Patent Publication Number: US-2005136764-A1

Title: Designed composite degradation for spinal implants

Description:
FIELD OF THE INVENTION  
      The present invention relates generally to composite materials to construct orthopedic devices for promoting bone fusion orthopedic devices and methods of using these materials and devices to treat orthopedic defects.  
      The mammalian skeletal system, including long, short, flat, and irregular bones, is vulnerable to disease, injury, and congenital deficiencies, all of which can cause defects to the bone. Disease, injury, and deformity may have a disastrous impact on patient well being, ranging from acute pain to chronic debilitating pain.  
      Common treatments for defective bone tissue include joining or fusing fractured bone segments or portions together to stabilize the affected parts and can include removing and/or replacing portions of affected bone tissue, either in part or in whole. A bone plate or other prosthetic device can be inserted to eliminate disparate motion between the two bone portions to allow arthrodesis.  
      It is important, particularly for load-bearing bone, that the prosthetic device not stress shield the new bone growth and permit a weakened juncture or pseudoarthrodesis between the bone portions or adjacent vertebrae to be fused. It is known that for load bearing bone members, stronger, denser bone tissue results when new bone growth occurs under pressure. The problem arising is when and how to determine the amount of pressure or force desirable to develop a strong junction between the bone portions. The bone portions should be secured and supported during bone growth. However, the optimum support necessary for desired bone growth may vary over time as the bony juncture or bridge develops between the bone portions.  
      Similarly, stretched and/or torn ligaments can be treated by initially securing/immobilizing the ligaments. This can be accomplished using either, or both, internal and external prosthetic devices to augment or replace the stability lost as a result of the damage to the ligaments. Further, once-damaged ligaments can be susceptible to repeated injury. Consequently, it may be desirable to augment the treated ligament by implanting a prosthesis or device that allows limited movement of the affected spinal components while preventing the components from moving far enough to incur re-injury of cause new damage. Current treatment methods do not allow for an implanted device to initially secure or immobilize the ligaments and then allow limited movement of the same without a subsequent surgical revisitation.  
      In light of the above, there is a continuing need for materials for use in orthopedic devices, novel orthopedic devices, and treatments using these materials to stabilize and support damaged bone tissues, bony structures, and connecting tissue. There is also a need for materials, which provide variable loads to growing bone, as well as a measure of flexible support to injury or disease prone bones and connecting tissue. The present invention addresses these needs and provides other benefits and advantages in a novel and nonobvious manner.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention relates to composite materials with anisotropic properties used to construct orthopedic devices, and the manufacture and use of these devices. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.  
      In one form, the present invention provides an anisotropic composite material used to construct orthopedic devices. The composite material comprises: a bio-stable flexible cord configured to be fixedly secured to two or more bone portions allowing translational, or rotational, or both translational and rotational movement of a first one of the bone portions relative to a second one of the bone portions. A more rigid and more biodegradable material engages with the cord such that the biodegradable material restricts the translational, rotational, or both the translational and rotational movement of the first of the bone portions relative to the second of the bone portions secured to the composite material.  
      The composite material can be used to construct orthopedic devices used to treat a variety of bone defects including, but not limited to, bone fractures, diseased bone tissues, spinal diseases, diseased/damaged vertebrae, torn or stretched ligaments, and the like.  
      In preferred embodiments, the devices comprising the composite material prevent, or at least reduce, stress shielding of new, developing bone tissue. In other embodiments, the orthopedic device of the present invention can be configured for articulating joints. In these embodiments, the composite material can allow a limited amount of movement, i.e. translation and/or rotation about the joint. The devices, with and without the biodegradable material, still provide a measure of support and/or restriction of the movement of bone portions attached to devices comprising the composite materials. In preferred embodiments, the devices of the present invention remain in place indefinitely.  
      Further objects, features, aspects, forms, advantages, and benefits shall become apparent from the description.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a perspective view partly broken away of a composite material comprising an elongate cord including wound filaments and encased within a biodegradable matrix in accordance with the present invention.  
       FIG. 2  is a perspective view partly broken away of an alternative embodiment of an elongate composite material in accordance with the present invention  
       FIG. 3  is a perspective view of a plurality of non-biodegradable filaments supported by at least one biodegradable filament in accordance with the present invention.  
       FIG. 4  is a perspective view of a cord including a plurality of non-biodegradable filaments and at least one filament encased within a biodegradable matrix in accordance with the present invention.  
       FIG. 4A  is a cross-sectional view of one of the filaments encased in a biodegradable matrix of the cord illustrated in  FIG. 4 .  
