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`Buopalsches Potent
`European Patent Office
`Office européen des brevets
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`MANIC
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`EP 0 T1 6 840 A2
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`EUROPEANPATENT APPLICATION
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`(43) Date of publication:
`19.06.1996 Bulletin 1996/25
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`(21) Application number: 95119558.5
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`(51) Int. cl®: AG1F 2/44
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`(22) Dateoffiling: 12.12.1995
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`(84) Designated Contracting States:
`DE ES FRGBIT
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`(30) Priority: 12.12.1994 US 354364
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`(71) Applicant: Surgical Dynamics,Inc.
`Concord, Ca 94520 (US)
`
`+ Winslow, Charles J.
`Walnut Creek, CA 94595 (US)
`« Jayne,Kirk
`Alameda, CA 94501 (US)
`« Klyce, Henry A.
`Piedmont, CA 94611 (US)
`
`(74) Representative: Marsh, Roy David et al
`HoffmannEitle & Partner
`(72) Inventors:
`Patent- und Rechtsanwalte
`» Pavlov, Paul W.,
`Arabellastrasse 4
`Sint Maartenskliniek
`81925 Munchen (DE)
`NL-6522 JV Nijmegen (NL)
`
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`(54)
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`Conically-shaped fusion cage and methodof implantation
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`A fusion cage 20 for vertebral body fusion is
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`conically-shaped. A thread 40 is formed as part of the
`external conical surface of the fusion cage. Apertures 54
`are defined through the fusion cage in orderto provide
`for contact between the engaged vertebral bone struc-
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`tures and bone growth inducing substances packed
`within the fusion cage. The fusion cage is introduced and
`maintains or increases the lordosis between adjacent
`vertebral bone structures.
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`»\
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`EP0716840A2
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`cages before the cages are implanted betweenthever-
`tebral body structures.
`
`Summaryof the Invention
`
`The present invention is directed to a fusion cage
`which has been designed to be implanted using princi-
`pally a posterior approach to the vertebral bone struc-
`tures.
`
`In a first embodiment of the present invention, the
`fusion cage includes a cage body having a proximal end
`and a distal end, said distal end having a diameter which
`is larger than the diameterof the proximal end. Thedistal
`end further is rounded with for example a bull nose in
`orderto facilitate the insertion of the cage bodyrelative
`to one or more bone structures. The distal end could
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`alternatively have a snub nose with or without a starter
`turn of a thread. The snub nose hasa starter diameter
`that is smaller than the diameter of the distal end. The
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`cage bodyis preferably conically-shaped. This shapeis
`particularly advantageous due to the fact that the normal
`lordosis of
`the vertebral bone structures defines a
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`wedged-shape space for a vertebral disk between, for
`example, lumbar vertebrae. Accordingly, the conically-
`shaped body cage can besized and selected in order to
`maintain or enlarge upon the normallordosis.
`In a second embodimentof the presentinvention the
`cage bodycaninclude a cylindrically-shaped portion and
`a conically-shaped portion. The cylindrically-shaped
`portion is located adjacent to the distal end and the con-
`ically-shaped portion extends from the cylindrically-
`shaped portion and tapers toward the proximal end.
`In a third embodiment of the present invention, a
`fusion cage includes a cage body having a proximal end
`and a distal end with the proximal end having a diameter
`whichis smaller than the diameter of the distal end. The
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`muchasthe flute placed on self-tapping screwsin order
`to facilitate the insertion of the fusion cage using a twist-
`ing motion between two vertebral bone structures.
