(19)
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`(12)
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`(cid:6)(cid:27)&(cid:11)(cid:11) (cid:12)(cid:11)(cid:19)(cid:14)(cid:15)(cid:12)(cid:23)(cid:12)(cid:6)
`EP 2 108 341 A1
`
`(11)
`
`(43) Date of publication:
`14.10.2009 Bulletin 2009/42
`
`EUROPEAN PATENT APPLICATION
`(51) Int Cl.:(cid:3)
`A61F2/44(2006.01)
`
`(21) Application number: 09164434.4
`
`(22) Date of filing: 14.03.2001
`
`(84) Designated Contracting States:
`AT BE CH CY DE DK ES FI FR GB GR IE IT LI LU
`MC NL PT SE TR
`
`(30) Priority: 14.03.2000 DE 20004692 U
`
`(62) Document number(s) of the earlier application(s) in
`accordance with Art. 76 EPC:
`01916659.4 / 1 265 561
`(71) Applicant: Warsaw Orthopedic, Inc.(cid:3)
`Warsaw, Indiana 46581 (US)(cid:3)
`
`(72) Inventors:
`• Früh, Hans-(cid:3)Joachim
`94469, Deggendorf (DE)(cid:3)
`
`(54)
`
`Synthetic threaded vertebral implant
`
`(57)
`This invention provides a synthetic threaded
`vertebral implant (10, 80, 100) for treatment of spinal de-
`formities. The implant can be formed of variety of mate-
`rials including synthetic organic materials, composites,
`and ceramics. The threaded implant can restore and
`
`• Ebner, Harald
`94469, Deggendorf (DE)(cid:3)
`• Estes, Bradley T.(cid:3)
`Durham, NC 27705 (US)(cid:3)
`
`(74) Representative: Viering, Jentschura & Partner
`Grillparzerstrasse 14
`81675 München (DE)(cid:3)
`
`Remarks:
`This application was filed on 02-07-2009 as a
`divisional application to the application mentioned
`under INID code 62.
`
`maintain a desired disc space height. In one embodi-
`ment, the threaded implant (10, 80, 100) has an elongate
`cylindrical body (12) with an external thread (26). Implant
`(10) terminates in a proximal end (16) and an opposite
`distal end (18). One or both of ends (16, 18) can include
`chamfer surfaces (20 and 22).
`
`Printed by Jouve, 75001 PARIS (FR)
`
`EP2 108 341A1
`
`1
`
`NUVASIVE 1057
`NuVasive, Inc. v. Warsaw Orthopedic, Inc.
`IPR2013-00206
`IPR2013-00208
`
`

`

`1
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`EP 2 108 341 A1
`
`2
`
`Description
`CROSS-(cid:3)REFERENCE TO RELATED APPLICATION
`(cid:3)[0001] The present application claims the benefit of
`German Utility Model Application No. 200 04 692.6 filed
`on March 14, 2000, which is hereby incorporated by ref-
`erence in its entirety.
`
`FIELD OF THE INVENTION
`(cid:3)[0002]
`In general this invention relates to a synthetic
`vertebral implant and methods of manufacturing and us-
`ing the implant. More specifically but not exclusively, this
`invention is directed to a synthetic, threaded vertebral
`implant suitable for restoring and or maintaining desired
`disc space height.
`
`BACKGROUND OF THE INVENTION
`(cid:3)[0003] For degenerated, diseased or otherwise dam-
`aged spinal columns and vertebrae, it is known to treat
`these defects by removal of all or a portion of the vertebral
`disk and inserting an implant such as a spinal spacer into
`the disc space to restore normal disk height and spine
`orientation, and repair the spinal defects. When desired,
`osteogenic material also can be implanted into the in-
`tervertebral space to promote arthrodesis, or spinal fu-
`sion between the two vertebrae adjacent to the interver-
`tebral space. Selected spacers are formed to provide a
`cavity for receipt of the osteogenic material.
