Abstract:
An apparatus and method for securing boney structures is disclosed which includes a compression mechanism and a force transfer mechanism. The compression mechanism may have bone engagement members that have one portion slideably coupled to a housing positioned within the implant and another portion rotatably coupled to the implant so that a movement of the housing causes the slideable portion to move within the housing and a penetrating member to rotate about the rotatably coupled portion. The force transfer mechanism may be coupled to the compression mechanism to move the housing.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application relates to, and claims the benefit of the filing date of, co-pending U.S. provisional patent application Ser. No. 60/987,111 entitled VERTEBRAL INTERBODY COMPRESSION IMPLANT, filed Nov. 12, 2007, the entire contents of which are incorporated herein by reference for all purposes. 
     
    
     BACKGROUND INFORMATION 
       [0002]    The invention relates in general to skeletal stabilization systems, and in particular to implants, surgical guides, delivery instruments and methods for delivering and attaching implants to bony structures such as a vertebrae. 
         [0003]    The human spine is a complex structure designed to achieve a myriad of tasks, many of them of a complex kinematic nature. The spinal vertebrae allow the spine to flex in three axes of movement relative to the portion of the spine in motion. These axes include the horizontal (i.e., bending either forward/anterior or aft/posterior), roll (i.e., lateral bending to either left or right side), and rotation (i.e., twisting of the shoulders relative to the pelvis). 
         [0004]    The intervertebral spacing (e.g., between neighboring vertebrae) in a healthy spine is maintained by a compressible and somewhat elastic disc. The disc serves to enable the spine to move about the various axes of rotation and through the various arcs and movements required for normal mobility. The elasticity of the disc maintains the spacing between the vertebrae during flexion and lateral bending of the spine, allowing room or clearance for compression of neighboring vertebrae. In addition, the disc enables relative rotation about the vertical axis of neighboring vertebrae, allowing for the twisting of the shoulders relative to the hips and pelvis. The clearance between neighboring vertebrae, as maintained by a healthy disc, is also important to allow the nerves from the spinal cord to extend out from the spine, e.g., between neighboring vertebrae, without being squeezed or impinged by the adjacent vertebrae. 
         [0005]    In situations (e.g., based upon injury or otherwise) where a disc is not functioning properly, the inter-vertebral disc tends to compress, and in doing so pressure is exerted on nerves extending from the spinal cord by the reduced inter-vertebral spacing. Various other types of nerve problems may be experienced in the spine, such as exiting nerve root compression in neural foramen, passing nerve root compression, and enervated annulus (i.e., where nerves grow into a cracked/compromised annulus, causing pain every time the disc/annulus is compressed), as examples. Many medical procedures have been devised to alleviate such nerve compression and the pain that results from the nerve pressure. Many of these procedures revolve around attempts to prevent the vertebrae from moving too close to each other by surgically removing an improperly functioning disc and replacing it with a lumbar interbody fusion device or spacer. Although prior interbody devices, including spacers, may be effective at improving the condition of a patient, the vertebrae of the spine, body organs, the spinal cord, other nerves, and other adjacent bodily structures make it difficult to obtain surgical access to the locations between the vertebrae where the spacer is to be installed. 
         [0006]    PLIF is an acronym for Posterior Lumbar Interbody Fusion. PLIF is a surgical procedure that may be used to treat the conditions mentioned above. In this procedure, a spacer or implant, bone graft, or a bone graft substitute, may be placed between vertebrae to fuse them and create more stable spine. The bone graft is inserted into the disc space from the back (posterior). In addition, spinal instrumentation such as screws and rods may be used to hold the spine in position and help promote successful fusion. ALIF stands for Anterior Lumbar Interbody Fusion. ALIF is a surgical procedure similar to PLIF, but it is done from the front (anterior) of the body, usually through an incision in the lower abdominal area or on the side. The incision may involve cutting through, and later repairing, the muscles in the lower abdomen. In recent years, surgeons have begun to use a TLIF procedure (Transforaminal Lumbar Interbody Fusion). A TLIF may accomplish the same goals as a PLIF procedure, however in the TLIF technique the bone graft or implant in inserted into the disc space laterally or from the side. The TLIF technique usually results in the nerve roots being moved less during the procedure, as compared to a PLIF, and may reduce the risk of scarring or damaging the nerve roots. XLIF stands for extreme Lateral Interbody Fusion. XLIF is also a relatively new surgical procedure and avoids an incision that traverses the abdomen and also avoids cutting or disrupting the muscles of the back. In surgical procedure, the disk space is accessed from a very small incision on the patient&#39;s side. The bone graft or implant may then be inserted into the disc space laterally or from the side. 
