Patent Publication Number: US-2007118128-A1

Title: Implant fixation methods and apparatus

Description:
BACKGROUND OF THE INVENTION  
      Disease, advancing age, and trauma can lead to changes in various bones, discs, joints, and ligaments of the body. Some changes and trauma often manifest themselves in the form of damage or degeneration to a spinal disc. This condition often results in chronic back pain, which can be anywhere from mild to severe. This pain can sometimes be eliminated by removing the disc tissue between adjacent vertebral bodies and replacing it with a prosthetic device.  
      One type of procedure is spinal fusion, in which two adjacent vertebral bodies are jointed together after removing the intervening intervertebral disc. A prosthetic device is usually placed between the two adjacent vertebral bodies, in place of the removed disc, to fill the space left by the removed disc and to allow bone to grow between the two vertebral bodies. Alternatively, proposals have been made to replace the defective disc with an artificial disc that preserves the natural mobility between adjacent vertebral bodies. For example, such prostheses can include first and second plates for fixing to adjacent vertebral bodies, the plates having low friction contact surfaces that allow articulation.  
      As part of the surgical procedure to replace a disc, the soft tissue connecting adjacent vertebral bodies is at least partially cut-away. This can cause a loss of stability, particular where a mobility retaining prosthesis is utilized. To replace the function of the connective tissue, a tissue implant can be implanted. For example, a tissue implant can fixed at a first end to a first vertebral body and fixed at a second end to second vertebral body. To fix the tissue implants to bone, a surgeon can drive a screw, tack, or staple through the tissue implant and into the native tissue.  
      One drawback of such procedures is that the tissue implant can be weakened by the fixation procedure. When the screw, tack, or staple is driven through the implant it creates a weak spot, which may tear under load. For example, the screw or staple could be pulled through the tissue implant when tension is applied. Another drawback of conventional fixation techniques is that the fixation devices hold only a minimal portion of the implant in contact with the native tissue surface.  
      Accordingly, there remains a need for improved devices for fixing tissue implants, particularly, methods and devices that can fix tissue while causing a minimum weakening of the implant and/or that can provide improved contact between the tissue implant and a native tissue surface.  
     SUMMARY OF THE INVENTION  
      Described herein are methods and apparatus for fixing implants to bone. Unlike traditional fixation devices, such as bone screws or staples, the device described herein can include a large surface area for holding an implant in place. In addition, in at least one embodiment, the device is adapted to hold an implant without penetrating the implant. For example, an implant can be fixed in place between the device and a native tissue surface by implanting a bone screw through a portion of the device that is spaced from the tissue implant.  
      In one embodiment, the tissue fixation device includes a plate body having an upper surface and a lower tissue contacting surface. The body can include an implant receiving opening defined by an elongate slot and at least one aperture. Each of the at least one apertures can be adapted to each receive a tissue fixation element. In use, a tissue implant can be positioned at least partially in the elongate slot and fixed between the plate and a tissue surface. The plate body can additionally include a second implant receiving opening. For example, first and second implant receiving openings can extend parallel to one another in the plate body.  
      In one aspect, each aperture is adapted to receive a fixation element selected from the group consisting of a pin, screw, staple, tine, anchor, expansion bolt, rivet, and combinations thereof In one exemplary embodiment, each aperture is shape to receive the head of a bone screw.  
      The plate body described herein can be shaped for positioning on a tissue surface such as, for example, a vertebral body. For example, the device can have a curvature that corresponds to the curvature of the surface of a vertebral body. In addition, or alternatively, the plate body can be flexible or malleable. When the device is implanted, the plate body can deform and/or bend to match the curvature of a tissue surface. In another aspect, the plate body is shaped and sized for positioning on a single vertebral body. For example, the apertures can be spaced for implantation in a single vertebral body.  
      The plate body can further include features to assist with fixing a tissue implant. In one aspect, a lower tissue contacting surface of the device includes a recess for seating an implant. In another aspect, the device can include surface features for gripping an implant.  
      In another embodiment described herein a method of implanting a soft tissue graft is provided. The method can include the step of providing a plate body that includes an implant receiving slot and at least two apertures. An implant can be threaded at least partially through the implant receiving slot. With the implant positioned in the implant receiving opening, the plate body can be fixed to a hard tissue surface by implanting bone screws in the at least two apertures.  
      In one aspect, the method further includes the step of threading a second end of the implant through an implant receiving slot of a second plate body. The first and second plate bodies can be fixed to first and second vertebral bodies.  
