WO2005065596A1

WO2005065596A1 - Intervertebral implants

Info

Publication number: WO2005065596A1
Application number: PCT/US2005/000058
Authority: WO
Inventors: Erik O. Martz; Daniel Rosenthal
Original assignee: Osteotech Inc.
Priority date: 2003-12-31
Filing date: 2005-01-03
Publication date: 2005-07-21

Abstract

An intervertebral implant is disclosed which is formed from a biocompatible material such as a polymer, a metal, bone or composites thereof. In one preferred embodiment, the implant includes a body having upper and lower bearing surfaces, front and rear walls and first, second, third and fourth side walls. The first and the second side walls are contiguous and define intersecting planes which define an obtuse angle θ1. The third and fourth side walls are contiguous and define intersecting planes which define a second obtuse angle θ2. In one preferred embodiment, θ1is substantially equal to θ2. One or more radiographic markers may be provided with the implant to facilitate identification of the position of the implant within the body using, for example, x-ray or fluoroscopy.

Description

INTERVERTEBRAL IMPLANTS

Background 1. Technical Field The present disclosure relates generally to intervertebral implants and, more particularly, to intervertebral implants having a configuration suitable for interbody spinal fusion. 2. Background of Related Art The spine is a flexible column formed of a series of bone called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The vertebrae are connected together by means of articular processes and intervertebral, fibro-cartilagineous spacers. The intervertebral fibro-cartilages are also known as intervertebral disks and are made of a fibrous ring filled with pulpy material. The disks function as spinal shock absorbers and also cooperate with synovial joints to facilitate movement and maintain flexibility of the spine. When one or more disks rupture or degenerate through accident or disease, nerves passing near the affected area may be compressed and are consequently irritated. The result may be chronic and/or debilitating back pain. Various methods and apparatus, both surgical and non-surgical, have been designed to relieve

