Patent Publication Number: US-2022233328-A1

Title: Standalone interbody implants

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     The present application is a continuation of U.S. patent application Ser. No. 16/732,393, filed on Jan. 2, 2020, which is a continuation of U.S. patent application Ser. No. 15/967,626 filed on May 1, 2018, which is a continuation of U.S. patent application Ser. No. 15/277,044 filed on Sep. 27, 2016, now issued U.S. Pat. No. 9,980,826, which is a continuation of U.S. patent application Ser. No. 14/556,345, filed Dec. 1, 2014, now issued U.S. Pat. No. 9,486,327, which is a continuation-in-part of U.S. patent application Ser. No. 14/278,898 filed on May 15, 2014, now issued U.S. Pat. No. 9,545,320, the entire disclosures of which are incorporated herein by reference in their entireties for all purposes. 
    
    
     FIELD OF THE INVENTION 
     The present disclosure generally relates to fixation devices for positioning and immobilizing adjacent vertebral bodies. In particular, the devices may include stand-alone interbody fusion devices. 
     BACKGROUND OF THE INVENTION 
     As people age, the intervertebral discs in the spinal column may start to deteriorate. Subsequently, the intervertebral discs being to lose height. As a result of the loss of height between vertebral bodies, the nerves exiting from the spinal canal become compressed and pinched, which causes pain among other neurological deficits. One solution is to insert a spacer in place of the disc to restore the height and to promote fusion between adjacent vertebral bodies to permanently maintain the height restoration. Additional fixation is also needed to stabilize the spinal segment. A plate is usually provided, and the plate may be positioned on the anterior portions of the adjacent vertebral bodies. In some cases, the profile of the plate becomes obstructive to the anatomy. The approach to the spine is also significant in that a direct anterior approach requires navigation or dissection of vascular anatomy. 
     As a result, there is a need to provide a spacer having fixation elements to attach the spacer directly to adjacent vertebrae, to limit any profile protruding out of the spine column anteriorly, and to avoid proximal anatomy from a direct anterior approach. The spacer alone, however, may not be strong enough to support fixation elements, such as screws, when the spacer is made solely from certain non-metallic materials, such as, polyether ether ketone (PEEK). Thus, there is also a need for frames or spacers at least partially constructed of strong materials or in such a manner so as to provide additional support for the fixation elements. 
     SUMMARY OF THE INVENTION 
     To meet this and other needs, stand-alone interbody fusion implants and devices are provided. The implants may be provided with a spacer and at least one insert or member. The implants may also be composed of a frame with one or more endplates affixed thereto. The inserts, members, or frames may be especially suited for defining apertures designed to secure fixation elements or fasteners, such as screws, staples, pins, nails, anchors, or the like, and the spacers to adjacent vertebrae. These implants provide for a spine stabilization system that promotes fusion of adjacent vertebrae while at the same time providing stabilization of the spinal area where fusion occurs. 
     According to one embodiment, an intervertebral implant for implantation in an intervertebral space between adjacent vertebrae includes a spacer and at least one insert. The spacer has a superior surface, an inferior surface, a proximal end, and a distal end. The superior surface and the inferior surface each have a contact area configured to engage adjacent vertebrae. The spacer defines an opening extending from the superior surface to the inferior surface of the spacer. The opening may be configured for receiving bone graft material to promote fusion of the adjacent vertebral bodies. The spacer defines one or more cutout extending from the proximal end to the opening. The spacer may also include a plurality of protrusions on the contact areas of the superior and inferior surfaces for engaging the adjacent vertebrae. 
     The insert at least partially defines a fastener aperture. These apertures may be in the form of through holes designed, sized, and dimensioned to accommodate and receive fixation devices or fasteners, such as bone screws or anchors. The insert is coupled to the spacer such that at least a portion of the insert is received in the cutout in the spacer. 
     The insert may be configured in such a way to enhance the strength and stability of the spacer. The insert may extend a distance beyond the superior surface, the inferior surface, or both surfaces of the spacer (e.g., a portion of the insert may extend above or below the superior and inferior surfaces of the spacer). For example, a front surface of the insert may include at least one eyebrow where the eyebrow projects past the superior surface, the inferior surface, or both surfaces of the spacer. The fastener aperture for receiving the fastener may traverse the front surface of the insert at an angle divergent to a horizontal plane in order to help secure the implant to one or both of the adjacent vertebrae. 
     Unlike a traditional plate, which is typically a thin, flat sheet or strip of material, the insert is provided with a given depth and dimension designed to integrate seamlessly with the spacer. In particular, the depth of the insert may be greater than the width and/or height of the insert. The insert may include a head portion and at least one arm projecting therefrom. The head portion may be enlarged to define the aperture configured for retaining the fastener. The arm may extend laterally, medially, and/or posteriorly away from the head portion. In particular, the arm may extend posteriorly and may be configured to mimic the shape and design of the spacer. The spacer may define at least one recess sized and dimensioned to retain at least a portion of the arm. For example, the arm may rest against a portion of the spacer or a recess therein to form a lap joint, half lap joint, stepped joint, or the like. Any type of joint formed between the insert and the spacer may be secured with one or more pins. 
     According to another embodiment, the insert may be provided in the shape of a ring, cylinder, c-shape, or the like. The ring or c-shaped insert may be provided with one or more slits, for example, to allow the insert to tightly mate with the cutout through the spacer and secure the insert to the spacer. In particular, one or more slits may be longitudinally positioned around a periphery of the ring or c-shaped insert. 
     According to yet another embodiment, a stand-alone implant for implantation in a treated area of an intervertebral space between vertebral bodies of a spine includes a spacer and at least one member. The spacer has a first spacer portion and a second spacer portion, each of the first and second spacer portions having a first end and a second end. The second end of the first spacer portion is coupled to the first end of the second spacer portion. The first and second spacer portions form a superior surface and an inferior surface, and the superior surface and the inferior surface each have a contact area configured to engage adjacent vertebrae. 
     The member has an upper surface, a lower surface, a first lateral portion, a second lateral portion, and at least one hole traversing the member for receiving a fastener. The member is coupled to the spacer such that the first end of the first spacer portion engages the first lateral portion of the member and the second end of the second spacer portion engages the second lateral portion of the member. 
     The first and second spacer portions may be joined together in any suitable manner. For example, the first and second spacer portions may be mated together by a splice joint, scarf joint, butt joint, or the like. In the alternative or in addition, the first and second spacer portions may be secured together with one or more connectors. For example, the connector may include at least first and second tenons sized and configured to be received within a first mortise in the second end of the first spacer portion and a second mortise in the first end of the second spacer portion. Any type of joint formed between the first and second spacer portions may be further secured with one or more pins or the like. 
     The spacer portions and the member may also be joined together in any suitable manner. Similar to the insert configuration, the member may rest against a portion of the spacer portions or a recess therein to form a lap joint, half lap joint, stepped joint, or the like. For example, the member may include a first extension extending from the first lateral portion and a second extension extending from the second lateral portion. The first extension may contact a first ledge on the first spacer portion to form a first half lap joint, and the second extension may contact a second ledge on the second spacer portion to form a second half lap joint. If desired, the first and second half lap joints may each be further secured with at least one pin. 
     According to a further embodiment, an implant for implantation in an intervertebral space between adjacent vertebrae includes a spacer and an anterior portion. The spacer has a superior surface, an inferior surface, a proximal end, and a distal end, for example, configured for insertion into the intervertebral space. The superior surface and the inferior surface each have a contact area configured to engage adjacent vertebrae. The spacer defines an opening extending from the superior surface to the inferior surface of the spacer. 
     The anterior portion extends from the proximal end of the spacer such that the anterior portion and the spacer are a single piece. The anterior portion has an upper surface, a lower surface, a first lateral portion, a second lateral portion, and at least one hole traversing the anterior portion for receiving a fastener. At least a portion of the upper surface or the lower surface of the anterior portion extends beyond the superior surface or the inferior surface of the spacer. For example, at least one beam may connect the anterior portion to the proximal end of the spacer to form a unitary piece. 
     The distal end of the spacer may have a first spring feature configured to allow for compression and expansion of the spacer. For example, the first spring feature may be in the form of a v-spring. In addition, the proximal end of the spacer may include a second spring feature. The second spring feature may also be in the form of a v-spring. In particular, the second spring feature may include more than one v-spring oriented in opposite directions. The first and second spring features may be configured such that the spacer simulates the modulus of elasticity of bone even when the spacer and the anterior portion are comprised of titanium. 
     According to another embodiment, an intervertebral implant for implantation in an intervertebral space between adjacent vertebrae may include a frame and at least one endplate. The frame may include a front portion, a first arm extending from a first end of the front portion, and a second arm extending from a second end of the front portion. The front portion may at least partially define at least one fastener aperture sized and dimensioned for receiving a fastener, such as a bone screw or an anchor. The endplate includes at least one outer surface having a contact area configured to engage adjacent vertebrae. The endplate is affixed to the frame such that the endplate contacts at least a portion of the plurality arms. 
     The frame may include a support member positioned centrally between the first and second arms. The support member may define at least one opening to retain a corresponding protrusion on the which is configured to provide for a friction fit between the endplate and the frame. The opening may be elongated with a beveled perimeter such that a corresponding protrusion on the endplate is configured to be snapped into the opening in the support member. The endplate may also defines at least one indentation on a lateral portion of the endplate to retain a corresponding protrusion on the first and/or second arms which is also configured to provide an interference fit between the endplate and the frame. The first and second arms may join together at a rear portion to form a ring-like structure. 
     The endplates may include at least two endplates: a first endplate configured to fit in a first opening between the first arm and the support member and a second endplate configured to fit in a second opening between the second arm and the support member. The endplate may be inserted from the top, bottom, or back of the implant. 
     The front portion of the frame may be a unitary piece or may be divided into two separate portions with a passage positioned therebetween. The endplate may include a central portion sized and configured to fit within the passage in the front portion. The central portion may define an opening sized and configured to receive an insert which accepts an anti-backout locking mechanism. In addition to the central portion, the endplate may include a first lateral wing and a second lateral wing. The first lateral wing may be configured to contact a portion of the first arm (e.g., forming at least a portion of an upper surface of the implant) and the second lateral wing may be configured to contact a portion of the second arm (e.g., forming at least a portion of a lower surface of the implant). 
     According to yet another embodiment, the implant may include a frame having a superior surface, an inferior surface, a proximal end, and a distal end, wherein the superior surface and the inferior surface each have a contact area configured to engage adjacent vertebrae, and the frame defines at least one opening extending from the superior surface to the inferior surface of the frame. The frame includes a front surface defining at least one fastener aperture provided at an angle divergent to a horizontal plane for receiving a fastener. The endplates may be sized and configured to fit within the openings in the frame, where the endplates are coupled to the frame by an interference fit and a ridge projecting around an outer perimeter of the endplate sized and configured to be received within a corresponding slot located within the opening. The slot may be located, for example, on a mid-transverse plane of the frame. 
     In any of the embodiments described herein, the implant may also include a locking mechanism, for example, disposed on the spacer, insert, member, or frame for preventing back out of the screws. For example, a cam-style blocking mechanism may be used with screws that capture the fixation device screws once they are inserted fully into the implant. 
     The implants may be formed from any suitable biocompatible materials. For example, the implant may be manufactured from a biocompatible metal, such as titanium, polyether ether ketone (PEEK), bone or the like. In one embodiment, the spacer or endplates is formed of a first material and the insert, member, or frame is formed of a second material different from the first material. The insert, member, or frame may be made of a stronger material designed to strength and reinforce one or more openings in the spacer (e.g., designed to retain bone screws) or as attached to the endplates. For example, the spacer or endplates may be formed from PEEK and the insert, member, and frame may be formed from titanium. In the embodiment where the anterior portion and the spacer form a single piece, titanium may be selected for the entire implant because the one or more spring features provide for the spacer to emulate the elasticity of bone. 
