; a back surface extending from the
superior surface to the inferior surface, and a pair of lateral
surfaces extending from the superior surface to the inferior
surface and extending from the front surface to the back surface;
wherein the pair of lateral surfaces each have a length extending
from the front surface to the back surface and wherein the front
and back surfaces each have a length extending between the pair of
lateral surfaces, the length of the lateral surfaces being at least
approximately twice as long as the length of the front and back
surfaces.
25. An intervertebral allograft implant for implantation between
adjacent first and second vertebrae, each of the first and second
vertebrae including an end-plate, the implant comprising: a
superior surface sized and configured to contact at least a portion
of the end-plate of the first vertebra, an inferior surface sized
and configured to contact at least a portion of the end-plate of
the second vertebrae, a front surface extending from the superior
surface to the inferior surface; a back surface extending from the
superior surface to the inferior surface, and a pair of lateral
surfaces extending from the superior surface to the inferior
surface and extending from the front surface to the back surface;
wherein the superior and inferior surfaces include a plurality of
teeth.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 11/150,608, filed Jun. 10, 2005, which is a
continuation of U.S. patent application Ser. No. 09/828,625, filed
Apr. 9, 2001 (now U.S. Pat. No. 6,986,788), which is a continuation
of U.S. patent application Ser. No. 09/363,844, filed Jul. 30, 1999
(now U.S. Pat. No. 6,258,125, and reissued as U.S. Reissue Pat. No.
RE38,614), which is a continuation-in-part of U.S. patent
application Ser. No. 09/219,439, filed Dec. 23, 1998 (now U.S. Pat.
No. 6,143,033), which claims priority to U.S. Provisional
Application No. 60/095,425, filed Aug. 5, 1998, U.S. Provisional
Application No. 60/095,209, filed Aug. 3, 1998, and U.S.
Provisional Application No. 60/073,271, filed Jan. 30, 1998, the
contents of all of which are expressly incorporated by reference
herein.
FIELD OF THE INVENTION
[0002] The present invention is directed to an allogenic implant
and, more particularly, to an allogenic intervertebral implant.
BACKGROUND OF THE INVENTION
[0003] A number of medical conditions such as compression of spinal
cord nerve roots, degenerative disc disease, and spondylolisthesis
can cause severe low back pain. Intervertebral fusion is a surgical
method of alleviating low back pain. In posterior lumbar interbody
fusion ("PLIF"), two adjacent vertebral bodies are fused together
by removing the affected disc and inserting an implant that would
allow for bone to grow between the two vertebral bodies to bridge
the gap left by the disc removal.
[0004] A number of different implants and implant materials have
been used in PLIF with varying success. Current implants used for
PLIF include threaded titanium cages and allografts. Threaded
titanium cages suffer from the disadvantage of requiring drilling
and tapping of the vertebral end plates for insertion. In addition,
the incidence of subsidence in long term use is not known. Due to
MRI incompatibility of titanium, determining fusion is problematic.
Finally, restoration of lordosis, i.e., the natural curvature of
the lumbar spine is very difficult when a cylindrical titanium cage
is used.
[0005] Allografts are sections of bone taken from a long bone of a
donor. A cross section of the bone is taken and processed using
known techniques to preserve the allograft until implantation and
reduce the risk of an adverse immunological response when
implanted. For example, U.S. Pat. No. 4,678,470 discloses a method
for processing a bone grafting material which uses glutaraldehyde
tanning to produce a non-antigenic, biocompatible material.
Allografts have mechanical properties which are similar to the
mechanical properties of vertebrae even after processing. This
prevents stress shielding that occurs with metallic implants. They
are also MRI compatible so that fusion can be more accurately
ascertained and promote the formation of bone, i.e.,
osteoconductive. Although the osteoconductive nature of the
allograft provides a biological interlocking between the allograft
and the vertebrae for long term mechanical strength, initial and
short term mechanical strength of the interface between the
allograft and the vertebrae are lacking as evidenced by the
possibility of the allograft being expelled after implantation.
