2. Background of Related Art Surgical implants for repairing or replacing defects in the skeletal system of an animal, e. g. , human, are well known. Such implants include surgical implants for replacing a vertebral body which was damaged as a result of trauma, tumor or infection and for fusing adjacent vertebrae together to treat back pain in patients with ruptured or degenerated intervertebral discs, scoliosis, spondylolisthesis or other pathologies. Typically, during a spinal fusion procedure, an implant is placed into an intervertebral space in a position to engage and support adjacent vertebrae. Preferably, the implant is constructed from a biocompatible material which is capable of or adapted to fuse with the adjacent vertebrae to maintain and/or restore proper spacing and lordosis between the adjacent vertebrae.

A variety of different types of surgical implants have been developed to effect spinal fusion. These implants include spinal fusion cages, threaded bone dowels, stepped bone dowels, ramp-shaped implants, C-shaped implants, etc.

These implants are constructed from a variety of biocompatible materials including autograft, allograft and xenograft bone, metals including titanium, ceramics, polymers, etc. Each of the materials of construction have advantages and disadvantages associated with there use.

The most common types of bone used for surgical implantation are allogenic and autogenic bone. Autogenic bone is bone harvested from the patient's own skeletal system, e. g. , the iliac crest. Grafts constructed of autogenic bone are referred to as"autografts". Allogenic bone is bone harvested from the skeletal system of another human source and grafts made from allogenic bone are referred to as"allografts". Typically, allogenic bone is harvested from cadavers and treated and stored in a bone bank until it is ultimately needed for implantation. Allogenic and autogenic bone are resorbable and are known to have osteoconductive and osteoinductive capabilities and, thus, are desirable for implant use.

The use of bone does have some drawbacks. For example, the use of bone is limited by its availability, geometry, compressive strength and remodeling characteristics. For example, cancellous bone, which has superior, osteoconductive and remodeling characteristics as compared to cortical bone, does not have good load bearing strength characteristics and may not be suitable for implantation in areas of the skeletal system subjected to high loads.

Conversely, while cortical bone has good load bearing characteristics, it exhibits slow and incomplete remodeling because it is revascularized through a limited number of preexisting blood vessel holes present in the bone. The decreased vascularization of cortical bone further limits the ability of cells to penetrate and remodel compact vascular regions of the bone. Many structural allografts are never fully incorporated by remodeling and replacement with host tissue due, in part, to the difficulty the host's blood supply has in penetrating cortical bone and to the poor osteoinductivity of mineralized bone. Thus, in applications where the mechanical load-bearing requirements of the graft are challenging, lack of replacement by host bone tissue may compromise the graft by subjecting it to repeated loading and cumulative unrepaired damage (mechanical fatigue) within the implant material. Additionally, natural donor bone must be cut and shaped into desirable sizes and geometric configurations. This processing of the donated graft tissue leads to waste of material.

Although metallic implants as well as ceramic, and some polymers have excellent load bearing capabilities and may assume any geometric configuration, these materials typically are not resorbable or do not remodel and have limited osteoinductive and osteoconductive capabilities that are inferior to natural bone.

Accordingly, there is an existing need in the art for a surgical implant which maximizes the use of natural graft tissue, is easily inserted into the graft site, and still has good load bearing characteristics as well as good osteoconductive, osteoinductive and remodeling properties.

SUMMARY The present invention is directed towards novel hybrid surgical implants, formed from bone and one or more biocompatible materials, for correcting defects in the skeletal system. The hybrid surgical implants disclosed herein are designed and configured to be easily manufactured, maximize the use of donor graft material while reducing waste and engage surgical instrumentation with ease. In one preferred embodiment, the implants are dimensioned to be placed in the intervertebral space, engage the vertebral endplates, support the vertebral column in a desired alignment and facilitate fusion between adjacent vertebrae.

The hybrid surgical implants may also be configured to replace an entire vertebral body and associated discs which were damaged as a result of trauma, tumor, infection or the like. Alternately, the hybrid surgical implants may be configured to correct skeletal defects in other areas of the body, e. g., arms, legs, hands, feet, skull, etc.

The hybrid implants disclosed herein include a first portion, which is formed of bone including allogenic, autogenic or xenogenic bone, bone composites, or combinations thereof and a second portion which is formed of a synthetic biocompatible material. The bone may be provided as a single piece or multiple pieces or particles to maximize the amount of donor bone utilized and reduce waste. The second portion of the implant is preferably formed from a resorbable or non-resorbable polymer or composite. The polymer or composite decreases the amount of bone needed to form the implant while holding the bone pieces or particles together and improving the mechanical strength of the implant. Alternately, other materials including ceramics and metals may be used to support and/or connect or join the bone pieces or particles.

At least one instrument interface may be provided to engage surgical instrumentation used in the insertion of the implant into the skeletal space. Since part of the hybrid implant is formed from a synthetic material, detailed and precise instrument interfaces may be employed to securely hold the implant during insertion.

