Abstract:
An vertebral implant for fusing adjacent vertebrae or for replacing vertebral bodies is disclosed. The implant is a biocompatible metal, resorbable, or radiolucent implant conforming substantially in size and shape with an end plate of a vertebra. The implant preferably has a wedge-shaped profile to restore disc height and the natural curvature of the spine. The top and bottom surfaces of the implant have areas with a plurality of teeth to resist expulsion and provide initial stability and areas devoid of any protrusions to receive implantation instrumentation. The implant also has a stackability feature. The implant provides initial stability needed for fusion without stress shielding.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 14/069,471 filed on Nov. 1, 2013, which is a continuation of U.S. patent application Ser. No. 13/537,186 filed on Jun. 29, 2012 (now U.S. Pat. No. 8,597,356), which is a continuation of U.S. patent application Ser. No. 11/672,593 filed on Feb. 8, 2007 (now U.S. Pat. No. 8,231,675), which is a continuation of U.S. patent application Ser. No. 10/322,609 filed on Dec. 19, 2002 (now U.S. Pat. No. 7,192,447), each of which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to an artificial biocompatible vertebral device and, more particularly, to an intervertebral spinal implant for use in the treatment of back pain. 
     BACKGROUND OF THE INVENTION 
     A number of medical conditions such as compression of spinal cord nerve roots, degenerative disc disease, tumor, and trauma can cause severe back pain. Intervertebral fusion is one surgical method of alleviating back pain. In intervertebral fusion, two adjacent vertebral bodies are fused together by removing the affected intervertebral disc and inserting an implant that would allow for bone to grow between the two vertebral bodies to bridge the gap left by the disc removal. Another surgical method of relieving back pain is by corpectomy. In corpectomy, a diseased or damaged vertebral body along with the adjoining intervertebral discs are removed and replaced by a spinal implant that would allow for bone to grow between the closest two vertebral bodies to bridge the gap left by the spinal tissue removal. 
     A number of different implant materials and implant designs have been used for interbody fusion and for vertebral body replacement with varying success. Current implant materials used include metals, radiolucent materials including plastics, elastic and polymeric materials, ceramic, and allografts. Current implant designs vary from threaded cylindrical implants to rectangular cages with teeth-like protrusions. 
     For example, U.S. Pat. No. 5,782,919 to Zdeblick et. al. discloses an interbody fusion device which has a tapered body defining a hollow interior for receiving a bone graft or bone substitute material. Furthermore, the body of the device defines exterior threads for gripping the adjacent vertebrae and has a series of vascularization openings for promoting bony ingrowth. A variant on this design is shown in U.S. Pat. No. 4,961,740 to Ray et. al. The Ray patent illustrates a hollow, cylindrical fusion cage having a helical thread disposed on the outer surface of the cage with a plurality of holes leading to the hollow center between the threads. 
     U.S. Pat. No. 5,766,252 to Henry et. al. discusses a rectangular interbody spinal spacer that has vertically opposite upper and lower load bearing surfaces spaced apart a distance corresponding to the desired spacing. The rigid member has a wedge-shaped configuration with an ogival tip at the front end of the member. 
     While each of the foregoing prosthesis, address some problems relating to intervertebral disc replacements or vertebral body and intervertebral disc replacements, they present others. Thus, there is a need for an intervertebral implant whose design takes into consideration the anatomy and geometry of the intervertebral space sought to be filled by the intervertebral prosthesis as well as the anatomy and geometry of the end plates of the adjacent vertebral bodies. There is also a need for a spinal disc implant which integrates well with the vertebral bone tissue of the adjacent vertebral bodies between which the implant is to be inserted. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an intervertebral implant for use when surgical fusion of vertebral bodies is indicated. The implant may be used to replace a diseased or damaged intervertebral disc or may be used to replace a diseased or damaged partial or complete vertebral body, or may be used to replace a diseased or damaged vertebral body and adjacent intervertebral discs. 
     In one embodiment, the implant comprises a body made from a biocompatible metal, radiolucent material, allograft, or resorbable material conforming substantially in size and shape with the end plates of the vertebrae, has a wedge-shaped profile, and has a central bore for receiving an osteoconductive material to promote the formation of new bone. The top and bottom surfaces may be flat planar surfaces, wedged, or curved surfaces. Preferably, the top and bottom surfaces mimic the topography of the vertebral end plates. The top and bottom surfaces each may have areas extending from an outer periphery of the implant to the central bore having a plurality of teeth for engaging the end plates of adjacent vertebra and each may also have areas extending from the outer periphery of the implant to the central bore that are substantially smooth for receiving a surgical instrument. The substantially smooth areas may extend in an anterior-posterior direction, a lateral direction, or may run in both directions. In addition, the substantially smooth area may run in an anterio-lateral direction. 
     The implant may have at least one channel on at least one side of the implant for receiving a surgical tool or instrument. This channel may also extend in at least an anterior-posterior direction, a lateral direction, or in both directions. 
     In another embodiment, instead of instrument receiving channels, the implant may have a threaded hole on the anterior, anterio-lateral, or lateral side of the implant for receiving a threaded arm of an insertion tool. 
