U.S. patent application number 10/787984 was filed with the patent office on 2004-09-02 for intervertebral implant for transforaminal posterior lumbar interbody fusion procedure.
This patent application is currently assigned to Synthes(U.S.A.). Invention is credited to Gerber, David, Messerli, Dominique, Paul, David.
Application Number | 20040172133 10/787984 |
Document ID | / |
Family ID | 25302574 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040172133 |
Kind Code |
A1 |
Gerber, David ; et
al. |
September 2, 2004 |
Intervertebral Implant for transforaminal posterior lumbar
interbody fusion procedure
Abstract
An intervertebral implant for fusing vertebrae is disclosed. The
implant has a body with curved, substantially parallel posterior
and anterior faces separated by two narrow implant ends, superior
and inferior faces having a plurality of undulating surfaces for
contacting upper and lower vertebral endplates, and at least one
depression at a first end for engagement by an insertion tool. The
arcuate implant configuration facilitates insertion of the implant
from a transforaminal approach into a symmetric position about the
midline of the spine so that a single implant provides balanced
support to the spinal column. The implant may be formed of a
plurality of interconnecting bodies assembled to form a single
unit. An implantation kit and method are also disclosed.
Inventors: |
Gerber, David; (CH-Arborn,
CH) ; Messerli, Dominique; (West Chester, PA)
; Paul, David; (Phoenixville, PA) |
Correspondence
Address: |
JONES DAY
222 EAST 41ST ST
NEW YORK
NY
10017
US
|
Assignee: |
Synthes(U.S.A.)
|
Family ID: |
25302574 |
Appl. No.: |
10/787984 |
Filed: |
February 26, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10787984 |
Feb 26, 2004 |
|
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09848178 |
May 3, 2001 |
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6719794 |
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Current U.S.
Class: |
623/17.11 |
Current CPC
Class: |
A61F 2002/30538
20130101; A61F 2/4465 20130101; A61F 2002/30383 20130101; A61F
2002/30904 20130101; A61F 2/4611 20130101; A61F 2002/30133
20130101; A61F 2002/30843 20130101; A61F 2002/30975 20130101; A61F
2250/0098 20130101; A61F 2002/30787 20130101; A61B 17/1604
20130101; A61F 2002/30797 20130101; A61F 2250/0006 20130101; A61F
2002/30604 20130101; A61F 2002/2835 20130101; A61F 2002/30507
20130101; A61F 2002/4628 20130101; A61F 2220/0025 20130101; A61F
2310/00359 20130101; A61F 2002/30492 20130101; A61F 2310/00017
20130101; A61F 2/28 20130101; A61B 17/1659 20130101; A61F 2/4684
20130101; A61F 2230/0015 20130101; A61F 2002/30594 20130101; A61B
17/1671 20130101; A61F 2002/3008 20130101 |
Class at
Publication: |
623/017.11 |
International
Class: |
A61F 002/44; A61F
002/46 |
Claims
What is claimed is:
1. An intervertebral implant comprising: a body having a
substantially curved anterior face, a substantially curved
posterior face, a pair of narrow ends separating the posterior and
anterior faces; a superior surface and an inferior surface for
contacting upper and lower vertebral endplates, the superior and
inferior surfaces defining a thickness of the implant; and first
and second non-threaded, horizontal channels configured and adapted
for engagement by an implant insertion tool, the first channel
disposed along at least a portion of the curved posterior face and
the second channel disposed along at least a portion of the curved
anterior face; wherein the first and second channels are curved
with the anterior and posterior faces.
2. The implant of claim 1, wherein the anterior face is convex and
the posterior face is concave.
3. The implant of claim 2, wherein the anterior face and the
posterior face are substantially parallel.
4. The implant of claim 3, wherein the anterior face has a radii of
curvature R1, the posterior face has a radii of curvature R2,
wherein R1 is approximately 28 millimeters and R2 is approximately
19 millimeters.
5. The implant of claim 1, wherein the thickness of the implant is
greatest approximately at a mid-section of the implant between the
ends of the implant.
