Abstract:
The present disclosure is directed towards a biomechanical implant and anterior, lateral or posterior instrumentation construct. The construct may be of unitary or modular construction, whereby a single molded construction can form the entire assembly, in which case the through holes may be adapted to receive a metallic insert for screw fixation; or alternatively be of a modular construction wherein the anterior/lateral instrumentation and intervertebral spacer are designed for removable locking engagement, one with the other, for insertion by the surgeon as a unitary construct. A unique feature of the construct resides within the instrumentation construction, whereby a single opening formed therein permits two bone screws, or the like fastener device, to be positioned within both the superior and inferior vertebral bodies surrounding the spacer implant, or, for example in the case of a corpectomy or diskectomy with cage insertion, wherein two screws can be fixed within a single vertebral body through a single through hole, and wherein the bone screws are constructed and arranged to cooperate with the retention plate so as to provide locking engagement, one to the other, with the retention plate, upon final fixation thereof. Screw retention elements of alternative shape, based upon the choice of vertical or horizontal orientation, based upon an opened figure eight design, are provided for insertion in a groove formed in the borehole of the instrumentation plate which allows insertion of each fixation element but will prevent a loosened fixation element from falling out of the plate.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims benefit of the filing date of U.S. Provisional Patent Application No. 61/154,038, filed on Feb. 20, 2009, and U.S. Provisional Patent Application No. 61/239,230, filed on Sep. 2, 2009, the contents of each of which is herein incorporated by reference in their entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to an interbody fusion system having an intervertebral retention assembly, and more particularly to intervertebral implants, and intervertebral implant assemblies incorporating a biomechanical implant construct inclusive of stabilizing instrumentation (an anterior, posterior or lateral stabilizer), constructed and arranged to provide superior and inferior vertebral fixation by multiple fixation elements via a single through hole, which through hole can accommodate a fixation element retainer component (hereinafter referred to as a screw retainer component, e.g. a third piece of instrumentation which acts as a retention device to prevent separation of a loosened fixation element from the stabilizing anterior, posterior or lateral instrumentation. 
       BACKGROUND OF THE INVENTION 
       [0003]    Intervertebral spacer implants, either alone or further provided as an assembly, inclusive of a retention mechanism to help alleviate expulsion and movement of the implant when placed in the spine, are well known. Such implant assemblies are advantageous in providing an implant that is easier to insert in the spine, and which resists expulsion subsequent to implantation. Intervertebral spacer implant assemblies which include a spacer and a plate, where the plate comprises a supplemental or alternative retention mechanism having one or more holes in the anterior end of the plate that are directed toward the superior, inferior or both endplates of adjacent vertebrae are also known in the art. Such implants are used to stabilize and immobilize the spinal segments in the treatment of single or multi-level degenerative disc disease, spinal stenosis, and failed previous fusions, as well as other spine conditions. 
         [0004]    The problem with many of these implants resides in preservation of the highest degree of mobility possible, while avoiding backing out or loosening of the implant assembly fastening elements, such as bone screws and the like. 
         [0005]    As will be illustrated herein, the prior art devices often lack sufficient means to insure lockable engagement of the anterior instrumentation and fastener elements, nor do they provide passive means to enable screw retention. In many instances the screw retainer components are provided as separate elements, which must be installed by the surgeon via a separate and distinct step subsequent to application of the fixation element. 
         [0006]    An additional deficiency of the prior art devices is that they are not designed to enable the surgeon to place multiple bone fasteners within a single entry point, so as to provide the surgeon with the freedom to moderate the angularity of the fastener elements in such a manner that they can be targeted for both the superior and inferior vertebral bodies surrounding the implant. 
         [0007]    The instant invention satisfies a long felt need in the art by providing a biomechanical implant with stabilizing instrumentation, (which instrumentation will alternatively be referred to as anterior, posterior or lateral instrumentation throughout the present disclosure) which provides stabilization to the adjacent vertebra wherein a single opening in such instrumentation permits bone screws or equivalent fixation elements to be positioned within both the superior and inferior vertebral body surrounding the implant, and wherein said bone screws or equivalent fixation elements are constructed and arranged to cooperate with an elongated and dished curvilinear opening formed within a first surface of the anterior instrumentation, effective to urge the fixation elements into locking engagement, one to the other, as well as with the anterior instrumentation, upon final fixation of the components, thereby forming a frictionally engaged assemblage. A further long felt need is met by the inclusion of a screw retainer component, which is in the form of a passive locking ring or equivalent device, which constitutes a third piece of instrumentation in this device. The screw retainer component resides in a mounting area formed near the first surface of the anterior instrumentation and is constructed and arranged to deflect from a resting position, so as to allow passage of each fastener element, subsequent to which passage, the screw retainer component returns to its initial position so as to block any of the fasteners from separating from the anterior instrumentation, should loosening or breakage occur. 
       DESCRIPTION OF THE PRIOR ART 
       [0008]    U.S. Pat. No. 7,041,135 (Michelson) is directed toward an apparatus including an interbody spinal fusion implant having a leading end, a trailing end, and a length therebetween, and opposed upper and lower portions adapted to contact each of the adjacent vertebral bodies. Each of the upper and lower portions has at least one screw hole passing there through proximate the trailing end. The apparatus further includes bone screws adapted for placement through the screw holes of the upper and lower portions and into each of the adjacent vertebral bodies adjacent the disc space to be fused and into which the implant is adapted to be positioned. Although an embodiment is shown containing a single recess opening having two exit holes, so that two screws are sited in the same aperture, the screws can not impinge upon each other to create a frictional locking engagement with the plate, and therefore, at least one lock is taught to prevent the bone screws from backing out of the vertebral bodies and implant, the necessity of which is eliminated by the instantly disclosed invention. 
