Abstract:
Implants and methods for augmentation of the disc space between two vertebral bodies to treat disease or abnormal pathology conditions in spinal applications. The implant includes a chain of biocompatible material suitable for insertion into a disc space between two adjacent vertebral bodies in a patient&#39;s spinal column, wherein the spinal disc space has a transverse plane. The chain comprises a plurality of adjacent bodies having a height configured to reside within the disc space between two adjacent vertebral bodies and a length configured to reside in the disc space between two adjacent vertebral bodies when the chain is curved in an orientation substantially along the transverse plane of the spinal disc space.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 11/633,131, filed Dec. 1, 2006, which claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 60/753,782, filed Dec. 23, 2005 and U.S. Provisional Patent Application No. 60/810,453, filed Jun. 2, 2006, the entirety of each of which is incorporated by reference herein. 
    
    
     FIELD OF INVENTION 
     The invention relates to implants, and more particularly to flexible chain implants for augmenting or supporting bones or other structures, such as, for example vertebral discs. 
     BACKGROUND OF THE INVENTION 
     Vertebral compression fractures, as illustrated in  FIG. 1 , represent a generally common spinal injury and may result in prolonged disability. These fractures involve collapsing of one or more vertebral bodies  12  in the spine  10 . Compression fractures of the spine usually occur in the lower vertebrae of the thoracic spine or the upper vertebra of the lumbar spine. They generally involve fracture of the anterior portion  18  of the affected vertebra  12  (as opposed to the posterior side  16 ). Spinal compression fractures can result in deformation of the normal alignment or curvature, e.g., lordosis, of vertebral bodies in the affected area of the spine. Spinal compression fractures and/or related spinal deformities can result, for example, from metastatic diseases of the spine, from trauma or can be associated with osteoporosis. Until recently, doctors were limited in how they could treat such compression fractures and related deformities. Pain medications, bed rest, bracing or invasive spinal surgery were the only options available. 
     More recently, minimally invasive surgical procedures for treating vertebral compression fractures have been developed. These procedures generally involve the use of a cannula or other access tool inserted into the posterior of the effected vertebral body, usually through the pedicles. The most basic of these procedures is vertebroplasty, which literally means fixing the vertebral body, and may be done without first repositioning the bone. 
     Briefly, a cannula or special bone needle is passed slowly through the soft tissues of the back. Image guided x-ray, along with a small amount of x-ray dye, allows the position of the needle to be seen at all times. A small amount of polymethylmethacrylate (PMMA) or other orthopedic cement is pushed through the needle into the vertebral body. PMMA is a medical grade substance that has been used for many years in a variety of orthopedic procedures. Generally, the cement is mixed with an antibiotic to reduce the risk of infection, and a powder containing barium ortantalum, which allows it to be seen on the X-ray. 
     Vertebroplasty can be effective in the reduction or elimination of fracture pain, prevention of further collapse, and a return to mobility in patients. However, this procedure may not reposition the fractured bone and therefore may not address the problem of spinal deformity due to the fracture. It generally is not performed except in situations where the kyphosis between adjacent vertebral bodies in the affected area is less than 10 percent. Moreover, this procedure requires high-pressure cement injection using low-viscosity cement, and may lead to cement leaks in 30-80% of procedures, according to recent studies. In most cases, the cement leakage does no harm. In rare cases, however, polymethyrnethacrylate or other cement leaks into the spinal canal or the perivertebral venous system and causes pulmonary embolism, resulting in death of the patient. 
     More advanced treatments for vertebral compression fractures generally involve two phases: (1) reposition, or restoration of the original height of the vertebral body and consequent lordotic correction of the spinal curvature; and (2) augmentation, or addition of material to support or strengthen the fractured or collapsed bone. 
     One such treatment, balloon kyphoplasty (Kyphon, Inc.), is disclosed in U.S. Pat. Nos. 6,423,083, 6,248,110, and 6,235,043 to Riley et al., each of which is incorporated by reference herein in its entirety. A catheter having an expandable balloon tip is inserted through a cannula, sheath or other introducer into a central portion of a fractured vertebral body comprising relatively soft cancellous bone surrounded by fractured cortical bone. Kyphoplasty then achieves the reconstruction of the lordosis, or normal curvature, by inflating the balloon, which expands within the vertebral body restoring it to its original height. The balloon is removed, leaving a void within the vertebral body, and PMMA or other filler material is then injected through the cannula into the void as described above with respect to vertebroplasty. The cannula is removed and the cement cures to augment, fill or fix the bone. 
     Disadvantages of this procedure include the high cost, the repositioning of the endplates of the vertebral body may be lost after the removal of the balloon catheter, and the possible perforation of the vertebral endplates during the procedure. As with vertebroplasty, perhaps the most feared, albeit remote, complications concerning kyphoplasty are related to leakage of bone cement. For example, a neurologic deficit may occur through leakage of bone cement into the spinal canal. Such a cement leak may occur through the low resistance veins of the vertebral body or through a crack in the bone which was not appreciated previously. Other complications include additional adjacent level vertebral fractures, infection and cement embolization. Cement embolization occurs by a similar mechanism to a cement leak. The cement may be forced into the low resistance venous system and travel to the lungs or brain resulting in a pulmonary embolism or stroke. 
     Another approach for treating vertebral compression fractures is the Optimesh system (Spineology, Inc., Stillwater, Minn.), which provides minimally invasive delivery of a cement or allograft or autograft bone using an expandable mesh graft balloon, or containment device, within the involved vertebral body. The balloon graft remains inside the vertebral body after its inflation, which prevents an intraoperative loss of reposition, such as can occur during a kyphoplasty procedure when the balloon is withdrawn. One drawback of this system, however, is that the mesh implant is not well integrated in the vertebral body. This can lead to relative motion between the implant and vertebral body, and consequently to a postoperative loss of reposition. Additional details regarding this procedure may be found, for example, in published U.S. Patent Publication Number 20040073308, which is incorporated by reference herein in its entirety. 
     Still another procedure used in the treatment of vertebral compression fractures is an inflatable polymer augmentation mass known as a SKy Bone Expander. This device can be expanded up to a pre-designed size and (Cubic or Trapezoid) configuration in a controlled manner. Like the Kyphon balloon, once optimal vertebra height and void are achieved, the SKy Bone Expander is removed and PMMA cement or other filler is injected into the void. This procedure therefore entails many of the same drawbacks and deficiencies described above with respect to kyphoplasty. 
     In some cases of fractured or otherwise damaged bones, bone grafts are used to repair or otherwise treat the damaged area. In the United States alone, approximately half a million bone grafting procedures are performed annually, directed to a diverse array of medical interventions for complications such as fractures involving bone loss, injuries or other conditions necessitating immobilization by fusion (such as for the spine or joints), and other bone defects that may be present due to trauma. infection, or disease. Bone grafting involves the surgical transplantation of pieces of bone within the body, and generally is effectuated through the use of graft material acquired from a human source. This is primarily due to the limited applicability of xenografts, transplants from another species. 
     Orthopedic autografts or autogenous grafts involve source bone acquired from the same individual that will receive the transplantation. Thus, this type of transplant moves bony material from one location in a body to another location in the same body, and has the advantage of producing minimal immunological complications. It is not always possible or even desirable to use an autograft. The acquisition of bone material from the body of a patient typically requires a separate operation from the implantation procedure. Furthermore, the removal of material, oftentimes involving the use of healthy material from the pelvic area or ribs, has the tendency to result in additional patient discomfort during rehabilitation, particularly at the location of the material removal. Grafts formed from synthetic material have also been developed, but the difficulty in mimicking the properties of bone limits the efficacy of these implants. 
     As a result of the challenges posed by autografts and synthetic grafts, many orthopedic procedures alternatively involve the use of allografts, which are bone grafts from other human sources (normally cadavers). The bone grafts, for example, are placed in a host bone and serve as the substructure for supporting new bone tissue growth from the host bone. The grafts are sculpted to assume a shape that is appropriate for insertion at the fracture or defect area, and often require fixation to that area for example by screws, pins, cement, cages, membranes, etc. Due to the availability of allograft source material, and the widespread acceptance of this material in the medical community, the use of allograft tissues is likely to expand in the field of musculoskeletal surgery. 