such back pain. One method, interbody fusion, involves fusion of adjacent vertebrae to restore the spine's natural position so that nerve root canal sizes are increased and nerve irritation is eliminated or reduced. The space between vertebrae is maintained by fusing the vertebrae in the affected area together at a fixed distance. Numerous prosthetic implants have been suggested to fill the void between vertebrae. Surgical procedures for fusing adjacent vertebrae to treat back pain in patients with ruptured or degenerated intervertebral discs, spondylolisthesis or other pathologies are well known. Typically during such a procedure, a spinal implant is placed into the intervertebral space in a position to engage adjoining vertebrae. The implant is constructed from a biocompatible material which may be adapted to fuse with the adjacent vertebrae and maintain proper spacing and lordosis between the adjacent vertebrae. SUMMARY In accordance with the present disclosure, a plurality differently configured intervertebral implants are disclosed. Each of the implants is constructed from a biocompatible material such as a polymer, a metal, bone or composites thereof. Each implant defines at least one cavity for receiving a bone growth material which stabilizes, controls, regulates, promotes or accelerates new bone growth, bone healing and/or bone remodeling. Each implant also includes upper and lower load bearing surfaces for supporting adjacent vertebral endplates. In one preferred embodiment, the upper and/or lower bearing surfaces includes an irregular surface for engaging and gripping a vertebral endplate to decrease the risk of implant explusion from an intervertebral space. In another preferred embodiment, the upper and/or lower bearing surface is configured to conform to, maintain and/or restore the natural curvature of the spine. In one preferred embodiment, the intervertebral implant defines an enlarged footprint. As discussed below, the term "footprint" as used herein is the area defined by the smallest rectangle which can be drawn about the implant as viewed from the top or bottom of the implant. By providing an enlarged footprint, increased stabilization of the adjacent vertebrae can be provided. A variety of other preferred embodiments of the presently disclosed intervertebral implants are disclosed in further detail below. Brief Description Of The Drawings Preferred embodiments of the presently disclosed intervertebral implant are described herein with reference to the drawings wherein: FIG. 1 is a top, side perspective view of one preferred embodiment of the presently disclosed intervertebral implant; FIG. 2 is a top view of the intervertebral implant shown in FIG. 1 ; FIG. 3 is a front view of the intervertebral implant shown in FIG. 1 ; FIG. 4 is a side view of the intervertebral implant shown in FIG. 1 ; FIG. 5 is a rear view of the intervertebral implant shown in FIG. 1; FIG. 6 is a top, side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; FIG. 7 is a top view of the intervertebral implant shown in FIG. 6; FIG. 8 is a front view of the intervertebral implant shown in FIG. 6; FIG. 9 is a side view of the intervertebral implant shown. in FIG. 6; FIG. 10 is a rear view of the intervertebral implant shown in FIG. 6; FIG. 11 is a top, side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; FIG. 12 is a top view of the intervertebral implant shown in FIG. 11 ; FIG. 13 is a front view of the intervertebral implant shown in FIG. 11; FIG. 14 is a side view of the intervertebral implant shown in FIG. 11; FIG. 15 is a rear view of the intervertebral implant shown in FIG. 11; FIG. 16 is a top, side perspective view of yet another preferred embodiment of the presently disclosed intervertebral implant; FIG. 17 is a top view of the intervertebral implant shown in FIG. 16; FIG. 18 is a front view of the intervertebral implant shown in FIG. 16; FIG. 19 is a side view of the intervertebral implant shown in FIG. 16; FIG. 20 is a rear view of the intervertebral implant shown in FIG. 16; FIG. 21 is a top, side perspective view of one preferred embodiment of the presently disclosed intervertebral implant; FIG. 22 is a top view of the intervertebral implant shown in FIG. 21 ; FIG. 23 is a front view of the intervertebral implant shown in FIG. 21 ; FIG. 24 is a side view of the intervertebral implant shown in FIG. 21; FIG. 25 is a rear view of the intervertebral implant shown in FIG. 21; FIG. 26 is a top, side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; FIG. 27 is a top view of the intervertebral implant shown in FIG. 26; FIG. 28 is a front view of the intervertebral implant shown in FIG. 26; FIG. 29 is a side view of the intervertebral implant shown in FIG. 26; FIG. 30 is a rear view of the intervertebral implant shown in FIG. 26; FIG. 31 is a top side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; FIG. 32 is a top view of the intervertebral implant shown in FIG. 31 ; FIG. 33 is a front view of the intervertebral implant shown in FIG. 31 ; FIG. 34 is a side view of the intervertebral implant shown in FIG. 31 ; FIG. 35 is a rear view of the intervertebral implant shown in FIG. 31; FIG. 41 is a top, side perspective view of one