    
    
     
       BRIEF DESCRIPTION OF DRAWING 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Included in the drawing are the following figures: 
         FIG. 1A  is a perspective view of a first embodiment suitable for cervical interbody fusion including a spacer with inserts configured to retain bone fasteners when secure to adjacent vertebrae; 
         FIG. 1B  is a front view of the embodiment shown in  FIG. 1A ; 
         FIG. 1C  is a top view of the embodiment shown in  FIG. 1A ; 
         FIG. 1D  is an exploded view of the embodiment shown in  FIG. 1A ; 
         FIG. 1E  is a lateral view of the embodiment shown in  FIG. 1A ; 
         FIG. 2A  shows a perspective view of an alternative embodiment of an interbody fusion device with inserts; 
         FIG. 2B  is a top view of the embodiment shown in  FIG. 2A ; 
         FIG. 2C  is an exploded view of the embodiment shown in  FIG. 2A ; 
         FIG. 2D  is a front view of the embodiment shown in  FIG. 2A ; 
         FIG. 2E  is a lateral view of the embodiment shown in  FIG. 2A ; 
         FIG. 3A  is a perspective view of a third embodiment including a spacer with recessed inserts; 
         FIG. 3B  shows an exploded view of the embodiment shown in  FIG. 3A ; 
         FIG. 3C  shows a front view of the embodiment shown in  FIG. 3A ; 
         FIG. 3D  is a top view of the embodiment shown in  FIG. 3A ; 
         FIG. 3E  is a lateral view of the embodiment shown in  FIG. 3A ; 
         FIG. 4A  shows a perspective view of a fourth embodiment of an implant suitable for lumbar interbody fusion including a spacer with three inserts; 
         FIG. 4B  is an exploded view of the embodiment shown in  FIG. 4A ; 
         FIG. 4C  is a front view of the embodiment shown in  FIG. 4A ; 
         FIG. 4D  is a bottom view of the embodiment shown in  FIG. 4A ; 
         FIG. 4E  is a lateral view of the embodiment shown in  FIG. 4A ; 
         FIG. 5A  is a perspective view of a fifth embodiment including inserts with head and arm portions; 
         FIG. 5B  shows an exploded view of the embodiment shown in  FIG. 5A ; 
         FIG. 5C  shows a top view of the embodiment shown in  FIG. 5A ; 
         FIG. 5D  is a lateral view of the embodiment shown in  FIG. 5A ; 
         FIG. 5E  is a front view of the embodiment shown in  FIG. 5A ; 
         FIG. 5F  is a cross-sectional view as designated in  FIG. 5E ; 
         FIG. 6A  is a perspective view of a sixth embodiment including a single insert recessed behind the front portion of the spacer; 
         FIG. 6B  shows an exploded view of the embodiment shown in  FIG. 6A ; 
         FIG. 6C  is a front view of the embodiment shown in  FIG. 6A ; 
         FIG. 6D  is a lateral view of the embodiment shown in  FIG. 6A ; 
         FIG. 6E  is a top view of the embodiment shown in  FIG. 6A ; 
         FIG. 7A  shows a perspective view of a seventh embodiment with alternative inserts; 
         FIG. 7B  shows an exploded view of the embodiment shown in  FIG. 7A ; 
         FIG. 7C  is a front view of the embodiment shown in  FIG. 7A ; 
         FIG. 7D  is a lateral view of the embodiment shown in  FIG. 7A ; 
         FIG. 7E  is a top view of the embodiment shown in  FIG. 7A ; 
         FIG. 8A  provides a perspective view of an eight embodiment where the inserts are in the form of rings; 
         FIG. 8B  shows an exploded view of the embodiment shown in  FIG. 8A ; 
         FIG. 8C  is a front view of the embodiment shown in  FIG. 8A ; 
         FIG. 8D  is a lateral view of the embodiment shown in  FIG. 8A ; 
         FIG. 8E  is a top view of the embodiment shown in  FIG. 8A ; 
         FIG. 9A  is a perspective view of a ninth embodiment where the inserts have a c-shaped configuration; 
         FIG. 9B  shows an exploded view of the embodiment shown in  FIG. 9A ; 
         FIG. 9C  is a front view of the embodiment shown in  FIG. 9A ; 
         FIG. 9D  is a lateral view of the embodiment shown in  FIG. 9A ; 
         FIG. 9E  is a top view of the embodiment shown in  FIG. 9A ; 
         FIG. 10A  is a perspective view of a tenth embodiment including a single insert with a clamp-like design; 
         FIG. 10B  is an exploded view of the embodiment shown in  FIG. 10A ; 
         FIG. 10C  is a lateral view of the embodiment shown in  FIG. 10A ; 
         FIG. 11A  shows an exploded view of an eleventh embodiment including a two-part spacer and a member; 
         FIG. 11B  shows a perspective view of the embodiment shown in  FIG. 11A ; 
         FIG. 11C  is a front view of the embodiment shown in  FIG. 11A ; 
         FIG. 11D  is a lateral view of the embodiment shown in  FIG. 11A ; 
         FIG. 11E  is a top view of the embodiment shown in  FIG. 11A ; 
         FIG. 12A  shows an exploded view of a twelfth embodiment where the two-part spacer is joined by a connecting member; 
         FIG. 12B  shows a perspective view of the embodiment shown in  FIG. 12A ; 
         FIG. 12C  is a front view of the embodiment shown in  FIG. 12A ; 
         FIG. 12D  is a lateral view of the embodiment shown in  FIG. 12A ; 
         FIG. 12E  is a top view of the embodiment shown in  FIG. 12A ; 
         FIG. 13A  is a perspective view from an anterior position of a thirteenth embodiment of a single piece implant having an anterior portion and a spacer portion; 
         FIG. 13B  is another perspective view from a posterior position of the embodiment shown in  FIG. 13A ; 
         FIG. 13C  is a lateral view of the embodiment shown in  FIG. 13A ; 
         FIG. 13D  is a top view of the embodiment shown in  FIG. 13A ; 
         FIG. 13E  is another perspective view of the embodiment shown in  FIG. 13A ; 
         FIG. 13F  is a front view of the embodiment shown in  FIG. 13A ; 
         FIG. 13G  is an alternative version of the embodiment shown in  FIG. 13A ; 
         FIG. 14  is an exploded view of a fourteenth embodiment of an implant having a frame with endplates configured to be affixed thereto; 
         FIGS. 15A and 15B  are exploded views of a fifteenth embodiment showing implants having a frame defining a ring-like shape where the endplates are secured with an interference fit; 
         FIGS. 16A and 16B  show exploded views of a sixteenth embodiment including implants having a frame including arms and a support member where the endplates are secured with an interference fit; 
         FIGS. 17A and 17B  show exploded views of a seventeenth embodiment including implants having a frame including arms and a centrally located support member and two endplates securable with interference features on the support member and the arms; and 
         FIGS. 18A and 18B  show exploded views of an eighteenth embodiment having a frame with a plurality of endplates configured to be received within the openings in the frame. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Embodiments of the disclosure are generally directed to stand-alone interbody fusion implants. Specifically, the implants include a spacer combined with at least one insert or member. The inserts or members may be included, for example, to provide openings such as through holes which are designed to retain bone fasteners, such as screws, anchors, staples, pins, nails, and the like. According to other embodiments, the implants include a frame combined with one or more endplates. The frame includes a portion with openings such as through holes which are designed to retain bone fasteners, such as screws, anchors, staples, pins, nails, and the like. The frame may also include arms and an optional support member designed to secure the endplates, for example, with an interference fit. 
     The embodiments of the disclosure and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments and examples that are described and/or illustrated in the accompanying drawings and detailed in the following description. The features of one embodiment may be employed with other embodiments as the skilled artisan would recognize, even if not explicitly stated herein. Descriptions of well-known components and processing techniques may be omitted so as to not unnecessarily obscure the embodiments of the disclosure. The examples used herein are intended merely to facilitate an understanding of ways in which the disclosure may be practiced and to further enable those of skill in the art to practice the embodiments of the disclosure. Accordingly, the examples and embodiments herein should not be construed as limiting the scope of the disclosure, which is defined solely by the appended claims and applicable law. Moreover, it is noted that like reference numerals represent similar parts throughout the several views of the drawings. 
     As used herein and in the claims, the terms “comprising” and “including” are inclusive or open-ended and do not exclude additional unrecited elements, compositional components, or method steps. Accordingly, the terms “comprising” and “including” encompass the more restrictive terms “consisting essentially of” and “consisting of.” 
     Certain embodiments may be used on the cervical, thoracic, lumbar, and/or sacral segments of the spine. For example, the size and mass increase of the vertebrae in the spine from the cervical to the lumbar portions is directly related to an increased capacity for supporting larger loads. This increase in load bearing capacity, however, is paralleled by a decrease in flexibility and an increase in susceptibility to strain. When rigid immobilization systems are used in the lumbar segment, the flexibility is decreased even further beyond the natural motion restriction of that segment. Replacing the conventional rigid immobilization systems with certain embodiments disclosed herein may generally restore a more natural movement and provide added support to the strain-susceptible areas. 
       FIGS. 1A-1E  illustrate different views of one particular embodiment of the stand-alone intervertebral implant  1 . As shown in the perspective view of  FIG. 1A , the implant  1  includes a spacer  12  and one or more inserts  50 . The inserts  50  may be especially designed and configured to define a fastener aperture  34  and/or stabilize, strengthen, and/or reinforce the spacer  12 . 
     The spacer  12  includes a superior surface  42  and an inferior surface  44 . The superior and inferior surfaces  42 ,  44  each have a contact area  22  configured to contact and engage adjacent vertebrae (not shown). The superior and inferior surfaces  42 ,  44  may be parallel, curved, or angled to help restore or recreate a lordosis angle (or other angle) of the human spine. In particular, the superior and inferior surfaces  42 ,  44  may have a convex curve on the upper and lower surfaces or may be angled from a distal end to a proximal end or from one lateral side to the other to account for curvature of the spine. In addition, the superior and/or inferior surfaces  42 ,  44  may be contoured to conform more closely to the concave endplates of the adjacent vertebra. 
     In order to engage the adjacent vertebrae, the spacer  12  may include a plurality of protrusions  13  or teeth on the contact areas  22  of the superior and/or inferior surfaces  42 ,  44 . The protrusions  13  on the superior and inferior surfaces  42 ,  44  of each implant  1  grip the endplates of the adjacent vertebrae, resist migration, and aid in expulsion resistance. The plurality of protrusions  13  may be pyramidal in shape, but the protrusions  13  can be configured to be any size or shape to enhance anchoring the spacer  12  and the implant  1  to each of the adjacent vertebrae. 
     The implant  1  may contain an opening  16 . The opening  16  may be in the form of an axial graft hole within the spacer  12  configured to provide the maximum amount of volume for bone graft packing. The opening  16  may be configured for receiving bone graft material, for example, to promote fusion of the adjacent vertebral bodies. The opening  16  may extend from the superior surface  42  to the inferior surface  44  of the spacer  12  to define a substantially hollow center suitable for retaining one or more bone graft materials. For example, cadaveric bone, autologous bone, bone slurry, BMP, or other similar materials, may enhance tissue growth within the intervertebral space. 
     The spacer  12  includes a distal end  46  and a proximal end  48 . The distal end  46  of the spacer  12  may include a leading taper  40  for ease of insertion into the disc space. The leading taper  40  may be in the form of a chamfer or a bevel which enables self-distraction of the adjacent vertebral bodies during insertion of the implant  1 . The leading taper  40  may be located along the insertion direction of the implant  1 . For example, the leading taper  40  may assist in an anterior approach to the disc space. 
     As provided in  FIG. 1D , the spacer  12  defines at least one cutout  24  extending from the proximal end  48  to the opening  16 . In particular, the cutout  24  may be in fluid communication with the opening  16 . The cutouts  24  may also be defined through a portion of the lateral sides  36 ,  38  to the opening  16 . The cutouts  24  may be of any suitable shape and configuration, but are preferably sized and dimensioned to receive and retain at least a portion of the insert  50 . For example, the cutout  24  may be sized and dimensioned to receive one or more faces or sides of the insert  50 . The cutout  24  may be uniform or non-uniform and may comprise any morphology of recesses and protrusions configured to mate with the insert  50 , for example, including a male/female mating. For example, the cutout  24  may be defined by one or more stepped projections  26  on the spacer  12 . The cutout  24  may be defined such that the spacer  12  remains a single continuous piece ( FIG. 1D ) or the cutout  24  may be defined such that the spacer is broken into separate sections or pieces (not shown). 
     The insert  50  may be configured to comprise a fastener aperture  34 , which is sized and dimensioned for receiving a fastener, such as a screw  30 . Thus, the implant  1  may be secured to the adjacent vertebrae using fasteners, such as screws, anchors, staples, pins, nails, or the like. 
