`OFFICE DE LA PROPRIETE
`INTELLECTUELLE DU CANADA
`
`CIPO PROPERTY OFFICE
`
`CANADIAN INTELLECTUAL
`
`(72) Kuslich, Stephen D., US
`(72) Corin, James D., US
`(72) Bagby, George W., US
`(73) Spine-Tech, Inc., US
`(51) Int.Cl.° A61B 17/70
`(30) 1989/07/06 (376,657) US
`(30) 1989/09/08 (405,564) US
`64) IMPLANT RACHIDIEN
`64) SPINAL IMPLANT
`
`aza9)cay Brevet-Patent
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`GD QOD(Cc) 2,0 15,507
`(22)
`1990/04/26
`(43)
`1991/01/06
`(45)
`1999/01/05
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`
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`(57) L’invention porte sur un implant pour la stabilisation
`rachidienne. Dans un modéle privilégié, l’implant est
`décrit comme un corps cylindrique creux ayant un
`filetage externe et une série d’ouvertures formées
`radialoment sur tout
`le corps et communiquant avec
`Pintérieur de ce dernier. Des bouchons, dont au moins un
`est fait d’un matériau perméable aux rayons X, sont
`prévus aux extrémités avant et arriére du corps.
`
`is disclosed for use in spinal
`(57) An implant
`stabilization. In one preferred embodiment, the implant
`is described as including a hollow, cylindrical body
`having external threading and a plurality of openings
`formed radially through the body in communication with
`the body interior. End caps are provided on the leading
`and trailing ends of the body, with at least one of the end
`caps formed from a radiolucent material.
`
`i<j] Industrie Canada—_Industry Canada
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`2015597
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`SPINAL IMPLANT
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`ABSTRACT OF THE DISCLOSURE
`
`An implant is disclosed for use in spinal
`stabilization.
`In one preferred embodiment,
`the implant is
`5 described as including a hollow, cylindrical body having
`external threading and a plurality of openings formed
`radially through the body in communication with the body
`interior.
`End caps. are provided on the leading and
`trailing ends of the body, with at least-one of the end
`caps formed from a radiolucent material.
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`SPINAL IMPLANT
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`BACKGROUND OF THE INVENTION
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`1.
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`Field of the Invention
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`This invention pertains a surgical procedures
`for stabilizing the spine. More particularly, this
`invention pertains to a novel
`implant for use in such
`a procedure.
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`2.
`
`Description of the Prior Art
`
`Chronic low back pain is one of the most common
`and perplexing problems facing the field of
`orthopedic surgery.
`In addition to patient
`discomfort, chronic low back pain has severe adverse
`societal impacts including lost income, possible
`chronic dependence on drugs, alcohol and public
`relief programs.
`low back pain can be avoided by
`In many cases,
`preventing relative motion between spinal vertebrae
`{commonly referred to as intervertebral
`stabilization).
`To abate low back pain,
`stabilization is directed to
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`Stabilizing contiguous vertebrae in the lumbar region of
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`the spine.
`Surgical techniques are known for use in spinal
`stabilization. Surgical techniques seek to rigidly join
`vertebrae which are separated by a degenerated disk.
`Ideally,
`the surgery effectively replaces the vertebra-—
`disk-vertebra combination with a single rigid vertebra.
`Various surgical techniques have developed which attempt to
`approach or approximate this ideal.
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`One technique known. in the art is to partially
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`remove a degenerated disk and to insert a bone graft into
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`the void formed by the removed disk. Other techniques
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`involve the use of an implant which, acting alone or in
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`-combination with bone’ fragments, replace the use of bone
`grafts. An example of such implant is shown in. U.S. Pat.
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`15_
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`No. 4,501,269 to Bagby dated February 26, 1985.
`
`In Bagby,
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`-a large, cylindrical basket is driven into a hole formed
`between bones which are to be joined. The basket is hollow
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`and is filled with bone fragments which are produced during
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`a boring step. Bone-to-bone fusion is achieved through and
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`about the basket.
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`In Bagby,
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`the hole for the Bagby is
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`slightly smaller than the diameter of the basket. This
`structure results in the spreading of the opposing bone
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`segments upon insertion of the basket. This results in
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`taughtness, which provides initial stabilization. Eventual
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`fusion of the opposing bone segments results from bone
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`growth through the basket.