`(cid:3)[0004] The spinal column can exert tremendous force
`on the individual vertebrae, and consequently also on
`any implant implanted in between the vertebrae. Spinal
`implants typically are formed of a metal such as titanium
`or surgical steel. While the selection of the implant con-
`figuration and composition can depend upon a variety of
`considerations, for arthrodesis it is often desirable to se-
`lect a material that does not stress shield the bone in-
`growth. Titanium and surgical steel provide the requisite
`strength to maintain correct disk space height and orien-
`tation; however, these materials have been shown to
`stress shield the bone. Bone and bone derived material
`can provide an acceptable material having the similar
`strength and compressibility as living bone tissue. How-
`ever, suitable donor bone is scarce. Further, extensive
`screening and sterilization must be strictly observed to
`minimize the risk of transmission of infections, either real
`or perceived, from the donor to the recipient.
`(cid:3)[0005] The following patents are representative of the
`current state of the art for the relevant technology.
`(cid:3)[0006]
`In United States patent 5,669,909 issued to
`Zdeblick et al. disclosed an interbody fusion device for
`threaded insertion into the intervertebral space. The de-
`vice has a generally elongate, conical body defining a
`series of interrupted external threads The elongate body
`has two truncated or flattened sidewalls diametrically op-
`posed to each other. The truncated sidewalls are touted
`
`to facilitate insertion of the implant into the intervertebral
`space. The body encloses a cavity for receipt of bony
`material. The device is inserted into the disk space so
`the opposing truncated sidewalls bear against the end-
`plate of adjacent vertebrae. Once inserted, the device is
`turned 90° to engage the interrupted threads with the
`bone tissue of the endplates.
`(cid:3)[0007] Brosnahan in U.S. Patent 5,766,253 discloses
`a solid spinal fusion device having a threaded exterior.
`The device includes two indentions on its outer surface
`for bone attachment material. This reference mentions
`that the fusion device can be formed of a biocompatable
`osteoconductive material such as bioactive hydroxyap-
`atite-(cid:3)polymer composites, preferably a hydroxyapatite
`reinforced polyethylene composite.
`(cid:3)[0008] Bagby in U.S. Patent No. 6,010,502 discloses
`a metallic cylindrical base body having a helically config-
`ured spline or thread configured on its outer surface. The
`body can have a hollow interior. Large and small circular
`fenestrations extend from the surface into the hollow in-
`terior. The metallic body can be fitted with a plastic cap
`to protect the spinal cord from abrading against the end
`of the metallic body.
`(cid:3)[0009] There remains a continuing need for advance-
`ments in the relevant field, including treatment of dam-
`aged or diseased spinal columns, improved implants, se-
`lection of suitable materials from which the implants are
`formed and methods of enhancing the bone fusion be-
`tween adjacent vertebrae. The present invention is such
`an advancement and provides a wide variety of benefits
`and advantages.
`
`DISCLOSURE OF INVENTION
`(cid:3)[0010] The present invention relates to spinal implants,
`the manufacture and use thereof to treat degenerated,
`diseased or otherwise damaged spinal columns. Various
`aspects of the invention are novel, nonobvious, and pro-
`vide various advantages. While the actual nature of the
`invention covered herein can only be determined with
`reference to the claims appended hereto, certain forms
`and features, which are characteristic of the preferred
`embodiments disclosed herein, are described briefly as
`follows.
`(cid:3)[0011] The invention provides a vertebral implant ca-
`pable of being threaded into an intervertebral space and
`which is stable with respect to the expected biomechan-
`ical forces. In one embodiment, the implant or interver-
`tebral spacer can be integrated into the bony tissue. In
`alternative embodiments the implant or spacer is biode-
`gradable. The implants according to this invention can
`be manufactured at low cost.
