U.S. patent application number 12/364682 was filed with the patent office on 2009-05-28 for tapered bone fusion cages or blocks, implantation means and method.
Invention is credited to Charles D. Ray.
Application Number | 20090138091 12/364682 |
Document ID | / |
Family ID | 34748929 |
Filed Date | 2009-05-28 |
United States Patent
Application |
20090138091 |
Kind Code |
A1 |
Ray; Charles D. |
May 28, 2009 |
TAPERED BONE FUSION CAGES OR BLOCKS, IMPLANTATION MEANS AND
METHOD
Abstract
Methods for fusion inside a forward widely tapering human disc
space. A stabilizing/guiding system is driven into and against the
disc space. The device is further stabilized by spreading and
gripping means inside both vertebral end plates. Rod retaining
members hold calibrated rod units whose adapted tips perform
reaming and threading of the disc space. Subsequently, the tapered
cage or implant can be inserted by a free-hand method under direct
vision into the prepared and tapered bed. Rod unit divergent
angulation is set to match that of the disc space as well as the
implants so they obtain optimal distributed purchase of vertebral
bone. In one embodiment, inserts are confluent with parallel medial
walls rather than their long axes, increasing torsional or lateral
translational stability and simplifying placement of additional
bone chips. No tubular guide means are required.
Inventors: |
Ray; Charles D.; (Santa
Barbara, CA) |
Correspondence
Address: |
DICKE, BILLIG & CZAJA
FIFTH STREET TOWERS, 100 SOUTH FIFTH STREET, SUITE 2250
MINNEAPOLIS
MN
55402
US
|
Family ID: |
34748929 |
Appl. No.: |
12/364682 |
Filed: |
February 3, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11025217 |
Dec 29, 2004 |
7485120 |
|
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12364682 |
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60533622 |
Dec 31, 2003 |
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Current U.S.
Class: |
623/17.16 ;
128/898; 623/17.11 |
Current CPC
Class: |
A61B 2017/0256 20130101;
A61F 2002/448 20130101; A61F 2002/4687 20130101; A61B 17/1757
20130101; A61F 2250/0006 20130101; A61F 2/4611 20130101; A61F
2002/30538 20130101 |
Class at
Publication: |
623/17.16 ;
128/898; 623/17.11 |
International
Class: |
A61F 2/44 20060101
A61F002/44; A61B 19/00 20060101 A61B019/00 |
Claims
1. A method of implanting a pair of fusion cages or similar
fusion-inducing devices in a spinal disc space, the method
comprising: providing an implantation system including a guide body
and first and second rod retaining members positioned at opposite
sides of the guide body, respectively; securing a distal end of the
guide body to the disc space; preparing a first intradiscal bed in
the disc space via at least one rod unit selectively maintained by
the first rod retaining member; preparing a second intradiscal bed
in the disc space via at least one rod unit selectively maintained
by the second rod retaining member; inserting a first
fusion-inducing device into the first intradiscal bed; and
inserting a second fusion-inducing device into the second
intradiscal bed; wherein the implantation system is configured to
form the intradiscal beds such that upon insertion, the first and
second fusion-inducing devices are angularly oriented relative to
one another in that corresponding distal ends of the inserted
devices are more closely spaced as compared to corresponding
proximal ends.
2. The method of claim 1, wherein the method is performed on an
L5-S1 disc space.
3. The method of claim 1, wherein the fusion-inducing devices are
tapered fusion cages.
4. The method of claim 3, wherein an angle of the intradiscal beds
relative to a centerline of the disc space approximates a taper of
the fusion cages.
5. The method of claim 1, wherein preparing a first intradiscal bed
includes manipulating the first rod retaining member to orient a
guide axis defined by the first rod retaining member to a desired
position relative to a central axis defined by the guide body.
6. The method of claim 1, wherein inserting a first fusion-inducing
device includes free hand implantation of the first fusion-inducing
device.
7. The method of claim 1, wherein the steps of preparing first and
second intradiscal beds occur while the distal end of the guide
body is secured to the disc space.