preferred embodiment of the presently disclosed intervertebral implant; FIG. 41 A is a top, side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; FIG. 42 is a top view of the intervertebral implant shown in FIG. 41 ; FIG. 42A is a top view of the intervertebral implant shown in FIG. 41 A; FIG. 43 is a front view of the intervertebral implant shown in FIG. 41 ; FIG. 44 is a side view of the intervertebral implant shown in FIG. 41 ; FIG. 45 is a rear view of the intervertebral implant shown in FIG. 41 ; FIG. 46 is a top, side perspective view of one preferred embodiment of the presently disclosed intervertebral implant; FIG. 47 is a top view of the intervertebral implant shown in FIG. 46; FIG. 48 is a front view of the intervertebral implant shown in FIG. 46; FIG. 49 is a side view of the intervertebral implant shown in FIG. 46; FIG. 50 is a rear view of the intervertebral implant shown in FIG. 46; FIG. 51 is a top, side perspective view of one preferred embodiment of the presently disclosed intervertebral implant; FIG. 52 is a top view of the intervertebral implant shown in FIG. 51; FIG. 53 is a front view of the intervertebral implant shown in FIG. 51 ; FIG. 54 is a side view of the intervertebral implant shown in FIG. 51; FIG. 55 is a rear view of the intervertebral implant shown in FIG. 41 ; FIG. 56 is a top, side perspective view of another preferred embodiment of the presently disclosed intervertebral implant; and FIG. 57 is a top view of the intervertebral implant shown in FIG. 56. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Preferred embodiments of the presently disclosed intervertebral implants will now be described in detail with reference to the drawings, in which like reference numerals designate identical or corresponding elements in each of the several views. FIGS. 1-5 illustrate one preferred embodiment of the presently disclosed intervertebral implant which is shown generally as 10. Intervertebral implant 10 includes a substantially rectangular body portion 12 having a pair of side walls 14a and 14b, a upper bearing surface 16, a lower bearing surface 18, a front wall 20 and a rear wall 22. Preferably, the upper and lower bearing surfaces, are defined by the upper and lower surfaces of the side walls, front wall and rear wall. Body portion 12 defines an internal cavity 24, which is open at its upper and lower ends adjacent upper and lower bearing surfaces 16 and 18. Cavity 24 is configured and dimensioned to receive a bone growth material to accelerate and/or promote fusion of adjacent vertebrae. The bone growth material may be osteoconductive and therefore provide a scaffold or matrix for new bone growth and remodeling. Additionally the bone growth material may be osteogenic and induce bone growth. Upper and lower bearing surfaces 16 and 18, respectively, preferably include a series of ridges 26 which are positioned to engage the vertebral endplates of adjacent vertebrae after implant 10 has been positioned in the intervertebral space. Ridges 26 function to minimize movement of implant 10 in relation to the adjacent vertebrae. It is envisioned that ridges 26 may be provided on only one or both of bearing surfaces 16 and 18 and that ridges 26 may be substituted with other known movement resistant structures, e.g., knurling, projections, ribs, grooves, pyramidal teeth, stepped projections, notches or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion, etc. In one embodiment, it is preferred that, the height of side walls 20 and 22 increases from front wall 20 towards rear wall 22 such that the natural curvature of the spine is maintained and/or restored when implant 10 is inserted between the adjacent vertebrae. This is especially desirable in the case of an implant used in a Posterior Lumbar Intervertebral fusion. The desired height change or slope will vary from patient to patient and on the location of implantation in the spine. The implant may be configured with generally flat upper and lower surfaces, generally convex upper and lower surfaces and/or discrete angled upper and lower surfaces to maintain and/or restore the natural or desired curvature of the spine. Front wall 20 includes tool engagement structure 30 for releasably engaging an implant insertion tool (not shown). Although engagement structure 30 is illustrated as a cylindrical opening, it is envisioned that engagement structure 30 may assume other configurations. For example, engagement structure 30 may include a threaded opening, multiple openings, or a rectangular, square or triangular slot or protrusion. Additionally, the implant may have multiple instrument engagement structures of varying shape, dimension, angulation and combinations thereof located on any suitable surface of the implant. The surfaces 16a and 18a of upper and lower bearing surfaces 16 and 18 adjacent rear wall 22 are preferably angled or tapered downwardly and upwardly. Angled surfaces 16a and 18a allow a surgeon to more easily insert end 22 of implant 10 between adjacent vertebrae. Intervertebral implant 10, as well as the implants to be described in detail hereinbelow, is intended to be positioned between adjacent vertebrae of the spine. When in place, upper and lower