       SUMMARY 
       [0007]    An implant for securing boney structures is provided, comprising an engagement mechanism having bone engagement members slideably and rotatably coupled to a moveable housing in the implant, where the bone engagement members rotate away from the implant when the housing is moved by a force transfer mechanism. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0008]    For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following Detailed Description taken in conjunction with the accompanying drawings, in which: 
           [0009]      FIG. 1  is a perspective view of one possible embodiment of a vertebral interbody compression implant; 
           [0010]      FIG. 2  is an exploded assembly view of one embodiment the vertebral interbody compression implant of  FIG. 1 ; 
           [0011]      FIG. 3  is a perspective cross section view of one possible embodiment of a main body which may be incorporated in the vertebral interbody compression implant of  FIG. 1 ; 
           [0012]      FIG. 4  is a perspective view of one possible embodiment a compression mechanism which may be incorporated in the vertebral interbody compression implant of  FIG. 1 ; 
           [0013]      FIG. 5  is an exploded view of one possible embodiment of the compression mechanism of  FIG. 4 ; 
           [0014]      FIG. 6  is a cross section view of the vertebral interbody compression implant of  FIG. 1  in a first position; 
           [0015]      FIG. 7A  is a perspective view of the vertebral interbody compression implant of  FIG. 1  in a first position; 
           [0016]      FIG. 7B  is a cross section view of the vertebral interbody compression implant of  FIG. 1  in a second position; 
           [0017]      FIG. 8  is a perspective view of one possible embodiment of an insertion instrument which may be used to implant the vertebral interbody compression implant of  FIG. 1 ; 
           [0018]      FIG. 9  is a flow diagram of one possible method for inserting the vertebral interbody compression implant of  FIG. 1 ; 
           [0019]      FIG. 10A  is a side view of the insertion instrument of  FIG. 8  inserting the vertebral interbody compression implant of  FIG. 1  between two adjacent vertebrae; and 
           [0020]      FIG. 10B  is a side view of two adjacent vertebrae with the insertion instrument of  FIG. 8  and the vertebral interbody compression implant of  FIG. 1  in a second position. 
       
    
    
       [0021]    It should be noted the drawings are not intended to represent the only aspect of the invention. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, and composition of matter, means, methods and steps described in the specification. As one will readily appreciate from the disclosure, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized. Accordingly, the invention is intended to encompass within its scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. 
       DETAILED DESCRIPTION  
       [0022]    Specific examples of components, methods, and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to limit the invention from that described in the claims. Well-known elements are presented without detailed description in order not to obscure the present invention in unnecessary detail. For the most part, details unnecessary to obtain a complete understanding of the present invention have been omitted inasmuch as such details are within the skills of persons of ordinary skill in the relevant art. 
         [0023]    Turning now to  FIG. 1 , there is presented a front perspective view of one possible embodiment of a perspective view of a vertebral interbody compression implant  10 . The implant  10  may incorporate a main body  100  and a compression mechanism  200 . The implant  10  may be inserted between two adjacent bony structures (for example two adjacent vertebrae of the spine) using various instruments to stabilize or fuse the adjacent bony structures. The compression mechanism  200  may aid in securing the implant  10  to the adjacent boney structures and may act to compress the adjacent boney structures against the implant  10  which may promote bone fusion. The implant  10  may be used alone or in conjunction with other implants to stabilize or fuse different bony structures. Accordingly, the main body  100  and the compression mechanism  200  may interrelate to securely attach and engage the implant  10  to two adjacent vertebral end plates a spine to provide for adequate stabilization or fusion. 
