Patent Publication Number: US-2011077741-A1

Title: Vertebral Fusion Implants and Methods of Use

Description:
RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 11/403,348, filed on Apr. 13, 2006, and incorporated in its entirety herein by reference. 
    
    
     BACKGROUND 
     Vertebral implants are often used in the surgical treatment of spinal disorders such as degenerative disc disease, disc herniations, curvature abnormalities, and trauma. Many different types of treatments are used. In some cases, spinal fusion is indicated to inhibit relative motion between vertebral bodies. Motion between vertebral bodies is naturally provided in part by the flexible disc material that resides between adjacent vertebral bodies. Spinal fusion often involves the removal of the vertebral disc and insertion of an interbody implant to create a fused junction between a pair of vertebral bodies. Fusion may also occur at multiple vertebral levels or between vertebral bodies that are several levels apart. Interbody implants may be coated, filled, or surrounded by growth promoting materials such as BMP, DBM, allograft, autograft or other osteoinductive growth factors to facilitate fusion between the vertebral bodies and the implant. 
     Conventionally, interbody implants are inserted into the space between vertebral bodies after the disc material has been removed and after the vertebral end plates are prepared. This end plate preparation may include shaping, planing, scraping, or other decorticating processes in which bone matter is removed and blood flow is initiated to enhance bone growth into the interbody implant. Ideally, new bone matter forms and bridges the gap between the vertebral bodies and the growth promoting material. In certain instances, particularly where the growth promoting material is contained within the interbody implant, new bone matter does not sufficiently span the gap between the vertebral endplate and the growth promoting material. Consequently, the fusion site may be compromised. 
     SUMMARY 
     Illustrative embodiments disclosed herein are directed to a vertebral implant for use in vertebral fusion surgeries. The vertebral implant includes a body with an exterior surface and an interior surface. The body may be shaped for use in ALIF, PLIF, and TLIF surgeries. 
     The implant may include a hollow body with an enclosed interior cavity. The body may include a first side configured to contact against the first vertebral member and a second side configured to contact against the second vertebral member after the implant has been inserted into the patient. A plurality of apertures and cutting features may be positioned about the first and second sides. Each of the apertures may extend through one of the first and second sides. Each of the cutting features may extend outward from the body at one of the plurality of apertures. Each of the cutting features may include a tapered shape that terminates at a pointed tip that cuts into one of the first and second vertebral members. The enclosed interior cavity may be configured to capture and maintain portions of the first and second vertebral members that are cut by the cutting features and enter the enclosed interior cavity through the plurality of apertures. 
     The implant may include a hollow body with an enclosed interior cavity. The body may include a first section configured to contact against the first vertebral member and a second section configured to contact against the second vertebral member after the implant has been inserted into the patient. A plurality of apertures and cutting features may be positioned about the first section. Each of the apertures may extend through the first section and into the interior cavity. Each of the cutting features may extend outward from the first section at one of the plurality of apertures. A first one of the cutting features may include a first leading surface facing a first direction and a second one of the cutting features may include a second leading surface facing a different second direction. The enclosed interior cavity may be configured to capture and maintain portions of the first and second vertebral members that are cut by the cutting features and enter the enclosed interior cavity through the plurality of apertures. 
