U.S. patent application number 15/499566 was filed with the patent office on 2017-08-10 for interbody fusion implant and screw guide.
The applicant listed for this patent is Vikram Talwar. Invention is credited to Vikram Talwar.
Application Number | 20170224508 15/499566 |
Document ID | / |
Family ID | 47744774 |
Filed Date | 2017-08-10 |
United States Patent
Application |
20170224508 |
Kind Code |
A1 |
Talwar; Vikram |
August 10, 2017 |
INTERBODY FUSION IMPLANT AND SCREW GUIDE
Abstract
An interbody fusion implant fits between adjacent vertebrae for
fixation during fusion thereof. Upper bores extend into a cephalid
surface of the implant and preferably include threads therein. A
guide tool is removably attachable to the implant which supports
guide bores along centerlines aligned with the upper bores in the
implant. A drill can pass along these guide bores to form holes in
a vertebra adjacent the cephalid surface of the implant which is
precisely aligned with the upper bores. A hybrid screw then passes
through these holes in the vertebra adjacent the cephalid surface
and threads into the upper bores to secure the implant to the
adjacent cephalid vertebra. Bone screws can also be used to secure
the implant to caudal vertebra by passing through bores passing
through the implant, such that the implant is securely mechanically
fastened to both cephalid and caudal vertebrae adjacent the
implant.
Inventors: |
Talwar; Vikram; (San Ramon,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Talwar; Vikram |
San Ramon |
CA |
US |
|
|
Family ID: |
47744774 |
Appl. No.: |
15/499566 |
Filed: |
April 27, 2017 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
13592178 |
Aug 22, 2012 |
9636230 |
|
|
15499566 |
|
|
|
|
61575639 |
Aug 25, 2011 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
A61F 2002/30672
20130101; A61F 2/4455 20130101; A61B 17/1671 20130101; A61B 17/1757
20130101; A61B 17/863 20130101; A61F 2/30771 20130101; A61F
2002/30558 20130101; A61F 2002/30787 20130101; A61F 2/4611
20130101; A61B 17/7055 20130101; A61F 2002/4687 20130101; A61F
2002/30785 20130101; A61F 2/442 20130101; A61F 2002/30774
20130101 |
International
Class: |
A61F 2/46 20060101
A61F002/46; A61F 2/30 20060101 A61F002/30; A61B 17/86 20060101
A61B017/86; A61B 17/17 20060101 A61B017/17; A61B 17/70 20060101
A61B017/70; A61F 2/44 20060101 A61F002/44; A61B 17/16 20060101
A61B017/16 |
Claims
1: A method for securing an implant to an adjacent structure,
including the steps of: identifying an implant having an anterior
surface and a cephalid surface opposite a caudal surface, the
implant having at least one bore extending into the cephalid
surface thereof along a bore centerline extending from the cephalid
surface toward the caudal surface and away from the anterior
surface and wherein the at least one bore extending into the
cephalid surface includes female threads thereon; identifying a
hybrid screw with a proximal end opposite a distal end, said
proximal end having a head with a torque applying interface thereon
and the distal end having male threads thereon, the hybrid screw
having a bone engaging structure on a proximal side of the male
threads and spaced from the male threads for engagement of a
vertebra adjacent the cephalid surface of the implant; selecting a
guide having a guide bore extending therethrough, the guide being
removably attachable to the implant; placing the implant at an
implant location with an adjacent structure covering the bore into
the cephalid surface; attaching the guide to the implant with the
guide bore aligned with the centerline of the bore into the
cephalid surface; cutting a hole through the adjacent structure
along the centerline to the bore, using the guide bore; placing the
hybrid screw with the male threads matching the female threads in
the bore through the hole in the adjacent structure formed during
said cutting step with the male threads engaging the female
threads; and threading the screw into the bore in the implant until
the adjacent structure is secured to the implant by the bone
engagement structure.
2: The method of claim 1 wherein said screw has both the male
threads and bone threads, with the male threads closer to a distal
end of the screw than the bone threads, and the bone threads
providing at least a portion of the bone engagement structure
securing the adjacent structure to the implant as part of said
threading step.
3: The method of claim 1 wherein said cutting step includes the
step of drilling a hole through the adjacent structure, the hole
having a diameter large enough to allow the screw to pass through
the hole during said placing a screw step.