`In a fourth embodiment of the invention, a fusion
`cage includes a cage body having a proximal end and a
`distal end, the proximal end having a diameter whichis
`smaller than the diameter of the distal end. The cage
`body has an outer surface and a thread formed as part
`of the outer surface. The thread aids the cage bodyin
`being inserted. As the cage is inserted,
`it gradually
`spreads apart the vertebral bone structures in order to
`regain or enlarge the naturallordosis of the adjacent ver-
`tebral bone structures. As with other embodimentsof the
`
`presentinvention, flutes can be provided in the thread in
`orderto allow for enhanced thread tapping by the cage
`and for a smootherinsertion of the fusion cage between
`the vertebral bone structures. Preferably two or three
`flutes would be formed spaced about the fusion cage in
`order that one flute would be engaging with or adjacent
`to an uppervertebral bone structures with anotherflute
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`tures is removed. A threaded tap is used to tap a com-
`plementary thread in the upper and lower vertebral bone
`structures preparatory to the insertion of
`the above
`fusion cage. Once such tapping has been accomplished,
`distal end has a flute formed therein. Additionally, the
`using an introduction tool, the fusion cage is screwed into
`cage body has an outer surface and at least one flute
`the space between the adjacent vertebral bone struc-
`formed in the outer surface. These flutes act asarelief
`tures. The thread bites into the bone of the upper and
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`lower vertebral bone structures, stabilizing the bone
`structures, and preventing the fusion cage from working
`out of this position due to patient movement. Generally
`two such fusion cages are applied using this technique.
`Oncethe two implants have been positioned, then bone
`growth inducing substances, such as bone chips, are
`packedinto the internal cavity of the fusion cages. These
`bone growth inducing substances comeinto immediate
`contact with the bone from the vertebral bone structures
`
`Description
`
`BACKGROUND
`
`Field of the Invention
`
`The present invention is directed to devices and
`methodsforfacilitating the fusing of bone structures and
`more particularly the fusing together of adjacent verte-
`bral bodies or bone structures.
`
`Background of the Invention
`
`Technicalliterature and patent documents disclose
`a number of devices and methods for fusing bones
`together. One such device which has proven to be suc-
`cessfulis disclosed in U.S. Patent 4,961 ,740, entitled "V-
`THREAD FUSION CAGE AND METHOD OF FUSING
`A BONE JOINT,” which patent has been assigned the
`present assignee and which patent
`is incorporated
`herein by reference. The referenced patent discloses a
`fusion cage which is preferably cylindrical and has a
`thread formed as part of the external cylindrical surface.
`The fusion cage defines an internal cavity and apertures
`through the wall of the cage which communicate the
`external cylindrical surface with the internal cavity. The
`apertures are formed in the valleys of the thread. Nor-
`mally two such cages are used to stabilized and fuse
`together adjacent vertebral bodies or bone structures.
`In practice, using a posterior approach, a patient's
`vertebral bone structures are exposed and degenerate
`disk material located between the vertebral bone struc-
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`which project into the internal cavity through the aper-
`tures. Such projection of bone is due to the fact that the
`apertures are formedin the valleys of the external thread
`of the fusion cage. Such immediate bone to bone contact
`between the vertebral bone structures and the bone pack
`within the fusion cages results in more rapid propagation
`of bonecells betweenthe adjacent vertebral bone struc-
`tures and thus a more rapid fusion of the adjacent ver-
`tebral bone structures.
`Itis to be understoodthat in the above method, bone
`growth inducing substances can be prepackedinto the
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`being engaging with or adjacent to alowervertebral bone
`structure. Such a relationship maintains alignment of the
`fusion cage and prevent wandering as the fusion cageis
`introduced between the two vertebral bone structures.
`
`Without two or moreflutes, wandering might occur due
`to the fact that the thread is only substantially engaged
`with the vertebral bone structures and not with the disk
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`material between the vertebral bone structures, which
`disk material does not provide support to the thread.
`In a further aspectof the invention, any of the above
`embodiments can be provided with a plurality of aper-
`tures through the fusion cage andaninternal cavity with
`the apertures communicating betweenthe internal cavity
`and the external surface of the fusion cage. Bone growth
`inducing substances, such as bone chips, can be packed
`into the internal cavity either before the fusion cage is
`Anterior Fusion Cage:
`inserted or after the fusion cage has reachedafinal
`insertion position, or packed in both before and after. The
`bone chips comein contact with the vertebral bone struc-
`tures through the apertures in orderto facilitate fusion
`betweenthe adjacent vertebral bone structures.
