1
`
`NUVASIVE 1033
`NuVasive, Inc. v. Warsaw Orthopedic, Inc.
`IPR2013-00206
`IPR2013-00208
`
`

`

`US 6,241,770 B1
`Page 2
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`US. PATENT DOCUMENTS
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`2,677,369
`3,426,364
`3,848,601
`3,867,728
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`4,070,514
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`4,349,921
`4,501,269
`4,599,086
`4,636,217
`4,714,469
`4,743,256
`4,759,766
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`4,820,305
`4,834,757
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`4,904,261
`4,911,718
`4,936,848
`4,955,908
`4,961,740
`5,015,247
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`5,026,373
`5,055,104
`5,059,193
`5,062,845
`5,071,437
`5,122,130
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`5,171,278
`5,192,327
`5,246,458
`5,258,031
`5,306,309
`
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`11/1991
`12/1991
`6/1992
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`Knowles .
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`.
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`OTHER PUBLICATIONS
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`Schmitz et a.l; Performance of Alloplastic Materials and
`Design of an Artificial Disc;
`the Artificial Disc, Brock,
`Mayer, Weigel; pp. 23—34 (1991).
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`Fusion L5—S1, Atlas of Spinal Operations, Thieme, pp.
`270—274 (1993).
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`tory of Lumbar Spine Surgery (1994) pp. 11—15; 27; 30;
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`7(2):135—156 (1997).
`
`* cited by examiner
`
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`US 6,241,770 B1
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`1
`INTERBODY SPINAL FUSION IMPLANT
`HAVING AN ANATOMICALLY CONFORMED
`TRAILING END
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates generally to interbody spinal
`fusion implants that are securely placed into the interverte-
`bral space created across the spinal disc between two
`adjacent vertebral bodies after the removal of damaged
`spinal disc material and preferably at least some vertebral
`bone from each of the adjacent vertebral bodies for the
`purpose of achieving interbody spinal fusion, which fusion
`occurs preferably at least in part through the spinal fusion
`implant itself. In particular, the present invention is directed
`to an improved,
`interbody spinal fusion implant having
`opposed arcuate surfaces for penetrably engaging each of
`the vertebral bodies adjacent a disc space in the human spine
`and having a trailing end configured to conform to the
`anatomic contour of the anterior and/or lateral aspects of the
`vertebral bodies, so as to not protrude beyond the curved
`contours thereof, and in one preferred embodiment of the
`present invention the above described implants are structur-
`ally adapted to be rotated for proper insertion.
`2. Description of the Related Art
`Surgical interbody spinal fusion generally refers to the
`methods for achieving a bridge of bone tissue in continuity
`between adjacent vertebral bodies and across the disc space
`to thereby substantially eliminate relative motion between
`the adjacent vertebral bodies. The term “disc space” refers to
`the space between adjacent vertebrae normally occupied by
`a spinal disc.
`Human vertebral bodies have a hard outer shell of com-
`
`pact bone (sometimes referred to as the cortex) and a
`relatively softer, inner mass of cancellous bone. Just below
`the cortex adjacent the disc is a region of bone referred to
`herein as the “subchondral zone”. The outer shell of compact
`bone (the boney endplate) adjacent to the spinal disc and the
`underlying subchondral zone are together herein referred to
`as the boney “end plate region” and, for the purposes of this
`application,
`is hereby so defined to avoid ambiguity. A
`circumferential ring of dense bone extends around the
`perimeter of the endplate region and is the mature boney
`successor of the “apophyseal growth ring”. This circumfer-
`ential ring comprises of very dense bone and for the pur-
`poses of this application will be referred to as the “apophy-
`seal rim”. The spinal disc that normally resides between the
`adjacent vertebral bodies maintains the spacing between
`those vertebral bodies and, in a healthy spine, allows for the
`normal relative motion between the vertebral bodies.