     Notably, the various bones of the body such as the femur (thigh), tibia and fibula (leg), humerus (upper arm), radius and ulna (lower arm) have geometries that vary considerably. In addition, the lengths of these bones vary; for example, in an adult the lengths may vary from 47 centimeters (femur) to 26 centimeters (radius). Furthermore, the shape of the cross section of each type of bone varies considerably, as does the shape of any given bone over its length. While a femur has a generally rounded outer shape, a tibia has a generally triangular outer shape. Also, the wall thickness varies in different areas of the cross-section of each bone. Thus, the use of any given bone to produce an implant component may be a function of the bone&#39;s dimensions and geometry. Machining of bones, however, may permit the production of implant components with standardized or custom dimensions. 
     As a collagen-rich and mineralized tissue, bone is composed of about forty percent organic material (mainly collagen), with the remainder being inorganic material (mainly a near-hydroxyapatite composition resembling 3Ca 3 (PO 4 ) 2 Ca(OH) 2 ). Structurally, the collagen assumes a fibril formation, with hydroxyapatite crystals disposed along the length of the fibril, and the individual fibrils are disposed parallel to each other forming fibers. Depending on the type of bone, the fibrils are either interwoven, or arranged in lamellae that are disposed perpendicular to each other. 
     Bone tissues have a complex design, and there are substantial variations in the properties of bone tissues depending upon the type of bone (i.e., leg, arm, vertebra) as well as the overall structure. For example, when tested in the longitudinal direction, leg and arm bones have a modulus of elasticity of about 17 to 19 GPa, while vertebra tissue has a modulus of elasticity of less than 1 GPa. The tensile strength of leg and arm bones varies between about 120 MPa and about 150 MPa, while vertebra have a tensile strength of less than 4 MPa. Notably, the compressive strength of bone varies, with the femur and humerus each having a maximum compressive strength of about 167 MPa and 132 MPa respectively. Again, the vertebra have a far lower compressive strength usually of no more than about 10 MPa. 
     With respect to the overall structure of a given bone, the mechanical properties vary throughout the bone. For example, a long bone (leg bone) such as the femur has both compact bone and spongy bone. Cortical bone, the compact and dense bone that surrounds the marrow cavity, is generally solid and thus carries the majority of the load in major bones. Cancellous bone, the spongy inner bone, is generally porous and ductile, and when compared to cortical bone is only about one-third to one-quarter as dense, one-tenth to one-twentieth as stiff, but five times as ductile. While cancellous bone has a tensile strength of about 10-20 MPa and a density of about 0.7 g/cm 3 , cortical bone has a tensile strength of about 100-200 MPa and a density of about 2 g/cm 3 . Additionally, the strain to failure of cancellous bone is about 5-7%, while cortical bone can only withstand 1-3% strain before failure. It should also be noted that these mechanical characteristics may degrade as a result of numerous factors such as any chemical treatment applied to the bone material, and the manner of storage after removal but prior to implantation (i.e. drying of the bone). 
     Notably, implants of cancellous bone incorporate more readily with the surrounding host bone, due to the superior osteoconductive nature of cancellous bone as compared to cortical bone. Furthermore, cancellous bone from different regions of the body is known to have a range of porosities. For example, cancellous bone in the iliac crest has a different porosity than cancellous bone in a femoral head. Thus, the design of an implant using cancellous bone may be tailored to specifically incorporate material of a desired porosity. 
     There remains a need in the art to provide safe and effective devices and methods for augmentation of fractured or otherwise damaged vertebrae and other bones, preferably devices that may be implanted utilizing minimally invasive methods of implantation. 
     SUMMARY OF THE INVENTION 
     A flexible chain according to one embodiment comprises a series or other plurality of preferably solid, substantially non-flexible body portions (also referred to as bodies or beads) and a series of flexible link portions (also referred to as links or struts). The preferably solid, substantially non-flexible body portions preferably are capable of withstanding loads that are applied in any direction, and the flexible link portions of the implant preferably are disposed between the substantially non-flexible body portions and preferably are flexible in any direction, although they may be flexible in only selected or desired directions. The bodies may be substantially solid, semi-solid or hollow and preferable of sufficient strength to support the loads typical for the body location in which they are implanted. The link portions may be solid, semi-solid, or hollow and preferably of sufficient flexibility to allow the adjacent bodies to touch one another upon bending of the elongate member or chain. The material of both portions, the flexible link and non-flexible body portions, preferably is the same and form one single, flexible monolithic chain (FMC). 
     In one aspect of the invention, an apparatus for augmentation of body tissue, for example bone, comprises a flexible elongated member, or chain, having a longitudinal length substantially larger than its height or its width. The flexible elongated member comprises a plurality of substantially non-flexible bodies and a plurality of substantially flexible links interconnecting the bodies. The bodies and links are connected end-to-end to form the elongated member, wherein the elongated member is formed of a biocompatible material. 
     The bodies may be different sizes and shapes than the links or they may be the same shape, same size, or both. In addition, each body and link may be a different size and shape than other bodies or links. In one embodiment, the beads can be shaped so that they can fit together to minimize interstial spaces. For example, the beads may be shaped as cubes or other polyhedrals that can be stacked together in such a way that there is little space between beads, or a predetermined percentage range of interstial space. 
     The elongated member may be formed as an integral monolithic chain, which may be formed of bone, such as, for example, allograft bone. The flexible links may be formed of bone that has been demineralized to a greater extent than the bodies. Optionally, a coating may be applied to at least a portion of the elongated member, e.g. a coating comprising a therapeutic agent, a bone cement, an antibiotic, a bone growth stimulating substance, bone morphogenic protein (BMP) or any combination thereof. Therapeutic agents, or drug agents (e.g., antibodies), or biologics (e.g., one or more BMPs) can be coated, or attached via peptides, adsorbed, sorbed or in some other way perfused onto or into the elongated member; either the bodies, the links or both. In some embodiments, the coating may comprise a bone cement that may be activated upon insertion into the bone. In other embodiments, at least a portion of the bodies comprise an outer surface configured to promote bone in-growth. 
     In another aspect, a flexible chain implant may be impacted or inserted into a cavity, void or hollow space, e.g., through a small narrow opening. Such cavities may be, for example, voids in long bones, intervertebral disc spaces or vertebral bodies. Such voids may have occurred due to infections, disease, trauma fractures, degenerative disc disease process, tumors or osteotomies. In other embodiments, a void may be created by using a tool to compact or remove cancellous or cortical bone or other tissue prior to implantation. The chain may thereafter be implanted to fill the created void. Depending on the insertion or impaction force and depending on the amount or the length of chain devices inserted, the device will fill and/or support the tissue structure, preferably bone structure to a restored size and/or height. In an alternative embodiment, no void or cavity may be present, and even if a void or cavity is present the chain implant or elongated member may be inserted and/or implanted in a manner to compact the material and bone cells within the bone and to further fill the bone in a manner that it can better support a load and preferably fill the bone in a manner to restore its original and/or treated size and height. 
     In another aspect, one or more flexible monolithic chains may be implanted into diseased, damaged or otherwise abnormal bones to treat, for example, long bone infections, comminuted complex fractures, tumor resections and osteotomies. An FMC device may also be used to treat disease or abnormal pathology conditions in spinal applications, including, for example, degenerative disc disease, collapsed intervertebral discs, vertebral body tumor or fractures, and vertebral body resections. The elongated member or chain device can be used as a preventive measure to augment a bone, spinal disc or an implant, e.g., and intervertebral body implant to promote fusion. The elongated member may be used within a vertebra or between two vertebra. The elongated member or chain also may be used for example in an intervertebral body fusion procedure, for example, as an implant inserted into the disc space between two vertebra, as an implant inserted into and retained by the disc annulus, or in combination with an additional implant inserted in the disc space between two vertebra. 
     In yet another embodiment, the present invention provides a method for augmenting adjacent vertebrae, the method comprising the steps of: creating a void in an intervertebral disc by removing tissue from the disc; inserting into the void an apparatus comprising a chain comprising at least one non-flexible body; and at least one flexible portion comprising a joint, wherein the at least one non-flexible body is adjacent to the at least one flexible portion, such that the chain fills the void created in the intervertebral disc. 
     In another embodiment, a kit comprises various combinations of assemblies and components according to the present invention. A kit may include, for example, a package or container comprising an elongated member, for example an FMC device, and a cannula or other introducer or device for implanting the elongated member. In other embodiments, a kit may comprise instruments to create a cavity (e.g., balloon catheter), an FMC device and a cement or other filler material and/or a syringe or other apparatus for injecting a FMC device and/or such filler material into a vertebral body. 