8. The method of claim 1, wherein preparing a first intradiscal bed
includes: assembling a first rod unit including an elongate rod and
a distal reaming member to the first rod retaining member such that
the rod extends along a guide axis defined by the first rod
retaining member; manipulating the first rod unit along the guide
axis such that the reaming member reams a passage into the disc
space; removing the first rod unit from the first rod retaining
member; assembling a second rod unit including an elongate rod and
a distal working member differing from the distal reaming member to
the first rod retaining member such that the rod of the second rod
unit extends along the guide axis; and manipulating the second rod
unit along the guide axis such that the distal working member
modifies the passage.
9. The method of claim 8, wherein the distal working member forms a
threaded surface and manipulating the second rod unit includes
tapping a surface of the passage.
10. The method of claim 8, wherein preparing a second intradiscal
bed includes: assembling a third rod unit including an elongate rod
and a distal reaming member to the second rod retaining member such
that the rod of the third rod unit extends along a guide axis
defined by the second rod retaining member; manipulating the third
rod unit along the guide axis of the second rod retaining member to
ream a second passage into the disc space; removing the third rod
unit from the second rod retaining member; assembling a fourth rod
unit including an elongate rod and a distal working member to the
second rod retaining member such that the rod of the fourth rod
unit extends along the guide axis of the second rod retaining
member; and manipulating the fourth rod unit along the guide axis
of the second rod retaining member such to modify the second
passage.
11. The method of claim 1, wherein the first and second rod
retaining members each form a guide axis, and further wherein the
guide axis intersect a central axis of the guide body distal the
distal end of the guide body.
12. The method of claim 1, wherein the distal end of the guide body
includes an expandable tip expandable from the first state to a
second state, and further wherein securing a distal end of the
guide body to the disc space includes: inserting the expandable tip
in the first state into the disc space; and expanding the
expandable tip toward the second state to rigidly mount the guide
body to the disc space.
13. The method of claim 12, wherein the expandable tip includes
opposing, first and second tip bodies pivotably connected to the
guide body and each defining an engagement surface, and further
wherein expanding the expandable tip includes: pivoting the first
tip body relative to the guide body such that the engagement
surface of the first tip body is forced into a superior end plate
of the disc space; and pivoting the second tip body relative to the
guide body such that the engagement surface of the second tip body
is forced into an inferior end plate of the disc space.
14. The method of claim 13, wherein the steps of pivoting the first
and second tip bodies occurs simultaneously.
15. The method of claim 14, wherein the steps of pivoting the first
and second tip bodies includes proximally retracting a wedge
between the tip bodies.
16. The method of claim 12, wherein expansion of the tip from the
first state toward the second state occurs in a plane perpendicular
to a common plane defined by guide axes of the rod retaining
members.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a divisional of U.S. patent application
Ser. No. 11/025,217 filed Dec. 29, 2004, and entitled "Tapered Bone
Fusion Cages or Blocks, Implantation Means and Method" which claims
the benefit of U.S. Provisional Patent Application Serial No.
60/533,622 filed Dec. 31, 2003 and entitled "Tapered Bone, Fusion
Cages or Blocks, Implantation Means and Method"; and the entire
teachings of which are incorporated herein by reference.
BACKGROUND
[0002] The present disclosure relates to fusions of the spine, more
specifically to intradiscal or interbody fusions utilizing hollow,
formed, perforated, threaded cages in severe, disabling discogenic
back pain problems, with or without a herniation (protrusion) of
the disc.
[0003] Degenerative changes of the human spinal column often are
accompanied by severe, disabling back pain; one method of success
in eliminating such pain originating from within the disc, called
discogenic pain, is to surgically eliminate the disc and create a
fusion or bony union between adjacent vertebrae, eliminating the
offending, painful disc. Several successful surgical devices and
methods are now available to obtain the desired bone or suitable
substitute fusion. One such valid method utilizes fusion cages that
are hollow, usually threaded devices, to contain and protect the
bone graft material; the cage is driven or screwed into the
prepared disc space to facilitate the development of a solid bony
fusion. Into these cages morcelized bone graft or substitute fusion
inducing material is placed with the fusion developing by a growth
of the contained material from one vertebra, through the multiple
perforations in the cage walls, into the adjacent vertebra. Such
devices are nearly all cylindrical with parallel walls; however, at
some disc spaces having a forward-opening taper, it is preferable
to use inserts having the same taper so they will more closely
conform to that disc space taper and provide an improved
distributed attachment of the insert along essentially all of the
tapering disc space. Further, tightness of the laminated,
circumferential collagen fibers of the annulus, the outer part of
the flexible disc structure, is essential for early stability of
the movable spinal segment. Thus, the goal is to immediately
stabilize the segment by the implant while the fusion slowly
develops. The device or material used to facilitate a fusion
formation must initially be able to support the vertical forces,
roughly up to 1.8 times the body weight and to induce or conduct
the fusion formation.