`(cid:3)[0012] The vertebral implant to be screwed into an in-
`tervertebral space according to one aspect of this inven-
`tion and comprises a hollow cylindrical base body ar-
`ranged to receive bone material and provided with an
`external thread so that the base body can be threadedly
`implanted by engaging the two vertebrae defining the
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`intervertebral space or disc space. The vertebral implant
`further comprises two holes preferably located diametri-
`cally opposing each other and extending across several
`thread ribs in the longitudinal direction of the base body
`so as to interrupt the course of the thread ribs. The holes
`are preferably elongated. Although it will be understood,
`that the holes can be provided in a wide variety of con-
`figurations. The holes allow a bone bridge to form be-
`tween the two vertebrae and through the implanted base
`body. The two circumferential wall portions of the base
`body disposed between the holes are each provided with
`at least one longitudinal through-(cid:3)slit extending in the lon-
`gitudinal direction of the base body and interrupting, at
`least partially, the course of the thread ribs. Each longi-
`tudinal slit is narrower and shorter than the elongated
`holes, and is designed to enable tissue lateral of the im-
`planted base body to grow sideways into the interior of
`the base body. The vertebral implant is preferably made
`of a synthetic material, for example, a polymeric material,
`a composite, a ceramic or a reinforced material.
`(cid:3)[0013] To insert the vertebral implant into an interver-
`tebral space according one embodiment of this invention,
`the implant is screwed or threaded into the intervertebral
`space. Thus, unlike an implant that has to be pushed,
`driven or impacted, the risk of the implant being suddenly
`displaced to an unintended position is minimized. Rather
`the implant can be gradually rotated and screwed axially
`forward into the intervertebral space and, thus, posi-
`tioned accurately in the intervertebral space without any
`hazard. To this end, the thread of the vertebral implant
`preferably has a small lead angle, advantageously less
`than about 10°, more preferably between about 2° and
`about 8°. Owing to its simple integral design, the implant
`has a smooth, tapering--(cid:3)albeit threaded profile, i.e. lack-
`ing any projections, so there is hardly any risk of hurting
`surrounding tissue when the implant is being screwed
`into the intervertebral space. This integral, compact and
`still sufficiently stable construction of the implant further
`allows it to be made of a synthetic material, for example,
`a reinforced material, a polymeric materiel, a composite
`or a ceramic. These materials are preferred for a variety
`of advantageous benefits including low cost, long dura-
`bility, strength and good biocompatability.
`(cid:3)[0014]
`In its implanted state, the implant is positioned
`in the intervertebral space such that the two elongated
`holes face the respective vertebrae so that a bone bridge
`can build up between these vertebrae through the elon-
`gated holes and the vertebral implant, i.e., spinal fusion
`of the adjacent vertebrae.
`(cid:3)[0015]
`Lateral portions of the circumferential wall are
`reinforced by thread ribs. The vertebral implant consti-
`tutes a sufficiently stable support to receive the biome-
`chanical forces occurring between the two vertebrae until
`the complete bone bridge has formed. As the elongated
`holes and slits are formed directly in (or through) the
`thread, the circumference for the base body is provided
`with thread ribs over a maximum surface of its outer pe-
`riphery, thus strengthening the circumferential walls of
`
`the implant.
`(cid:3)[0016] This design increases the stability of the im-
`plant. At the same time, this design enables the vertebral
`implant to be fixed in a reliable manner because the grow-
`ing bone tissue intimately engages the thread ribs, which
`are interrupted completely by the elongated holes and at
`least partially by the longitudinal slits. Moreover, the
`number of manufacturing steps is also reduced. The slits
`arranged in the two circumferential wall portions between
`the elongated holes form a sufficiently large passage for
`vascular tissue lateral of the implanted implant to grow
`into the implant, thus improving the nutritional supply of
`the bone material accommodated in the implant. At the
`same time, however, the slits are sufficiently small not to
`jeopardize the stability of the implant. In addition, this
`enabled lateral nutritional supply stimulates the bone tis-
`sue in the implant to also grow from inside into the lateral
`slits thus further improving the fit of the implant.