6. The implant of claim 5, wherein the thickness of the implant
tapers from the mid-section of the implant to the ends of the
implant.
7. The implant of claim 5, wherein the superior and inferior
surfaces have a convex-arcuate shape with a radii of curvature of
approximately 100 mm.
8. The implant of claim 7, wherein the thickness of the implant
does not taper along a transverse axis of the implant so that the
distance between the superior and inferior surfaces remain
substantially constant for any given cross section taken
perpendicular to the longitudinal axis of the implant.
9. The implant of claim 5, wherein the thickness of the implant at
the mid-section is approximately 7.0 millimeters to approximately
17.0 millimeters and the thickness at the ends of the implant is
approximately 1.5 millimeters to approximately 2.0 millimeters less
than the thickness at the mid-section.
10. The implant of claim 1, wherein the implant has a longitudinal
length measured along a longitudinal axis of the implant from
approximately 26 millimeters to approximately 32 millimeters and a
transverse width from approximately 9 millimeters to approximately
11 millimeters.
11. The implant of claim 1, wherein the implant is formed of a
plurality of interconnecting bodies assembled to form a single
unit.
12. The implant of claim 11, wherein the plurality of
interconnecting bodies have interlocking grooves and pallets to
press-fit the bodies together.
13. The implant of claim 12, further comprising at least one pin
extending through an opening in the plurality of bodies to hold the
bodies together as a single unit.
14. The implant of claim 12, further comprising at least one screw
extending through an opening in the plurality of bodies to hold the
bodies together as a single unit.
15. The implant of claim 11, wherein the implant is formed from
exactly two pieces, the first piece has an inferior surface for
engaging an adjacent vertebral and a top surface, the second piece
has a superior surface for engaging an adjacent vertebral and a
bottom surface for interlocking with the top surface of the first
piece so that the pieces are stacked one on top of the other.
16. The implant of claim 15, wherein the first and second pieces
are formed allograft bone.
17. The implant of claim 1, wherein the implant is formed from the
group consisting of metal, allograft, a metal allograft composite,
a carbon-fiber polymer, a polymer, or plastic.
18. The implant of claim 1, further comprising a plurality of
projections on the superior and inferior faces for engaging the
adjacent vertebrae.
19. The implant of claim 18, wherein the projections are teeth for
providing a mechanical interlock between the superior and inferior
surfaces of the implant and the end plates of the adjacent
vertebral.
20. The implant of claim 1, wherein at least one of the narrow ends
is rounded.
21. The implant of claim 1, wherein at least one of the narrow ends
is substantially straight.
22. An intervertebral implant comprising: a body having a curved
posterior face and a curved anterior face, both curved posterior
and anterior faces extending in the direction of a longitudinal
axis of the implant body; a pair of narrow end faces separating the
posterior and anterior faces; superior and inferior faces for
contacting upper and lower vertebral endplates, the superior and
inferior surfaces defining a thickness of the implant; and first
and second non-threaded, horizontal channels configured and adapted
for engagement by an implant insertion tool, the first channel
disposed along at least a portion of the curved posterior face and
the second channel disposed along at least a portion of the curved
anterior face; wherein the posterior face and the anterior face are
both curved substantially from one of the end faces to the other
end face.
23. The implant of claim 22, wherein the first and second channels
are curved with the anterior and posterior faces.
24. The implant of claim 23, wherein the anterior face is convex
and the posterior face is concave.
25. The implant of claim 24, wherein the anterior face and the
posterior face are substantially parallel.
26. The implant of claim 24, wherein the anterior face has a radii
of curvature R1, the posterior face has a radii of curvature R2,
wherein R1 is approximately 28 millimeters and R2 is approximately
19 millimeters.
27. The implant of claim 22, wherein the thickness of the implant
is greatest approximately at a mid-section of the implant between
the end faces of the implant.
28. The implant of claim 27, wherein the thickness of the implant
tapers from the mid-section of the implant to the end faces of the
implant.
29. The implant of claim 27, wherein the superior and inferior
surfaces have a convex-arcuate shape with a radii of curvature of
approximately 100 mm.