     In another aspect, the present invention provides a system suitable for insertion between two vertebral bodies to treat disease or abnormal pathology conditions in spinal applications, the system comprising: a chain of biocompatible material suitable for insertion into a disc space between two adjacent vertebral bodies in a patient&#39;s spinal column, wherein the spinal disc space has a transverse plane, the chain comprising: a plurality of adjacent bodies having a height configured to reside within the disc space between two adjacent vertebral bodies and a length configured to reside in the disc space between two adjacent vertebral bodies when the chain is curved in an orientation substantially along the transverse plane of the spinal disc space; and wherein the plurality of adjacent bodies are interconnected such that the adjacent bodies can angulate during insertion into the spinal disc space with respect to each other along the transverse plane of the spinal disc and into a curved orientation that allows the chain to reside within the spinal disc space. 
     In yet another embodiment, the present invention provides a method for augmenting adjacent vertebrae, the method comprising the steps of: creating a space in an intervertebral disc by removing tissue from the disc, wherein the intervertebral disc is located between two adjacent vertebral bodies in a patient&#39;s spinal column, wherein the space has a transverse plane; inserting through a cannula into the space an apparatus comprising a chain of biocompatible material suitable for insertion into the space, the chain comprising: a plurality of adjacent bodies having a height and length configured to reside within the space when the chain is curved in an orientation substantially along the transverse plane of the space; and wherein the plurality of adjacent bodies are interconnected such that the adjacent bodies can angulate during insertion into the space with respect to each other along the transverse plane of the disc and into a curved orientation that allows the chain to reside within the space. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention can be better understood by reference to the following drawings, wherein like references numerals represent like elements. The drawings are merely exemplary to illustrate certain features that may be used singularly or in combination with other features and the present invention should not be limited to the embodiments shown. 
         FIG. 1  is a side view of a portion of a spine with a vertebral compression fracture. 
         FIG. 2A  is a side view of a flexible monolithic chain according to an embodiment of the present invention. 
         FIG. 2B  is a close-up cross-sectional side view of the flexible monolithic chain of  FIG. 2A  taken through line B-B. 
         FIGS. 3  A-D is an illustration depicting a method of fabricating a flexible monolithic chain. 
         FIGS. 4A-C  are perspective views of other embodiments of a flexible monolithic chain having flexible portions and non-flexible portions with substantially uniform dimensions. 
         FIG. 5  is a perspective, cross-sectional view of another embodiment of a flexible monolithic chain. 
         FIGS. 6A  and B are side cross-sectional views of a flexible monolithic chain being implanted within a fractured vertebral body. 
         FIG. 7  is a cross-sectional top view of a flexible monolithic chain implanted within a vertebral body. 
         FIG. 8A  is a cross-sectional side view of a vertebra having a flexible monolithic chain implanted within a vertebral body. 
         FIG. 8B  is a cross-sectional side view of a vertebra having an implanted flexible monolithic chain as in  FIG. 8A , showing an end of the chain extending from the vertebra. 
         FIG. 8C  is a cross-sectional side view of a vertebra having an implanted flexible monolithic chain as in  FIG. 8A , and further including a pedicle screw implant. 
         FIGS. 9A-D  are top views depicting a minimally invasive method for implanting a flexible monolithic chain within a vertebral body. 
         FIG. 10A  is a cross-sectional top view of another method of implanting a flexible monolithic chain within a vertebral body. 
         FIG. 10B  is a top view of a flexible monolithic chain that may be used in the method of  FIG. 10A . 
         FIG. 10C  is a side view of another embodiment of a flexible monolithic chain that may be used in the method of  FIG. 10A . 
         FIG. 11A  is a side view of a screw device for driving a chain implant through an introducer. 
         FIG. 11B  is an end view of a screw device for driving a chain implant through an introducer. 
         FIG. 12  is a side view of a plunger device for driving a chain implant through an introducer. 
         FIG. 13  is a side view of a sprocket device for driving a chain implant through an introducer. 
         FIGS. 14A  and B are cross-sectional side views of a flexible monolithic chain implanted into the head of a femur. 
         FIG. 15  is a cross-sectional view of a chain implant inserted through a cannula into the head of a femur. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 2 , a chain  200  (sometimes referred to as an elongated member) comprises one or more bodies  210  (sometimes referred to as beads). Chain  200  is preferably a monolithic chain, e.g., formed from a single, common material or type of material forming an integral structure. Bodies  210  are preferably substantially non-flexible, and may be solid, semi-solid, porous, non-porous, hollow, or any combination thereof. Chain  200  may also comprise one or more linking portions  220 , also sometimes referred to as struts or links  220 . Struts  220  may be disposed between each pair of adjacent bodies  210 . Struts  220  are preferably substantially flexible or semiflexible, e.g. to allow for bending of the chain  200  between bodies  210 . 
     Bodies  210  of chain  200  are preferably formed of bone, e.g., cortical bone, cancellous bone or both, but preferably cortical bone. In other embodiments, chain  200  may be comprised of any biocompatible material having desired characteristics, for example a biocompatible polymer, metal, ceramic, composite or any combination thereof. Bodies  210  may be absorbable or resorbable by the body. For some applications, the bodies  210  preferably have osteoinductive properties or are made at least partly from osteoinductive materials. The outer circumferential shape of the body may be the same as adjacent links. Alternatively or in addition, the outer circumferential shape of the body may be the same size as adjacent links. Bodies  210  may be of uniform or non-uniform size, shape and/or materials, and may be linked in series, for example by one or more flexible or semi-flexible linking portions  220 , which can form struts of any desired length between bodies  210 . Linking portions are preferably, although not necessarily, formed of the same material as bodies  210 . 
     A chain  200  may have any desired number of linked bodies  210 , and may have a first end  202  and a second end  204 . In other embodiments, chain  200  may be formed in a loop, ring, or other configuration having no ends, or may be configured to have multiple extensions and/or multiple ends, for example like branches of a tree. 
     The one or more linking portions  220  may be comprised of any biocompatible material having desired characteristics of flexibility, strength, and the like. In preferred embodiments, linking portions  220  may be formed, at least in part, of substantially the same material as bodies  210 . In some embodiments, chain  200 , including bodies  210  and/or linking portions  220 , may be resorbable. The bodies  210  may be of uniform or non-uniform size, and may be spaced by linking portions  220  at uniform or non-uniform increments. 
       FIG. 2B  is a close up cross-sectional view of chain  200 , taken at line B-B in  FIG. 2A . In this example, chain  200  is a monolithic chain, with bodies  210  and flexible portions  220  formed from a uniform material, e.g., bone. Although bodies  210  are shown as substantially spherical, and linking portions  220  are shown as substantially cylindrical, numerous other shapes are contemplated. In fact, chains  200 , including body  210  and/or linking portion  220 , may be of any desired shape, such as for example, cylindrical, elliptical, spherical, rectangular, etc. Body  210  and/or linking portion  220  may also be of any particular cross sectional shape such as round hexagonal, square, etc. Bodies  210  and linking portions  220  may have the same or different shapes. In certain embodiments the configurations of bodies  210  may vary within a chain  200 , for example as described herein with respect to  FIGS. 5 and 10 . Alternatively or in addition thereto, the configuration of links  220  may vary within a chain. In one embodiment, the bodies can be shaped so that they fit together to minimize interstitial spacing or provide a predetermined range of interstitial spacing. 
     All dimensional aspects of the chain  200  can be made to fit any particular anatomy or delivery device. For example, for applications of vertebral body augmentation, the diameter  230  of bodies  210 , e.g., as shown in  FIG. 2B , may be between about 1 mm and about 15 mm, preferably between about 2 mm and about 8 mm, or more preferably between about 4 mm and about 6 mm. Preferably, the non-flexible bodies  210  are larger in shape and size than the flexible struts  220 . For example, height  232  of struts  220  may be between about 0.5 mm and about 8 mm, preferably between about 0.8 mm and about 4 mm, and may depend in part upon the size of bodies  210 . Struts  220  may have any desired length  238 , e.g., between about 0.5 mm and about 5.0 mm, preferably between about 1.5 mm and 3.5 mm, or greater than 5 mm. Similarly, distance  234  between bodies  210  may be any desired distance, e.g., depending upon the size of bodies  210  and/or length  238  struts  220 . In some embodiments, for example, distance  234  may be between about 4 mm and about 15 mm, or between about 6 mm and about 10 mm. The junctions between bodies  210  and struts  220  may have a radius  236  of any desired dimension, e.g., less than 1.0 mm, between about 1.0 mm and about 2.0 mm, or greater than about 2.0 mm. 