      Further features of the invention, its nature and various advantages, will be more apparent from the accompanying drawings and the following detailed description of the drawings and the preferred embodiments. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:  
       FIG. 1A  is a top view of one exemplary embodiment of a tissue fixation device described herein;  
       FIG. 1B  is a side view of the device of  FIG. 1A ;  
       FIG. 2  is a cross-sectional view of the device of  FIG. 1A  implanted on a vertebral body;  
       FIG. 3A  is a top view of another embodiment of a device described herein;  
       FIG. 3B  is a side view of the device of  FIG. 3A ;  
       FIG. 3C  is a perspective view of the device of  FIG. 3A ;  
       FIG. 4A  is a top view of yet another embodiment of a device described herein;  
       FIG. 4B  is a perspective view of the device of  FIG. 4A ;  
       FIG. 5A  is a top view of still another embodiment of a device described herein;  
       FIG. 5B  is a perspective view of the device of  FIG. 5A ;  
       FIG. 6A  is a top view of another embodiment of a device described herein;  
       FIG. 6B  is a side view of the device of  FIG. 6A ;  
       FIG. 6C  is a partial cross-sectional view of the device of  FIG. 6A ;  
       FIG. 7A  is a side view of a two-plate embodiment of a device described herein;  
       FIG. 7B  is a perspective view of the device of  FIG. 7A ;  
       FIG. 7C  is another side view of the device of  FIG. 7A ;  
       FIG. 8A  is a perspective view of an embodiment of a device described herein that is adapted for positioning on an edge of a vertebral body;  
       FIG. 8B  is a side view of the device of  FIG. 8A ;  
       FIG. 8C  is another side view of the device of  FIG. 8A ;  
       FIG. 9  is a perspective view of the device of  FIG. 8A  with an implant positioned therein;  
       FIG. 10A  is a perspective view of one embodiment of a single fixation device described herein;  
       FIG. 10B  is a side view of the device of  FIG. 10A ;  
       FIG. 10C  is another side view of the device of  FIG. 10A ;  
       FIG. 11A  is a perspective view of another embodiment of a device described herein;  
       FIG. 11B  is a side view of the device of  FIG. 11A ;  
       FIG. 11C  is another side view of the device of  FIG. 11A ;  
       FIG. 12A  is a perspective view of yet another embodiment of a device described herein;  
       FIG. 12B  is a top view of the device of  FIG. 12A ;  
       FIG. 13A  is a side view of one embodiment of a device described herein that includes mating features;  
       FIG. 13B  is a perspective view of the device of  FIG. 13A ;  
       FIG. 14A  is a top view of one embodiment of a device described herein that includes an extension portion;  
       FIG. 14B  is a perspective view of the device of  FIG. 14A ;  
       FIG. 14C  is a side view of the device of  FIG. 14A ;  
       FIG. 15  is a side view of the device of  FIG. 14A  implanted on a vertebral body;  
       FIG. 16A  is a perspective view of one embodiment of a device described herein that includes a hinge;  
       FIG. 16B  is a top view of the device of  FIG. 16A ;  
       FIG. 16C  is a cross-sectional view of the device of  FIG. 16A ;  
       FIG. 17A  is a cross-sectional view of another embodiment of a device described herein;  
       FIG. 17B  is another cross-sectional view of the device of  FIG. 17A   
       FIG. 18  is a top view of an embodiment of a device described herein that includes multiple implant receiving openings;  
       FIG. 19A  is a cross-sectional side view of another embodiment of a device described herein; and  
       FIG. 19B  is a perspective view of the device of  FIG. 19A . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention  
      Various exemplary methods and devices are provided for fixing an implant to native tissue, such as, bone. One such device includes at least one plate having a body with an upper surface and a lower tissue contacting surface. The body provides a large contact area for fixing the tissue implant to bone, such that the implant can be securely held in position without requiring penetration of the implant. In one embodiment, the plate body can include at least one aperture for receiving a fixation device and a tissue implant receiving opening through which a tissue implant can be threaded prior to fixing the plate to bone. A tissue implant can be positioned in the implant receiving opening and then fixed to bone by implanting a bone screw in the at least one aperture. In an alternative embodiment, two plate bodies can be used to fix a tissue implant in place. For example, first and second plate bodies can be implanted on native tissue with a tissue implant fixed therebetween. In yet another embodiment, the plate body can include two segments joined with a hinge. At least one of the segments can be pivoted to close a portion of an implant therebetween and to fix the implant in position.  