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`Prostheses such as that shown in U.S. Pat. No.
`4,501,269 are promising. However,
`improvedimplant design
`is necessary to enhance patient safety and the probability
`
`of a satisfactory recovery.
`
`Til.
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`‘SUMMARY OF THE INVENTION
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`According to a preferred embodiment of the present.
`invention, an implant is disclosed for insertion into a
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`bore formed between opposing vertebrae of an animals.
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`..
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`spine. The implant includes a rigid body having aleading:
`end and a trailing end spaced apart along a longitudinal.
`axis of the body. The body has exposed threads which are
`disposed between the leading and trailing ends. The
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`is -
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`threads are: selectedtoengage: vertebra material. and draw-.-
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`the body along the direction of the axis upon rotation of
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`the body about the axis.
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`The body defines a chamber which
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`is exposed through the body by a plurality of radially
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`extending openings.
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`The chamber may be filled with bone
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`fragments which can fuse with the vertebra bone material
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`through the openings.
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`In an alternative embodiment of the invention
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`disclosed herein, a generally oval~shaped implant is
`disclosed which is hammered into an elongated bore between
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`2075507
`The oval-shaped implant has
`two opposing vertebrae.
`enhanced surface area contact between the vertebrae
`and provides greater integrity against rotational
`motion between opposing vertebrae.
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`Other aspects of this invention are as follows:
`
`An implant for insertion into a bore formed
`between opposing vertebrae of a spine where said
`vertebrae are separated by a spacing with a disk
`Material having an annulus disposed within said
`spacing, said implant comprising:
`a rigid body having a leading end and a
`trailing end spaced apart by a longitudinal axis
`of said body;
`said body comprising at least exposed
`. threads disposed at least partially between said
`leading end and said trailing end, said threads
`selected to engage vertebra material and draw
`-° Said “body along a direction of said axis upon’.
`“ “otation of said body about. said axis;
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`said body having a hollow, .enerally
`cylindrical shell with said threads disposed on
`an ‘exterior surface of said shell;
`Said body having. means. defining a chamber
`disposed within said body and said body is
`provided with a rib disposed within said
`cylindrical shell and extending radially
`inwardly toward said longitudinal axis, said rib
`dividing said chamber into a leading end chamber
`and a trailing end chamber, and said rib
`including at least a rigid extension extending
`between and connecting diametrically opposed
`sides of said body;
`said body having means defining at least
`one opening formed through said body in
`communication with said chamber and with said
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`20715507
`opening extending generally radially to said
`axis; and
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`said body having a transverse dimension
`generally transverse to said longitudinal axis
`and dimensioned so as to be greater than said
`bore for said body to urge said opposing
`vertebrae apart and to stretch said annulus upon
`insertion of said body into said bore between
`said vertebrae with a portion of said body
`opposing a first of said opposing vertebrae and
`with an opposite side of said body opposing a
`second of said opposing vertebrae.
`
`An implant for insertion into a bore formed
`between opposing vertebrae of a spine where said
`vertebrae are separated: by a spacing with a disk
`material having an annulus disposed within said
`spacing, said implant comprising:
`a rigid body having a leading end and a
`trailing end spaced apart by a longitudinal axis
`of said body;
`a
`said body comprising at least exposed
`threads disposed at least partially between said
`leading end and said trailing end, said threads
`- selected to.engage. vertebra material and draw
`said body along a direction of said axis upon
`rotation of said body about said axis;
`said body having a hollow, generally
`cylindrical shell with said threads disposed on
`an exterior surface of said shell;
`said body having means defining a chamber
`disposed within said body;
`said body having means defining at least
`one opening formed through said body in
`communication with said chamber and with said
`opening extending generally radially to said
`axis, said opening comprising a hole having a
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`hole axis extending generally perpendicular to a
`plane defined by said opening at an exterior
`surface of said shell, said hole formed through
`said shell with said hole disposed with said
`hole axis offset from said longitudinal axis;
`and
`
`said body having a transverse dimension
`generally transverse to said longitudinal axis
`and dimensioned so as to be greater than said
`bore for said body to urge said opposing
`vertebrae apart and to stretch said annulus upon
`insertion of said body into said bore between
`said vertebrae with a portion of said body
`opposing a first of said opposing vertebrae and.
