`Michelson
`
`US006241770B1
`(10) Patent N0.2
`US 6,241,770 B1
`(45) Date of Patent:
`Jun. 5, 2001
`
`OTHER PUBLICATIONS
`_
`_
`_
`_
`Muschler, et al.; The Biology of Spmal Fusion; Spinal
`Fusion Science and Technique, Cotler and Cotler, pp. 9—13.
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`. Steel Baskets;
`.
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`Research Society, vol. 8, p. 407, Mar. 8—10 (1983).
`Otero—Vich, Jose M.; Anterior Cervical Interbody Fusion
`With Threaded Cylindrical Bone; J. Neurosurg 63:750—753
`(Nov- 1985)
`Butts, MK» 94 a1; Biomechanical Analysis of a New
`Method for Spinal Interbody Fixation; 1987 Symposiutm
`American Society of Mechanical Engineers, “Advances in
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`CraWley et a1.; AModi?ed CloWard’s Technique for Arthro
`desis of the Normal Metacarpophalangeal Joint in the Horse;
`Veterinary Surgery, vol. 17, No. 3, pp. 117—127 (1988).
`Bagby, G.W.; Arthrodesis by the Distraction—Compression
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`II, No. 6, pp. 931—934 (Jun. 1987).
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`Repair—Clinical Evaluation of Bone Union and Graft Incor
`poration; J. Jpn. Orthop. Assoc. 62:461—469 (1988).
`
`(List continued on neXt page.)
`
`Primary Examiner—David H. Willse
`(74) Attorney, Agent, or Firm—Martin & Ferraro, LLP
`(57)
`ABSTRACT
`
`An interbody spinal fusion implant adapted for placement at
`least in part across an intervertebral space formed across a
`disc space betWeen tWo adjacent vertebral bodies and for
`penetrating engagement into each of those vertebral bodies,
`the implant having a trailing end adapted to sit upon and not
`gzitiglklfzlféggl the anterolateral peripheral rim of bone of the
`y‘
`
`104 Claims, 9 Drawing Sheets
`
`(54) INTERBODY SPINAL FUSION IMPLANT
`HAVING AN ANATOMICALLY CONFORMED
`TRAILING END
`
`(76) Inventor; Gary K_ Michelson, 438 Sherman
`Canal, Venice, CA (Us)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U-S-C- 154(k)) by 0 days-
`
`(21) Appl, No.1 09/263,266
`
`Mar‘ 5’ 1999
`(22) Filed:
`(51) Int. c1.7 ...................................................... .. A61F 2/44
`(52) us. c1. ......................................................... .. 623/1711
`(58) Field of Search ............................................... .. 623/17
`
`(56)
`
`References Cited
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`US 6,241,770 B1
`Page 2
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`SchmitZ et a.l; Performance of Alloplastic Materials and
`Design of an Arti?cial Disc; the Arti?cial Disc, Brock,
`Mayer, Weigel; pp. 23—34 (1991).
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`Fusion L5—S1, Atlas of Spinal Operations, Thieme, pp.
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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
`
`2
`
`
`
`U.S. Patent
`U.S. Patent
`
`Jun. 5, 2001
`Jun. 5, 2001
`
`Sheet 1 0f 9
`Sheet 1 of 9
`
`US 6,241,770 B1
`US 6,241,770 B1
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`U.S. Patent
`
`Jun. 5, 2001
`
`Sheet 2 0f 9
`
`US 6,241,770 B1
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`FIG. 5
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`Jun. 5, 2001
`Jun. 5, 2001
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`Sheet 3 0f 9
`Sheet 3 of 9
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`US 6,241,770 B1
`US 6,241,770 B1
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`Jun. 5, 2001
`Jun. 5, 2001
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`Jun. 5, 2001
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`Jun. 5, 2001
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`Jun. 5, 2001
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`
`Jun. 5, 2001
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`Sheet 8 0f 9
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`Jun. 5, 2001
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`Sheet 9 0f 9
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`US 6,241,770 B1
`
`1
`INTERBODY SPINAL FUSION IMPLANT
`HAVING AN ANATOMICALLY CONFORMED
`TRAILING END
`
`BACKGROUND OF THE INVENTION
`
`15
`
`2
`FIG. 3 is a top plan vieW of a ?fth 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 inde?nitely 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 con?guration 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
`
`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 con?gured 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 de?ned 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).
`
`25
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`US 6,241,770 B1
`
`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 sacri?ces 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 sacri?ces 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 ?ll 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 ?ll 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 ?nd 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 ?ll 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
`
`5
`
`15
`
`25
`
`35
`
`45
`
`55
`
`65
`
`4
`vertebral body V unoccupied by the implant Which area
`Would be useful for contact for fusion and for support of the
`implant. The con?guration 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 ?ll of the disc space With the implant, and little
`of the implant sitting on the apophyseal rim.
`The con?guration 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 ?tting 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 speci?cally 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 bene?t 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 ?lling 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 ?rst into the disc
`space, and an opposite trailing end. The trailing end of this
`embodiment of the implant of the present invention is
`generally con?gured 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.
`More speci?cally, in the present invention, While the
`implant overall may be enlarged relative to the siZes possible
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`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 ?rst into the disc
`space, and an opposite trailing end. The trailing end is
`con?gured 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 arti?cial 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 ?ber 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 ?fth 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 ?t 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 ?rst 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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`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 ?rst 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 con?gured 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 de?ning 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 con?guration, When implant 100 is
`inserted betWeen tWo adjacent vertebral bodies, implant 100
`is contained Within the vertebral bodies and does not dan
`gerously protrude from the spine. Speci?cally, the most
`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.
`Further, the present invention includes such implants
`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 t