`
`Reference is made throughout this Background section to
`the attached drawings in order to facilitate an understanding
`of the related art and problems associated therewith. In FIG.
`1, a cross-sectional top plan view of a vertebral body V in
`the lumbar spine is shown to illustrate the dense bone of the
`apophyseal rim AR present at the perimeter of the vertebral
`body V about the endplate region and an inner mass of
`cancellous bone CB. The structure of the vertebral body has
`been compared to a core of wet balsa wood encased in a
`laminate of white oak. From the top plan view in FIG. 1, it
`can be seen that the best structural bone is peripherally
`disposed.
`FIG. 2 is a top plan view of a fourth level lumbar vertebral
`body V shown in relationship anteriorly with the aorta and
`vena cava (collectively referred to as the “great vessels”
`GV).
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`FIG. 3 is a top plan view of a fifth lumbar level vertebral
`body V shown in relationship anteriorly with the iliac
`arteries and veins referred to by the designation “IA-V”. The
`location of these fragile blood vessels along the anterior
`aspects of the lumbar vertebrae makes it imperative that no
`hardware protrude dangerously therefrom where the vessels
`could be endangered.
`Implants for use in human spinal surgery can be made of
`a variety of materials such as surgical quality metals,
`ceramics, plastics and plastic composites, cortical bone and
`other materials suitable for the intended purpose, and further
`may be absorbable and or bioactive as in being osteogenic.
`Fusion implants preferably have a structure designed to
`promote fusion of the adjacent vertebrae by allowing bone
`to grow through the implant from vertebral body to adjacent
`vertebral body to thereby fuse the adjacent vertebrae. This
`type of implant is intended to remain indefinitely within the
`patient’s spine or if made of bone or other resorbable
`material to eventually be replaced with the patient’s bone.
`Michelson, Ray, Bagby, Kuslich, and others have taught
`the use of hollow, threaded perforated cylinders to be placed
`across a disc space between two adjacent vertebrae in the
`human spine to encourage interbody spinal fusion by the
`growth of bone from one vertebra adjacent a disc to the other
`vertebra adjacent
`that disc through such implants.
`Michelson, Zdeblick and others have also taught the use of
`similar devices that either have truncations of their sides
`
`such that they are not complete cylinders, and/or are tapered
`along their longitudinal axis much like a cylinder which has
`been split longitudinally and then wedged apart. All of these
`implants have in common opposed arcuate surfaces for
`penetrably engaging into each of the vertebral bodies adja-
`cent a disc space to be fused. Such implants now in common
`use throughout
`the spine, may be used individually or
`inserted across the disc space in side-by-side pairs, and may
`be insertable from a variety of directions.
`It is commonly held by surgeons skilled in the art of spinal
`fusion that the ability to achieve spinal fusion is inter alia
`directly related to the vascular surface area of contact over
`which the fusion can occur, the quality and the quantity of
`the fusion mass (e.g. bone graft), and the stability of the
`construct. However,
`the overall size of interbody spinal
`fusion implants is limited by the shape of the implants
`relative to the natural anatomy of the human spine. For
`example, such implants cannot dangerously protrude from
`the spine where they might cause injury to one or more of
`the proximate vital structures including the large blood
`vessels.
`
`With reference to FIG. 4, a top plan view of the endplate
`region of a vertebral body V is shown to illustrate the area
`H available to safely receive an implant(s) inserted from the
`anterior aspect (front) of the spine, with the blood vessels
`retracted.