`with. an opposite side of said body opposing a
`second of said opposing vertebrae.
`
` ~Anm-implant for insertion into a bore formed
`between opposing vertebrae of a spine where said
`vertebrae are separated: by a spacing with a disk
`“material. having an annulus disposed within said..
`spacing, said implant comprising:
`a-rigid body having a leading end anda
`trailing end spaced apart by a longitudinal axis.
`-o£.said body;
`said. body comprising at least exposed
`threads disposed at least partially between said
`leading end and said trailing end, said threads
`selected to engage vertebra material and draw
`said body along a direction of said axis upon
`rotation of said body about said axis;
`said body having a hollow, generally
`cylindrical shell with said threads disposed on
`an exterior surface of said shell;
`said body having means defining a chamber
`disposed within said body and said body is
`provided with a rib disposed within said
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`207135507
`cylindrical shell and extending radially
`inwardly toward said longitudinal axis, said rib
`including at least a rigid extension extending
`between and connecting diametrically opposed
`sides of said body;
`said body having means defining at least
`one opening formed through said body in
`communication with said chamber and with said
`opening extending generally radially to said
`axis; and
`
`said body having a transverse dimension
`generally transverse to said longitudinal axis
`and dimensioned so as to be greater than said
`bore for said body to urge said opposing
`vertebrae apart and to stretch said annulus upon
`insertion of said body into said bore between
`said vertebrae with a portion of said body
`opposing a first of said opposing vertebrae and
`with an opposite side of said body opposing a
`‘second of. said opposing. vertebrae;
`.
`Said: rib is disposed between said leading and
`trailing ends, said implant further including a first.
`flange at said leading end and a second flange at.
`said trailing end, said first and second flanges
`extending radially into said chamber.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`1 is a perspective exploded of view of an
`Fig.
`implant according to a preferred embodiment of the
`present invention;
`Fig.
`2 is a side elevation view of a body
`portion of the implant of Fig. 1;
`Fig. 2A is a side elevation view of an
`alternative embodiment of a body portion of an
`implant according to the present invention;
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`20715507
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`3 is an end view taken in elevation of the
`Fig.
`trailing end of the body portion of Fig.
`2
`taken
`along line 3-3 of Fig. 2;
`Fig. 3A is the same view as Fig.
`alternative embodiment;
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`3 showing an
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`4 is a view taken along lines 4-4 of
`
`Fig.
`Fig. 2;
`Fig. 4a is the same view as Fig.
`alternative embodiment;
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`4 showing an
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`Fig.
`Fig.
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`5 is a view taken along line 5-5 of Fig. 2;
`6 is a view taken along lines 6-6 of
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`Fig. 3;
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`Fig. 7 is an enlarged view,
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`taken in section, of
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`the threads of the body of Fig. 2 adjacent the trailing
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`end;
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`taken in section, of the
`Pig. JA is a view,
`>
`threads of the body portion of Fig. 2 adjacent a leading.
`end of the body;
`.
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`Fig. 8 is a side sectional view of a leading end
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`cap of the implant of Fig. 1;
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`Fig. 9 is an inside end elevation view of the end
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`cap of Fig.
`8 taken along line 9-9 of Fig. 8;
`Fig 10 is a side sectional view of a trailing end
`cap of the implant of Fig. 1;
`Fig. 11 is an end elevation view of the end cap of
`Fig. 10 taken along line 11-11 of Fig 10;
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`Fig. 12 is a top plan view showing insertion of a
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`single implant of Fig.
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`1 into an intervertebral space;
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`Fig. 12A is a view taken along lines 12A-12A of
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`Fig. 12;
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`Fig. 13 is a top plan view showing an alternative
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`20
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`embodiment of the present invention in place in a vertebra;
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`Fig. 13A is a view taken along lines 13A-13A of
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`Fig. 13;
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`Fig. 14 is a perspective view of an alternative
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`embodiment of the present invention showing an implant body
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`25 -
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`leading end, side and top;
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`Fig. 15 is a perspective view of the body of
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`Fig. 14 showing a trailing end, side and top;
`Fig. 16 is a top plan view of the embodiment of
`Pigs. 14 and 15;
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`Dot
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`Fig. 17 is a side sectional view taken along lines
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`17-17 of Fig. 16;
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`Fig. 18 is a side elevation view of a trailing end
`cap for use with the embodiment of Figs. 14 and 15;.
