USOO8444696B2
`
`US 8,444,696 B2
`(10) Patent No.:
`(12) Un1ted States Patent
`
`Michelson
`(45) Date of Patent:
`*May 21, 2013
`
`(54) ANATOMIC SPINAL IMPLANT HAVING
`ANATOMIC BEARING SURFACES
`
`(75)
`
`Inventor: Gary Karlin Michelson, Venice, CA
`(US)
`
`(73) Assignee: Warsaw Orthopedic, Inc., Warsaw, IN
`(US)
`
`( * ) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U30 1540’) by 3 days‘
`This patent is subject to a terminal dis-
`claimer.
`
`(21) Appl. No.: 13/235,998
`
`(22)
`
`Filed:
`
`Sep. 19, 2011
`
`(65)
`
`Prior Publication Data
`
`US 2012/0071982 A1
`
`Mar. 22, 2012
`
`Related US. Application Data
`
`(60) Continuation of application No. 12/807,489, filed on
`Sep. 7, 2010, now Pat. No. 8,021,430, which is a
`continuation of application No. 10/926,766, filed on
`Aug. 26, 2004, now Pat. No. 7,789,914, which is a
`continuation of application No. 10/237,751, filed on
`Sep. 9, 2002, now Pat. No. 7,503,933, which is a
`continuation of application No. 09/412,090, filed on
`Oct. 4, 1999, now Pat. No. 6,447,544, which is a
`continuation of application No. 08/813,283, filed on
`Mar. 10, 1997, now Pat. No. 6,302,914, which is a
`division ofapplicationNo. 08/482,146, filed on Jun. 7,
`1995, now Pat. No. 5,609,635.
`
`11:131512/44
`(51)
`(52) US. Cl.
`USPC ....................................................... 623/17.16
`
`(2006 01)
`'
`
`(58) Field of Classification Search
`USPC .......... 623/17.11717.16, 16.11, 14.12, 18.11;
`606/2467249, 99
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`US. PATENT DOCUMENTS
`2,372,622 A
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`FOREIGN PATENT DOCUMENTS
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`W0
`W0
`
`W0 93/01771 A1
`WO 95/08306
`
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`3/1995
`
`OTHER PUBLICATIONS
`
`Request for Inter Partes Reexamination 0fU.S. Patent No. 8,021,430,
`dated Sep. 14, 2012, 477 pages.
`
`(Continued)
`
`Primary Examiner 7 Alvin Stewart
`(74) Attorney, Agent, or Firm 7 Martin & Ferraro, LLP
`
`ABSTRACT
`(57)
`The present application is directed to an interbody spinal
`implant having a structural configuration that provides for
`maintaining the normal anatomic relationship oftwo adjacent
`vertebrae ofthe spine. The spinal implant is sized to fit within
`the disc space created by the removal ofdisc material between
`two adjacent vertebrae and conform wholly, or in part, to the
`disc space created. The spinal implant ofthe present invention
`has first and second sides with upper and lower bearing sur-
`faces that form a support structure for bearing against the end
`plates of the adjacent vertebrae. The upper and lower bearing
`surfaces ofthe first and second sides are shaped to create an
`anatomic fit with the endplates of the adjacent vertebrae.
`
`19 Claims, 11 Drawing Sheets
`
`THIRD
`
`BEARING
`
`”R57
`BEARING
`
`[-312
`
`
`
`320
`
`318
`
`SECOND
`TERMIAML
`PART
`
`BEARING
`SURFACE
`
`314 BEARING
`SURFACE
`
`1
`
`NUVASIVE1002
`
`1
`
`

`

`US 8,444,696 B2
`
`Page 2
`
`U.S. PATENT DOCUMENTS
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`-
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`-
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`
`OTHER PUBLICATIONS
`
`Office Action from Reexamination Proceeding No. 95/002,380;
`
`[IASmendment 1n ReexamControl No.95/002,380,filedFeb. 19, 2013,
`Pages
`.
`ThlrdPartyComments1nReexamControlNo.95/002,380,filedMar.
`21,2013, 52 pages.
`in Reexamination Control No.
`Decision Expunging Papers
`95/002,380, Mar. 26, 2013,4pages.