     In some embodiments, each of the bodies  210  and struts  220  of a chain may be of the same configuration and/or dimensions as other bodies  210  and struts within the chain  200 . In other embodiments, bodies  210  and/or struts  220  within a chain may have different configurations or dimensions. In still other embodiments, the non-flexible bodies  210  and flexible portions  220  may be of the same shape and size to form a relatively uniform structure, for example as shown in  FIG. 4 . 
     A chain  200  may be made as long as practical for a particular application. For example, an exemplary chain  200  for implantation into a bone may be about 100 mm in length. In other embodiments, chain  200  may be of other lengths, for example less than about 1 mm, between about 1 mm and about 100 mm, or greater than 100 mm. In some embodiments, two or more chains  200  and/or other implants may be used in combination with each other. Chain  200  may be connected end to end to form larger chains. 
     While the present invention is preferably directed to the creation of implants from allograft material, the present invention may also be applied to implants that utilize other materials, including but not limited to the following: xenograft, autograft, metals, alloys, ceramics, polymers, composites, and encapsulated fluids or gels. Furthermore, the implants described herein may be formed of materials with varying levels of porosity, such as by combined bone sections from different bones or different types of tissues and/or materials having varying levels of porosity. 
     Also, the implants described herein may be formed of bone materials with varying mineral content. For example, cancellous or cortical bone may be provided in natural, partially demineralized, or demineralized states. Demineralization is typically achieved with a variety of chemical processing techniques, including the use of an acid such as hydrochloric acid, chelating agents, electrolysis or other treatments. The demineralization treatment removes the minerals contained in the natural bone, leaving collagen fibers with bone growth factors including bone morphogenic protein (BMP). Variation in the mechanical properties of bone sections is obtainable through various amounts of demineralization. Advantageously, use of a demineralizing agent on bone, e.g., cortical or cancellous bone, transforms the properties of the bone from a stiff structure to a relatively pliable structure. Optionally, the flexibility or pliability of demineralized bone may be enhanced when the bone is hydrated. Any desired portions of bone components, e.g., ink portions  220  or any other desired portion, may be demineralized or partially demineralized in order to achieve a desired amount of malleability, elasticity, pliability or flexibility, generally referred to herein as “flexibility”. The amount of flexibility can be varied by varying in part the amount of demineralization. 
     In some embodiments, flexibility of demineralized or partially demineralized regions may be further enhanced by varying the moisture content of the implant or portions thereof. Bone components initially may be provided with moisture content as follows: (a) bone in the natural state fresh out of the donor without freezing, (b) bone in the frozen state, typically at −40° C., with moisture content intact, (c) bone with moisture removed such as freeze-dried bone, and (d) bone in the hydrated state, such as when submersed in water. Using the expansion and contraction properties that can be obtained during heating and cooling of the bone material, and the concomitant resorption of moisture along with swelling for some bone material, permits alternate approaches to achieving a desired flexibility of an implant within a bone or other region. 
     The implants may be formed entirely from cortical bone, entirely from cancellous bone, or from a combination of cortical and cancellous bone. While the implants may be created entirely from all bone material, it is also anticipated that one or more components or materials may be formed of non-bone material, including synthetics or other materials. Thus, while the implants disclosed herein are typically described as being formed primarily from bone, the implants alternatively may be formed in whole or in part from other materials such as stainless steel, titanium or other metal, an alloy, hydroxyapatite, resorbable material, polymer, or ceramic, and may additionally incorporate bone chips, bone particulate, bone fibers, bone growth materials, and bone cement. Also, while solid structures are described herein, the structure optionally may include perforations or through bores extending from one outer surface to another outer surface, or recesses formed in outer surfaces that do not extend through inner surfaces (surface porosity), or recesses formed internally. Surface texture such as depressions and/or dimples may be formed on the outer surface. The depressions and/or dimples may be circular, diamond, rectangular, irregular or have other shapes. 
     The flexible monolithic chain devices described herein may be used to treat disease and pathological conditions in general orthopedic applications such as long bone infections, comminuted complex fractures, tumor resections and osteotomies. 
     Additionally the device can be used to treat disease and pathological conditions in spinal applications, such as, for example, degenerative disc disease, collapsed intervertebral discs, vertebral body tumor or fractures, vertebral body resections or generally unstable vertebral bodies. In other embodiments, a flexible monolithic chain device may be used in maxillofacial applications or in non-fusion nucleus replacement procedures. 
       FIG. 3  shows an example of a method  300  for fabricating a monolithic chain device  200  out of bone material  310 . In this example, allograft femoral bone  310  is used as a base material, preferably, cortical allograft bone. Other bones may be used for forming implants, for example, radius, humerous, tibia, femur, fibula, ulna, ribs, pelvic, vertebrae or other bones. 
     As shown in  FIG. 3A , an initial step comprises machining a rough monolithic chain  200 ′, having a desired general shape, out of the raw material  310 , preferably bone. For example, conventional milling and/or other fabrication techniques may be used. Device  200 , may have any desired shape, for example including generally elliptical or spherical bodies  210  separated by cylindrical linking portions  220  as shown. Alternatively, chain  200  may be formed of a substantially uniform shape as shown, for example, in  FIG. 4 . 
     After machining the general desired shape in step A of  FIG. 3 , the rough monolithic device  200 ′ may then be removed from the raw material  310 , as shown for example in step B. In this example, an upper side  312  of the rough device  200 ′ has been fabricated to have a desired general shape as described above. An opposite side  314 , however, may include excess material that was not removed in step A. 
     In step C of the exemplary method of  FIG. 3 , opposite side  314  is machined to remove excess material, for example using conventional milling methods. Side  312  may also be further machined or shaped as desired, in order to form a monolithic chain device  200  having the desired shapes and configurations of bodies  210  and linking portions  220 . 
     In step D, the shaped chain  200 , if formed of bone, may be demineralized, e.g., in container  320  containing a demineralizing solution  322  (e.g., hydrochloric acid) or using another method. Demineralization may be allowed to occur for a specified amount of time, for example to allow the smaller, lower volume portions  220  of the device  200  to become more flexible or elastic, while the larger bodies  210  of the device remain structurally intact and substantially rigid. The amount of time and/or the concentration or composition of the demineralizing solution may be varied to provide the desired amount of flexibility or elasticity. 
     In some embodiments, this secondary process of demineralization can be applied to specific portions of the device  200 , e.g., by masking or shielding the portions that do not or should not be treated. For example, by masking the non flexible portions  210 , the flexible portions  220  can be partially or entirely demineralized, and the nonflexible portions  210  may retain their original mineralized state prior to the masking. Alternatively, an allograft device may be submerged entirely into demineralization acid without masking any portions of the device. Due to the relatively smaller shape and size of the flexible portions  220 , including the surface area exposed to the demineralized agent, and depending for example upon the amount of exposure to the demineralization acid, the flexible portions  220  may demineralize entirely, or at least substantially more than the larger portions  210 , which may undergo only surface demineralization. Therefore, the smaller portions  220  may become flexible and elastic while the larger portions  210  may remain relatively stiff and substantially non-flexible. For example,  FIG. 2B  shows regions  240  that are substantially demineralized and regions  242  that have substantially their natural or original composition and mineralization content. 
     The following Table 1 provides examples of demineralization times of four monolithic chains having different strut configurations. Each of the chains were formed of cortical allograft bone and had body portions  210  that were approximately 5 mm in diameter. Configurations and dimensions of the struts  220  differed between the samples. In all four samples, the struts were fully demineralized between about 3½ and 4 hours, while the beads were demineralized to an extent, but were not fully demineralized across their entire thickness. Strut dimensions correspond to distance  238  in  FIG. 2B , while strut radius corresponds to radius  236  in  FIG. 2B . Full flexibility is considered to be the condition when the chain can be bent until two adjacent beads contact each other without the chain cracking or breaking. While the foregoing is one manner to measure sufficient flexibility, other measures of flexibility are also contemplated and the invention should not be limited by such measure of flexibility. For example, less than full flexibility may be sufficient and desirable for insertion into vertebrae to augment and support the vertebral end plates. 
     