     The implant may include a hollow body with an enclosed interior cavity. The body may include a first side configured to contact against the first vertebral member and a second side configured to contact against the second vertebral member after the implant has been inserted into the patient. The first side may include an inner surface that faces into the interior cavity and an opposing outer surface. A plurality of paired cutting features may be positioned about the first side. Each of the paired cutting features may include an aperture that extends through the first side and into the interior cavity and a tooth at the aperture that extends outward from the outer surface. The body may have different thickness over the first side with the inner surface of the first side having a different geometry than the outer surface of the first side. The enclosed interior cavity may be configured to capture and maintain portions of the first vertebral member that are cut by the plurality of paired cutting features and enter the enclosed interior cavity through the plurality of apertures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a vertebral implant according to one embodiment; 
         FIG. 2  is a side section view, including a partial detail, of a vertebral implant according to one embodiment; 
         FIG. 3  is a side section view of a vertebral implant according to one embodiment shown relative to vertebral bodies; 
         FIG. 4  is a side section view of a vertebral implant according to one embodiment shown relative to vertebral bodies; 
         FIG. 5  is a side section view of a vertebral implant according to one embodiment shown relative to vertebral bodies; 
         FIG. 6  is a front view of a vertebral implant according to one embodiment; 
         FIG. 7  is a side view of a vertebral implant according to one embodiment; 
         FIG. 8  is a side view of a vertebral implant according to one embodiment shown relative to vertebral bodies; 
         FIG. 9  is a side view of a vertebral implant according to one embodiment shown relative to vertebral bodies; 
         FIG. 10  is a top view of a vertebral implant according to one embodiment shown relative to a vertebral body; 
         FIG. 11  is a perspective view of a vertebral implant according to one embodiment; 
         FIG. 12  is a front view of a vertebral implant according to one embodiment; 
         FIG. 13  is a top view of a vertebral implant according to one embodiment; 
         FIG. 14  is a side view of a vertebral implant according to one embodiment; 
         FIG. 15  is a side view of a vertebral implant according to one embodiment; 
         FIG. 16  is a side view of a vertebral implant according to one embodiment; 
         FIG. 17  is a partial section view of a vertebral implant illustrating a profile of a cutting feature according to one embodiment; 
         FIG. 18  is a partial section view of a vertebral implant illustrating a profile of a cutting feature according to one embodiment; 
         FIG. 19  is a partial section view of a vertebral implant illustrating a profile of a cutting feature according to one embodiment; 
         FIG. 20  is a partial section view of a vertebral implant illustrating a profile of a cutting feature according to one embodiment; 
         FIG. 21  is a top view of a vertebral implant according to one embodiment; and 
         FIG. 22  is a side section view of a vertebral implant according to one embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     The various embodiments disclosed herein relate to a vertebral implant in which bone-contact surfaces are constructed with cutting features that remove bone matter from vertebral bodies in the human spine. Further, the cutting features are configured to guide the removed bone matter through apertures in the vertebral implant and into contact with bone-growth-promoting material contained therein. Reference number  10  in  FIG. 1  generally identifies one example of an implant with cutting features on the bone-contact surfaces. The representative vertebral implant  10  is illustrated as a disc replacement implant that is inserted between vertebral bodies of a patient as part of a disc replacement surgery. The exemplary vertebral implant  10  includes a perimeter wall  12  that extends between a superior surface  14  and an inferior surface  16 . The superior surface  14  and inferior surface  16  are bone-contact surfaces in that they are positioned adjacent to and face a vertebral endplate once the vertebral implant  10  is inserted into a patient. 
     The vertebral implant  10  shown in  FIG. 1  includes a simple disc shape, though other shapes and contours may be used. In further embodiments, the vertebral implant  10  may take on other types of configurations, such as, for example, a circular shape, kidney shape, semi-oval shape, bean-shape, D-shape, elliptical-shape, egg-shape, or any other shape that would occur to one of skill in the art. The vertebral implant  10  may take on substantially solid configurations, such as, for example, block-like or plate-like configurations that do not define an open inner region. In other embodiments, the vertebral implant  10  could also be described as being annular, U-shaped, C-shaped, V-shaped, horseshoe-shaped, semi-circular shaped, semi-oval shaped, or other similar terms defining an implant including at least a partially open or hollow construction. 
     The vertebral implant  10  may be constructed from biocompatible metal alloys such as titanium, cobalt-chrome, and stainless steel. The vertebral implant  10  may be constructed from non-metallic materials, including for example, ceramics, resins, or polymers, such as UHMWPE and implantable grade polyetheretherketone (PEEK) or other similar materials (e.g., PAEK, PEKK, and PEK). The vertebral implant  10  may be constructed of synthetic or natural bone or bone composites. Those skilled in the art will comprehend a variety of other material choices that are suitable for the illustrated vertebral implant  10 . 
     The exemplary vertebral implant  10  includes a plurality of apertures  18  disposed about the superior surface  14 . The apertures  18  are shown as substantially cylindrical, though it should be understood that other shapes, including for example, square, hex, triangular, diamond, crescent, elliptical apertures may be used. Additional apertures  18  are also disposed about the inferior surface  16 , though their existence is not immediately apparent from  FIG. 1 . In an alternative embodiment, the apertures  18  are disposed about one of the superior  14  and inferior  16  surfaces but not the other. The vertebral implant  10  also includes one or more side apertures  26  disposed about the perimeter wall  12 . The side apertures  26  provide a passage from the exterior of the vertebral implant into an interior cavity  30  that is more clearly visible in  FIG. 2  and discussed in greater detail below. The side apertures  26  may also provide a location at which to grasp the vertebral implant  10  during surgical installation. 