`In another aspect of the invention which can be
`included in any of the above embodiments, the cage
`body can have a round or bull nose distal end with one
`or moreflutes formedin the round or bull nose distal end
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`fusion cage to promote bone to bone contact and sub-
`sequentfusion.
`It
`is to be understood that although the above-
`embodiments have been described with respect to the
`fusion of adjacent vertebral bodies or bone structures,
`that the present
`invention can be used (1)
`to fuse
`together a variety of bone structures, in addition (2) to
`being fused to one bone structure and usedas,for exam-
`ple, a base for an implant or (3) to being used to reunite
`the pieces of a broken bone.
`Other objects and advantages of the invention can
`be obtained through a review of the specification and the
`figures.
`
`Brief Description of the Figure
`
`is a partially sectional side view of an
`Figure 1
`embodiment of the anterior fusion cage of the invention.
`Figure 2 depicts a left end (distal end) view of the
`fusion cage of Figure 1.
`Figure 3 depicts a right end (proximal end) view of
`the fusion cage of Figure 1.
`Figure 4 depicts a view through line 4-4 of the fusion
`cage of Figure 1.
`Figure 5 depicts the fusion cage of Figure 1
`junction with an introduction tool.
`Figure 6 depicts an alternative embodimentof the
`introductiontool.
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`in con-
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`Figures 7, 8, and 9 depict progressive stagesin the
`method of inserting the anterior fusion cage between
`adjacent vertebral bone structures.
`Figure 10 depicts a side view of an alternative
`embodimentof the anterior fusion cage of the invention.
`Figure 11 depicts the left end (distal enc) view of the
`fusion cage of Figure 10.
`Figure 12 depicts the right end (proximal end) view
`of the fusion cage of Figure 10.
`Figure 13 depicts a side view of yet another embod-
`imentof the anterior fusion cage of the presentinvention.
`Figure 14 depicts a left distal end (distal end) view
`of the fusion cage of the invention of Figure 13.
`Figure 15 depicts a right end (proximal end) view of
`the fusion cage of the invention of Figure 13.
`Figure 16 depicts a sectional view taken through line
`16-16 of Figure 13.
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`Posterior Fusion Gage:
`
`Figure 17 is a partially sectional side view of an
`embodimentof the posterior fusion cage of the invention.
`Figure 18 depicts a left end (distal end) view of the
`fusion cage of Figure 17.
`Figure 19 depicts a right end (proximal end) view of
`the fusion cage of Figure 17.
`Figure 20 depicts a view through line 20-20 of the
`fusion cage of Figure 17.
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`in order to enhancethe self-tapping nature of the fusion
`cage andto prevent the cage from wandering.
`In yet another aspectof the invention, introduction
`tools allow the fusion cage to be accurately positioned
`betweenthe vertebral bone structures. A preferred intro-
`duction tool allows for the cage to be implanted and
`thereafter allows an end cap of the cage to be conven-
`iently removed, if desired, in order to place bone growth
`inducing substancesin the cage.
`The method of the presentinvention affords access
`to adjacent vertebral bone structures using an posterior
`approach and procedure. Such posterior approach and
`procedure can be performed percutaneously using a
`minimally invasive technique with an introduction set
`including cannulas. Such a procedureis minimally inva-
`sive as the tissues can be spread using a set of cannula
`of increasing size and a small opening thereby devel-
`opedthrough whicha fusion cage canbeinserted. Such
`a procedureis less traumatic to the tissue than analter-
`nate posterior approach and procedure, also known as
`an posterior lumbar interbody fusion, where an incision
`is made, through the tissues.It is to be understood how-
`ever that either posterior approach and procedure can
`be used with the fusion cage and fall within the scope of
`the invention.