       FIG. 5  is a perspective view of a bone having a bone defect which has been treated using an orthopedic device prepared using one of the cords illustrated in  FIGS. 1, 2 , or  3 .  
       FIG. 6  illustrates one embodiment of a composite material including a web material embedded within a biodegradable polymeric matrix.  
       FIG. 7  is a cross-sectional view of one embodiment of a composite material including a non-biodegradable cloth embedded between two biodegradable matrices in accordance with the present invention.  
       FIG. 8  is a cross-sectional view of an alternative embodiment of a fabric encased between two biodegradable matrices in accordance with the present invention.  
       FIG. 9  is a perspective view of a section of a spine, having a defect, which has been treated using a composite matrix in accordance with the present invention.  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated herein, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications in the described devices, systems, and treatment methods, and any further applications of the principles of the invention as described herein, are contemplated as would normally occur to one skilled in the art to which the invention relates.  
      In preferred embodiments, the present invention provides a composite material for use in the construction of an implantable orthopedic device or prosthesis used to facilitate support and repair of defective bone structures and/or connective tissue. The defective bone structures can be the result of damaged, traumatized, and/or diseased tissue. By use of the term “orthopedic device”, it is intended to include within its meaning a device or implant that can be used to treat or repair defective, diseased, or damaged tissue of the muscular/skeletal system(s).  
      The biodegradable material of the present invention provides a composite material that includes a supporting matrix and a cord for an implantable orthopedic device. This supporting matrix can provide rigidity and support for both the implanted orthopedic fusion device and, consequently, the attached bone structures. In use, the biomechanical load supported by the composite material and/or orthopedic devices incorporating the composite can vary over time. This allows the orthopedic device to become dynamizable, or change its physical properties in vivo. This change in physical properties can be particularly important for developing strong, new bone tissue at the bone defection or fusion site. This prevents stress shielding of the new bone in-growth and minimizes the risk for the development of pseudoarthrodesis.  
      In one form, degradation of the matrix can occur naturally without the use of subsequent treatment. In other forms, degradation of the matrix can be initiated (or triggered), induced, and/or completed at a selected or predetermined time after implantation. The device and/or composite material can include a polymer susceptible to or sensitive to radiation energy, light (UV), solvents with different pH levels, thermal energy, or temperature, to initialed degradation. The treatment can include both invasive and non-invasive treatments. Preferably, the treatment can be accomplished using a UV radiation probe inserted in close proximity to the device (or composite material).  
      The following description specifically describes non-limiting, specific embodiments for use with the present invention.  
       FIG. 1  is a perspective view of one embodiment of a composite material  10  including a cord  12  and a matrix  14 . Cord  12  can be provided as a single elongate filament  16 , or alternatively, as a plurality of filaments  18   a,    18   b,  and  18   c,  . . . , collectively referred to as filament  18 . When cord  12  is a single filament, it can be provided as a large diameter rod or solid core encased within matrix  14 . Implant  10  defines a longitudinal axis  20 . In preferred embodiments, cord  16  and/or individual filaments  18   a,    18   b,    18   c,  extend substantially in the direction of longitudinal axis  20 . Although it will be understood that one or more of individual elements  18   a,    18   b,    18   c,  . . . , while extending generally in the direction of longitudinal axis  20 , can either wind around that direction and extend substantially orthogonal or at an angle oblique to that direction at any given location within implant  10 . In other embodiments, the plurality of filaments  18   a,    18   b,    18   c,  . . . can be woven together to provide a flat mesh or a three-dimensional network of filaments.  
      Matrix  14  can substantially encase cord  12 . Alternatively, at least a portion of cord  12  can extend through or beyond the surface of matrix  14 . Matrix  14  can provide support to maintain a desired shape for an orthopedic device. Consequently, matrix  14  can be provided as a variety of biodegradable materials. Some of the materials can be readily formable in the operating room, for example, by heating the material and shaping the composite into a desired configuration to either conform to the bone defect and/or to induce the bone defect to be retained in a desired configuration. Alternatively, matrix  14  can be pre-formed or shaped by the supplier or manufacturer. Matrix  14  is illustrated as a substantially cylindrical elongate configuration. It should be understood that matrix  14  can be provided in any desirable configuration including as a substantially bent, planar, or flat configuration. Alternatively, matrix  14  can be provided in any desirable shape including a substantially spherical, square, rectangular, or amorphous configuration, which, as noted above, may or may not be moldable by hand either at elevated temperatures or under other conditions including light, moisture, or solvent activated.  
      In alternative embodiments, matrix  14  is bonded to cord  12 . A biocompatible chemical adhesive can be used to bond the matrix and cord  12  together. The bond can also be derived from a mechanical interlock between the matrix  14  and the cord  12 .  