`
`As can be seen in FIG. 5, a top plan view of the endplate
`region of a vertebral body V with the outlines of two
`differentially sized prior art implants A and B installed, one
`on each side of the midline of the vertebral body V, are
`shown. The implantation of such prior art implants A and B
`is limited by their configuration and the vascular structures
`present adjacent anteriorly to the implantation space. For
`example, the great vessels GV present at the L4 level and
`above are shown in solid line in FIG. 5, and for the L5 and
`S1 levels, the iliac artery and vein IA-V are shown in dotted
`line. As shown in FIG. 5, prior art implant A represents an
`attempt by the surgeon to optimize the length of the implant
`which is inhibited by a limiting corner LC. Implant A, the
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`US 6,241,770 B1
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`3
`longest prior art implant that can be inserted without inter-
`fering with the great vessels GV adjacent the vertebral body
`V, leaves cross-hatched area X of a cross section the verte-
`bral body at the endplate region wasted which would be a
`very useful surface for contact for fusion and for support of
`the implant by the vertebral body. Similarly, implant B is an
`attempt by the surgeon to optimize the width of an implant
`which is also inhibited by a limiting corner LC'. Implant B,
`the widest prior art implant that can be inserted without
`interfering with the great vessels GV adjacent the vertebral
`body V, leaves cross-hatched area Y of the cross section of
`the vertebral body adjacent
`the endplate region wasted
`which could otherwise be a very useful surface area for
`contact for fusion and for support of the implant by the
`vertebral body. The presence of limiting corners LC and LC'
`on any such implants precludes the surgeon from safely
`utilizing an implant having both the optimal width and
`length, that is the length of implant A and the width of
`implant B combined, as such an implant would markedly
`protrude from the spine and endanger the large blood
`vessels.
`FIG. 5 illustrates the maximum dimensions for the above
`
`discussed prior art implants A and B to be safely contained
`within the spine so that a corner LC or LC' of the trailing end
`(side wall to trailing end junction) or the most rearward
`extension of that sidewall does not protrude outward beyond
`the rounded contour of the anterior (front) or the anterolat-
`eral (front to side) aspect of the vertebral bodies. Prior art
`implant A maximizes length, but sacrifices width and for the
`most part fails to sit over the best supportive bone periph-
`erally of the apophyseal rim as previously shown in FIG. 1.
`Prior implant B maximizes width, but sacrifices length and
`again fails to sit over the best structural bone located
`peripherally in the apophyseal rim of the vertebral body,
`comprising of the cortex and dense subchondral bone. Both
`prior art implants A and B fail to fill the area available with
`a loss of both vital surface area over which fusion could
`occur and a loss of the area available to bear the considerable
`
`loads present across the spine.
`Similarly, FIG. 6A shows the best prior art cross-sectional
`area fill for a pair of inserted threaded implants G as per the
`current prior art. Note the area Y anterior to the implants G,
`including the excellent structural bone of the apophyseal rim
`AR, is left unused, and thus implants G fail to find the best
`vertebral support. Since the wasted area Y anterior to the
`implants G is three dimensional, it also wastes a volume that
`optimally could be utilized to hold a greater quantity of
`osteogenic material. Finally, the implants of the prior art fail
`to achieve the optimal stability that could be obtained by
`utilizing the greater available surface area of contact and
`improved length that an implant with the maximum width
`and length would have, and thereby the best lever arms to
`resist rocking and tilting, and increased contact area to carry
`further surface protrusions for providing stability by engag-
`ing the vertebrae, such as with the example shown of a
`helical thread.
`
`FIG. 11 shows the best fill obtained when a prior art
`implant C is inserted, from a lateral approach to the spine
`(from a position anterior to the transverse processes of the
`vertebrae) referred to herein as the “translateral approach” or
`“translaterally” across the transverse width W of vertebral
`body V. Some examples of implants inserted from the
`translateral approach are the implants disclosed in US. Pat.
`No. 5,860,973 to Michelson and preferably inserted with the
`method disclosed in US. Pat. No. 5,772,661 to Michelson.
`Implant C does not entirely occupy the cross-sectional area
`of the end plate region and leaves cross-hatched area Z of the
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`vertebral body V unoccupied by the implant which area
`would be useful for contact for fusion and for support of the
`implant. The configuration of the trailing corner LC" of the
`prior art implant C prevents implant C from being sized
`larger and prevents the full utilization of the surface area of
`contact of the vertebral body cross-sectional area resulting in
`a sub-optimal fill of the disc space with the implant, and little
`of the implant sitting on the apophyseal rim.