         [0009]    U.S. Published Patent Application 2005/0071008 (Kirschman) relates to a spinal fusion system and method for use as a prosthetic implant. The system and method includes a housing dimensioned to be situated between adjacent spinal bones, such as adjacent vertebrae. The housing cooperates with the spinal bones to define a graft area for receiving graft material, which may be inserted anteriorly into the housing during a surgical operation such as a vertebrectomy or discectomy. A housing may have various features such as migration preventers to prevent the housing from migrating posteriorly towards a spinal column and can be used with a cover that permits the housing to “float” relative thereto. Screws are provided in one embodiment and are dimensioned or configured to lock against each other to retain the screws and, consequently, the cover in place. The publication fails to teach or suggest a construction wherein a single opening permits a bone screw to be positioned within both the superior and inferior vertebral body surrounding the implant, or wherein two bone screws or the like are positionable through a single hole within a particular vertebral body, and wherein said bone screws or the like are in locking engagement with the intervertebral implant assembly. 
         [0010]    U.S. Published Patent Application 2005/0187551 (Orbay et al) is directed toward a bone plating system which includes a plate, fixed angle and variable angle bone screws, and corresponding set screws for each type of the bone screws. The plate includes common openings adapted to receive the variable and fixed angle bone screws, both of which can be locked relative to the plate with the set screws. In all modes of use, a set screw, sometimes in combination with a sliding washer, is then used to fix the level of compression and prevent loosening. In one mode of use, a bone screw can also be driven to cause displacement of the plate such that pressure is applied to maintain bone parts together about a fracture in tight engagement. It is noted that in  FIG. 15 , screw head  775  locks down on adjacent screw head  161 , and that  FIG. 3  teaches an oval opening into which the screws are inserted. Again, the publication fails to teach or suggest a construction wherein a single opening permits a bone screw to be positioned within both the superior and inferior vertebral body surrounding the implant, or wherein two bone screws or the like are positionable through a single hole within a particular vertebral body, and wherein said bone screws or the like are in locking engagement with the intervertebral implant assembly. 
         [0011]    WO 2007098288 (Messerli et al) shows an implant with anterior plate means to affix the bone spacer by means of screws directed both inferiorly and superiorly of the anterior plate. This device does not include an oval hole receiving two screws but rather has separate screw holes directed upwardly and downwardly. See  FIGS. 2 ,  3  and  5  as exemplary thereof. This publication also fails to teach or suggest a construction wherein a single opening permits a bone screw to be positioned within both the superior and inferior vertebral body surrounding the implant, or wherein two bone screws or the like are positionable through a single hole within a particular vertebral body, and wherein said bone screws or the like are in locking engagement with the intervertebral implant assembly. 
         [0012]    U.S. Published Patent Application 2006/0085071 (Lechmann) teaches an intervertebral implant having a three-dimensional body (10) and a securing plate (1). The three-dimensional body (10) includes an upper side (1) and an underside (2) which are suitable for abutting the end plates of two adjacent vertebral bodies, a left side surface (3) and a right side surface (4), a front surface (5) and a rear surface (6), a horizontal middle plane (7) between the upper side (1) and the underside (2), and a vertical middle plane (12) extending from the front surface (5) to the rear surface (6). The three-dimensional body further includes a plurality of boreholes (9a) passing through the body (10), which are suitable for accommodating longitudinal fixation elements (20). The intervertebral implant also includes a front plate (8) displaceably disposed as an insert with the front side (5) of the three-dimensional body, the front plate (8) having a plurality of boreholes (9) in which the longitudinal fixation elements (20) can be anchored, and whose openings overlap with the openings of the boreholes of the three-dimensional body (10). A securing plate can be fastened essentially parallel to the front plate (8) at the three-dimensional body (10) in such a manner that the boreholes of the front plate (9) are covered at least partly by the securing plate (18). By virtue of the configuration of the intervertebral implant, a rigid, firm connection between the intervertebral implant and the longitudinal fixation elements used to fasten it, is possible. This publication likewise fails to teach or suggest a construction wherein a single opening permits a bone screw to be positioned within both the superior and inferior vertebral body surrounding the implant, or wherein two bone screws or the like are positionable through a single hole within a particular vertebral body, and wherein said bone screws or the like are in locking engagement with the intervertebral implant assembly. On the contrary, the reference requires the use of a secondary locking plate in order to prevent backing out or loosening of the bone screws. 
         [0013]    U.S. Reissue 28,841 (Allgower et al) and U.S. Published Patent Application 2002/0045901 (Wagner) are exemplary of bone plates having an oval screw opening. They disclose a bone plate which includes an upper surface, a bone contacting surface, and at least one hole extending through the upper and bone contacting surfaces. The bone plate defines a longitudinal axis. The at least one hole defines a central axis and is elongated in a direction substantially aligned with the longitudinal axis. The hole may include a threaded portion and a non-threaded portion, and the threaded portion may extend through an angle of between about 190° and about 280° with respect to the central axis. 
         [0014]    U.S. Published Patent Application 2006/0247639 (Anderson) shows dual screw holes connected by a slot, and in one embodiment ( FIG. 10 ) illustrates divergent screw holes. 