bearing surfaces 16 and 18 engage and support the endplates of adjacent vertebrae to restore and/or maintain the desired distance between the adjacent vertebrae. Preferably, the implants disclosed herein are constructed from biocompatible materials such as polymers, eg. poly-ether-ether-keytone (PEEK), carbon reinforced polymers, stainless steel, titanium, chrome cobalts, and/or bone polymer composites and any combinations thereof. Alternately, other materials including cortical, cancellous and cortico-cancellous bone of autogenic, allogenic or xenogenic origin, and any combinations thereof, may be used to construct part or all of the implant. As known in the art, bone growth material may be loaded into the cavity or cavities of the implant at a location to communicate with the recipient's bone. The bone growth material can be any material or substance, which stabilizes, controls, regulates, promotes or accelerates new bone growth, bone healing and/or bone remodeling. This may be a result of some osteogenic, osteoconductive and/or osteoinductive effect of the bone growth material. Examples of bone growth materials which can be incorporated into the implants disclosed in this application include, e.g., collagen, insoluble collagen derivatives, etc., and soluble solids and/or liquids dissolved therein, e.g., antiviral agents, particularly those effective against HIV and hepatitis; antimicrobials, antibiotics and/or antimycotics such as erythromycin, bacitracin, neomycin, penicillin, polymyxin B, tetracyclines, viomycin, chloromycetin and streptomycins, cefazolin, ampicillin, azactam, tobramycin, clindamycin and gentamicin, etc.; biocidal/biostatic sugars such as dextrose, glucose, etc.; amino acids, peptides, vitamins, inorganic elements, co-factors for protein synthesis; hormones; endocrine tissue or tissue fragments; synthesizers; enzymes such as collagenase, peptidases, oxidases, etc.; polymer cell scaffolds with parenchymal cells; angiogenic drugs and polymeric carriers containing such drugs; collagen lattices; antigenic agents; cytoskeletal agents; cartilage fragments, living cells such as chondrocytes, bone marrow cells, mesenchymal stem cells, natural extracts, tissue transplants, bone, demineralized bone, partially demineralized bone, mineralized bone, bone graft substitutes such as hydroxylapatite, tricalcium phosphate, polycrystalline calcium, calcium carbonate, coralline calcium, calcium phosphate, calcium hydrogen phosphate, calcium phosphosilicate, tetrabasic calcium phosphate, sodium chondroitin sulfate, sodium succinate anhydride, calcium sulfate, magnesium stearate, calcium sulfate dihydrate, polyvinyl pyrilodone, propylene glycol-Co-Fumaric acid, calcified polyurethane, baria-boroalumino-silicate glass, polylactide-co-glycolide, autogenous tissues such as blood, serum, soft tissue, bone marrow, etc.; bioadhesives, bone morphogenic proteins (BMPs), transforming growth factor (TGF-beta), insulin-like growth factor (IGF-1); growth hormones such as estrogen and sonatotropin; bone digestors; antitumor agents; immunosuppressants; angiogenic agents such as basic fibroblast growth factor (bFGF); permeation enhancers, e.g., fatty acid esters such as laureate, myristate and stearate monoesters of polyethylene glycol, enamine derivatives, alpha-keto aldehydes, etc.; and, nucleic acids. In certain embodiments, the implant may be filled or loaded with any piece or pieces of bone including; cortical, cancellous and cortico-cancellous bone of autogenic, allogenic or xenogenic origin, and any combinations thereof, e.g., demineralized cortical fibers with mineralized cancellous chunks. The bone may be surface demineralized, partially demineralized, fully demineralized, fully mineralized, surface deorganified, partially deorganified, fully deorganified, fully organified or any desirable combination thereof. In other embodiments the bone is precisely cut to fit within the interior space of the implant. FIGS. 6-10 illustrate another preferred embodiment of the presently disclosed intervertebral implant which is shown generally as 100. Implant 100 includes a substantially rectangular body portion 112 having a pair of side walls 114a and 114b, a upper bearing surface 116, a lower bearing surface 118, a front wall 120 and a rear wall 122. Body portion 112 defines a plurality of interconnected throughbores 124 which extend from upper surface 116 to lower surface 118. Although three interconnected throughbores 124 are illustrated, it is envisioned that one or more throughbores may be provided and that the throughbores may be spaced from each other (See FIGS. 11-15 illustrating implant 100'). Throughbores 124 are configured to receive bone growth material as discussed above with respect to cavity 24 of implant 10. The inner surface of throughbores 124 may be ridged, barbed, rasped, or notched to frictionally engage the plugs or blocks. The bone growth material may be provided in the form of cylindrical plugs, blocks or other shapes formed of cortical, cancellous and cortico-cancellous bone. Alternately, other known bone growth materials may be provided including those listed above. Additionally, some embodiments may include retention structures to