     In the illustrated embodiment, a cutting feature  20  is associated with each aperture  18 . In other embodiments, the vertebral implant  10  may have apertures without associated cutting features  20  or cutting features  20  without associated apertures  18 . The cutting features  20  may be implemented as teeth, hooks, serrations, blades, or other features adapted to remove cortical bone from a vertebral body as the vertebral implant  10  is inserted. The cutting features  20  may be constructed of the same material as the remainder of the vertebral implant  10  as described above. In one embodiment, the cutting features  20  are constructed of rigid, hardened materials such as titanium, ceramic, or polymers impregnated with carbon fibers. In the embodiment illustrated in  FIG. 1 , the cutting features  20  are oriented in a common direction so as to define a cutting direction C. As described below, this cutting direction C may coincide with the insertion direction. Accordingly, the vertebral implant  10  may include an insertion feature  36  to which an insertion tool (see  FIG. 4 ) may be attached. The insertion feature  36  may be an aperture, such as a threaded hole or a slot that is engageable by a male insertion tool. Alternatively, the insertion features  36  may be a protruding feature that is engageable by a female insertion tool. 
     The lateral cross section view of the vertebral implant  10  provided in  FIG. 2  shows the aforementioned interior cavity  30 . This cavity  30  is defined in part by an interior surface  28 . In the embodiment shown, the interior surface  28  follows a contour similar to the outer surfaces  12 ,  14 ,  16  of the vertebral implant such that the thickness T of wall  34  is approximately the same throughout. In other embodiments, the interior cavity  30  may include a different shape than the outer geometry of the vertebral implant  10 . In either case, the interior cavity  30  is configured to receive bone growth promoting material such as BMP, DBM, allograft, autograft or other osteoinductive growth factors to facilitate fusion between vertebral bodies and the implant  10 . The apertures  18  disposed about the superior surface  14  and inferior surface  16  provide a passage through which blood and removed bone material may pass from outside the vertebral implant  10  to the interior cavity  30  where the bone growth promoting material is placed. This removed bone material may be scoured by the cutting features  20  and diverted through the apertures  18  into the interior cavity  30  as denoted by the arrows labeled B. 
     The right side of  FIG. 2  also depicts a detail view of the exemplary cutting features  20 . The cutting features  20  extend generally outward from the superior surface  14  and inferior surface  16 . Relative to the cutting direction C, the cutting features  20  include a leading surface  24  and a trailing surface  32 . The leading surface  24  and trailing surface  32  curve generally towards the cutting direction C. This curvature improves the overall strength and cutting ability of the cutting features  20 . Further, the leading surface  24  and the trailing surface converge at a cutting edge  22  that is advantageously sharpened to allow the cutting feature  20  to remove bone material from vertebral bodies during implant  10  insertion. Notably, the cutting feature  20  is raked in the cutting direction such that the cutting edge  22  is disposed at least partly above the aperture  18  with which the cutting feature  20  is associated. 
     In the depicted embodiment, the leading surface  24  of the cutting feature  20  extends generally upward from the aperture  18  in the walls  34  of the vertebral implant  10 . In this configuration, the leading surface  24  and aperture  18  share a common wall. Thus, the cutting feature  20  curves at least partly around the aperture. In other embodiments, the aperture  18  may have straight sides and the leading surface  24  may share one or more sides of the aperture  18 . Further, the leading surface  24  is generally concave, bent, or curved in the direction of the aperture  18 . Consequently, through motion of the vertebral implant  10  in the cutting direction C, the leading surface  24  tends to divert removed bone matter through the aperture  18 , past the interior surface  28  and into the interior cavity  30 .  FIGS. 3 ,  4 , and  5  illustrate this sequence, which occurs as the vertebral implant  10  is inserted into a patient. 
     Specifically,  FIG. 3  shows two vertebrae  102 ,  104  and a disc  116  therebetween. Each vertebra  102 ,  104  includes a generally cylindrical body  106 ,  108  that contributes to the primary weight-bearing portion of the spine  100 . Further, each vertebra  102 ,  104  includes various bony processes  110 ,  112  extending posterior to the body  106 ,  108 . Adjacent vertebrae  102 ,  104  may move relative to each other via facet joints  114  and due to the flexibility of the disc  116 . For instances where the disc  116  is herniated or degenerative, the entire disc  116  may be replaced with the vertebral implant  10  using an anterior approach as shown. 