     The insert  50  is provided with a given depth and dimension designed to integrate seamlessly with the spacer  12 . In particular, the depth of the insert  50  may be greater than the width and/or height of the insert  50 . In addition, the insert  50  may not span across an entire frontage of the spacer  12 . Instead, the inserts  50  may be provided as discrete units designed to marry with the spacer  12  only at locations needed to reinforce and/or position bone fasteners, such as screws  30 . Thus, the inserts  50  may form only a portion of the front or an area proximate to the front of the implant  1 . In the embodiment shown in  FIG. 1A  when two inserts  50  are present, the inserts  50  may be separated a distance apart with a portion of spacer  12  positioned between the two inserts  50 . 
     A shown in  FIG. 1D , the insert  50  may include a head portion  52  and at least one arm  54  projecting therefrom. The head portion  52  may be enlarged to define the opening or fastener aperture  34  configured for retaining the fastener. The head portion  52  may include a cylindrical portion forming the fastener aperture  34 . The arm  54  may extend from the head portion  52  in one or more directions to contact and integrate with the spacer  12 . For example, the arm  54  may extend laterally, medially, and/or posteriorly away from the head portion  52 . In particular, the arm  54  may extend posteriorly away from the head portion  52  and toward the distal end  46  of the spacer  12  when attached thereto. 
     The insert  50  including a portion of the arm  54  and/or a portion of the head portion  52  may be configured to mirror the shape and design of the spacer  12 . The spacer  12  may define at least one recess, projection, etc. sized and dimensioned to retain at least a portion of the arm  54 . For example, the arm  54  or any portion of the insert  50  may rest against a portion of the spacer  12  or a recess formed therein to provide a joint, such as a lap joint, half lap joint, dovetail lap joint, beveled lap joint or scarf joint, stepped lap joint, tabled lap joint, or the like. In particular, a lap joint may include joining two pieces of material together by at least partially overlapping them (e.g., at least a portion of the insert  50  and a portion of the spacer  12  are overlapped). In a full lap, no material is removed from either of the members to be joined, resulting in a joint which is the combined thickness of the two members. In a half lap joint, material is removed from each of the members so that the resulting joint is the thickness of the thickest member. In the embodiment shown in  FIG. 1E , the joint portion between the insert  50  and the spacer  12  is at least partially a half lap joint such that the joint does not increase the height of the spacer  12 . 
     As shown in  FIG. 1E , the insert  50  may join the spacer  12  with a stepped lap joint. A portion of the insert  50  may be stepped with a male projection to mate with a stepped female configuration of the spacer  12 . A series of offset planar surfaces having a rise and a run may form the stepped profile. For example, the arm  54  of the insert  50  may be stepped with a male projection configured to mate with corresponding stepped projections  26  on the spacer  12 . Depending on the configuration of the joint, the joint may form a press-fit or friction-fit engagement to secure the insert  50  to the spacer  12  or the joint may be further secured, for example, with adhesive, pins  78 , or the like. 
     The insert  50  is coupled to the spacer  12  such that at least a portion of the insert  50  is received in the cutout  24  in the spacer  12 . The spacer  12  and the insert  50  may be coupled, removably coupled, connected, or attached together in any suitable manner known in the art. The spacer  12  and the insert  50  may also be coupled together through appropriate coupling means or fasteners. For example, the insert  50  and cutout  24  may be configured to provide male and female edges, which are the mechanical interfaces between the two pieces. Portions of the spacer  12  and the insert  50  may be assembled together using, alone or in combination, a friction fit, a dovetail assembly, dowel pins, hooks, staples, screws, adhesives, and the like, or any suitable fasteners known in the art, which can be used to permanently attach the spacer  12  and the insert  50  together. 
     In addition or in the alternative, the spacer  12  and the inserts  50  may be secured together with pins  78  which traverse at least a portion of the spacer  12  and/or the insert  50 . For example, the arm  54  may include one or more openings  80  extending therethrough sized and configured to receive a portion of pin  78 . Similarly, the corresponding portion of the spacer  12  may include one or more openings  80  extending therethrough sized and configured to receive the remainder of pin  78  to secure the arm  54  to the spacer  12 . These openings  80  may or may not be threaded. The pins  78  may pass through holes  80 , for example, in a substantially perpendicular manner relative to a horizontal plane to secure the joint between the insert  50  and the spacer  12 . For example, the pins  78  may be oriented substantially perpendicular relative to the superior and/or inferior surfaces  42 ,  44  of the spacer  12 . The pins  78  may be in the form of dowels or may be fully or partially threaded. The pins  78  may be formed from a biocompatible material, such as titanium, or the pins  78  may be formed from tantalum, for example, to enable radiographic visualization. 
     The head portion  52  of the insert  50  may include an upper surface  62  and a lower surface  64  depending on the orientation of the insert  50 . For example, the two inserts  50  depicted in  FIG. 1D  are identical except the inserts  50  are oriented in opposite directions to fit the respective cutouts  24  in the spacer  12 . The first insert  50   a  is oriented such that the upper surface  62  is configured to mate with a portion of the superior surface  42  of the spacer  12  and the lower surface  64  is configured to mate with a portion of the inferior surface  44  of the spacer. Conversely, the second insert  50   b  is oriented such that the lower surface  64  is configured to mate with a portion of the superior surface  42  of the spacer  12  and the upper surface  62  is configured to mate with a portion of the inferior surface  44  of the spacer. 
     The upper surface  62  and/or lower surface  64  of the head portion  52  of the insert  50  may extend a distance beyond the superior surface  42 , the inferior surface  44 , or both surfaces  42 ,  44  of the spacer  12 . In particular, a portion of the head portion  52  of the insert  50  may extend above or below the superior and inferior surfaces  42 ,  44  of the spacer  12 . For example, the lower surface  64  of the first insert  50   a  may extend beyond the inferior surface  44  and the lower surface  64  of the second insert  50   b  may extend beyond the superior surface  42  of the spacer  12 . 
     The projection of the lower surfaces  64  of the first and second inserts  50   a ,  50   b  may be in the form of an eyebrow  60 . The eyebrows  60  may fully capture the bone screws  30  while still allowing for the screw  30  to reside about, below, or above the base plane of the superior and inferior surfaces  42 ,  44 . For example, a front surface  65  of the insert  12  may include at least one eyebrow  60  where the eyebrow  60  projects past the superior surface  42 , the inferior surface  44 , or both surfaces  42 ,  44  of the spacer  12 . The eyebrow  60  may include a rounded portion. The eyebrow  60  may include a smooth surface or a roughened surface. As shown in  FIG. 1B , the eyebrow  60  may be comprised of a smooth and curved surface. A lateral portion of the eyebrow  60  may further include one or more torsional stabilizers  70  configured to prevent or minimize torsional motion of the implant  1  once implanted. The torsional stabilizers  70  may act as extensions or fins, which may serve as knife edges to further purchase into the bone of the adjacent vertebrae or serve as a stop to abut anterior aspects of the adjacent vertebrae. The torsional stabilizer  70  may include a spiked or pointed projection or extension configured to engage adjacent vertebrae. In particular, the torsional stabilizer  70  may have a width substantially the same or less than a width of the eyebrow  60 . 
     A portion of each of the upper surfaces  62  of the inserts  50  may also include an additional torsional stabilizer  70 , for example, positioned opposite to the eyebrows  60 . The torsional stabilizer  70  on the upper surfaces  62  may be the same or different than the torsional stabilizer  70  extending from the eyebrows  60 . The upper surfaces  62  of the inserts  50  may complete a surface of the superior and inferior surfaces  42 ,  44  of the spacer  12  to enhance anchoring of the spacer  12 . As shown in  FIG. 1D , the spacer  12  may include a notch  23  in the cutout  24  in the superior and/or inferior surfaces  42 ,  44  of the spacer  12 . The extension of the upper surface  62  including the torsional stabilizer  70  may fit in this notch  23  to form a continuous and contiguous superior and/or inferior surface for the implant  1 . The notch  23  may be uniform in shape and dimension or non-uniform. In particular, the notch  23  may have a partial rectangular cross-section or may be any suitable shape to compliment the upper surface  62  of the insert  50  and complete the superior and/or inferior surfaces  42 ,  44  of the spacer  12 . 
     Each insert  50  includes a screw hole or fastener aperture  34  sized and dimensioned to receive a fastener, such as screw  30 . The screws  30  may be any suitable screws known in the art including fixed or variable angle. The screw hole  34  is configured to receive the screw  30  at a given angle. For example, the screw holes  34  for receiving the screw  30  may traverse the front surface  65  of the insert  50  at an angle divergent to a horizontal plane in order to secure the implant  1  to one of the adjacent vertebrae. Thus, in the case of implant  1  having two inserts  50  as shown in  FIG. 1A , the screws  30  enter the screw holes  34  at specified angles to enter each of the adjacent vertebrae at the optimal locations. In particular, the screws  30  may be inserted at an angle for maximum screw purchase into the superior and inferior vertebral bodies. 
     The intervertebral implant  1  may be positioned in the spine after the disc portion between the two vertebral bodies is exposed and removed, for example, using rongeurs or other suitable instruments. The posterior and lateral walls of the annulus are generally preserved to provide peripheral support for the implant  1  and graft materials. A trial device attached to a trial holder may then be inserted into the disc space to determine size of the implant  1 . This procedure is generally conducted using fluoroscopy and tactile feel. The implant  1  may be available in various heights and geometric options to fit the anatomical needs of a wide variety of patients. After the appropriate sized implant  1  is selected and attached to an implant holder and drill guide (not shown), the implant  1  may be inserted into the disc space. Before or after the implant  1  is positioned within the disc space, supplemental graft material can be used to enhance fusion. The implant  1  may be implanted in the vertebral space using an anterior, posterior, lateral, anterolateral, oblique, and/or transforaminal approach. The implant  1  shown in  FIG. 1A  may be particularly suitable for an anterior cervical procedure. The implant  1  may be in the form of a stand-alone fusion device to provide structural stability and a low or zero profile design. The implant  1  is preferably assembled before insertion into the disc space. 
     Once the implant  1  is positioned inside the disc space, an awl or any similar type of instrument, for example, can be used to drill through the screw hole and break the cortex of the adjacent vertebral body. The surgeon performing this procedure may then use a depth gauge to determine the screw length. Once the appropriate screw length is determined, screws  30  may be inserted using a self-retaining screwdriver, for example. Any suitable type of screw  30  may be selected by one of ordinary skill in the art. For example, the screws  30  may include fixed or variable angle screws of any suitable size with appropriate thread spacing, thread pitch, head design, length, and the like. 
     Once inserted, the screws  30  may be secured with an anti-back out prevention or locking mechanism  20 . The locking mechanism  20  may be in the form of one or more blocking screw  32  to capture the sides of the inserted screws to prevent screw back out. As depicted in  FIG. 1B , the locking mechanism  20  may be disposed on the spacer  12  for preventing back out of the screws  30 . For example, a cam-style blocking mechanism may be used with screws  30  that capture the fixation device screws  30  once they are inserted fully into the inserts  50 . The insert  50  may include a cutout  56  in the outer periphery of the head portion  52  configured such that the locking mechanism  20  may block or unblock the head of the screw  30 . As shown, the anti-back out mechanism  20  may include a single set screw  32  that retains the screws  30  with the implant  1 , although any suitable anti-back out mechanism  20  may be selected by one of ordinary skill in the art. 
       FIGS. 2A-2E  show alternative views of a second embodiment of an implant  10 . In general, most of the structure of implant  10  is similar or comparable to the structure of implant  1 . In this particular embodiment, the torsional stabilizers  70  on the upper surfaces  62  are replaced with a plurality of protrusions  13  or teeth. As shown in  FIG. 2B , a portion of the upper surfaces  62  of the inserts  50   a ,  50   b  may include an extension with a plurality of protrusions  13  or teeth designed to extend the contact areas  22  of the superior and/or inferior surfaces  42 ,  44  of the spacer  12 . The protrusions  13  on the upper surfaces  62  of the inserts  50   a ,  50   b  may complete a surface of the superior and inferior surfaces  42 ,  44  of the spacer  12  to enhance anchoring of the spacer  12 . As shown in  FIG. 2C , the spacer  12  may include the notch  23  in the cutout  24  in the superior and/or inferior surfaces  42 ,  44  of the spacer  12 . The notch  23  may be uniform in shape and dimension or non-uniform. In particular, the notch  23  may have a partial rectangular cross-section. The extension of the upper surface  62  including the plurality of protrusions  13  may fit in this notch  23  to form a continuous and contiguous superior and/or inferior surface for the implant  10 . The plurality of protrusions  13  may be the same or different than the protrusions  13  provided on the remainder of the spacer  12 . 