4: The method of claim 1 wherein said identifying an implant step
includes said implant having at least one additional bore extending
into the cephalid surface of the implant along a separate bore
centerline oriented non-parallel with said bore centerline of said
at least one bore, wherein said selecting a guide step includes the
guide having at least one additional guide bore with the at least
one additional guide bore aligned with the separate bore centerline
for at least one additional bore extending into the cephalid
surface of the implant, wherein said cutting step includes cutting
at least one additional hole through the adjacent structure aligned
with the at least one additional bore in the implant, and wherein
said placing step includes placing at least one additional screw
into the at least one additional hole formed in the adjacent
structure during said cutting step, and threaded into the at least
one additional bore in the cephalid surface of the implant.
5: The method of claim 4 wherein said identifying step includes the
implant having throughbores extending from said anterior surface
through said caudal surface, and at least one bone screw sized to
pass through said throughbore from said anterior surface through to
said caudal surface with threads on the bone screw engaging a
structure adjacent the caudal surface of the implant and with the
bone screw also engaging at least a portion of the implant for
attachment of the implant to the structure adjacent the caudal
surface of the implant.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. patent application
Ser. No. 13/592,178 filed on Aug. 22, 2012, which claims the
benefit under Title 35, United States Code .sctn.119(e) of U.S.
Provisional Application No. 61/575,639 filed on Aug. 25, 2011.
FIELD OF THE INVENTION
[0002] The following invention relates to implantable medical
devices such as those used for interbody fusion between adjacent
vertebrae, and especially between lumbar vertebrae and the sacrum.
More particularly, this invention relates to interbody fusion
implant cages which accommodate screws for attachment of the
implant to vertebrae on both cephalid and caudal sides of the
implant.
BACKGROUND OF THE INVENTION
[0003] Anterior lumbar interbody fusion (ALIF) has become an
increasingly useful approach for fusing the lumbar spine. With ALIF
procedures, a disk between adjacent vertebrae is removed and a
fusion cage implant is inserted into the disk space. Through known
techniques, bone growth through and around the cage is promoted to
fuse the adjacent vertebrae together. In one ALIF procedure, a
condition known as spondylolisthesis A can be treated (FIG. 1) by
removal of the disk D between the sacrum (S1) and the adjacent
lumbar vertebrae (L5). Other disk spaces between other adjacent
disks can also be treated with this ALIF procedure.
[0004] There is some inherent difficulty in placing screws between
the cage and a higher vertebra in the spine to fix the cage in
place, particularly when fusing L5 and S1, and when the L5-S1 disk
orientation is more angled toward the pubis rather than
horizontally situated. Because of such angularity, upwardly angled
bone screw supporting bores in the cage cannot be readily accessed.
Accordingly, a need exists for a superior method for securing the
interbody fusion cage implant to adjacent vertebrae which can be
accessed conveniently in a wider variety of anatomical
presentations for adjacent vertebrae to be fused.
SUMMARY OF THE INVENTION
[0005] With this invention, an improved spinal fusion cage implant
and associated screw guide tool and screw orientation, as well as a
unique hybrid screw are provided. Whereas the classic design of
ALIF implants has been to go through the implant first and then
into the end plate and vertebral body, with this type of cage and
screw technique, the screw first enters the bone and then captures
the implant cage distally in an upper cephalid surface of the cage.
The angle of attack of this screw is more in-line with the approach
to the anterior lumbar spine so that hybrid screws supporting and
securing the cephalid vertebrae to the cage implant can be readily
placed for fixation.
[0006] Utilizing this invention, the ALIF procedure begins as is
known in the prior art. In particular, the disk is removed and the
interbody cage implant is placed within the disk space. Bone screws
are utilized to secure the cage to the sacrum (S1) or other lower
caudal vertebrae adjacent the disk space. These bone screws extend
diagonally, typically from an anterior side of the cage and then
out of a caudal surface of the cage and into the end plate of the
lower caudal vertebral body (typically S1). The cage has now been
secured to the lower vertebral body (S1 or other lower vertebral
body).
[0007] With this invention, a tool is provided having an elongate
primary shaft or other element which can be removably attached to
the anterior surface or other portion of the interbody fusion cage.