[0004] The threaded fusion cage system was designed to simplify the
surgery for spine fusion. Each cage of the pair ordinarily used in
the procedure is inserted into the surgically prepared and tapped
or threaded hole formed between the two adjacent vertebrae,
penetrating into the bone of each. Although shaped bone grafts or
substitute material may be used instead of the cages to accomplish
the fusion in many cases, the cages permit the use of disorganized
bone chips being held into position by the cage structure. The
optimal penetration, called purchase, of each cage into each of the
opposing vertebral bodies to be united by bone growth, known as a
fusion process, has led to substantial success in fusing the spine
for over 14 years and cages of various manufactures have been
implanted in perhaps 500,000 patients worldwide. Cages are hollow
threaded titanium devices nearly always formed as straight
non-tapering cylinders and are appropriate for most applications
since the end plates of the vertebral bodies are generally quite
parallel.
[0005] Anatomically, however, some of the disc spaces are not
parallel, particularly at the lowest lumbar space which adjoins the
top of the sacrum bone. This space, called Lumbar 5-Sacral 1 (or
L5-S1) is commonly involved in the disabling, degenerative
discogenic pain process. The L5-S1 disc space normally has a taper,
with a larger opening at the front. When parallel-walled fusion
cages are inserted into the L5-S1disc space, more commonly from a
frontal or anterior approach through the abdomen, sections of the
usual parallel walled cages maybe too deeply purchased towards the
posterior portion of the disc space and essentially have little or
no purchase into the more anterior or frontal portion of the
tapering disc space. One solution to this problem to obtain good
purchase along the majority of the disc space is to use a tapered
fusion cage whose angle of taper is chosen to more closely match
the forwardly widening angle of the disc. To suit a variety of
anatomical variations, a range of tapering angles of cages is
needed, usually 6.degree., 9.degree. and 12.degree., larger towards
the front. In addition, with this normally greater forward opening
of the taper, it is extremely unlikely that it would be practical
or safe (relative to posterior nerve issues) to utilize a posterior
approach for implantation. Various tapered cage designs and methods
of implant are described in Ray C D, Dickhudt E A: V-threaded
fusion cage and method of fusing a joint. U.S. Pat. No. 4,961,740;
and, Ray C D, Dickhudt E A: Surgical method and apparatus for
fusing adjacent bone structures. U.S. Pat. No. 5,026,373; and Ray C
D: Surgically implanting threaded fusion cages between adjacent
low-back vertebrae by an anterior approach. U.S. Pat. No.
5,05.5,_04; and Ray C D: Instrumentation and method for
facilitating insertion of spinal implant. U.S. Pat. No. 6,042,582;
and Winslow C J, Mitchell S T, Jayne K, Ray C D: Open posterior
lumbar fusion cage insertion set and method. U.S. Pat. No.
6,083,225 Systems presently manufactured by Stryker Spine, Inc., of
Allendale, N J, as the Ray Threaded Fusion Cage and associate
instruments are also instructive. Additionally, other tapered cage
systems have been allowed US patent coverage by other
inventors.