`
`2
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`THIRD
`FIRST
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`SURFACE
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`320
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`FIG. 13
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`TERMINAL
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`

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`U.S. Patent
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`Sheet 6 of 11
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`US 8,444,696 B2
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`US 8,444,696 132
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`U.S. Patent
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`US. Patent
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`US. Patent
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`US. Patent
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`US 8,444,696 B2
`
`1
`ANATOMIC SPINAL IMPLANT HAVING
`ANATOMIC BEARING SURFACES
`
`This application is a continuation of application Ser. No.
`12/807,489, filed Sep. 7, 2010, now US. Pat. No. 8,021,430;
`which is a continuation of application Ser. No. 10/926,766,
`filed Aug. 26, 2004, now US. Pat. No. 7,789,914; which is a
`continuation ofapplication Ser. No. 10/237,751, filed Sep. 9,
`2002 now US. Pat. No. 7,503,933; which is a continuation of
`application Ser. No. 09/412,090, filed Oct. 4, 1999, now US.
`Pat. No. 6,447,544; which is a continuation ofapplication Ser.
`No. 08/813,283, filed Mar. 10, 1997, now US. Pat. No. 6,302,
`914; which is a divisional ofapplication Ser. No. 08/482, 146,
`filed Jun. 7, 1995, now US. Pat. No. 5,609,635; all ofwhich
`are incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`The present invention relates generally to interbody spinal
`fusion implants, and in particular to spinal fusion implants
`configured to restore and maintain two adjacent vertebrae of
`the spine in correct anatomical angular relationship.
`2. Description of the PriorArt
`Both the cervical and lunbar areas of the human spine are,
`in a healthy state, lordotic such that they are curved convex
`forward. It is not uncommon that in degenerative conditions
`of the spine that lordosis is lost. This effectively shortens the
`spinal canal which decreases its capacity. Further, the absence
`of lordosis moves the spinal cord anteriorly where it may be
`compressed against the posterior portions of the vertebral
`bodies and discs. Finally, such a loss of lordosis disturbs the
`overall mechanics of the spine which may cause cascading
`degenerative changes throughout the adjacent spinal seg-
`ments.
`
`The surgical treatment of those degenerative conditions of
`the spine in which the spinal discs are in various states of
`collapse, and out of lordosis, commonly involves spinal
`fusion. That is the joining together of adjacent vertebrae
`through an area of shared bone. When the sharedbone is in the
`area previously occupied by the intervertebral disc that is
`referred to as an interbody fusion. Further history in this
`regard is provided in application Ser. No. 08/263,952 entitled
`Artificial Spinal Fusion Implants (“Parent Application”)
`incorporated herein by reference.
`The Parent Application taught the use of artificial spinal
`fusion implants that were capable of being placed between
`adjacent vertebrae, and which implants were capable of con-
`taining and providing fusion promoting substances including
`bone at the fusion site. These devices were further capable of
`restoring the height of the disc space and of supporting the
`spine, and were self-stabilizing as well as being stabilizing to
`the spinal area where implanted.
`
`SUMMARY OF THE INVENTION
`
`The present invention is directed to interbody spinal fusion
`implants having a structural configuration that provides for
`the maintaining and creating of the normal anatomic angular
`relationship oftwo adjacent vertebrae ofthe spine to maintain
`and create spinal lordosis. The spinal fusion implants of the
`present invention are sized to fit within the disc space created
`by the removal of disc material between two adjacent verte-
`brae and conform wholly or in part to the disc space created.
`The spinal fusion implants of the present invention have
`upper and lower surfaces that form a support structure for
`bearing against the end plates ofthe adjacent vertebrae. In the
`
`5
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
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`60
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`65
`
`2
`
`preferred embodiments, the upper and lower surfaces are
`disposed in a converging angular relationship to each other
`such that the implants ofthe present invention have an overall
`“wedged-shape” in an elevational side view. The angular
`relationship of the upper and lower surfaces places and main-
`tains the vertebrae adjacent to those surfaces in an angular
`relationship to each other, creating and maintaining the
`desired lordosis.
`
`The implants of the present invention may have surface
`irregularities to increase their surface area, and/or to further
`engage the adjacent vertebrae and to enhance stability. The
`lordotic implants of the present invention may have surface
`irregularities that are uniform in height along the longitudinal
`axis of the upper and lower vertebrae engaging surfaces, or
`may increase in height from one end of the implant to the
`other. That is, the implant body and the surface formed and the
`projections may be similarly wedged. The outer contour of
`the surface projections may be more or less rectangular while
`the underlying implant may be wedge- shaped; or the reverse
`wherein the underlying implant body is more or less rectan-
`gular while the contour of the surface projections are wedge-
`shaped from one end of the implant to the other.