In one embodiment, the cage implant has a threaded tool port bore
extending into the anterior surface of the cage. The shaft of the
tool has a threaded coupling tip which can thread into this tool
port to removably secure the shaft to the cage implant. As
rotational displacement of the primary shaft of the tool relative
to the cage is important to control for this invention, the
threaded tip of the primary shaft can abut some form of stop when
precisely aligned where desired, rather than merely tightening
through the threads alone, such that rotational alignment of the
primary shaft relative to the cage is precisely controlled. Other
forms of attachment could also be provided between the shaft and
the cage implant which eliminates relative motion or misalignment
between the shaft of the tool and the implant.
[0008] The tool includes a guide block or other structure extending
up from the shaft or other implant engaging element of the guide
tool. This guide block or other structure has at least one guide
bore passing therethrough, and preferably a pair of guide holes
which are oblique to each other to facilitate oblique screw
alignment paths into an adjacent upper vertebral body (typically
L5). The upper caudal surface of the interbody cage also includes
at least one and typically two threaded bores extending thereinto
at oblique angles. These bores are shown as blind bores.
Optionally, these bores could extend through the cage and out a
lower surface. In such an instance, a hole could be drilled in the
lower vertebral body (e.g. S1), or a guide wire could pass through
the bore and into the lower vertebral body so that a cannulated
screw could extend through both the upper and lower vertebral body
and through the implant. With use of two long screws at skewed
angles to each other, secure rotation of the two intervertebral
bodies and the cage would be maintained during bone fusion.
[0009] A centerline of these bores into the upper cephalid surface
of the interbody implant are precisely aligned with the guide bores
in the guide block of the tool. This precise alignment of the guide
bores and the upper bores in the interbody cage allows a drill,
and/or a bone screw to pass through the guide hole along an
alignment axis which precisely aligns with the blind bore (or
through bore) in the upper cephalid surface of the implant. Thus, a
method for attachment of the hybrid screw of this invention or some
other bone screw is facilitated between the upper vertebral body
(typically L5) and the implant (and optionally also the lower
vertebral body (typically S1)).
[0010] In a preferred form, this method includes first utilizing a
drill which passes through the guide bore in the guide block or
other guide tool structure and then drills the hole through the
upper vertebral body (typically L5). This hole extends diagonally
along the centerline from an anterior side of the higher vertebral
body (typically L5) and through the lower end plate of this higher
vertebral body, in alignment with the centerline of the upper bore
in the cephalid surface of the implant.
[0011] The hybrid bore can then be precisely passed through the
bore and engage the threaded blind bore in the upper surface of the
cage implant to secure the upper vertebral body and the cage
implant together (and optionally also the lower vertebral body as
well). This hybrid bone screw can pass through the guide hole in
the guide block, or the tool can be removed from the implant first
(or rotated out of position) so that the guide block does not block
the hybrid bone screw. The hybrid bone screw can then be passed
through the hole in the upper vertebra and into the implant. The
bore can be formed with a step so that a head of the hybrid screw
can abut this step within the higher vertebral body. As an
alternative, the head of the hybrid bone screw can merely abut the
anterior side of the higher vertebral body, or the hybrid screw can
be headless with just a torque applying tool interface at a
proximal end thereof.
[0012] The hybrid screw preferably has finer threads at a tip
thereof and cancellous threads for engaging bone closer to a
proximal end of the screw. With such a configuration, the fine
threads provide a secure attachment to the cage while the larger
bone threads engage the upper vertebral body. Pitches of these
threads can be identical or differential to provide a closing force
between the cage and the upper vertebral body. A major diameter of
the smaller threads is less than that of the bone threads so that
the smaller threads can pass through the hole in the upper
vertebral body without interference. In one embodiment, the hybrid
screw only has the smaller threads at the tip and utilizes a head
thereof, without bone threads or only a limited amount of bone
threads, so that the head of the hybrid screw draws the higher
vertebral body securely down against the cage when the hybrid screw
is tightened. While two hybrid screws are shown for attachment of
the implant to the upper vertebra, a number of screws could be as
few as just one screw or more than two screws and still function
according to this invention.
OBJECTS OF THE INVENTION
[0013] Accordingly, a primary object of the present invention is to
provide an interbody fusion cage implant which can be secured to
both cephalid and caudal vertebral structures adjacent the
implant.