Either or both of the first and second portions'upper and lower surfaces may comprise surface modifications designed to prevent expulsion of the implant from the intervertebral space and enhance fusion with a portion of the skeletal system, e. g. , the vertebral endplates. These surface modifications may be projections, recesses, chemical treatments or enzymatic treatments or any combination thereof.

Where the implant is dimensioned and configured to effect spinal fusion, either or both of the first and second portions may be lordose or otherwise angled to restore desirable curvature to the spine after insertion. Either or both of the first and second portions may have a convex configuration to conform to the shape of the vertebral bodies. Either or both of the first and second portion may contain bores or through bores to improve vascularization of the implant and improve remodeling. The first portion of the implant may be configured as a central core around which the second portion is at least partially configured as an outer casing. The association of the first and second portion of the hybrid implant may provide increased mechanical strength in the hybrid implant compared to either part taken individually.

Brief Description of the Drawings Preferred embodiments of the presently disclosed hybrid implants are described herein with reference to the drawings wherein: FIG. 1 is a side perspective view from above one preferred embodiment of the presently disclosed hybrid implant ; FIG. 2 is a side perspective view from above of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 3 is a side cross-sectional view of the hybrid implant shown in FIG. 2; FIG. 4 is a side perspective exploded view from above of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 5 is a side view of the hybrid implant shown in FIG. 4; FIG. 6 is a side view of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 7A is a rear view of the hub member of the hybrid implant shown in FIG. 6; FIG. 7B is a rear view of an alternate embodiment of the hub member of the hybrid implant shown in FIG. 6; FIG. 7C is a rear view of another alternate embodiment of the hub member of the hybrid implant shown in FIG. 6; FIG. 7D is a rear view of yet another alternate embodiment of the hub member of the hybrid implant shown in FIG. 6; FIG. 8 is a side perspective view from above another preferred embodiment of the presently disclosed hybrid implant; FIG. 9 is a top view of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 10 is a cross-sectional view taken along section lines 10-10 of FIG. 9; FIG. 11 is a top view of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 12 is a top, cutaway view of a casing thoughbore of the hybrid implant shown in FIG. 9; FIG. 13 is a top view of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 14 is a side view of the hybrid implant shown in FIG. 13; FIG. 15 is a top view of another preferred embodiment of the presently disclosed hybrid implant ; FIG. 16 is a top view of another preferred embodiment of the presently disclosed hybrid implant with parts separated; FIG. 17 is a side view of the hybrid implant shown in FIG. 16 with the parts attached; FIG. 18 is a top view of yet another preferred embodiment of the presently disclosed hybrid implant ; FIG. 19 is a side perspective view of yet another preferred embodiment of the presently disclosed hybrid implant ; and FIG. 20 is a perspective view from one side of still yet another preferred embodiment of the presently disclosed hybrid implant.

Detailed Description Of Preferred Embodiments Preferred embodiments of the presently disclosed hybrid 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.

The term"osteogenic"as utilized herein shall be understood as referring to the ability of an osteoimplant to enhance or accelerate the growth of new bone tissue by one or more mechanisms such as osteogenesis, osteoconduction and/or osteoinduction.

The term"osteoinductive"as utilized herein shall be understood to refer to the ability of a substance to recruit cells from the host that have the potential for forming new bone and repairing bone tissue. Most osteoinductive materials can induce bone formation and stimulate the formation of ectopic bone in soft tissue.

The term"osteoconductive"as utilized herein shall be understood to refer to the ability of a substance to serve as a suitable template or substrate along which bone may grow. Additionally, the term osteoconductive refers to the ability of a material to provide a three-dimensional porous framework, a scaffold or matrix for new bone growth and remodeling which conducts the ingrowth of new living bone into the framework, scaffold or matrix.

The term"osteoimplant"as utilized herein contemplates any device or material for implantation that aids or augments bone or other hard tissue formation or healing for human or animal use. Osteoimplants are often applied at <BR> <BR> a bone defect or dental repair site, e. g. , one resulting from injury, defect brought about during the course of surgery, infection, malignancy or developmental malformation. Osteoimplants are envisioned as being suitably sized and shaped as required for use in a wide variety of orthopedic, neurosurgical, oral and maxillofacial and dental surgical procedures, such as the repair of simple and compound fractures and non-unions, external and internal fixations, joint reconstructions such as arthrodesis, general arthroplasty, deficit filling, discectomy, laminectomy, anterior cervical and thoracic operations, spinal fusions, dental restorations, etc. Therefore, the osteoimplants herein are intended for implantation at a bony site. As used herein, the term"osteoimplant" is to be interpreted in its broadest sense and is not intended to be limited to any particular shape, size, configuration or application.