     According to a third embodiment,  FIGS. 3A-3E  show alternative views an implant  100 . In general, most of the structure of implant  100  is similar or comparable to the structure of implant  1 . In this particular embodiment, different inserts  150  are provided. In particular, the upper surfaces  162  of the inserts  150   a ,  150   b  do not include a plurality of protrusions and are instead smooth. These smooth upper surfaces  162  do not complete the superior and inferior surfaces  142 ,  144  of the spacer  112 . Instead, the smooth upper surfaces  162  are recessed and mated beneath the superior and inferior surfaces  142 ,  144  of the spacer  112 . In addition, the cutouts  124  are modified from those shown in implant  1 . For example, the superior and inferior surfaces  142 ,  144  of the spacer  112  are not notched to receive a portion of the insert  150 , but instead extend to the proximal end  48  of the spacer. As is evident in  FIG. 3B , a portion of the stepped projection  126  on the spacer  112  is extended to be contiguous and flush with the proximal end  48  of the spacer  112 . 
     According to a fourth embodiment,  FIGS. 4A-4E  show an implant  200 , which may be particularly suitable for an anterior lumbar procedure. In general, most of the structure of implant  200  is similar or comparable to the structure of implant  1 . In this particular embodiment, three different inserts  250  provide the fastener apertures  234 . 
     A shown in  FIG. 4B , a first insert  250   a  is identical to a second insert  250   b  except as mirror images of one another to fit the respective cutouts  224  in the spacer  212 . The first and second inserts  250   a ,  250   b  each define a fastener aperture  234 . The first and second inserts  250   a ,  250   b  are each configured to allow a bone screw  230  to engage superior or inferior vertebra. Similar to implant  1 , the spacer  212  may include one or more cutouts  224  sized and configured to retain the inserts  250 . The cutouts  224  may further define a stepped projection  226  configured to mate with the arm  254  of the insert  250 . The arm  254  may also be stepped and configured to mate with corresponding stepped projections  226  on the spacer  212 . A portion of the insert  250  may be stepped with a male projection to mate with a stepped female configuration of the spacer  212 . The arm  254  may include a series of offset planar surfaces, for example, having a rise and a run, to form the stepped profile. The cutouts  224  may be in fluid communication with the opening  216  extending from the superior surface  242  to the inferior surface  244  of the spacer  212 . 
     In addition, the spacer  212  may include one or more notches  223  in the cutout  224  in the superior surface  242  and/or inferior surface  244  of the spacer  212 . The extension of the upper surface  262  of the insert  250  including the plurality of protrusions  213  may fit in the respective notch  223  to form a continuous and contiguous superior surface for the implant  200 . A third insert  250   c  is provided between the first and second inserts  250   a ,  250   b . The third insert  250   c  is different from the first and second inserts  250   a ,  250   b  and allows a bone screw  230  to engage a superior vertebra. Although the third insert  250   c  is depicted with a smooth upper surface  262 , the third insert  250   c  may also include projections  213 , torsional stabilizers, or the like. 
     The fastener apertures  234  may be configured such that the locking mechanism  220  may block or unblock the heads of the screws  230  in the respective fastener apertures  234 . As shown, the anti-back out mechanism  220  may include a first set screw  232   a  that is configured to block a portion of the screw  230  in the first insert  250   a  and the screw  230  in the third insert  250   c  and a second set screw  232   b  that is configured to block a portion of the screw  230  in the second insert  250   b  and the screw  230  in the third insert  250   c.    
       FIGS. 5A-5F  show a fifth embodiment of an implant  300 . In general, most of the structure of implant  300  is similar or comparable to the structure of implant  1 . In this particular embodiment, two different inserts  350  provide the fastener apertures  334 . In this case, modified arms  354  are at least partially received in at least one recess  318  in the spacer  312  to join the insert  350  to the spacer  312 . The recess  318  may extend a set depth into the spacer  312  from the opening  316 . The recess  318  may be in fluid communication with the opening  316 . The recess  318  may be formed in the lateral portions and/or the distal portion of the opening  316 . The recess  318  may be positioned substantially medially between and substantially parallel to the superior and/or inferior surfaces  342 ,  344  of the spacer  312 . The recess  318  may be sized and dimensioned to retain at least a portion of the arm  354  of the insert  350 . 
     The two inserts  350  depicted in  FIG. 5B  are identical except are oriented in opposite directions to fit the respective cutouts  324  in the spacer  312 . The insert  350  may include head portion  352  and arm  354  extending therefrom. The arm  354  may extend posteriorly away from the head portion  352  and toward the distal end  346  of the spacer  312  when attached thereto. The arm  354  may be angled relative to the head portion  352  such that the arm  354  is oriented in a medial direction, for example, to mimic the shape of the spacer  312 . 
     Each arm  354  of the insert  350  may include a first arm portion  354   a  and a second arm portion  354   b . The first arm portion  354   a  may connect the head portion  352  of the insert  350  to the second arm portion  354   b . The second arm portion  354  may be angled relative to the first arm portion  354   a . The first arm portion  354   a  may engage the lateral portions of the recess  318  in the spacer  312 , and the second arm portion  354   b  may engage the distal portion of the recess  318  in the spacer  312 . The upper surface  362  of the insert  350  including the head portion  352 , the first arm portion  354   a , and the second arm portion  354   b  may be a continuous and contiguous coplanar surface. In the alternative, the arm  354  may be recessed beneath the upper surface  362  of the head portion  352 . The arms  354  of the inserts  350  may join the spacer  312  via a press-fit or friction-fit engagement to secure the insert  350  to the spacer  312  or the joint may be further secured, for example, with adhesive, pins, or the like. 
     Similar to implant  1 , the lower surface  364  of the head portion  352  of the insert  350  may extend a distance beyond the superior surface  342 , the inferior surface  344 , or both surfaces  342 ,  344  of the spacer  312 . For example, the lower surface  364  of the first insert  350   a  may extend beyond the inferior surface  344  and the lower surface  364  of the second insert  350   b  may extend beyond the superior surface  342  of the spacer  312 . The projection of the lower surfaces  364  of the first and second inserts  350   a ,  350   b  may be in the form of eyebrows  360 . In this embodiment, the eyebrow  360  includes a substantially smooth and curved surface. In the embodiment shown, no torsional stabilizers are present, but one or more torsional stabilizers may be added if desired. 
     Similar to implant  100 , the upper surfaces  362  of the inserts  350   a ,  350   b  do not include a plurality of protrusions and are instead smooth. These smooth upper surfaces  362  do not complete the superior and inferior surfaces  342 ,  344  of the spacer  312 . Instead, the smooth upper surfaces  362  are recessed and mated beneath the superior and inferior surfaces  342 ,  344  of the spacer  312 . In addition, the cutouts  324  are different from those shown in implant  1 . For example, the superior and inferior surfaces  342 ,  344  of the spacer  312  are not notched to receive a portion of the insert  350 , but extend to the proximal end  348  of the spacer. 
       FIGS. 6A-6E  show a sixth embodiment of an implant  400  including a single member  450  recessed behind the front portion of the spacer  412 . In general, most of the structure of implant  400  is similar or comparable to the structure of implant  1 . Unlike the individual inserts  50  provided for each fastener aperture  34  in implant  1 , in this particular embodiment, a single member  450  provides all of the fastener apertures  434 . 
     In this embodiment, the single member  450  provides two fastener apertures  434  to secure fasteners in both the superior and inferior vertebrae. This member  450  may be provided with or without arms. The member  450  may be recessed in the spacer  412  and positioned posterior to the front surface  465  of the spacer  412 . In particular, the member  450  may be positioned within the opening  416  such that a first portion of the member  450  is received in a first cutout  424  in the spacer  412  and a second portion of the member  450  is received a second cutout  424  in the spacer  412 . The member  450  may be curved and contoured to follow a proximal portion of the spacer  412 . 
     Similar to implant  1 , the upper and/or lower surfaces  462 ,  464  of the member  450  may extend a distance beyond the superior surface  442 , the inferior surface  444 , or both surfaces  442 ,  444  of the spacer  412 . For example, a portion of the upper surface  462  of the member  450  may extend above the superior surface  442  and a portion of the lower surface  464  may extend below the inferior surface  444  of the spacer  412 . The projections of the upper and lower surfaces  462 ,  464  of the single member  450  may be in the form of eyebrows  460 . In this embodiment, the eyebrows  460  include a substantially smooth and curved surface. In the embodiment shown, torsional stabilizers  470  are provided opposite to the eyebrows  460  and are also provided substantially medially on the member  450  projecting superiorly and inferiorly from both the upper and lower surfaces  462 ,  464 , respectively. The torsional stabilizers  470  may include a spiked or pointed projection or extension configured to engage adjacent vertebrae. 
     According to a seventh embodiment,  FIGS. 7A-7E  depict an implant  500  with a different type of insert  550 . In general, most of the structure of implant  500  is similar or comparable to the structure of implant  1 . Unlike the inserts  50  provided with arm  54  in implant  1 , in this particular embodiment, the insert  550 , which provides the fastener aperture  534 , does not contain an arm and is directly recessed into at least one slot  518  in the spacer  512 . 
     The two inserts  550  depicted in  FIG. 7B  are identical except are oriented in opposite directions to fit the respective cutouts  524  in the spacer  512 . The insert  550  may be curved or may contain one or more angled transitions. At least a portion of the inserts  550  may join the spacer  512  via a press-fit or friction-fit engagement to secure the insert  550  to the spacer  512  or the joint may be further secured, for example, with adhesive, pins, or the like. 
     In this embodiment, the inserts  550  are at least partially received in at least one slot  518  in the spacer  512  to join the insert  550  to the spacer  512 . The slot  518  may extend a set depth into the spacer  512  from the cutout  524 . For example, the slot  518  may be formed in an inferior or superior portion of the cutout  524  and may be in fluid communication with the cutout  524 . The slot  518  may include more than one portion including an angled portion, for example. The angled portion may connect the eyebrow  560  to a planar portion. The planar portion may be positioned substantially perpendicular to the superior and/or inferior surfaces  542 ,  544  of the spacer  12 . The slot  518  may be sized and dimensioned in any suitable configuration to retain at least a portion of the insert  550 . For example, the upper surface  562  of the insert  550  may contact and fit within the slot  518 . The upper surfaces  562  of the inserts  550  may be substantially smooth or may be textured. The upper surface  562  may also be curved or rounded as shown. These smooth upper surfaces  562  are recessed and mated beneath the superior and inferior surfaces  542 ,  544  of the spacer  512 . 
     In this embodiment, the depth of the insert  550  may be the same or smaller than the depth of the proximal portion of the spacer. In other words, the insert  550  does not need to fill the entire depth of the cutout  524 . As shown in  FIG. 7E , the insert  550  fills only a portion of the cutout  524 . In this embodiment, the insert  550  is positioned substantially centrally in the cutout  524 , but it is envisioned that the insert  550  may be positioned at any suitable location in the cutout  524 . 
     Similar to implant  1 , the lower surface  564  of the insert  550  may extend a distance beyond the superior surface  542 , the inferior surface  544 , or both surfaces  542 ,  544  of the spacer  512 . For example, the lower surface  564  of the first insert  550   a  may extend below the inferior surface  544  and the lower surface  564  of the second insert  550   b  may extend above the superior surface  542  of the spacer  512 . The projection of the lower surfaces  564  of the first and second inserts  550   a ,  550   b  may be in the form of an eyebrow  560 . In this embodiment, the eyebrow  560  includes a substantially smooth and curved surface. In the embodiment shown, no torsional stabilizers are present, but one or more torsional stabilizers may be added if desired. 
       FIGS. 8A-8E  provide an eighth embodiment of an implant  600  where the inserts  650  are in the form of rings. In general, most of the structure of implant  600  is similar or comparable to the structure of implant  1 . In addition, this embodiment is similar to the implant  500  discussed above. 