30. The implant of claim 29, wherein the thickness of the implant
does not taper along a transverse axis of the implant so that the
distance between the superior and inferior surfaces remain
substantially constant for any given cross section taken
perpendicular to the longitudinal axis of the implant.
31. The implant of claim 27, wherein the thickness of the implant
at the mid-section is approximately 7.0 millimeters to
approximately 17.0 millimeters and the thickness at the end faces
of the implant is approximately 1.5 millimeters to approximately
2.0 millimeters less than the thickness at the mid-section.
32. The implant of claim 22, wherein the implant has a longitudinal
length measured along a longitudinal axis of the implant from
approximately 26 millimeters to approximately 32 millimeters and a
transverse width from approximately 9 millimeters to approximately
11 millimeters.
33. The implant of claim 22, wherein the implant is formed of a
plurality of interconnecting bodies assembled to form a single
unit.
34. The implant of claim 33, wherein the plurality of
interconnecting bodies have interlocking grooves and pallets to
press-fit the bodies together.
35. The implant of claim 34, further comprising at least one pin
extending through an opening in the plurality of bodies to hold the
bodies together as a single unit.
36. The implant of claim 34, further comprising at least one screw
extending through an opening in the plurality of bodies to hold the
bodies together as a single unit.
37. The implant of claim 33, wherein the implant is formed from
exactly two pieces, the first piece has an inferior surface for
engaging an adjacent vertebral and a top surface, the second piece
has a superior surface for engaging an adjacent vertebral and a
bottom surface for interlocking with the top surface of the first
piece so that the pieces are stacked one on top of the other.
38. The implant of claim 37, wherein the first and second pieces
are formed allograft bone.
39. The implant of claim 22, wherein the implant is formed from the
group consisting of metal, allograft, a metal allograft composite,
a carbon-fiber polymer, a polymer, or plastic.
40. The implant of claim 22, further comprising a plurality of
projections on the superior and inferior faces for engaging the
adjacent vertebrae.
41. The implant of claim 40, wherein the projections are teeth for
providing a mechanical interlock between the superior and inferior
surfaces of the implant and the end plates of the adjacent
vertebral.
42. The implant of claim 22, wherein at least one of the end faces
is convex.
43. The implant of claim 22, wherein at least one of the end faces
is substantially straight.
44. An intervertebral implant comprising: a body having a
substantially convex anterior face, a substantially concave
posterior face, wherein the convex anterior face has a radii of
curvature of approximately 28 millimeters, the concave posterior
face has a radii of curvature of approximately 19 millimeters; a
pair of narrow ends separating the posterior and anterior faces; a
superior convex surface and an inferior convex surface for
contacting upper and lower vertebral endplates, the superior and
inferior surfaces defining a thickness of the implant, wherein the
thickness of the implant is greatest approximately at a mid-section
of the implant between the ends of the implant, and the superior
and inferior surfaces have a radii of curvature of approximately
100 mm; so that the thickness of the implant at the mid-section is
approximately 7.0 millimeters to approximately 17.0 millimeters and
the thickness at the ends of the implant is approximately 1.5
millimeters to approximately 2.0 millimeters less than the
thickness at the mid-section; and first and second non-threaded,
horizontal channels configured and adapted for engagement by an
implant insertion tool, the first channel disposed along at least a
portion of the curved posterior face and the second channel
disposed along at least a portion of the curved anterior face;
wherein the first and second channels are curved with the anterior
and posterior faces.
45. An intravertebral implant for maintaining a desired space
between vertebral bodies comprising: a solid body having a convex
anterior face, the anterior face shaped to match the shape of the
anterior perimeter of the vertebrae; a concave posterior face;
arcuate convex end faces connected between the posterior and
anterior faces, the posterior and anterior faces being at least
double the length of the end faces and the posterior and anterior
faces each having at least one curved channel extending from one of
the end faces toward the other end face configured and adapted to
be engageable with an insertion tool; and superior and inferior
faces for contacting upper and lower vertebral end plates, the
superior and inferior faces having teeth, wherein the implant is
configured and adapted to be inserted into the disc space through a
transforaminal window formed in the posterior of the spinal column
and positioned behind the dura between vertebral end plates to
maintain balanced support about the midline of the spine.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application is a continuation of U.S. patent
application Ser. No. 09/848,178, filed May 3, 2001, the contents of
which is expressly incorporated herein by reference thereto.