[0006] Related Art-in the past various instruments and methods have
been developed for anterior insertion of various appropriately
shaped supportive materials that can induce or conduct the
formation of a solid fusion. Such materials have included solid
bone autografts (the patient's own shaped bone) or allografts
(shaped cadaver bone), shaped artificial bone substitutes
(bioceramics or ocean coral) or a variety of appropriately shaped
cage-like devices, each of which is cut or formed to match the
desired angle of forward taper. The greatest problems associated
with the instrumentation used for the implantation of these
materials or devices to be implanted have been: (1) rigidly
attaching a guiding assembly (usually tubular) onto or within the
disc space of adjacent vertebrae for subsequent preparation of the
bed and subsequent insertion of the appropriately tapered devices
or cages while maintaining the proper spacing (for a plurality of
implants) and angulation of the devices to be used, (2) reaming
(tapered drilling) the recipient bed while rigidly maintaining the
direction and depth of this process, creating the appropriate
recipient bed, (3) tapping the recipient bed, or utilizing
self-tapping cages, while maintaining the same initial angulation
and spacing used in the above earlier stages, and (4) appropriate
tightening of the circumferential fibers of the annulus with
stabilization of the operated segment through a means to expand the
disc. For such procedures, most commonly utilized is an essentially
tubular guiding means through which the preparation and steps of
implantation are performed. Such tubular means are temporarily
attached across or within the disc space. This tubular means,
usually a singular or double-barreled device, is forcefully driven
onto or into the disc space. Through this stabile tubular device,
the bed for the paired cage is formed by boring or reaming, then
the tapping, and followed by cage or device insertion. Subsequently
or prior to insertion, the utilized cages are filled with
appropriate bone chips or substitute. Importantly, all such
procedures place the tapered cages or materials with their long
axes parallel to each other. Since the disc space and matching
angulated cages are larger in front, and after insertion may even
touch, the placement of ancillary bone outside and between the
implants, as many surgeons prefer, is inhibited. Further, because
the overall width of the two adjacent implants is twice their
diameters, the pair of implants may be excessively wide for that
disc space.
SUMMARY
[0007] The novel systems and methods in accordance with one
embodiment utilizes a variety of related instruments. Following
adequate anterior lumbar transabdominal surgical approach and
preparation of the affected disc space, including the scraping of
end plate cartilages away from the adjacent vertebral bodies, a rod
stabilizing/guiding instrument is driven into the disc space using
a hammer striking against a removable plate. The guide has means to
expand vertically to appropriately tighten its grip inside the
tapering disc space while minimally changing the disc taper angle,
by its expanding/lifting upper and lower knurled surfaces engaging
the end plates along the majority length of their angulated central
disc space surfaces. Each desired angulation, preferably 6.degree.,
9.degree. or 12.degree. has a set of reaming or boring, threading
or tapping instruments coded for ease in matching their various
angulated components. The stabilizer/guide of this novel set of
instruments is adjustable to accommodate various disc taper angles.
Once the guide device is driven and stabilized inside the disc
space and tightened, appropriately guided ancillary rod-mounted
instruments are used to ream and tap for the later insertion of
suitable tapered cages with great precision. These rod-mounted
components pass through lateral guiding members, fixably removable
and changeable as the procedure progresses. These rod guiding
members are appropriately marked as to depth of penetration into
the disc space. At conclusion of the prepared threaded recipient
bed, the stabilizing/guiding unit is unlocked and removed from the
vertebrae. The tapered insert is attached to the insertion rod and
following the visible tapped recipient bed, screwed into position
freehand under direct observation and by intraoperative
fluoroscopy, a technique familiar to skilled surgeons such as is
performed routinely in the insertion of pedicle screws and the
like. When a prepared cage with arcs cut into the outer sides is
used, it is implanted as first of the pair where the second may or
may not have such side cuts. The pair of cages will this be nestled
closer together, with a narrower total width, than if cages with no
such side cut arcs were used. Since the insert is tapered, the disc
space does not require a support to keep it open after the guide
unit is removed; the taper will reopen the disc according to the
depth of insertion of the tapered insert. Additional bone may be
packed posterior and lateral to the cages.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a simplified, top plan view of a system for
implanting tapered spinal fusion cages or similar devices in
accordance with the present disclosure in conjunction with a spinal
disc space;
[0009] FIG. 2 is a perspective, exploded view of a portion of the
system of FIG. 1;
[0010] FIG. 3 is a cross-sectional view of the system of FIG.
2;
[0011] FIG. 4 is a perspective view of various rods useful with the
system of FIG. 1;
[0012] FIG. 5 is a simplified, top plan view of an alternative
embodiment system in accordance with the present disclosure;
and
[0013] FIG. 6 is an enlarged, cross-sectional view of two tapered
fusion cages following implant using the system and method of the
present disclosure.