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`Fig. 19 is an end view taken in elevation of the
`end cap of Fig. 18;
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`Fig. 20 is an elevation view a trailing end. of the
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`embodiment of Figs. 14 and 15;
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`Fig. 21 is an elevation view of .a leadingend of
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`the body of the embodiment of Figs. 14 and 15;
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`Fig. 22 is a side elevation view of the body
`-portion of Figs. 14 and 15;
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`Fig. 23 is a top plan view of an assembled implant
`including body portion and end cap shown in place in a
`vertebra body;
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`Fig. 24 is an anterior elevation view showing a
`bore drilling sequence prior to insertion of the implant as
`shown in Fig. 23;
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`Fig. 25 is a view taken along lines 25-25 of
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`Fig. 23;
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`Vv.
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`DESCRIPTION OF THE PREFERRED EMBODIMENT
`SRERREDEIBODIERIE
`
`A.
`
`General.
`Reference is now directed to Figs.’ 1 and 12.
`1 is an exploded perspective view of an implant
`Fig.
`according to a preferred embodiment of the present
`invention.
`The implant is shown generally at 10. Fig. 12
`shows the implant 10 inserted within a bore 102 formed in a
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`10
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`human vertebra body 100.
`the implant 10 (as well
`For ease of description,
`as alternative embodiments of the invention) will be
`3
`described for use in a human spine. Further, dimensions,
`_. when given, will be preferred dimensions for use in a
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`as
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`specific spinal location of a particular class of humans --
`notably,
`the L-5 vertebra of a typical adult male.
`It will
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`be appreciated that the present invention is intended for
`use in a wide variety of vertebra sizes and a wide variety
`ef animal species.
`The dimensions of the implant 10 (as
`well as the dimensions of the alternative embodiments) will
`vary necessarily with the size of the vertebra in which the
`implant 10 is to be used. However, making variations to
`the dimensions and sizes in order to accommodate differing
`sizes of vertebrae will be well within the skill of the
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`art.
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`B.
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`First Preferred Embodiment.
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`With reference now directed to Figs. 1-12, a first
`preferred embodiment of the present invention will now be
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`Identical elements are numbered identically
`described.
`.
`throughout.
`.
`whe implant 10 includes a body 12 (shown
`separately in Figs. 2, 3~6) having a leading end 14 and a
`trailing end 16 which are spaced apart along a longitudinal
`axis X-K of the body 12.
`. The implant also includes a
`leading end cap 18 and a trailing end cap 20 (shown
`separately in Pigs. 8-9 and Figs. 10-11, respectively).
`Body12 is integrally constructed from a rigid,.
`biocompatiblematerial. While any rigid, biocompatible
`material (such as a ceramic) could be used, body 12 is
`' preferably formed from titanium and/or its alloys..
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`Titanium and/or its alloys is preferred since itis
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`“noncorrosive and fatigue resistent. Also,
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`titanium-is
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`widely used in prosthetic devices and the material has a
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`proven record of satisfactory performance.
`With best reference to Figs. 2-7 and 7A, the body
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`12 includes a hollow cylindrical shell 22 of predetermined
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`diameter D, (see Fig. 3).
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`For reasons that will be later
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`described D, is selected to be about
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`.5 inches.
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`The shell 22 surrounds and defines an interior
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`- chamber 24. Chamber 24 has a diameter -D, of preferably
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`about
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`.384 inches.
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`Threads 26 and 28 are formed on the exterior
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`surface of shell 22 spirally wound around shell 22 and
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`integral therewith. While double threading is shown,
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`single threading or multiple threading in excess of double
`threading could be applied. Threads 26, 28 are disposed.
`and selected for the threads 26, 28 to engage the bone
`material of opposing vertebrae and draw the body 12 in the
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`direction of axis X-X upon rotation of the body 12 about
`axis X-X.