     In this embodiment, the insert  650  is in the form of a ring or cylinder. The ring insert  650  may be provided with one or more slits  658 , for example, to allow the insert  650  to tightly mate with the cutout  624  through the spacer  612  and secure the insert  650  to the spacer  612 . In particular, one or more slits  658  may be longitudinally positioned around a periphery of the ring-shaped insert  650 . The slits  658  may be uniformly or non-uniformly positioned around the insert  650 . As shown in  FIG. 8B , the slits  658  may be positioned in 90° increments around the ring insert  650 . For example, four slits  658  may be positioned around the periphery of the ring insert  650 . The slits  658  may be oriented such that the open ends of the slits  658  face anteriorly. 
     The insert  650  may be received in a recess in the cutout  624  or may be positioned within the cutout  624 . The cutouts  624  may be in fluid communication with the opening  616  extending from the superior surface  642  to the inferior surface  644  of the spacer  612 . The insert  650  may be configured to at least partially define and reinforce the fastener aperture  634 . At least a portion of the inserts  650  may join the spacer  612  via a press-fit or friction-fit engagement to secure the insert  650  to the spacer  612 . The insert  650  may be further secured, for example, with adhesive or the like. 
     In this embodiment, the depth of the insert  650  may be the same or smaller than the depth of the proximal portion of the spacer. In other words, the insert  650  does not need to fill the entire depth of the cutout  624 . In this embodiment, the insert  650  is positioned at an angle in the cutout  624  to accommodate the angles of the bone screws  630 . It is envisioned that the insert  650  may be positioned at any suitable location in the cutout  624 . 
       FIGS. 9A-9E  provide a ninth embodiment of an implant  700 . In general, most of the structure of implant  700  is similar or comparable to the structure of implant  1 . In addition, this embodiment is substantially the same as the implant  600  discussed above, and the discussion for implant  600  applies equally here. In this particular embodiment, the insert  750  has a c-shaped cross-section instead of being in the form of a ring. The c-shaped inserts  750  shown in  FIG. 9B  are the same except are oriented differently. The c-shaped inserts  750  are substantially the same as the ring inserts  650  except a gap separates the insert  750  to allow for further compression and/or expansion of the insert  750 . 
     The c-shaped insert  750  may also be provided with one or more slits  758 , for example, to allow the insert  750  to tightly mate with the cutout  724  through the spacer  712  and secure the insert  750  to the spacer  712 . In particular, one or more slits  758  may be longitudinally positioned around a periphery of the c-shaped insert  750 . The slits  758  may be uniformly or non-uniformly positioned around the insert  750 . The slits  758  may also positioned in 90° increments around the c-shaped insert  750 . For example, three slits  758  may be positioned around the periphery of the ring insert  750 . The slits  758  may be oriented such that the open ends of the slits  758  face anteriorly. 
     The insert  750  may be received in a recess in the cutout  724  or may be positioned within the cutout  724 . The cutouts  724  may be in fluid communication with the opening  716  extending from the superior surface  742  to the inferior surface  744  of the spacer  712 . The insert  750  may be configured to at least partially define the fastener aperture  734 . At least a portion of the inserts  750  may join the spacer  712  via a press-fit or friction-fit engagement to secure the insert  750  to the spacer  712 . The insert  750  may also be secured, for example, with adhesive or the like. In this embodiment, the depth of the insert  750  may be the same or smaller than the depth of the proximal portion of the spacer. Similar to insert  650 , the c-shaped insert  750  does not need to fill the entire depth of the cutout  724 . In this embodiment, the insert  750  is positioned at an angle in the cutout  724  to accommodate the angles of the bone screws  730 , but it is envisioned that the insert  750  may be positioned at any suitable location in the cutout  724  so long as the necessary reinforcement is provided to the fasteners. 
     According to a tenth embodiment,  FIGS. 10A-10C  provide an implant  800  with a member  850 . In general, most of the structure of implant  800  is similar or comparable to the structure of implant  1 . Unlike the individual inserts  50  provided for each fastener aperture  34  in implant  1 , in this particular embodiment, a member  850  provides all of the fastener apertures  834 . The member  850  may be in the form of a clamp or clip, which surrounds a proximal portion of the spacer  812 . 
     In this embodiment, the member  850  provides two fastener apertures  834  to secure fasteners in both the superior and inferior vertebrae. This member  850  may be provided with or without arms. The member  850  may be positioned posterior to the front surface  865  of the spacer  812 . In particular, the member  850  may be positioned to surround or envelop a portion of at least one lateral side  836 ,  838  and a portion of the superior and/or inferior surfaces  842 ,  844  of the spacer  812 . The member  850  may be contoured, for example, to begin at one lateral side  836  wrap around a portion of the superior surface  842  to define one of the fastener apertures  834 , wrap around the other lateral side  838 , wrap under a portion of the inferior surface  844  to define the other fastener aperture  834 , and terminate at the lateral side  836 . The member  850  may begin and terminate at one lateral side  836 ,  838 , for example, using one or more clamping features  882 . The clamping features  882  may include prongs or springs which attach or secure the member  850  to the spacer  812 . Although the member  850  is depicted as a single piece, it is envisioned that the clamping member  850  may be comprised of more than one part so long as the member  850  may clamp to the spacer  812  and provide the fastener apertures  834 . 
     A portion of the upper and/or lower surfaces  862 ,  864  of the member  850  may extend a distance beyond the superior surface  842 , the inferior surface  844 , or both surfaces  842 ,  844  of the spacer  812 . For example, a portion of the upper surface  862  may extend above the superior surface  842  and a portion of the lower surface  864  may extend below the inferior surface  844  of the spacer  812 . The projections of the upper and lower surfaces  862 ,  864  of the single insert  850  may be in the form of eyebrows  860 . In this embodiment, the eyebrows  860  include a substantially smooth and curved surface. In the embodiment shown, torsional stabilizers  870  are also provided substantially medially and laterally on the member  850  projecting superiorly and inferiorly from both the upper and lower surfaces  862 ,  864 , respectively. The torsional stabilizers  870  may include a spiked or pointed projection or extension configured to engage adjacent vertebrae. 
       FIGS. 11A-11E  provide an eleventh embodiment of an implant  900 . In general, the structure of implant  900  is similar or comparable to the structure of implant  1 . In this embodiment, the inserts  50  have been replaced with a member  950  and the spacer  912  includes multiple components. 
     The spacer  912  has a first spacer portion  972  and a second spacer portion  974 . The first spacer portion  972  has a first end  972   a  and a second end  972   b , and the second spacer portion  974  has a first end  974   a  and a second end  974   b . The second end  972   b  of the first spacer portion  972  is coupled to the first end  974   a  of the second spacer portion  974 . The first and second spacer portions  972 ,  974  form the superior surface  942  and the inferior surface  944  of the spacer  912 . The superior surface  942  and the inferior surface  944  each have a contact area  922  configured to engage adjacent vertebrae. The first and second spacer portions  972 ,  974  and the member  950  join to form an opening  916  extending from the superior surface  942  to the inferior surface  944  of the spacer  912 . 
     The first and second spacer portions  972 ,  974  may be joined together in any suitable manner. For example, the first and second spacer portions  972 ,  974  may be mated together by a splice joint, scarf joint, butt joint, or the like. The splice joint may include, for example, a half lap splice joint, a bevel lap splice joint, a tabled splice joint, or the like. In particular, the splice joint may include joining two pieces of material together by at least partially overlapping them (e.g., overlapping at least a portion of the first spacer portion  972  and at least a portion of the second spacer portion  974 ). In the embodiment shown in  FIG. 11A , the joint portion between first and second spacer portions  972 ,  974  is at least partially a half lap splice joint such that the joint does not increase the height of the spacer  912 . In a half lap splice joint, material is removed from each of the members so that the resulting joint is the thickness of the two members as combined. Although not shown, the splice joint between the first and second spacer portions  972 ,  974  may be beveled or scarfed, stepped, notched, keyed, nibbed, or the like. Any type of joint formed between the first and second spacer portions  972 ,  974  may be further secured with one or more pins  978  or the like. 
     The member  950  has an upper surface  962 , a lower surface  964 , a first lateral portion  966 , a second lateral portion  968 , and at least one hole  934  traversing the member  950  for receiving a fastener, such as a screw  930 . The upper surface  962  and/or lower surface  964  may extend a distance beyond the superior surface  942 , the inferior surface  944 , or both surfaces  942 ,  944  of the spacer  912 . In particular, a portion of member  950  may extend above or below the superior and inferior surfaces  942 ,  944  of the spacer  912 . The projections of the upper and lower surfaces  962 ,  964  may each be in the form of an eyebrow  960 . The eyebrow  960  may include a rounded portion, for example, with a smooth surface. The upper and lower surfaces  962 ,  964  may further include one or more torsional stabilizers  970  configured to prevent or minimize torsional motion of the implant  900  once implanted. The torsional stabilizers may be positioned, for example, substantially medially and laterally along the length of the member  950 . The torsional stabilizers  970  may include a spiked or pointed projection or extension configured to engage adjacent vertebrae. 
     The member  950  is coupled to the spacer  912  such that the first end  972   a  of the first spacer portion  972  engages the first lateral portion  966  of the member  950  and the second end  974   b  of the second spacer portion  974  engages the second lateral portion  968  of the member  950 . The spacer portions  972 ,  974  and the member  950  may also be joined together in any suitable manner. The member  950  may be configured to mirror the shape and design of the spacer  912 . The spacer  912  may define at least one recess, projection, etc. sized and dimensioned to retain at least a portion of the member  950 . Similar to the insert configurations discussed in this document, member  950  may rest against a portion of the spacer portions  972 ,  974  or a recess therein to form a joint, such as a lap joint, half lap joint, dovetail lap joint, beveled lap joint or scarf joint, stepped lap joint, tabled lap joint, or the like. In particular, at least a portion of the member  950  may at least partially overlap at least a portion of the spacer  912  or vice versa. In the embodiment shown in  FIG. 11A , the joint portions between the member  950  and the spacer  912  are at least partially a half lap joint such that the joint does not increase the height of the spacer  912 . 
     For example, the member  950  may include a first extension  967  extending from the first lateral portion  966  and a second extension (not visible) extending from the second lateral portion  968 . The first extension  967  and second extension may extend posteriorly away from a front surface  965  of the member  950  and toward the distal end  946  of the spacer  912  when attached thereto. The first extension  967  may contact a first ledge  973  on the first spacer portion  972  to form a first half lap joint. Similarly, the second extension may contact a second ledge on the second spacer portion  974  to form a second half lap joint. The extensions  967  and ledges  973  may be configured to be complimentary and mate together, for example, with planar surfaces, curved surfaces, tapers, bevels, notches, or the like. Depending on the configuration of the joints, the joints may form a press-fit or friction-fit engagement to secure the member  950  to the spacer  912  or the joints may be further secured, for example, with adhesives, pins  978 , or the like. For example, the first and second half lap joints may each be further secured with at least one pin  978 . 
     When present, the pins  978  may traverse at least a portion of the spacer  912  and/or the member  950 . For example, the extensions  967  may include one or more openings  980  extending therethrough sized and configured to receive a portion of pin  978  to secure the member  950  to the spacer  912 . Similarly, the corresponding portion of the spacer  912  may include one or more openings  980  extending therethrough sized and configured to receive the remainder of pin  978  to secure the member  950  to the spacer  912 . These openings  980  may or may not be threaded. The pins  978  may pass through holes  980 , for example, in a substantially perpendicular manner relative to a horizontal plane to secure the joints between the member  950  and the spacer  912 . For example, the pins  978  may be oriented substantially perpendicular relative to the superior and/or inferior surfaces  942 ,  944  of the spacer  912 . The pins  978  may be in the form of dowels (as shown connecting the first spacer portion  972  to the second spacer portion  974 ) or may be at least partially threaded (as shown connecting the member  950  to the spacer  912 ). The pins  978  may be formed from a biocompatible material, such as titanium, or the pins  978  may be formed from tantalum, for example, to enable radiographic visualization. 
     The implant  900  may also include a locking mechanism  920  disposed on the member  950  for preventing back out of the screws  930 . For example, a cam-style blocking mechanism may be used with screws  930  that capture the fixation device screws  930  once they are inserted fully through the member  950 . As shown, the anti-back out mechanism  920  may include a single set screw  932  that retain the screws  930  with the implant  900 , although any suitable anti-back out mechanism  920  may be selected by one of ordinary skill in the art. 