      While composite  10  is illustrated as an elongate cylinder, it will be understood that other configuration are contemplated and are intended to be included within the scope of the present invention. For example composite  10  can be bent, planar, cuboid, spherical or of an amorphous shape as desired. Further composite  10  (and cord  12 ) can include various structures to permit it to be secured to bone tissues. Examples of various structures include without limitation: eyelets, loops, hooks, bone fasteners, pins, pegs, cements, glues, and combinations thereof  
      Cord  12  extends through at least a portion of matrix  14 . Cord  12  can be formed or composed of a variety of individual filaments either separated from each other in matrix  14  or in direct contact with each other or loosely bundled together. Filaments  18   a,    18   b,    18   c,  . . . can be  10  braided or woven together and extend at least partially through matrix  14 . Alternatively, filaments  18   a,    18   b,    18   c,  . . . can extend parallel to each other through at least a portion of matrix  14 . In still other embodiments, cord  12  and/or filament  18  can be substantially embedded within and completely surrounded by matrix  14 , such that no portion of the cords or filaments are exposed or visible.  
      Each of filaments  18   a,    18   b,    18   c,  . . . can be formed of the same material and/or of the same shape, diameter, and length. Alternatively, one or more of  18   a,    18   b,    18   c,  . . . can be provided as a different material or formed in a different shape, diameter, length, or configuration as desired. Providing the individual filaments  18   a,    18   b,    18   c,  . . . in different materials, shapes, and sizes can induce the implant to produce different desirable physical properties and, consequently, an orthopedic implant can be prepared tailored to treat the individual orthopedic defect or disease.  
      In one embodiment, cord  12  is elastic and/or flexible. Consequently, one or more of filaments  18   a,    18   b,    18   c,  . . . can be an elastic or flexible material. Weaving the filaments  18   a,    18   b,    18   c,  . . . together can modify the cord&#39;s elasticity or flexibility. For example, using either a loose weave or a tight weave, differing sizes of spaces  24  can exist between the individual filaments  18   a,    18   b,    18   c,  . . . and can allow cord  12  to exhibit varying degrees of flexibility.  
      Cord  12  (and filaments,  18   a,    18   b,    18   c  . . . ) can exhibit a smooth exterior surface.  
      Alternatively, cord  12  (and filaments,  18   a,    18   b,    18   c  . . . ) can exhibit an exterior surface that is roughened pitted, grooved, or knurled. The textured exterior surface of cord  12  can facilitate bonding the matrix material to the cord via a mechanical interlocking mechanism either solely or in conjunction with an adhesive. The three dimensional network of the filaments  18   a,    18   b,    18   c  . . . making up cord  12  can include voids or spaces which can also facilitate bonding the matrix material  14  to the cord  12  via a mechanical interlocking mechanism. Additionally the surface of either matrix  14  or the cord  12  can be treated to facilitate good adherence. Such surface treatment can include corona discharge, plasma discharge, chemical etching, electron or ion beam radiation, and laser radiation, and the like as is known in the art.  
      Cord  12  can be provided as a non-biodegradable material. Examples of non-biodegradable materials are discussed more fully below. In addition, cord  12  can include one or more individual filaments, which may be composed of a biodegradable material. The biodegradable material for the filaments can compose a shape memory polymer, and/or other biocompatible polymeric material.  
      In one preferred embodiment, matrix  14  is composed of a biodegradable material  22 . In vivo, matrix  14  erodes or biodegrades. As matrix  14  biodegrades, the rigidity of composite  10  decreases. In preferred embodiments, this decrease in rigidity is substantially linear over time. As discussed more fully below, the nature and composition of matrix  14  can be varied to allow matrix  14  to degrade over varying time periods including periods between a few days, a few weeks, a few months, and even over the course of one or more years. Matrix  14  can be formulated to have a desired half-life in vivo. By use of the term “half life”, it is intended to mean that matrix  14  degrades to about one-half of its initial mass in the specified time period. In one preferred embodiment, matrix  14  has a half-life, in vivo, of less than about 6 months; more preferably, matrix  14  has a half-life of less than about 12 months; still more preferably, matrix  14  has a half-life of less than about 18 months. In other embodiments, matrix  14  can be formulated to have a half-life that is greater than or equal to one year; more preferably greater than or equal to 18 months.  
       FIG. 2  is a perspective view of an alternative embodiment of an elongate composite material  30  in accordance with the present invention. Elongate composite  30  defines a central axis  35 . Composite material  30  includes matrix  32  and a cord  34  engaged therein and extending generally along the axis  35 . Cord  32  can comprise a single filament  36   a  or a plurality of filaments  36   a,    36   b,    36   c,  . . . , collectively referred to as filament  36 . In the illustrated embodiment, filaments  36   a,    36   b,   36   c,  . . . are wound together to provide cord  34 .  