     In yet another embodiment, the implant may have a stackability feature wherein the implant is modular and comprises an upper endcap, and a lower endcap; or an upper endcap, a lower endcap, and at least one body portion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a top view of a first embodiment of the implant according to the present invention; 
         FIG. 2  is a cross-sectional side view of the implant of  FIG. 1 ; 
         FIG. 3  is an axial cross-sectional view of the implant of  FIG. 1 ; 
         FIG. 4  is a front or anterior view of the implant of  FIG. 1 ; 
         FIG. 4A  is a top view of a another embodiment of the implant of  FIG. 1 ; 
         FIG. 4B  is a top view of a another embodiment of the implant of  FIG. 1 ; 
         FIG. 5  is a top view of a second embodiment of the present invention; 
         FIG. 6  is a cross-sectional side view of the implant of  FIG. 5 ; 
         FIG. 7  is an axial cross-sectional view of the implant of  FIG. 5 ; 
         FIG. 8  is a front or anterior view of the implant of  FIG. 5 ; 
         FIG. 9  is a top view of a third embodiment of the present invention; 
         FIG. 10  is a side view of the implant of  FIG. 9 ; 
         FIG. 11  is an axial cross-sectional view of the implant of  FIG. 9 ; 
         FIG. 12  is a front or anterior view of the implant of  FIG. 9 ; 
         FIG. 13  is a top view of a fourth embodiment of the present invention; 
         FIG. 14  is a side view of the implant of  FIG. 13 ; 
         FIG. 15  is an axial cross-sectional view of the implant of  FIG. 13 ; 
         FIG. 16  is a front or anterior view of the implant of  FIG. 13 ; 
         FIG. 16A  is a perspective view of a fifth embodiment of the present invention; 
         FIG. 17  is a top view of an upper endcap of the implant of  FIG. 16A ; 
         FIG. 18  is a bottom view of the upper endcap of  FIG. 17 ; 
         FIG. 19  is a cross-sectional view taken at line A-A of the upper endcap of  FIG. 17 ; 
         FIG. 20  is a cross-sectional view taken at line B-B of the upper endcap of  FIG. 17 ; 
         FIG. 21  is a front or anterior view of the upper endcap of  FIG. 17 ; 
         FIG. 22  is a top view of a lower endcap of the implant of  FIG. 16A ; 
         FIG. 23  is a bottom view of the lower endcap of  FIG. 22 ; 
         FIG. 24  is a cross-sectional view taken at line A-A of the lower endcap of  FIG. 22 ; 
         FIG. 25  is a cross-sectional view taken at line B-B of the lower endcap of  FIG. 22 ; 
         FIG. 26  is a front or anterior view of the lower endcap of  FIG. 22 ; 
         FIG. 27  is a top view of an alternate upper endcap of a fifth embodiment of the present invention; 
         FIG. 28  is a bottom view of the upper endcap of  FIG. 27 ; 
         FIG. 29  is a cross-sectional view taken at line A-A of the upper endcap of  FIG. 27 ; 
         FIG. 30  is a cross-sectional view taken at line B-B of the upper endcap of  FIG. 27 ; 
         FIG. 31  is a front or anterior view of the upper endcap of  FIG. 27 ; 
         FIG. 32  is a top view of an alternate lower endcap of a fifth embodiment of the present invention; 
         FIG. 33  is a bottom view of the lower endcap of  FIG. 32 ; 
         FIG. 34  is a cross-sectional view taken at line A-A of the lower endcap of  FIG. 32 ; 
         FIG. 35  is a cross-sectional view taken at line B-B of the lower endcap of  FIG. 32 ; 
         FIG. 36  is a front or anterior view of the lower endcap of  FIG. 32 ; 
         FIG. 37  is a front or anterior view of a body portion of the implant of  FIG. 16A ; 
         FIG. 38  is a cross-sectional view taken at line A-A of the body portion of  FIG. 37 ; 
         FIG. 39  is a top view of the body portion of  FIG. 37 ; 
         FIG. 40  is a bottom view of the body portion of  FIG. 37 ; 
         FIG. 41  is a cross-sectional view taken at line B-B of the body portion of  FIG. 37 ; 
         FIG. 42  is a top view of an endcap of a sixth embodiment of the present invention; 
         FIG. 43  is a bottom view of the endcap of  FIG. 42 ; 
         FIG. 44  is a cross-sectional view taken at line A-A of the endcap of  FIG. 42 ; 
         FIG. 45  is a side or lateral view of the endcap of  FIG. 42 ; 
         FIG. 46  is a front or anterior view of the endcap of  FIG. 42 ; 
         FIG. 47  is a top view of an alternate endcap of a sixth embodiment of the present invention; 
         FIG. 48  is a bottom view of the endcap of  FIG. 47 ; 
         FIG. 49  is a cross-sectional view taken at line A-A of the endcap of  FIG. 47 ; 
         FIG. 50  is a side or lateral view of the endcap of  FIG. 47 ; 
         FIG. 51  is a front or anterior view of the endcap of  FIG. 47 ; 
         FIG. 52  is a top view of an alternate endcap of a sixth embodiment of the present invention; 
         FIG. 53  is a bottom view of the endcap of  FIG. 52 ; 
         FIG. 54  is a cross-sectional view taken at line B-B of the endcap of  FIG. 52 ; 
         FIG. 55  is a side or lateral view of the endcap of  FIG. 52 ; 
         FIG. 56  is a front or anterior view of the endcap of  FIG. 52 ; 
         FIG. 57  is a top view of a body portion of a sixth embodiment of the present invention; 
         FIG. 58  is a bottom view of the body portion of  FIG. 57 ; 
         FIG. 59  is a cross-sectional view of the body portion of  FIG. 57 ; 
         FIG. 60  is a cross-sectional view taken at line B-B of the body portion of  FIG. 57 ; 
         FIG. 61  is a front or anterior view of the body portion of  FIG. 57 ; 
         FIG. 62  is a side or lateral view of the body portion of  FIG. 57 ; 
         FIG. 63  is a top view of an endcap of a seventh embodiment of the present invention; 
         FIG. 64  is a bottom view of the endcap of  FIG. 63 ; 
         FIG. 65  is a cross-sectional view taken at line A-A of the endcap of  FIG. 63 ; 
         FIG. 66  is a side or lateral view of the endcap of  FIG. 63 ; 
         FIG. 67  is a top view of a body portion of a seventh embodiment of the present invention; 
         FIG. 68  is a bottom view of the body portion of  FIG. 67 ; 
         FIG. 69  is a side or lateral view of the body portion of  FIG. 67 ; and 
         FIG. 70  is a perspective view of an implant of a seventh embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  shows a top view of a first embodiment of intervertebral spacer or implant  10  according to the present invention. Implant  10  has a generally kidney-bean shaped footprint which includes anterior side  12 , posterior side  14 , and first and second lateral sides  16 ,  18 . Anterior side  12  and lateral sides  16 ,  18  are all substantially arcuate, preferably convex, in shape while posterior side  14  is substantially arcuate, preferably concave, in shape. 