hold the inserted bone growth material in place. These retention structures include but are not limited to tabs, bars, pins, meshes and adhesives. Upper and/or lower bearing surfaces 116 and 118 define curved surfaces, which slope outwardly from front wall 120 to rear wall 122 and are configured to conform to, maintain and/or restore the natural curvature of the spine. Front wall 120 includes tool engagement structure 130 for releasably engaging an implant insertion tool. As discussed above with respect to tool engagement structure 30 of implant 10, tool engagement structure 130, although illustrated as a cylindrical throughbore, may include a variety of different configurations and may be positioned on any available surface of implant 100. The surfacesl 16a and/or 118a of upper bearing surface 116 and lower bearing surface 118 adjacent rear wall 122 are preferably tapered or angled towards rear wall 122 to allow for easier insertion of implant 100 into an intervertebral space. The surfaces of 116a and/or 118a may also comprise ridges, grooves, pyramidal teeth, notches or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion. FIGS. 16-20 illustrate yet another preferred embodiment of the presently disclosed intervertebral implant shown generally as 200. Implant 200 is similar in construction to implant 10 and includes a substantially rectangular body portion 212 having a pair of side walls 214a and 214b, a upper bearing surface 216, a lower bearing surface 218, a front wall 220 and a rear wall 222. Body portion 212 defines an internal cavity 224 which extends between upper and lower bearing surfaces 216 and 218, respectively. Implant 200 differs from implant 10 in that upper and lower bearing surfaces 216 and 218 do not include ridges or the like. Alternately, these surfaces may comprise protrusions and/or recesses of any of the shapes and/or configurations disclosed herein. Further, implant 200 can be oversized in relation to a respective intervertebral space to frictionally retain the implant in the intervertebral space such as by press-fitting or the like. FIGS. 21-25 illustrate another preferred embodiment of the presently disclosed intervertebral implant shown generally as 200'. Implant 200' is similar in construction to implant 200 but differs in that upper and lower bearing surfaces 216' and 218' define substantially linear surfaces which are angled between front wall 220' and rear wall 222' and upper and lower bearing surfaces 216 and 218 of implant 200 define curved surfaces which slope outwardly between front wall 220 and rear wall 222. FIGS. 26-30 illustrate another preferred embodiment of the presently disclosed intervertebral implant shown generally as 300. Implant 300 includes a body portion 312 having a substantially pentagonal shape. Body portion 312 has a first substantially linear side wall 314a, a pair of angled side walls 314b and 314c, a upper bearing surface 316, a lower bearing surface 318, a front wall 320 and a rear wall 322. Body portion 312 defines an internal cavity 324 which extends between upper and lower bearing surfaces 316 and 318 and is configured to receive bone growth material. Front and rear walls 320 and 322 preferably define substantially parallel planes. Side wall 314b extends from front wall 320 towards rear wall 322 and defines an obtuse angle with respect to front wall 320. Side wall 314c extends from rear wall 322 towards front wall 320 and defines an obtuse angle with respect to rear wall 322. Side walls 314b and 314c define an obtuse angle with respect to each other. The disclosed configuration of body portion 312 defines an enlarged footprint to provide increased stabilization of adjacent vertebrae. The term "footprint" as used herein is the area defined by the smallest rectangle which can be drawn about the implant as viewed from the top or bottom of the implant, i.e., the load bearing surface. By providing side walls 314b and 314c which angle away from side wall 314a, the footprint for a given overall perimeter of the implant is increased to provide improved vertebral stabilization. As discussed with respect to the implants disclosed above, top and bottom bearing surfaces 316 and 318 include angled portions 316a and 318a adjacent leading wall 322. Angled portions 316a and 318a allow a surgeon to more easily insert end 322 of implant 300 between adjacent vertebrae. Rear wall 320 also includes insertion tool engagement structure such as disclosed above. Alternately, insertion tool engagement structure may be provided on any available surface of implant 300. FIGS. 31-35 illustrate another preferred embodiment of the presently disclosed intervertebral implant shown generally as 400. Implant 400 includes a body portion 412 having a substantially hexagonal "V" shape. Body portion 412 includes a first pair of angled side walls 414a and 414b, a second pair of angled side walls 414c and 414d, a upper bearing surface 416, a lower bearing surface 418, a front wall 420 and a rear wall 422. Body portion 412 defines an internal cavity 424 which extends between upper and lower bearing surfaces 416 and 418. Side wall 414a of the first pair of angled side walls has a first end connected to front wall 420 