       
         
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Examples of demineralization times for 5 mm diameter chains 
               
               
                 having different strut configurations. 
               
             
          
           
               
                   
                   
                 Strut 
                 Chain 
                   
               
               
                   
                 Strut Dimensions 
                 Radius* 
                 Length 
                 Demineralization 
               
               
                 Sample 
                 (w × h × 1, in mm) 
                 (mm) 
                 (mm) 
                 Time** (min) 
               
               
                   
               
             
          
           
               
                 1 
                 1.5 × 1.5 × 3.2 
                 — 
                 76 
                 210 
               
               
                 2 
                 1.5 × 1.5 × 3.2 
                 1.57 
                 101 
                 255 
               
               
                 3 
                 1.0 × 1.4 × 3.0 
                 1.57 
                 93.35 
                 180 
               
               
                 4 
                 1.5 × 1.5 × 3.0 
                 1.57 
                 101 
                 180 
               
               
                   
               
               
                 *Radius between body 210 and strut 220 on top and bottom only 
               
               
                 **Time in hydrochloric acid IN solution to achieve full flexibility 
               
             
          
         
       
     
     Table 2 below provides an example of approximate incremental changes in flexibility of strut portions  220  of a sample, e.g., Sample 1 of Table 1, as a function of duration of exposure to the hydrochloric acid bath. 
     
       
         
               
             
               
               
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Incremental changes in flexibility of struts with exposure to acid bath. 
               
             
          
           
               
                   
                 Exposure Time 
                 Flexibility 
               
               
                   
                 (min) 
                 (% of maximum) 
               
               
                   
                   
               
             
          
           
               
                   
                 0-5 
                 0 
               
               
                   
                  5-10 
                 0 
               
               
                   
                 10-15 
                 10 
               
               
                   
                 15-20 
                 15 
               
               
                   
                 20-30 
                 25 
               
               
                   
                 30-45 
                 35 
               
               
                   
                 45-90 
                 50 
               
               
                   
                  90-140 
                 70 
               
               
                   
                 140-200 
                 85 
               
               
                   
                 200-240 
                 100 
               
               
                   
                   
               
             
          
         
       