`The implants of the present invention have various faces
`which may be curved so as to conform to the shape of the
`vertebral surfaces adjacent to the area of the disc removal.
`Specifically the upper and/or lower surfaces may be convex,
`and/or the front and/or rear surfaces may be convex. The
`surfaces of the implants of the present invention may have
`openings which may or may not pass all the way through
`them, and a central chamber in communication to the surface
`through holes. The openings may be of random sizes, and/or
`shapes, and/or distributions. The implants themselves may be
`composed of materials, and/or have surface treatments, to
`encourage microscopic bone ingrowth into the implants.
`In the performing of a posterior lumbar interbody fusion, it
`is not possible to replace the removed portions of the disc, if
`a total nuclear discectomy has been performed, with a single
`large implant as the delicate dural sac containing the spinal
`cord, and the nerve roots cover at all times at least some
`portion of the posterior disc space. As set forth in the Parent
`Application, the use of “modular implants” is appropriate in
`such cases. The modular implants being approximately as
`long as the depth of the disc material removed, but being
`considerably narrower, such that they can be introduced into
`the disc space from the posterior aspect to either side of the
`dural sac, and then aligned side to side within the disc space
`so that a number ofthem each having a length consistent with
`the depth of the disc removed in that area would in combina-
`tion have a width equal to the width of the disc material
`removed.
`
`The modular implants of the present invention may be
`generally wedge-shaped and may have upper and lower sur-
`faces conforming to the contours of the vertebral endplates,
`which contours include but are not limited to being relatively
`flat or convex. As the disc spaces in the lumbar spine are
`generally lordotic, said implants in the preferred embodiment
`would be taller anteriorly, that is at the implant’s insertion
`end, and less tall posteriorly, that is at the implant’s trailing
`end. To introduce an implant that is taller at its insertion end
`than the space available at the posterior aspect of the disc
`space, even when that disc space is optimally distracted, is
`problematic.
`The modular implants ofthe present invention provide two
`solutions to the problem. In the first embodiment, the modular
`implants may have a reduced size at their insertion end,
`including but not limited to a bullet nose, a convexity, and a
`chamfer to a smaller front surface. This then provides that the
`
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`

`US 8,444,696 B2
`
`3
`implant has an area small enough to be introduced into the
`posterior aspect of the disc space when the disc space is
`adequately distracted and the contour ofthat specialized lead-
`ing portion of the implant is such that it then allows for a
`ramping up ofthe adjacent vertebrae relative to the implant as
`the implant is advanced forward into the disc space.
`The implants of the present invention provide a second
`solution to this same problem. In the preferred embodiment of
`the modular implant, the implant is again wedge-shaped in
`the side elevational view and is taller at its insertion end than
`
`at its trailing end. However, the implant incorporates at its
`trailing end a means for engaging insertion instrumentation
`such as the box and threaded opening configuration disclosed
`in the Parent Application. Since in the preferred embodiment
`these implants are wedge-shaped in the side elevational view
`when upright but are generally rectangular when viewed from
`the top plan view, these implants are therefore designed to be
`introduced into the disc space on their side such that the side
`walls of the implants are adjacent to the end plates of the
`adjacent vertebrae. The implants have a side-to-side dimen-
`sion that is less than the dimension through the insertion end
`ofthe implant when upright, it is possible to easily insert these
`implants with them on their side and then to use the insertion
`instrument engaged to the implant to rotate the implants
`ninety degrees into the fully upright position, once they have
`been fully inserted. Once inserted, the upper and lower sur-
`faces are adjacent to the endplates of the adjacent vertebrae
`and create and maintain the desired angular relationship of
`the adjacent vertebrae as the upper and lower walls are angled
`with respect to each other.