     Initially, the disc  116  is removed from the space between the vertebrae  102 ,  104 . Also, the vertebral implant  10  is packed with a bone growth promoting material such as those described above. The bone growth promoting material is identified by numeral  40  in  FIG. 4 .  FIG. 4  also shows an insertion tool  42  attached to the vertebral implant  10 . Using the insertion tool  42 , the vertebral implant  10  is guided towards and between the vertebral bodies  106 ,  108 . An insertion force is applied in the direction of the arrow labeled N. This insertion force causes the cutting features  20  to engage and remove bone matter from the vertebral bodies  106 ,  108 . This bone matter is identified by number  44  in  FIG. 4 . The shape and configuration of the cutting feature  20 , and specifically leading surface  24 , tend to guide the removed bone matter  44  from the exterior of the vertebral implant  10 , through the apertures  18 , into the interior cavity  30 , and into contact with the bone growth promoting material  40 . 
     Ultimately, once the vertebral implant  10  is inserted completely between the vertebral bodies  106 ,  108  as shown in  FIG. 5 , the insertion tool  42  may be removed. At this juncture, bone matter  44  has been removed by the cutting features  20  and packed through the apertures  18 . Some of the removed bone matter  44  travels through the apertures  18  and into contact with the bone growth promoting materials  40 . Some of the removed bone matter  44  remains in the apertures  18 . Further, some of the removed bone matter  44  remains near the cutting features  20  and adjacent to the vertebral bodies  106 ,  108 . Accordingly, a bridge comprising bone matter  44  is formed between the vertebral bodies  106 ,  108  and the bone growth promoting material  40 . 
       FIG. 6  shows a frontal view of the exemplary vertebral implant  10 . In this orientation, the cutting direction C described above is directed out of the page.  FIG. 6  specifically illustrates an overlapping configuration for the plurality of cutting features  20  and leading surfaces  24  on both the superior surface  14  and inferior surface  16 . The overlap is in a direction T that is substantially parallel to the superior surface  14  (and inferior surface  16 ), but transverse to the cutting direction C. The cutting features  20  may be disposed in a staggered configuration such that they overlap across multiple rows oriented in the transverse direction T. In other words, the cutting features  20  shown in  FIG. 6  may be arranged in a single row in the transverse direction T or at different depths into or out of the page to achieve the overlapping configuration. As a result, the cutting features  20  are able to remove significant amounts of bone matter from the vertebral bodies  106 ,  108  as the vertebral implant  10  is inserted in the cutting direction C. 
     In one embodiment, the cutting features  20  overlap one another in the transverse direction T by an amount that leaves a nominal space  46  between the cutting features  20 . This space  46  may permit the removed bone matter  44  to fill gaps between the vertebral implant  10  and the vertebral bodies  106 ,  108 . That is, the space  46  strikes a balance between directing all removed bone matter  44  into the interior cavity  30  of the vertebral implant  10  and allowing the removed bone matter  44  to fill gaps between the vertebral implant  10  and the vertebral bodies  106 ,  108 . 
     Embodiments described above included a plurality of cutting features  20  arranged along a common cutting direction C. In the embodiment of the vertebral implant  110  shown in  FIG. 7 , some of the cutting features  20  are arranged in a first cutting direction C while other cutting features  20  are arranged in a second, different cutting direction C′. With the cutting features  20  configured in this manner, a surgeon may be able to remove additional bone matter  44  by imparting a reciprocating motion as indicated by the arrows labeled B in  FIG. 8 . The reciprocating motion B may be imparted through an insertion tool  42 . With each pass in the forward and backward direction, the cutting features  20  are able to remove more bone matter  44 . Ultimately, as  FIG. 9  shows, if enough bone matter  44  is removed, the cutting features  20  dig into the cortical bone of the vertebral bodies  106 ,  108  by an amount sufficient to bring the vertebral bodies (in the directions D, D′) into close proximity with the superior surface  14  and the inferior surface  16  of the vertebral implant  110 . 
     The cutting features  20  may be incorporated on different types of fusion implants, including ALIF cages similar in structure to the above-described embodiments. The cutting features  20  may be incorporated in PLIF or TLIF cages as well.  FIGS. 10 ,  11 ,  12 , and  13  illustrate embodiments of this type that may be inserted from a posterior, transforaminal, or lateral direction.  FIG. 10  shows one implementation where vertebral implants  210  are inserted using a posterior approach. Accordingly, the vertebral implants  210  include a plurality of cutting features  20  adapted as described above to remove bone matter from vertebral body  106  as the vertebral implants  210  are inserted in the cutting direction C. Concurrent with the action of cutting bone matter from the vertebral body  106 , the cutting features  20  direct at least some of the bone matter through the apertures  18  into an interior cavity (not shown) in the vertebral implant  210 . 