      Generally, composite material  30  can be provided substantially as has been described above for composite material  10 , including the description of the matrix  22  and and/or filaments  18   a,    18   b,    18   c,  . . . The winding of filaments  36   a,    36   b,    36   c,  . . . can provide differing properties of that exhibited by the braiding of filaments  18   a,    18   b,  and  18   c  including the ability to define a central cavity  38  therein. Central cavity  38  extends substantially parallel to axis  35 . In one embodiment, central cavity  38  is substantially filled with the material of matrix  34 . In other embodiments, yet another filament or cord can extend through central cavity  38 . In effect, filaments  36   a,    36   b,    36   c,  . . . can be wound around the central cord or filament. The central cord or filament can be the same or different from either cord  34  or filament  36 . Additionally, the winding of filaments  36   a,    36   b,    36   c,  . . . also generates additional spaces or voids  40  between individual filaments, for example, between filaments  36   a  and  36   b.  In still other embodiments cavity  38  can be filed with a therapeutic agent or osteogenic material.  
       FIG. 3  is a perspective view of one embodiment of a composite material  49  that includes a tether or cord  50  in accordance with the present invention. Cord  50  comprises a plurality of filaments extending generally along a central axis  51 . In preferred embodiments, cord  50  includes a first set of filaments  52  and at least a second set of filaments  54 . Other sets or individual filaments can also be included within cord  50 . In the illustrated embodiment, first set of filaments  52  can include a plurality of individual filaments  56   a,    56   b,    56   c  . . . Filaments  56   a,    56   b,    56   c  . . . can be the same filaments and can have the same length or configuration. Alternatively, a select one or more of filaments  56   a,    56   b,    56   c  . . . can be different from the other filaments in either composition, physical properties, size, diameter, length, and the like. First set of filaments  52  can be provided substantially as has been described for filament  18  (and for cord  12 ). Additionally, it will be understood that the relative arrangements of filaments  56   a,    56   b,    56   c  . . . can be either provided as a plurality of parallel filaments, wound filaments, braided filaments, and the like. One or more of filaments  56   a,    56   b,    56   c  . . . can be provided as a substantially rigid filament formed of a non-biodegradable material, which is discussed in more detail below.  
      Cord  50  also includes a second set of filaments  54 . Second set of filaments  54  can include a single filament  58  or a plurality of filaments arranged similarly to that discussed above for first set of filaments  52 .  
      Filament  58  can be composed of a biodegradable material, discussed more fully below. Additionally, filament  58  can be a substantially rigid filament that provides support for cord  50  and/or lends further support to individual filaments of the first set of filaments  52 . In the illustrated embodiment, filament  58  is provided to substantially interweave or woven into the plurality of filaments  56   a,    56   b,    56   c  . . . In other embodiments, filament  58  can be provided to extend substantially parallel to one or more filaments of the first set of filaments  52 , wrap around one or more filaments of the first set of filaments  52 , and/or be spirally wound within the first set of filaments  52 . Filament  58  can be provided to degrade in vivo at a desired degradation rate or within a desired time period. The degradation rate or the half-life of filament  58  can be tailored to suit the particular need, treatment, and/or application of cord  50 . In one embodiment, the half-life of filament  58  is selected to be greater than about  6  months; more preferably, greater than or equal to about  1  year; still yet more preferably, greater than or equal to about  18  months. In other embodiments, filament  58  can be provided to have a half-life of less than about  1  year. Furthermore, filament  58  can be provided to have substantially the same configuration, length, diameter, mass, and/or tensile strength as that exhibited by either the individual filaments of the first set of filaments  52  and/or one ore more filaments  56   a,    56   b,    56   c . . .    
      In use, as the filaments of the second set  54  degrade in vivo, the rigidity of cord  50  and/or one or more of the individual filaments of the first set  52  can be decreased. This allows cord  50  and/or one or more filaments of the first set  52  to become more flexible. Consequently, if the bone portions to which cord  50  and/or the first set of filaments  52  are attached articulate, the flexibility or increasing flexibility over time allows increased movement of the articulating joint as new bone tissue grows and the defect is corrected. It will be understood that in preferred embodiments cord  50  remains secured to the bone portions albeit minus some or all of the filaments of the second set  54 . Furthermore, it will be understood that in other aspects, cord  50  can be substantially as provided as described above for cords  12  and  34 .  