and a second end connected to a first end of side wall 414b. The second end of side wall 414b is connected to rear wall 422. Side walls 414a and 414b are angled inwardly towards side walls 414c and 414d and have axes which together define an external obtuse angle θ-i. Side walls 414c and 414d extend from front wall 420 and rear wall 422, respectively, in a direction away from side walls 414a and 414b. The axes of side walls 414c and 414d together define an obtuse angle θ₂. Although θι is illustrated as being substantially the same as θ₂, it is envisioned that θι may be equal to, greater or less than θ₂. The obtuse angle may be any obtuse angle (exceeding 90 degrees but less than 180 degrees) but preferably 120 degrees to 180 degrees, and most preferably 140 degrees to 170 degrees. As discussed above with respect to implant 300, the configuration of implant 400 provides an enlarged footprint to improve stabilization of adjacent vertebrae. Further, where the implant must be inserted through an access channel during implantation, implant 400 can be inserted through a channel having a width smaller than the width of the footprint defined by the implant. This is accomplished by inserting leading wall 422 of implant 400 through the access channel and rotating or shifting the implant 400 when the junction of side walls 414a and 414b and side walls 414c and 414d reaches the access channel. Implant 400 also includes insertion tool engagement structure 430 as discussed above. Upper and lower bearing surfaces 416 and 418 include angled portions 416a and 418a, respectively, adjacent rear wall 422 to allow a surgeon to easily insert implant 400 between adjacent vertebrae. Although not shown, the surfaces of 416 and/or 418 may comprise ridges, grooves, pyramidal teeth, notches or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion. The implant 400 may be configured with generally flat upper 416 and lower 418 surfaces as shown, or convex upper and lower surfaces and/or discrete angled upper and lower surfaces to restore the desired curvature of the spine. Any implant surface angle or curvature that achieves the desired relationship between the adjacent vertebrae is envisioned by this invention. FIGS. 36-40 illustrate yet another preferred embodiment of the presently disclosed intervertebral implant shown generally as 500. Implant 500 includes a body portion 512 having a first linear side wall 514, a second semi-circular side wall 516, a pair of spaced semi-cylindrical corner portions 518a and 518b, a upper bearing surface 520, and a lower bearing surface 522. Cylindrical corner portions 518a and 518b are positioned on opposite ends of side wall 514 and interconnect side wall 514 and side wall 516. Body portion 512 defines a cavity 524 which extends between upper and lower bearing surfaces 520 and 522. Corner portions 518a and 518b also define cylindrical cavities 526. Cavity 524 communicates with cavities 526 through slot 528 formed in each of corner portions 518a and 518b. Slots 528 extend from upper bearing surface 520 to lower bearing surface 522. Cavity 524 and/or cavities 518a and 518b can be filled with bone growth material as discussed above. The configuration of implant 500, like implant 400, allows implant 500 to be inserted through an opening having a width smaller than the width of the footprint defined by the implant. It is noted that implant 500 may be modified to include insertion tool engaging structure and/or movement restricting structure, such as ridges or protrusions formed on upper and/or lower bearing surfaces 520 and 522. Although not shown, the surfaces of 520 and/or 522 may comprise ridges, grooves, pyramidal teeth, notches or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion. The implant 500 may be configured with generally flat upper 520 and lower 522 surfaces as shown, or convex upper and lower surfaces and/or discrete angled upper and lower surfaces to restore the desired curvature of the spine. Any implant surface angle or curvature that achieves the desired relationship between the adjacent vertebrae is envisioned by this invention. FIGS. 41-45 illustrate another preferred embodiment of the presently disclosed intervertebral implant shown generally as 600. Implant 600 includes a body portion 612 having a first pair of angled side walls 614a and 614b, a second pair of angled side walls 614c and 614d, a upper bearing surface 616, a lower bearing surface 618, a front wall 620 and a rear wall 622. Body portion 612 including side walls 614a-d is substantially similar to body portion 412 of implant 400 including side walls 414a-d as discussed above with a few exceptions. Thus, the similarities will not be discussed in further detail herein. Body portion 612, unlike body portion 412 of implant 400, includes a plurality of spaced cylindrical cavities 624 which extend between upper and lower bearing surfaces 616 and 618. Cavities 624 are configured to receive any bone growth material or combination thereof as discussed above. Upper and lower bearing surfaces 616 and 618 also include transverse ridges 616 which extend in a direction substantially parallel to a plane defined by front wall 620. Ridges 626 minimize movement of