      While the methods and devices are described herein with respect to implantation on a vertebral body, one skilled in the art will appreciate that the devices can be implanted on a variety of native tissue surfaces for fixing a variety of tissue implants. Exemplary tissue surfaces include the variety of hard tissue surfaces that may or may not be covered with soft tissue. In particular, the terms “hard tissue surface,” “bone,” and “vertebral body” do not exclude structures having a native soft tissue coating or layer that may, for example, include cartilage, tendons, ligaments, meniscus, other soft tissue structures.  
      Unlike conventional devices, such as bone screws, the apparatus described herein can fix a tissue implant to bone without penetrating the implant. Conventional tissue implant fixation procedures can weaken a tissue implant, specifically in the region where the implant is penetrated. In addition, the plates described herein provide a large surface area, which can join the tissue implant to bone and provide additional securement. Thus, even if an implant is penetrated by a securement device described herein, the implant contacting surfaces of the device can help to prevent tearing of the tissue implant when tension is applied to the implant. The devices described herein can also allow an implant to be tensioned prior to fixation.  
      In one embodiment, illustrated in  FIGS. 1A through 6C , a single plate device  10  is described. As shown in  FIGS. 1A through 1B , plate  10  can include body  12  having a top surface  14  and a lower tissue contact surface  16 . Body  12  can also include an implant receiving opening  18  and apertures  20 . In use, an implant  22  can extend across bottom surface  16  of the body, through implant receiving opening  18 , and can wrap around top surface  14 . The implant is fixed in place by pinning the tissue implant between lower surface  16  and a tissue surface as shown in  FIG. 2 . For example, with implant  22  in position, bone screws  24  can be implanted through apertures  20  to fix body  12  and implant  22  in place.  
      Body  12  can have a variety of shapes and sizes, including, for example, an elongate shape extending along a longitudinal axis L from a first end  26  to a second end  28  and can include lateral sides  27 ,  29 . One skilled in the art will appreciate that body  12  could alternatively have a variety of other shapes such as a circular, triangular, or irregular shape. In one aspect, the shape and size of body  12  is adapted for positioning on a vertebral body, such as on a single vertebral body. To assist with fixation, body  12  can include a curvature adapted to match the anatomical curvature of the surface onto which device  10  will be implanted (i.e., the curvature of the surface of a vertebral body).  FIG. 2  illustrates body  12  having a curvature C along longitudinal axis L that allows body  12  to conform to the curvature of a boney tissue (e.g., vertebral body). Body  12  can also, or alternatively, have a curvature along an axis that is different from longitudinal axis L, such as, for example along a transverse axis. One skilled in the art will appreciate that the shape and size of body  12  can be adapted to various surfaces and curvatures of vertebral bodies as discussed in more detail below.  
      Body  12  can be, in one embodiment, flexible or semi-rigid and/or deformable, such that device  10  will conform to the tissue surface on which it is implanted, thereby enhancing contact and securement between native tissue and the tissue implant. Alternatively, body  12  can be rigid and/or non-deformable. One skilled in the art will appreciate that body  12  can be produced from the variety of materials used in orthopaedic or implantable devices, such as, for example metals, polymers, and/or natural materials. Examples include Ti64, CoCr, resorbable and non-resorbable polymers, allografts, autografts, xenografts, and combinations thereof.  
      Tissue receiving opening  18  in body  12  can be adapted for receiving a variety of tissue implants. The shape and size of opening  18  can be adapted to the implant shape and size, including generally planar implants such an implant  22 . In one aspect, opening  18  is defined by a longitudinally extending slot that allows passage of at least a portion of implant  22  therethrough. One skilled in the art will appreciate that opening  18  can have a variety of alternative shapes and sizes that could receive implants of various shapes and sizes (e.g., implants having a circular, triangular, or irregular shape). In addition, slot shaped opening  18  could receiving a variety of differently sized and shaped implants.  
      To assist with threading an implant through opening  18 , the top and or bottom surfaces of body  12  can include a gradient around opening  18  that slopes toward the opening. In use, the sloped surfaces can help direct the implants into opening  18 . In addition, once the implant is positioned within opening  18 , the sloped surfaces can help to reduce abrading and/or point loading of the implant. Other surface of body  12  can also include a gradient to reduce point loadings, such as, for example, at least one of lateral sides  27 ,  29 .  