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`In a preferred embodiment, body 12 is
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`the threading 26, 28 (see Fig. 2).
`- self-tapping. Mainly,
`adjacent leading end 14 is tapered as shown byangle. A, -
`(which is preferably about 15°, see Fig. 2).
`-Away.-from the
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`tapered end 14, and adjacent the trailing end 16, the .
`threads 26, 28 present flat, annular surfaces. 30. which are >
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`in alignment andparallel to shell 22. Accordingly,
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`the.
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`‘thread profile presents a generally bullet-shaped.profile-.
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`which is cylindrical along the majority of the body 12 and
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`tapers inwardly toward axis X-X at the leading end 14.
`The tapered portion of body 12 preferably has a
`length IL, of about
`.198 inches.
`The overall length of body
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`12, l,, is preferably about
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`.740 inches.
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`(See Fig. 2).
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`To assist in the self-tapping,
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`the threads 26, 28
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`experience a change in profile from the leading end 14 to
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`25.
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`the trailing end 16. At the leading end 14,
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`the threads
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`are sharp, as shown in Fig. 7A. When the taper portion of
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`body 12 is passed,
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`the threads 26, 28 assume a profile
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`which is generally rectangular as shown in Fig. 7. For
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`ease of discussion,
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`the sharp portions of threads 26, 28
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`oe.
`are. numbered 26a, 28a in the drawings.
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`The changing thread profiles are selected to
`assist in advancing the implant 10 into an intervertebral
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`Space and to a hold the implant 10 securely in place when
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`fully advanced.
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`The sharp portion of threads 26, 28
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`(thread portions 26a, 28a shown in Fig. 7A) cut bone better
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`40°
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`and assist in advancing the implant 10.
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`The generally
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`rectangular thread profile (Fig.-7) has greater cross-
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`‘sectional area and better opposes bone
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`surfaces to hold
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`“the implant 10 in place.
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`Preferred dimensions of. the threading 26, 28 are
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`15.
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`shown in Figs.
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`7 and 7A with a pitch, P,
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`(distance between
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`- opposing threads) equaling about
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`.10 inch for both the
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`“rectangular ‘and sharp threading of Figs.
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`7 and. 7A... The
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`bevel B,, of the sharp threading (Fig. 7A) is preferably
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`about 57°.
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`The bevel, B,, of the rectangular thread
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`portion (Fig. 7)
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`is preferably about 5°.
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`The height, H, of
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`the rectangular thread is about
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`.10 inches. This,
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`together
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`with the diameter D, (see Fig. 3) of the shell 22 results
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`in overall diameter of the body 12 being about
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`.6 inches.
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`It will be appreciated that these dimensions as well as
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`remaining dimensions given throughout this application are
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`preferred dimensions and may be varied while retaining the
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`structure and function of the present invention. The scope
`of the claims of the present invention is not intended to
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`be limited by dimensions which are set forth only to.
`illustrate a preferred embodiment.
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`The body 12 has a plurality of holes 32 formed .
`radially through the shell 22 and threads 26, 28.
`The
`holes 32 provide communication between interior chamber 24
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`and an exterior of the body 12.
`The holes 32 are identical and each is preferably
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`about
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`.125 inches in diameter.
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`Shown best in Fig. 4, each.
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`of the holes 32:includes a countersunk portion 34 at the
`radially outer surface of threads 26, 28. Preferably, the.
`countersunk portion 34 has a diameter of about
`.155inches.
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`.The countersunk portion 34 creates cutting a
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`beveled edge.33 on the rectangular threads 26, 28 in the
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`location of the holes 32. This cutting edge 33 is best.
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`‘:shown in Fig. 6. The cutting edges 33 chip away bone as.
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`the body 12 is rotated.
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`The bone chips will migrate
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`through the holes 32 into chamber 24. As will be
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`described, it is anticipated that this chipping action will
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`enhance the bone-to-bone fusion sought with the present
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`invention.
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`In the region of the self-tapping sharp threads
`26a, 28a (Fig. 7A),
`the threads 26a, 28a are shown self-
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`25.
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`tapping in Fig.
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`5 to present self-tapping cutting edges 36
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`set at a 90° cutting angle A,.
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`The cutting edges 36 are
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`shown spaced apart by an angle A, of about 120°.