`
`After such access,using preferably a minimally inva-
`sive technique, degenerate disk material can be
`removed and, using a cannula and insertion tool, an
`appropriately shaped fusion cage can be screwedinto
`place betweenthe vertebral bone structures in orderto
`stabilize the vertebral bone structures and allow for
`
`fusion. Either preparatory to insertion of the fusion cage
`or after it has been inserted, bone chips or other bone
`growth inducing substances can be inserted into the
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`all the way to the central point 48 on the longitude axis
`50. Still in other embodiments, the flutes can be elimi-
`nated from the distal end 24 and such embodiments are
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`still within the spirit and scope ofthe invention.
`The flutes extend from the distal end 24 toward the
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`A thread 40is defined as partof the outercylindrical
`Figures 21, 22, and 23 depict progressive stagesin
`surface 41 of the body 22. It is to be understood that the
`the method of
`inserting the posterior
`fusion cage
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`between adjacent vertebral bone structures using the thread can be replaced withaplurality of discrete threads
`cage depicted in Figure 25.
`ora plurality of projections, ridges, protrusions, barbs,or
`spurs and be within the spirit and scope of the invention.
`Figure 24 depicts a side view of an alternative
`The roundeddistal end 24, and at least some of the
`embodiment of the posterior fusion cage of the invention.
`Figure 25 depicts a side view of another embodi-
`turns of thread 40 definedflutes or relief grooves 42, 44,
`mentof the posterior fusion cage of the invention.
`and 46. (Figures 1, 2.) Ina preferred embodiment,flutes
`Figure 26 depicts a left end (distal end) view of the
`42, 44, and 46 meet at a central point 48 of the distal end
`embodimentof the fusion cage of Figure 25.
`24 onthe longitudalaxis 50 of the fusion cage 20. In other
`embodiments the flutes can be smaller and not extend
`Figure 27 depicts the fusion cage of Figure 25in con-
`junction with a new preferred insertion tool that can pref-
`erably be used with the anterior fusion cages of Figure
`1, 10 and 13, and with the posterior fusion cages of Fig-
`ure 17 and 25.
`
`Figure 28 depicts an end view of the insertion tool
`of Figure 27 alongline 28-28.
`Figure 29 depicts a partially broken away view of the
`fusion cage and the insertion tool of Figure 27 connected
`together.
`Figure 30 depicts a perspective view of the end of
`the insertion tool depicted in Figure 28.
`Figure 31 depicts a partially sectional view of the
`handle of the insertion tool of Figure 27.
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`Detailed Description of the Preferred Embodiment
`
`Anterior Fusion Gage:
`
`With respectto the figures in a particular Figure 1,
`a side view of the preferred embodiment of the fusion
`cage 20is depicted. Fusion cage 20 includes a fusion
`cage body 22 whichin this preferred embodimentis pro-
`vided in the shape of a cone. Fusion cage 20 includes a
`distal end 24 and a proximal end 26. The distal end 24
`in a preferred embodimentis rounded or bull nosed in
`orderto facilitate the insertion of the fusion cage 20rel-
`ative to one or more bone structures. The proximal end
`26 includes an opening 28 which communicateswith an
`internal cavity 30 defined by the fusion cage 20. The
`opening 28 in a preferred embodimentis threaded so
`that it can receive an end capor plug 32 (Figure 5). End
`Cap 32 is used to close off the proximal end 26 and retain
`bone growth inducing substances packed therein as
`described herein-below. As can be seenin Figure 5, end
`cap 32 includes a threaded bore 34 whichis designed to
`receive an insertion tool. The threaded bore 34 has an
`
`initial unthreaded, square or hex-shaped section 35
`which can be used with a socket wrenchto tightly posi-
`tion end cap 32 in opening 28 and which can be engaged
`by a preferred insertion tool of Figure 27. Further the
`unthreaded portion of bore 34 could equally be cylindri-
`cal with anirregularity to allow for mating with an inser-
`tion tool, as well as having a variety of other shapes. The
`proximal end 26 further define first and second periph-
`eral indentations 36, 38. These peripheral indentations
`36, 38 receive tangs from an insertion tool as described
`hereinbelow for facilitating the insertion of the fusion
`cage 20.