         [0024]    In certain embodiments, the main body  100  may have a leading end  14  and a trailing end  12  opposite the leading end  14 . The leading end  14  and the trailing end  12  may be connected by a pair of opposite sides  16  and  18 . The leading end  14  and trailing end  12  may have a length and a height and the pair of opposite sides  16  and  18  may have a height and a width. In certain embodiments, the length of the leading end  14  and the trailing end  12  may be greater than the width of the opposite sides  16  and  8 . The main body  100  may have one or more reinforcing walls  20   a  and  20   b  connecting the leading end  14  and the trailing end  12  which may be located between the pair of opposite sides  16  and  18 . The reinforcing walls  20   a  and  20   b  may run generally through the center of the body between the pair of opposite sides  16  and  18 . The main body  100  may have one or more openings  22   a  and  22   b  located between the opposite sides, between the lead and trailing ends  14  and  12  and bounded by the reinforcing walls  20   a  and  20   b.  The openings  22   a  and  22   b  may be filled with bone growth material such as BMP (bone morphogenetic protein), autograft, allograft, ceramics or other biocompatible material that aids in bone fusion. The leading end  14 , the trailing end  12  and the reinforcing walls  20   a  and  20   b  may define a slot  108  of the implant  10 . that extends through the main body  100 . The slot  108  may at least partially enclose the compression mechanism  200 . The leading end  14 , the trailing end  12 , the opposite sides  16  and  18  may have a contoured upper surface and a contoured lower surface that conforms to the shape of a vertebral endplate. The upper surface and the lower surfaces may have projections, such as teeth, which may aid in gripping the vertebral end plate surface. 
         [0025]    Referring to  FIG. 2 , there is presented an exploded assembly view of one embodiment the implant  10  illustrating the main body  100  and the compression mechanism  200 . The reinforcing walls  20   a  and  20   b  may each have an upper aperture  112   a  and  112   b  and a lower apertures  114   a  and  114   b  extending generally transversely into the reinforcing walls  20   a  and  20   b.  The upper apertures  112   a  and  112   b  and the lower apertures  114   a  and  114   b  may aid in coupling the compression mechanism  200  to the main body  100 . The main body  100  may have an inner surface defining a generally rectangular shaped passage  110  that is dimensioned to slidingly receive the compression mechanism  100 . The passage  110  may extend from the trailing end  14  toward the leading end along a longitudinal axis of the main body  100 . One or more sides of the passage  110  may be enlarged, which may allow the main body  100  to receive the compression mechanism  200 . 
         [0026]    As will be explained in greater detail later, the compression mechanism  200  may include a pair of bone engagement members  240   a  and  240   b  and a drive element  210 . In certain embodiments there may be a plurality of bone engagement members  240   a  and  240   b  which may be arranged in an anterior-posterior direction or a medial-lateral direction with respect to a pair of vertebral end plates. The drive element  210  may be dimensioned to pass through the passage  110 . The leading end  14  of the main body  100  may have a first inner surface  120  adjacent to the passage  110  that defines a bore that is dimensioned to receive at least a portion of the drive element  210  and a portion of the compression mechanism  200  (as well be described in greater detail in  FIGS. 6 ,  7 A,  7 B). The pair of bone engagement members  240   a  and  240   b  may be dimensioned to at least partially pass through the slot  108  of the main body  100 . 
         [0027]    Referring now to  FIG. 3 , there is shown is a perspective cross sectional view of the main body  100  taken along a longitudinal axis(line  3 - 3  shown in  FIG. 1 ) between the leading end  14  and the trailing end  12 . The main body  100  may have a second inner surface  122  adjacent to and coaxial with the first inner surface that defines a recess that extends into the leading end  14 . In certain embodiments, the diameter of the first inner surface  120  may be less than a diameter of the second inner surface  122 . The second inner surface  122  may be dimensioned to receive at least a portion of the drive element  210  and a portion of the coupling mechanism  200 . A shoulder  124  may be located between the first inner surface  120  and the second inner surface  122 . 
         [0028]    Referring to  FIG. 4 , there is shown a perspective view of the compression mechanism  200 . In certain embodiments the compression mechanism  200  may incorporate the pair of bone engagement members  240   a  and  240   b,  a first and second coupling members  252   a  and  252   b,  a housing  230 , the drive element  210  and a drive shaft  220 . As will be explained in greater detail below, the drive element  210  and the drive shaft  220  may apply a force to the housing  230  to move the bone engagement members  240   a  and  240   b.  The compression mechanism  200  may have a first position and a second position. The second position may allow the bone engagement members  240   a  and  240   b  to secure and/or compress a pair of adjacent boney structures (not shown). 