implant 600 in relation to the vertebral endplates after implant 600 has been positioned between adjacent vertebrae. The surfaces of 616 and/or 618 may comprise ridges, grooves, pyramidal teeth, notches or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion. As illustrated in FIG. 44, the height of implant 600 preferably increases from front wall 620 to rear wall 622 to maintain and/or restore the natural curvature of the spine after implant 600 has been positioned in the intervertebral space. In an alternate embodiment shown in FIGS. 46-50, wherein like parts are labeled "'", implant 600' does not include ridges or movement limiting structure on upper and lower bearing surfaces 616' and 618'. Further, upper and lower bearing surfaces 616' and 618' are substantially planar, i.e., implant 600' does not increase in height from front wall 620' to rear wall 622'. The implant 600 may be configured with generally flat upper 616' and lower 618' surfaces as shown, or, alternately, have convex upper and lower surfaces and/or discrete angled upper and lower surfaces to restore the desired curvature of the spine. Any implant surface angle or curvature that achieves the desired relationship between the adjacent vertebrae is envisioned by this invention. FIGS. 41 A and 42A illustrate another preferred embodiment of the presently disclosed intervertebral implant shown generally as 600". Implant 600" is substantially similar to implant 600 in may respects but includes a single elongated cavity 624" extending between upper and lower bearing surfaces 616" and 618" rather than a plurality of spaced cavities 624. Also, each side wall 614a"-614d" includes an opening 670" which communicates with elongated cavity 624". Openings 614a"-614d", besides limiting the amount of material required to construct implant 600', provide increased exposure to the bone growth material within cavity 624". Although openings 670" are illustrated in each of side walls 614a"-d", it is contemplated that openings 670" may be provided in one or more of the side walls. FIGS. 51-55 illustrate yet another preferred embodiment of the presently disclosed intervertebral implant shown generally as 700. Implant 700 includes a substantially rectangular body portion 712 having a pair of side walls 714a and 714b, a upper bearing surface 716, a lower bearing surface 718, a front wall 720 and a rear wall 722. Body portion 712 defines a cavity 724 which extends from upper bearing surface 716 to lower bearing surface 718 and is configured to receive bone growth material. Upper and/or lower bearing surfaces 716 and 718 include movement limiting structure, e.g., ridges 726 to prevent or limit movement of implant 700 in relation to adjacent vertebrae after implant 700 has been inserted into the spine. Front wall 720 includes insertion tool engagement structure, here shown as cylindrical bore 730. FIGS. 56 and 57 illustrate yet another preferred embodiment of the presently disclosed intervertebral implant shown generally as 800. Implant 800 is substantially identical in configuration to implant 600' shown in FIGS. 46-50. Implant 800 further includes a radiographic marker positioned within implant 800. In this embodiment, the radiographic marker includes a plurality of metallic pins 802a-802c positioned at identifiable location within implant. Metallic pins 802a-802c are visible via x-ray or fluoroscopy during and after a spinal fusion surgery procedure. As such, metallic pins 802a-802c allow a surgeon to accurately identify the location of the implant in the body during and after a surgical procedure. Although the radiographic marker is illustrated as including metallic pins positioned within the implant, the use of other radiopaque or detectable materials, including tapes, bands, dyes, etc., which can be viewed while positioned within the body using an energy source positioned externally of the body may be used. Further, the radiographic marker need not be positioned within the implant, but rather may be secured to an external surface thereof, e.g. taped thereon. Although not shown, a radiographic marker may be incorporated into⁶any of the implant embodiments disclosed above. When constructing any of the implants disclosed above from bone, the bone may be subjected to different treatments to render it more suitable for its intended use. For example, the bone used to construct the implant or the implant itself may be subjected to a demineralization process to reduce the inorganic mineral content of the bone. Demineralization has the effect of increasing the susceptibility of the bone to fusion while reducing the load bearing capacity of the bone. The degree of demineralization will depend upon the intended use of the implant and its required load bearing strength. Typically, the top and bottom load bearing surfaces of the implant will be surface demineralized to improve the susceptibility of the bone to fusion while not substantially reducing the load bearing strength of the implant. Other bone treatments may include the addition of antiviral agents, antimicrobials, antibiotics, vitamins, etc., to the bone or implant. It will be understood that various modifications may be made to the embodiments