`(cid:3)[0017] The reinforced implant can include a wide va-
`riety of reinforcing materials included fibers, platelets,
`and/or particulate elements. The fiber-(cid:3)reinforced implant
`material may be embodied by glass fibers, ceramic fibers
`or carbon fibers. Preferably, the implant material com-
`prises long carbon fibers, in particular endless carbon
`fibers, allowing a predetermined high strength to be
`achieved at low manufacturing cost.
`(cid:3)[0018] The implant can also be formed of a polymeric
`material, for example, polyanhydrides; polyamides, poly
`(amino acids), polycaprolactones, polylactate, poly(cid:3)(lac-
`tide-(cid:3)co-(cid:3)glycolide); polyorthoesters; acrylics; polycar-
`bonates; polyesters; polyethers, poly(cid:3)(ether ketone); poly
`(ether, ether ketone) (PEEK); poly(cid:3)(aryl ether ketones)
`(PAEK; poly(cid:3)(ether ether ketone ether ketone) (PEEKEK);
`poly(cid:3)(ethylene terephthalate) (PET), poly(cid:3)(acrylate) poly
`(methyl (meth)(cid:3)acrylate), polyolefins, polysulfones, poly-
`urethane; poly(cid:3)(vinyl chloride), epoxy resins, carbon re-
`inforced composites, glass reinforced composite, ceram-
`ic reinforced composites, and mixtures thereof. Alterna-
`tively the implant can be formed of a ceramic, for exam-
`ple, a material selected from the group of: hydroxylapa-
`tite; alumina, zirconia and mixtures thereof.
`(cid:3)[0019] Each longitudinal through-(cid:3)slit preferably ex-
`tends across at least one rib of the thread. The bone
`material can grow sideways through the longitudinal
`through-(cid:3)slit and through a complete gap of the course of
`the thread rib of the implant. This inhibits axial rotation
`of the implant. The inhibition of axial rotation of the im-
`plant is even enhanced with respect to a situation where
`bone material can primarily grow sideways around the
`outside parameter of the implant between two adjacent
`thread ribs.
`(cid:3)[0020] The base body may be circular or slightly con-
`ical or may have at least one conical end portion. Pref-
`erably, the overall shape of the base body is cylindrical;
`this can allow it to be manufactured even more easily
`and at lower costs. A separating force (or distraction) can
`be exerted on the vertebrae; this can be achieved by
`distraction during surgery using distractors. Additionally
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`the implant itself can provide distraction by selecting a
`base body having a diameter greater than the existing
`disc space height between the adjacent vertebrae. The
`selected implant can be threaded into the disc space.
`The threads of the implant engage in the opposing sur-
`faces of the vertebrae, and pulling the implant into the
`disc space and consequently distracting the disc space
`as the implant becomes fully seated or positioned at a
`desired position within the disc space.
`(cid:3)[0021]
`In other embodiments the base body can define
`a lordotic profile. In this configuration the circumferential
`wall portions are shaped to provide a spacer that con-
`forms to the desired lordosis or natural curvature of the
`spine. In one form the circumferencetial wall portions are
`formed as conical wall portions while still retaining an
`exterior thread.
`(cid:3)[0022] The longitudinal openings or slits can be ar-
`ranged at any place in the circumferential wall portions,
`it is preferred that the longitudinal openings or slits op-
`pose each other diametrically. It will be understood that
`one, two, three or more pairs of longitudinal openings
`can be provided in the circumferential wall portions of the
`implant. This arrangement allows the vascular tissue lat-
`eral of the implanted implant to communicate with the
`osteogenic material deposited in the implant so that the
`nutritional supply of the bone material is greater and more
`homogeneous. The blood supply, and thus, the supply
`of nutrition to the bone tissue growing through the implant
`are further improved enabling the implant to be integrally
`incorporated in the growing bone tissue.