     Implant  10  further includes central bore  26  which can be filled with bone growth inducing substances to allow bony ingrowth and to further assist in the fusion of the adjacent vertebrae and the implant. Central bore  26  has a generally kidney-bean shape that substantially conforms to the kidney-bean shaped footprint of implant  10 . The radius of curvature  23  of the arcuate, preferably convex, sides of central bore  26  may be about 6.5 mm to about 8.5 mm, preferably about 7.5 mm, and the radius of curvature  25  of the areas between the preferably convex and concave sides are about 3 mm to about 3.4 mm, preferably about 3.2 mm. 
     In addition, implant  10 , on its upper  15  and lower  30  surfaces, has sections or areas having teeth  20 , spikes, or similar gripping structures to facilitate engagement of implant  10  with the end plates of the adjacent vertebra. The teeth may be pyramidal, saw toothed or other similar shapes. Ridges may also be used to facilitate gripping adjacent vertebrae. Implant  10  may also have sections or areas  22  or  24  or both which are essentially smooth and devoid of any protrusions. Sections  22 ,  24  are provided to assist the surgeon in implantation of the spacer as will be discussed below. 
     As mentioned above, implant  10  has a generally kidney-bean shaped footprint. This footprint is designed to conform in size and shape with the general perimeter and shape of the end plates of the vertebrae between which implant  10  is to be implanted thereby providing maximum support while avoiding the intravertebral foramen of the vertebral bodies. The intravertebral foramen or the spinal canal is the portion of the vertebral body that houses the spinal cord and nerve roots. Generally, a portion of the intravertebral foramen extends into the body portion or end plate portion of the vertebra. This portion of the intravertebral foramen, in effect, changes the perimeter of the body portion of the vertebra from substantially an oval shape to substantially a kidney-bean shape. Accordingly, the footprint of implant  10  is kidney-bean shaped to emulate the general shape and perimeter of the body portion of the adjacent vertebrae. 
     Implant  10  preferably also has a generally wedge-shaped, side-view profile that is designed to restore the natural curvature or lordosis of the spine after the affected disc or affected vertebral body and adjoining discs have been removed. As shown in  FIGS. 2 and 4 , this wedge shape results from a gradual increase in height from anterior side  12  followed by a decrease in height as posterior side  14  is approached. The implant has a generally constant height from lateral side  16  to lateral side  18 . In another preferred embodiment, the implant may have a gradual increase in height followed by a gradual decrease in height from lateral side  16  to lateral side  18 . The substantially convex curvature of upper surface  15  and lower surface  30  change the height of implant  10  in the anterior to posterior direction. In another preferred embodiment, the substantially convex curvature of upper surface  15  and lower surface  30  change the height of implant  10  in the lateral direction. Implant  10  preferably has the greatest height generally midway between anterior side  12  and the center of implant  10 . In an exemplary embodiment, upper surface  15  and lower surface  30  may also be flat planar surfaces or flat angled surfaces. Alternatively, the upper surface  15  and lower surface  30  may be substantially curved surfaces, preferably shaped to mimic the topography of the vertebral end plates. 
     In order to facilitate insertion of implant  10 , posterior side  14  and anterior side  12  transition to upper and lower surfaces  15 ,  30  with rounded edges  40 . Rounded edges  40  may enable implant  10  to slide between the end plates while minimizing the necessary distraction of the end plates. In a preferred embodiment, rounded edges  40  have a radius of curvature ranging from about 0.75 mm to 1.75 mm, but preferably is about 1.25 mm. In another preferred embodiment, rounded edges  40  may extend around the periphery of implant  10 . Rounded edges  40  may also be used as a means to clean the edges of the implant  10  by eliminating any half or partial teeth located on or near the edge of the implant  10 . 
     As shown in  FIG. 2  and  FIG. 3 , channel  32  runs through implant  10  from anterior side  12  through central bore  26  to posterior side  14 . Channel  32  is sized to receive a surgical instrument such as an inserter for implantation of implant  10 . In addition, located along the side of channel  32 , near anterior side  12 , are retaining grooves  34  which further assist with coupling the implantation instrument to implant  10 . Using the implantation instrument with channel  32  and retaining grooves  34 , implant  10  can be inserted in an anterior approach where posterior end  14  is the first side to be introduced to the intervertebral space. 
     Extending from a first lateral side  16  to a second lateral side  18  may be a second instrument receiving channel  38 . Channel  38  is also sized to receive a surgical instrument such as an inserter for implantation of implant  10  and has retaining grooves  36  and  37  to further assist with coupling the implantation instrument to implant  10 . Using the implantation instrument with channel  38  and retaining grooves  36 , implant  10  can be inserted in a lateral approach where lateral side  16  is the first side to be introduced into the intervertebral space. Alternatively, using the implantation instrument with channel  38  and retaining grooves  37 , implant  10  can be inserted in a lateral approach where lateral side  18  is the first side to be introduced into the intervertebral space. 
     Although spinal spacer insertion instruments are well known in the art, an inserter used with implant  10  may be modified to optionally include releaseable engaging members configured and dimensioned to mate with retaining grooves  34 ,  36 ,  37  to further assist with holding the implant during the insertion and installation procedure. 
     As can be seen in  FIGS. 2 and 3 , channel  32  is shown extending the entire length of the lateral sides  16 ,  18  of the implant  10 . However, in an exemplary embodiment, channel  32  may extend only a portion of the length of lateral sides  16 ,  18 , or may extend the length of only one of the lateral sides  16 ,  18 . Likewise, channel  38  may extend only a portion of the length of sides  12 ,  14  or may extend along one of the sides  12 ,  14 . 