[0006] Currently commercially available allografts are simply
sections of bone not specifically designed for use in PLIF. As a
result, the fusion of the vertebral bodies does not occur in
optimal anatomical position. A surgeon may do some minimal
intraoperative shaping and sizing to customize the allograft for
the patient's spinal anatomy. However, significant shaping and
sizing of the allograft is not possible due to the nature of the
allograft. Even if extensive shaping and sizing were possible, a
surgeon's ability to manually shape and size the allograft to the
desired dimensions is severely limited.
[0007] Most PLIF implants, whether threaded cages or allograft, are
available in different sizes and have widths that vary with the
implant height. For example, the width of a cylindrical cages will
be substantially equivalent to the height. Although larger heights
may be clinically indicated, wider implants are generally not
desirable since increased width requires removal of more of the
facet, which can lead to decreases stability, and more retraction
of nerve roots, which can lead to temporary or permanent nerve
damage.
[0008] As the discussion above illustrates, there is a need for an
improved implant for fusing vertebrae.
SUMMARY OF THE INVENTION
[0009] The present invention relates to an allogenic intervertebral
implant for use when surgical fusion of vertebral bodies is
indicated. The implant comprises a piece of allogenic bone
conforming in size and shape with a portion of an end plates of the
vertebrae and has a wedge-shaped profile with a plurality of teeth
located on top and bottom surfaces. The top and bottom surfaces can
be flat planar surfaces or curved surfaces to mimic the topography
of the end plates. The implant has a channel on at least one side
for receiving a surgical tool. This channel runs in the anterior
direction to accommodate a variety of surgical approaches. A
threaded hole on the anterior, posterior, posterior-lateral, or
lateral side can be provided for receiving a threaded arm of an
insertion tool.
[0010] In another embodiment, the implant has an interior space for
receiving an osteoconductive material to promote the formation of
new bone.
[0011] In another embodiment, the implant is made of a plurality of
interconnecting sections with mating sections. Preferably, the
implant is made in two halves: a top portion having a top
connecting surface and a bottom portion having a bottom connecting
surface. The top connecting surface mates with the bottom
connecting surface when the top and bottom portions are joined. The
top and bottom portions have holes that align for receiving a pin
to secure the top and bottom portions together. The pin can be made
of allogenic bone.
[0012] In a different embodiment, the medial side of the implant
has a scalloped edge such that when a first implant is implanted
with a second implant with the medial sides facing each other, the
scalloped edges define a cylindrical space.
[0013] The present invention also relates to a discrete spacer used
in conjunction with any of the other embodiments of the implant.
The spacer comprises a piece of allogenic bone conforming in size
and shape with a portion of an end plates of the vertebrae and has
a wedge-shaped profile with substantially smooth top and bottom
surfaces. The intersecting regions between the top and bottom
surfaces and at least one of the lateral sides and the intersecting
regions between the anterior and posterior sides and the same
lateral side are curved surfaces to facilitate implantation of the
spacer. Thus, the spacer can be implanted through an opening on one
side of the spinal canal and moved with a surgical instrument to
the contralateral side.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a top view of a first embodiment of the implant
according to the present invention;
[0015] FIG. 2 is a side view of the implant of FIG. 1;
[0016] FIG. 3 is a back view of the implant of FIG. 1;
[0017] FIG. 4 is a top view of a second embodiment of the
implant;
[0018] FIG. 5 is a side view of the implant of FIG. 4;
[0019] FIG. 6 is a top view of a third embodiment of the
implant;
[0020] FIG. 7 is a side view of the implant of FIG. 6;
[0021] FIG. 8A is a top view of a top connecting surface of a top
portion of the implant of FIG. 6;
[0022] FIG. 8B is a top view of a bottom connecting surface of a
bottom portion of the implant of FIG. 6;
[0023] FIG. 9 is a perspective view of a fourth embodiment of the