[0014] Another object of the present invention is to provide an
interbody fusion cage which can be mechanically affixed in a space
between the L5 vertebra and the S1 sacrum and be mechanically
attached to both the L5 vertebra and the S1 sacrum to support the
L5 vertebra and the S1 sacrum for interbody fusion thereof.
[0015] Another object of the present invention is to provide an
implant and associated guide tool which facilitates precise
formation of a hole in a vertebra or other structure on a cephalid
side of the implant precisely located to align with a bore in the
implant in advance of placement of a screw therein for
fixation.
[0016] Another object of the present invention is to provide a
method for forming holes in vertebra adjacent an interbody fusion
cage implant and for placement of screws between an interbody
fusion cage implant and adjacent vertebra for secure fixation
during interbody fusion, especially of the L5/S1 joint.
[0017] Another object of the present invention is to provide a
hybrid screw for fixation of an interbody fusion implant cage to an
adjacent vertebrae or other structure, which screw has a distal
portion adapted to thread into the implant cage and a proximal
portion configured to both receive torque and to engage a vertebral
structure to be held against the implant.
[0018] Other further objects of the present invention will become
apparent from a careful reading of the included drawing figures,
the claims and detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a side elevation view of the lumbar spine of a
human including the sacrum and illustrating a spine exhibiting
spondylolisthesis, and showing an L5/S1 joint which is a candidate
for fusion utilizing the implant of this invention and according to
the method of this invention.
[0020] FIG. 2 is a side elevation view of a portion of that which
is shown in FIG. 1 after a disk has been removed from the L5/S1
joint and the implant according to this invention has been placed
therein, and with portions of vertebrae adjacent the implant cut
away and with the cage implant shown in full section to reveal
interior structures of the implant and operation of the guide tool
and alignment of various screws for secure attachment of the cage
implant to the L5 vertebra and to the S1 sacrum.
[0021] FIG. 3 is a side elevation exploded view of the implant,
tool and screws of FIG. 2, but shown without the spine portions
present, and without the guide block and associated guide bores,
and with interior structures of the implant shown in broken
lines.
[0022] FIG. 4 is a side elevation view of a hybrid screw for use
according to this invention to secure the L5 vertebra (or other
structure adjacent a cephalid side of the implant) to the implant.
FIG. 4 also shows in broken lines a variation on the hybrid screw
where threads are only provided at a distal end and a head having a
greater diameter than a shaft is provided instead of or in addition
to bone threads for engagement of an adjacent upper vertebral
structure.
[0023] FIG. 5 is a side elevation view similar to that which is
shown in FIG. 4, but for an embodiment of the screw which includes
a self-tapping cutting groove therein, and illustrating pitch
angles for the various threads.
[0024] FIG. 6 is a top plan view of the implant and tool and
attachment threads with broken lines depicting paths of the guide
bores in the guide tool and a tool port within the implant for
removable attachment of a coupling tip of the guide tool
thereto.
[0025] FIG. 7 is a side elevation view similar to that which is
shown in FIG. 2, but with the tool removed and after completion of
the interbody fusion procedure, with the interbody fusion cage
fastened to both the cephalid L5 vertebra and the caudal S1
sacrum.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0026] Referring to the drawings, wherein like reference numerals
represent like parts throughout the various drawing figures,
reference numeral 10 is directed to a cage implant for use in a
vertebral interbody fusion procedure (FIGS. 2 and 7), according to
a preferred embodiment of this invention. The implant 10 is
utilized as part of a system 100 which includes a guide tool 60,
drill 70 or other hole forming tool and bone screws 30 and hybrid
screws 50 for securing of the implant 10 to adjacent structures
such as the L5 vertebra and the S1 sacrum adjacent the implant,
when used at the L5/S1 joint. Following the system 100 of this
invention, the implant 10 is mechanically secured to both cephalid
and caudal adjacent structures for secure fixation of the implant
10 during fusion of the adjacent vertebral structures together.
While depicted primarily for interbody vertebral fusion, and
especially fusion of portions of the lumbar spine S, and in
particular the L5/S1 joint, the implant 10 and system 100 of this
invention could be utilized for fusion of other bones or other
structures together with modification of size and shape to match
varying anatomy for such other uses.