     To further assist with the insertion and implantation of implant  10 , implant  10  has areas  22  and  24 , located on the upper  15  and lower  30  surface of implant  10 , which are substantially smooth and are sized to receive an instrument such as a distractor, which is well known in the art. In this particular embodiment, area  22  extends in an anterior-posterior direction helping facilitate anterior implant insertion and area  24  extends in a transverse or lateral direction helping facilitate transverse implant insertion. Although in  FIG. 1  area  22  is shown as extending along the entire longitudinal length of implant  10 , from the perimeter edge of anterior side  12  to the perimeter edge of posterior side  14 , area  22  may extend only partially along the longitudinal length of implant  10 . The preceding is also applicable to area  24 . Area  24  is shown to extend along the entire transverse length of implant  10 , however, area  24  may extend only partially along the transverse length of implant  10 . Furthermore, in an exemplary embodiment, only area  22 , as shown in  FIG. 4A , or only area  24 , as shown in  FIG. 4B , may be present on upper and lower surfaces  15 ,  30  of implant  10 . 
     Implant  10  may be fabricated from pure titanium or an alloy thereof, preferably anodized to increase its biocompatiblity by making it more inert. Implant  10  may also be fabricated from a radiolucent material, such as polyetheretherketone or polyetherketoneketone, and may include a radiopaque marker, such as a titanium alloy pin. The radiopaque marker may be located along any of the implant sides such as anterior side  12 , posterior side  14 , or lateral sides  16 ,  18 . By using a radiolucent material, the progression and status of the fusion can be tracked through the use of X-rays or similar devices while the radiopaque marker will indicate the position of the implant with respect to the adjacent vertebral bodies. Implant  10  may also be fabricated from other biocompatible materials, such as allografts, and/or other resorbable materials. 
     The dimensions of the implant  10  may vary depending on where in the spine the implant will be inserted. The vertebral bodies in the lumbar area of the spine, for example, are larger than the vertebral bodies in the thoracic area. Therefore, an implant intended for the thoracic region would be smaller than one for the lumbar region. Likewise, lower lumbar disc replacements would be larger than upper ones. A person of ordinary skill could adapt the basic dimensions of the implant to make them occupy the space formerly occupied by the particular vertebral disc which needs replacement. Implant  10  is generally sized for anterior, lateral, or anterio-lateral approaches where inserting the implant around the spinal cord or spinal dural sac is not necessary as in a posterior approach. An exemplary embodiment of implant  10  may have a width (extending from anterior side  12  to posterior side  14 ) ranging from 15 mm-40 mm, but preferably about 22-26 mm, and most preferably about 24 mm, and a length (extending from lateral side  16  to lateral side  18 ) ranging from 20 mm-50 mm, but preferably about 28-32 mm, and most preferably about 30 mm. In addition, in an exemplary embodiment, the height of implant  10 , measure as the distance between upper surface  15  and lower surface  30 , when used as an intervertebral spacer, may be in the range of about 5 mm to about 25 mm. When using implant  10  as a corpectomy device, the height of implant  10  may range from about 17 mm to about 100 mm. Furthermore, in an exemplary embodiment, the radius of curvature  19  (shown in  FIG. 1 ) of the concave and the radius of curvature  17  (shown in  FIG. 1 ) of the convex sides may range from about 8 mm to about 30 mm, but preferably are about 13 mm. The radius of curvature  21  (shown in  FIG. 1 ) of transition areas  13  which connect concave side  14  with convex sides  16 ,  18  may be about 4 mm to about 8 mm, but preferably are about 6 mm. Also, in an exemplary embodiment, the radius of curvature of the upper and lower surfaces of implant  10  from anterior side  12  to posterior side  14  may range from about 40 mm to about 100 mm, but preferably about 50 mm. The upper and lower surfaces  15 ,  30  are preferably flat between lateral sides  16 ,  18 . 
       FIG. 5  shows a top view of a second embodiment of an implant  100 . In general, most of the structure of implant  100  is similar or comparable to the structure of implant  10 . Accordingly, the equivalent structures of implant  100  have been numbered the same as implant  10  and discussion of the similar components and features is not believed necessary. In this particular embodiment, located on upper surface  15  and lower surface  30  of implant  100 , is area  110 . Area  110  extends simultaneously in a longitudinal and lateral direction diagonally across implant  110  to facilitate anterio-lateral implant insertion. Although in  FIG. 5  area  110  is shown as extending along the entire length of implant  100 , area  110  may extend only partially along the length of implant  100 . 
     Similar to implant  10  discussed above, implant  100  has the two sets of instrument receiving channels to increase surgical flexibility when inserting implant  100  and to facilitate the insertion process by creating more surgical insertion alternatives. In the case of an anterio-lateral insertion, either channel  38  with retaining grooves  36  and  37  may be used or channel  32  with retaining grooves  34  may be used. 
       FIG. 9  shows a top view of a third embodiment of an implant  200 . In general, most of the structure of implant  200  is similar or comparable to the structure of implant  10 . Accordingly, the equivalent structures of implant  200  have been numbered the same as implant  10  and discussion of the similar components and features is not believed necessary. In this particular embodiment, instead of having instrument receiving channels, implant  200  has threaded bores  210 ,  212 . Threaded bores  210 ,  212  are sized to receive an implantation instrument such as a threaded inserter. 
     As can best be seen in  FIGS. 10 and 11 , threaded bore  210  is located on lateral side  18 . This location allows for insertion of implant  200  in a lateral fashion. Although, threaded bore  210  is located on lateral side  18 , it may also be located on lateral side  16 . This location also allows for insertion of implant  200  in a lateral direction.  FIGS. 11 and 12  show threaded bore  212  which is located on anterior side  12  of implant  200 . This location allows for insertion of implant  200  in an anterior direction with posterior side  14  being the first side to be introduced to the intervertebral space. 
       FIG. 13  shows a top view of a fourth embodiment of an implant  300 . In general, most of the structure of implant  300  is similar or comparable to the structure of implant  100 . Accordingly, the equivalent structures of implant  300  have been numbered the same as implant  100  and discussion of the similar components and features is not believed necessary. In this particular embodiment, instead of having instrument receiving channels, implant  300  has threaded bore  310 . Threaded bore  310 , is sized to receive an implantation instrument such as a threaded inserter. 
     As can best be seen in  FIGS. 15 and 16 , threaded bore  310  is located on an anterio-lateral side (between anterior side  12  and lateral side  16 ) of implant  300 . This location allows for insertion of implant  200  in an anterio-lateral fashion. Although, threaded bore  310  is located on an anterior-lateral side (between anterior side  12  and lateral side  16 ), it can also be located on an opposite anterio-lateral side (between anterior side  12  and lateral side  18 ) also allowing for an anterio-lateral implantation. 