implant;
[0024] FIG. 10A is a side view of one embodiment of the teeth on
the implant;
[0025] FIG. 10B is a side view of a second embodiment of the teeth
of the implant;
[0026] FIG. 11 is a side view of an embodiment of the implant
similar to the embodiment of FIGS. 6-8;
[0027] FIG. 12 is a top view of a vertebral bone characteristic of
those of the cervical, thoracic, and lumbar spine;
[0028] FIG. 13 is a side view of sequentially aligned vertebral
bones, such as are found in the cervical, thoracic, or lumbar
spine;
[0029] FIG. 14 is a posterior view of a sequence of vertebrae;
and
[0030] FIG. 15 is an end view of another embodiment of the
implant.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] FIG. 1 shows a top view of a first embodiment of
intervertebral allograft spacer or implant 10 according to the
present invention. Implant 10 conforms in size and shape with a
portion of end plates of the vertebrae between which implant 10 is
to be implanted. Because implant 10 is an allograft, implant 10
promotes the formation of new bone to fuse the two vertebral bodies
together. Although implant 10 will probably be predominantly used
in the lumbar region of the spine, implant 10 can be configured for
implantation in any region of the spine. Implant 10 has a plurality
of teeth 12 on superior and inferior surfaces 14, 16 which provide
a mechanical interlock between implant 10 and the end plates. Teeth
12 provide the mechanical interlock by penetrating the end plates.
The initial mechanical stability afforded by teeth 12 minimizes the
risk of post-operative expulsion of implant 10. Teeth 12 can be
pyramid-shaped (FIG. 10A). Preferably, the angle formed from the
tip to the base is approximately 60 degrees. Alternatively, teeth
12 have a saw tooth shape with the saw tooth running in the
anterior-posterior direction (FIG. 10B).
[0032] As shown in FIG. 2 and FIG. 3, a first lateral side 18 has a
channel 20 and a second lateral side 22 also has a channel 20.
Channels 20 are sized to receive a surgical instrument such as an
inserter for implantation of implant 10. If the inserter has a
threaded arm, implant 10 can be provided with a threaded hole 24.
In FIG. 2, channel 20 is shown extended only partially along first
lateral side 18. Channel 20 can extend along the entire length of
first lateral side 18 as shown in the embodiment of FIG. 5. In FIG.
3, channels 20 are shown on both first and second lateral sides 18,
22. It should be noted that implant 10 can also have no channels or
channels on one lateral side only as shown in the embodiment of
FIG. 9.
[0033] The dimensions of implant 10 can be varied to accommodate a
patient's anatomy. Typically, implant 10 would have a width between
6-15 mm (in the medial-lateral direction), a length between 15-30
mm (in the anterior-posterior direction), and a height between 4-30
mm (maximum height in the superior-inferior direction). The size of
implant 10 allows implant 10 to be implanted using conventional
open surgical procedures or minimally invasive procedures, such as
laparoscopic surgery. Additionally, because the width is kept to a
restricted size range and does not necessarily increase with
implant height, taller implants can be used without requiring wider
implants. Thus, facet removal and retraction of nerve roots can
remain minimal.
[0034] In order to restore the natural curvature of the spine after
the affected disc has been removed, implant 10 has a wedge-shaped
profile. As shown in FIG. 2, this wedge shape results from a
gradual decrease in height from an anterior side 26 to a posterior
side 28. In anatomical terms, the natural curvature of the lumbar
spine is referred to as lordosis. When implant 10 is to be used in
the lumbar region, the angle formed by the wedge should be
approximately between 4.20 and 150 so that the wedge shape is a
lordotic shape which mimics the anatomy of the lumbar spine.
[0035] In order to facilitate insertion of implant 10, anterior
side 26 transitions to superior and inferior surfaces 14, 16 with
rounded edges 30. Rounded edges 30 enable implant 10 to slide
between the end plates while minimizing the necessary distraction
of the end plates.
[0036] Although implant 10 is typically a solid piece of allogenic
bone, implant 10 can be provided with a hollow interior to form an
interior space. This interior space can be filled with bone chips
or any other osteoconductive material to further promote the
formation of new bone.