         [0015]    The prior art fails to provide a construction wherein a single opening permits bone screws to be positioned within both the superior and inferior vertebral body surrounding the implant, or wherein two bone screws or the like are positionable through a single hole within a particular vertebral body, and wherein said bone screws or the like are in locking engagement with the intervertebral implant assembly, upon final fixation thereof. 
       SUMMARY OF THE INVENTION 
       [0016]    The present invention is directed towards an integratable biomechanical implant construct comprising plural components inclusive of 1) a biomechanical spacer implant for insertion within an intervertebral space, 2) an anterior, posterior or lateral instrumentation component effective for vertebral body fixation and maintenance of the biomechanical spacer implant within the intervertebral space, and 3) a plurality of fastener components effective for securing the biomechanical implant construct to the vertebral bodies. The biomechanical spacer implant and anterior instrumentation component are designed for removable locking engagement, one with the other, for insertion by the surgeon as a unitary construct. It is contemplated that the biomechanical implant construct may be of either a unitary or a modular construction. When a unitary construction is provided, a single molded construction, e.g. of PEEK, titanium, or the like, can form the entire construct. In the case where the unitary construct is formed from a polymeric material, the through holes formed within the anterior instrumentation component may be reinforced for retention of the screw retainer components by incorporation of a metallic insert to make possible the novel anterior instrumentation/fastener component locking feature specific to the present invention. 
         [0017]    A unique feature of the construct resides within the anterior instrumentation construction, whereby a single opening formed within the anterior instrumentation permits two bone screws, or the like fastener elements, to be positioned within both the superior and inferior vertebral bodies surrounding the spacer implant or, for example in the case of a corpectomy or diskectomy with cage insertion, wherein two screws can be fixed within a single vertebral body through a single through hole, and wherein the bone screws are constructed and arranged to cooperate with the anterior instrumentation so as to provide locking engagement, one to the other, with the anterior instrumentation, upon final fixation thereof. The use of a single screw hole allows the use of a relatively smaller faceplate than is possible with prior art designs, thus providing a more compact device which decreases the profile of the implant and concomitantly results in a decrease in esophageal compression. 
         [0018]    Alternative embodiments are illustrated inclusive of a horizontal spaced orientation and a vertical spaced orientation. In the horizontal spaced orientation the screws are aligned side-by-side with alternate screws targeting the superior and inferior vertebral bodies respectively. In the vertical spaced orientation, the screws are stacked one above the other to allow for a more compact footprint, and again alternate between the superior and inferior vertebral bodies. Common to all embodiments is a borehole or through-hole assembly, which includes arcuate and dished curvilinear sidewalls. These sidewalls are designed to cooperate with the curved faces of the screwheads to urge the screwheads into a convergent relationship with one another and with the borehole assembly, whereby the act of tightening the bone screws within the common borehole assembly forces the screwheads and borehole assembly into locking engagement with one another when fully seated. 
         [0019]    As an additional safety feature to guard against screw separation in the event of accidental backing out or breakage of the screws, a unique screw retainer component is further provided. The screw retainer component comprises an “open eight” retention clip within an area of the anterior instrumentation designed to receive it. In the horizontal spaced orientation the screw retainer component is illustrated as being in the form of a planar retention clip, while in the vertical spaced orientation, the clip is bent to conform to the internal shape of the anterior instrumentation access hole. In both cases, the screw retainer component is designed to deflect during insertion of each screw, and then return to its original position to prevent a loosened or broken screw from falling out of the anterior instrumentation. 
         [0020]    The implant of the present invention preferably may be inserted using a one-step implantation process, as compared to a two-step process. Furthermore, the aspect is minimized due to the novel construction of the retention plate portion, thereby permitting the inferior and superior fixation to be essentially coplanar, thus eliminating the exacerbation of instability that may be caused by off-center loading resulting from the placement of multiple fasteners about areas of flexion or extension. The use of minimal aspect fixation should further minimize irritation of soft tissue, while providing improved segmental stability in flexion, extension and rotation. 
         [0021]    Accordingly, it is an objective of the instant invention to provide a biomechanical implant and anterior instrumentation construct comprised of an intervertebral implant and a retention member which are constructed and arranged to form a permanent, rigid connection with bone fixation elements, so that, even if the bone structure is weakened, there is no loosening between the anterior instrumentation and the bone fixation elements. Moreover, the construct with biomechanical implant (stabilizer) enables superior and inferior vertebral fixation by multiple bone fixation elements via a single through hole, such that, upon fixation to the bony elements, said multiple fixation elements are in frictional engagement with each other and with the implant retention member, whereby all bone fixation elements are secured simultaneously. 
         [0022]    It is an additional objective of the instant invention to provide a screw retainer component to guard against escape of a dislodged screw from the device. 
         [0023]    It is a further objective of the instant invention to provide an intervertebral biomechanical implant and anterior instrumentation construct suitable for insertion by either an anterior, posterior or lateral surgical approach. 
         [0024]    It is yet an additional objective of the instant invention to provide an alternative embodiment which will further enhance the frictional engagement and locking characteristics of the present invention by modifying the instantly disclosed anterior instrumentation and bone fastener elements to utilize elements of the TIFIX® locking technology, in accordance with the teaching of U.S. Pat. No. 6,322,562, the contents of which is herein incorporated by reference, whereby each screw head forms an autogenic lock to the plate upon insertion. 