`In an alternative embodiment of the present invention, a
`mechanical implant which may be inserted in a collapsed
`position and which may then be adjusted to increase in height
`so as to provide for the optimal restoration ofthe height of the
`space between the adjacent vertebrae is disclosed. The
`mechanical implant may be wedge-shaped, and have upper
`and lower surfaces, the contours of which generally conform
`to the contacted areas of the adjacent vertebral endplates and
`which contours may include but are not limited to being
`relatively flat, or convex. Further, the mechanical implant
`may be wedge-shaped or generally rectangular, but capable of
`increasing in both height and the extent of wedging when
`adjusted. This may easily be achieved by having one of the
`two wedge mechanisms employed in the example givenbeing
`larger, or steeper than the other. Alternatively, a single wedge
`may be utilized, and if it is desired to achieved increased
`height at one end of the implant while restricting the height at
`the other, then the end ofthe implant may incorporate a hinge
`means and the height expansion at the other end achieved by
`drawing a wedge member, bar, ball, or other means from the
`far end toward the hinged end so as to drive said upper and
`lower surfaces apart in a wedged fashion.
`In an alternative embodiment of the present invention, an
`implant having a mechanically deployable bone engaging
`means is taught. Such an implant is generally wedge-shaped
`in the side elevational view and has upper and lower surfaces
`generally conforming to the contour of the vertebral end-
`plates where contacted by the implant, and which upper and
`lower surfaces may be but are not limited to being either flat
`or convex. The use of such deployable bone engaging means
`are particularly of value in that the largest possible implant
`may be inserted into a disc space and the vertebral engaging
`means, which if fixed to the surface would have blocked the
`insertion of the implant, may then be deployed after the
`insertion such that the distance from the tip of the upper and
`lower boite engagement means exceeds the height of the
`space available for insertion. Such a feature is of particular
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`value when the implant itself is wedge-shaped as the consid-
`erable compressive loads across the lumbar spine would tend
`to drive a wedge-shaped implants out of the disc space.
`
`OBJECTS OF THE PRESENT INVENTION
`
`It is an object of the present invention to provide a spinal
`fusion implant that is easily inserted into the spine, having a
`tapered leading end;
`It is another object of the present invention to provide a
`spinal fusion implant that tapers in height from one end to the
`other consistent with the taper of a normal spinal disc;
`It is yet another object ofthe present invention to provide a
`spinal fusion implant that is capable of maintaining anatomic
`alignment and lordosis of two adjacent vertebrae during the
`spinal fusion process;
`It is still another object of the present invention to provide
`a spinal fusion implant that is self stabilizing within the spine;
`It is yet another object ofthe present invention to provide a
`spinal fusion implant that is capable of providing stability
`between adjacent vertebrae when inserted;
`It is further another object of the present invention to pro-
`vide a spinal fusion implant that is capable of spacing apart
`and supporting adjacent vertebrae in an angular relationship
`during the spinal fusion process;
`It is still further another object of the present invention to
`provide a spinal fusion implant that fits between to adjacent
`vertebrae and preserves the end plants ofthose vertebrae; and
`It is another object of the present invention to provide a
`spinal fusion implant having a shape which conforms to the
`endplates of the adjacent vertebrae; and
`invention will
`These and other objects of the present
`become apparent from a review of the accompanying draw-
`ings and the detailed description of the drawings.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 is a perspective view ofthe lordotic interbody spinal
`fusion implant of the present invention with a slidable door
`shown in a partially open position providing access to the
`internal chamber of the implant.
`FIG. 2 is a top plan view of the lordotic interbody spinal
`fusion implant of the present invention.
`FIG. 3 is a left side elevational view of the lordotic inter-
`
`body spinal fusion implant of the present invention.
`FIG. 4 is a right side elevational view of the lordotic inter-
`body spinal fusion implant of the present invention.
`FIG. 5 is a front end view of the lordotic interbody spinal
`fusion implant of the present invention showing the slidable
`door in a partially open position.
`FIG. 6 is a rear end view of the lordotic interbody spinal
`fusion implant ofthe present invention showing the means for
`engaging insertion instrumentation.
`FIG. 7 is an enlarged fragmentary view along line 7 ofFIG.
`2 illustrating the bone engaging surface configuration of the
`lordotic interbody spinal fusion implant of the present inven-
`tion.
`
`FIG. 7A is an elevational side view of a segment of the
`spinal column having the lordotic implant of the present
`invention inserted in the disc space at different disc levels
`between adjacent vertebrae to restore and maintain the cor-
`rect anatomical alignment of the adjacent vertebrae.
`FIG. 8 is a top plan view of an alternative embodiment of
`the lordotic interbody spinal fusion implant of the present
`invention.