[0037] FIG. 4 shows a top view of a second embodiment of an implant
40 according to the present invention. In general, most of the
structure of implant 40 is like or comparable to the structure of
implant 10. Accordingly, discussion of the like components is not
believed necessary. The superior and inferior surfaces 14, 16 of
implant 10 are flat planar surfaces. As seen best in FIG. 5,
superior and inferior surfaces 14, 16 of implant 40 are curved
surfaces which still retain the wedge-shaped profile. The curved
surfaces of superior and inferior surfaces 14, 16 of implant 40 are
a mirror-image of the topography of the vertebral end plates. Thus,
the curved surfaces conform to the contours of the end plates.
[0038] FIG. 6 shows a top view of a third embodiment of an implant
50 according to the present invention. In general, most of the
structure of implant 50 is like or comparable to the structure of
implants 10, 40. Accordingly, discussion of the like components is
not believed necessary. As best seen in FIG. 7, implant 50
comprises a top portion 52 joined to a bottom portion 54. As it may
be difficult to obtain a single section of allogenic bone from
which implant 50 is to be made, fabricating implant 50 in two
pieces, i.e. top and bottom portions 52, 54, allows smaller
sections of allogenic bone to be used. A top connecting surface 56
and a bottom connecting surface 58 define the interface between top
and bottom portions 52, 54. As shown in FIGS. 8A and 8B, top and
bottom surfaces 56, 58 have ridges 60 that mate with grooves 62 to
interlock top and bottom portions 52, 54. Preferably, ridges 60 and
grooves 62 are formed by milling top and bottom surfaces 56, 58 in
a first direction and then milling a second time with top and
bottom surfaces 56, 58 oriented 90 degrees. with respect to the
first direction.
[0039] A pin 64 passing through aligned holes 66 in top and bottom
portions 52, 54 serves to retain top and bottom portions 52, 54
together. Although pin 64 can be made of any biocompatible
material, pin 64 is preferably made of allogenic bone. The number
and orientation of pins 64 can be varied.
[0040] FIG. 11 shows an embodiment of an implant 80 which, like
implant 50, is made in multiple pieces. In general, most of the
structure of implant 80 is like or comparable to the structure of
implants 10, 40, 50. Accordingly, discussion of the like components
is not believed necessary. Implant 80 has a top portion 82, a
middle portion 84, and a bottom portion 86. As was the case for
implant 80, the surfaces between the portions are mating surfaces
with interlocking surface features, such as ridges and grooves. One
or more pins preferably hold top, middle, and bottom portions 82,
84, 86 together.
[0041] FIG. 9 shows a perspective view of a fourth embodiment of a
first implant 70 according to the present invention. A second
implant 70', which is substantially similar to first implant 70, is
also shown. In general, most of the structure of first and second
implants 70, 70' is like or comparable to the structure of implants
10, 40, 50. Accordingly, discussion of the like components is not
believed necessary. First lateral sides 18 of first and second
implants 70, 70' are scalloped to have a C-shape. When first and
second implants 70, 70' are placed side by side with the first
lateral sides 18 facing each other, a cylindrical space 72 is
formed. When first and second implants 70, 70' are implanted
together, cylindrical space 72 can be filled with osteoconductive
material to help promote the formation of new bone. First and
second implants 70, 70' can be provided with locking pins 74 which
engage apertures 76 to maintain the spatial relationship between
first and second implants 70, 70'.
[0042] The use of the implant according to the present invention
will now be described with reference to FIGS. 12-14 and using
posterior lumbar interbody fusion as an example. As the implant
according to the present invention conforms in size and shape to a
portion of end plates 100, preoperative planning is recommended for
proper sizing. Determine the appropriate implant height by
measuring adjacent intervertebral discs 102 on a lateral
radiograph. The implant must be seated firmly with a tight fit
between end plates 100 when the segment is fully distracted. The
tallest possible implant should be used to maximize segmental
stability. Due to variability in degrees of magnification from
radiographs, the measurements are only an estimate.