[0027] In essence, and with particular reference to FIGS. 1 and 2,
basic details of the implant 10 of this invention and other
portions of the system 100 are described, according to this
preferred embodiment. The implant 10 is a rigid cage structure
sized to fit within an interbody space between adjacent structures
to be fused together, such as adjacent vertebrae, and in this
example the L5 vertebrae and the S1 sacrum. The implant 10 can have
any of a variety of different geometries and configurations known
for interbody fusion cages, with the implant 10 depicted herein
having a generalized shape. The implant 10 includes standard bores
passing entirely through the implant 10. These standard bores are
oriented to allow standard bone screws to pass into the standard
bores and thread into the sacrum S1 or other structure adjacent a
caudal side of the implant 10. The standard bone screw 30 is thus
utilized to secure the implant 10 to the sacrum S1.
[0028] Upper bores 40 are provided extending into a cephalid
surface of the implant 10. A hybrid screw 50 is provided to secure
the L5 vertebra or other structure adjacent a cephalid side of the
implant 10 to the implant 10 through the upper bores 40. To allow
this hybrid screw 50 to pass into the upper bores 40, holes H must
first be formed in the L5 vertebra, or other structure adjacent the
cephalid side of the implant 10, which are precisely aligned with
the upper bores 40. A guide tool 60 is provided which is removably
attachable to the implant 10. This guide tool 60 includes guide
bores 68 which are aligned with the upper bores 40 in the implant
10. A drill 70 or other cutting tool can pass through the guide
bores 68 to form the holes H aligned with the upper bores 40 in the
implant 10. The hybrid screws 50 can then pass through these holes
H and be threaded into the upper bores 40, so that the implant 10
can be securely attached to the L5 vertebra or other vertebra on a
cephalid side of the implant 10. In this way, the implant 10 is
securely attached to adjacent structures, such as the L5 vertebra
and the S1 sacrum, on either side of the implant 10 for secure
holding of the L5 vertebra and S1 sacrum or other adjacent
vertebrae together during the fusion process.
[0029] More specifically, and with particular reference to FIGS. 2,
3, 6 and 7, details of the implant 10 are described, according to
this most preferred embodiment. Interbody fusion cages such as the
implant 10 come in a variety of different sizes, shapes and
configurations, and exhibiting a variety of different surfaces and
attributes, to optimize placement within an intervertebral space
and fixation of adjacent vertebrae during a fusion procedure. The
implant 10 of this invention can be utilized with a variety of such
cages, so that the implant 10 generally references some form of
cage or other interbody implant without particular requirement of
any details of this cage implant 10.
[0030] Generally, the implant 10 includes a cephalid surface 14
opposite a caudal surface 16, which are spaced apart generally by a
height of the implant 10. An anterior surface 12 is provided
generally extending between the cephalid surface 14 and the caudal
surface 16. This anterior surface 12 generally defines a portion of
the implant 10 which is on an anterior side of the implant 10.
These surfaces 12, 14, 16 could have a variety of different
contours including generally flat, curving, or with other
geometries or surface attributes as are known in the spinal fusion
cage arts.
[0031] The implant 10 includes a tool port 18, preferably in the
anterior surface 12. This tool port 18 is most preferably in the
form of a threaded blind bore extending into the anterior surface
12 perpendicular to the anterior surface 12. This tool port 18 is
provided for secure but removable attachment of the guide tool 60
thereto. The tool port 18 could have a configuration other than
that of a threaded blind bore, with the primary function of the
tool port 18 being secure removable attachment of the guide tool 60
to the implant 10 in a precise alignment between the guide tool 60
and the implant 10.
[0032] Most preferably, when the tool port 18 is in the form of a
blind threaded bore, threads are formed and the bore formed so that
the coupling tip 64 of the guide tool 60 which threads into this
tool port 18 bottoms out within a bottom of the tool port 18 before
the threads wedge the coupling tip 64 too tightly into the tool
port 18. In this way, the guide tool 60 stops at a reliable
rotational orientation relative to the implant 10, such that guide
bores 68 associated with the guide tool 60 are reliably aligned
precisely with the upper bores 40 in the implant 10. As a further
alignment aid, a stop could be placed within or adjacent the tool
port 18 which acts on the guide tool 60 to stop and hold its
orientation where desired after coupling to the tool port.