The term"shaping"refers to any of the various methods that can be used, individually or in combination, to provide an osteoimplant of a desired size and configuration. Such methods are known to those skilled in the art include, for example, machining, laser etching, welding, assembling of parts, cutting, milling, reactive etching, etc. Where the osteoimplant comprises particles or pieces, "shaping"also refers to extruding, injection molding, solvent casting, vacuum forming, sintering, melt forming, reaction molding, compression molding, transfer molding, blow molding, rotational molding, thermoforming, machining, CAD/CAM procedures, and the like. Shaping also includes any post-shaping operations that may be utilized to modify the internal and/or external structure of the osteoimplant and/or modify its properties, e. g. , selective removal of a filler component to provide voids, application of a layer of biologically active material to part or all of the surface and/or subsurface region of the osteoimplant, etc.

The term"biocompatible"and expressions of like import shall be understood to mean the absence of any undesirable biological response to an implant. Optional components that are useful can be considered biocompatible if, at the time of implantation, they do not elicit a significant undesirable response in vivo.

The term"piece"or"particle"as applied to the bone component of an osteoimplant includes bone pieces of all shapes, sizes, thicknesses and configurations such as fibers, threads, narrow strips, thin sheets, chips, coils, coiled coils, shards, powders, etc. , that posses regular, irregular or random geometries. It should be understood that some variation in dimension may occur in the production of bone particles, and bone particles demonstrating considerable variability in dimensions and/or size are within the scope of this invention. Bone particles that are useful herein can be homogeneous and/or heterogeneous and can include mixtures of human, xenogenic and/or transgenic material.

The term"human"as utilized herein in refers to suitable sources of bone which is taken from at least one site in the graftee and implanted in another site of the graftee as well as allograft bone which is human bone taken from a donor other than the graftee.

The term"autograft"as utilized herein refers to grafts made of autogenic bone that is obtained from the intended recipient of the implant.

The term"allograft"as utilized herein refers to grafts, from a donor of the same species, which may be processed to remove cells and/or other components, intended for implantation that is taken from a different member of the same species as the intended recipient. Thus, the term"allograft"includes bone from which substantially all cellular matter has been removed (processed cellular bone) as well as cell-containing bone.

The term"xenogenic"as utilized herein refers to material intended for implantation obtained from a donor source of a different species than the intended recipient. For example, when the implant is intended for use in an <BR> <BR> animal such as a horse (equine), xenogenic tissue of, e. g. , bovine, porcine,<BR> caprine, etc. , origin may be suitable.

The term"transgenic"as utilized herein refers to tissue intended for implantation that is obtained from an organism that has been genetically modified to contain within its genome certain genetic sequences obtained from the genome of a different species.

The term"composite"as utilized herein refers to the mixture of materials and/or components used in preparing an osteoimplant where the bone component of the osteoimplant is in particle form.

The terms"whole"and"non-demineralized"are used interchangeably herein and refer to bone that contains its full, or original, mineral content. Non- demineralized bone provides strength to the osteoimplant and allows it to initially support a load.

The term"partially demineralized"as utilized herein refers to bone possessing less than about 66% mineral content and is intended to cover all bone and/or bone particles that have had some portion of their original mineral content removed by a demineralization process. As used herein,"partially demineralized"bone includes bone that has only had a portion of its surface demineralized. Demineralized bone induces new bone formation at the site of the demineralized bone and permits adjustment of the overall mechanical properties of the osteoimplant.

The term"shape"as applied to the osteoimplant herein refers to a determined or regular form or configuration and is characteristic of such materials as sheets, plates, disks, spheres, cubes, cores, pins, screws, tubes, teeth, bones, portions of bones, wedges, cylinders, threaded cylinders, cages, and the like. This includes forms ranging from regular geometric shapes to irregular, angled, or non-geometric shapes, and combinations of features having any of these characteristics.

The term"implantable"as utilized herein refers to a biocompatible device retaining potential for successful surgical placement within a mammal.

The expression"implantable device"and expressions of like import as utilized herein refer to any object implantable through surgical, injection, or other suitable means whose primary function is achieved either through its physical presence or mechanical properties.

The term"bioresorbable"as utilized herein refers to those materials of either synthetic or natural origin which, when placed in a living body, are degraded through either enzymatic, hydrolytic or other chemical reactions or cellular processes into by-products which are either integrated into, or expelled from, the body. It is recognized that in the literature, the terms"resorbable", "absorbable","bioresorbable"and"bioabsorbable"are frequently used interchangeably.

The term"polymeric"as utilized herein refers to a material of natural, synthetic or semisynthetic origin that is made of large molecules featuring characteristic repeating units.

The expression"alternating copolymers"as utilized herein refers to copolymers with a regular or alternating repeating unit sequence. The expression"thermoplastic elastomers"as utilized herein refers to melt- processable copolymers which possess elastomeric mechanical properties as a result of a crystallizable"hard"segment and an amorphous"soft"segment possessing a Tg below its service temperature.

The term"blends"as utilized herein refers to polymeric materials that are melt-mixed to achieve compounding between two or more different polymeric compositions that are not covalently bonded to each other. For the purposes of this application, a melt-miscible blend is a polymeric mixture that possesses sufficient miscibility in the melt to be useful in shaping.