     The vertebral implants  210  may include a generally rectangular shape as depicted in the perspective view in  FIG. 11 . In this embodiment, the cutting features  20  are included in one or both of the superior surface  214  and inferior surface  216 . The lateral surfaces  212  may include apertures  18  and/or cutting features  20 , though neither is shown in  FIG. 11 . 
     In one embodiment shown in  FIGS. 12 and 13 , the vertebral implants  310 ,  410  include a generally cylindrical shape. In each embodiment, the cylindrically shaped implant  310 ,  410  extends along a longitudinal axis A. Each vertebral implant  310 ,  410  may be inserted along this longitudinal axis A.  FIG. 12  shows an end view of a vertebral implant  310  where cutting features  20  are disposed about the cylindrical outer wall  312 . Furthermore, the cutting features  20  are arranged to create two different cutting directions C and C′ that traverse a substantially arcuate path. Specifically, the cutting features on the left side of the dashed line  48  in  FIG. 12  are oriented in a first direction associated with cutting direction C. The cutting features on the right side of the dashed line in  FIG. 12  are oriented in a second direction associated with cutting direction C′. Notably, the cutting directions C, C′ do not necessarily coincide with the direction of insertion, which may be along the longitudinal axis A. 
     The vertebral implant  310  may include an insertion feature  336  to which an insertion tool (not shown) may be attached. The insertion feature  336  may be elongated or may comprise multiple features disposed on opposite sides of the longitudinal axis A. This type of insertion feature may allow a surgeon to impart a rotating, reciprocating motion about axis A, in the two different cutting directions C and C′ to remove bone matter along a generally cylindrical pattern. This rotating motion is in contrast with the non-rotating motion imparted on previously described embodiments to remove the bone matter. 
       FIG. 13  shows another embodiment of a cylindrically-shaped vertebral implant  410 . In embodiments disclosed above, cutting features  20  that are facing different cutting directions were generally grouped in different portions of the implant (see e.g.,  FIG. 7  or  FIG. 12 ). However, as  FIG. 13  shows, the cutting features  20  may be oriented so that different cutting directions C, C′ are interspersed about the vertebral implant  410 . This configuration may be implemented in the different types of vertebral implants, including the PLIF, TLIF, and ALIF implants. 
     The cutting features  20  may be arranged at gradually increasing heights in a manner similar to a broach.  FIGS. 14 and 15  illustrate examples of vertebral implants  510 ,  610  where the cutting features  20  are arranged at progressively taller heights. In both embodiments of the vertebral implant  510 ,  610 , the cutting height increases from a leading end  522 ,  622  (relative to the cutting direction C) to a trailing end  524 ,  624  of the implant  510 ,  610 . That is, the cutting features  20  disposed towards the leading end  522 ,  622  include a first associated height H 1 . However, the cutting features  20  disposed towards the trailing end  524 ,  624  include a larger, second associated height H 2 . 
     In the first exemplary embodiment, the cutting features  20  are substantially the same size. Therefore, the increase in height of the cutting features  20  primarily derives from an increase in the height of the implant body  512  from a first height D 1  at the leading end  522  to a larger second height D 2  at the trailing end  524 . Alternatively, the increase in height may be obtained through different size cutting features  20   a,    20   b,    20   c  as shown in  FIG. 15 . In this embodiment, the height D 3  of the implant body  612  remains substantially the same. However the cutting features  20   a  disposed near the leading end  622  of the vertebral implant  610  are smaller than cutting features  20   b,    20   c  disposed towards the trailing end  624  of the vertebral implant  610 . In one embodiment, the increase in height of the cutting features  20  may be obtained through a combination of a change in contour of the implant body  610  and a change in size of the cutting features  20 . 
     Embodiments described above related to vertebral implants that are implanted into the space normally occupied by a vertebral disc. In other procedures, such as vertebrectomies or corpectomies, one or more vertebral bodies are removed and an implant is inserted in the space left by the removed vertebrae. These types of devices, such as the vertebral implant  710  shown in  FIG. 16 , include multiple components, including spacers, a cage, rods, or other fixed or expandable members  700  spanning a distance between first and second end plates  702 ,  704 . The various types and arrangements for the cutting features  20  described above may be used with these types of devices as well as those disclosed above. That is, the cutting features  20  may be disposed on separate end plates  702 ,  704  and not on the same body as disclosed in other embodiments. 