      As shown in  FIG. 1A , a single opening  18  can extend along the longitudinal axis L. Alternatively, opening  18  could be offset from longitudinal axis L and/or be positioned at an angle with respect to axis L. In another embodiment, illustrated in  FIGS. 3A through 3C , body  12  could include more than one opening. Device  10  can include one, two, three, or more than three openings  18 , each adapted to receive at least a portion of an implant. The two-opening embodiment shown in  FIGS. 3A through 3C  includes two parallel openings  18   a,    18   b  through which an implant could be threaded. For example, an implant could extend from bottom surface  16  through opening  18   a,  over top surface  14 , and back through opening  18   b.  In the case of three or more openings, the implant could be threaded through the three or more successive openings. While openings  18   a,    18   b  are illustrated in a parallel configuration, one skilled in the art will appreciate that openings  18   a,    18   b  could alternatively extend at an angle with respect to one another.  
       FIGS. 4A and 4B  illustrates an opening  18 ′ that extends longitudinally as well as transversely. For example, opening  18 ′ extends to the lateral edge  27  of body  12  to provide an “open” configuration. In an alternative embodiment, illustrated in  FIGS. 5A and 5B , two openings  18 ′ a,    18 ′ b  are present and each extends laterally to lateral sides  27 ,  29  and include non-contiguous lateral edges  27 ,  29 . The implant can be seated in openings  18 ′ a,    18 ′ b  without having to thread the end of the implant through the openings  18 ′ a,    18 ′ b.    
      As shown in  FIGS. 1A through 6C , opening  18 ,  18 ′ and apertures  20  are positioned such that when a fixation device is inserted through the apertures, the fixation device does not penetrate an implant. In one aspect, apertures  20  are positioned longitudinally with respect to opening  18  as shown in  FIGS. 1A through 5C . When the implant is threaded through opening  18  the implant only covers a portion of lower surface  16 , leaving unobstructed the lower surface adjacent to body ends  26 ,  28 . Fixation device can then be implanted through apertures  20  without impinging on the implant.  
      Alternatively, as shown in  FIGS. 6A through 6C , apertures  20  can be positioned transversely with respect to openings  18   a,    18   b.  An implant can be threaded through and wrapped around a portion of body  12 , leaving a portion of upper and lower surfaces  14 ,  16  adjacent to lateral edge  27  unobstructed. In use, fixation devices can be inserted through apertures  20  without penetrating an implant seated within openings  18   a,    18   b.    
      Body  12  of device  10  can include any number of apertures  20 . In one embodiment, body  12  includes a single aperture (not shown). Alternatively, body  12  can include two or more apertures  20 . One skilled in the art will appreciate that the quantity of apertures can depend on a number of factors including, the degree of securement required, the securement surface, the expected strains and stresses, the type of fixation devices used, and placement of the device.  
      Apertures  20 , in one embodiment, are each adapted to receive a different fixation device. In use, the number of apertures can correspond to the number of fixation devices used to implant the device. For example, where two apertures are used, two bone screws are used to implant device  10 . In one aspect, top surface  14  of body  12  adjacent to apertures  20  can have a shape suitable to receive the fixation device, such as, for example a bone screw.  FIGS. 1A and 1B  illustrate body  12  with recessed area  36  around apertures  20  that has a shape corresponding to a head  38  of bone screws  24 . When bone screws  24  are positioned in apertures  20 , bone screw head  38  is seated at least partially within recessed area  36 .  
      Alternatively, or additionally, device  10  can include features to mate a bone screw with body  12 . For example, bone screws  24  can be held within apertures  20  by way of a snap-ring, webs, locking screw, snap-fit, friction fit, or other alternative configuration.  FIG. 6C  illustrates a cross-section of a portion of plate body  12 . Seated within plate body  12  is a retaining ring  33  that is adapted to mate with bone screw  24 . As bone screw  24  is implanted through aperture  20 , the head  38  of bone screw  24  will mate with retaining ring  33  and be held in position. One skilled in the art will appreciate that device  10  can include a variety of features for mating body  12  with fixation devices. Alternatively, bone screws  24  can be pre-assembled with device  10  and permanently positioned within body  12 .  
      A variety of fixation devices can be used to implant device  10 . In one embodiment, the fixation devices are bone fixation elements, including for, example, bone screws, pins, tines, wires, rivets, anchors, expansion bolts, and combinations thereof. One skilled in the art will appreciate that a wide variety of fixation devices can be used with the methods and apparatus described herein.  