       FIGS. 12A-12E  provide a twelfth embodiment of an implant  1000 . In general, most of the structure of implant  1000  is similar or comparable to the structure of implant  1 . In addition, this embodiment is substantially the same as the implant  900  discussed above, and the discussion for implant  900  applies equally here with the same reference numbers provided for unchanged elements. In this particular embodiment, the first and second spacer portions  1072 ,  1074  are connected together by a connector  1084  instead of being attached directly to one another. This allows the first and second spacer  1072 ,  1074  to be spaced apart with respect to one another. The connector  1084  may also be formed of a material different from the spacer portions  1072 ,  1074 , for example, to allow for strength, support, radiographic visualization, or the like. 
     The first and second spacer portions  1072 ,  1074  may be secured together with one or more connectors  1084 . The connector  1084  may be sized, shaped, and configured in any suitable manner to join the second end  1072   b  of the first spacer portion  1072  to the first end  1074   a  of the second spacer portion  1074 . Any of the joints discussed in this document may be suitable to join the first and second spacer portions  1072 ,  1074  using connector  1084 . 
     In the embodiment depicted in  FIG. 12A , the connector  1084  has a substantially t-shaped, plus-shaped, or cross-shaped configuration. For example, the connector  1084  may include at least first and second tenons  1086  sized and configured to be received within mortises  1088  in the spacer portions  1072 ,  1074 . For example, a first tenon  1086  projecting laterally from the connector  1084  may be size and configured to be received within a first mortise  1088  in the second end  1072   b  of the first spacer portion  1072  and the second tenon  1086  projecting laterally in the other direction from the connector  1084  may be sized and configured to be received with the second mortise  1088  in the first end  1074   a  of the second spacer portion  1074 . 
     The tenons  1086  may include additional superior and inferior projections, for example, which mate with a substantially t-shaped, plus-shaped, or cross-shaped mortise  1088 . The mortise and tenon configuration may be of any suitable size, shape, and dimension to join the connector  1084  to the respective spacer portions  1072 ,  1074 . As in the other embodiments, the joint may be further secured with one or more pins  1078 . In particular, the pins  1078  may be positioned through each of the tenons  1086  to affix the connector  1084  to the respective spacer portions  1072 ,  1074 . The pins  1078  may be positioned through openings  1080  in the tenons  1086  and corresponding openings  1080  in the spacer portions  1072 ,  1074 . 
     According to a thirteenth embodiment shown in  FIGS. 13A-13G , a single piece or unitary implant  1100  is provided with an anterior portion  1150  and a spacer portion  1112 . Certain features of implant  1100  are similar or comparable to the structure of implant  1 . In this embodiment, the inserts  50  have been replaced with an anterior portion  1150 , and the spacer  1112  and the anterior portion  1150  form a one piece, standalone design. 
     The spacer  1112  has a superior surface  1142 , an inferior surface  1144 , a distal end  1146 , a proximal end  1148 , and first and second lateral sides  1136 ,  1138 . The superior surface  1142  and the inferior surface  1144  each have a contact area  1122  configured to engage adjacent vertebrae. The contact areas  1122  may include one or more protrusions  1113  on the superior and inferior surfaces  1142 ,  1144  of each implant  1100  designed to grip the endplates of the adjacent vertebrae, resist migration, and aid in expulsion resistance. The plurality of protrusions  1113  may be pyramidal in shape and may form a series of ridges and grooves (as shown), but the protrusions  1113  can be configured to be any size or shape to enhance anchoring the spacer  1112  and the implant  1100  to each of the adjacent vertebrae. 
     The spacer  1112  defines an opening  1116  extending from the superior surface  1142  to the inferior surface  1144  of the spacer  1112  configured to receive bone graft materials. The spacer also defines openings  1117  extending through the lateral sides  1136 ,  1138  and into to the opening  1116 . These lateral openings  1117  may be in fluid communication with the central opening  1116 . These openings  1117  may be configured to allow for compression and expansion of the superior and inferior portions of the spacer  1112 . 
     The distal end  1146  of the spacer  1112  may include a leading taper  1140  for ease of insertion into the disc space. The leading taper  1140  may be in the form of a chamfer or a bevel which enables self-distraction of the vertebral bodies during insertion of the implant  1100 . The leading taper  1140  may be located along the insertion direction of the implant  100 . For example, the leading taper  1140  may assist in an anterior approach to the disc space. The distal end  1146  may also include a groove or recess extending between the lateral sides  1136 ,  1138  to facilitate compression and expansion of the implant  1100 . 
     The anterior portion  1150  has an upper surface  1162 , a lower surface  1164 , a first lateral portion  1166 , a second lateral portion  1168 , and at least one hole  1134  traversing the anterior portion  1150  for receiving a fastener, such as a screw  1130 . At least a portion of the upper surface  1162  or the lower surface  1164  of the anterior portion  1150  extends beyond the superior surface  1142  or the inferior surface  1144  of the spacer  1112 . The projections of upper surface  1162  and/or lower surface  1164  may be in the form of an eyebrow  1160 . The eyebrow  1160  may include a rounded portion having a smooth surface. The upper surface  1162  and/or lower surface  1164  may further include one or more torsional stabilizers  1170  configured to prevent or minimize torsional motion of the implant  1100  once implanted. The torsional stabilizer  1170  may include a spiked or pointed projection or extension, for example, positioned medially and/or laterally on the anterior portion  1150 . 
     The anterior portion  1150  extends from the proximal end  1148  of the spacer  1112  such that the anterior portion  1150  and the spacer  1112  are a single piece. As a single, unitary piece the anterior portion  1150  and the spacer  1112  may be formed from a single piece of material, such as titanium. By way of example as shown in  FIGS. 13C and 13D , at least one beam  1188  may connect the anterior portion  1150  to the proximal end  1148  of the spacer  1112  to form a unitary piece. The beam  1118  may extend from a substantially medial position to a lateral position of the spacer  11112 . The beam  1118  may extend across the entire width of the spacer  1112  or a portion thereof. The beam  1118  may be interrupted by a gap, for example, positioned substantially medially. No additional fixation devices or mechanisms are required to attach the anterior portion  1150  to the spacer portion  1112 , but any suitable fixation systems may be selected by one of ordinary skill in the art. 
     The spacer  1112  includes one or more spring features  1190 , for example, to allow for compression and/or expansion of the implant  1100 . Thus, the spacer  1112  has a flexible nature with flexible sections or portions. In particular, the spring features  1190  are designed such that the spacer  1112  is able to mimic the properties of bone and/or PEEK especially when implanted between adjacent vertebrae. For example, the modulus of elasticity for bone, depending on the type, temperature, strain rate, and other factors, may range from about 0.5-25 GPa. In particular, cancellous bone has a modulus of elasticity of about 0.5-5 GPa. The Young&#39;s modulus of PEEK is about 3-4 GPa. Thus, PEEK is often used due to its bone-like modulus of elasticity. A solid block of titanium, on the other hand, has a much higher modulus of about 100-110 GPa. As a replacement to traditional PEEK implants, implant  1100  is provided with spring-like features  1190  such that the implant  1100 , even when formed of titanium, can emulate the modulus of elasticity of cancellous bone. For example, the spacer  1112  may provide for a modulus of elasticity of about 0.5-5 GPa, about 1-5 GPa, about 2-5 GPa, or about 3-4 GPa for the implant  1100 . 
     The spacer  1112  may provide for additional flexibility and an additional range of motion with respect to the two adjacent vertebrae. For example, the spacer  1112  may allow for at least two degrees of motion depending upon the direction and location of the applied force. In particular, the implant  1100  may allow for forward/anterior or aft/posterior bending and lateral bending to the left or right sides. This type of motion and flexibility may allow for more natural movement of the spinal column. 
     The spring features  1190  may be of any suitable design or configuration to provide compression and/or expansion of superior and inferior surfaces  1142 ,  1144  of the spacer  1112 . For example, the spring feature  1190  may be in the form of a cantilevered v-spring having an elongated solid spring member with a cross-sectional configuration in the form of a V. As shown, the distal end  1146  of the spacer  1112  may have a first spring feature  1190 . For example, the first spring feature  1190  may be in the form of a first v-spring. In addition, the proximal end  1148  of the spacer  1112  may include a second spring feature  1190 . The second spring feature  1190  may also be in the form of a second v-spring. The first and second spring features  1190  may be the same or different. The first and second spring features  1190  may be configured such that the spacer  1112  simulates the modulus of elasticity of bone even when the spacer  1112  and the anterior portion  1150  are comprised of titanium or a titanium alloy. 
     As shown in  FIG. 13C , the first spring feature  1190  on the distal end  1136  may include two longitudinal walls  1191   a ,  1191   b  provided with an angle therebetween. The angle between the two longitudinal walls  1191   a ,  1191   b  of the v-spring may range from about 45°-170°, about 60°-150°, about 80°-130°, or about 70°-100°, for example. The distal portions of the two longitudinal walls  1191   a ,  1191   b  may be anchored to the superior and inferior portions of the spacer  1112  by additional v-spring configurations. For example, the first longitudinal wall  1191   a  may interface with the superior portion of the spacer  1112  by a v-spring, which is inverted relative to the v-spring provided between the first and second longitudinal walls  1191   a ,  1191   b . Similarly, the second longitudinal wall  1191   b  may interface with the inferior portion of the spacer  1112  by another v-spring, which is inverted relative to the v-spring provided between the first and second longitudinal walls  1191   a ,  1191   b . Thus, the first spring feature  1190  provided on the distal end  1136  may include a zig-zag of three v-springs oriented in opposite directions. The angle of the v-spring between the first and second longitudinal walls  1191   a ,  1191   b  may be greater than the angles connecting the respectively longitudinal walls  1191   a ,  1191   b  to the superior and inferior portions of the spacer  1112 . 
     The implant  1100  may include a second spring feature  1190  on the proximal end  1148  of the spacer  1112 . The second spring feature  1190  may also include two longitudinal walls  1192   a ,  1192   b  provided with an angle therebetween. The angle between the two longitudinal walls  1192   a ,  1192   b  of the v-spring may again range from about 45°-170°, about 60°-150°, about 80°-130°, or about 70°-100°, for example. This angle may be the same, larger, or smaller than the angle between the first and second longitudinal walls  1191   a ,  1191   b  at the distal end  1136 . The apex of the angle may form a junction to connect with the beam  1188 , which connects the spacer portion  1112  to the anterior portion  1150 . 
     The distal portions of the two longitudinal walls  1192   a ,  1192   b  may be anchored to the superior and inferior portions of the spacer  1112 , respectively by additional v-spring configurations. For example, the first longitudinal wall  1192   a  may interface with the superior portion of the spacer  1112  by a v-spring, which is inverted relative to the v-spring provided between the first and second longitudinal walls  1192   a ,  1192   b . Similarly, the second longitudinal wall  1192   b  may interface with the inferior portion of the spacer  1112  by another v-spring, which is inverted relative to the v-spring provided between the first and second longitudinal walls  1192   a ,  1192   b . Thus, the second spring feature  1190  provided on the proximal end  1148  may include a zig-zag of three v-springs oriented in opposite directions. The angle of the v-spring between the first and second longitudinal walls  1192   a ,  1192   b  may be the same or greater than the angles connecting the respectively longitudinal walls  1192   a ,  1192   b  to the superior and inferior portions of the spacer  1112 . Additional recesses  1194  may be provided on the superior and inferior portions of the spacer  1112  to allow for proper movement of the v-springs. In particular, the recesses  1194  may be formed such that the apexes of the upper and lower v-portions are revealed. As shown in  FIG. 13C , the recesses  1194  may be rounded or curved. In an alternative embodiment shown in  FIG. 13G , the recesses  1194  may be angled or pointed. 
     Although a v-shaped spring is exemplified in this embodiment, the spring portions  1190  may be formed in any suitable shape or configuration not limited to the v-shape, and may include, for example, U-shape, S-shape, coiled, square, rectangular, sinusoidal, corrugated and accordion pleated. In addition, the shape of the spring features  1190  may be symmetrical or non-symmetrical. For example, the longitudinal walls  1191   a ,  1191   b ,  1192   a ,  1192   b  may be symmetrical or non-symmetrical with respect to one another. 