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`in the preferred embodiment as shown, holes. 32
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`. extend through the threads 26 and 28.
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`An alternative
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`embodiment would have the threads 26 and 28 spaced apart.a
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`distance greater than that shown in the present drawings,
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`“with the holes 32 extending through the shell 22 and not
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`passing through threads 26 and 28.
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`Such a design presents
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`enhanced structural integrity since the more massive
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`“10.
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`threads 26 and 28 are not being broken. However,such an
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`alternative design forgoes the anticipated benefits which.
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`“may be attributed to the chipping action of thecutting.
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`edges 33.of the threads adjacent holes 32.
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`“The number of holes 32 in the body 12 as shown. is.- |
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`twenty. This number may vary.
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`The number .is selected to
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`‘be as many and.as large as possible (to enhance bone.
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`-fusion), while. not compromising the strength ofthe body
`12.
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`As previously indicated,
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`the body 12 extends from
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`20
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`a leading end 14 to a trailing end 16. Leading end 14 has
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`a circular axial opening 40 formed therethrough in
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`communication with chamber 24. Disposed inwardly from
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`leading end 14 is an annular groove 42 (see Fig. 6)
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`provided to facilitate attachment of leading end cap 18 as
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`will be described.
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`Trailing end 16 has an inwardly projecting flange
`44. Opposing surfaces of flange 44 define a centrally
`located hexagon-shaped axial.opening 46.
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`aan
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`When the implant 10 is in place inan
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`intervertebral space, circular axial opening 40 and hexagon
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`axial opening 46 are covered by caps 18 and 20.
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`Shown best
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`in Figs. 8 and 9, the leading end cap 18 includes a
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`cylindrical hub portion 50 and an annular flange 52
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`extending from hub portion 50. Also extending from hub
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`portion 50 on the side opposite flange 52 is a tapered cap
`‘portion 54 which extends from a large diameter 55 and
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`tapers inwardly to a smaller diameter terminal end 56. An
`angle of taper A, (Pig. 8)is preferably about. 15° to
`“ correspond with the angle of taper A, (Fig. 2)0f body 12.
`“The large diameter 55 is preferably selected to equal the
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`_ diameter of body 12 at leading end 14. Flange 52 is
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`selected to be snap received into annular. groove 42...
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`So
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`received, cap 18 is permanently attached to the leading end
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`14 covering axial opening 40.
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`Trailing end cover 20 (Figs. 10 and 11)
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`includes
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`an arcuate cap 58 sized to cover end 16 with a flat surface
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`portion 59 of cap 20 abutting trailing end 16.
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`Six
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`flexible retaining clips 60 are provided centrally
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`extending from surface 59. Clips 60 are sized to be snap
`- received within hexagon-shaped opening 46. Accordingly,
`the cooperation of surface 59 and the barbed portion 61 of
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`clips 60 capture flange 44 to thereby hold trailing end cap
`20 securely against trailing end 16. For reasons that will.
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`be described, each of caps 18 and 20 are preferably formed
`from high-density polyethylene.
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`ot
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`Cc. Method of Use.
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`10
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`15
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`20
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`the method cf use
`Referring to Figs. 12 and 12A,
`In use of the
`of the implant 10 will now be described.
`implant 10, a surgeon forms a bore 102 through the
`intervertebral space in a disk 114 separating two opposing
`vertebral bodies 100 and 100a.
`The bore 102 is sized to be
`as large as possible toremove disk material 114 and to at.
`least partially cut into opposing surfaces of the boneof
`vertebra bodies 100,100a.
`It will be appreciated that it
`is well within the skill of the art to form bores such as
`bore 102.
`:
`|
`.
`Fig. 12 and, 12A show a“bore 102 formed througha
`posterior approach through a spine.
`In a posterior
`approach, a surgeon approaches the vertebra through the
`
`.
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`back of the patient. Preferably,
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`the axis of the bore 102
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`is formed an angle with the anterior-posterior axis, A-P,
`of the vertebra body 100, 100a. As shown in the preferred
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`25
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`surgical approach,
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`the angle A, between the A-P axis and
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`the bore axis is about 10°.