      Body  12  can include a variety of features to assist with implantation/securement and/or tissue in-growth. In one aspect, body  12  includes surface features  30  that will contact native tissue when device  10  is implanted. Such surface features can include, for example, barbs, tines, fins, ribs, securement ridges, porous beading, and/or other coatings/treatments that promote soft or boney tissue apposition, integration, and/or plate resporbtion. Surface features  30  can be positioned, for example, on the tissue contacting tissue surface of device  10 , i.e., on lower surface  14 . In addition, such surface features can be positioned on body  12  such that they contact implant  22 . For example, such surface features can be positioned on top surface  14  and/or bottom surface  16  where the implant will contact device  10 . In one aspect, were surface features  30  contact implant  22 , the surface features are adapted such that they do not penetrate the implant.  
       FIG. 6B  illustrates body  12  with surface features  30  (i.e., ridges  31 ) positioned on bottom surface  16  of device  10 . Ridges  31  are positioned transversely across body  12  and extend the full length of bottom surface  16 . In use, ridges  31  can contact native tissue, as well as, an implant positioned between bottom surface  16  and native tissue.  
      In another embodiment described herein, device  100  includes two or more plates that can work together to fix a tissue implant. Device  100 , as shown in  FIGS. 7A through 12B , can include a first, bottom plate body  112   a  and a second, top plate body  112   b  adapted to receive at least a portion of a tissue implant therebetween. Plate bodies  112   a,    112   b  can provide a large surface area for holding a tissue implant such that the implant can support a maximum load without tearing.  
      In use, an implant can be fixed between the bottom plate body and native tissue, as well as, between the plate bodies, thereby providing securement of the implant. In one embodiment, the implant extends across a bottom surface  116   a  of the bottom plate  11   2   a,  then wraps around a lateral edge  127   a  (or  129   a ) of the bottom plate, and extends between a top surface  114   a  of the bottom plate and a bottom surface  116   b  of the top plate  112   b  as generally shown in  FIG. 9 . The top and bottom plate are then implanted using fixation devices. In an alternative embodiment, the implant can also, or alternatively, extend through a tissue receiving opening in one of the plates.  
       FIGS. 7A through 7C  illustrate one embodiment of device  100  having plate bodies  112   a,    112   b  of similar size and shape, both including apertures  120  for receiving fixation devices  24 . Inserting the fixation devices through apertures  120  implants plate bodies  112   a,    112   b  on native tissue while fixing a tissue implant in position. Bottom plate  112   a  includes a tissue contacting lower surface  116   a  and an implant contacting upper surface  114   a,  while the upper plate  112   b  includes an implant contacting lower surface  116   b  and an upper surface  114   b.  In one embodiment, at least a portion of upper surface  114   a  can nest within lower surface  116   b  when the plate bodies are implanted.  
      In one aspect, both plate bodies  112   a,    112   b  are similar to body  12  described above and can be shaped and sized according to the anatomical features of the tissue to which they will be implanted. In one embodiment, illustrated in  FIGS. 7A through 7C , plate bodies  112   a,    112   b  have an elongate shape with a curvature adapted for positioning on a vertebral body. For example, the plates can have a concave lower surface  116   a,    116   b  and a convex upper surface  114   a,    114   b,  such that a curvature extends along the longitudinal axis L and along an axis perpendicular to the longitudinal axis. In use, the plate bodies can be positioned on a generally convex surface.  
      In an alterative embodiment, device  100  can include plate bodies  112   a,    112   b  sized and shaped for implantation on an edge of a vertebral body. Plate bodies  112   a,    112   b  can include a minor curvature along longitudinal axis L and a major curvature along an axis perpendicular to the longitudinal axis, the major curvature corresponding to the curvature of an edge of a vertebral body.  FIGS. 8A through 9  illustrates one such embodiment of device  100 . Elongate plate bodies  112   a,    112   b  have a major curvature such that the plate bodies include first segments  132   a,    132   b  and second segments  134   a,    134   b,  where the first and second segments are positioned at an angle with respect to one another. In use, the first plate segment  132   a,    132   b  can be positioned on a first surface of a vertebral body and the second plate segment  134   a,    134   b  can be positioned on a second surface of a vertebral body.  
       FIG. 9  illustrates the plates of  FIGS. 8A and 8B  implanted on a vertebral body. The curvature of the plate bodies  112   a,    112   b  is generally complementary to the curvature of the vertebral body. One skilled in the art will appreciate that the angle at which segments  132   a,    132   b  are positioned with respect to segments  134   a,    134   b  can be varied according to the shape of the vertebral body. In one aspect, the first and second segments are positioned at an angle with respect to one another that is in the range of about 15 degrees and 150 degrees, and more preferably in the range of about 80 degrees and 130 degrees.  