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`proximal end 26 as shownin Figure 1 with respectto flute
`42. These flutes are defined by the sections 52 which
`are removed from the thread. Ina preferred embodiment,
`the flutes become narrower as they approachthe proxi-
`mal end 26 due to the fact that threadrelief for purposes
`of self-tapping becomes less important as the cage
`reaches a final resting position. As shown in other
`embodiments, the flutes can be deeper and extend from
`the distal end completely to the proximal end. Still further
`in other embodiments the flutes can be confined to the
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`first several turns of the thread adjacentto the distal end
`and/orto just the distal end.
`As can be seenin Figures 1, 4, a plurality of aper-
`tures 54 are provided through wall 56 of the fusion cage
`20. In a preferred embodiment, these apertures 54 are
`formed by broaching grooves 58in the internal surface
`60 of the internal cavity 30. The effect of such broaching
`is to remove material from the valleys betweenthe turns
`of the thread 40, thus defining the aperture 54. The
`advantages of such an arrangementare taught by the
`above-referenced U.S. Patent No. 4,961,740, which pat-
`ent is incorporated herein by reference and allows for
`immediate bone to bone contact between the vertebral
`
`bodies or bone structures and the bone packed within
`the internal cavity 30 of the fusion cage 20.
`The apertures 54 in a preferred embodiment
`increasein size from smaller apertures closer to the dis-
`tal end 24 to a larger aperture closer to the proximal end
`26. This increasein size allows for more bone to bone
`
`contact. Alternatively in the embodiment as shownin Fig-
`ure 1, all the apertures are of the samesize.
`As can be seenin Figure 4, the apertures are clus-
`tered about a transverse axis 51, both at the upper and
`lower end of the axis. This is so that in position, the aper-
`tures come into contact with the upper and lowerverte-
`bral bone structures (Figure 9)
`to encourage bone
`growth through the fusion cage from the vertebral bone
`structures. The lateral section of the fusion cage found
`along the other transverse access 53 do not have aper-
`tures in order to prevent growth of disk material which
`might interfere with the bone fusing process.
`A preferred embodiment of the conically-shaped
`fusion cage 20 includes a fusion cage which is 23 mil-
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`IBLE TROCAR WITH CURVED CANNULA,” which is
`incorporated by reference, but howeverwith larger diam-
`eter instruments, an amountof disk material is removed
`between the two vertebral bodies or bone structures
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`handle includes a bore 68 for receiving the inner handle
`64. Handles 64, 66 include knobs 70, 72 respectively.
`The distal end of inner handle 64 defines a threaded
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`shaft 74, having a reverse thread to facilitate easy
`removal, and the distal end of handle 66 define a cylin-
`drical disk 76 which hasfirst and second tangs 78, 80,
`projecting from the peripheral edge of the cylindrical disk
`76. These tangs 78, 80 are designed to mate with the
`peripheral indentation 36, 38 of the fusion cage 20. For
`purposesof inserting the fusion cage betweenthe ver-
`tebral bodies, the end cap 32 is inserted into the fusion
`cage 20 as shownin Figure 5. Then the threaded shaft
`74 of the inner handle is introduced into the threaded
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`bore 34 of the end cap 32. After this is accomplished, the
`outer handle 66is slid over the inner handle 64 and the
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`tangs 78, 80 are positioned into engagement with the
`indentations 36, 38. In this arrangement, the fusion cage
`20 can be anteriorly inserted into the space between the
`vertebral body structure using the insertion tool 62.
`An alternative embodimentof the insertion tool is
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`limeters in length having a distal end 24 with a diameter
`of 14 millimeters and a proximal end 26 with a diameter
`of 18 millimeters. The cage bodyis a right circular cone.