     In a fifth embodiment, implant  400  is similar to the previously disclosed embodiment but now has a stackability feature. As will be further explained below, implant  400  includes an upper endcap and a lower endcap which may be stacked to form the spacer or implant. As shown in  FIG. 16A , implant  400  may also include at least one body portion which may be stacked between the upper endcap and the lower endcap to form the spacer or implant.  FIG. 17  shows a top view of upper endcap  402  of implant  400 . Upper endcap  402  has a generally kidney-bean shaped footprint which includes anterior side  403 , posterior side  404 , and first and second lateral sides  406 ,  408 . Anterior side  403  and lateral sides  406 ,  408  are all substantially arcuate, preferably convex, in shape while posterior side  404  is substantially arcuate, preferably concave, in shape. 
     As shown in  FIGS. 17-20 , upper endcap  402  also includes two elongated bores  410  which can be filled with bone growth inducing substances to allow bony ingrowth and to further assist in the fusion of the adjacent vertebrae. Upper endcap  402  further includes a central bore  411  for receiving a fastening member, such as a screw. In addition, upper endcap  402 , on its upper surface  405 , has sections or areas having teeth  412  or similar gripping means to facilitate engagement of implant  400  with the end plates of the adjacent vertebra, and has sections or areas  414 ,  416  which are substantially smooth and devoid of any protrusions. Although in  FIG. 17  sections  414 ,  416  are shown as extending along the entire length of upper endcap  402 , from perimeter edge to perimeter edge, sections  414 ,  416  may extend only partially along the length of upper endcap  402 . Sections  414 ,  416  are provided to assist the surgeon in anterior or lateral implantation of the implant as was discussed above with respect to sections  22 ,  24 . As can be seen in  FIGS. 18 and 21 , upper endcap  402  has a generally rectangular protrusion  418  configured and dimensioned to interface and mate with a recess portion of the implant body or with the lower endcap. While protrusion  418  has been shown and described as generally rectangular, it can be appreciated that protrusion  418  can be any shape desired. A lower surface  407  surrounds the protrusion  418 . Lower surface  407  is illustrated as surrounding and encircling completely protrusion  418 , but it can be appreciated that lower surface  407  may only partially surround protrusion  418 . 
     Upper endcap  402  may have a generally wedge-shaped, side profile that is designed to restore the natural curvature or lordosis of the spine after the affected disc or affected vertebral body and adjoining discs have been removed. As shown in  FIG. 19 , this wedge shape results from a gradual increase in height from anterior side  403  followed by a decrease in height as posterior side  404  is approached. The substantially convex curvature of upper surface  405  changes the height of implant  400  along its width. In an exemplary embodiment, upper surface  405  may also be a flat planar surface, a flat angled surface, or a substantially curved surface, preferably shaped to mimic the topography of the adjacent vertebral end plates. The radius of curvature for upper surface  405  may be the same as described for the one-piece implant described earlier. 
       FIG. 22  shows a top view of a lower endcap  420 . In general, most of the structure of endcap  420  is similar or comparable to the structure of endcap  402 . Accordingly, the equivalent structures of endcap  420  have been numbered the same as endcap  402  and discussion of the similar components and features is not believed necessary. As discussed with endcap  402 , endcap  420  also has a generally kidney-bean shaped footprint which includes anterior side  403 , posterior side  404 , and first and second lateral sides  406 ,  408 . Anterior side  403  and lateral sides  406 ,  408  are all substantially arcuate, preferably convex, in shape while posterior side  404  is substantially arcuate, preferably concave, in shape. As can be seen in  FIGS. 37-41 , on lower surface  407 , lower endcap  420  has a shoulder  424  defining a cavity  422  configured and dimensioned to interface and mate with a portion of the implant body. Shoulder  424  has been shown as surrounding cavity  422  entirely, but it should be appreciated that shoulder  424  may only partially surround cavity  422 . 
     Turning now to  FIGS. 27-31 , an alternative embodiment of upper endcap  430  can be seen. In general, most of the structure of upper endcap  430  is similar or comparable to the structure of upper endcap  402 . Accordingly, the equivalent structures of upper endcap  430  have been numbered the same as upper endcap  402  and discussion of the similar components and features is not believed necessary. In this particular embodiment, located on upper surface  405  of upper endcap  430 , is area  432 . Area  432  extends simultaneously in a longitudinal and lateral direction diagonally across upper endcap  430  to facilitate antcrio-lateral implant insertion. Although in  FIGS. 27-31 , area  432  is shown as extending along the entire length of upper endcap  430 , area  432  may extend only partially along the length of upper endcap  430 . 
       FIG. 32  shows a top view of a lower endcap  440 . In general, most of the structure of lower endcap  440  is similar or comparable to the structure of lower endcap  420 . Accordingly, the equivalent structures of lower endcap  440  have been numbered the same as lower endcap  420  and discussion of the similar components and features is not believed necessary. As can be seen in  FIGS. 32-36 , located on lower surface  405  of lower endcap  440 , is area  432 . Area  432  extends simultaneously in a longitudinal and lateral direction diagonally across lower endcap  440  to facilitate anterio-lateral implant insertion. Although in  FIGS. 32-35 , area  432  is shown as extending along the entire length of lower endcap  440 , area  432  may extend only partially along the length of upper endcap  440 . 