      The apertures  120  can be positioned in plates  112   a,    112   b  in a variety of location as described above. For example,  FIG. 9  illustrates apertures in first plate segments  132   a,    132   b.  Alternatively, apertures  120  could be positioned closer to the major curvature of plates  112   a,    112   b  and/or in second plate segments  134   a,    134   b.  In one aspect, apertures  120  are positioned in plates  112   a,    112   b  such that fixation elements inserted through apertures  120  can be implanted in the thick cortical rim of a vertebral body. For example,  FIG. 15  (discussed below) includes apertures  120  positioned such that bone screws are implanted into the cortical rim and angled away from the disc space. This configuration can provide additional bone depth for fixation element implantation, thereby improving securement of plates  112   a,    112   b.  In addition, locating apertures  120  close to the major curvature can improve surgical access, minimizing the amount of soft tissue damage.  
      Plates  11   2   a,    112   b  of device  100  can have a variety of shapes and sizes as mentioned above.  FIGS. 10A and 10B  illustrate yet another embodiment of plates  112   a,    112   b  having a generally trapezoidal shape and a single aperture  20 . In use, an implant can be positioned between plate bodies  112   a,    112   b  and fixed in place with a single fixation device. The small profile of the plate bodies allows for fixation of implants on smaller surfaces and/or for applications where it is preferable to use only a single fixation device.  
      To assist with fixation, plate bodies  112   a,    112   b  can include surface features  130  adapted to grip an implant.  FIGS. 11A through 11C  illustrate plate bodies  112   a,    112   b  with surface features  130  positioned on the top surface  114   a  of plate body  112   a.  As shown, ridges can extend longitudinally across the top of plate  112   a  and be positioned across the entire surface of the plate. In another example, shown in  FIG. 11C , the surface features  130  can extend transversely to the longitudinal axis of the plate body. One skilled in the art will appreciate that ridges  131  can alternatively be positioned on only a portion of the plate surface (not shown). For example, ridges  131  could be positioned only on the portions of the plate surface that will contact an implant positioned between the plates. In addition to top surface  114   a,  the bottom surface  116   b  of plate body  112   b  can include surface features. In one embodiment, top plate  112   b  can include surface features that are complementary to the surface features on top surface  114   a.    
      Exemplary surface features  130  can include barbs, tines, fins, ribs, securement ridges, porous beading, and/or other coatings/treatments. In one embodiment, surface features  130  are adapted to grip the implant without penetrating the implant. One skilled in the art will appreciate that the “penetrating” nature of surface features can depend on the geometry of the surface features as well as the amount of force which the plates apply to the implant. Conversely, since the implant is pinned at two locations (i.e., between the lower plate and native tissue and between the plate bodies  112   a,    112   b ), implant penetrating surface features can be located on the surface(s) between plate bodies  112   a,    112   b.    
      Plate bodies  112   a,    112   b  can include a variety of other features as disclosed with respect to the single plate embodiment described above. In one embodiment, device  100  can include an implant receiving opening  118 .  FIGS. 12A and 12B  illustrate device  100  with opening  118  in upper plate body  112   b.  In use, an implant can extend between the plate bodies and through opening  118 . One skilled in the art will appreciate that plate bodies  112   a,    112   b  can include more than one opening  118 .  
      In another embodiment of device  100 , plates  112   a,    112   b  can be adapted to mate with one another. For example, mating features can be positioned plate bodies  112   a,    112   b  to allow mating of the plates to one another after positioning an implant therebetween. The mating features can facilitate implantation of device  100  by keeping apertures  120  of plate bodies  112   a,    112   b  aligned during fixation of the device. Plate bodies  112   a,    112   b  can be mated in a variety of permanent or non-permanent ways, including, for example, snap-fit, friction fit, tongue and groove, crimping (including cold compression welding and/or bending of the plate bodies), welding (including thermal, mechanical, ultrasonic, and RF), and combinations thereof.  
       FIGS. 13A and 13B  illustrate exemplary plate bodies  112   a,    112   b  having a snap-fit arrangement. Plate body  112   b  includes a protrusion portion  141  that is adapt to sit within a recess  143 . After an implant is positioned in recess  143 , protrusion portion  141  of plate  112   b  can be seated at least partially within recess  143 . Protrusion portion  141  can be sized and shaped to snap into recess  143  and thus be held in place. One skilled in the art will appreciate that a variety of other mating techniques can be used with the devices described herein.  