[0033] The implant 10 preferably has both standard bores 20 and
upper bores 40. In alternative embodiments, the implant 10 could be
provided merely with the upper bores 40. Also, it is conceivable
that only one standard bore 20 would be provided, or that more than
two standard bores 20 would be provided into the implant 10.
Similarly, while two upper bores 40 are provided extending along
non-parallel centerlines, only one upper bore 40 could be provided
or more than two upper bores 40 could be provided according to
alternatives to this invention. The standard bores 20 and the upper
bores 40 could be oriented parallel to each other when viewed from
the side (FIGS. 2, 3 and 7) or could be otherwise oriented. Such a
generally parallel orientation minimizes the area needed by a
surgeon outside the surgical site to utilize the drill 70 or other
cutting tool and to place the screws 30, 50 into the implant
10.
[0034] The standard bores 20 preferably pass entirely through the
implant 10, extending in this preferred embodiment from the
anterior surface 12 through the caudal surface 16 along bone screw
axis B. Preferably, two such standard bores 20 are provided. These
standard bores 20 thus have an entrance 22 adjacent the anterior
surface 12 and a exit 26 adjacent the caudal surface 16. The
entrance 22 can be near a junction between the anterior surface 12
and the cephalid surface 14, or conceivably slightly onto the
cephalid surface 14, but near the anterior surface 12.
[0035] A step 24 is preferably provided between the entrance 22 and
the exit 26 in the standard bores 20. This step 24 provides a shelf
against which a bone screw head 32 of a standard bone screw 30 can
abut when the standard bone screw 30 has been passed through the
standard bore 20 and threaded into the S1 sacrum or other vertebrae
or other structure on a caudal side of the implant 10. Preferably,
the standard bone screw 30 includes the bone screw head 32 opposite
a tip 36 with bone screw threads 34 adjacent the tip 36 and
extending up toward the bone screw head 32. These bone screw
threads 34 are cancellous threads or otherwise threads formed for
engagement with bony structures such as within the S1 sacrum. These
bone screw threads 34 can be configured to tap complementary
threads in the sacrum S1.
[0036] As an alternative, a tapping tool can be utilized and a
drill utilized to first drill a hole in the sacrum S1 and then form
threads in the hole formed in the sacrum S1, so that the bone screw
30 does not need to form a hole and/or form threads in the sacrum
S1, or other vertebrae or other structure, but rather merely is
threaded into such a hole. As another alternative, the standard
bone screw 30 could be a cannulated bone screw which is configured
to follow a guide wire which has been previously fitted into the
sacrum S1, such as with the assistance of a fluoroscope to ensure
precise orientation of the standard bone screws 30. Most
preferably, the standard bone screws 30 are oriented non-parallel
to each other, for maximum mechanical coupling of the implant 10 to
the sacrum S1 or other vertebrae or other structure adjacent the
caudal surface 16 of the implant 10.
[0037] As shown in FIG. 2, portions of the tool 60 can conceivably
block the standard bores 20 in the implant 10. The standard bone
screws 30 can be placed into the standard bores 20 when the guide
tool 60 is detached from the implant 10, or the guide tool 60 can
be provided with holes or a shape which leaves the standard bores
20 substantially open so that the guide tool 60 can be attached to
the implant 10 when the standard bone screws 30 are attached to the
implant 10 and to the sacrum S1 or other vertebrae or other
structure on a caudal side of the implant 10. As the standard bone
screws 30 are tightened, the bone screw head 32 abuts against the
step 24 and the implant 10 is drawn tight against the sacrum S1 or
other vertebral structure adjacent the caudal surface 16 of the
implant 10.
[0038] The upper bores 40 preferably are blind bores which extend
from an entrance 42 and terminate within an interior of the implant
10. Female machine threads 44 are formed on these upper bores 40.
As an alternative, the upper bores 40 could pass entirely through
the implant 10 out the caudal surface 16, and with the entrance 42
still located in the cephalid surface 14. If the upper bores 40 are
in the form of such throughbores, the upper bores 40 could
optionally have no threads therein.
[0039] Before the upper bores 40 can be utilized, holes H are
formed in the L5 vertebra or other vertebral structure adjacent the
cephalid surface 14 of the implant 10. Once such a hole H has been
formed, a hybrid screw 50 can be passed through this hole H and
with male machine threads 57 on a distal end 56 of the hybrid screw
50 sized to match the female machine threads 44 in the upper bore
40 for securing of the hybrid screw 50 to the implant 10.