`The configuration of prior art implants prevents the uti-
`lization of the apophyseal rim bone, located at the perimeter
`of the vertebral body to support the implants at their trailing
`ends. The utilization of this dense bone would be ideal.
`
`Therefore, there is a need for an interbody spinal fusion
`implant having opposed arcuate portions for penetrably
`engaging adjacent vertebral bodies,
`including implants
`requiring rotation for proper insertion into an intervertebral
`space formed across the disc space between two adjacent
`vertebrae,
`that
`is capable of fitting within the external
`perimeter of the vertebral bodies between which the implant
`is to be inserted to maximize the surface area of contact of
`the implant and vertebral bone without the danger of inter-
`fering with the great vessels adjacent to the vertebrae into
`which the implant is to be implanted. There exists a further
`need for an implant that is adapted to utilize the dense
`cortical bone in the perimeter of the vertebral bodies in
`supporting such an implant installed in a disc space.
`SUMMARY OF THE INVENTION
`
`The present invention relates to preformed, manufactured
`interbody spinal fusion implants for placement between
`adjacent vertebral bodies of a human spine at least in part
`across the disc space between those adjacent vertebral
`bodies, without dangerously extending beyond the outer
`dimensions of the two adjacent vertebral bodies adjacent
`that disc space,
`to maximize the area of contact of the
`implant with the vertebral bone. For example, the present
`invention specifically excludes bone grafts harvested from a
`patient and shaped by a surgeon at the time of surgery such
`as those of cancellous or corticocancellous bone. The
`
`present invention can benefit implants requiring an element
`of rotation for proper insertion into the implantation space,
`and more generally, any and all interbody spinal fusion
`implants having opposed arcuate surfaces spaced apart to
`penetrably engage within the substance of the opposed
`adjacent vertebral bodies, as opposed to merely contacting
`those vertebral bodies at their exposed boney end plates.
`In one embodiment of the present invention, an implant
`for insertion from the anterior approach of the spine and for
`achieving better filling of the anterior to posterior depth of
`the disc space between two adjacent vertebral bodies com-
`prises opposed arcuate portions for penetrably engaging the
`bone of the adjacent vertebral bodies deep into the boney
`endplate, a leading end which is inserted first into the disc
`space, and an opposite trailing end. The trailing end of this
`embodiment of the implant of the present
`invention is
`generally configured to conform to the natural anatomical
`curvature of the perimeter of the anterior aspect of vertebral
`bodies, such that when the implant is fully inserted and
`properly seated within and across the disc space, the surface
`area of the vertebral bone in contact with the implant is
`maximized safely. Moreover,
`the implant of the present
`invention is able to seat upon the dense compacted bone in
`the perimeter of the vertebral bodies for supporting the load
`through the implant when installed in the intervertebral
`space.
`invention, while the
`in the present
`More specifically,
`implant overall may be enlarged relative to the sizes possible
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`US 6,241,770 B1
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`5
`with prior implants, the limiting corner of the trailing end
`and side wall at the trailing end has been removed. It has
`been the need in the past to keep this limiting corner of the
`implant from protruding beyond the perimeter of the disc
`space that has prevented these same implants from being of
`the optimal size overall so as to maximize the area of contact
`and to seat upon and be supported by the peripheral rim of
`densely compacted bone.
`As another example, for an implant to be inserted from the
`lateral aspect of the spine,
`the implant of the present
`invention has opposed arcuate surfaces for penetrably
`engaging each of the vertebral bodies adjacent the disc space
`to be fused, a leading end which is inserted first into the disc
`space, and an opposite trailing end. The trailing end is
`configured to conform to the curvature of the lateral aspect
`of the perimeter of the vertebral bodies adjacent the disc
`space and without dangerously extending beyond the outer
`dimensions of the two vertebral bodies, such that when the
`implant is inserted in the disc space, the surface area of the
`vertebral bone in contact with the implant is maximized
`without interfering with any of the vital structures adjacent
`to those vertebral bodies.