     
     Of course, other samples will attain different flexibility in different exposure times depending upon a host of factors, including concentration of acid bath, chain dimensions, temperature, original bone sample mineralization and condition, etc. 
     Various other configurations and methods for manufacturing monolithic or other chain implants may be used. The choice of methods may depend, at least in part, on the material or materials to be used in the particular chain device  200 . If the device is made of a biocompatible polymeric material, the device can be manufactured by using conventional manufacturing methods such as but not limited to milling and turning. Alternatively, if the chain device  200  is made out of a biocompatible polymeric material, the entire device can also be injection molded. 
     If the chain  200  is made of a metallic material, it can be manufactured by using conventional manufacturing methods such as but not limited to milling and turning. However, the flexible components may undergo secondary processes such as annealing. The secondary process can be limited to the flexible portions of the device only, for example by masking or shielding the non-flexible portions. 
     In some embodiments, a chain implant  200  can be formed of any type of biocompatible material that will allow for sufficient flexibility in areas of reduced material sections (e.g., relatively narrow and flexible portions  220 ), while having larger sections (e.g., bodies  210 ) that are substantially rigid and allow for load bearing characteristics. The reduced material portions  220  may be flexible, pliable, or have elastic properties in all directions preferably without fracturing or breaking. Alternatively, the reduced material portions  210  may allow for fracture during device  200  insertion, or at another stage in a method, to allow for proper void filling. Materials may be metallic and include but are not limited to titanium and steels. Polymeric and alternatively allograft tissue materials can be used. Instead of or in addition to bone device  200  may comprise one or more other materials, e.g., a metal (titanium, a steel, or other metal), an alloy, or a polymer. In some embodiments, the material of the device  200  may have osteoconductive, osteoinductive, and/or osteogenic properties. In other embodiments, the implant device  200  may be made out of non-monolithic materials. 
     Referring to  FIGS. 4A-C , a chain  200  may have any desired geometric configuration. For example, rigid portions  210  and flexible portions  220  may have the same or different shapes, such as cubes, cylinders, any polyhedral shapes, balls, banana or kidney shaped, or any combination thereof. Portions  210  and/or  220  may have any desired cross-sectional shape, such as for example rectangular, circular, elliptical, pentagonal, hexagonal, etc. The flexible  220  and non-flexible  210  portions may be of the same shape to form relatively uniform shaped structures as shown in  FIGS. 4A-C . 
     As shown in  FIG. 5 , one or more bodies  210  may have cavities  510  or central holes  512 . Such holes  512  or cavities  510  may be empty or may be filled, for example with a cement, bone filler, adhesive, graft material, therapeutic agent, or any other desired materials. The filling material may incorporate radiopaque agents so that the chain, or bodies can be visualized during and after a procedure. In other embodiments, an implant device  200  may be coated with different substances that will support and promote bone healing, reduce infections and/or deliver therapeutic agents to the treated site. For example, the device  200  or portions thereof may be coated with antibiotics, BMP, bone growth enhancing agents, porous or non-porous bone ingrowth agents, therapeutic agents, etc. The implant may be coated with a material that may incorporate a radiopaque agent so that the implant may be visualized during or after implantation. In addition, therapeutic agents, drug agents, BMPs, tissue growth enhancing agents, osteoinductive agents may be absorbed, sorbed or otherwise perfused onto or into some portion of the chain implant. Additionally, the solid, non-flexible portions  210  may have cavities, axial or side holes or a combination thereof that can be filled with different substances or agents. 
     As shown in  FIGS. 6A and 6B , a minimally invasive method  600  of augmenting a damaged vertebral body  12 , e.g., following a vertebral compression fracture, may comprise implanting one or more chains  200  into an inner portion  612  of a vertebral body  12  between endplates  614  and  616 . Of course, one or more chains  200  may be implanted as a preventive measure to augment a vertebra before compression or a compression fracture. A hole may be formed in the outer coritcal shell of vertebral body  12  by a trocar, drill or other instrument. Chain  200  may then be implanted, for example, through a cannula  602  or other introducer inserted into vertebral body  12 . Suitable procedures and materials for inserting a cannula through which chain  200  may be introduced are known in the art, and may be similar to those described above for kyphoplasty and other procedures. For example, cannula  602  may be introduced through the posterior portion  16  of vertebral body  12 , e.g., through pedicle  14  (e.g., transpedicular approach). A chain  200  may be inserted and may compact the cancellous and osteoporotic bone inside the vertebral body. 
     Prior to insertion of the cannula, a passageway may be formed into the interior of the vertebral body, for example using a drill or other instrument. The chain  200  may then be inserted through the passageway, and may compact or compress the bone material inside the vertebral body. Alternatively, after the passageway is formed in the vertebral body, instruments such as, for example, currettes or balloon catheter may be used to compress and compact the bone inside the vertebral body to create a cavity. The instruments may then be removed. Alternatively, the balloon portion of the catheter may remain within the vertebral body or may form a container for the implant. The cavity in the vertebral body also may be formed by removing bone material as opposed to compacting the bone. For example, a reamer or other apparatus could be used to remove bone material from the inside of the vertebral body. 
     Whether a cavity is first formed in the bone structure or the chain(s) are inserted without first creating a cavity, as more linked bodies  210  of chain  200  are inserted into vertebral body  12 , they may fill central portion  612  and provide structural support to stabilize a vertebral body. In a vertebra that has collapsed, as the chain implant  200  fills central portion  612  the implant, and particularly the linked bodies  210 , can push against the interior or inner sides of endplates  614  and  616 , thereby tending to restore vertebral body  12  from a collapsed height h 1  to its original or desired treated height h 2  and provide structural support to stabilize vertebral body  12 . Instead of using the insertion of the chain implant to restore the height of the vertebra, an instrument can be inserted through the passageway to restore the height of the vertebra and plates. For example, a balloon catheter can be inserted to restore vertebra end plates, or an elongated instrument that contacts the inside of the end plates and pushes on them may be utilized. Additionally, the flexibility of one or more portions  220  between bodies  210  may allow bending of chain within space  612 , e.g., in a uniform pattern or in a nonuniform or tortuous configuration, to aid in ensuring a thorough integration of the implant  200  within the bone  12 . The configuration of bodies  210  attached by flexible portions also may permit bending to substantially fill the cavity and/or vertebral bone so no large pockets or voids are created or remain which may result in weak spots or a weakened bone structure. The flexible links may also allow the chain to collapse and possibly become entangled so that it becomes larger than its insertion hole so that it cannon be easily ejected. 
     In other embodiments, chain  200  may be inserted into a bone such as a vertebral body  12 , e.g., through the lumen  604  of a cannula  602  or other sheath, and such sheath may be removed after implantation within the bone  12 . In such embodiments, chain  200 , or a portion thereof, may remain in vertebral body  12 , for example, to continue augmenting the vertebra and maintain proper lordosis. In other embodiments, PMMA or another bone cement or filler (for example bone chips) may be inserted sequentially or simultaneously into vertebral body  12 , e.g., through shaft and/or a cannula  602 , along with bodies  210  to further enhance fixation or repair of the damaged region. Alternatively, only a plug of bone cement may be inserted into the hole that was initially formed to insert chains  200  (e.g., plug  812  of  FIG. 8A ). The plug may cover the insertion hole to prevent the implant (chains) from being removed or ejected. In other embodiments, some or all of bodies  210  of chain  200  may be removed after repositioning the bone, and PMMA or another bone cement or filler may be injected into a void created by chain  200 . Alternatively a bone growth promoting filler may be inserted into vertebral body  12  and a plug of bone cement utilized to hold the linked bodies and filler material in the vertebrae. 