         [0025]    The present invention accomplishes the objectives set out above by providing a biomechanical implant and anterior instrumentation construct, comprising a three-dimensional body having an upper side and an under side which are suitable for abutting the end plates of two adjacent vertebral bodies. The three-dimensional body further includes a left side surface and a right side surface, a front surface and a rear surface, a horizontal middle plane between the upper side and the under side, and a vertical middle plane extending from the front surface to the rear surface. The intervertebral implant assembly further includes a construct inclusive of a biomechanical implant and anterior instrumentation which may form a unitary construct inclusive of the implant or be designed for removable engagement with the three-dimensional intervertebral implant body, wherein the retention member includes a plurality of boreholes, each of said boreholes designed for reception of at least two bone fixation elements, positionable in the superior and inferior vertebral bodies adjacent the intervertebral implant, such that, upon fixation to the bony elements, said multiple fixation elements are in frictional engagement with each other and with the implant retention member, whereby all bone fixation elements are secured simultaneously. 
         [0026]    Other objects and advantages of this invention will become apparent from the following description taken in conjunction with any accompanying drawings wherein are set forth, by way of illustration and example, certain embodiments of this invention. Any drawings contained herein constitute a part of this specification and include exemplary embodiments of the present invention and illustrate various objects and features thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0027]      FIG. 1  illustrates a cross-sectional view of a biomechanical implant construct, in accordance with the instant invention, inserted within the intervertebral space, and fixated to both the superior and inferior vertebral bodies adjacent thereto; 
           [0028]      FIG. 2A  illustrates a top-view of a biomechanical implant construct as positioned in  FIG. 1 , illustrating the bone fixation elements positioned in the adjacent superior and inferior vertebral bodies, and in locking engagement with the retention member; 
           [0029]      FIG. 2B  illustrates a top-view of a biomechanical implant construct as positioned in  FIG. 1 , illustrating through holes positioned so as to enable two bone fixation elements to be separately positioned within one or both of the adjacent superior or inferior vertebral bodies, and in locking engagement with the retention member; 
           [0030]      FIG. 3A  is an illustrative embodiment of a biomechanical implant construct; 
           [0031]      FIG. 3B  is a further illustrative embodiment of a biomechanical implant construct; 
           [0032]      FIG. 3C  is yet another illustrative embodiment of a biomechanical implant construct; 
           [0033]      FIG. 4  illustrates a perspective view of a biomechanical implant and anterior instrumentation construct in accordance with the instant invention, in a vertically spaced configuration; 
           [0034]      FIG. 5  illustrates a top-view of the biomechanical implant and anterior instrumentation construct of  FIG. 4 ; 
           [0035]      FIG. 6  illustrates a bent open eight screw retainer component for use in the biomechanical implant construct of  FIGS. 4 and 5 ; 
           [0036]      FIG. 7  is an illustrative embodiment of a biomechanical implant body alone; 
           [0037]      FIG. 8  illustrates a first perspective view of a biomechanical implant and anterior instrumentation construct in accordance with the instant invention, in a horizontally spaced configuration; 
           [0038]      FIG. 9  illustrates a second perspective view of the biomechanical implant and anterior instrumentation construct of  FIG. 8 ; 
           [0039]      FIG. 10  illustrates a flat open eight screw retainer component for use in the intervertebral implant assembly of  FIGS. 8 and 9 ; 
           [0040]      FIG. 11  illustrates an alternative view of the biomechanical implant and anterior instrumentation construct of  FIGS. 8 and 9 ; 
           [0041]      FIG. 12  is an illustrative embodiment of the biomechanical implant body alone; 
           [0042]      FIG. 13  illustrates the cooperation between the dished and curvilinear seat of the anterior instrumentation and the bone fastening elements upon tightening, to affect a locking engagement therebetween; 
           [0043]      FIG. 14  illustrates a lower side view of the exiting of the bone fastening elements from the anterior instrumentation of the implant of  FIG. 13 ; 
           [0044]      FIG. 15A  is a top view of an elongated borehole slot surrounded by an arcuate and curvilinear seat formed within an anterior instrumentation; 
           [0045]      FIG. 15B  is a cross-sectional view of  FIG. 15A  along line A-A; 
           [0046]      FIG. 15C  is a cross-sectional view of  FIG. 15A  along line B-B; 
           [0047]      FIG. 16  is a front perspective view, partially in section, of a vertically spaced biomechanical implant assembly further including anchoring tabs for attachment to the anterior cortical vertebral surfaces; 
           [0048]      FIG. 17  is a front perspective view, partially in section, of a horizontally spaced biomechanical implant assembly further including anchoring tabs for attachment to the anterior cortical vertebral surfaces; 
           [0049]      FIG. 18  is a front perspective view, partially in section, of a horizontally spaced biomechanical implant assembly for lateral insertion, including anchoring tabs for attachment to the lateral cortical vertebral surfaces; 
           [0050]      FIG. 19  is a front perspective view, partially in section, of a vertically spaced biomechanical implant assembly for lateral insertion, including anchoring tabs for attachment to the lateral cortical vertebral surfaces; 