`
`The spinal implants of the present invention may also
`have at
`least one opening allowing for communication
`between the opposed upper and lower vertebrae engaging
`surfaces to permit for bone growth in continuity through the
`implant from the adjacent vertebral bodies for fusion across
`the disc space of the adjacent vertebral bodies, and through
`the implant.
`For any of the embodiments of the present invention
`described herein, the implants may include protrusions or
`surface roughenings for engaging the bone of the vertebral
`bodies adjacent to the implant. The material of the implant
`may be an artificial material such as titanium or one of its
`implant quality alloys, cobalt chrome, tantalum, or any other
`metal appropriate for surgical implantation and use as an
`interbody spinal fusion implant, or ceramic, or composite
`including various plastics, carbon fiber composites, and can
`include materials which are at least in part bioresorbable.
`The materials of the implant also can include transplants of
`cortical bone or other naturally occurring materials such as
`coral, and the implants may further comprise osteogenic
`materials such as bone morphogenetic proteins, or other
`chemical compounds, the purpose of which is to induce or
`otherwise encourage the formation of bone, or fusion,
`including genetic material coding for production of bone.
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a top plan view of a horizontal cross-section
`through a boney endplate region of a vertebral body.
`FIGS. 2—3 are top plan views of the fourth and fifth level
`lumbar vertebral bodies in relationship to the blood vessels
`located anteriorly thereto.
`FIG. 4 is a top plan plan view of an endplate region of a
`vertebral body illustrating the area available to safely
`receive an implant(s) inserted from the anterior aspect of the
`spine and the area of the annulus that typically remains from
`an implantation from an anterior approach.
`FIG. 5 is a top plan view of a lumbar vertebral body
`depicting the safe area of insertion for variously propor-
`tioned prior art implants for placement to either side of the
`midline.
`
`FIG. 6A is a top plan view of the endplate region of a
`vertebral body depicting the best fit for two threaded spinal
`implants of the prior art implanted on either side of the
`midline.
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`FIG. 6B is a top plan view of the endplate region of the
`vertebral body shown in FIG. 6A illustrating the optimal
`proportions and shape of an embodiment of an implant in
`accordance with the present invention.
`FIG. 6C is a top plan view of the endplate region of the
`vertebral body shown in FIG. 6A and two threaded spinal
`fusion implants of the present invention depicting the opti-
`mal proportions and shape for such interbody fusion
`implants.
`FIG. 7A a top plan view of threaded spinal fusion implant
`of the present invention with a driver instrument for engag-
`ing the trailing end of the implant.
`FIG. 7B is cross-sectional view along lines 7B—7B of
`FIG. 7A.
`FIG. 7C is cross-sectional view of an alternative embodi-
`ment.
`
`FIG. 8 is a front elevational view of two adjacent vertebral
`bodies with the outline of another embodiment of the
`
`implant of the present invention inserted centrally from an
`anterior approach to the spine.
`FIG. 9 is a top plan view of the endplate region of a
`vertebral body and implant along line 9—9 of FIG. 8.
`FIG. 10 is a top plan view of the endplate region of a
`vertebral body with the outlines of two implants in accor-
`dance with another embodiment of the present invention
`implanted to either side of the midline.
`FIG. 11 is a top plan view of the endplate region of a
`vertebral body with a prior art implant implanted translat-
`erally across the transverse width of the vertebral body from
`a lateral aspect of the spine.
`FIG. 12A is a top plan view of the endplate region of the
`vertebral body of FIG. 11 with an implant of the present
`invention implanted translaterally across the transverse
`width of the vertebral body from a lateral aspect of the spine.