DETAILED DESCRIPTION
[0014] In the following Detailed Description, reference is made to
the accompanying drawings, which form a part hereof, and in which
is shown by way of illustration specific embodiments in which the
disclosure may be practiced. In this regard, directional
terminology, such as "top," "bottom," "front," "back," "leading,"
"trailing," etc., is used with reference to the orientation of the
Figure(s) being described. Because components of embodiments of the
present disclosure can be positioned in a number of different
orientations, the directional terminology is used for purposes of
illustration and is in no way limiting. It is to be understood that
other embodiments may be utilized and structural or logical changes
may be made without departing from the scope of the present
disclosure. The following detailed description, therefore, is not
to be taken in a limiting sense, and the scope of the present
disclosure is defined by the appended claims.
[0015] FIG. 1 is a composite, diagrammatic plan view from above
showing one embodiment of a stabilizing/guiding system 1 in
accordance with the present disclosure engaged against the anterior
aspect of a vertebra 2 and a portion extending inside a vertebral
disc space 3 with tabs 4 firmly against the anterior aspect of the
vertebrae 2, along with a generic representation of a tapered cage
14. In general terms, and with additional reference to FIG. 2, the
system 1 includes a guide body 50 defining a proximal surface 6 and
a distal end forming tabs 4 and stabilizer tips 9 that are
pivotable about a corresponding hinge point 10 via interface with a
wedge or similar device 8. Movement of the wedge 8 is dictated by a
central drive body 52 (e.g., a shaft) otherwise proximally
accessible via a knob 54. In addition, the system 1 includes
opposing lateral guide or rod retaining members 11 attached to the
guide body 50. The lateral guide members 11 are, in one embodiment,
releasably secured to the guide body 50 by a plate 17. Further,
each of the lateral guide members 11 defines a selectively
accessible passage 56 adapted to selectively receive and maintain a
rod unit 12 via, for example, a winged knob 15 secured within a
socket 18. The rod unit 12 is described in greater detail below
with reference to FIG. 4, but generally includes a distal, working
end and a proximal knob 13 or similar structure. During use, the
system 1 is driven into the surgically prepared disc space 3 using
a hammer (not shown) struck against a removable striking block 5
which is temporarily positioned against the proximal surface 6 by
indexing pins 7.
[0016] After driving the system 1 against the vertebrae 2, the
striking block 5 is removed and the tightening knob 54 is rotated
which pulls the wedge or other means 8 inside the knurled
stabilizer tips 9 causing their knurled surface to be temporarily
imbedded into the opposing walls of the vertebral end plates (not
shown). The knurled stabilizer tips 9 are hinged 10 so they may
spread apart inside the disc space 3. The lateral guide or rod
retaining members 11 for guidance of rod units 12 having suitable
knobs 13 for hand drilling or reaming, tapping or threading of the
bed for later free hand cage 14 insertion is thus under firm and
repeatable control. The lateral guide members 11 are opened for
changing the rod units 12 then firmly held in proper position using
winged knobs 15, or similar means, as needed to drill or ream the
recipient bone bed, thread or tap the bed and provide the suitable
bed for subsequent freehand implantation of the suitable tapered
cages 14. The angulation 16 of the lateral guide members 11
relative to the midline is selected and fixably alterable to be the
same as the angulation of the tapered cages 14. The lateral guide
members 11 are removably attached to the guide body 50. A hinged
screw 15 on the lateral guide member 11 fits into the rounded
socket 18 and held firmly by means such as winged knobs 15. The
adjoining surfaces of the subsequently implanted, paired cages 14
are closely paralleled to each other.
[0017] FIG. 2 is a diagrammatic perspective view seen laterally of
the stabilizing/guiding system or unit 1 and associated components.
As shown in FIG. 1, the long axis of the system 1 is driven into
the surgically prepared disc space 3 until the tabs 4 engage the
anterior vertebral margins, utilizing the block 5 removably
attached to the end 6 by index pins 7. After firmly seating the
stabilizing/guiding system 1, the striking block 15 is removed and
the fixation knob 54 is rotated pulling the wedge 8 or suitable
means inside the knurled stabilizer tips 9, hinged 10 on the
stabilization/guiding system 1, thus firmly anchoring the deep end
of the unit tips 9 inside the disc space 3 and maximally opening
and tightening the fibers of the circumferential, ligamentous
vertebral annulus (unnumbered). The angulated lateral guide members
11 are opened laterally for placement of the rod units 12 for
drilling (reaming) and tapping (threading) to prepare the recipient
bed for subsequent insertion of cages 14. The lateral guide members
11 are removably attached to the stabilization/guiding unit 1 by
suitable means such as screws (not shown). The tapered half-sockets
18 are shown where the bases of the screws with winged knobs are
seated when tightened.