     According to a fourteenth embodiment shown in  FIG. 14 , which may be particularly suitable for an anterior cervical procedure, an implant  1200  including a frame  1250  with one or more endplates  1212  is provided.  FIG. 14  depicts an exploded view of the implant  1200 . The frame  1250  may be substantially in the form of a split-ring or partial loop of material with a central opening. When combined with the endplates  1212 , which may be shaped and configured to match the central opening in the frame  1250 , the opening may provide for a graft opening area configured to provide the maximum amount of volume for bone graft packing. The graft area may be configured for receiving bone graft material, for example, to promote fusion of the adjacent vertebral bodies. 
     The frame  1250  may include a front portion  1265 . The front portion  1265  may define one or more fastener apertures  1234  configured to secure fasteners, such as bone screws (not shown), in both the superior and inferior vertebrae. The front portion  1265  may be a unitary piece or may be divided into two separate portions with a passage or gap  1224  positioned therebetween. The front portion  1265  may include an upper surface  1262  and a lower surface  1264 . A first arm  1254  may extend from a first end of the front portion  1265  and a second arm  1254  may extend from a second end of the front portion  1265  of the frame  1250 . The arms  1254  may join together to form the full or partial ring-like structure. The frame  1250  may also include a rear portion  1255 . The arms  1254  may meet at the rear portion  1255  of the frame  1250 , for example. The front portion  1265  may have a height greater than the height of the arms  1250  and the rear portion  1255 . 
     One or more endplates  1212  are positioned on and affixed to the frame  1250  such that at least a portion of the ring portion of the frame  1250  is covered or housed within the endplates  1212 . Preferably, the front portion  1265  of the frame  1250  is not covered by the endplates  1212 . The endplates  1212  may form a superior surface  1242  and an inferior surface  1244  configured to contact and engage adjacent vertebrae (not shown). The superior and inferior surfaces  1242 ,  1244  may be parallel, curved, or angled to help restore or recreate a lordosis angle (or other angle) of the human spine. In addition, the superior and/or inferior surfaces  1242 ,  1244  may be contoured to conform more closely to the concave endplates of the adjacent vertebra. 
     In order to engage the adjacent vertebrae, the endplates  1212  may include a plurality of protrusions  1213  or teeth on the contact areas of the superior and/or inferior surfaces  1242 ,  1244 . The protrusions  1213  may help to grip the endplates of the adjacent vertebrae, resist migration, and aid in expulsion resistance. The plurality of protrusions  1213  may be pyramidal in shape, but the protrusions  1213  can be configured to be any size or shape to enhance anchoring of the implant  1200  to each of the adjacent vertebrae. 
     As shown in  FIG. 14 , two endplates  1212  may be provided. A first endplate  1212  may have a substantially c-shaped configuration designed to follow the shape of the rear portion  1255  of the frame  1350 . The endplate  1212  may include a recess or channel  1223  designed and configured to retain at least a portion of the ring and, in particular, at least the rear portion  1255  and a portion of the arms  1254  of the frame  1250 . This endplate  1212  may also include a leading taper configured to ease insertion of the implant  1200  into the disc space. 
     A second endplate  1212  may be provided to at least partially reside within the passage or gap  1224  in the front portion  1265  of the frame  1250 . In particular, this endplate  1212  may include a central portion  1235  sized and configured to fit within the gap  1224 . The central portion  1235  may form a portion of the superior surface  1242  (e.g., having protrusions  1213  extending superiorly) and a portion of the inferior surface  1244  (e.g., having protrusions  1213  extending inferiorly). In addition, the central portion  1235  may include an opening sized and configured to receive an insert  1252  which accepts an anti-backout locking mechanism  1220 . The locking mechanism  1220  may be provided to block or unblock the heads of the fasteners or screws when positioned within the respective fastener apertures  1234 . The anti-back out mechanism  1220  may include, for example, a set screw configured to block a portion of the fasteners positioned through the frame  1250 . 
     In addition to the central portion  1235 , the endplate  1212  may also include a first lateral wing  1236  and a second lateral wing  1238 . The first lateral wing  1236  may be configured to contact a first side of one of the arms  1254  and the second lateral wing  1238  may be configured to contact a second side of the other arm  1254 . In this manner, the endplate  1212  may be positioned such that the first lateral wing  1236  forms a portion of the superior surface  1242  (e.g., having protrusions  1213  extending superiorly) and the second lateral wing  1238  forms a portion of the inferior surface  1244  (e.g., having protrusions  1213  extending inferiorly). It is envisioned that the positions of the wings  1236 ,  1238  may be changed or reversed as one of ordinary skill in the art may recognize. 
     One or more of the endplates  1212  may be secured to the frame  1250  using any of the mechanisms or techniques described herein. In particular, one or more of the endplates  1212  may be secured with one or more pins  1278 . Any suitable number, type, and location for the pins  1278  may be selected. For example, two pins  1278  may be positioned within openings located adjacent to and on opposite sides of the front portion  1265  of the frame  1250 . 
     In this embodiment, the frame  1250  provides two fastener apertures  1234  to secure fasteners, such as bone screws, in both the superior and inferior vertebrae. For example, the fastener apertures  1234  may extend through the front portion  1265  of the frame  1250  at an angle. A portion of the upper and/or lower surfaces  1262 ,  1264  of the frame  1250  may extend a distance beyond the superior surface  1242 , the inferior surface  1244 , or both surfaces  1242 ,  1244  of the endplates  1212 . The projections of the upper and lower surfaces  1262 ,  1264  of the frame  1250  may be in the form of eyebrows  1260 . In this embodiment, the eyebrows  1260  include a substantially smooth and curved surface. One or more torsional stabilizers  1270  may also be provided and configured to prevent or minimize torsional motion of the implant  1200  once implanted. The torsional stabilizers  1270  may include a spiked or pointed projection or extension configured to engage adjacent vertebrae. 
     According to a fifteenth embodiment shown in  FIGS. 15A and 15B , which may be particularly suitable for an anterior lumbar procedure, implants  1300   a ,  1300   b  include a frame  1350   a ,  1350   b  with one or more endplates  1312   a ,  1312   b .  FIGS. 15A and 15B  depict exploded views of the implants  1300   a ,  1300   b . The frames  1350   a ,  1350   b  may be substantially in the form of a ring or loop of material with a central opening divided into two equal halves. The endplates  1312   a ,  1312   b , for example, in the form of PEEK or allograft spacers, may be sized and configured to fit within the openings. 
     The frames  1350   a ,  1350   b  may each include a front portion  1365   a ,  1365   b , which defines one or more fastener apertures  1334   a ,  1334   b  configured to secure fasteners, such as bone screws (not shown), in both the superior and inferior vertebrae. The front portion  1365   a ,  1365   b  may extend from a first lateral end to a second lateral end of the frame  1350   a ,  1350   b . A first arm  1354   a ,  1354   b  may extend from a first end of the front portion  1365   a ,  1365   b  and a second arm  1354   a ,  1354   b  may extend from a second end of the front portion  1365   a ,  1365   b  of the frame  1350   a ,  1350   b . The arms  1354   a ,  1354   b  may join together to form the ring-like structure of the frame  1350   a ,  1350   b . The frame  1350   a ,  1350   b  may include a rear portion  1355   a ,  1355   b  where the arms  1354   a ,  1354   b  connect together. 
     In this embodiment, the frame  1350   a ,  1350   b  provides three fastener apertures  1334   a ,  1334   b  to secure fasteners, such as bone screws, in both the superior and inferior vertebrae. For example, the fastener apertures  1334   a ,  1334   b  may extend through the front portion  1365   a ,  1365   b  of the frame  1350   a ,  1350   b  at an angle. As described herein, once inserted through the fastener apertures  1334   a ,  1334   b , the fasteners may be secured with an anti-back out prevention or locking mechanism  1320   a ,  1320   b , such as by using one or more blocking screw to capture a portion of the fasteners to prevent back out. 
     The frame  1350   a ,  1350   b  may also include a support member  1356   a ,  1356   b . The support member  1356   a ,  1356   b  may divide or segment the central opening and provide stability to the frame  1350   a ,  1350   b . As shown, the support member  1356   a ,  1356   b  may be a medial portion of the implant  1300   a ,  1300   b , which is positioned centrally to divide the central opening into two equal halves. It is envisioned, however, that the support member  1356   a ,  1356   b  may be absent creating a single large opening, the support member  1356   a ,  1356   b  may be offset such that the two openings are not equal in size, or more than one support member  1356   a ,  1356   b  may be provided to create multiple openings for the endplates  1312   a ,  1312   b  to reside. The support member  1356   a ,  1356   b  may also have at least one opening  1358   a ,  1358   b  extending therethrough to retain a corresponding protrusion  1314   a ,  1314   b  on the endplates  1312   a ,  1312   b . The opening  1358   a ,  1358   b  in the support member  1356   a ,  1356   b  may be elongated with a curved or beveled perimeter designed to provide an interference fit when the endplate  1312   a ,  1312   b  is snapped into the openings of the frame  1350   a ,  1350   b . Although a single opening  1358   a ,  1358   b  in the support member  1356   a ,  1356   b  is shown, additional openings may also be provided to secure the endplates  1312   a ,  1312   b . In addition or alternatively, similar openings may be provided in the arms  1354   a ,  1354   b  of the frame  1350   a ,  1350   b  to secure the endplates  1312   a ,  1312   b . The front portion  1365   a ,  1365   b  may have a height greater than the height of the arms  1354   a ,  1354   b  and/or the rear portion  1355   a ,  1355   b . In addition, the support member  1356   a ,  1356   b  may have a height greater than the height of the arms  1354   a ,  1354   b.    
     One or more endplates  1312   a ,  1312   b  are positioned on and affixed to the frame  1350   a ,  1350   b  such that at least a portion of the endplates  1312   a ,  1312   b  is received within the openings in the frame  1350   a ,  1350   b . The endplates  1312   a ,  1312   b  may be inserted from the top or the bottom of the implant  1300   a ,  1330   b . The endplates  1312   a ,  1312   b  may include upper and lower surfaces configured to contact and engage adjacent vertebrae (not shown). The upper and lower surfaces may be parallel, curved, or angled to help restore or recreate a lordosis angle (or other angle) of the human spine. In addition, the upper and/or lower surfaces may be contoured to conform more closely to the concave endplates of the adjacent vertebra. 
     The endplates  1312   a ,  1312   b  may be L-shaped with a stepped configuration, for example, or may include a raised portion sized and configured to fit within the central opening of the frame  1350   a ,  1350   b . For example, the raised portion may form a portion of the upper and/or lower surfaces. This configuration may allow for the endplates  1312   a ,  1312   b  to bottom out on the frame  1350   a ,  1350   b  preventing excessive force from pushing the endplates  1312   a ,  1312   b  out the other end of the implant  1300   a ,  1300   b  upon insertion. The endplates  1312   a ,  1312   b  may include a plurality of protrusions  1313   a ,  1313   b  or teeth on the contact areas of the upper and/or lower surfaces to engage the adjacent vertebrae. The protrusions  1313   a ,  1313   b  may help to grip the endplates of the adjacent vertebrae, resist migration, and aid in expulsion resistance. The plurality of protrusions  1313   a ,  1313   b  may be pyramidal in shape and may form a series of ridges and grooves (as shown), but the protrusions  1313   a ,  1313   b  can be configured to be any size or shape to enhance anchoring the implant  1300   a ,  1300   b  to each of the adjacent vertebrae. 
     As shown in  FIGS. 15A and 15B , two endplates  1312   a ,  1312   b  may be provided for each implant  1300   a ,  1300   b . The endplates  1312   a ,  1312   b  for each respective implant  1300   a ,  1300   b  may be mirror images of one another. The endplates  1312   a ,  1312   b  may include a lateral surface having at least one protrusion  1314   a ,  1314   b  extending outwardly therefrom. The edges of the protrusion  1314   a ,  1314   b  may be chamfered or beveled such that the protrusion  1314   a ,  1314   b  provides an interference fit with the opening  1358   a ,  1358   b  in the support member  1356   a ,  1356   b . Although depicted with the protrusions  1314   a ,  1314   b , the endplates  1312   a ,  1312   b  may be secured to the frame  1350   a ,  1350   b  using any of the mechanisms or techniques described herein. 