`(cid:3)[0023]
`It is further preferred that at least one longitu-
`dinal slit is disposed in the circumferential wall at an an-
`gular distance of about 90° from the respective elongated
`hole, as seen in the circumferential direction of the base
`body. This design allows the vascular tissue a more direct
`path into the implant. An additional advantage resides in
`that the bone tissue can grow orthogonally through the
`implant resulting in a particularly stable crosswise an-
`choring of the implant or pair of implants.
`(cid:3)[0024] A preferred embodiment provides two longitu-
`dinal slits in each circumferential wall portion between
`the elongated holes of the base body. The two longitu-
`dinal slits are disposed at a distance from each other in
`the longitudinal direction of the base body. Owing to this
`design, a circumferential web remains between the two
`longitudinal slits in the axial direction of the implant and
`ensures sufficient stability of the implant with respect to
`the compressive forces to be received. The circumferen-
`tial web between the two longitudinal slits is preferably
`wide enough to carry at least one uninterrupted thread
`rib, preferably two or more interrupted thread ribs, ther-
`eon. It is further preferred for the slits to be arranged
`symmetric with respect to the longitudinal center of the
`base body. This can facilitate the osteogenic material or
`bone material within the implant to contact vascular tis-
`sue from the lateral side of the implant as far as possible
`over the entire length of the implant without jeopardizing
`the inherent stability of the implant.
`
`EP 2 108 341 A1
`6
`(cid:3)[0025] The thread may be embodied by any type of
`thread, such as a sharp, triangular, or rounded-(cid:3)over
`thread. It is preferred, however, that the external thread
`be formed as a trapezoidal thread. The natural thickness
`of the ribs of a trapezoidal thread inhibits the implant from
`sinking or subsiding into the vertebrae, particularly into
`degenerative vertebrae. Further, the wide thread ribs al-
`so increase the reinforcement of the circumferential wall.
`According in a preferred embodiment of the invention the
`average thickness of the thread ribs is in the range of
`between about 1/25 to 1/15 of the overall length of the
`implant, more preferably about 1/20 of the overall length
`of the implant.
`(cid:3)[0026]
`In order to facilitate the screwing of the implant
`into a prepared threaded bore between the vertebrae and
`also to facilitate the threading operation on the implant
`during manufacture thereof, the two axial ends of the
`base body are preferably provided with beveled edges.
`The beveled edges may be tapered or round chamfers,
`for example. According to a preferred embodiment, the
`axial front end portion of the base body is provided with
`an insertion end tapering axially from the larger first, outer
`diameter of the implant to a smaller second,(cid:3) outer diam-
`eter proximate the front end. The insertion end can be
`arranged to be set onto the vertebrae when the implant
`is threaded into the intervertebral space. This particularly
`applies to cases where the vertebrae are to be spread
`apart by means of the implant to a larger extent, i.e.,
`using the implant itself to distract the adjacent vertebrae.
`In an alternative form, the insertion end does not include
`an external thread. To this end, initially the implant can
`be easily driven or impacted into the intervertebral space
`to initially spread the vertebrae apart and to enter the
`intervertebral space until the thread on the circumferen-
`tial wall portion engages the opposing end plates or sur-
`faces of the adjacent vertebrae. In still other alternative
`embodiments, the insertion end includes a threaded por-
`tion. In this embodiment, the implant can be threadedly
`implanted into the disc space without the necessity of
`impaction. Regardless, after initial placement the implant
`can be positioned accurately in the intervertebral space
`by screwing the implant in the axial direction, with re-
`duced risk of the implant damaging or penetrating adja-
`cent tissue or structures, for example, the spinal cord.
`The implant can include a set-(cid:3)head, which is preferably
`at least 1/10 of the base body in the axial direction thereof.