The term"incorporation"utilized herein refers to the biological mechanism whereby host cells gradually remove portions of the osteoimplant and replace the removed portions with native host bone tissue while maintaining strength. This phenomenon is also referred to in the scientific literature by such expressions as <BR> <BR> "creeping substitution, ""wound healing response"and"cellular based<BR> remodeling. "Therefore, the term"incorporation"shall be understood herein as embracing what is considered by those skilled in the art to be conveyed by the foregoing expressions, especially"remodeling".

The expression"further treatment"as utilized herein refers to procedures such as lyophilization, re-mineralization, sterilization, etc. , performed either before, during or after the step of shaping the denatured cortical bone-containing osteoimplant. It further includes treatment (s) applied at the time of surgery such as rehydration, combining with cellular materials, application of growth factors, etc.

The expression"wet compressive strength"as utilized herein refers to the compressive strength of an osteoimplant after the osteoimplant has been immersed in physiological saline (water containing 0.9 g NaCI/100 ml water) for a minimum of 12 hours and a maximum of 24 hours. Compressive strength is a well known measurement of mechanical strength and is measured using the procedure described herein.

The surgical implants disclosed herein include a first portion which is formed of bone including allogenic, autogenic or xenogenic bone, bone composites, or combinations thereof and a second portion which is formed of a biocompatible material. The bone may be provided as a single piece or multiple pieces or particles. The second portion of the implant is preferably formed from a resorbable polymer, e. g. , tyrosine polycarbonates, other aliphatic-aromatic Dihydroxy polymers, tyrosine polyarylates, polyester amides, polyminocarbonates, polyalkylene oxides, . Alternately, other resorbable and non-resorbable biocompatible materials may be used to form the second portion of the implant such as poly-ether-ketone-ether-ketone-ketone, poly-ether-ether- ketone, carbon fiber, graphite, cyanoacrylates ; epoxy-based compounds; dental resin sealants ; bioactive glass ceramics (such as apatite-wollastonite), dental resin cements; glass ionomer cements (such as lonocapo and Inoceme available from lonos Medizinische Produkte GmbH, Greisberg, Germany); gelatin- resorcinol-formaldehyde glues ; collagen-based glues ; cellulosics such as ethyl cellulose ; bioresorbable polymers, natural, synthetic and semisynthetic, such as starches, polylactic acid, polyglycolic acid, polylactic-co-glycolic acid, polylactide, polyglycolide, poly (lactide-co-glycolide), polydioxanone, polycaprolactone, polycarbonates, polyorthoesters, polyamino acids, polyanhydrides, polyhydroxybutyrate, polyhydroxyvalyrate, poly (propylene glycol-co-fumaric acid), polyhydroxyalkanoates, polyorthoesters, polyanhydrides, polyphosphazenes, poly (alkylcyanoacrylates), degradable hydrogels, poloxamers, polyarylates, amino-acid derived polymers, amino-acid-based polymers, particularly tyrosine-based polymers, including tyrosine-based polycarbonates and polyarylates, pharmaceutical tablet binders (such as Eudragit binders available from Huls America, Inc.), polyvinylpyrrolidone, cellulose, ethyl cellulose, micro-crystalline cellulose and blends thereof; starch ethylenevinyl alcohols, polycyanoacrylates ; nonbioabsorbable polymers such as polyacrylate, polymethyl methacrylate, polytetrafluoroethylene, polyurethane and polyamide ; etc. Among the preferred polymeric binders are those described in U. S. Patent Nos. 5,216, 115; 5,317, 077; 5,587, 507; 5, 658, 995; 5, 670,602 ; 5,695, 761; 5, 981, 541; 6,048, 521; 6,103, 255; 6,120, 491; 6, 284, 862; 6,319, 492; and, 6,337, 198, the contents of which are incorporated by reference herein. The polymeric binders described in these patents include amino acid-derived polycarbonates, amino acid-derived polyarylates, polyarylates derived from certain dicarboxylic acids and amino acid-derived diphenols, anionic polymers derived from L-tyrosine, polyarylate random block copolymers, polycarbonates, poly (a-hydroycarboxylic acids), poly (caprolactones), poly (hydroxybutyrates), polyanhydrides, poly (ortho esters), polyesters and bisphenol-A based poly (phosphoesters). Additional preferred polymeric binders are the copolymers of polyalkylene glycol and polyester of U. S. Patent Application Publication 2001/0051832, the contents of which are incorporated by reference herein. The biocompatible material is provided to confine and/or provide load bearing support for the bone and/or bone pieces, particles or bone composite.

Although the following disclosure focuses primarily on surgical implants which are dimensioned to be implanted between adjacent vertebrae to effect spinal repair, it is envisioned that the present disclosure of augmenting a surgical implant by providing a synthetic portion for supporting and/or joining bone particles is applicable to implants dimensioned to be used in all areas of the skeletal system including the arms, legs, hands, feet, skull, etc.