[0018] FIG. 3 is a diagrammatic cross-section showing the wedge 8
inside the knurled tips 9 of the stabilizing/guiding unit 1 and the
cages (not shown), one with arcuate lateral cuts, are closely
approximated.
[0019] FIG. 4 is a composite diagram of the two rod units 12 for
drilling (reaming) A, tapping (threading) B, and the separate rod
later used for subsequent free hand cage insertion C. Each rod unit
12 is hand torqued using its knob 13. Each rod 12 unit is
calibrated in millimeter/centimeter increments 20 as referenced to
the outer margin of the lateral guide member 11 (FIG. 2) to
indicate the depth of reaming or tapping. Each rod unit 12 is
changeably removable from the lateral guiding member 11 as needed
without disturbing the stability or guidance of the main unit. The
"A" rod unit 12A has an odd plurality of sharp flat cutting
(reaming) vanes 19, usually three, where the odd number provides a
more uniform torque on reaming between the parallel vertebral end
plate surfaces than would be obtained if the reamer used an even
number of vanes. The vanes 19 may also be slightly spiraled for
even more uniform torque and spontaneous removal of debris. The
tapping rod unit 12B has an odd fluted spiraled tap 21 for even
torque on tapping the reamed hole. The subsequently free-hand cage
insertion rod unit 12C has a suitable engaging means 22 to
removably connect a cage mounted on its tip. A ball detent or
similar means serves to removably retain the cage (not shown) until
it is firmly installed. The handle of this rod unit 12C is oval
with directional markings to indicate the position of the
potentially arcuate side cuts of cages, if they are provided, that
must face the full cage. The insertion rod unit 12C, or similar
insertion device, can be used apart from the system 1 (e.g.,
freehand, with the system 1 removed from the disc space 3), or with
the system 1 still in place.
[0020] FIG. 5 is a composite, diagrammatic plan view of an
alternative embodiment stabilizing/guiding system 1' closely
reflecting major details of FIG. 1. The system 1' is adapted to
selectively retain rod units 12 (FIG. 1), such as rod units for
reaming 12A (FIG. 4), tapping 12B (FIG. 4), and subsequent
free-hand insertion 12C (FIG. 4) of the tapered cages 14, 24. To
this end, the system 1' is adapted to direct the rods 12 towards a
virtual confluent or hinge point 23 near the distal margin of the
vertebral bodies 2. Maintenance of correct angulation for
implantation of tapered cages, determined by the angular opening of
the disc space between the adjacent vertebral bodies, matched with
tapered cage angulation, is determined by rod attachment member 60
having a sector plate 25 and adjustable components having the same
virtual hinge point 23.
[0021] The sector plate 25 has a flat upper surface and a keystone
mortised under surface 26 into which a sliding guide 27 closely and
fixably fits. The sliding guide 27 is adapted to receive one of the
rods units 12. The upper surface of the sector plate 25 has a
curving slot 28 through which a screw 62 provided with the rod
attachment member 60 passes to be movably fixated at a desired
position by tightening a wing nut 15. This fixation simultaneously
fixates the sliding guide 27, and thus the associated rod unit.
Markings 29 on the sector plate 25 denote the chosen angulation.
Markings 30 on the rod units 12 indicate the depth of penetration
into the disc space by their tip structures.
[0022] FIG. 6 is a diagrammatic cross-sectional view of two,
implanted Stryker Spine, Inc. Ray `Unite`.TM. tapered fusion cages.
The elevating and fixating spreader tips 31 having knurled outer
surfaces associated with the stabilizing/guiding unit of the
present disclosure are adjusted to accommodate the contour of the
appropriate tapered cages. In the Unite cage implantation version,
the first implanted of the pair, cage A has relieved medial walls
32 one on each side, 180.degree. apart, against either of which the
second cage B with a standard wall closely fits. Two `Unite` or
similar cages (having arcuate side cuts) may also be used. This
configuration permits a closer proximity of the centers of the two
cages and a reduced overall width of the combined implants than
would be permitted by two fully cylindrical cages.