`FIG. 9 is a left side elevational view of the lordotic inter-
`
`body spinal fusion implant of FIG. 8.
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`US 8,444,696 B2
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`5
`FIG. 10 is a front end view of the lordotic interbody spinal
`fusion implant of FIG. 8.
`FIG. 11 is a rear end view of the lordotic interbody spinal
`fusion implant of FIG. 8 showing the means for engaging
`insertion instrumentation.
`FIG. 12 is an enlarged fragmentary view along line 12 of
`FIG. 8 illustrating the surface configuration the lordotic inter-
`body spinal fusion implant of the present invention.
`FIG. 13 is a top plan view of an alternative embodiment of
`the lordotic interbody spinal fusion implant of the present
`invention made of a mesh-like material.
`FIG. 14 is a left side elevational view of the lordotic inter-
`body spinal fusion implant of FIG. 13.
`FIG. 15 is a front end view of the lordotic interbody spinal
`fusion implant of FIG. 13.
`FIG. 16 is a rear end view of the lordotic interbody spinal
`fusion implant of FIG. 13 showing the means for engaging
`insertion instrumentation.
`FIG. 17 is an enlarged fragmentary view along line 17 of
`FIG. 13 illustrating the surface configuration of the lordotic
`interbody spinal fusion implant of the present invention.
`FIG. 18 is a perspective view of an alternative embodiment
`of the lordotic interbody spinal fusion implant of the present
`invention.
`FIG. 19 is a top plan view of the lordotic interbody spinal
`fusion implant of FIG. 18.
`FIG. 20 is a left side elevational view of the lordotic inter-
`body spinal fusion implant of FIG. 18.
`FIG. 21 is a rear end view of the lordotic interbody spinal
`fusion implant of FIG. 18.
`FIG. 22 is a front end view of the lordotic interbody spinal
`fusion implant of FIG. 18.
`FIG. 23 is an enlarged fragmentary view along line 23 of
`FIG. 22 illustrating the surface configuration the lordotic
`interbody spinal fusion implant of the present invention.
`FIG. 24 is a top plan view of an alternative embodiment of
`the lordotic interbody spinal fusion implant of the present
`invention.
`FIG. 25 is a left side elevational view of the lordotic inter-
`body spinal fusion implant of FIG. 24.
`FIG. 26 is a rear end view of the lordotic interbody spinal
`fusion implant of FIG. 24.
`FIG. 27 is a front end view of the lordotic interbody spinal
`fusion implant of FIG. 24.
`FIG. 28 is an enlarged fragmentary view along line 28 of
`the lordotic interbody spinal fusion implant of FIG. 24 illus-
`trating the surface configuration of the lordotic interbody
`spinal fusion implant of the present invention.
`FIG. 29 is a sectional view along lines 29-29 of FIG. 28 the
`lordotic interbody spinal fusion implant of the present inven-
`tion.
`FIG. 30 is a side elevational view of a segment of the
`human spinal column shown with an alternative embodiment
`of the lordotic spinal fusion implant of the present invention
`that is adjustable and expandable shown in sectional view
`inserted in the disc space levels to restore and maintain the
`correct anatomical alignment of the adjacent vertebrae.
`FIG. 31 is a side cross sectional view of, an alternative
`embodiment of the lordotic implant of the present invention
`having movable projections, in the form of spikes 708, which
`are movable from a first position within the implant 700 to a
`second position extending to the exterior of the implant.
`FIG. 32 is a perspective view of the embodiment of FIG.
`31.
`
`DETAILED DESCRIPTION OF THE PREFERRED
`EMBODIMENT
`
`Referring to FIGS. 1 through 7 the lordotic interbody spi-
`nal fusion implant of the present invention for use in the disc
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`space between two adjacent vertebrae, generally referred to
`by the numeral 100, is shown. The implant 100 has a generally
`rectangular configuration, having an upper surface 112 and a
`lower surface 114. In the preferred embodiment, the upper
`and lower surfaces 112 and 114 of implant 100 are disposed
`in a converging angular relationship toward each other such
`that the implant 100 appears “wedge-shaped” from a side
`elevational view as shown in FIGS. 3 and 4. The upper and
`lower surfaces 112 and 114 have an interior surface which
`
`form a support structure for bearing against the endplates of
`the adjacent vertebrae between which the implant 100 is
`inserted. The angular relationship of the upper and lower
`surfaces 112 and 114 places and maintains the vertebrae
`adjacent to those surfaces in an angular relationship, creating
`and maintaining the desired lordosis of the spine.