     In some embodiments, flexible chain  200  may be coated with an adhesive, such that chain  200  may be inserted into vertebral body  12  in a flexible state and may become tangled and/or convoluted during or after insertion. After insertion, bodies  210  may become attached together by the adhesive so that the flexible chain becomes a mass that may be locked into the vertebral body, or otherwise secured such that chain  200  may not be easily removed through the insertion opening. 
     In other embodiments, linked bodies  210  may be coated with an adhesive and chain may be inserted, with or without becoming tangled or convoluted, into a vertebral body. During or after insertion of some or all linking bodies  210  of a chain  200 , a portion of chain  200  may be exposed to an energy source (e.g., an ultraviolet light, ultrasonic radiation, radio waves, heat, electric filed, magnetic field), for example to activate the adhesive, such that the exposed portion of chain  200  becomes joined to form a mass, or becomes rigid, or both, thereby further augmenting the vertebral body  12  and/or preventing removal or ejection of chain  200  through the insertion opening. 
       FIG. 7  is a top cross-sectional view illustration of a vertebral body  12  having one or more chains  200  implanted within portion  612  of vertebral body  12 . The one or more chains  200  may comprise a plurality of bodies  210 , which may be joined in series by one or more linking portions as described above. One or more cannulae  602 , each for example having a lumen  604  of sufficient size for passing linked bodies  210 , can be used to implant chain  200  into vertebral body. The one or more cannulae  602  may be inserted into vertebral body  12 , preferably through pedicles  14 . In some embodiments, the one or more cannulae  602  may be left within vertebral body  12 , and remain extending from pedicles  14 , for example held in place by sutures (not shown). 
     In some embodiments, chains  200  may be implanted completely within vertebral body  12  as shown in  FIG. 8A , and the cannulae or other introducer may be removed. The chains may remain entirely within the interior of the bone. A passageway  810  through which chains  200  were inserted may be filled with a plug  812 , e.g., a bone cement plug. Alternatively, as shown in  FIG. 8B , an end  204  of chain  200  may be left extending through the insertion hole of the bone, for example through the pedicle  14  of vertebra  12 . In other embodiments, as shown in  FIG. 8C , other implants or apparatus, such as for example a bone screw  800 , may be inserted into vertebral body  12  in conjunction with chain implant  200  to further augment vertebral body  12 . The extended end  204  or additional implant  800  may be used, for example, as an anchoring element for imparting an eternal force on vertebra to reposition the vertebra  12 . Screw  800  may be inserted into the opening used to insert the chains, and may further serve as a plug to prevent removal or ejection of the chains. Screw  800  may be hollow or solid, and may be comprised of stainless steel, a metal alloy, a ceramic, polymer, composite or any other desired material. In some embodiments, screw  800  may be hollow, e.g., including a lumen such as lumen  604  of cannula  602 , and used as an introducer to create a passage for passing chain  200  into vertebral body  12 . A bone cement or other material may be injected into vertebral body  12  to further secure implants  200  and/or  800  and augment vertebral body  12 . The bone cement or other material may be inserted through the cannulation of the screw. 
       FIGS. 9A-D  show another example of a flexible monolithic chain device being implanted into vertebral body. In  FIG. 9A , after a chain device  200  is unpacked, e.g., from a sterile package or container, it may be placed into an introducer or delivery device  910  that aids in insertion and/or impaction of the chain  200  to a desired cavity, void, space or interior of a bone. In this example, delivery device  910  has an elongated cannula-like shaft  912  having a lumen through which chain  200  may pass. Device may have a funnel  914  or other structure to facilitate loading of the chain  200  and/or for holding a portion of the chain  200  prior to implantation. An insertion end  916  of the insertion device  910  may have a tip  918 , which may be blunt, pointed, tapered or otherwise configured as desired to facilitate insertion of end  916  into a bone or other structure. 
       FIG. 9B  shows end  916  of insertion device  910  being inserted through pedicle  14  of vertebra  12 , such that tip  918  enters interior portion  612  of the vertebral body. An access hole may be formed in the outer cortical shell of the vertebral body by a trocar, drill or other instrument to provide a passage through which introducer  910  device may be inserted. After insertion of end  916  of delivery device  910  into the desired region, e.g., into a vertebral body  12 , preferably through a pedicle, chain  200  may be inserted. 
       FIG. 9C  shows first end  202  of a chain  200  being inserted through the introducer  910  into space  612  of vertebral body  12 . Chain  200  may be forced into vertebral body  12 , for example by manually applying an axial force from opposite end  204  of chain  200  to drive chain  200  through introducer  910 . In other embodiments, a displacement member, sprocket, screw mechanism, or other device is used to apply an axial force for implanting chain  200 , for example as described below with respect to  FIGS. 11-13 . In some embodiments, one long flexible monolithic device  200  may be inserted and impacted into the surgical site. Alternatively, multiple shorter or different chain devices  200  and/or other implants can be impacted or otherwise inserted into the desired cavity, void or space. The multiple shorter chain devices may be attached to each other sequentially end to end as they are inserted. In this manner as one chain is almost inserted, and with an end extending out of the patient, the leading end of the next chain is attached to the chain that is partially inserted.  FIG. 9D  shows the one or more chains  200  completely inserted into the central portion  612  of vertebral body  12 . 
     Other suitable procedures and materials for inserting a cannula through which an FMC may be introduced are described, for example, in U.S. Provisional Patent Application No. 60/722,064, filed Sep. 28, 2005 entitled “Apparatus and Methods for Vertebral Augmentation using Linked Bodies”, which is incorporated by reference herein in its entirety. A chain or other implant  200  may compact the cancellous and/or osteoporotic bone inside a collapsed vertebral body during insertion into the vertebral body. Alternatively, a tool such as, for example, currettes or balloon catheter may be used to compress and compact the bone inside the vertebral body to create a cavity. The cavity in the vertebral body also may be formed by removing bone material as opposed to compacting the bone. For example, a reamer or other apparatus could be used to remove bone material from the inside of the vertebral body. 
     In other embodiments, PMMA or another bone cement or filler (for example bone chips or material collected from reaming the bone) may be inserted into vertebral body  12 , e.g., through the introducer  910  or another cannula, sheath, syringe or other introducer, simultaneously with implant  200  to further enhance fixation or repair of a damaged region. Alternatively, the PMMA, bone cement or filler may be inserted into the interior of the bone after the chains (or portions thereof) have been inserted into the interior of the bone. Alternatively a bone growth promoting filler may be inserted into the vertebral body, and a plug of bone cement may be utilized to hold the implant  200  and filler material in the vertebrae  12 . In this manner, the plug of cement is not inserted into the interior of the bone, but covers the opening created in the bone to insert the implant. 
     A minimally invasive system for fusion or non-fusion implants and insertion instruments is shown in  FIGS. 10A-C . As described above, a flexible monolithic chain device  1000  device may be inserted into a vertebral body  12 , e.g., through a cannula  1030  or other introducer inserted through a pedicle  14  as shown in  FIG. 10A . 
     Optionally, a guide or other tool  1032  having a curved or otherwise configured tip  1034  may also be inserted through the cannula  1030  and serve to distract the end plates of the vertebral body  12  and/or guide the bodies  1010  of chain  1000  in a desired direction. As chain  1000  is forced into vertebral body  12 , flexible portions  1020  of chain  1000  may bend or flex to allow chain  1000  to curve or otherwise convolute in a desired fashion to fill the central portion  612 . The flexible portions allow the implant to fold and collapse upon itself to substantially fill the interior of the bone preferably with minimal porosity or open spaces. 
     As shown in  FIG. 10B , chain  1000  may have flexible portions, or struts,  1020  and non-flexible portions  1010  of different shapes. For example, flexible joints  1010  may be narrower than the non-flexible portions  1020 , which may be kidney shaped, rectangular, or any other shape. Some of the non-flexible bodies may be a different size or shape than others, for example they may increase in size from a first non-flexible body  1010 - 1  having a width Y 1  to a last non-flexible body  1010 - 5  having a width Y 2  that is larger than width Y 1 . For example, in the exemplary embodiment of  FIG. 10B , width Y 1  may be between about 5 mm and about 2 mm or less, and width Y 2  may be between about 6 mm and about 8 mm or less. Similarly, body  1010 - 1  may have a length X 1  that is substantially shorter than the length X 2  of body  1010 - 5 . For example, in the exemplary embodiment of  FIG. 10B , length X 1  may be between about 2 mm and about 6 mm, and length X 2  may be between about 6 mm and about 14 mm. Overall length of chain  1000  may vary depending upon the desired application, for example from about 10 mm to about 150 mm, more preferably from about 40 mm to about 100 mm. Of course various other sizes and relative differences in size or configuration of width, circumference, shape, curvature, or other dimensions of bodies  1010  and/or flexible portions  1020  may be employed without departing from the scope of the present invention. 