`FIG. 12B is a top plan view of the endplate region of the
`vertebral body of FIG. 11 with an alternative embodiment of
`implants of the present invention implanted translaterally
`across the transverse width of the vertebral body from a
`lateral aspect of the spine, with the gap between the implants
`exaggerated for visual effect.
`FIG. 12C is a trailing end view of a first of the implants
`shown in FIG. 12B.
`
`FIG. 12D is a leading end view of a second of the implants
`shown in FIG. 12B.
`
`FIG. 13A is a side elevational view of two adjacent
`vertebral bodies with two implants of another embodiment
`of the present invention implanted translaterally side-by-
`side across the transverse width of the vertebrae from a
`
`lateral aspect of the spine.
`FIG. 1 3B is a top plan view of the endplate region of a
`vertebral body along lines 13B—13B of FIG. 13A.
`FIG. 14A is a side elevational view of two adjacent
`vertebral bodies with two implants of another embodiment
`of the present invention implanted translaterally across the
`transverse width of the vertebral from a lateral aspect of the
`spine.
`FIG. 14B is a top plan view of the endplate region of a
`vertebral body along line 14B—4B of FIG. 14A.
`FIGS. 15A and 15B are top plan views of alternative
`embodiments of the implant of the present invention illus-
`trated in outline form.
`
`FIG. 16A is a top view of an alternative embodiment of
`the implant of the present invention illustrated in outline
`form.
`
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`

`US 6,241,770 B1
`
`7
`FIG. 16B is a side elevational View of the implants of
`FIGS. 15A, 15B, and 16A from long side “L”.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`FIG. 6B shows in outline form the optimal area available
`to be occupied by one fusion implant 100 to be inserted into
`the intervertebral space in side by side pairs.
`With reference to FIGS. 6C, 7A, and 7B, a first embodi-
`ment of the present invention comprising an interbody spinal
`implant generally referred by the numeral 100, is shown
`inserted from the anterior aspect of a vertebral body V to
`each side of the midline M in the lumbar spine. In one
`embodiment of the present invention, implant 100 has a
`leading end 102 for insertion into the disc space, an opposite
`trailing end 104 configured to generally conform to at least
`a portion of the natural anatomical curvature of the anterior
`aspect of the vertebral bodies adjacent the disc space, and
`more narrowly to be foreshortened at that aspect of the
`implant trailing end, that would be most lateral within the
`disc space when implanted within the spine. Implant 100 has
`opposed arcuate portions 106 and 108 that are oriented
`toward and adapted to penetrably engage within the adjacent
`vertebral bodies when inserted across the intervertebral
`
`space. Opposed arcuate portions 106 and 108 have a dis-
`tance therebetween defining an implant height greater than
`the height of the disc space at implantation. Preferably, each
`of the opposed arcuate portions 106 and 108 have at least
`one opening 110 in communication with one another to
`permit for the growth of bone in continuity from the adjacent
`vertebral bodies and through implant 100, and as herein
`shown implant 100 may further be hollow or at least in part
`hollow. Implant 100 may also include surface roughening
`such as thread 120 for penetrably engaging the boned of the
`adjacent vertebral bodies.
`As a result of its configuration, when implant 100 is
`inserted between two adjacent vertebral bodies, implant 100
`is contained within the vertebral bodies and does not dan-
`
`the most
`gerously protrude from the spine. Specifically,
`lateral aspect of the implanted implant at the trailing end has
`been relieved, foreshortened, or contoured so as to allow the
`remainder of the implant to be safely enlarged so as to be
`larger overall than the prior art implants without the trailing
`end lateral wall protruding from the disc space so as to
`endanger the adjacent blood vessels (though overall enlarge-
`ment is not a requisite element of the invention).
`The present invention is not limited to use in the lumbar
`spine and is useful throughout the spine. In regard to use in
`the cervical spine, by way of example, in addition to various
`blood vessels the esophagus and trachea would also be at
`risk.