FIG. 1 illustrates one preferred embodiment of the presently disclosed hybrid implant shown generally as 10. Hybrid implant 10 includes a central core 12 formed from cortical, cancellous or cortico-cancellous bone and an outer casing 14. Although illustrated as being of monolithic construction, central core 12 may be formed from bone pieces, particles or a composite of bone and polymer. Outer casing 14 is preferably formed from a resorbable polymer, although the use of non-resorbable polymers and other non-resorbable and resorbable biocompatible materials are also envisioned. The resorbable polymer may include bone particles which form part of the polymeric chain or are dispersed throughout the polymer matrix. Casing 14 may also have some flexibility to facilitate receipt of irregular shape bone pieces or particles. A cavity 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.

Either or both of core 12 and outer casing 14 may be load bearing members. For example, core 12 may be constructed from cancellous bone (mineralized, demineralized or partially demineralized), cortical bone or a composite of cortical bone and polymer capable of supporting adjacent vertebrae and outer casing 14 may be a non-load bearing structure functioning only to confine the pieces of bone into a desired configuration. Alternately, casing 14 may be a load bearing structure and core 12 may have limited load bearing capabilities, e. g., cancellous bone, bone particles, composite of cancellous bone and polymer etc. It is also envisioned that both core 12 and casing 14 may have load bearing capabilities.

The top and bottom surfaces of the load bearing member, i. e. , surfaces 12a and 12b of core 12 and/or surfaces 14a and 14b of casing 14, may be generally flat, generally convex and/or angled to maintain and/or restore the desired curvature of the spine. In one embodiment, it is preferred that the height of side walls vary such that the natural curvature of the spine is maintained and/or restored when implant is inserted between the adjacent vertebrae. This is especially desirable in the case of an implant used in a Posterior Lumbar Intervertebral fusion or Transforaminal Lumbar Interbody 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 desired curvature of the spine. Further, surfaces 12a and 12b and/or surfaces 14a and 14b may be formed with movement resistant structures to minimize movement of implant 10 in relation to adjacent vertebrae after implant 10 has been positioned in an intervertebral space. It is envisioned that these movement resistant structures may be ridges or any other known movement resistant structures, e. g., knurling, projections, ribs, grooves, pyramidal teeth, stepped projections, notches, grooves or other such protrusions and recesses or any combination thereof to engage the vertebral endplates and decrease the risk of implant expulsion, etc.

Bone or bone particles forming core 12 may be subjected to a demineralization process to reduce the inorganic mineral content of the bone. <BR> <BR> <P>The bone may be wholly or partially demineralized, e. g. , surface demineralized.

Demineralization has the effect of increasing the susceptibility of the bone to fusion while reducing the load bearing capacity of the bone.

Outer casing 14 may be in the form of a polymeric, e. g., plastic, holder into which the central core 12 is received and retained such as by snap-fitting or <BR> <BR> friction. A locking member (not shown), e. g. , a pin, a screw, a rib, a tab, an<BR> overhang, etc. , may be provided or associated with outer casing 14 to secure core 12 within casing 14. In another preferred embodiment, the polymer casing may be molded about core 12. Further, the polymer may be porous, or contain through bores to allow for osteoconduction and vascularization. Although illustrated as being substantially cylindrical in shape, other implant configurations <BR> <BR> are envisioned, e. g. , cuboid, pyramidal, spherical, etc. with square, rectangular, triangular, circular, tetrahedral, etc. cross-sections.

Bone growth material may be loaded into a cavity or cavities of the implant at a location to communicate with the recipient's bone, e. g. , the vertebral endplates. For example, where bone particles are used to form core 12, bone growth material may be loaded into the bone interstices. The bone growth material can be any material or substance, which stabilizes, controls, regulates, promotes or accelerates new bone growth, bone healing or bone remodeling.

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 of bone including cortical, cancellous and cortico- cancellous bone of autogenic, allogenic or xenogenic origin, and any combinations thereof. 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.

FIGS. 2 and 3 illustrate another preferred embodiment of the presently disclosed hybrid implant shown generally as 100. Hybrid implant 100 includes an outer casing 110, at least one load bearing core member 112 and at least one drive member 114. Casing 110 includes a rectangular body 116 defining a throughbore 118 for slidably receiving load bearing core member (s) 112 and a second bore 120 for slidably receiving drive member 114. Bore 120 is substantially orthogonal to throughbore 118. Each load bearing core member 112 has a load bearing surface 122 positioned to engage a vertebral endplate (not shown) and an abutment surface 124. Abutment surface 124 defines an angle 0 of between about 5 degrees and about 45 degrees with respect to a longitudinal axis"A"of bore 120. At least a portion of a drive end of drive member 114 includes an angled surface 114a that defines an angle which corresponds to angle 0. Angled surface 114a is positioned to engage abutment surface 124 such that when drive member 114 is advanced into bore 120 along axis A, load bearing core member 112 is pushed outwardly from throughbore 118 along axis B. Although hybrid implant 100 is illustrated as having a pair of load bearing core members 112, it is contemplated that hybrid implant 100 may include a single core member 112 and that outer casing 110 may include a load bearing surface. It is also contemplated that only one of the pair of core members 112 may be movable and that a second core member may be fixedly retained at a position extending from outer casing 110.