         [0029]    Referring to  FIG. 5 , there is shown an exploded assembly view of the compression mechanism  200  illustrating the pair of bone engagement members  240   a  and  240   b,  a first and second coupling members  252   a  and  252   b,  the housing  230 , the drive element  210  and the drive shaft  220 . The drive element  210  may have an inner surface  218  that defines an opening there through. The inner surface  218  may be partially threaded (not shown) and dimensioned to receive the drive shaft  220 . 
         [0030]    The drive element  210  may incorporate a force transfer member  212 , a centering element  214  and a shoulder  216 . The force transfer member  212  may have an outer surface that may be utilized as a driving means to translate the force transfer member  212  in relation to the drive shaft  220 . A surgeon may apply a linear or non linear force (for example torque) to the force transfer member  212 . The outer surface of the force transfer member  212  may have various geometries such as torx, hex, stars, oblong, rectangular and square shapes which may allow for the transfer of a linear or non linear force. In alternative embodiments the inner surface of the force transfer member may have various geometries such as torx, hex, stars, oblong, rectangular and square shapes which may allow for the transfer of a linear or non linear force. The centering element  214  may be generally cylindrical in shape which may aid in the alignment of the compression mechanism relative to the implant  100 . As will be described in greater detail below, the shoulder  216  may be generally circular in shape and may aid in securing the compression mechanism  200  to the implant  100 . 
         [0031]    The drive element  210  may couple to the drive shaft  220 . The drive shaft  220  may be generally cylindrical in shape and may extend along a longitudinal axis. The drive shaft  220  may have a threaded outer surface that engages the threaded inner surface of the drive element  210 . One end of the drive shaft  220  may couple to the housing  230 . The drive shaft  220  and the housing  230  may be an integral component or a two piece design assembled using conventional assembly methods such as welding, pinning, adhesives, press fits or other means known to those skilled in the art. The housing  230  may extend along a longitudinal axis  235  and may have a first end and a second end. The housing  230  may have a generally rectangular or cylindrical shape. In certain embodiments, the housing  230  may have a pair of arms  232   a  and  232   b  located between the first end and the second end that extend out in a first direction and define an open channel there between. Each arm  232   a  and may have a slot  234   a  and  234   b  that extends in a generally transverse direction to the longitudinal axis  235  of the housing  230 . 
         [0032]    The bone engagement members  240   a  and  240   b  may be dimensioned to be received within the channel of the housing  230 . In certain embodiments the bone engagement members  240   a  and  240   b  may have a first arm  242   a  and  242   b  that extend along a first axis and a second arm  244   a  and  244   b  that extend along a second arcuate axis, respectively. The first arms  242   a  and  242   b  may each have a first end and a second end. The first end of the first arms  242   a  and  242   b  may have tab portions, such as first boss  248   a  and  248   b  (not shown) and the second end of the first arms  242   a  and  242   b  may have second boss  250   a  and  250   b,  respectively. The first boss  248   a  and  248   b  and the second boss  250   a  and  250   b  may extend in a generally transverse direction to the first axis. The first boss  248   a  and  248   b  may be dimensioned to be received within the slots  234   a  and  234   b  of the first and second arms  232   a  and  232   b,  respectively. In certain embodiments, the second boss  250   a  and  250   b  may extend in a generally opposite direction to the first boss  248   a  and  248   b,  and may have an inner surface defining a bore there through that is dimensioned to receive the first and second coupling members  252   a  and  252   b  (as shown in  FIG. 4 ). The distance D (shown in  FIG. 5 ) between the first boss  248   a  and  248   b  and the second boss  250   a  and  250   b  may provide for a moment arm about which the first arms  242   a  and  242   b  may rotate. 
         [0033]    The second arms  244   a  and  244   b  may have a first end and a second end. The first end of the second arms  244   a  and  244   b  may couple to the first end of the first arms  248   a  and  248   b,  respectively. The second end of the second arms  244   a  and  244   b  may have one or more bone penetrating elements  246   a  and  246   b,  such as a spike or a trocar shaped end. 