      In addition or as an alternative to holding plates together, the mating features can assist with alignment. For example, the protrusion/recess of plates  112   a,    112   b  in  FIG. 13A and 13B  can be sized and shaped such that they will only match up when plates  112   a,    112   b  are properly aligned. The mating features can thereby provide a signal that plates  112   a,    112   b  and apertures  120  are properly aligned. In one aspect, the mating features can be designed to provide tactile and/or auditory feedback when the plates are aligned.  
      In one embodiment, the implant fixation device described herein can assist with retention of prosthetic discs or disc implants. For example, an extension portion  140  can be positioned on at least one of the plate bodies  112   a,    112   b  such that when device  100 ′ is implanted, extension portion  140  extends into the space disc space between vertebral bodies. If a disc prosthesis tends to back out of the disc space it will encounter extension portion  140  and be prevented from further movement.  FIGS. 14A through 14C  illustrate one example of device  100 ′ with extension portion  140  extending from top plate body  112   b.  Extension portion  140  is sized and shaped such that when plate bodies  112   a,    112   b  are implanted on a vertebral body, the extension portion will extend into the space between adjacent vertebral bodies. In one aspect, extension portion  140  is defined by a fin-like protrusion that extends from a portion of plate body  112   b  (e.g., it extends from second plate segment  134 ).  
       FIG. 15  illustrates device  100 ′ is implanted on an inferior corner of a vertebral body  70  such that extension portion  140  extend into the inferior disc space. While extension portion  140  is illustrated with respect to the two-plate-body embodiment of device  100 , one skilled in the art will appreciate that extension portion  140  can similarly be applied to any of the embodiments described herein.  
      In another embodiment of the methods and apparatus described herein, a hinged device  200  is provided. Device  200  can include a plate body having two segments joined by a hinge, such that the two segments can pivot with respect to each other. A user can position an implant between the segments and then pivot at least one of the segments to pin the implant between the segments and thereby hold the implant in place. In one aspect, the plate body can include one, two, or more than two implant receiving openings. The implant can extend through the opening(s) and into an area between the two segments of the plate body. In an alternative embodiment, the plate body does not include any implant receiving openings. One skilled in the art will appreciate that the hinged plate can include the various features described above with respect to the devices  10 ,  100 ,  100 ′ including for example, apertures for receiving fixation devices, surface features for gripping the implant and/or native tissue, and/or features for mating the plate segments similar to those used to mate the two plate devices  100 ,  100 ′.  
      One embodiment of device  200  is illustrated in  FIGS. 16A through 16C , including a single implant receiving opening  218  and apertures  220  for receiving fixation device. Plate body  212  has an upper surface  214  and a lower native tissue contacting surface  216  as well as a first plate body segment  252  and a second plate body segment  254 . Segments  252 ,  254  are joined by hinge  256 . Between segments  252 ,  254  is a slot  255 , at least a portion of which defines implant receiving opening  218 . Opening  218  allows an implant to be positioned such that it extends across a portion of lower plate surface  216 , through implant receiving opening  218 , and between plate segments  252 ,  254 . Pivoting plate segment  252  toward plate segment  254  fixes the implant in position. Implant  222  can also be fixed by implanting plate body  218 , with the implant located between lower surface  216  and native tissue.  
      As shown in  FIG. 16B , slot  255  is defined by a gap between segments  252 ,  254 . Segment  254  has a generally rectangular shape with one side connected to segment  252  via hinge  256 . Slot  255  extends around three sides of segment  254  such that it has a generally “U” type shape. While an implant can be extended through any portion of slot  255 , in one embodiment implant receiving opening  218  is defined by the longitudinally extending portion of slot  255 .  
      As shown in the cross-sectional view of device  200  provided by  FIG. 16C , opening  218  extends through plate body  212  at an angle with respect to top and bottom surface  214 ,  216 . For example, opening  218  can be non-perpendicular with respect to the upper and/or lower surfaces of the device. This provides implant contact areas  258 ,  260  for gripping an implant. With an implant positioned between implant contact areas  258 ,  260 , segments  252  and  254  can be brought together to fix the implant in position.  
      In an alternative embodiment, opening  218  can be positioned perpendicularly with respect to top and bottom plate surfaces  214 ,  216 .  FIGS. 17A and 17B  illustrate plate body  212  with implant receiving opening  218  positioned in plate segment  254 . An implant can extend through opening  218  and be fixed in position between contact areas  258 ,  260  of plate segments  252 ,  254 .  