     A sixteenth embodiment is shown in  FIGS. 16A and 16B , which depict exploded views of implants  1400   a ,  1400   b . This embodiment is substantially the same as the implants  1300   a ,  1300   b  discussed above, and the discussion for implants  1300   a ,  1300   b  applies equally here. In this particular embodiment, implants  1400   a ,  1400   b  include a frame  1450   a ,  1450   b  with one or more endplates  1412   a ,  1412   b . Instead of forming a ring or loop, the frame  1450   a ,  1450   b  includes extensions or arms  1454   a ,  1454   b  and support member  1456   a ,  1456   b  to secure the endplates  1412   a ,  1412   b . The endplates  1412   a ,  1412   b  may be in the form of PEEK or allograft spacers, for example, sized and configured to fit within the openings or channels defined between the arms  1454   a ,  1454   b  and support member  1456   a ,  1456   b.    
     The front portion  1465   a ,  1465   b  of the frame  1450   a ,  1450   b  defines one or more fastener apertures  1434   a ,  1434   b  configured to secure fasteners, such as bone screws (not shown), in both the superior and inferior vertebrae. In this embodiment, the frame  1450   a ,  1450   b  provides three fastener apertures  1434   a ,  1434   b  extending through the front portion  1465   a ,  1465   b  of the frame  1450   a ,  1450   b  at an angle to secure fasteners, such as bone screws, in both the superior and inferior vertebrae. As described herein, once inserted through the fastener apertures  1434   a ,  1434   b , the fasteners may be secured with an anti-back out prevention or locking mechanism  1420   a ,  1420   b , such as by using one or more blocking screw to capture a portion of the fasteners to prevent back out. 
     The frame  1450   a ,  1450   b  may include a first arm  1454   a ,  1454   b  extending from a first end of the front portion  1465   a ,  1465   b  and a second arm  1454   a ,  1454   b  extending from a second end of the front portion  1465   a ,  1465   b . A support member  1456   a ,  1456   b  may be positioned between the arms  1454   a ,  1454   b . As shown, the support member  1456   a ,  1456   b  may be positioned at a medial portion of the implant  1400   a ,  1400   b , and may be positioned centrally between the arms  1454   a ,  1454   b . It is envisioned, however, that the support member  1456   a ,  1456   b  may be absent creating a single large opening, the support member  1456   a ,  1456   b  may be offset creating unequally sized openings, or more than one support member  1456   a ,  1456   b  may be provided to create multiple locations for the endplates  1412   a ,  1412   b  to reside. 
     The support member  1456   a ,  1456   b  may also have at least one opening  1458   a ,  1458   b  extending therethrough to retain a corresponding protrusion  1414   b  (protrusion not visible in  FIG. 16A ) on the endplates  1412   a ,  1412   b . The opening  1458   a ,  1458   b  in the support member  1456   a ,  1456   b  may be elongated with a curved or beveled perimeter designed to provide an interference fit when the endplate  1412   a ,  1412   b  is snapped into openings or channels between the arms  1454   a ,  1454   b  and support member  1456   a ,  1456   b . Although a single opening  1458   a ,  1458   b  in the support member  1456   a ,  1456   b  is shown, additional openings may also be provided to secure the endplates  1412   a ,  1412   b . In addition or alternatively, similar openings may be provided in the arms  1454   a ,  1454   b  of the frame  1450   a ,  1450   b  to secure the endplates  1412   a ,  1412   b.    
     One or more endplates  1412   a ,  1412   b  are configured to be positioned on and/or affixed within openings or channels between the arms  1454   a ,  1454   b  and support member  1456   a ,  1456   b . The endplates  1412   a ,  1412   b  may be inserted from the top, bottom, or back of the implant  1400   a ,  1400   b . The endplates  1412   a ,  1412   b  may include upper and lower surfaces configured to contact and engage adjacent vertebrae (not shown). The upper and lower surfaces may be parallel, curved, or angled to help restore or recreate a lordosis angle (or other angle) of the human spine. In addition, the upper and/or lower surfaces may be contoured to conform more closely to the concave endplates of the adjacent vertebra. 
     The endplates  1412   a ,  1412   b  may be notched or provided with a stepped configuration or may include a raised portion sized and configured to fit between the arms  1454   a ,  1454   b  and support member  1456   a ,  1456   b . This configuration may allow for the endplates  1412   a ,  1412   b  to bottom out on the frame  1450   a ,  1450   b  preventing excessive force from pushing the endplates  1412   a ,  1412   b  out the other end upon insertion. The endplates  1412   a ,  1412   b  may include protrusions  1413   a ,  1413   b  or teeth on the contact areas of the implant  1400   a ,  1400   b  as discussed herein. 
     As shown in  FIGS. 16A and 16B , two endplates  1412   a ,  1412   b  may be provided for each implant  1400   a ,  1400   b . The endplates  1412   a ,  1412   b  for each respective implant  1400   a ,  1400   b  may be mirror images of one another. The endplates  1412   b  may include a lateral surface having at least one protrusion  1414   b  extending outwardly therefrom. Similar protrusions are provided on endplates  1412   a  in  FIG. 16A , which are not visible in the view provided. The edges of the protrusion  1414   b  may be chamfered or beveled to provide an interference fit with the opening  1458   b  in the support member  1456   b . Although shown to be secured with the protrusions  1414   b , the endplates  1412   a ,  1412   b  may be additionally or alternatively secured to the frame  1450   a ,  1450   b  using any of the mechanisms or techniques described herein. 
     As shown in  FIGS. 17A and 17B , a seventeenth embodiment includes exploded views of implants  1500   a ,  1500   b . This embodiment is substantially the same as the implants  1400   a ,  1400   b  discussed above, and the discussion for implants  1400   a ,  1400   b  applies equally here. Implants  1500   a ,  1500   b  include a frame  1550   a ,  1550   b  with one or more endplates  1512   a ,  1512   b  configured to be positioned between the extensions or arms  1554   a ,  1554   b  and support member  1556   a ,  1556   b  to secure the endplates  1512   a ,  1512   b . This embodiment includes protrusions  1514   a ,  1514   b  on the medial portion of the endplate  1512   a ,  1512   b  as well as indentations  1516   a ,  1516   b  on the lateral portion of the endplate  1512 ,  1512   b  to provide an interference fit with the frame  1550   a ,  1550   b . The endplates  1512   a ,  1512   b  may be in the form of PEEK or allograft spacers, for example, sized and configured to fit within the openings or channels between the arms  1554   a ,  1554   b  and support member  1556   a ,  1556   b.    
     The frame  1550   a ,  1550   b  may include a first arm  1554   a ,  1554   b  extending from a first end of the front portion  1565   a ,  1565   b  and a second arm  1554   a ,  1554   b  extending from a second end of the front portion  1565   a ,  1565   b . The support member  1556   a ,  1556   b  may be positioned between the arms  1554   a ,  1554   b , for example, at a central location between the arms  1554   a ,  1554   b . The support member  1556   a ,  1556   b  may have at least one opening  1558   a ,  1558   b  extending therethrough to retain a corresponding protrusion  1514   a ,  1514   b  on the medial portion of the endplates  1512   a ,  1512   b . The opening  1558   a ,  1558   b  in the support member  1556   a ,  1556   b  may be elongated with a curved or beveled perimeter designed to provide an interference fit when the endplate  1512   a ,  1512   b  is snapped into openings or channels between the arms  1554   a ,  1554   b  and support member  1556   a ,  1556   b . The lateral portion of the endplates  1512   a ,  1512   b  may include at least one indentation  1516   a ,  1516   b  therein to retain a corresponding protrusion  1518   a ,  1518   b  on an interior surface of the arms  1554   a ,  1554   b . The indentation  1516   a ,  1516   b  in the endplates  1512   a ,  1512   b  may be substantially square with a curved or beveled perimeter designed to provide an interference fit when the endplate  1512   a ,  1512   b  is snapped into openings or channels between the arms  1554   a ,  1554   b  and support member  1556   a ,  1556   b . The protrusions  1514   a ,  1514   b  on the endplates  1512   a ,  1512   b  may be larger in size and shape than the protrusions  1518   a    1518   b  on the arms  1554   a ,  1554   b , for example. Although it is envisioned that any size, shape, dimension, and position for the protrusions  1514   a ,  1514   b ,  1518   a ,  1518   b  may be selected by one of ordinary skill in the art. 
     The endplates  1512   a ,  1512   b  may be notched and contoured to fit between the arms  1554   a ,  1554   b  and support member  1556   a ,  1556   b . As shown in  FIGS. 17A and 17B , two endplates  1512   a ,  1512   b  may be provided for each implant  1500   a ,  1500   b . The endplates  1512   a ,  1512   b  for each respective implant  1500   a ,  1500   b  may be mirror images of one another. The endplates  1512   a ,  1512   b  may be inserted from the top, bottom, or back of the implant  1500   a ,  1500   b . The endplates  1512   a ,  1512   b  may include upper and lower surfaces configured to contact and engage adjacent vertebrae (not shown). The upper and lower surfaces may be parallel, curved, angled, contoured, or the like to conform more closely with the endplates of the adjacent vertebra. 
       FIGS. 18A and 18B  illustrate stand-alone intervertebral implants  1600   a ,  1600   b , which may be suitable for an anterior lumbar procedure. The implants  1600   a ,  1600   b  include a spacer or frame  1650   a ,  1650   b  and one or more endplates  1612   a ,  1612   b . The endplates  1612   a ,  1612   b  may be in the form of PEEK or allograft spacers, for example, sized and configured to fit within the openings in the frame  1650   a ,  1650   b.    
     The frame  1650   a ,  1650   b  includes upper and lower surfaces each having contact areas (e.g., a plurality of protrusions  1613   a ,  1613   b ) configured to contact and engage adjacent vertebrae (not shown). The frame  1650   a ,  1650   b  may contain one or more openings which extend from the upper surface to the lower surface. The openings may be in the form of oval holes, for example. As shown, three openings may be provided: two posterior openings and one anterior opening. The openings may be configured for receiving bone graft material, for example, to promote fusion of the adjacent vertebral bodies. 
     In one embodiment, the openings may be configured to receive corresponding endplates  1612   a ,  1612   b . The endplates  1612   a ,  1612   b  may be inserted from the top or the bottom of the implant  1600   a ,  1600   b . The endplates  1612   a ,  1612   b  may be retained in the openings by a ridge  1614   a ,  1614   b  and corresponding slot or groove  1616   a ,  1616   b  located on a mid-transverse plane on the implants  1600   a ,  1600   b . The ridge  1614   a ,  1614   b  may project around a perimeter of each endplate  1612   a ,  1612   b . The ridge  1614   a ,  1614   b  may be centrally located between the upper and lower surface of the implant  1600   a ,  1600   b , but is also envisioned that additional ridges may be provided or the ridge may be offset from the center line. 
     The endplate  1612   a ,  1612   b  upon insertion has an interference fit and then snaps into the corresponding groove  1616   a ,  1616   b  on the frame  1650   a ,  1650   b . The endplates  1612   a ,  1612  may be in the shape of ovals although any suitable shape is envisioned. The posterior ovals are substantially the same and are interchangeable. The anterior oval has a distinct feature on its bottom; namely, a slot for the fastener, to distinguish it from the posterior ovals. The endplates  1612   a ,  1612   b  may also include protrusions on the upper and/or lower surfaces which match and align with the protrusions  1613   a ,  1613   b  on the frame  1650   a ,  1650   b.    
     The inserts, members, frames, spacers, and endplates described in this document may be comprised of any suitable materials. The spacers or endplates can be comprised of any material that is conducive to the enhancement of fusion between the two adjacent vertebrae. In one particular embodiment, the spacer or endplate is made of a biocompatible plastic, like polyether ether ketone (PEEK), polyetherketoneketone (PEKK), ultra-high molecular weight (UHMW) polyethylene, or other polymers and plastics known in the art which are physiologically compatible. Any other materials that are physiologically compatible may also be used such as bone or metal. The inserts, members, or frames can also be comprised of any physiologically compatible materials. In the preferred embodiment, the inserts, members, or frames are composed of a biocompatible metal, such as stainless steel, titanium, titanium alloys, surgical steel, and metal alloys, for example. Preferably, the inserts, members, or frames are formed from titanium or a titanium alloy. Any other materials that are physiologically compatible may also be used such as bone or plastic. 
     Although the invention has been described in detail and with reference to specific embodiments, it will be apparent to one skilled in the art that various changes and modifications can be made without departing from the spirit and scope of the invention. Thus, it is intended that the invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents. It is expressly intended, for example, that all ranges broadly recited in this document include within their scope all narrower ranges which fall within the broader ranges. It is also intended that the components of the various devices disclosed above may be combined or modified in any suitable configuration.