`The thread hasa pitch of 30° and there are ten turns per
`whichareto be fused together. This procedure is accom-
`inch with a thread depth of .053 inches. Further the cage
`plished through a cannula position adjacent to the ver-
`is made of a titanium metal or alloy such as Ti64. Pref-
`tebral bone structures. With the same or a larger
`erably this and the other disclosed fusion cages dis-
`diameter cannula, the fusion cage 20 can be introduced
`closed are machined. However, the processes such as
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`molding, casting, or sintering can be used to accom- adjacent to the vertebral bonestructures. Inafirst pro-
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`cedure, the fusion cage is packed with bone growth sub-
`stances and the end cap32is affixed to the fusion cage
`The cage is inserted betweenvertebral bodies using
`20. Insertion tool 62 is then secured to the fusion cage
`an insertion tool 62 (Figure 5). Insertion tool 62 includes
`an inner handle 64 and an outer handle 66. The outer
`20 and the fusion cage is guided through the cannula to
`a location adjacentto the upper and lowervertebral body
`such as presented schematically in Figures 7, 8, 9, by
`upper body 98 and lower body 100.In the initial position
`as shownin Figure 7, the fusion cage 20 is adjacent to
`the anterior surfaces 102, 104 of the vertebral bodies 98,
`100. As the introduction tool is turned, the thread 40 of
`the fusion cage 20bitesinto the vertebral bodies 98, 100.
`Furtherturning of the introduction tool causesthe fusion
`cage to move through the position shownin Figure 8 to
`the final resting position shown in Figure 9, where the
`distal end 24 is moved adjacent to the posterior sections
`106, 108 of the vertebral bone structures 98, 100. As this
`occurs, the fusion cage 20 increases the lordosis or
`spacing betweenthe vertebral bodies, basically distract-
`ing the vertebral bodies and causing the vertebral bodies
`to pivot about the posterior sections 106, 108, with such
`posterior sections acting like a hinge.It is noted that most
`of the distraction occurs adjacent to the anterior sections,
`but that distractions also occur at the posterior sections
`where the hinged effect is exhibited. Preferably, the lor-
`dosis is increased over the normal lordosis in order to
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`stabilize the vertebral bone structures prior to fusion
`occurring. Stabilization occurs due to the fact
`that
`tool 82 distal from the knob 86is a cylindrical disk 88
`increased lordosis places additional stress on the ante-
`whichhasfirst and second tangs 90, 92, which have the
`rior longitudinal ligaments which are part of the anatomy
`samefunction as the above tangs 78, 80. Extending from
`holding the vertebral bodiesin place.
`the centerof the cylindrical disk 88 along the centerline
`40
`of the insertion tool 82 is a shaft 94 which hasaball
`Oncethe fusion cage 20 is appropriately positioned,
`the handle 64 of the insertion tool 62 is unscrewed from
`detent 96. For use with insertion tool 82, the threaded
`bore 34 of the end cap 32 would be replaced with a bore
`having a lip which could engage with the ball detent 96
`of the insertion tool 82.
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`shownin Figure6.In this figure, insertion tool 82 includes
`a handle 84 with a knob 86. At the end of the insertion
`
`Itis to be understood that the insertion tool depicted
`in Figure 27 and described below is preferable to the
`above described insertion tools for both the anterior
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`fusion cages and the below described posterior fusion
`cages.
`The methodfor inserting the fusion cage 20 of Fig-
`ure 1 using an anterior approach and procedure to the
`vertebral bodiesis as follows. It is to be understood that
`
`althoughthe focusof this discussion is on a laparoscopic
`procedure,that the anterior approach and procedure can
`also include a more invasive procedure wherea longinci-
`sion is made in the abdomenwall.
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`With an anterior approach, using an introduction set
`such as described by way of exampleonly, in U.S. Patent
`4,863, 430, entitled "INTRODUCTION SET WITH FLEX-
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`the cap 32 and the fusion handle 62 is pulled away from
`the fusion cage.
`Analternative embodiment of a fusion cage 200is
`shown in Figures 10, 11, and 12. Fusion cage 200
`includes a distal end 202 and an a proximal end 204.