      Implant receiving opening  218  of device  200  can be positioned in a variety of locations on plate body  212 . For example, opening  218  can be defined by an elongate slot that runs parallel to hinge  256 . More than one opening  218  can also be included in plate body  212 .  FIG. 18  illustrates plate body  212  with a first implant receiving opening  218   a  and a second implant receiving opening  218   b.  An implant can be threaded through first opening  218   a  between segments  252 ,  254  and then back through opening  218   b,  such that the implant wraps around a portion of body  212 . One skilled in the art will appreciate that opening(s)  218  can have a variety of different sizes and shapes.  
      Alternatively, plate body  212  can be designed without an implant receiving opening. An implant can be laid between segments  252 ,  254  without extending through an implant receiving opening as shown in  FIGS. 19A and 19B . The joinder of segments  252  and  254  will hold the implant therebetween.  
      Hinges  256  allow relative movement of segments  252 ,  254 . A variety of hinges can be used with device  200 , and in one embodiment, plate body  212  is a contiguous single body and hinge  256  is a living hinge. Living hinge  256  can be created by forming a thin area in plate body  212  that allows bending of plate body  212 . One skilled in the art will appreciate that the creation of a living hinge will depend on a number of factors including the materials from which the plate body is created and the geometry of the plate body. In one embodiment plate body  212  is formed from materials that are flexible or pliable as described above.  
      Aperture(s)  220  in plate body  212  can be located such that when the fixation devices are implanted the fixation devices do not penetrate the implant. In addition, apertures  220  can be positioned such that when a fixation device is implanted through the aperture, it causes plate segments  252 ,  254  to pivot toward one another and fixes segments  252 ,  254  relative to one another. As shown in the cross-section view provided in  FIG. 16C , apertures  220  extend through plate segment  252 . When fixation devices are implanted through segment  252 , segment  252  is pivoted toward segment  254 , bringing the segments together and fixing an implant therebetween. Alternatively, apertures  220  can extend through both segments  252 ,  254 . The cross-sectional view provided by  FIGS. 17A and 17B  shows aperture  220  extending through both segments  252 ,  254  and positioned such that when a fixation device is implanted it will fix segments  252 ,  254  relative to one another.  
      Segments  252 ,  254  can include surface features to assist with gripping implant  222 . For example, segments  252 ,  254  as illustrated in  FIGS. 17A and 17B  include surface features  230  on implant contacting surfaces  258 ,  260 . Implant contacting surface  260  includes a recess  262  that can receive a protrusion  264  on surface  258 . When segment  252  is pivoted into contact with segment  254 , at least a portion of implant  222  is forced into recess  262  by protrusion  264 . One skilled in the art will appreciate that a variety of surface features can be used with device  200 . In one embodiment, surface features are adapted to grip an implant without penetrating the implant. Alternatively, surface features can puncture the implant. The large surface area of implant contacting surfaces  258 ,  260  can provides support for implant  222  where it is pierced.  
      As mentioned above, the devices described herein can be used to fix a variety of implants. In one embodiment, the implant is a soft tissue implant formed from materials, such as, for example resorbable and non-resorbable polymers, allografts, autografts, xenografts, and combinations thereof. In one aspect, the implant is formed from graft materials, such as, for example tendenous, cartilaginous, ligamentous, protein or collagen based materials, extra-cellular matrices (ECMs), or other synthetic resorbable or non-resorbable graft materials. In yet another embodiment, the implant is formed from small intestine submucosa (SIS). The implant can also be reinforced/enhanced with a variety of materials to augment its natural properties and/or promote tissue growth. In one aspect, the implant can include a coating or laminate of resorbable polymers and/or be treated or coated with a variety of growth factors, anti-coagulants and/or lubricants. In addition, or alternatively, the implant can be oriented to minimize local soft tissue adhesion by positioning the implant such that the treated or luminal side (if ECM) is oriented toward local soft tissue.  
      Fixation of the implant can also be augmented with materials to enhance securement, apposition, integration, and/or to fill voids created by a device/implant recessed within a bone hole. Exemplary augmentation materials can include adhesives (e.g., fibrin, polymeric glues, etc.), bone void fillers (e.g., hydroxyapatite, tricalcium phosphate, DBM putty, bone cement, and combinations thereof, etc.), injectable bone substitutes (e.g., collagen, BMP, etc.), growth factor delivery systems (e.g., osteoconductive matrix formulations (Healos), recombinant human growth/differentiation factor-5 (MP52), etc.), and combinations thereof. Augmentation can also be in the form of sutures wrapped around the implant and/or device. An alternative method of augmentation can include a plug or a second bone anchor that can fill voids between, above, or below the implanted device.  
      One of ordinary skill in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.