FIELD OF THE INVENTION
[0002] The present invention is directed to an intervertebral
implant, its accompanying instrumentation and their method of use.
More particularly, the present invention is directed to an
intervertebral implant and instrumentation for use in a
transforaminal posterior lumbar interbody fusion procedure.
BACKGROUND OF THE INVENTION
[0003] A number of medical conditions such as compression of spinal
cord nerve roots, degenerative disc disease, herniated nucleus
pulposis, spinal stenosis 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 one or more implants that
would allow for bone to grow between the two vertebral bodies to
bridge the gap left by the disc removal.
[0004] One variation of the traditional PLIF technique is the
transforaminal posterior lumbar interbody fusion (T-PLIF)
technique. Pursuant to this procedure, an implant is inserted into
the affected disc space via a unilateral (or sometimes bilateral),
posterior approach, offset from the midline of the spine, by
removing the facet joint of the vertebrae. The T-PLIF approach
avoids damage to nerve structures such as the dura and the nerve
root, but the resulting transforaminal window available to remove
the affected disc, prepare the vertebral endplates, and insert the
implant is limited laterally.
[0005] A number of different implants typically used for the
traditional PLIF procedure have been used for the T-PLIF procedure,
with varying success. These include threaded titanium cages,
allograft wedges, rings, etc. However, as these devices were not
designed specifically for the T-PLIF procedure, they are not shaped
to be easily insertable into the affected disc space through the
narrow transforaminal window, and may require additional retraction
of nerve roots. Such retraction can cause temporary or permanent
nerve damage. In addition, some of these implants, such as the
threaded titanium cage, suffer from the disadvantage of requiring
drilling and tapping of the vertebral endplates for insertion.
Further, the incidence of subsidence in long term use is not known
for such cages. Finally, restoration of lordosis, i.e., the natural
curvature of the lumbar spine is very difficult when a cylindrical
titanium cage is used.
[0006] As the discussion above illustrates, there is a need for an
improved implant and instrumentation for fusing vertebrae via the
transforaminal lumbar interbody fusion procedure.
SUMMARY OF THE INVENTION
[0007] The present invention relates to an intervertebral implant
("T-PLIF implant") and its use during a transforaminal lumbar
interbody fusion procedure. In a preferred embodiment, the T-PLIF
implant has an arcuate body with curved, substantially parallel
posterior and anterior faces separated by two narrow implant ends,
and superior and inferior faces having a plurality of undulating
surfaces for contacting upper and lower vertebral endplates. The
undulating surfaces may be projections, such as teeth, of a
saw-tooth or pyramidal configuration, or ridges which penetrate the
vertebral endplates and prevent slippage. The narrow implant ends
may be rounded or substantially flat. The arcuate implant
configuration facilitates insertion of the implant via a
transforaminal window. The implant, which may be formed of
allogenic bone, metal, or plastic, may also have at least one
depression, such as a channel or groove, at a first end for
engagement by an insertion tool, such as an implant holder. In a
preferred aspect, the superior and inferior faces are convex, and
the thickness of the implant tapers with its greatest thickness in
the middle region between the narrow ends of the implant, i.e., at
a section parallel to a sagittal plane, and decreasing toward each
of the narrow ends.
[0008] In another preferred embodiment, the implant is formed of a
plurality of interconnecting bodies assembled to form a single
unit. In this configuration, the plurality of interconnecting
bodies forming the T-PLIF implant may be press-fit together and may
include at least one pin or screw extending through an opening in
the plurality of bodies to hold the bodies together as a single
unit. Adjacent surfaces of the plurality of bodies may also have
mating interlocking surfaces that aid in holding the bodies
together as a single unit.