         [0034]    Turning now to  FIG. 6 , there is shown a perspective cross sectional view taken along line  6 - 6  shown in  FIG. 1  of the implant  10  illustrating the main body  100  coupled to the compression mechanism  200 . The housing  230 , the bone engagement members  240   a  and  240   b,  the drive shaft  220  and the shoulder  216  of the drive element  210  may slide into and fit within the passage  110 . The shoulder  216  may act as a stop to prevent the compression mechanism from advancing too far into the bore  120 . The centering element  214  may fit within the bore  120  (not shown) and the force transfer member  212  may fit within the recess  122  of the main body  100 . The second boss  250   a  (not shown) may be aligned with lower apertures  114   a  and  114   b.  The coupling element  252   a  may pass through the lower apertures  114   a  and  114   b  and the bore of the second boss  250   a  to couple the bone engagement member  240   b  to the main body  100 . The second boss  250   b  may be aligned with upper apertures  112   a  and  112   b.  The coupling element  252   b  may pass through the upper apertures  112   a  and  112   b  and the bore of the second boss  250   b  to couple the bone engagement member  240   a  to the main body  100 . The compression mechanism  200  is shown in the first position in  FIG. 6 . In the first position the housing  230  may be located adjacent to the force transfer element  210  and the bone penetrating elements  246   a  and  246   b  may be located within the slot  108  of the main body  100  or slightly protruding. 
         [0035]    The compression mechanism  200  may move from the first position to the second position as illustrated in  FIG. 7A and 7B . The main body  100  in  FIG. 7A  is shown as transparent or removed for clarity purposes. The force transfer mechanism  212  may be moved by a surgeon such that the drive shaft  220  and the attached housing  230  travels axially in relation to the drive element  210 , as represented by arrow F 1 . As the housing  230  travels axially, the arms  232   a  and  232   b  of the housing  230  may apply a force on the first boss  248   a  and  248   b  of the first end of the first arms  242   a  and  242   b,  respectively, causing the first arms  242   a  and  242   b  to pivot about the coupling members  252   a  and  252   b.  As the first arms  242   a  and  242   b  pivot, the first boss  248   a  and  248   b  (not shown)may travel axially within the slot  234   a  (not shown) and  234   b  of the housing  230 . In certain embodiments, the outer surfaces may make contact with the inner surfaces of the slots  234   a  and  234   b  to move the first boss  248   a  and  248   b  along the slot  234   a  and  234   b.  The distance D between the first boss  248   a  and  248   b  and the second boss  250   a  and  250   b  may provide a moment arm whereby a force applied at the first boss  248   a  and  248   b  may cause a torque to be applied to the bone engagement members  240   a  and  240   b.  The bone engagement members  240   a  and  240   b  may move both with the housing  230  along the longitudinal axis  235 , and the bone engagement members  240   a  and  240   b  may rotate relative to the housing  230  and the implant  10  about the coupling of the bone engagement members  240   a  and  240   b  to the housing  230  at the second boss  250   a  and  250   b.  The second arms  244   a  and  244   b  may travel along a curved path, as represented by dotted arrows R 1  and R 2 . 
         [0036]    As shown in  FIG. 7B , the second arms  244   a  and  244   b  continue to rotate and protrude out of the slot  108  of the main body  100 .  FIG. 6C  illustrates the implant  10  illustrating the compression mechanism  200  in the second position. In the second position, the housing  230  may be located distal of the force transfer member  210  and the bone engagement members  240   a  and  240   b  may protrude out of the slot  108  of the implant  100 . The bone penetrating elements  246   a  and  246   b  may engage one or more adjacent bony structures, for example a pair of vertebrae (not shown). The second arms  244   a  and  244   b  may continue to rotate into the adjacent vertebrae which may pull or compress the vertebrae against the implant  10 . 
         [0037]    It should be noted that other means and mechanisms may be used to deploy the bone engagement anchors from the first position to the second position. The drive element  210  and the drive shaft  220  are only one example of such a means. Other mechanisms may include cams, linkages and wedges which may apply a force on the bone engagement anchors and cause them to at least partially rotate out of the slot  108  and into the adjacent boney structure. 