Outer casing 110 of hybrid implant 100 is preferably formed from a resorbable polymer, e. g., plastic. Alternately, other resorbable and non- resorbable biocompatible materials may be used to form outer casing 110. Core members 112 are preferably formed from cortical, cancellous, or cortico- cancellous bone of autogenic, allogenic or xenogenic origin. Bearing surfaces 122 may be flat, generally convex, or angled to restore and/or maintain a desired or natural curvature of the spine. Bearing surfaces 122 may also include <BR> <BR> movement resistant structure, e. g. , ridges, ribs, projections, knurling, grooves,<BR> pyramidal teeth, stepped projections, notches, recesses, etc. , which are positioned to engage the vertebral endplates to minimize the risk of expulsion of the implant from the intervertebral space.

Drive member 114 and/or the inner walls of bore 120 preferably includes retaining structure for securing drive member 114 at a fixed position within bore 120. The retaining structure, not shown, which may be formed on drive member 114, and or casing 110, may include ridges, teeth, ratchet members, a locking pin, friction, detents, etc. Although drive member 114 is illustrated having a rectangular cross-section, it is envisioned that drive member 114 may be in the form of a cylindrical screw which includes threads which mate with corresponding threads formed on the abutment surfaces 124 of core members 112. Drive member 114 may be adjusted prior to insertion of implant 10 into an intervertebral space to provide the appropriate disk separation. Disk separation will be the distance between the load bearing surfaces 122 of core members 112.

Alternately, drive member 114 may be positioned in the intervertebral space and then adjusted to distract the adjacent vertebrae and provide the appropriate disk separation.

FIGS. 4 and 5 ililustrate another preferred embodiment of the presently disclosed hybrid implant shown generally as 200. Implant 200 includes a casing 210 and a plurality insert or core members 212. Casing 210 includes a body 214 defining a stepped bore 216. Stepped bore 216 includes a plurality of spaced slots 218, each slot being configured to slidably receive an insert or core member 212. Core members 212 have a height h dimensioned to extend through a respective slot 218 and extend from each end of casing 210 (see FIG. 5).

Preferably, the inserts or core members 212 are formed from load bearing bone, e. g., cortical bone, etc. and vary in height along the length of casing 210 such that the load bearing surfaces 212a of core members 212 together define a surface which maintains and/or restores a desired or natural curvature of the spine. Alternately, core members 212 may be of equal heights to provide substantially flat upper and lower load bearing surfaces or of different heights to provide angled upper and lower load bearing surfaces.

Core members 212 may be retained at a fixed position within casing 210 by pins 222 which extend though openings 210a formed in casing 210 and openings 212b formed in core members 212. Pins 222 are preferably formed from a resorbable material such as cortical bone, polymers, etc. A resorbable suture may be used in place of the pins. Alternately, core members 212 may be retained within casing 210 by friction, detents formed in casing 210 and/or screws.

Casing 210 is preferably formed from a resorbable polymer although casing 210 may be formed from other resorbable and non-resorbable biocompatible materials. Preferably, a bone growth material, such as any of those listed above, is positioned in stepped bore 216 of casing 210 between core members 212.

FIGS. 6-7D illustrate another preferred embodiment of the presently disclosed hybrid implant shown generally as 300. Hybrid implant 300 includes a central hub member 310 and a plurality of disks 312. Hub member 310 is preferably formed from a resorbable polymer although hub member 310 may be formed from other non-resorbable and resorbable materials. Hub member 310 includes a first end 31 Oa having a transverse portion or head 314 and a hub portion 316. Transverse portion 314 defines a retaining plate for preventing disks 312 from sliding off first end 310a of hub member 310. Transverse portion 314 may have any geometrical configuration including cylindrical (see FIGS. 7A-7C), rectangular (see FIG. 7D), triangular, etc.

Disks 312 are preferably formed from cortical, cancellous and/or cortico- cancellous bone. It is noted that each disk may be formed from a different type of bone, e. g., two disks may be formed from cortical bone and one disk may be formed from cancellous bone. Disks 312 may be load bearing or non-load bearing bone as will be discussed in further detail below. Disks 312 may also be cylindrical, rectangular or any other desired configuration. Each disk 312 has a central throughbore dimensioned and configured to be slidably received about hub portion 316 of hub member 310. The length of hub portion 316 may be chosen to receive a desired number of disks 312 to provide the appropriate or desired length to hybrid implant 300. The height of disks 312 may vary from disk to disk to provide a load bearing surface which is convex or angled to restore and/or maintain a desired or natural curvature of the spine.