disclosed herein. For example, although each of the implants disclosed above is

described as being dimensioned to replace a damaged intervertebral disk, it is

contemplated that each implant may be dimensioned and configured for vertebral

body replacement. As such, the height of the implant would be increased to

replace a vertebral body and the disk spaces above and/or below the vertebral

body. Therefore, the above description should not be construed as limiting, but merely as exemplifications of preferred embodiments. Those skilled in the art will envision other modifications within the scope and spirit of the claims appended hereto.

Claims

WHAT IS CLAIMED IS: 1. An implant comprising: a body having first, second, third and fourth sidewalls, a front wall, a rear wall, a upper bearing surface, and a lower bearing surface, wherein the first and second side walls are contiguous and define intersecting planes which define an obtuse angle θi and the third and fourth side walls are contiguous and define intersecting planes which define an obtuse angle θ₂.

2. An implant according to Claim 1 , the first side wall is substantially parallel to the third side wall and the second side wall is substantially parallel to the fourth side wall.

3. An implant according to Claim 1 , wherein θi is substantially equal to θ₂.

4. An implant according to Claim 3, wherein θi and θ₂ are between about 90° and about 180°.

5. An implant according to Claim 4, wherein θi and θ₂ are between about 120° and about 180°.

6. An implant according to Claim 5, wherein θi and θ₂ are between about 140° and about 170°.

7. An implant according to Claim 1 , wherein the upper and/or lower bearing surface includes movement resistant structure.

8. An implant according to Claim 7, wherein the movement resistant structure is selected from the group consisting of knurling, projections, ribs, grooves, ridges, pyramidal teeth, stepped projections and notches.

9. An implant according to Claim 1 , wherein the body defines a cavity which extends between the upper and lower bearing surfaces.

10. An implant according to Claim 9, further including at least one opening extending through at least one of the side walls, the opening communicating with the cavity.

11. An implant according to Claim 10, wherein the at least one opening includes a plurality of openings which extend through a plurality of the side walls.

12. An implant according to Claim 1 , wherein the body further includes insertion tool engagement structure.

13. An implant according to Claim 12, wherein the insertion tool engagement structure is positioned on the front wall.

14. An implant according to Claim 13, wherein the insertion tool engagement structure is selected from the group consisting of a cylindrical opening or openings, threaded and/or non-threaded openings, non-circular openings, and protrusions.

15. An implant according to Claim 1 , wherein the upper and/or lower bearing surfaces are angled towards the front and/or rear walls to facilitate insertion of the implant into an intervertebral space.

16. An implant according to Claim 1 , further including a radiographic marker.

17. An implant according to Claim 16, wherein the radiographic marker includes at least one metallic pin.

18. An implant according to Claim 17, wherein the radiographic marker includes a plurality of metallic pins embedded within the body of the implant.