       FIG. 4  is a perspective view of an alternative embodiment of a composite material  70  for use in forming orthopedic devices in accordance with the present invention. Composite material  70  includes a cord  72  comprising a first set of filaments  74  and at least a second set of filaments  76 . First set of filaments  74  can be provided substantially as has been described above for first set of filaments  52  for cord  50  and can include a plurality of individual filaments  75   a,    75   b,    75   c,  . . . Second set of filaments  76  can comprise one, two, three, or more filaments, collectively referred to as filament  78 . Referring additionally to  FIG. 4A , filament  78  includes at least an outer coating or matrix  80  composed of a biodegradable material, discussed more fully below and an inner core material  77  that comprises one of: a large diameter rod, a solid core, a smaller wire, filament, braid, or plurality of filaments as desired. In one embodiment, the inner core material  77  can comprise a filament of cord similar to that defined by the first set of filaments  74 . Alternatively, inner core material  77  can be the same or can be different from any one of filaments  75   a,    75   b,    75   c,  . . . Additionally, core  77  can either be formed of a biodegradable material and/or a non-biodegradable material, both of which are discussed more fully below. Filament  78  including core material  77  and matrix  80  can be substantially rigid or provide rigidity to cord  72 .  
      As matrix  80 , comprising a biodegradable material, begins to erode, in vivo, the rigidity of filament  78  and/or core  77  begins to decrease. Consequently, the rigidity of cord  72  also begins to decrease. This allows the bone portions to which an implant is attached to articulate or carry an increasing amount of load to promote formation of hard cortical bone tissue and prevent pseudoarthrodesis. In other aspects, such as rigidity, size, configuration, diameter, half life, and the like, filament  78  can be provided substantially as has been described above for any one of the filaments  58  or cord  50 . Additionally, cord  72  can be encased or substantially encased within a matrix such as matrix  14  or  32  of composite material  10  or  30 , respectively.  
      One or more of filaments  75   a,    75   b,    75   c  and filament  78  can be bundled together to define an interior region  82  therein. Interior region can be a void, contain the matrix material, or a therapeutic agent, osteogenic material or another cord of plurality of filaments as discussed above for cavity  38 . In other embodiments, the plurality of filaments  75   a,    75   b,    75   c,  . . . can be woven together to provide a flat mesh or three-dimensional network of filaments.  
       FIG. 5  is a perspective view of one embodiment of a bone  90  having a defect  92  therein. An orthopedic implant  94  comprised of an elongate composite material  95  is illustrated as attached to bone  90  and spanning defect  92 . Orthopedic implant  94  can be comprised of a composite material as has been discussed above such as any one of composite materials  10 ,  30 ,  70  or cords  50  or  72  described above. In the illustrated embodiment, orthopedic implant  94  includes an outer matrix  96  substantially encasing a cord  98 . Cord  98  comprises a first filament  100  and a second filament  102 . The orthopedic implant  94  can be attached to the bone portions by any means commonly used and/or known in the art including, without limitation, bone screws  104   a,    104   b,    104   c,  and  104   d,  staples, wire, cable, and the like. It will be observed from the illustration that some of screws, such as  104   a  and  104   d,  can extend solely through cord  98  with or without going through matrix  96 . Other screws, such as those listed as  104   b  and  104   c,  may extend through outer matrix  96  and may or may not contact cord  98 . In use, outer matrix  96  slowly degrades, in vivo. After degrading, the residual portion of the implant, i.e., cord  98 , can remain secured to the bone portions to provide additional support and/or restraint. However, as noted above and discussed more fully below, degradation of outer matrix  96  can allow increasingly greater stress on new bone growth within defect  92 . This can provide optimal bone tissue growing conditions to ensure hard, dense cortical bone grows into the defect. In addition, an osteogenic material can be added to the bone defect, either supplied separately, combined with the outer matrix, and/or incorporated into the cord.  
       FIG. 6  is perspective view of another embodiment of composite material  120  for use in the present invention. Composite material  120  comprises a woven or an array of cords to provide a mesh  122  and a matrix  124 . Mesh  122  can be a flat (two-dimensional), fabric, or cloth-like material or three-dimensional network. Matrix  124  can be formed similarly as described above for matrices  96 ,  80 , and  14 . Consequently, matrix  124  can be a biodegradable or bioerodable material that can provide rigid support to the orthopedic implant formed from the composite material  120 .  