[0023] The structure of the principal stabilizing/guiding unit or
system of the present disclosure may be constructed essentially
oval in cross section as well as essentially flat as shown.
Depending on the width of the surgical approach and the depth to
the target vertebrae, varying with the obesity of the patient's
abdomen, various implantation/guidance units may be of different
size or may be constructed with length telescoping/expanding
capability. Other variations may include torque knob design,
internal low friction bearing surfaces of the lateral guiding
members or methods of attachment of these members to the main unit
as well as variations in means of closure of the guiding surface
halves of these members. Design of the cages may be simple tapered
adaptations of the present Ray threaded fusion cages, similar to
considerably smaller, tapered ones now manufactured by Stryker
Spine for fusions of the cervical spine (neck).
EXAMPLE AND METHOD OF USE
[0024] A suitable patient having discogenic, painful degenerative
disc disease is examined using x ray techniques and on finding that
the angulation between the particular vertebral end plates is 6
degrees or greater, the surgeon may decide-to use tapered rather
than parallel cylindrical cages for his patient. If the segment to
be operated is at L5-S1 (the usual one), the surgeon then notes the
anatomical position of the top of the symphysis pubis, where the
pelvis joins at the front of the body. He then draws a line through
the middle of the disc to be operated extending it in the direction
of the symphysis. If this line extends below the top of the
symphysis, it indicates that the stabilizing/guiding unit may be
too large, vertically, and therefore not usable on this patient.
This means that the angle of taper as well as the segment tilt
angle through the disc centrum relative to the symphysis are both
important in patient selection. In some patients the tilt angle is
so vertically severe that an anterior approach to the L5-S1 disc
space may not be possible. Fortunately, this situation is quite
uncommon.
[0025] The appropriate tapered cages or suitable insert and
associated instruments are chosen and made ready. The patient is
anesthetized and appropriately positioned, the abdomen is prepared
with an exposure usually via a retroperitoneal dissection (moving
the abdominal organs from the patient's left to the right side,
along with the intact peritoneal sac). The abdominal exposure must
be wide enough to accommodate the angulation of the rods used in
the procedure to ream, tap and then insert. The major anterior
vessels and other important structures are mobilized and handled as
for any routine anterior retroperitoneal fusion approach, a common
technique during anterior spinal fusion procedures. The anterior
annulus is removed sufficient only to accommodate the width of the
pair of cages or inserts; the entire cartilage of the end plates is
scraped away down to bleeding bone but not to penetrate the bone of
the end plates. The stabilizing/guiding unit is driven into
position against the anterior aspect of the vertebra and its
locking tip is expanded to fully stabilize the unit and this
stability is evaluated by moving the unit in several planes,
showing that the two vertebrae and the unit move essentially as
though a single structure. The reaming and tapping into the disc
space as indicated above. The guide unit is removed and the tapered
cage is inserted free hand using its rod, carefully inserting the
first arcuate side cut cage then the fully round one. The final
positioning of the cage pair is demonstrated by intraoperative
x-ray fluoroscopy then the cages are filled with morsels of bone or
substitute and the procedure finished by routine closure of the
tissue layers and the skin incision. In that the procedure closely
parallels common anterior fusions, patients should respond quite
well to the procedure and post-operative care. Patients ordinarily
wear a corset but in some cases a rigid brace may be needed for a
few months. Subsequent office visits should include repeat x-rays
to determine the progress of the fusion and if any displacements or
other problems have arisen before the fusion becomes fully solid
(in about 3-5 months).