`Fusion cage 200 includes an internal cavity 206. End
`caps not shown can be usedto close the ports 208, 210
`of distal and proximal ends 202, 204. A thread 212 is
`defined on the external conical surface 214 of the fusion
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`cage 200. Defined bythe thread 212 are first and second
`flutes 216, 218, which in this embodiment extend from
`the distal end 202 to the proximal end 204. Theseflutes
`provide thread relief allowing the fusion cage 200 to be
`self-tapping.
`The fusion cage 200 includesa plurality of elongated
`apertures 220 which are formed through the side walls
`of a fusion cage 200. The elongated apertures 202 are
`formed in such a waythat the internal conical surface
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`214 is spaced away from the internal surface 224 of the
`internal cavity 206 by the thicknessof the sidewall 222.
`A further embodiment of the invention is shown in
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`Figures 13, 14, 15 and 16. In Figure 16 the fusion cage
`300 hasdistal and proximal ends 302 and 304 respec-
`tively. The fusion cage 300 definesaninternal cavity 306,
`and ports 308 and 310 defined through the distal and
`proximal ends 302 and 304 respectfully. A thread 312 is
`defined as part of the external conical surface 314 of the
`fusion cage 200. First, second andthird flutes 316, 318,
`and 320, are defined in the thread 312 from the distal
`end 302 to the proximal end 304. Theseflutes give the
`fusion cage 300 an enhancedself-tapping advantage.
`These flutes are equally spaced about the fusion cage
`300 in a mannersimilar to the flutes of the fusion cage
`embodiment 20 in Figure 1.
`A plurality of aperture 322 is provided through the
`external conical surface 314 of the fusion cage 300 and
`through the side wall 324 openinginto the internal cavity
`306. Accordingly, at the location of the aperture 322 the
`external surface 314 is held away from the internal sur-
`face 326 bythe thickness of the side wall 324.
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`Posterior Fusion Caqe:
`
`With respectto the figures in a particular Figure 17,
`a side view of the preferred embodimentof the posterior
`fusion cage 420 is depicted. Fusion cage 420 includes
`a fusion cage body 422 whichin this preferred embodi-
`mentis provided with a conically-shaped portion 423 and
`a cylindrically-shaped portion 425.It is to be understood
`that alternatively the entire body 422 can be conically-
`shaped. Further, as appropriate the shape of the cage
`body 422 can be more complex with various conical
`and/or cylindrical configurations. Fusion cage 420
`includes a distal end 424 and a proximal end 426. The
`distal end 424 in a preferred embodimentis rounded or
`bull nosed in orderto facilitate the insertion of the fusion
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`cage 420relative to one or more bone structures. The
`proximal end 426 includes an opening 428 (Figure 19)
`which communicates with an internal cavity 430 (Figure
`20) defined by the fusion cage 420. The opening 428in
`a preferred embodimentis threadedso thatit can receive
`an end cap or plug such as 32 of the embodimentin Fig-
`ure 5. End capis used to close off the proximal end 426
`and retain bone growth inducing substances, such as
`bone chips, packed therein as described herein-below.
`As can be seen in the embodiment of Figure 5, end cap
`32 includes a threaded bore 34 which is designed to
`receive an insertion tool. The threaded bore 34 has an
`
`initial unthreaded, square or hex-shaped portion 35
`which can be used with a socket wrenchto tightly posi-
`tion end cap 32 in opening 428 and which canalso be
`engaged by the insertion tool of Figure 27 described
`below. Portion 35 can be otherwise shaped as described
`above.
`
`The proximal end 426 of the embodimentof Figure
`19 further define first and second peripheral indentations
`436, 438 which are centered about transverse axis 453.
`
`10
`
`15
`
`20
`
`26
`
`30
`
`35
`
`40
`
`45
`
`50
`
`55
`
`These peripheral indentations 436, 438 receive tangs
`from an insertion tool as described below forfacilitating
`the insertion of the fusion cage 420. These identifications
`are also used to line up the cage 420for properinsertion
`betweenthe vertebral bodies as discussed below.