      The mesh  122  can comprise a first set of filaments  126  and at least a second set of filaments  128 . In the illustrated embodiment, first and second sets of filaments  126  and  128  are provided to lie substantially orthogonal to each other. It will be understood by those skilled in the art that the relative orientation of first set of filaments  126  and second set of filaments  128  can be provided as desired, including substantially parallel to each other, woven, braided, or oriented at an angle oblique to each other. Furthermore, first set of filaments  126  and second set of filaments  128  can comprise substantially the same material or comprise a different material from each other. Furthermore, first set of filaments  126  and second set of filaments  128  can have substantially the same properties including tensile strength, diameter, length, shape, and the like, or the two sets of filaments can have different tensile strength, diameter, length, shape and the like from each other. Additionally, first set of filaments  126  can be provided substantially as described above for first set of filaments  74  and/or first set of filaments  52 . Similarly, second set of filaments  128  can be provided substantially as has been described above for first set of filaments  74  and  52 , or second set of filaments  76  and/or  54 .  
      First set of filaments  126  and second set of filaments  128  can be engaged with or secured to each other. The engagement can be in the form of bonding with or without glue, woven together, knotted together, overmolded on top of each other, or secured via a mechanical interlocking mechanism as desired.  
      In the illustrated embodiment, first and second sets of filaments  126  and  128 , respectively, are substantially encased within matrix  124 . It will be understood that one or more, or both, of first set of filaments  126  and second set of filaments  128  can be exposed or at least partially exposed extending out of matrix  124 .  
      First set of filaments  126  can comprise a plurality of filaments  127   a,    127   b,    127   c,  . . . and each filament can be composed of the same material and/or exhibit the same physical properties, size, and shape. Alternatively, each of filaments  127   a,    127   b,    127   c,  . . . can be of a different material or of a different size, shape, or physical properties as desired.  
      Similarly, the individual filaments  129   a,    129   b,    129   c,  . . . making up of the second set of filaments  128  can be of the same materials and/or same physical properties and sizes or they can be of different materials, sizes, and/or physical properties as desired.  
      In another embodiment, the first set of filaments  126  and second set of filaments  128  are composed of different materials and/or having different physical properties, sizes, and shapes. This can be used to prepare an orthopedic matrix having anisotropic properties, i.e., exhibiting different properties in different directions. For example, the second set of filaments  128  can comprise a biodegradable or non-biodegradable material. For example, the first and second set of filaments  126  and  128  can both be composed of biodegradable material either the same or different second material. The degradation rates or half-lives of the two materials may be different.  
      Alternatively, the first set of filaments  126  can be composed of a biodegradable material while the second set of materials are composed of a non-biodegradable material. Consequently, the second set of filaments  128  remains in vivo while the first set of filaments  126  erode away.  
      In yet another embodiment, the size and/or shape of the filaments in the first set of filaments  126  can be different from the filaments in the second set of filaments  128 . One set of filaments can persist in vivo for a longer period of time.  
      This provides an orthopedic implant having various properties, which properties can be tailored to suit the particular application and treatment method used on the orthopedic defect.  
      Matrix  124  can be provided as a moldable or shapeable material that can be rigid in vivo and at ambient temperature and/or under pharmacological conditions. However, if desired, matrix  124  can be formulated to be hand or machine moldable either at an elevated temperature within a specified solvent or under specific conditions. For example, the matrix material  124  can comprise one or more cross-linkable polymeric materials such that upon initiation, the matrix material forms a cross-linked matrix having the desired or preformed configuration. Matrix material  124  can be bonded or secured to first set of filaments  126  and/or the second set of filaments  128  as desired with or without glue, overmolded, or secured via a mechanical interlocking mechanism.  
       FIG. 7  is a cross-sectional view of one embodiment of a composite material  140  for use in the present invention. Composite material  140  can be provided substantially as has been described above for composite material  120 . Alternatively, composite material  140  can be different from that described above. For example, composite material  140  can comprise a first matrix  142  and at least a second matrix  144 . First and/or second matrix can be made of the same or different material. For example, first matrix  142  can be formed of a first biodegradable material, and second matrix  144  can be formed of a second biodegradable material. Additionally, a loose weave or cloth-like material  146  comprising a first set of filaments,  150  and a second set of filaments  152 . The weave or cloth-like material  146  can be disposed in between first matrix  142  and at least a second matrix  144 . Weave or material  146  can be provided substantially as has been described above for mesh  122 . In selected embodiments, one or both of first matrix  142  and second matrix  144  can be bonded, over molded, or engaged to woven material  146 , and more specifically, to fibers  148  composing the woven material  146 . In other embodiments, first matrix and/or second matrix can be glued using a biocompatible adhesive to one or more of the woven material  146  and/or fibers  148 .  