[0009] In still another preferred embodiment, the present invention
relates to a kit for implanting an intervertebral implant into an
affected disc space of a patient via a transforaminal window. The
kit includes an implant having an arcuate body with curved,
substantially parallel posterior and anterior faces separated by
two narrow implant ends, superior and inferior faces preferably
having a plurality of undulating surfaces, such as projections or
teeth, for contacting upper and lower vertebral endplates. The
superior and inferior faces may define a thickness. Preferably the
implant has at least one depression at a first end for engagement
by an insertion tool. The kit may further include at least one
trial-fit spacer for determining the appropriate size of the
implant needed to fill the affected disc space, an insertion tool
having an angled or curved neck for holding and properly
positioning the implant during insertion through the transforaminal
window, and an impactor having an angled or curved neck for
properly positioning the implant within the affected disc space.
The face of the impactor may be concavely shaped to mate with the
narrow end of the T-PLIF implant during impaction. The kit may
further include a lamina spreader for distracting vertebrae
adjacent to the affected disc space, an osteotome for removing
facets of the vertebrae adjacent to the affected disc space to
create a transforaminal window, one or more curettes, angled and/or
straight, for removing all disc material from the affected disc
space, a bone rasp for preparing endplates of the vertebrae
adjacent the affected disc space, and a graft implant tool for
implanting bone graft material into the affected disc space. The
kit may still further include a curved guide tool to guide the
implant into the affected disc space.
[0010] In yet another aspect, a method for implanting an
intervertebral implant into an affected disc space of a patient via
a transforaminal window is described. The transforaminal window is
created and bone graft material is inserted into the affected disc
space. Using an insertion tool, an implant is inserted into the
affected disc space via the transforaminal window, the implant
having an arcuate body with curved, substantially parallel
posterior and anterior faces separated by two narrow implant ends,
superior and inferior faces having a plurality of undulating
surfaces for contacting upper and lower vertebral endplates, and
preferably at least one depression at a first end for engagement by
the insertion tool. In the present method, the arcuate implant
configuration facilitates insertion of the implant via the
transforaminal window. The method may further comprise impacting
the implant with an impactor tool to properly position the implant
within the affected disc space. Either or both the insertion tool
and the impactor tool may be angled to facilitate insertion,
alignment, placement and/or proper seating of the implant.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a top view of a typical human vertebrae showing
the transforaminal window through which an implant according to the
present invention is inserted;
[0012] FIG. 2A is a cross-section view of an embodiment of an
implant according to the present invention;
[0013] FIG. 2B is a side view along the longer axis of the implant
of FIG. 2A;
[0014] FIG. 2C is a cross-section view taken along line 2C-2C of
FIG. 2B;
[0015] FIG. 2D is a perspective view of the implant of FIG. 2A;
[0016] FIG. 3A is a partial cross-section view of another
embodiment of an implant according to the present invention;
[0017] FIG. 3B is a partial cross-section view along the longer
axis of the implant of FIG. 3A;
[0018] FIG. 3C is a cross-section view taken along line 3C-3C of
FIG. 3B;
[0019] FIG. 3D is a perspective view of the implant of FIG. 3A;
[0020] FIG. 4 is a perspective view of still another embodiment of
the implant of the present invention;
[0021] FIG. 5 is an axial view of a typical human vertebrae showing
the implant of FIG. 4 in an asymmetric final position.