       FIG. 37  shows a front or anterior view of a body portion  450 . In general, some of the structure of body portion  450  is similar or comparable to the structure of upper and lower endcaps  402 ,  420 ,  430 ,  440 . Accordingly, the equivalent structures of body portion  450  have been numbered the same as upper and lower endcaps  402 ,  420 ,  430 ,  440  and discussion of the similar components and features is not believed necessary. As can be seen in  FIGS. 37-40 , body portion  450  has a generally kidney-bean shape footprint. Located on upper surface  455 , body portion  450  has a shoulder  462  defining a cavity  464  and located on lower surface  457 , body portion  450  has a generally rectangular protrusion  456 . While shoulder  462  is shown as completely enclosing and surrounding cavity  464 , shoulder  462  may only partially surround cavity  464 . Likewise, lower surface  457  is shown as completely surrounding protrusion  456 , but it can be appreciated that lower surface  457  may only partially surround protrusion  456 . Shoulder  462  and cavity  464  are configured and dimensioned to interface and mate with either rectangular protrusion  418  of upper endcaps  402 ,  430  or rectangular protrusion  456  of another body portion  450 . Protrusion  456  of body portion  450  is configured and dimensioned to interface and mate with either cavity  422  of lower endplates  420 ,  440  or cavity  464  of another body portion  450 . Again, while the protrusions have been described as rectangular, any geometric shape is contemplated. 
     As mentioned above, implant  400  is a stackable implant comprising an upper endcap  402 ,  430 , a lower endcap  420 ,  440 , and, if necessary, at least one body portion  450 . It is also possible for implant  400  to include an upper endcap  402 ,  430  and a lower endcap  420 ,  440 . The modularity of implant  400 , allows implant  400  to have a variable height, thereby allowing a surgeon to create an implant sized to appropriately fit the surgical space. In use, once the implant height that will be needed for the surgical procedure is determined, the desired implant can be created from the endcaps and, if necessary, one or more body portions. If a smaller implant is needed, implant  400  may comprise upper endcap  402 ,  430 , and lower endcap  420 ,  440 . If a larger implant is needed, implant  400  may comprise upper endcap  402 ,  430 , lower endcap  420 ,  440  and at least one body portion  450 . Body portions  450  may be the same size or of various sizes. Upper and lower endcaps  402 ,  420 ,  430 ,  440  and body portion  450  are configured and dimensioned to mate with each other via an interference or similar fit. For further fixation of the endcaps and body portion together, a fixation screw may be threaded into central bore  411 . Additional screws and bores my also be used. 
     Body portion  450  also may include channels  464 ,  466  or threaded bores  458 ,  460  for implantation of the assembled implant  400 . Channel  464  runs anterior to posterior through body portion  450  from anterior side  403  to posterior side  404 . Channel  464  is sized to receive a surgical instrument such as an inserter for implantation of implant  400 . Using the implantation instrument, implant  400  can be inserted in a lateral approach where the contra-lateral side is the first side to be introduced into the intervertebral space. Alternatively, using the implantation instrument with channel  464 , implant  400  may be inserted in a lateral approach where lateral side  408  is the first side to be introduced to the intervertebral space. 
     Extending from a first lateral side  406  to a second lateral side  408  may be a second instrument receiving channel  466  (not shown). Channel  466  is also sized to receive a surgical instrument such as an inserter for implantation of implant  400 . Using the implantation instrument with channel  466 , implant  400  may be inserted in an anterior approach where posterior end  404  is the first side to be introduced to the intervertebral space. 
     Although channel  464  is described as extending the entire length of the lateral sides  406 ,  408  of the implant  400 , channel  464  may extend only a portion of the length of lateral sides  406 ,  408 , or may extend the length of only one of the lateral sides  406 ,  408 . Likewise, channel  466  may extend the length of one of the sides  403 ,  404  or may extend only a portion of the length of sides  403 ,  404 . 
     Implant  400 , instead of having instrument receiving channels, may have threaded bores  458 ,  460 . Threaded bores  458 ,  460  are sized to receive an implantation instrument such as a threaded inserter. 
     As can best be seen in  FIGS. 37 and 41 , threaded bore  458  is located on lateral side  406 . This location allows for insertion of implant  400  in a lateral fashion. Although, threaded bore  458  is located on lateral side  406 , it may also be located on lateral side  408 . This location also allows for insertion of implant  400  in a lateral direction.  FIG. 41  shows threaded bore  460  which is located on anterior side  403  of implant  400 . This location allows for insertion of implant  400  in an anterior direction with posterior side  404  being the first side to be introduced to the intervertebral space. 
     In a sixth embodiment, implant  500  is similar to the previously disclosed stackable embodiment, however implant  500  has a different coupling configuration for stacking. As will be further explained below, implant  500  includes a plurality of endcaps which may be stacked to form the spacer or implant. Implant  500  may also include at least one body portion which may be stacked between the endcaps to form the implant.  FIG. 42  shows a top view of endcap  502  of implant  500 . Fndcap  502  has a generally kidney-bean shaped footprint which includes anterior side  503 , posterior side  504 , and first and second lateral sides  506 ,  508 . Anterior side  503  and lateral sides  506 ,  508  are all substantially arcuate, preferably convex, in shape while posterior side  504  is substantially arcuate, preferably concave, in shape. 
     As shown in  FIGS. 42-46 , endcap  502  also includes two elongated bores  510  which can be filled with bone growth inducing substances to allow bony ingrowth and to further assist in the fusion of the adjacent vertebrae. Endcap  502  further includes a central bore  511  for receiving a fastening member, such as a screw, sleeve, or nut. In addition, endcap  502 , on its upper surface  505 , has sections or areas having gripping structures  512  to facilitate engagement of implant  500  with the end plates of the adjacent vertebra, and has sections or areas  516  which are substantially smooth and devoid of any protrusions. Although in  FIG. 42  sections  516  are shown as extending along the entire length of endcap  502 , from perimeter edge to perimeter edge, sections  516  may extend only partially along the length of endcap  502 . Sections  516  are provided to assist the surgeon in anterior or lateral implantation of the implant as was discussed above with respect to section  22 . As can be seen in  FIGS. 43 and 46 , endcap  502  has a generally rectangular protrusion  518  configured and dimensioned to interface and mate with a recess portion of the implant body or another endcap. While protrusion  518  has been shown and described as generally rectangular, it can be appreciated that protrusion  518  can be any shape desired. A lower surface  507  surrounds the protrusion  518 . Lower surface  507  is illustrated as surrounding and encircling completely protrusion  518 , but it can be appreciated that lower surface  507  may only partially surround protrusion  518 . Located proximate to protrusion  518 , on lower surface  507 , is a shoulder  515  defining a cavity  513 . Cavity  513  is configured and dimensioned to interface and mate with a portion of the implant body or another endcap. Shoulder  515  has been shown as surrounding cavity  513  entirely, but it should be appreciated that shoulder  515  may only partially surround cavity  513 . This different coupling configuration allows for interchangeability of the endcaps. 