      Referring additionally, to  FIG. 8 , a composite material  160  is illustrated. Composite material  160  is similar to that illustrated above for composite material  140 . Consequently, like reference numbers will be used to denote like components. Composite material  160  comprises a first matrix  142  and a second matrix  144  and a woven material  146  between. Additionally, a third set of filaments  162  is illustrated as a weaving or suturing to bind together first matrix  142 , second matrix  144 , and woven material  146 . Third set of filaments  162  can be comprised substantially as has been described above for the first set of filaments  74 ,  52 ,  36 , and  18 . Alternatively, third set of filaments  162  can be provided as has been described above for second set of filaments  77  and  58 . In yet another alternative, first matrix  142 , second matrix  144 , and woven material  146  can be fastened together by any means commonly used or known in the art including cords, strings, filaments, staples, clips, ties, bands, glues, cements, and combinations thereof.  
       FIG. 9  is an illustration of a portion of a spinal column  170  with a defect and including a first vertebrae  172  and a second vertebrae  174 . The bone defect can be treated using an orthopedic device  176 . Orthopedic device  176  can comprise a material such as that described above for composite material  160 ,  140 , and/or  120 . In use, as the biodegradable component of orthopedic device  176  degrades, the residual component, i.e., either a woven matrix and/or a portion of a woven matrix, can remain secured to one or both of first and second vertebrae  172  and  174 , respectively. This can allow the two vertebrate to articulate relative to each other, yet maintain the integrity and restrict movement or allow limited movement of the spinal column.  
      The biodegradable material included in one or more cords, filaments, and/or matrices described above can be formed or composed of a variety of materials including, without limitation, degradable or resorbable polymeric materials, composite materials, and ceramic materials.  
      In one embodiment, the biodegradable material can include polymeric materials formed from oligomers, homopolymers, copolymers, and polymer blends that include polymerized monomers derived from l, d, or d/l lactide (lactic acid); glycolide (glycolic acid); ethers; amino acids; anhydrides; orthoesters; hydroxy esters; and mixtures of these monomeric repeating units.  
      Use of the term “copolymers” is intended to include within the scope of the invention polymers formed of two or more unique monomeric repeating units. Such copolymers can include random copolymers; graft copolymers; body copolymers; radial body, dibody, and tribody copolymers; alternating copolymers; and periodic copolymers. Use of the term “polymer blend” is intended to include polymer alloys, semi-interpenetrating polymer networks (SIPN), and interpenetrating polymer networks (IPN).  
      In a preferred embodiment, the biodegradable material comprises a biodegradable polymeric material including: poly(amino acids), polyanhydrides, polycaprolactones, poly(lactic-glycolic acid), polyhydroxybutyrates, polyorthoesters, and poly(d,l-lactide).  
      In other embodiments, the biodegradable material can comprise biodegradable ceramic materials and ceramic cements. Examples of biodegradable ceramic materials include: hydroxyapatite, hydroxyapatite carbonate, corraline, calcium phosphate, tricalcium phosphatem, and hydroxy-apatate particles. Examples of biodegradable ceramic cements include calcium phosphate cement. Such calcium phosphate cements are preferably synthetic calcium phosphate materials that include a poorly or low crystalline calcium phosphate, such as a low or poorly crystalline apatite, including hydroxyapatite, available from Etex Corporation and as described, for example, in U.S. Pat. Nos. 5,783,217; 5,676,976; 5,683,461; and 5,650,176, and PCT International Publication Nos. WO 98/16268, WO 96/39202 and WO 98/16209, all to Lee et al. Use of the term “poorly or low crystalline” is meant to include a material that is amorphous, having little or no long range order, and/or a material that is nanocrystalline, exhibiting crystalline domains on the order of nanometers or Angstroms.  
      In still other embodiments, the biodegradable material can be formed of composite materials. Examples of composite materials include as a base material or matrix, without limitation: ceramics, resorbable cements, and/or biodegradable polymers listed above. Each of the base materials can be impregnated or interspersed with fibers, platelets, and particulate reinforcing materials.  
      In one form, the biodegradable material comprises a resorbable, moldable material that can be molded at an elevated temperature and then allowed to set up into a hardened material at around body temperature, such as the material sold under the trade name BIOGLASS® discussed in WO 98/40133, which is incorporated by reference herein.  
      The composite material of the present invention can be tailored to degrade at a predetermined or pre-selected rate by suitably selecting the size, thickness, and/or biodegradable material. In preferred embodiments, the biodegradable material degrades at a rate comparable to the new bone in-growth into the bone defect or bone fusion site. In particularly preferred embodiments, the rigid biodegradable component has an in vivo half life of greater than three months, more preferably the in vivo half life of the restricting component is greater than six months; still more preferably the in vivo half life is greater than one year. By use of the term “half life”, it is understood that the degradation rate of the restricting component is such that the restricting component loses half of its initial mass in vivo, presumably due to resorption, degradation, and/or elimination.  