           [0051]      FIG. 20  is a cross-sectional view of a prior art TIFIX plate and screw combination. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0052]    Now referring to  FIG. 1 , the intervertebral implant assembly, generally referred to by numeral  10 , includes an implant member  12 , and a retention member  14 , illustrated as, albeit not limited to, a bone plate. Both plate  14  and implant  12  may be formed of PEEK (poly(ether ether ketone)), titanium, titanium alloy, stainless steel, allograft bone or any other suitable, biocompatible material. It is contemplated that implant  12  may be formed of bone, or an artificial material other than bone which may be harder and/or stronger than bone, such as plastic or ceramic materials. It is further contemplated that the implant material will have the same, more or less elasticity than bone. The implant  12  may include, or be treated with, a bone growth promoting material such as, but not limited to, bone morphogenic protein, hydroxyapatite, and genes coding for the production of bone. Implant  12  may be a source for osteogenesis, be at least in part bioabsorbable, and be treated with, or applied in conjunction with a substance, as known in the art, to inhibit scar formation and/or promote fusion of the bones. Preferably retention member  14  is formed of metal or metal alloy and the spacer is formed of PEEK or other polymer, or alternatively bone or ceramic or radiolucent biocompatible material. Bone fixation elements  16 , illustrated, albeit not limited to bone screws, may be formed of titanium, titanium alloy or stainless steel. The bone fixation elements  16  may be in the form of a screw, a staple or nail, a fluted cannulated screw or nail with collapsible/deployable spurs which are deployed and thereby embedded within the bone upon insertion of a secondary nail or screw within the cannulated space, or similar functionally equivalent elements. Furthermore, the implant  12  may include one or more openings ( FIGS. 3B ,  42 ) designed to receive bone graft material. Subsequent to insertion of the intervertebral implant assembly  10  within the intervertebral space, bone fixation elements, e.g. screws  16 , are driven into the inferior  20  and superior  18  adjacent vertebral bodies, via access through hole  17 . Upon being fixated within said access hole  17 , the elements  16  are urged into locking engagement with the curvilinear seat of anterior instrumentation retention member  14 , and each other, so as to reduce or eliminate the possibility of loosening. Due to the single access hole design, the screws essentially reside in a single plane common to the superior and inferior vertebral bodies, and have adjustable angularity at the surgeon&#39;s discretion. 
         [0053]    It is contemplated by the invention that the access through hole  17  may include a single exit aperture or dual diverging exit apertures. The seat of each aperture, whether integral with the assembly, or formed within a metallic insert which is subsequently inserted into the assembly, may include a spherical or semi-spherical dished and curvilinear seat for each fastener. This feature will provide for variation in screw trajectory and increased face contact between the fixation elements and the plate or seat. In a preferred albeit non-limiting embodiment, the fastener will be formed with a spherical or semi-spherical head with a substantially flat upper surface. Such construction will allow the spherical surface of the second fastener, e.g. screw, to engage the top surface of the first screw regardless of trajectory of both screws. Such construction insures repeatable and reliable head-to-head contact independent of fastener trajectories. 
         [0054]    In a particular embodiment of this invention the stabilizing bone plate useful in an interbody fusion system for stabilizing a biomechanical spinal implant will be comprised of a bone plate having a left side surface and a right side surface, a top surface and a bottom surface, a first upper surface and a second lower surface, with a distance between said first upper surface and said second lower surface defining a thickness of said plate, a horizontal middle plane between the first upper surface and the second lower surface and a plurality of boreholes suitable for accommodating longitudinal fixation elements extending through said thickness of said plate, wherein each of said boreholes has an elongated slot located at or near said horizontal middle plane, and surrounded by arcuate and dished curvilinear sidewalls which form an engagement seat extending from said elongated slot to said first upper surface for receiving at least two bone fixation elements therein, each of said bone fixation elements having a screw head adapted to engage or be engaged by an engaging surface of each screw head to urge the screw heads into a convergent and interference relationship with one another and with said engagement seat upon tightening, thereby resulting in a locking engagement of said bone plate engagement seat and said fixation elements and a diverging outlet portion extending from said elongated slot toward said second lower surface, said divergent outlet being adapted to provide a range of angulation of each said fixation elements, whereby each of said fixation elements is individually positionable within both an inferior and superior vertebral body associated with said interbody fusion system. 
         [0055]    Now referring to  FIG. 2A , the interlocking frictional engagement of the elements  16  and retention member  14  are further illustrated as they reside in through hole  17 . Alternatively, as illustrated in  FIG. 2B , the through hole(s)  17  may be formed so as to enable two bone fixation elements  16  to be deployed through a single through hole  17 , and to be separately positioned within one or both of the adjacent superior or inferior vertebral bodies, and in locking engagement with the retention member  14 . 
         [0056]    With reference to  FIGS. 3A ,  3 B and  3 C, alternative illustrative embodiments, in accordance with the inventive concept are illustrated. Such embodiments are for illustration purposes, and are not meant to limit the invention, as further equivalent alternative embodiments are contemplated. 
         [0057]    Referring to  FIG. 3A , implant  12 A shows one illustrative embodiment of a biomechanical implant element wherein the element includes one or more keel-like members  30 . The attachment of plate  14 A and implant  12 A is accomplished via pins  32 , which are designed for frictional insertion and engagement with mating recesses (not shown), in plate  14 A. When positioned within the intervertebral space, fixation elements, e.g. screws  16 , are inserted via access through-hole  17 , and may follow the trajectory delineated by optional upper and lower guides  48  and  49  respectively. 
         [0058]    Referring to  FIG. 3B , implant  12 B shows another illustrative embodiment of a biomechanical implant element wherein the element includes openings  42  for the insertion of bone graft material. The attachment of plate  14 B and implant (graft/spacer)  12 B is accomplished via coupling of male and female T-slot members  44  and  46 . When positioned within the intervertebral space, fixation elements, e.g. screws  16  (not shown), are inserted via access through-holes  17  and  17 ′, and may follow the trajectory delineated by optional upper and lower guides  48  and  49  respectively. It is noted that this embodiment illustrates plural access through holes  17  and  17 ′, and when plate  14 B is constructed from PEEK, the curvilinear through-hole engagement surface is formed from a metallic material, e.g. titanium, and inserted or molded into the PEEK implant to form a reinforced version of through-holes as illustrated at  17  and  17 ′. 