     The cutting features  20  illustrated in  FIGS. 1-16  include similar geometries. As described above, the leading surface  24  and trailing surface  32  of the cutting feature  20  intersect at a generally arcuate leading edge  22 . In other embodiments, the cutting features may include different geometries that include straight, tapered, flared, or blunt geometries.  FIGS. 17-20  illustrate some exemplary geometries that may be used for the cutting features. For instance, the cutting feature  220  may be triangular, pyramid-like, or diamond-like as shown in  FIG. 17 . In  FIG. 18 , the exemplary cutting feature  320  is generally dome or oval-shaped.  FIG. 19  depicts an embodiment where the cutting feature  420  is squared while  FIG. 20  depicts a generally trapezoidal cutting feature  520 . Accordingly, the shape of the cutting features may be varied to achieve different cutting characteristics and/or to remove different amounts and different sizes of bone fragments. Each of these exemplary cutting features may be raked towards the cutting direction as in previously described embodiments. Further each of these exemplary cutting features may extend at least partially around the aperture with which the cutting feature is associated. 
     In one embodiment shown in  FIGS. 21 and 22 , the vertebral implant  810  includes a generally cylindrical shape with a generally circular outer perimeter  812 ,  816 . A cylindrical column  814  that includes a smaller diameter compared to the outer perimeter  812 ,  816  is disposed in a central portion of the vertebral implant  810 , between end surfaces  830 ,  840 . The vertebral implant  810  further includes an interior volume  850  that may be packed with a bone growth promoting material as previously described. The vertebral implant  810  includes superior  830  and inferior  840  surfaces that are positioned adjacent to vertebral endplates when the implant is inserted. As with previously described embodiments, the vertebral implant  810  includes cutting features  20  associated with apertures  18  that permit bone material to pass from the cutting features  20  and into an interior volume  850 . The cutting features  20  may be disposed on both superior  830  and inferior  840  surfaces. 
     As  FIG. 21  shows, the cutting features  20  are disposed in a radial manner so that the cutting direction follows an arcuate path defined by the orientation of the cutting features  20 . The cutting features  20  may include substantially similar heights or may gradually increase or decrease in height around the perimeter  812 ,  816  of the implant  810  as described above. Though not illustrated, additional cutting features may be disposed interior to the depicted cutting features  20 . Further the cutting features  20  may be oriented along the same cutting direction or different cutting directions than those illustrated in  FIG. 21 . The vertebral implant  810  may be inserted between vertebral bodies and rotated in the cutting direction by engaging the implant  810 , for example at surface  814 , with an unillustrated insertion tool. As described above, the cutting features  20  may be aligned along a common cutting direction or different cutting directions. 
     Spatially relative terms such as “under”, “below”, “lower”, “over”, “upper”, and the like, are used for ease of description to explain the positioning of one element relative to a second element. These terms are intended to encompass different orientations of the device in addition to different orientations than those depicted in the figures. Further, terms such as “first”, “second”, and the like, are also used to describe various elements, regions, sections, etc and are also not intended to be limiting. Like terms refer to like elements throughout the description. 
     As used herein, the terms “having”, “containing”, “including”, “comprising” and the like are open ended terms that indicate the presence of stated elements or features, but do not preclude additional elements or features. The articles “a”, “an” and “the” are intended to include the plural as well as the singular, unless the context clearly indicates otherwise. 
     The present invention may be carried out in other specific ways than those herein set forth without departing from the scope and essential characteristics of the invention. For instance, aside from the disclosed apertures  18  and cutting features  20 , embodiments disclosed above have not included any particular surface geometry, coating, or porosity as are found in conventionally known vertebral implants. Surface features such as these are used to promote bone growth and adhesion at the interface between an implant and a vertebral body. Examples of features used for this purpose include, for example, teeth, scales, keels, knurls, and roughened surfaces. Some of these features may be applied through post-processing techniques such as blasting, chemical etching, and coating, such as with hydroxyapatite. The superior and inferior bone interface surfaces of the vertebral implant may also include growth-promoting additives such as bone morphogenetic proteins. Alternatively, pores, cavities, or other recesses into which bone may grow may be incorporated via a molding process. Other types of coatings or surface preparation may be used to improve bone growth into or through the bone-contact surfaces. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive, and all changes coming within the meaning and equivalency range of the appended claims are intended to be embraced therein.