[0040] The hybrid screws 50 are configured to engage both the
implant 10 and the L5 vertebra or other vertebral structure
adjacent the cephalid surface 14 of the implant 10. In the
preferred embodiment, the hybrid screw 50 includes a proximal end
52 opposite a distal end 56. A hybrid screw head 54 is provided at
the proximal end 52. A torque applying structure is associated with
the hybrid screw head 54, such as a allen wrench recess formed in
the hybrid screw head 54. Such a recess is shown in broken lines in
FIGS. 4 and 5.
[0041] Bone threads 55 are provided adjacent the proximal end 52
and with male machine threads 57 provided adjacent the distal end
56. The male machine threads 57 are referred to as "machine
threads" because they are configured to thread into the female
machine threads 44 pre-formed in the upper bores 40, with precise
matching of pitch angles and major and minor diameters for secure
attachment of the male machine threads 57 with the female machine
threads 44 in the upper bores 40.
[0042] The bone threads 55 are configured to engage walls of the
hole H formed in the L5 vertebra or other vertebral structure
adjacent the cephalid surface 14 of the implant 10. In one
embodiment, the hole H has a diameter similar to a minor diameter
of the hybrid screw 50. The bone threads 55 thus thread into walls
of the hole H as the hybrid screw 50 is advanced along a centerline
of the hole H and the upper bores 40. As the hybrid screw 50
advances, the male machine threads 57 adjacent the distal end 56
engage the female machine threads 44 and the hybrid screw 50 is
then coupled through both the male machine threads 57 engaging the
female machine threads 44 in the upper bores 40 of the implant 10,
as well as the bone threads 55 simultaneously engaging walls of the
hole H in the L5 vertebra or other vertebral structure adjacent the
cephalid surface 14 of the implant 10. The bone threads 55 can be
self-tapping, such as by including a self-tapping cutting groove
160 in the alternative hybrid screw 150 depicted in FIG. 5.
[0043] Also in FIG. 5, pitch angles for the male machine threads 57
and the bone threads 55 are depicted. Angle .alpha. depicts a pitch
angle for the male machine threads 57. Angle .beta. depicts the
pitch angle for the bone threads 55. Preferably, the pitch angle
for the male machine threads 57 and the pitch angle for the bone
threads 55 are substantially identical. Because the male machine
threads 57 in this embodiment are finer than the bone threads 55,
the male machine threads 57 can be compound threads to allow the
pitch angles .alpha., .beta. to match each other. As another
alternative, the male machine threads 57 could be provided no finer
than the bone threads 55.
[0044] In one embodiment, a slight differential is provided between
the pitch angle .alpha. and the pitch angle .beta., with the pitch
angle .alpha. being slightly steeper than the pitch angle .beta..
In this way, portions of the hybrid screw 50 adjacent the distal
end 56 advance at a greater rate per turn of the hybrid screw 50
than portions of the screw 50 adjacent the proximal end 52, so that
the implant 10 is drawn toward the L5 vertebra or other vertebral
structure adjacent the cephalid surface 14 of the implant 10. With
such a configuration, an initially somewhat loose threading of the
hybrid screw 50 through the hole H and into the upper bore 40
becomes a tight fit as the hybrid screw 50 continues to be
rotationally advanced into the upper bores 40 and this differential
in the pitch angles of the male machine threads 57 and bone threads
55 cause a tightening of the L5 vertebra or other vertebral
structure adjacent the cephalid surface 14 of the implant 10 to be
drawn tightly against the cephalid surface 14 of the implant
10.
[0045] In another alternative depicted in FIG. 4 in broken lines, a
further alternative hybrid screw 250 is depicted which has no bone
threads thereon. Rather, an alternative hybrid screw head 254 is
provided which has a diameter greater than that of an alternative
hybrid screw shaft 253. In this embodiment, the hole H would be
provided with a step therein, such as midway between an anterior
side of the L5 vertebra and a surface of the L5 vertebra adjacent
the cephalid surface 14 of the implant 10. The alternative hybrid
screw head 254 would abut this shelf and then apply a compressing
force on the L5 vertebra compressing it against the implant 10 as
further turning of the hybrid screw 50 and further engagement of
the male machine threads 57 of the hybrid screw 50 with the female
machine threads 44 in the upper bores 40 of the implant 10 draws
the hybrid screw 50 further down into the implant 10.