`
`It is recognized that there are limits on the
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`maximum size of a bore 102 that can directly drilled in a
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`vertebra body via a posterior approach. Limitations on the
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`14
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`diameter of the bore 102 include location of important
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`nerves and blood vessels which can be damaged by
`excessively large bore drilling operations.
`The maximum
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`size bore that can be cut will depend on the particular
`location ef the spine, the species of the animal, age and
`sex.
`A common safe maximum for an adult male spine in the
`L-5 area would be a bore diameter of about
`.5 inches.
`|
`For reasonsthat will be described, it is
`preferred that the bore diameter will be smaller than the
`‘diameter, D,, of body shell 22. Specifically, it is
`10
`mo anticipated that a bore diameter of about 3 millimeters
`less than diameter D, will be preferred. With: such...
`structure,
`the body. 12 spreads apart opposing vertebrae
`upon insertion.
`By virtue of the spreading effect, the
`disk: annulus becomes taught,
`thereby providing for the
`~ initial stabilization between the opposing vertebrae.
`(Those skilled in the art will recognize the annulus ASlo oe ee
`being the fibrous outer circumferential portion of the
`disk).
`In the drawings,
`the implant is shown spreading
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`15-
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`20
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`apart the vertebrae and stretching the annulus. Eventual
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`fusion of the cpposing vertebrae results from bone growth
`
`through body 12, as will be described.
`
`The implant 10 is partially assembled with leading
`end cap 18 snapped onto leading end 14. With trailing end
`cap 20 removed,
`the implant 10 is partially placed within
`bore 102 with the tapered leading end 14 received within
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`25-
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`bore 102.
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`An advancing tool (the tip of which is shown in
`
`Fig. 1)
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`is provided having a hexagon-shaped tip 200
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`complementarily sized to be received within opening 46.
`The. tip 200 is inserted by the surgeon into opening 46.
`The surgeon then turns the tool and, hence,
`the body 12,.in
`a clockwise direction (from the perspective of the
`
`surgeon).
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`The turning action of the body 12 causes the
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`sharp threads 26a, 28a (Fig. 7A) to cut into the bone of
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`the opposing vertebrae bodies 100, 100a to advance the body
`
`10
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`12 into bore 102 to the fully inserted position shown in
`. Fig. 12. The rectangular threads 26, 28 (Pig. 7) retain
`‘ the body 12 in the desired axial. position relative to bore
`
`102. Leading end cap 18. covering axial opening -40 prevents
`disk material from migrating through axial opening 40 into
`chamber 24. during insertion of implant. 10 as well as. during
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`15:
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`the patient’s recovery phase.
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`Withthe implant body 12 fully inserted as shown... ..
`
`in Fig. 12,
`
`the trailing end cap 18 has not yet been
`
`installed. Accordingly, axial opening 46 exposes chamber
`24 to the surgeon once the tool tip 200 is removed. With
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`20
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`opening 46 still exposing chamber 24, a surgeon can impact
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`a graft medium 202 (preferably bone chips) into chamber 24
`
`(see Fig. 12A). Any impacted bone chips will supplement
`
`bone chips that may migrate through holes 32 as a result of
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`25 -
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`the cutting action of cutting edges 33-against the vertebra
`
`bone surfaces.
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`16
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`With the graft medium fully applied to chamber 24,
`the surgeon snaps cap 20 into hole 46 to cover the trailing.
`end 16. Figs. 12 and 12A show such a fully assembled and
`.
`
`inserted implant 10.
`The surgeon can then close the
`patient through any suitable technique. With the completed
`implant 10 installed in the manner indicated,
`the bone
`graft 202 within chamber 24 and openings 32 fuses together
`
`with the bone of the opposing vertebrae 100, 100a to
`
`thereby join the vertebrae 100, 100a together.
`
`As: previously indicated, end caps 18, 20 are
`
`preferably formed from high density polyethylene.
`
`Such
`
`material is nonabrasive and inert, and has a slippery
`touch. This latter feature is particularly valuable for.
`trailing end cap 20, which may oppose the epidural tissue.