Advantages
[0026] The disclosure has the novel ability to utilize a pair of
fusion cages or suitable material blocks having the selected
angulation of taper to, match the tapering angles found in several
patients having disabling discogenic pain and disc degeneration,
particularly at the L5-S1 space. The divergent angulation of the
approach to insert the cages or blocks of material being the same
as the actual taper angle of the disc space permits the facing or
medial edges of the implants inside the disc space to be parallel
along their lengths, uniquely improving the availability of
surrounding disc space for a narrower overall width of the implant
pair plus additional bone graft placement. The angulation of the
set of appropriate instruments and the cage pair to be used is
determined preoperatively and the overall procedure is uniquely
well controlled by the means of central stabilization of the disc
space and the ancillary guidance components. The
stabilizing/guiding unit firmly controls the approach angle
bilaterally throughout the procedure without slipping or
dislocation assuring excellent matching of the steps of the
procedure and therefore the overall fusion rate and success.
Further, the vertical opening or expansion of the knurled fixation
member is placed at or close to its virtual disc center of
flexion/extension motion of the disc and therefore on distraction,
elevation and tightening of the circumferential annuls fibers, the
taper angle is largely unchanged. If the disc space is tilted
laterally, as in cases with localized scoliosis, the taper angle is
generally the same but the height of the disc space is different on
the two sides. By inserting the tapered cage of block more or less
into the depths of the disc space, thus difference in height can be
adjusted or even corrected; not possible when using straight
cylindrical cage implants. Therefore, the require accuracy of the
implantation is controlled throughout the reaming and threading
steps of the procedure in preparation for the final direct visual
free-hand insertion of the tapered cages, all of which expectedly
will improve on the overall results where occasional surgical
problems have arisen from other instrument methods not so well
controlled. Since the entire procedure is as well under direct
vision by the surgeon, the steps are better controlled than with
implantation techniques utilizing essentially blinded tubular
guides for each stage from the reaming to the insertion. Lastly,
the angulation for the final position of the implants has a
confluent and not parallel insertion path, there should be an
improvement in the rotary and lateral translocation stability of
the final result.
[0027] The novel system places the tapered cages or fusion inducing
devices material with their long axes convergent posteriorly where
the convergent angle is the same as the taper angle of the disc
space. Therefore, the cages come close together at a constant
distance between them, throughout their lengths. Cages machined
with arcs cut from one or more outer surfaces equal to their
circumferential contour permit them to be brought into close
contact at a width less than the combined diameters, throughout
their lengths. At the deep converging tip of the implants,
sufficient width within the vertebrae remains so additional graft
material can be placed, as may be desired by the surgeon.
Additionally, with the cage's long axes nested together, the disc
is more stable against lateral translocation or "side roll". The
depth of insertion of the tapered implants is useful to wedge
tighten the annular fibers, promoting immediate stability over
parallel walled implants. The novel system stably achieves the
boring or reaming and tapping in preparation for cage insertion
quite accurately, utilizing a rod alignment/guiding instrument and
attachments. A tubular guide unit is not employed for any of these
steps and the common rod guidance is utilized only for the boring
or reaming and threading or tapping steps. That is, once the
reaming or boring and tapping are performed, the guiding assembly
is removed and the insertion of cages installed by hand into the
provided appropriately oriented and tapered cavities. The
angulation and orientation for boring and tapping provided by the
adjustable long rod/guide assembly are selected and fixed according
to the required taper angle of the disc space and selected cage
implant. Further, prior to attachment of the guiding/stabilizing
assembly, the deep central disc space may be prepared laterally
into the vertebral bone for ancillary bone placement outside the
anticipated confluence of the cage tips. The fixed (static) and
opening up or spinal extension position (dynamic) tapering angles
which the implants should closely match are determined in advance
of the surgery utilizing lateral x-ray views of the lumbar spine in
neutral, forward flexion and reverse extension positions. In
addition to determining the taper angle of the disc space, this
maneuver aids in assessing the flexibility of the space. That is,
the more flexible the disc the more it will open on extension and
the greater the cage taper angle that may be needed following the
attachment of the stabilizing/guiding assembly. The novel
stabilizing/guiding instrument is adjustable to the same angular
taper as the implants to be used, primarily 6.degree., 9.degree. or
12.degree. or other suitable angle as indicated. Those skilled in
these arts may provide other means for adjustment of the guiding
instrument to suit various taper angles, in addition to the rod
assembly herewith disclosed without departing from the intent and
novelty of the present disclosure.
[0028] Although the present disclosure has been described with
reference to preferred embodiments, workers skilled in the art will
recognize that changes can be made in form and detail without
departing from the spirit and scope of the present disclosure.
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