[0022] FIG. 6 is a posterior view of a section of human spine prior
to preparation of the transforaminal window;
[0023] FIG. 7 is a posterior view of a section of human spine with
the transforaminal window prepared;
[0024] FIG. 8A depicts an angled bone curette for use during the
T-PLIF procedure;
[0025] FIG. 8B depicts another angled bone curette for use during
the T-PLIF procedure;
[0026] FIG. 8C depicts an angled bone curette removing disc
material from an affected disc space;
[0027] FIG. 9A depicts an angled bone rasp for use during a T-PLIF
procedure;
[0028] FIG. 9B depicts an angled bone rasp removing material from
an affected disc space;
[0029] FIG. 10A depicts a trial-fit spacer for use during a T-PLIF
procedure;
[0030] FIG. 10B depicts a trial-fit spacer being inserted into an
affected disc space via a transforaminal window;
[0031] FIG. 11A depicts an implant holder for use during a T-PLIF
procedure;
[0032] FIG. 11B depicts the tips of the implant holder shown in
FIG. 11A;
[0033] FIG. 11C depicts a top view of a human vertebrae showing a
T-PLIF implant being inserted with in an implant holder;
[0034] FIG. 11D depicts an posterior view of the human spine
showing a T-PLIF implant being inserted with an implant holder;
[0035] FIG. 12 depicts an implant guide tool for use with the
T-PLIF implant;
[0036] FIG. 13A depicts an angled impactor tool for use with the
T-PLIF implant;
[0037] FIG. 13B is a close-up view of the tip of the impactor tool
shown in FIG. 13A;
[0038] FIG. 14 is a top view of a typical human vertebrae showing
an implant according to the present invention being properly
positioned into an affected disc space using the impactor tool
shown in FIG. 13A; and
[0039] FIG. 15 is a top view of the vertebrae of FIG. 1 showing the
T-PLIF implant in a final position.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0040] An implant according to the present invention, referred to
herein as a transforaminal posterior lumbar interbody fusion
implant ("T-PLIF implant"), is designed for use as an
intervertebral spacer in spinal fusion surgery, where an affected
disk is removed from between two adjacent vertebrae and replaced
with an implant that provides segmental stability and allows for
bone to grow between the two vertebrae to bridge the gap created by
disk removal. Specifically, the T-PLIF implant is designed for the
transforaminal lumbar interbody fusion (T-PLIF) technique, which,
as shown in FIG. 1, involves a posterior approach 12, offset from
the midline 14 of the spine, to the affected intervertebral disk
space 16. The window 18 available for implant insertion using the
T-PLIF technique is limited laterally by the dura 20 and the
superior exiting nerve root (not shown).
[0041] As shown in FIGS. 2A through 2D, in a preferred embodiment,
the T-PLIF implant has an arcuate, "rocker-like" body 22 with
curved anterior and posterior faces 24, 26 to facilitate the offset
insertion of the implant through the narrow approach window 18 into
the disk space. Preferably, the anterior and posterior faces 24 and
26 are substantially parallel, separated by a pair of narrow ends
25. Narrow ends 25 may be rounded or blunt. The superior and
inferior surfaces 28, 30 have projections, such as teeth 32, for
engaging the adjacent vertebrae. Teeth 32 on superior and inferior
surfaces 28, 30 preferably provide a mechanical interlock between
implant 22 and the end plates by penetrating the end plates. The
initial mechanical stability afforded by teeth 32 minimizes the
risk of post-operative expulsion/slippage of implant 10. Teeth 32
may have a saw-tooth shape, where one side of the tooth is
perpendicular to the superior or inferior surface, or a pyramid
shape, where each tooth has four sides and forms an acute angle
with the superior or inferior face. Preferably, implant body 22 has
at least one channel or slot 34 on one end of implant 22 for
engagement by a surgical instrument, such as an implant holder 66
(shown in FIG. 11A). It should be noted that implant 22 may also be
configured with a channel 34 on only one side or without channels
altogether. Other known methods for engaging the surgical
instruments with the implant, such as a threaded bore for receiving
the threaded end of a surgical tool, may also be used.
[0042] As shown in FIG. 2B, thickness 31 of implant 22 is greatest
at the mid-section between the two narrow implant ends 25 and
tapers gradually along the longitudinal axis 36 of implant 22 so
that it is thinnest at the narrow ends 25 of implant 22. This
convex configuration provides a proper anatomical fit and
facilitates insertion of implant 22 into the affected disc space.