A retaining member 322 may be provided on a distal end of hub portion 316 to secure disks 312 to hub portion 316. Retaining member 312 may be secured to hub portion 316 by screw threads or the like. It is also contemplated that hub portion 316 and or the central throughbore of some or all of disks 312 may be ribbed, grooved, knurled, or the like to retain disks 312 on hub portion 316. It is also envisioned that transverse portion 314 of hub member 310 and retaining member 322, which is also preferably formed from a resorbable polymer, can be load bearing members. As such, disks 312 need not be load bearing members.

FIG. 8 illustrates another preferred embodiment of the presently disclosed hybrid implant shown generally as 400. Implant 400 includes an outer housing or casing 410 having a body 412 defining a plurality of bores 414 and upper and lower load bearing surfaces 418 and 420. Although body 412 and bores 414 are <BR> <BR> illustrated as being cylindrical, other configurations are envisioned, e. g. , square, rectangular, etc. Casing 410 is preferably formed from a resorbable polymer although casing 410 may be formed from other resorbable and non-resorbable biocompatible materials.

Each of bores 414 is dimensioned to receive a core material 416 which is preferably bone, bone pieces or bone particles. The bone or bone pieces may be cylindrical or semi-cylindrical bone pieces cut from a source bone and/or bone pieces or particles which are positioned in each bore. A bone growth material such as Grafton@ or any of those listed above may be packed into some or all of bores 414 about core material to promote bone fusion. Upper and lower load bearing surfaces 418 and 420 may be flat, generally convex and/or angled to maintain and/or restore the desired or natural curvature of the spine.

FIGS. 9 and 10 illustrate another preferred embodiment of the presently disclosed hybrid implant shown generally as 500. Implant 500 includes a housing or casing 510 and a plurality of inner core members 512. Casing 510 is preferably formed from a resorbable polymer although casing 510 may be formed from other resorbable and non-resorbable biocompatible materials. Casing 510 includes a body 514 defining a plurality of throughbores 516, each being dimensioned to receive and frictionally retain a respective core member 512.

Although two throughbores 516 are illustrated in FIGS. 9 and 10, casing 510 may include one or more throughbores 516. For example, FIG. 11 illustrates another preferred embodiment of the presently disclosed implant shown generally as 500'. Implant 500'is substantially the same as implant 500 but includes a casing 510'which has six throughbores 516'. Each throughbore 516'is dimensioned to receive and frictionally retain a core member 512'.

Referring again to FIGS. 9 and 10, each core member 512 is preferably formed from cortical, cancellous or cortico-cancellous bone and has upper and lower bearing surfaces 518 and 520. Upper and lower bearing surfaces 518 and 520, although shown as being flat, may be generally convex or angled to maintain and/or restore the natural and/or desired curvature of the spine.

Further, upper and lower bearing surfaces 518 and/or 520 may include movement resistant structure, e. g. , projections, ribs, grooves, pyramidal teeth, stepped projections, notches or other such protrusions and/or recesses, to engage the vertebral endplates and decrease the risk of implant expulsion.

Referring to FIG. 12, in one preferred embodiment, throughbores 516 are defined by a wall 516a having an irregular shape. The irregular shape functions to retain a respective core member 512 within bore 516 of casing 510 and defines interstices into which bone growth material, such as Grafton@ or any of the materials listed above, can be packed. The irregular shape may include a series of convexities 516b, protrusions, or the like.

FIGS. 13 and 14 illustrate yet another preferred embodiment of the presently disclosed hybrid implant shown generally as 600. Implant 600 includes a casing 610 and a core member 612. Casing 610 includes a body 614 defining a throughbore 615 which is preferably formed from a resorbable polymer although body 614 may be formed from other resorbable and non-resorbable biocompatible materials. Body 614 includes a connector, e. g. , a dovetail connector 616, formed on one side thereof and a recess 618 for receiving a connector 616 on an opposite side thereof. Connector 616 is slidably receivable in recess 618 to releasably join body 614 to body 614a of a second casing 61 osa.

Connector 616 and recess 618 allow multiple casings to be connected together to provide an adjustable size implant.

Throughbore 615 of casing 610 is dimensioned and configured to receive and frictionally retain a core member 612 which is preferably formed from cancellous, cortical and/or cortico-cancellous bone. Each core member 612 includes a body 620 and upper and lower bearing surfaces 622 and 624.

Although illustrated as being flat, bearing surfaces 622 and/or 624 may be generally convex or angled to maintain and/or restore the natural and/or desired curvature of the spine. Bearing surfaces 622 and/or 624 may also include <BR> <BR> movement resistant structure, e. g. , projections, ribs, grooves, pyramidal teeth,<BR> stepped projections, notches, recesses, etc. , to engage the vertebral endplates and decrease the risk of implant expulsion.