         [0038]    Turning to  FIG. 8 , there is shown one possible embodiment of an implant inserter  300  which may be used to insert the implant  10  shown in  FIGS. 7A and 7B . The implant inserter  300  may have a first end and a second end. The first end of the implant inserter  300  may have a handle  310 . The proximal end of the handle  310  may have an impaction surface  320 . The impaction surface  320  may have a curved or dome-shaped geometry to receive an impact force from another instrument, such as a mallet. The distal end of the handle  310  may couple to a shaft  330 . The handle  310  and the shaft  330  may be permanently attached or may be temporarily attached with a quick release mechanism. The distal end of the shaft  330  may have an outer surface that is dimensioned to fit within the second inner surface  122  of the main body  100 . The distal end of the shaft  330  may have an inner surface  340  that is dimensioned to couple and apply a linear or non linear force to the driver element  210  (not shown). The geometry of the inner surface  340  may correspond to the geometry of the outer surface of the force transfer member  212 , as shown in  FIG. 7A . The inner surface  340  may have various geometries such as torx, hex, stars, oblong, rectangular and square shapes which may allow for the transfer of a linear or non linear force. In alternative embodiments the outer surface of the distal end of the shaft  330  may have various geometries such as torx, hex, stars, oblong, rectangular and square shapes which may allow for the transfer of a linear or non linear force to the implant  10 . The inner surface  340  may engage the force transfer member  212  to deploy the bone engagement members  240   a  and  240   b,  as shown in  FIG. 7A . In some embodiment, the handle  310  may be actuated to rotate the implant inserter  300 . 
         [0039]    Referring to  FIG. 9  there is shown a flow diagram of one possible method of inserting the implant  10  between a pair of adjacent vertebrae. A surgeon or technician may make an incision in a patient, as shown in step  510 . The incision may be made interiorly through the patient&#39;s abdomen, posteriorly through the patient&#39;s back or laterally through the patient&#39;s side. It should be noted that even though the implant  10  is described as having a leading end  14  and a trailing end  12 , any portion of the device, depending on the technique chosen by the surgeon, may be the portion of the implant  10  that is introduced first into the disc space. The implant  10  may be utilized for an ALIF, PLIF, TLIF or XLIF technique. 
         [0040]    The surgeon may use various instruments, such as retractors and rongeurs to gain access to a vertebral disc space (step  520 ) of the patient&#39;s spine. If needed, the surgeon may remove some of the disc space to allow for insertion of an implant  10 . As shown in step  530 , the surgeon may push the implant  10  having bone engagement members into the disc space with the implant inserter  300 . The desired location of the implant may be located and verified  540  through visualization, probes, guides or fluoroscopy. 
         [0041]    Referring briefly to  FIGS. 10A and 10B , a side view of the insertion instrument  300  is shown with the implant  10  inserted between two adjacent vertebrae  400   a  and  400   b.  Once the desired location is achieved, the surgeon may impact the implant inserter  300  to drive bone the engagement members  240   a  and  240   b  of the implant  10  into the vertebrae  400   a  and  400   b.  The surgeon may use an instrument, such as a mallet (not shown), to impact the proximal end of the inserter  300  which may move the compression mechanism  200  on the implant  10 . The impaction force may cause the ends of the bone the engagement members  240   a  and  240   b  to penetrate the vertebrae. As shown in step  560  of  FIG. 9  (and in  FIG. 10B ), the implant inserter  300  may be rotated by use of the handle  310 , to deploy the bone engagement members  240   a  and  240   b,  as described in  FIGS. 7A and 7B , from a first position to a second position in which the vertebrae  400   a  and  400   b  may be compressed against the implant  10 . 
         [0042]    Other embodiments may include the engagement members  240   a  and  240   b  that are deployed in opposite directions. For example the bone engagement member  240  may deploy in an anterior direction and the engagement member  240   b  may deploy in a posterior direction. In  FIG. 10B  both engagement members  240   a  and  240   b  are shown deployed in an anterior direction, but both engagement members  240   a  and  240   b  may also be deployed in a posterior direction or a lateral direction. 
         [0043]    In certain embodiments the main body  100  and the compression mechanism  200  may be manufactured using conventional manufacturing techniques such as casting, machining, molding or thermoforming. The main body  100  may be manufactured from metals (such as stainless steel or titanium), plastics (such as PEEK or UHMWPE), bone, ceramic, composites or any combination thereof. In certain embodiments the compression mechanism  200  may be manufactured from metals (such as stainless steel or titanium), plastics (such as PEEK or UHMWPE) or a combination. 
         [0044]    Although only a few exemplary embodiments of this disclosure have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this disclosure. Also, features illustrated and discussed above with respect to some embodiments can be combined with features illustrated and discussed above with respect to other embodiments. Accordingly, all such modifications are intended to be included within the scope of this disclosure.