[0046] To form such a stepped hole in the L5 vertebra, or other
vertebral structure adjacent the cephalid surface 14 of the implant
10, a drill bit can be utilized which has a stepped character. As
another alternative, two separate drill bits having different sizes
can be sequentially utilized. A first smaller drill bit would
follow a centerline C entirely through the L5 vertebra to form the
hole H. Then a second larger drill bit would be advanced only
partway along the same centerline C, with perhaps a stop on the
drill bit or other technique to precisely control a depth of the
larger diameter portion of the hole H.
[0047] Hybrid screws 50 having such an alternative hybrid screw
head 254 and without bone threads (or optionally with both the
alternative hybrid screw head 254 and bone threads 55) could be
provided with different lengths in small increments, so that if the
hybrid screw 50 is found to be too long or too short, a separate
hybrid screw can be selected which has an appropriate length to
maximize secure attachment of the L5 vertebra (or other vertebral
structure adjacent the cephalid surface 14 of the implant 10) to
the upper bores 40 of the implant 10.
[0048] With particular reference to FIGS. 2, 3 and 6, details of
the guide tool 60, according to one embodiment of the system 100 of
this invention, are described. In operating the system 100 and
method of this invention it is important that the hole H be
precisely formed that is aligned with the centerline C of the upper
bores 40 in the implant 10. To achieve this precise alignment, the
guide tool 60 is provided. The guide tool 60 is removably
attachable securely to the implant 10 so that guide bores 68 in the
guide tool 60 can be precisely aligned with the upper bores 40 in
the implant 10 along the common centerline C.
[0049] In the preferred embodiment, this guide tool 60 includes a
handle 62 coupled to one end of a guide tool shaft 63 with a
coupling tip 64 at an opposite end of the guide tool shaft 63. This
coupling tip 64 is threaded to thread into the tool port 18 in the
anterior surface 12 of the implant 10. As an alternative, some
other form of rigid removable coupling can exist between the guide
tool 60 and the implant 10 for secure attachment of the guide tool
60 to the implant 10. Importantly, this attachment not only
provides for elimination of movement between the implant 10 and the
guide tool 60, but also provides for precise orientation of guide
bores 68 of the guide tool 60 relative to the implant 10.
[0050] The guide tool shaft 63 in this embodiment supports a guide
block 66 extending therefrom. Multiple guide bores 68 pass through
this guide block 66 which guide bores 68 are aligned with the upper
bores 40 in the implant 10 when the coupling tip 64 of the guide
tool 60 is coupled to the implant 10. Once so attached, the drill
70 can be utilized passing through the guide bores 68 to form the
holes H through which the hybrid screws 50 pass, for secure
attachment to the upper bores 40 of the implant 10.
[0051] While the guide tool 60 is described in this manner, a
variety of different guides could be provided, so long as guide
bores are oriented where required and precisely aligned with the
centerline C of the upper bores 40 of the implant 10, so that a
drill 70 or other cutting tool can be precisely passed along this
centerline C to cut a hole through the L5 vertebra or other
vertebral structure adjacent the cephalid surface 14 of the implant
10, to form the hole H precisely aligned with the upper bores 40 in
the implant 10. In one embodiment, the guide tool 60 is attached to
multiple locations on the anterior surface 12 or other portions of
the implant 10, to ensure very precise alignment of the guide bores
68 associated with the guide tool 60 with the centerlines C of the
upper bores 40 in the implant 10.
[0052] This disclosure is provided to reveal a preferred embodiment
of the invention and a best mode for practicing the invention.
Having thus described the invention in this way, it should be
apparent that various different modifications can be made to the
preferred embodiment without departing from the scope and spirit of
this invention disclosure. When structures are identified as a
means to perform a function, the identification is intended to
include all structures which can perform the function specified.
When structures of this invention are identified as being coupled
together, such language should be interpreted broadly to include
the structures being coupled directly together or coupled together
through intervening structures. Such coupling could be permanent or
temporary and either in a rigid fashion or in a fashion which
allows pivoting, sliding or other relative motion while still
providing some form of attachment, unless specifically
restricted.
* * * * *