It should be noted that in a preferred embodiment, thickness 31
does not taper along the shorter axis 37 of implant 22. Thus, as
shown in FIG. 2C for any given cross section taken perpendicular to
the longitudinal axis 36 of the implant, the distance between the
superior and inferior surfaces 28 and 30 remains substantially
constant. In alternate embodiments, however, thickness 31 may taper
along shorter axis 37 of implant 22. The dimensions of implant 22
can be varied to accommodate a patient's anatomy, and the thickness
of the implant is chosen based on the size of the disk space to be
filled. Preferably, implant 22 has a maximum thickness 31 at its
mid-section of about 7.0 to about 17.0 mm, and may be formed of
metal, allograft, a metal-allograft composite, a carbon-fiber
polymer, pure polymer or plastic. The thickness at the narrow ends
25 of implant 22 may range from about 1.5 to about 2.0 mm less than
the maximum thickness at the mid-section. The implant may range
from about 26 to about 32 mm in length, and have a width from about
9 to 11 mm. Implant 22, which as shown most clearly in FIG. 2A is
symmetric about at least one axis of rotation 37, is intended for
symmetric placement about the midline 14 of the spine (see FIG.
19). The arcuate configuration of implant 22 facilitates insertion
of the implant from the transforaminal approach into a symmetric
position about the midline of the spine so that a single implant
provides balanced support to the spinal column.
[0043] As shown in FIGS. 3A-3D, in an alternate embodiment implant
22 may be formed of two or more pieces 38 having interlocking
grooves 39 and pallets 40 that are press-fit and fastened together
with pins or screws 42. The number and orientation of pins or
screws 42 can be varied. This multi-component configuration may be
particularly useful for implants formed of allograft bone, since it
may be difficult and/or impractical to obtain a single,
sufficiently large piece of allograft for some applications. In the
case of implants formed completely of artificial (i.e.,
non-allograft) materials, such as steel, plastic or metallic or
non-metallic polymer, a one-piece implant may be more
practical.
[0044] As in the previous embodiment, the anterior and posterior
faces 24, 26 are substantially parallel, and, as shown, may be
defined by radii of curvature R1 and R2, where R1, for example, may
be in the range of about 28 mm and R2, for example, may be in the
range of about 19 mm. The superior and inferior surfaces 28, 30 are
arcuate shaped and the implant has a thickness 31, which is
preferably greatest at a center portion between narrow ends 25 and
gradually tapers becoming thinnest at narrow ends 25. Tapering
thickness 31 may be defined by a radius of curvature R3, where R3
for example, may be in the range of about 100 mm. As shown, the
component pieces 46, 48 of implant 22 have holes 44 to accommodate
pins or screws 42. Holes 44 are preferably drilled after component
pieces 38 have been stacked one on top of the other. The multiple
pieces 38 are then assembled with screws or pins 42 so that
practitioners receive the implant 22 as a single, pre-fabricated
unit. The upper component piece 46 has an arcuate superior surface
preferably with teeth 32, while its bottom surface is configured
with grooves and pallets to interlock with the upper surface of
lower component piece 48. The arcuate inferior surface 30 of lower
component piece 48 also preferably has teeth 32 for engaging the
lower vertebral endplate of the affected disc space. Either or both
superior and inferior surfaces 28, 30 may have ridges or some other
similar form of engaging projection in place of teeth 32.
[0045] Reference is now made to FIG. 4 which is a perspective view
of another embodiment an implant. As in the previous embodiment,
implant 23 has a curved body with substantially parallel arcuate
anterior and posterior faces 24, 26, convex superior and inferior
surfaces 28, 30 contributing to a tapering thickness 31, and
channels 34 for engaging a surgical instrument, such as an
insertion tool. In this embodiment, implant 23 has a substantially
straight or blunted narrow end 50 and a curved narrow end 52
separating parallel, arcuate anterior and posterior faces 24, 26.
As shown in FIG. 5, the final position of implant 23 in disc space
16 may be asymmetric with respect to midline 14 of the patient's
spine.
[0046] As shown in FIGS. 2A & 3A, and FIG. 11C, the rocker-like
shape of implant 22 enables the surgeon to insert the implant
through the narrow transforaminal window, typically on the range of
about 9.0 mm wide, and seat the implant in the disc space behind
the dura without disturbing the anterior curtain of the disc space.
The typical surgical technique for the T-PLIF procedure begins with
the patient being placed in a prone position on a lumbar frame.
Prior to incision, radiographic equipment can assist in locating
the precise intraoperative position of the T-PLIF implant.