`
`invention includes such implants
`the present
`Further,
`having opposed arcuate surface portions as just described
`whether said opposed portions are generally parallel along
`the length of the implant or in angular relationship to each
`other such that the opposed arcuate surfaces are closer to
`each other proximate one end of the implant than at the
`longitudinally opposite other end, or allowing for a variable
`surface, or any other configuration and relationship of the
`opposed arcuate surfaces.
`As shown in FIG. 6C, two implants 100 are implanted into
`the intervertebral space side-by side. The implants 100 of the
`present invention optimally fill the available area and opti-
`mally sit on the anterior aphophyseal rim. It can be seen that
`in one embodiment of the implant 100 of the present
`invention, trailing end 104 is arcuate to be in conformation
`
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`15
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`20
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`25
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`30
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`35
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`40
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`45
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`to the peripheral profile of the anterior aspect of the vertebral
`bodies where the implant is in contact with the vertebral
`bodies so as to allow the implant to have both a maximum
`safe width and length, and to sit on the peripheral vertebral
`body rim, including the anterior cortex and/or the apophy-
`seal rim. This allows the implants of the present invention to
`have the maximum surface area of contact with the
`
`the greatest volume for holding osteogenic
`vertebrae,
`material, to sit upon the very good structural bone present at
`the periphery of the vertebral bodies,
`to have a greater
`surface over which to have bone engaging surface
`irregularities, and as a result of this combination to have the
`greatest stability of the implant itself and in turn to stabilize
`the vertebrae relative to each other.
`
`As shown in FIG. 7A, trailing end 104 may be configured
`to complementary engage an instrument 130 for driving
`implant 100 into the installation space. Instrument 130 may
`have a centrally disposed projection 132 and an off-center
`projection 134 for engaging recesses 142 and 144 of trailing
`end 104, respectively. Projection 132 is preferably threaded
`as is recess 142.
`
`While the implants of FIGS. 6C, 7A, and 7B are shown
`as cylindrical, the implant of the present invention includes
`the novel
`teaching as applied to any implants having
`opposed, at least in part, arcuate surfaces for penetrably
`engaging into the vertebral bodies adjacent the disc space
`across which the implant is implanted for the purpose of
`achieving fusion. These implants may have flattened or
`modified sides to be less wide. Some examples of such
`implants are taught by Michelson in US. Pat. Nos. 5,593,
`409 and 5,559,909, and co-pending application Ser. Nos.
`08/408,908 and 08/408,928, all of which are incorporated
`herein by reference.
`With reference to FIGS. 8 and 9, when such a teaching is
`applied for use with a solitary, centrally placed implant 200
`to be implanted anteriorly and generally along the midline of
`the disc space, the trailing end 204 of implant 200 would be
`arcuate as shown, such that trailing end 204 is not rotation-
`ally symmetrical about the mid longitudinal axis MLA of
`implant 200,
`the trailing end 204 might,
`in a preferred
`embodiment, for such use be symmetrical left and right of
`the mid-longitudinal axis MLA when properly inserted
`alternatively, though not preferred, the implant 200 of FIG.
`9 for
`implantation anteriorly could have a rotationally
`symmetrical, or even a rounded trailing end.
`With reference to FIG. 10, while not achieving the maxi-
`mum advantage of the present inventive teaching, implants
`300a and 300b (shown in outlined form) may be used in side
`by side pairs, each being symmetrically arcuate left and
`right, but not rotationally, about the mid-longitudinal axis
`MLA to provide the advantage that there need not be mirror
`image implants or oppositely threaded (left and right)
`implants provided, and such implants if requiring continuing
`rotation for their insertion (designed to be screwed in) can be
`properly situated by half turns rather than full turns. That is,
`the correct alignment of the implant occurs every 180° of
`rotation.
`
`FIG. 10 further shows the area available to safely be filled
`and the silhouette of a pair of implants 300a and 300b
`having symmetrically extended trailing ends 304a and 304b
`for allowing for improved filling of the disc space and
`having relieve