Although hybrid implant 600 is illustrated as being configured to receive a substantially cylindrical core member 612, other configurations are envisioned, e. g. , rectangular, square, etc. Further, although casing 610 is illustrated with dove-tailed connectors, the use of other known connectors is contemplated. For example, FIG. 15 illustrates another preferred hybrid implant, shown generally as 700, which includes a casing 710 having a rectangular throughbore 715 for receiving and frictionally retaining a correspondingly shaped core member (not shown). Casing 710 includes a first connector 716 including a prong having a pair of nubs 716a and a second connector 718 defining a slot having recesses 718a for releasably receiving nubs 716a. Connectors 716 and 718 are releaseably engageable with the connectors of a second casing 71 Oa to allow multiple casings to be releasably secured together to provide an implant of adjustable size.

FIGS. 16 and 17 illustrate another preferred embodiment of the presently disclosed hybrid implant shown generally as 800. Implant 800 includes a casing 810 having a body 812. Body 812 is preferably formed from a resorbable polymer although body 812 may be formed from other known resorbable and non-resorbable biocompatible materials. Body 812 includes a first C-clip 814a and a second C-clip 814b which are connected together by a central spacer 816.

C-clips 814a and 814b are preferably resilient and are capable of flexing outwardly to receive and retain a core member 820 therein. Alternately C-clips 814a and 814b may be rigid but capable of slidably receiving a core member 820. A C-clip 814c from a second casing 81 Oa can be positioned about a core member 820 already received in casing 810 to releasably secure multiple casings and core members together as a single unit (See FIG. 17).

Each core member 820 is preferably formed from cancellous, cortical or cortico-cancellous bone and includes upper and lower load bearing surfaces 822 and 824, respectively. Bearing surfaces 822 and 824 may be flat, generally convex and/or angled to maintain and/or restore the natural or desired curvature of the spine. Bearing surfaces 822 and 824 may also include movement resistant structure, e. g. , projections, ribs, grooves, pyramidal teeth, stepped projections, notches, or other such protrusions and/or recesses, to engage the vertebral endplates and decrease the risk of implant expulsion.

FIG. 18 illustrates another preferred embodiment of the presently disclosed hybrid implant shown generally as 900. Hybrid implant 900 includes a band or strap member 910 and a plurality of core members 912. Band or strap member 910 which may be adjustable, e. g. , a hose clamp, or resilient or stretchable, is positioned about a plurality of core members 912 to fasten the core members into a integral structure. Alternately, band 910 may be woven about the core members to secure the core members in an integral unit.

Preferably, band or strap member 910 is constructed from a resorbable polymer.

Alternately, the band or strap member may be constructed from other resorbable and non-resorbable biocompatible materials. Core members 912 are preferably formed from cancellous, cortical, and/or cortico-cancellous bone of autogenic, allogenic or xenogenic origin. As discussed with respect to the embodiments disclosed above, at least some of core members 912 include upper and lower bearing surfaces which may be flat, generally convex, and/or angled to maintain and/or restore the natural or desired curvature of the spine. The upper and lower bearing surfaces may also include movement resistant structure as identified above, to minimize the risk of implant expulsion from the intervertebral space.

FIG. 19 illustrates yet another embodiment of the presently disclosed hybrid implant shown generally as 1000. Hybrid implant 1000 includes a first portion including a plurality of core members, e. g. , bone particles 1012a and 1012b and a second portion 1010 including at least one suture for securing the bone particles 1012a and 1012b together into a load bearing construct. Although only first and second bone particles are illustrated, a multiplicity of bone particles can be secured together to construct an implant having any desired shape, e. g., cylindrical, rectangular, tapered, or any other irregular or regular shape desired.

Referring to FIG. 20, it is also envisioned that a plurality of bone particles 1112a-d can be joined together using pins 1110, screws or the like. Although implant 1100 is illustrated as being a rectangular block, other regular and irregular implant shapes are envisioned. Suture 1010 and pins 1110 any of the resorbable or non-resorbable materials identified above. Further, in addition to the pins and sutures disclosed above, a variety of different types of connectors <BR> <BR> may be used to secure the core members, e. g. , bone particles, together, e. g., clips.

Each of the hybrid implants disclosed above may include insertion tool engagement structure for releasably attaching the implant to an implant insertion tool. The insertion tool engagement structure may be any structure capable of <BR> <BR> performing the desired function, e. g. , threaded bore (s), slots, triangular, square, circular openings or protrusions, etc. Preferably, the insertion tool engagement structure is formed in or on the resorbable polymer portion of the implant, although it is envisioned that this structure could be formed into bone. The implants disclosed above may also be assembled at the time of manufacture, by a surgeon immediately prior to implantation or during a surgical procedure in the intervertebral space.

It will be understood that various modifications may be made to the embodiments disclosed herein. For example, each of the hybrid implants disclosed may be dimensioned to replace an entire vertebral body and its associated disks or reconfigured and dimensioned to serve as an implant to correct other defects in the skeletal system. Moreover, tissue other than bone may be augmented using the techniques described herein. For example, synthetic pins or clips may be used to join pieces of tissue, e. g., <BR> <BR> tendons, ligaments, etc. , to facilitate repair of other body parts. 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.