`
`A thread 440 is defined as part of the outer cylindri-
`cal surface 441 of the body 422.
`It is to be understood
`that the thread can bereplaced with a plurality of inter-
`rupted or discrete threads or a plurality of projections,
`ridges, protrusions, barbs, or spurs and be within the
`spirit and scope of the invention.
`The rounded distal end 424, and at least some of
`the turns of thread 440 can in a preferred embodiment
`candefine flutesorrelief grooves 442, 444, and 446 (Fig-
`ures 24, 25).
`It is to be understood that in alternative
`embodimentsthe flutes can be eliminated from the distal
`
`end 424 and the thread 440, since for example, the bore
`for the insertion of the fusion cage 420 betweenthe ver-
`tebral bodies can be pre-tapped. Still
`in alternative
`embodiment, the flutes on the distal end can remain to
`assist in the insertion of the cage 420 betweenthe ver-
`tebral bodies.
`In a preferred embodiment, flutes 442,
`444, and 446 meet ata central point 448 of the distal end
`424 on the longitudal axis 450 of the fusion cage 420.In
`other embodiments the flutes can be smaller and not
`
`extend all the way to the central point 448 on the longi-
`tude axis 450. Still as indicated above in other embodi-
`ments, the flutes can be eliminated from the distal end
`424 and the thread 440 and such embodimentsarestill
`
`within the spirit and scope of the invention.
`The flutes can extend from the distal end 424 toward
`
`the proximal end 426 as shownin the alternative embod-
`iment in Figure 24 with respectto flute 542. Theseflutes
`are defined by the sections 552 which are removed from
`the thread. In this embodiment, the flutes become nar-
`rower as they approachthe proximal end 526 dueto the
`fact
`that
`thread relief
`for purposes of self-tapping
`becomesless important as the cage reachesa finalrest-
`ing position. As shownin other embodiments,the flutes
`can be deeperand extend from the distal end completely
`to the proximal end. Still further in other embodiments
`the flutes can be confinedto the first several turns of the
`
`thread adjacentto the distal end and/orto just the distal
`end.
`
`With respect to Figures 17, 20, a plurality of aper-
`tures 454 are provided through wall 456 of the fusion
`cage 420.
`In a preferred embodiment, these apertures
`454 are formed by broaching grooves 458in the internal
`surface 460 of the internal cavity 430. The effect of such
`broachingis to remove material from the valleys between
`the turns of the thread 440, thus defining the aperture
`454. The advantagesof such an arrangement are taught
`by the above-referenced U.S. Patent No. 4,961,740,
`which patent is incorporated herein by reference and
`allows for immediate bone to bone contact between the
`
`vertebral bodies or bone structures and the bone packed
`within the internal cavity 430 of the fusion cage 420.
`The apertures 454 in a preferred embodiment
`increase in size from smaller apertures closer to the
`
`
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`11
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`EP 0 716 840 A2
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`12
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`proximal end 426to a larger aperture closer to the distal
`end 424. This increase in size allows for more bone to
`
`bone contact. Alternatively in the embodiment as shown
`in Figure 17, all the apertures are of the same size.
`As can be seenin Figure 20, the apertures are clus-
`tered about a transverse axis 451, both at the upper and
`lower end of the axis. This is so that in position, the aper-
`tures comeinto contact with the upper and lower verte-
`bral bone structures (Figure 23) to encourage bone
`growth through the fusion cage from the vertebral bone
`structures. Thelateral sections of the fusion cage found
`along the other transverse axis 453 do not have aper-
`tures in order to prevent growth of disk material which
`mightinterfere with the bone fusing process. As can be
`seen viewing both Figures 19 and 20 together, the inden-
`tation 436 and 438 are centered on the axis 453 with the
`
`aperture 454 centered on axis 451. Axis 451 is preferably
`perpendicular to axis 453. The insertion tool has tangs
`that are inserted in indentation 436 and 438. Accordingly,
`the position of the insertion tool defines the position of
`the apertures 454 in that upon insertion the apertures
`454 can be put in contact with th