     In some embodiments, one or more of the bodies  1010  may have one or more openings or cavities  1012  or  1014 . Such openings or cavities  1012 ,  1014  may be empty or may be filled, for example with a cement, bone filler, adhesive, graft material, therapeutic agent, or any other desired materials. In other embodiments, an implant device  1000  may be coated with different substances that will support and promote bone healing, reduce infections and/or deliver therapeutic agents to the treated site. Additionally, the non-flexible or flexible portions may also have porous surfaces  1016 , for example to facilitate in growth of bone or other tissues. 
       FIG. 10C  shows another embodiment of a chain  1050 , having substantially rectangular or cylindrical bodies  1010 - 1 ,  1010 - 2 ,  1010 - 3 ,  1010 - 4  and  1010 - 5 , which may be separated by flexible link portions  1020 , and may have the same or different dimensions as each other. In  FIG. 10C  all of the bodies  1010 - 1 ,  1010 - 2 ,  1010 - 3 ,  1010 - 4  and  1010 - 5  have the same height h but different lengths. The struts  1020  in  FIG. 10C  have a different smaller height than the bodies  1010 . 
       FIG. 11  is a side view illustration of an insertion device  1100  for implanting a chain  200  into a bone or other desired structure. For example, insertion device  110  may include an insertion tube or cannula  1120  having a wall  1122  and a lumen  1223 . Disposed within and extending through at least a portion of lumen  1223  is a rotatable screw mechanism  1110  having spiral threads  1114  surrounding an axial shaft  1112 . Threads  1114  preferably extend from shaft and are dimensioned and spaced to engage chain  200 , e.g., between bodies  210 . When screw  1110  is rotated, e.g., by turning a handle  1130 , the threads  1114  engage bodies  210  and force chain  200  axially through the lumen  1223  of the cannula and into the desired bone or other region. Such an insertion device may allow for enhanced insertion force of an implant, for example in order to move vertebral end plates to restore the height of the end plates of a vertebra, to compress cancellous bone in a region of the implant, or to otherwise force the implant into a desired area. 
       FIGS. 12 and 13  show other mechanisms for forcing a chain  200  through an introducer and into a desired region. In particular,  FIG. 12  shows a plunger, pusher or other displacement member  1200  inserted within cannula  1102 . Displacement member  1200  may be used to displace or push bodies  210  of chain through cannula  1102  and into vertebral body  12 . Displacement member  1200  may be driven, for example, by pressure, e.g., from a syringe, rod, or other apparatus that forces displacement member  1200  into cannula  1102  and towards vertebral body  12 . In the embodiment of  FIG. 13 , a sprocket  1300  or apparatus that may be wheel-like and have teeth, gears or other extensions  1302  may be configured to engage bodies  210  of chain  200 . Sprocket  1300  rotates about a central axis  1304 , for example in a direction shown by arrow  1306 , teeth  1302  may engage bodies  210  and force chain  200  through cannula  1102  and into portion  612  of vertebral body  12 . In other embodiments, sprocket  1300  may be rotated in an opposite direction to remove some or all of chain  200 , for example after restoring a height of vertebral body  12 . The flexible monolithic chain devices and/or methods described herein may be used in conjunction with or instead of other methods or devices for augmenting vertebral bodies or other bones, such as, for example are described in U.S. Provisional Patent Application No. 60/722,064, filed Sep. 28, 2005 entitled “Apparatus and Methods for Vertebral Augmentation using Linked Bodies”, which is incorporated by reference herein in its entirety. 
     Although the apparatus and methods described herein thus far have been described in the context of repositioning and augmenting vertebrae for example in the context of vertebral compression fractures and deformations in spinal curvature, various other uses and methods are envisioned. For example, in some embodiments, an implantable monolithic chain  200  may be used to augment vertebrae where a compression or a compression fracture has not yet occurred and thus can be preventative in nature. Also, in some embodiments the chain can be used in-between two vertebra. For example, the chain implant can be inserted in the annulus of a spinal disc, or the disc can be removed and the chain implant inserted in-between adjacent vertebra to promote fusion of adjacent vertebrae. The chain implant in some embodiments may be insertable in an additional implant, such as a cage implanted in-between adjacent vertebrae. The chain implant may also be used to reposition and/or augment other damaged bone regions such as a fractured or weakened proximal femur  1400  as shown in  FIG. 14 . In such embodiments, for example, one or more chains  200  may be inserted into a head  1410  of femur  1400 , e.g., through a cannula  1102  or other introducer as show in  FIG. 15 . Once inserted, chain  200  may compact material within head  1410  and provide solid support to augment the head  1410 . A bone cement or other filler may also be used to aid augmentation. In other embodiments, another implant  1420  may be inserted in addition to or instead of one or more chains  200 . 
     In some embodiments, the implants and methods described herein may be used in conjunction with other apparatus and methods to restore lordosis and augment the vertebral body. For example, one or more chains  200  may be used in conjunction with known procedures, e.g., a balloon kyphoplasty, that may be used to begin repositioning of a vertebral body and/or create a space within the body for chain  200 . In other embodiments, one or more chains  200  may be used in conjunction with other tools or external fixation apparatus for helping to manipulate or fix the vertebrae or other bones in a desired position. 
     In another embodiment, a kit comprises various combinations of assemblies and components. A kit may include, for example, a cannula or other introducer and one or more flexible monolithic chains  200 . The one or more chains  200  may be provided in different sizes, e.g., different lengths and/or diameters. In other embodiments, a kit may include an introducer, one or more chains, and a syringe or other apparatus for injecting a cement or other filler into a vertebral body or other space. In other embodiments, a kit may comprise one or more balloon catheters, curettes, and other instruments and may additionally include anchoring elements, tensioning members, fixation members, or any combination thereof, for example as described in U.S. Provisional Patent Application No. 60/1722,064, entitled “Apparatus and Method for Vertebral Augmentation using Linked Bodies”, filed Sep. 28, 2005, which is incorporated by reference herein in its entirety. One skilled in the art will appreciate that various other combinations of devices, components and assemblies can be made and are intended to fall within the scope of the present invention. 
     In other embodiments, various minimally invasive implants and methods for alleviating discomfort associated with the spinal column may employ anchors and other implants described herein. For example, a monolithic chain implant within an expandable container (not shown), may be implanted between spinous processes of adjacent vertebrae to distract the processes and alleviate pain and other problems caused for example by spinal stenosis, facet arthropathy, and the like. For example, augmentation systems described herein may be used instead of or in addition to expandable interspinous process apparatus and methods described in U.S. Patent Publication number 2004/018128 and U.S. Pat. No. 6,419,676 to Zucherman et al. For example, a cannula may be inserted laterally between adjacent spinous processes to insert a container that may be filled with the flexible chains and expand the container and thus keep the adjacent spinous processes at the desired distance. Alternatively, a balloon container, with a deflatable balloon portion can be inserted laterally through adjacent spinous processes and filled with the flexible chains to expand the balloon to a desired size to hold adjacent spinous processes at a desired distances. The balloon can thereafter be sealed and detached from the catheter. Other materials may be inserted within the balloon volume to supplement flexible bodies. 
     While the foregoing description and drawings represent the preferred embodiments of the present invention, it will be understood that various additions, modifications and substitutions may be made therein without departing from the spirit and scope of the present invention as defined in the accompanying claims. In particular, it will be clear to those skilled in the art that the present invention may be embodied in other specific forms, structures, arrangements, proportions, and with other elements, materials, and components, without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, and not limited to the foregoing description.