     Endcap  502  may have a generally wedge-shaped, side profile that is designed to restore the natural curvature or lordosis of the spine after the affected disc or affected vertebral body and adjoining discs have been removed. As shown in  FIG. 44 , this wedge shape results from a gradual increase in height from anterior side  503  followed by a decrease in height as posterior side  504  is approached. The substantially convex curvature of upper surface  505  changes the height of implant  500  along its width. In an exemplary embodiment, upper surface  505  may also be a flat planar surface, a flat angled surface, or a substantially curved surface, preferably shaped to mimic the topography of the adjacent vertebral end plates. The radius of curvature for upper surface  505  may be the same as described for the one-piece implant described earlier. 
       FIG. 47  shows a top view of another endcap  520 . In general, most of the structure of endcap  520  is similar or comparable to the structure of endcap  502 . Accordingly, the equivalent structures of endcap  520  have been numbered the same as endcap  502  and discussion of the similar components and features is not believed necessary. As discussed with upper endcap  502 , endcap  520  also has a generally kidney-bean shaped footprint which includes anterior side  503 , posterior side  504 , and first and second lateral sides  506 ,  508 . Anterior side  503  and lateral sides  506 ,  508  are all substantially arcuate, preferably convex, in shape while posterior side  504  is substantially arcuate, preferably concave, in shape. As can be seen in  FIGS. 47-51 , endcap  520  also includes two elongated bores  510  which can be filled with bone growth inducing substances to allow bony ingrowth and to further assist in the fusion of the adjacent vertebrae. Endcap  520  further includes a central bore  511  for receiving a fastening member, such as a screw, sleeve or nut. In addition, endcap  520 , on its upper surface  505 , has sections or areas having gripping structures  512  to facilitate engagement of implant  500  with the end plates of the adjacent vertebra, and has sections or areas  517  which are substantially smooth and devoid of any protrusions. Although in  FIG. 47  sections  517  are shown as extending along the entire length of endcap  520 , from perimeter edge to perimeter edge, sections  517  may extend only partially along the length of endcap  520 . Sections  517  are provided to assist the surgeon in transverse implantation of the implant as was discussed above with respect to section  24 . As can be seen in  FIGS. 48 and 51 , endcap  520  has a generally rectangular protrusion  518  configured and dimensioned to interface and mate with a recess portion of the implant body or another endcap. While protrusion  518  has been shown and described as generally rectangular, it can be appreciated that protrusion  518  can be any shape desired. A lower surface  507  surrounds the protrusion  518 . Lower surface  507  is illustrated as surrounding and encircling completely protrusion  518 , but it can be appreciated that lower surface  507  may only partially surround protrusion  518 . Located proximate to protrusion  518 , on lower surface  507 , is a shoulder  515  defining a cavity  513 . Cavity  513  is configured and dimensioned to interface and mate with a portion of the implant body or another endcap. Shoulder  515  has been shown as surrounding cavity  513  entirely, but it should be appreciated that shoulder  515  may only partially surround cavity  513 . 
     Endcap  520  may have a generally wedge-shaped, side profile that is designed to restore the natural curvature or lordosis of the spine after the affected disc or affected vertebral body and adjoining discs have been removed. As shown in  FIG. 49 , this wedge shape results from a gradual increase in height from anterior side  503  followed by a decrease in height as posterior side  504  is approached. The substantially convex curvature of upper surface  505  changes the height of implant  500  along its width. In an exemplary embodiment, upper surface  505  may also be a flat planar surface, a flat angled surface, or a substantially curved surface, preferably shaped to mimic the topography of the adjacent vertebral end plates. The radius of curvature for upper surface  505  may be the same as described for the one-piece implant described earlier. 
     Turning now to  FIGS. 52-56 , an alternative embodiment of endcap  530  can be seen. In general, most of the structure of endcap  530  is similar or comparable to the structure of endcap  502 . Accordingly, the equivalent structures of endcap  530  have been numbered the same as endcap  502  and discussion of the similar components and features is not believed necessary. In this particular embodiment, located on upper surface  505  of endcap  530 , is area  519 . Area  519  extends simultaneously in a longitudinal and lateral direction diagonally across endcap  530  to facilitate anterio-lateral implant insertion. Although in  FIGS. 52-56 , area  519  is shown as extending along the entire length of endcap  530 , area  519  may extend only partially along the length of endcap  530 . 
       FIG. 57  shows a top view of a body portion  550 . In general, some of the structure of body portion  550  is similar or comparable to the structure of endcaps  502 ,  520 , and  530 . Accordingly, the equivalent structures of body portion  550  have been numbered the same as endcaps  502 ,  520 , and  530  and discussion of the similar components and features is not believed necessary. As can be seen in  FIGS. 57-62 , body portion  550  has a generally kidney-bean shape footprint. Located on upper surface  555  and lower surface  557 , body portion  550  has a shoulder  562  defining a cavity  564  and a generally rectangular protrusion  556 . While shoulder  562  is shown as completely enclosing and surrounding cavity  564 , shoulder  562  may only partially surround cavity  564 . Likewise, upper surface  555  and lower surface  557  are shown as completely surrounding protrusions  556 , but it can be appreciated that upper surface  555  and lower surface  457  may only partially surround protrusions  556 . Shoulder  562  and cavity  564  are configured and dimensioned to interface and mate with either rectangular protrusion  518  of endcaps  502 ,  520 ,  530  or rectangular protrusion  556  of another body portion  550 . Protrusion  556  of body portion  550  is configured and dimensioned to interface and mate with either cavity  513  of endcaps  502 ,  520 ,  530  or cavity  564  of another body portion  550 . Again, while the protrusions have been described as rectangular, any geometric shape is contemplated. 