`(cid:3)[0027] While the implant may be gripped manually or
`with a tong-(cid:3)type tool and threaded into the intervertebral
`space in any manner, the axial rear end of the base body
`advantageously comprises a receiving means or tool en-
`gaging portion for receiving a manipulation tool in order
`to exert a torque on the base body. This receiving means
`enables a more accurate implantation process, and min-
`imizes damage to the implant during surgery, which fi-
`nally better ensures a durable functionality of the implant
`in the implanted state thereof.
`(cid:3)[0028]
`In one embodiment the receiving means can be
`embodied by two or more holes, for example, arranged
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`in the front wall of the base body. The holes are provided
`for mating engagement with matching pins of the manip-
`ulation tool. A torsional moment torque can be exerted
`on the implant by rotating the engaged manipulation tool.
`In other embodiments, the receiving means preferably
`comprises two grooves opposite each other with respect
`to the cavity of the base body, and a mating blade or a
`matching counterpart on the manipulation tool can en-
`gage these grooves from outside. The manipulation tool
`can be prevented from slipping inadvertently off and
`away from the end of the implant by providing an engage-
`ment groove or other engagement means with an under-
`cut portion or a dove tail, for example, that can be de-
`tachable locked or engaged with a matching counterpart
`overcut portion of the manipulation tool.
`(cid:3)[0029] Preferably, the receiving means also comprises
`a threaded central bore into which a corresponding
`threaded counterpart of the manipulation tool, for exam-
`ple, a threaded pin can be screwed in such a manner
`that the manipulation tool is firmly engaged to the implant.
`This provides the advantage that the implant is coupled
`integrally to the manipulation tool and can be manipulat-
`ed accurately together with the manipulation tool by the
`surgeon.
`(cid:3)[0030] The above-(cid:3)described implants can be prepared
`of a wide variety of materials including synthetic organic
`materials, composites, and ceramics. Preferably the im-
`plants are formed of a synthetic, non-(cid:3)metallic material.
`The implants of the present invention can be either es-
`sentially permanent implants, which do not readily bio-
`degrade. These implants can remain in the intervertebral
`space and often are incorporated into the bony tissue.
`Alternatively, the implant can biodegrade or erode over
`time and are substantially replaced by bone tissue.
`(cid:3)[0031] Examples of nondegradable polymeric or oligo-
`meric materials include the, polyacrylates, polyethers,
`polyketones, polyurethanes, epoxides and copolymers,
`alloys and blends thereof. Use of the term co-(cid:3)polymers
`is intended to include within the scope of the invention
`polymers formed of two or more unique monomeric re-
`peating units. Such co-(cid:3)polymers can include random co-
`polymers, graft copolymers, block copolymers, radial
`block, diblock, triblock copolymers, alternating co-(cid:3)poly-
`mers, and periodic co-(cid:3)polymers. Specific examples of
`nondegradable polymeric materials include: poly(cid:3)(vinyl
`chloride) (PVC); polyacrylates, poly(cid:3)(methyl (meth)(cid:3)acr-
`ylate); acrylics; polyamides; polycarbonates; polyesters;
`polyethylene terephthalate; polysulfones; polyolefins,
`i.e. polyethylene, polypropylene, and UHMWPE (ultra
`high molecular weight polyethylene); polyurethane; pol-
`yethers, i.e., epoxides; poly(cid:3)(ether ketones) (PEK), poly
`(ether, ether ketones) (PEEK), poly(cid:3)(aryl ether ketones)
`(PAEK), and poly(cid:3)(ether ether ketone ether ketone)
`(PEEKEK). A wide variety of suitable poly(cid:3)(ether-(cid:3)co-(cid:3)ke-
`tone) containing materials are commercially available.