         [0059]    Referring to  FIG. 3C , implant  12 C shows another illustrative embodiment of a biomechanical implant element wherein the element includes facets  50  for enhanced gripping of the adjacent vertebral bodies  18  and  20 . The attachment of plate  14 C and biomechanical implant  12 C is illustratively accomplished via coupling of plural male and female T-slot members  44 C and  46 C. When positioned within the intervertebral space, fixation elements, e.g. screws  16  (not shown), are inserted via access through-hole  17 , and may follow the trajectory delineated by optional upper and lower guides  48  and  49  respectively. 
         [0060]    In a particular embodiment, the biomechanical spacer implant of the invention is adapted for insertion within an intervertebral space between a superior vertebral body and an inferior vertebral body and includes a first insertion end portion, a second end portion opposite the first end portion, a first lateral side portion, a second lateral side portion, an upper surface and a lower surface. 
         [0061]    The particular surface shape and curvature, or taper in the anterior-posterior direction as well as between the lateral side surfaces will depend upon the location at which the spacer is intended to be inserted. The shape of the perimeter of the spacer can be modified for cervical applications, or for other areas such as in the lumbar or thoracic area of the spine. 
         [0062]    Forms of attachment between the biomechanical implant element and the anterior instrumentation member are not limited to the mechanisms depicted. Furthermore, the number and position of access through-holes e.g. two, three, four or the like, is dictated by the particular patient&#39;s anatomy or other surgical considerations, and is also not intended to be limited by the type of attachment mechanism between the biomechanical implant and anterior instrumentation. 
         [0063]    It is contemplated that the implant may include a series of teeth ( FIGS. 1 ,  19 ), knurling, ridges or similar projections, to aid in securing the implant to the vertebral endplates. It is also contemplated that the upper and/or lower surfaces of implant  12  may be smooth, having ridges (not shown) that run laterally with respect to the spacer, or ridges running from front to back. 
         [0064]    It is further contemplated that the access through holes  17  provided in the plates may be threaded or smooth, and the screws or alternative bone fasteners inserted through the plate may have a head that also may be threaded or smooth. In this regard, and with reference to  FIG. 20 , the present invention contemplates an embodiment which incorporates the TIFIX technology disclosed by Wolter, in U.S. Pat. No. 6,322,562, wherein the bone screw may further include a preformed thread below the bone screw seat surface, the preformed thread deforming a portion of the passage hole below the seat surface of the connection carrier when the bone screw is screwed in so that a thread connection is formed between the bone screw thread and the connection carrier, the deformation being formed by rotating the bone screw at a certain angle to the connection carrier. In addition to use of bone screws, per se, such as disclosed by Wolter, the present invention further contemplates alternative embodiments wherein the preformed thread consists of a harder material than the deformable projection, wherein the bone screw or its casing is of a harder material than the connection carrier or the region to be deformed, wherein the casing region of the locking bolt has a lesser hardness than the bonemarrow nail at least in the region of the inner thread, wherein the connection carrier comprises a sensor for determining the force transmitted by the connection carrier between the bone ends and a transmitter for the telemetric transfer of the readings, and wherein the sensor and/or transmitter are integrated into a cavity of the connection carrier. 
         [0065]    The implants described herein may be sized and configured for anterior, posterior or lateral approaches and insertion. In addition to the features shown the implants, spacers, and plate/spacer constructs may have threaded holes, slots or channels to mate with instruments to facilitate holding and inserting the implants. 
         [0066]    To improve the anchoring of the bone fixation element in any of the illustrative embodiments contemplated by the present invention where the retention member is formed of a polymeric material, a metal sleeve with or without an internal thread, as illustrated in  FIG. 3B , may be inserted in the access through hole  17 . The intervertebral implant may also consist only partially of an x-ray transparent plastic and, in the region of the upper and lower guides ( 48 , 49 ) consist of a metal, such as titanium or a titanium alloy. Improved guidance and anchoring of the bone fixation elements may thereby be achieved. Further, the access through-holes may have a smooth internal wall, into which the threaded head or body of a metallic, longitudinal fixation element may cut or be molded. 
         [0067]    Now referring to  FIG. 4 , the biomechanical implant and anterior instrumentation construct, generally referred to by numeral  10 , includes an implant member  12 , and a retention member  14 , illustrated as, albeit not limited to, a bone plate. Both biomechanical implant  12  and anterior instrumentation construct  14  may be formed of PEEK, titanium, titanium alloy, stainless steel, allograft bone or any other suitable, biocompatible material. Preferably retention member  14  is formed of metal or metal alloy and the spacer is formed of PEEK or other polymer, or alternatively bone or ceramic or radiolucent biocompatible material. Bone fixation elements  16 , illustrated, albeit not limited to bone screws, may be formed of titanium, titanium alloy, stainless steel or other biocompatible materials. The bone fixation elements  16  may be in the form of a screw, a staple or nail, a fluted cannulated screw or nail with collapsible/deployable spurs which are deployed and thereby embedded within the bone upon insertion of a secondary nail or screw within the cannulated space, or similar elements. Furthermore, the implant  12  may include one or more openings (not shown) designed to receive bone graft material. Subsequent to insertion of the biomechanical implant and anterior instrumentation construct  10  within an intervertebral space (not illustrated), bone fixation elements, e.g. screws  16 , are driven into the inferior and superior adjacent vertebral bodies, via an access through hole or borehole  17 . Upon being fixated within said access hole  17 , the elements  16  are in locking engagement with the retention member  14 , and each other, so as to reduce or eliminate the possibility of loosening. In the vertical spaced orientation as shown, due to the single access hole design, the screws essentially reside in a single plane common to the superior and inferior vertebral bodies. 