`To avoid damage or irritation of the dura, the slippery, -
`inert, nonabrasive polyurethane trailing end cap 20 is
`provided. Trailing end cap 20 is intended to cover axial ....»..,
`
`opening 46 and retain the bone chips within chamber 24
`
`while providing a nonabrasive and nonirritating surface
`opposing the epidura. Also,
`like leading end cap 18,
`trailing end cap 20 prevents disk material from entering
`chamber 24.
`
`10
`
`15
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`20
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`In a preferred embodiment,
`
`the end caps 18, 20
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`formed of polyethylene which is radiolucent. Radiolucent
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`25 -
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`material permits X-rays to pass. Accordingly, with
`
`radiolucent end caps 18, 20, an attending physician can
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`17
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`2015507
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`‘study the growth of bone within chamber 24 without the need
`
`for exploratory surgery.
`
`,
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`It will be appreciated that radiolucent end cap
`18, 20, while desirable in a preferred embodiment, are not
`necessary to the practice of the full scope of the present
`invention.
`For example, the leading end 14 could taper
`completely as an integral portion of the solid body12 as
`
`shown in Fig. 2A.
`
`In such an embodiment, the body 12’
`
`10°
`
`assumes a more complete hollow bullet-shaped profile where
`“the leading edge 14’
`includes a sharp point.-15’..to better.
`“assist the insertion and advancement of the body::12/ .into
`“ the°intervertébral space.
`
`' “In Figs. -:12 and 12A,
`
`the implant:10 is: shown.
`
`installed on the left side (from the patient’s perspective),
`-of the anterior-posterior axis, A-P.
`For a posterior
`15°
`“approach as shown in Fig. 12, it is anticipated-that two
`
`‘prostheses 10 will be used, with a.secondimplant. disposed.-
`
`on the right side of the anterior-posterior axis, A-P, and
`installed in a manner identical to that of implant 10 on
`
`20
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`the left side. However, for ease of illustration, the
`right side implant is not shown installed. When installed,
`such prostheses would be positioned with the right and left
`
`prostheses being symmetrically disposed about axis A-P.
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`25
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`D. Alternative Design
`
`Figs. 3A and 4A show an alternative.
`
`The implant
`
`10’’’ of the embodiment of Figs.
`
`3A and 4A is identical to
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`18
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`that discussed above except as to the placement of holes
`
`327°’, For ease of understanding the comparison between
`implant 10’’’ and implant 10,
`the reader will note that
`
`Figs. 3A and 4A are the same view of implant 10'*’' as Figs.
`
`3 and 4 are of implant 10.
`implant 10’°'* does not have
`Unlike implant 10,
`holes 32’’' circumferentially spaced about body 12'’'.
`
`Instead, as best shown in Fig. 4A, holes 32'’* are placed
`
`on diametrically opposed sides of body 12°''.
`
`“10°
`
`Upon insertion of theimplant 10/".",
`
`the surgeon
`
`positions the implant 10’’’ with holes 32°'*opposing the
`
`.100a.. AS a
`“bone material of the vertebra bodies 100,
`: result, no disc material 114 may enter into chamber 24'°°'.
`. This prevents possible interference of disc material with
`
`“15
`
`the bone fusion process.
`
`To assist a surgeon, indicia markings 15’’’ are
`
`placed on flange 44’’". The markings 15'/’’ are aligned
`
`with the axis of holes 32’'’.
`
`The surgeon turns body 12''*.
`
`into position until markings 15’'’’ are aligned pointing to
`
`20
`
`bodies 100, 100a.
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`So positioned,
`
`the surgeon knows the
`
`holes 32'’' are opposing bone and not disc material.
`
`E. Alternative Method and Apparatus for Anterior
`Approach.
`
`25
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`The foregoing description and illustration
`
`describe the insertion of an implant 10 through a posterior
`
`approach. Figs. 13 and 13A show an alternative embodiment
`
`19
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`of the invention for use in an anterior approach where a
`bore 102’ is formed from the front of the spine and axially
`aligned with the anterior-posterior axis, A-P. Since the
`bore 102’ is formed from an anterior approach,
`the size
`restrictions of a posteriorly formed bore (namely,
`locations of nerves and blood vessels) are largely avoided.
`
`As a result, a large diameter bore 102’ can be formed.
`
`A
`
`comparison of Figs..12A and 13A show the relative increase
`
`of bore diameter.:.This