`(cid:3)[0032] Alternatively, implants of this invention can be
`made of a material that either biodegrades or is bioab-
`sorbed. Typically, biodegradable material is a polymeric
`
`material or oligomeric material and often the monomers
`are joined via an amide linkage such as is observed in
`poly(cid:3)(amino acids). When the implant is formed of material
`that biodegrades, it is desirable to provide a biodegrad-
`able material that degrades at a rate comparable to the
`bony ingrowth characteristic of bone fusion often referred
`to as creeping substitution. It is still more preferred to
`select the biodegradable material to remain in situ and
`capable of providing sufficient biomechanical support for
`the spine even after a bone bridge has grown and formed
`through the through-(cid:3)holes of the implant. The biodegra-
`dation rate of the implant can be varied by selecting an
`appropriate synthetic material. The degradation rate of
`the selected material can be further modified; for exam-
`ple, the degradation rate can be decreased by increasing
`the amount of crosslinking between the polymer chains
`and/or the increasing the degree of polymerization. Fur-
`ther, it is not intended to limit the preferred materials to
`substances that are partly or totally reabsorbed within
`the body. Rather substances that can be broken down
`degraded and eventually flushed from the body are also
`intended to come within the scope of this invention.
`(cid:3)[0033] Examples of biodegradable polymers for use
`with this invention include poly(cid:3)(amino acids), polyanhy-
`drides, polycaprolactones, polyorthoesters, polylactic
`acid, poly(cid:3)(lactide-(cid:3)co-(cid:3)glycolide), i.e., copolymers of lactic
`acid and glycolic acid, including either D, L and D/L iso-
`mers of these components. One example of a preferred
`biodegradable polymer for use with this invention is a
`copolymer of 70:(cid:3)30 poly(cid:3)(L, DL) lactate commercially
`available from Boehringer Ingelheim.
`(cid:3)[0034] A particularly advantageous benefit provided by
`this invention is the ease of manufacturing suitable syn-
`thetic implants. Implants formed of polymeric, oligomeric
`and composite material can be manufactured using
`known fabricating techniques, including various extru-
`sion, injection molding and blow molding processes. In
`addition, selected polymeric materials are provided by
`suppliers in a form that can readily formed, and/or mold-
`ed, usually at an elevated temperature. A copolymer of
`D/L lactate is one specific example. This material can be
`obtained in a wide variety of forms including pellets or
`granules, sheets, ingots. The material can be molded at
`a temperature of about 55°C or greater to provide a de-
`sired shaped and sized implant. The material can be re-
`peatedly heated and contoured without any significant
`change in its material or chemical properties. In addition,
`material is readily cut using a cautery to readily conform
`the implant to the bone. The lower cautery temperature
`even permits cutting the material during the operation.
`(cid:3)[0035] Specific examples of ceramic materials for use
`with this invention include glass, calcium phosphate, hy-
`droxyapatite, alumina, zirconia, and mixtures of these
`materials.
`(cid:3)[0036] Composites are also useful with this invention.
`Composites can combine two or more of the desired ma-
`terials to form an implant body for implantation. Examples
`of composites include combinations of ceramics, glass
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`20
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`25
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`35
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`5
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`9
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`EP 2 108 341 A1
`
`10
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`and/or polymeric materials. Preferred composites in-
`clude a reinforcing material. The reinforcing material can
`include platelets, particulates or fibers.
`(cid:3)[0037] The following provides an advantageous fila-
`ment winding method for manufacturing an implant for
`use in the present invention from a fiber reinforced ma-
`terial, such as a glass or carbon fiber-(cid:3)reinforced material.
`First, the fibers are impregnated with a liquid synthetic
`material. A particularly preferred material is an epoxy res-
`in. The impregnated fibers are wound about a winding
`spindle. The fibers are preferably carbon fibers. Prefer-
`ably the fibers are wound on the winding spindle in the
`form of a bundle using a filament winding process. There-
`after the synthetic material is cured; this is preferably
`carried out by a controlled temperature treatment. A sim-
`ple, hollow, rod-(cid:3)shape implant can be prepared by wind-
`ing the fibers around a winding spindle having the simple
`rod-(cid:3)shape. More sophisticated shaped implants can be
`manufactured by a more sophisticated-(cid:3)shaped spindle.