[0043] With the patient in a prone position on a lumbar frame,
radiographic equipment can assist in confirming the precise
intraoperative position of the implant. The surgeon incises and
dissects the skin from the midline laterally and locates spinous
process 104, lamina 106, dura 108, and nerve roots of the
appropriate level(s). As much as facets 110 as possible should be
preserved to provide stability to the intervertebral segment. The
surgeon performs a laminotomy to the medial aspect of facet 110 and
reflects dura 108 to expose an approximately 13 mm window to the
disc space. Disc 102 is removed through the window until only
anterior 112 and lateral 114 annulus remain. The superficial layers
of the entire cartilaginous end plates 100 are also removed to
expose bleeding bone. Excessive removal of the subchondral bone may
weaken the anterior column. Furthermore, if the entire end plate is
removed, this may result in subsidence and a loss of segmental
stability.
[0044] Distraction can be done with either a surgical distractor or
a trial spacer implant. In the first method, the distractor blades
are placed into the disc space lateral to dura 108. The curve on
the neck of the distractor should be oriented toward the midline.
The distractor blades should be completely inserted into the disc
space so that the ridges at the end of the blades rest on vertebral
body 116. Fluoroscopy can assist in confirming that the distractor
blades are parallel to end plates 100. Correct placement will angle
the handles of the distractor cranially. particularly at L5-S1. The
handle of the distractor is squeezed to distract the innerspace.
The distraction is secured by tightening the speed nut on the
handle.
[0045] Using the preoperatively determined size, a trial spacer is
inserted in the contralateral disc space with gentle impaction.
Fluoroscopy and tactile judgment can assist in confirming the fit
of the trial spacer until a secure fit is achieved. Using either
the slots or threader hole on the implant, the selected implant is
inserted in the contralateral disc space. Alternatively, the
channels on the implant allow distraction and insertion to occur on
the same side. Regardless of the side the implant is inserted in,
autogenous cancellous bone or a bone substitute should be placed in
the anterior and medial aspect of the vertebral disc space prior to
placement of the second implant. The distractor is removed and a
second implant of the same height as the first implant is inserted
into the space, using gentle impaction as before. Preferably, the
implants are recessed 2-4 mm beyond the posterior rim of the
vertebral body.
[0046] As previously noted, the implant according to the present
invention can be inserted using minimally invasive procedures. In
some of these procedures, only one side of the spinal cord needs to
be approached. This minimizes muscle stripping, scar tissue in the
canal, and nerve root retraction and handling. In clinical
situations in which bilateral implant placement is required, proper
implantation on the side opposite the incision can be difficult.
FIG. 15 shows a beveled spacer 120 that facilitates placement on
the side contralateral to the incision. In general and unless
otherwise described, most of the structure of beveled spacer 120 is
like or comparable to the structure of implants 10, 40, 50, and 80.
Accordingly, discussion of the like components is not believed
necessary. First lateral side 18 transitions to superior and
inferior surfaces 14, 16 with rounded edges 30. First lateral side
18 also transitions to anterior and posterior sides 26, 28 with
rounded edges 30. Additionally, spacer 120 has no teeth. The lack
of teeth and rounded edges 30 enable spacer 120 to slide between
the end plate and across the evacuated disc space (from one lateral
annulus to the other) to the contralateral side. As first lateral
side 18 is the side that must promote movement of spacer 120, the
use of rounded edges 30 on second lateral side 22 is optionally.
Once spacer 120 has been placed on the side contralateral to the
single incision using a surgical instrument to push spacer 120,
bone graft or other osteoconductive material is packed in the disc
space. Finally, an implant (any of implant 10, 40, 50, 70, or 70'
can be used) is implanted in the side proximal to the incision.
[0047] While it is apparent that the illustrative embodiments of
the invention herein disclosed fulfill the objectives stated above,
it will be appreciated that numerous modifications and other
embodiments may be devised by those skilled in the art. Therefore,
it will be understood that the appended claims are intended to
cover all such modifications and embodiments which come within the
spirit and scope of the present invention.
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