         [0068]    It is contemplated by the invention that each borehole  17  may include a single exit aperture or dual diverging exit apertures at the rear surface of the anterior instrumentation  14 . The engagement seat of each aperture, whether integral with the assembly, or formed within a metallic insert that is subsequently inserted into the assembly, may include a spherical or semi-spherical dished and curvilinear seat for each fastener. This feature will enable variations in the choice of screw trajectory and increased face contact between the fixation elements and the plate or seat. In a preferred albeit non-limiting embodiment, the fastener element  16  will be formed with a spherical or semi-spherical head with a substantially flat upper surface. Such construction will allow the spherical surface of the second fastener, e.g. screw, to engage the top surface of the first screw regardless of trajectory of both screws, as the second screw is tightened and urged into frictional engagement with the first screw by contact with the dished and curvilinear engagement seat formed within the upper or entry surface of borehole  17 . Such construction insures repeatable and reliable head-to-head contact independent of fastener trajectories. 
         [0069]    Now referring to  FIG. 5 , a top-view of the intervertebral implant assembly  10  of  FIG. 4  is illustrated. This view best illustrates the bent open eight retention clip  15  as positioned within a prefabricated groove in borehole  17 . In order to form a prefabricated and unitary assembly for simplified insertion during surgery, clip  15  is initially compressed by inserting a tool into holes  19  so as to enable the compressed clip to be inserted and thereby engage with reception grooves formed at the periphery of borehole  17 . Subsequent to compression of the clip via holes  19  and insertion into borehole  17 , the retention ring/clip  15  and retention member  14  form a unitary assembly. Each of the fixation elements  16  can be inserted individually in their respective apertures, and the retention ring  15  is designed to deflect so as to enable the heads of the fixation elements  16  to pass therethrough, and then return to its prior position to prevent the fixation element from falling out of borehole  17  should it become loosened. 
         [0070]    Referring to  FIG. 6  the bent open eight retention clip  15  is more clearly illustrated. The bent configuration allows functionality in the vertical spaced orientation as illustrated, by providing a single clip which functions for both fixation elements. 
         [0071]    Referring to  FIG. 7  implant member  12  is an illustrative embodiment of an implant element. The element may contain openings (not shown here) for the insertion of bone graft material. The attachment of plate  14  and implant  12  is accomplished via coupling of male and female T-slot members  44  and  46  (more clearly illustrated in  FIG. 9 ). When positioned within an intervertebral space, fixation elements, e.g. screws  16  (not shown), are inserted via access through-holes  17 , and may follow the trajectory delineated by optional guides  48  and  49  respectively. 
         [0072]    Referring to  FIG. 8  illustrated herein is a first perspective view of a biomechanical implant and anterior instrumentation construct, in accordance with the instant invention, in a horizontally spaced configuration. Although the configuration of the boreholes and plates is slightly different between the vertically and horizontally spaced embodiments, the numbering has nevertheless been left consistent for ease of explanation. This is an alternative embodiment wherein, dependent upon the physiology and anatomy, it may be more desirable to position fixation elements  16  side by side, as opposed to vertically stacked. The functioning of the various elements is otherwise equivalent, except for the fact that the open eight screw retainer component  15 , as illustrated in  FIG. 10  is of a flat, rather than a bent, design. 
         [0073]    Referring to  FIG. 9 , a second perspective view of the biomechanical implant and anterior instrumentation construct of  FIG. 8  is illustrated which more clearly depict the male/female T-slot configuration by which members  12  and  14  are assembled. It is stressed that this is merely one illustrative means of attachment of members  12  and  14  and any other functionally equivalent means of attachment are deemed to be within the purview of this invention. 
         [0074]    Referring to  FIG. 10 , illustrated here is a flat open eight screw retainer component  15  for use in a biomechanical implant and anterior instrumentation construct of  FIGS. 8 and 9 . The functionality is equivalent to that of the bent design of  FIG. 6  as previously outlined above. 
         [0075]    Referring to  FIG. 11  an alternative view of the biomechanical implant and anterior instrumentation construct of  FIGS. 8 and 9  is further illustrated. 
         [0076]    Referring to  FIG. 12 , an illustrative embodiment of the intervertebral biomechanical implant member  12  is shown which illustrates the trajectory guiding elements  48  and  49 , as they are positioned within the horizontally spaced configuration. Although a very basic illustration of implant member  12  is shown for ease of illustration, it is understood that the implant element  12  may include facets for enhanced gripping of the adjacent vertebral bodies. The particular surface shape and curvature, or taper in the anterior-posterior direction as well as between the lateral side surfaces will depend upon the location the spacer is intended to be inserted. The shape of the perimeter of the spacer can be modified for cervical applications, or for other areas such as in the lumbar or thoracic areas of the spine. 
         [0077]    It is contemplated that the implant may include a series of teeth, knurling, ridges or similar projections, to aid in securing the implant to the vertebral endplates. It is also contemplated that the upper and/or lower surfaces of implant  12  may be smooth, having ridges (not shown) that run laterally with respect to the spacer, or ridges running from front to back. 