`For example an implant having elongated through-(cid:3)holes
`can be prepared by using a spindle having corresponding
`protuberances to define the through-(cid:3)holes. The final di-
`mensions of the implant can be defined by the dimen-
`sions of the winding spindle so that little if any machining
`of the inner surfaces of the walls defining the cavities is
`required.
`(cid:3)[0038]
`In a subsequent step, the outer periphery of the
`base body is machined so that the implant body has a
`rectangular cross-(cid:3)section.
`(cid:3)[0039]
`In a machining process, which preferably in-
`cludes a milling/(cid:3)cylindrical grinding steps, the body is pro-
`vided with a circular cross-(cid:3)section; longitudinal slits are
`formed in the circumferential wall between the two elon-
`gated through-(cid:3)holes; and an external thread is formed
`about the exterior of the circumferential wall. If desired,
`a smoother and often stronger surface can be obtained
`by corundum blasting the implant body in an additional
`processing step.
`(cid:3)[0040] Optionally, the tool engaging end of the implant
`can provided with a transverse groove and a bore, which
`may or may not be threaded. The groove and bore can
`be machined using known techniques for drilling and/or
`milling processes.
`(cid:3)[0041]
`In order to avoid any damage to the inner sur-
`faces of the implant body during the drilling and/or milling
`process steps, i.e. in order to prevent undesirable cracks
`in the material, a wood core, in particular beech wood
`core, is inserted in the implant body in place of the winding
`spindle, during the processes. The wood core can be
`wetted to swell to the inside geometry of the implant.
`(cid:3)[0042] This method provides a highly stable vertebral
`implant from fiber-(cid:3)reinforced material at low costs. In ad-
`dition the fibers can be orientated to wind in a single di-
`rection or optionally in varying directions.
`(cid:3)[0043] Alternatively, the implant formed of a fiber com-
`posite material can be prepared using a pultrusion meth-
`od by saturating individual fibers or bundles of fibers with
`a resin, for example one the polymeric materials de-
`
`scribed above, and pulling the resin saturated fibers
`through a die to provide the profile of the desired implant.
`The resulting implant can be machined as described
`above to provide the final configuration including a
`threaded exterior, chamfer surfaces and openings. Im-
`plants prepared according the this pultrusion method
`generally have fibers orientated in the same direction,
`for example in an direction orientated to lie substantially
`parallel to the longitudinal axis, substantially perpendic-
`ular to the longitudinal axis or oblique to the longitudinal
`axis.
`(cid:3)[0044]
`In yet another method the fiber reinforced com-
`posite can be prepared using chopped fibers, platelets,
`or particulates as reinforcing elements that have been
`embedded within a curable resin, for example one or
`more of the polymers described above. The reinforced
`material can be cured, molded and/or extruded according
`to techniques known in the art.
`(cid:3)[0045] The osteogenic compositions used in this in-
`vention preferably comprise a therapeutically effective
`amount to stimulate or induce bone growth or healing of
`a substantially pure bone inductive factor such as a bone
`morphogenetic protein in a pharmaceutically acceptable
`carrier. The preferred osteoinductive factors include, but
`are not limited to, the recombinant human bone morpho-
`genic proteins (rhBMPs) because they are available in
`unlimited supply and do not transmit infectious diseases.
`Most preferably, the bone morphogenetic protein is a rh-
`BMP-(cid:3)2, rhBMP-(cid:3)4 or heterodimers thereof. The concen-
`tration of rhBMP-(cid:3)2 is generally between about 0.4 mg/ml
`to about 1.5 mg/ml, preferably near 1.5 mg/ml. However,
`any bone morphogenetic protein is contemplated includ-
`ing bone morphogenetic proteins designated as BMP-(cid:3)1
`through BMP-(cid:3)13. BMPs are available from Genetics In-
`stitute, Inc., Cambridge, Massachusetts and may also be
`prepared by one skilled in the art as described in U.S.
`Pa