Following incision, the facets, lamina and other anatomical
landmarks are identified. The affected vertebrae are distracted
using a lamina spreader or a lateral distractor, both of which are
commonly known in the art. In the latter case, screws may be
inserted into the vertebrae to interface with the lateral
distractor. As shown in FIGS. 6 & 7, following distraction, the
transforaminal window 54 is created by removing the inferior facet
56 of the cranial vertebrae and the superior facet 58 of the caudal
vertebrae using one or more osteotomes 59 of different sizes. A
discectomy is performed during which all disc material from the
affected disc space may be removed using a combination of straight
and angled curettes. Angled curettes, which may be configured with
rounded profile 60 (FIG. 8A) or a rectangular profile 61 (FIG. 8B),
enable removal of material on the far side 63 of the disc space
opposite transforaminal window 54, as shown in FIG. 8C.
[0047] After the discectomy is complete, the superficial layers of
the entire cartilaginous endplates are removed with a combination
of straight and angled bone rasps. As shown in FIGS. 9A and 9B,
angled rasps 62 may be angled to reach far side 63 of the disc
space opposite transforaminal window 54. Rasps 62 expose bleeding
bone, but care should be taken to avoid excess removal of
subchondral bone, as this may weaken the anterior column. Entire
removal of the endplate may result in subsidence and loss of
segmental stability. Next, an appropriately sized trial-fit T-PLIF
spacer/template 64, shown in FIGS. 10A and 10B, may be inserted
into the intervertebral disc space using gentle impaction, to
determine the appropriate implant thickness for the disc space to
be filled. Fluoroscopy can assist in confirming the fit of the
trial spacer. If the trial spacer 64 appears too loose/too tight,
the next larger/smaller size trial spacer should be used until the
most secure fit is achieved. For example, if a trial fit spacer
with a maximum thickness of 11 mm is too loose when inserted into
the disc space, a physician should try the 13 mm thick spacer, and
so on. Trial fit spacers preferably range in height from about 7 mm
to about 17 mm.
[0048] Upon identifying and removing the best fitting trial spacer,
a T-PLIF implant of appropriate size is selected. At this time,
prior to placement of the T-PLIF implant, bone graft material, such
as autogenous cancellous bone or a bone substitute, should be
placed in the anterior and lateral aspect of the affected disc
space. As shown in FIGS. 11C and 11D, T-PLIF implant 22 is then
held securely using a surgical instrument such as implant holder 66
(shown more clearly in FIG. 11A), which engages the channels or
slots 34 at one end of implant 22. The tips 67 of implant holder 66
may be curved or angled to mate with curved implant 22 and
facilitate insertion of implant 22 into disc space 16. T-PLIF
implant 22 is then introduced into the intravertebral disc space 16
via the transforaminal window, as shown in FIG. 11D. A guide tool
having a curved blade 68 (shown in FIG. 12) to match the curvature
of the anterior face of implant 22 may be used to properly guide
the implant into affected disc space 16. Slight impaction may be
necessary using implant holder 66 (shown in FIG. 11A) or an
impactor tool 70 (shown in FIG. 13A) to fully seat the implant. As
shown in FIGS. 13A & 13B, impactor tool 70 may also be curved
or angled to facilitate seating of the implant through the narrow
transforaminal window. Also, the face 71 of impactor 70 may be
concavely shaped to mate with the end of implant 22, as shown in
FIG. 14. Once the T-PLIF implant is in the desired final position,
such as the symmetric final position shown in FIG. 15 or the
asymmetric position shown in FIG. 5, implant holder 66, and
possibly guide tool 68, is removed and additional bone graft
material 73 may be inserted. Preferably, T-PLIF implant 22 should
be recessed from the anterior edge 72 of the vertebral body. As
shown in FIG. 15, the curvature of anterior face 24 of implant 22
is substantially the same as the curvature of anterior edge 72 of
disc space 16. In the symmetric seated position shown in FIG. 15, a
single T-PLIF implant 22 provides balanced support to the spinal
column about the midline of the spine.
[0049] While certain preferred embodiments of the implant have been
described and explained, 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.
* * * * *