`The upper and lower surfaces 112 and 114 of the implant
`100 may be flat or curved to conform to the shape of the end
`plates of the adjacent vertebrae between which the implant
`100 is inserted. The implant 100 conforms to the shape of the
`nucleus pulposus and a portion of the annulus fibrosus
`removed from the vertebrae. The upper and lower surfaces
`112 and 114 comprise surface roughenings that provide a
`surface suitable for engaging the adjacent vertebrae to stabi-
`lize the implant 100 within the disc space once surgically
`implanted. The surface roughenings of the upper and lower
`surfaces 112 and 114 comprise a surface knurling 121 and/or
`grooves.
`Referring to FIG. 7, an enlarged fragmentary view of the
`surface knurling 121 of the implant 100 is shown as a dia-
`mond-shaped bone engaging pattern. The implant 100 may
`have surface knurling 121 throughout the entire upper and
`lower surfaces 112 and 114, throughout only a portion of the
`upper and lower surfaces 112 and 114, or any combination
`thereof, without departing from the scope of the present
`invention. It is also appreciated that the surface knurling 121
`may have various configuration other than the configuration
`shown.
`
`In this embodiment, the implant 100 is hollow and com-
`prises a plurality of openings 115 of passing through the
`upper and lower surfaces 112 and 114 and into a central
`hollow chamber 116. The openings 115 provide for bone
`growth to occur from the vertebrae through the openings 115
`to the internal chamber 116. While the openings 115 have
`been shown in the drawings as being circular, it is appreciated
`that the openings 115 may have any shape, size, configuration
`or distribution suitable for use in a spinal implant without
`departing from the scope of the present
`invention. For
`example, the openings may have a tear-drop configuration as
`shown in opening 11511 in FIGS. 1 and 2. The upper and lower
`surfaces 112 and 114 of the implant 100 are supported and
`spaced apart by a side wall 118, which may also comprise a
`plurality of openings 122.
`The implant 100 has an insertion end 120 and a trailing end
`130 both of which may be curved or flat. The trailing end 130
`of the implant may be convex to conform to the curvature of
`the vertebrae and has a means for engaging an implant inser-
`tion instrument comprising a depressed portion 124 with a
`central threaded opening 126 for receiving the engaging end
`of a driving instrument. The insertion end 120 of the implant
`100 comprises an access opening 132 and a slidable door 134
`which closes the opening 132. The slidable door 134 covers
`the opening 132 into the chamber 116 and permits the inser-
`tion of autogenous bone material into the chamber 116.
`In use, the slidable door 134 is placed in the open position
`for loading material into the chamber 116. The slidable door
`134 has a depression 136 for facilitating the opening and
`closing of the door 134. The internal chamber 116 can be
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`US 8,444,696 B2
`
`7
`filled and hold any natural or artificial osteoconductive,
`osteoinductive, osteogenic, or other fusion enhancing mate-
`rial. Some examples of such materials are bone harvested
`from the patient, or bone growth inducing material such as,
`but not limited to, hydroxyapatite, hydroxyapatite tricalcium
`phosphate; or bone morphogenic protein. The implant 100
`itself is made ofmaterial appropriate for human implantation
`such as titanium and/or may be made of, and/or filled and/or
`coated with a bone ingrowth inducing material such as, but
`not limited to, hydroxyapatite or hydroxyapatite tricalcium
`phosphate or any other osteoconductive, osteoinductive,
`osteogenic, or other fusion enhancing material.
`The fusion enhancing material that is packed within the
`chamber 116 of the implant 100 serves to promote bone
`ingrowth between the implant 1 00 and the adjacent vertebrae.
`Once the bone ingrowth occurs, the implant 100 will be a
`permanent fixture preventing dislodgement of the implant as
`well as preventing any movement between the adjacent ver-
`tebrae.
`
`The slidable door 134 is then closed prior to implantation.
`In the closed position, the slidable door conforms to the
`curvature of the insertion end 120 ofthe implant 100. Various
`methods of packing the implant 100 with the autogenous
`bone material may be used to obtain a completely packed
`implant 100.
`The method of inserting the implant 100 is set forth in
`detail in application Ser. No. 08/263,962, incorporated herein
`by reference. The threaded end of a driving instr