      Further, the biodegradable material can be formulated to degrade or can be induced to begin degradation by application of external stimuli. For example, the biodegradable material can degrade upon application of radiation such as UV radiation, thermal energy, and/or solvent—either neutral, basic, or acidic.  
      A nonbiodegradable or biostable material for use in the present invention can include resilient materials such as, without limitation, nitinol, titanium, titanium-vanadium-aluminum alloy, cobalt-chromium alloy, cobalt-chromium-molybdenum alloy, cobalt-nickel-chromium-molybdenum alloy, biocompatible stainless steel, tantalum, niobium, hafnium, tungsten, and alloys thereof; polymeric materials include polymerized monomers derived from: olefins, such as ethylene, propylene, butene-1, pentene-1, hexene-1, 4-methylpentene-1, styrene, norbornene and the like; butadiene; polyfunctional monomers such as acrylate, methacrylate, methyl methacrylate; esters, for example, caprolactone and hydroxy esters; and mixtures of these monomeric repeating units. Preferred polymers for use in the present invention include carbon poly(ether, ether, ketone) (PEEK), poly(aryl ether, ketone) (PAEK), and the like.  
      In addition or in the alternative, it may be desirable to promote bone fusion between the adjacent vertebrae or between any bone portions on either side of a bone defect. In this embodiment, it may be desirable to include an osteogenic material or a bone growth material such as an osteoinductive or an osteoconductive material. For example, it may be desirable to introduce an osteogenic factor such as a bone morphogenic protein (BMP) or a gene encoding the same operationally associated with a promoter which drives expression of the gene in the animal recipient to produce an effective amount of the protein. The bone morphogenic protein (BMP) in accordance with this invention is any BMP able to stimulate differentiation and function of osteoblasts and osteoclasts. Examples of such BMPs are BMP-2, BMP-4, and BMP-7, more preferably rhBMP-2 or rhBMP-7, LIM mineralization protein (LMP) or a suitable vector incorporating a gene encoding the same operably associated with a promoter, as described in WO99/06563 (see also Genbank accession No. AF095585).  
      The composite materials and orthopedic devices of the present invention can be used by themselves or in conjunction with one or more known orthopedic devices as deemed medically prudent. Additionally or in the alternative, the present invention can be used with one or more devices disclosed in co-pending U.S. patent applications Ser. No. 10/689,981 filed on Oct. 21, 2003 entitled, “Apparatus and Method for Providing Dynamizable Translation to a Spinal Construct,” and Ser. No. 10/690,451 filed on Oct. 21, 2003 entitled, “Dynamizable Orthopedic Implants and Their Use in Treating Bone Defects.” 
      In preferred embodiment, the composite material of the present invention can provide initial support and/or fixation of selected bone structures. After a selected period of time or under certain conditions, the amount and nature of the support/fixation can vary to facilitate a desirable treatment. For example, use of a composite material according to the present invention allows that variable or dynamizable support develops new, strong bone tissue, thus minimizing the risk of pseudoarthrodesis.  
      The composite material of the present invention also finds advantageous use in the treatment of connecting tissue such as ligaments. For example, devices comprising the composite material can augment connecting tissue. After a predetermined period of time or condition, the composite material can allow limited translational, rotational, or translational and rotational movement of the connecting tissue and/or bone structures attached to the orthopedic device incorporating the composite. For example, if the natural connecting tissue is elastic, the composite material can serve to limit or restrict the overall length or amount that the connecting tissue stretches. This restriction can vary depending upon the length of time or pre-selected conditions used in forming the composite material used in constructing and using the device.  
      While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is considered to be illustrative and not restrictive in character, it is understood that only the preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. Any reference to a specific directions, for example, references to up, upper, down, lower, and the like, is to be understood for illustrative purposes only or to better identify or distinguish various components from one another. These references are not to be construed as limiting in any manner to the orthopedic device and/or methods for using the orthopedic device as described herein.  
      Further, all publications, patents, and patent applications cited in this specification are herein incorporated by reference as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference and set forth in its entirety herein.  
      Unless specifically identified to the contrary, all terms used herein are used to include their normal and customary terminology. Further, while various embodiments of medical devices having specific components and structures are described and illustrated herein, it is to be understood that any selected embodiment can include one or more of the specific components and/or structures described for another embodiment where possible.  
      Further, any theory of operation, proof, or finding stated herein is meant to further enhance understanding of the present invention and is not intended to make the scope of the present invention dependent upon such theory, proof, or finding.