         [0078]    It is reiterated that forms of attachment between the implant element  12  and the anterior instrumentation  14  are not limited to the mechanisms depicted. Furthermore, the number and position of access through-holes e.g. two, three, four or the like, is dictated by the particular patient&#39;s anatomy or other surgical considerations, and is also not intended to be limited by the type of attachment mechanism between the implant  12  and the biomechanical implant and anterior instrumentation construct  14 . 
         [0079]    As previously set forth, it is further contemplated that the access through holes  17  provided in all plates illustrated herein, may be threaded or smooth, and the fixation elements  16 , such as screws or alternative bone fasteners inserted through the plate may have a head that also may be threaded or smooth. 
         [0080]    All implants described herein may be sized and configured for anterior, posterior or lateral approaches and insertion. In addition to the features shown the implants, spacers, and plate/spacer constructs may have threaded holes, slots or channels to mate with instruments to facilitate holding and inserting the implants. 
         [0081]    Referring to  FIG. 13  the cooperation between the dished and curvilinear seat illustrated within the entry area of borehole  17  is illustrated, showing the cooperation between the seat area and the heads of the bone fastening elements  16  upon tightening, to affect a locking engagement therebetween; 
         [0082]    With reference to  FIG. 14  illustrates, a view of the lower side of instrumentation plate  14 A shows divergent exiting of the bone fastening elements  16  toward the inferior and superior vertebral bodies, from the anterior instrumentation of the implant of  FIG. 13 ; 
         [0083]    Now referring to  FIG. 15A  is an illustrative embodiment showing a top view of an elongated borehole slot  17 B surrounded by an arcuate and dished curvilinear seat  17 A formed within the instrumentation plate  14 A; 
         [0084]    Referring to  FIG. 15B , illustrated herein is a cross-sectional view of  FIG. 15A  along line A-A, showing the dished and curvilinear shape of seat  17 A, which will cooperate with relatively congruent shaped screw heads provided to bone screws  16  (not shown here for clarity), in order to enhance the cooperation between these elements during the fixation process, so as to urge the screw heads and engagement seat into a locking frictional engagement; 
         [0085]    With further reference to  FIG. 15C , shown here is a cross-sectional view of  FIG. 15A  along line B-B, which illustrates the exit aperture  17 C, which enables the discretion in angular placement of the fixation elements  16 , into the vertebral bodies, as desired by the surgeon. 
         [0086]    Referring now to  FIG. 16 , is a front perspective view is shown, partially in section, of a vertically spaced biomechanical implant assembly  12 , with stabilizing anterior instrumentation  14 , further including anchoring tabs  50  for attachment to the anterior cortical vertebral surfaces. This embodiment provides the surgeon with the utility of attachment of additional stabilization through the anterior cortical bone surfaces by insertion of a fastener element  16 , through tab  50 , which is retained by deflectable retention element  15 A, which is a further variation on the “open-eight” retention element technology illustrated in earlier embodiments. The partial sectional view affords an alternative view of the relationship of bent retention element  15 B, within a reception groove formed in plate  14 , in this vertically oriented configuration. 
         [0087]    With reference to  FIG. 17 , a front perspective view, partially in section, of a horizontally spaced biomechanical implant assembly further including anchoring tabs for attachment to the anterior cortical vertebral surfaces is shown. This assemblage is essentially the same as that described in  FIG. 16  above, save for the fact that it is configured to be horizontally oriented so as to provide an alternate bone screw placement. The flat open eight retention member  15 C is illustrated placed within a retention groove formed with instrumentation plate  14  for retention thereof. 
         [0088]    Referring to  FIG. 18 , shown herein is a front perspective view, partially in section, of a horizontally spaced biomechanical implant assembly, as illustrated in  FIG. 17 , however configured for lateral insertion, including anchoring tabs for attachment to the lateral cortical vertebral surfaces. 
         [0089]    With further reference to  FIG. 19 , a front perspective view, partially in section, of a vertically spaced biomechanical implant assembly for lateral insertion, including anchoring tabs for attachment to the lateral cortical vertebral surfaces is also shown. 
         [0090]      FIG. 20  is a cross-sectional view of a prior art TIFIX plate and screw combination. It is contemplated that any of the herein illustrated and referenced embodiments could be modified to contain the TIFIX technology. Such incorporation might include merely selecting the relative hardnesses of the materials used in the fixation elements  16  and plates  14 ,  14 A, etc. so as to provide thread forming ability and autogenic locking, in the manner described by Wolter &#39;562. Additionally, it is further contemplated to modify the bone fixation elements  16 , to include secondary threads for locking into the plate as shown in prior art FIG. 20 from the Wolter &#39;562 patent. 
         [0091]    All patents and publications mentioned in this specification are indicative of the levels of those skilled in the art to which the invention pertains. All patents and publications are herein incorporated by reference to the same extent as if each individual publication was specifically and individually indicated to be incorporated by reference. 
         [0092]    It is to be understood that while a certain form of the invention is illustrated, it is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the invention and the invention is not to be considered limited to what is shown and described in the specification and any drawings/figures included herein. 
         [0093]    One skilled in the art will readily appreciate that the present invention is well adapted to carry out the objectives and obtain the ends and advantages mentioned, as well as those inherent therein. The embodiments, methods, procedures and techniques described herein are presently representative of the preferred embodiments, are intended to be exemplary and are not intended as limitations on the scope. Changes therein and other uses will occur to those skilled in the art which are encompassed within the spirit of the invention and are defined by the scope of the appended claims. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in the art are intended to be within the scope of the following claims.