     As mentioned above, implant  500  is a stackable implant comprising two endcaps  502 ,  520 ,  530 , and, if necessary, at least one body portion  550 . The modularity of implant  500 , allows implant  500  to have a variable height, thereby allowing a surgeon to create an implant sized to appropriately fit the surgical space. In use, once the implant height that will be needed for the surgical procedure is determined, the desired implant can be created from the endcaps and, if necessary, one or more body portions. If a smaller implant is needed, implant  500  may comprise two endcaps  502 ,  520 ,  530 . If a larger implant is needed, implant  500  may comprise endcaps  502 ,  520 ,  530 , and at least one body portion  550 . Body portions  550  may be the same size or of various sizes. Endcaps  502 ,  520 ,  530 , and body portion  550  are configured and dimensioned to mate with each other via an interference or similar fit. For further fixation of the endcaps or the endcaps and body portion together, a fixation screw may be threaded into central bore  511 . Additional screws and bores my also be used. 
     Body portion  550  also may include channels  563 ,  566  and/or threaded bores  558 ,  560  for implantation of the assembled implant  500 . Channel  563  runs anterior to posterior through body portion  550  from anterior side  503  to posterior side  504 . Channel  563  is sized to receive a surgical instrument such as an inserter for implantation of implant  500 . Using the implantation instrument, implant  500  can be inserted in a lateral approach where the contra-lateral side is the first side to be introduced into the intervertebral space. Alternatively, using the implantation instrument with channel  563 , implant  500  may be inserted in a lateral approach where lateral side  508  is the first side to be introduced to the intervertebral space. 
     Extending from a first lateral side  506  to a second lateral side  508  may be a second instrument receiving channel  566 . Channel  566  is also sized to receive a surgical instrument such as an inserter for implantation of implant  500 . Using the implantation instrument with channel  566 , implant  500  may be inserted in an anterior approach where posterior end  504  is the first side to be introduced to the intervertebral space. 
     Although channel  563  is described as extending the entire length of the lateral sides  506 ,  508  of the implant  500 , channel  563  may extend only a portion of the length of lateral sides  506 ,  508 , or may extend the length of only one of the lateral sides  506 ,  508 . Likewise, channel  566  may extend the length of one of the sides  503 ,  504  or may extend only a portion of the length of sides  503 ,  504 . 
     Implant  500 , instead of or in addition to having instrument receiving channels, may have threaded bores  558 ,  560 . Threaded bores  558 ,  560  are sized to receive an implantation instrument such as a threaded inserter. 
     As can best be seen in  FIGS. 59, 61, and 62 , threaded bore  558  is located on lateral sides  506 ,  508 . This location allows for insertion of implant  500  in a lateral fashion.  FIG. 59  shows threaded bore  560  which is located on anterior side  503  of implant  500 . This location allows for insertion of implant  500  in an anterior direction with posterior side  504  being the first side to be introduced to the intervertebral space. 
     As can best be seen in  FIG. 59 , body portion  550  may also include openings  561 , which preferably extend from the outer surface of body portion  550  to elongated bores  510 . Openings  561  may be packed with bone growth inducing substances to further aid in the fixation and fusion of the implant. 
     In a seventh embodiment, implant  600  is similar to the previously disclosed stackable embodiment, however implant  600  has a slightly different structure and footprint. Preferably, the structure and footprint of implant  600  allows implant  600  to be particularly suited for implantation in the cervical region of the spine.  FIG. 63  shows a top view of endcap  602  of implant  600 . Endcap  602  has a generally oblong octagonal shaped footprint which includes anterior side  603 , posterior side  604 , and first and second lateral sides  606 ,  608 . 
     As shown in  FIGS. 63-66 , endcap  602  also includes an elongated bore  610  which can be filled with bone growth inducing substances to allow bony ingrowth and to further assist in the fusion of the adjacent vertebrae. Endcap  602  further includes a central bore  611  for receiving a fastening member, such as a screw. In addition, endcap  602 , on its upper surface  605 , has sections or areas having gripping structures  612  to facilitate engagement of implant  600  with the end plates of the adjacent vertebra, and has sections or areas  616  which are substantially smooth and devoid of any protrusions. Although in  FIG. 63  section  616  is shown as extending along a partial length of endcap  602 , sections  616  may extend along the entire length of endcap  602 , from perimeter edge to perimeter edge. Section  616  may be provided to provide a recess allowing a screw head to be recessed so as not to extend upwardly beyond the upper ends of the gripping structures  612 . As can be seen in  FIGS. 65 and 66 , endcap  602  has a protrusion  618  configured and dimensioned to interface and mate with a recess portion of the implant body or another endcap. It can be appreciated that protrusion  618  may be any shape desired. A lower surface  607  surrounds the protrusion  618 . Lower surface  607  is illustrated as surrounding and encircling completely protrusion  618 , but it can be appreciated that lower surface  607  may only partially surround protrusion  618 . Located proximate to protrusion  618 , on lower surface  607 , is a shoulder  615  defining a cavity  613 . Cavity  613  is configured and dimensioned to interface and mate with a portion of the implant body or another endcap. Shoulder  615  has been shown as surrounding cavity  613  entirely, but it should be appreciated that shoulder  615  may only partially surround cavity  513 . 
     Endcap  602  may have a generally wedge-shaped, side profile that is designed to restore the natural curvature or lordosis of the spine after the affected disc or affected vertebral body and adjoining discs have been removed. As shown in  FIG. 66 , this wedge shape results from a gradual increase in height from anterior side  603  to the posterior side  604 . In an exemplary embodiment, upper surface  605  may also be a flat planar surface, a convexly-curved surface, or a substantially curved surface, preferably shaped to mimic the topography of the adjacent vertebral end plates. The radius of curvature for upper surface  605  may be the same as described for the one-piece implant described earlier. 
       FIG. 67  shows a top view of a body portion  650 . In general, some of the structure of body portion  650  is similar or comparable to the structure of endcap  602 . Accordingly, the equivalent structures of body portion  650  have been numbered the same as endcap  602  and discussion of the similar components and features is not believed necessary. As can be seen in  FIGS. 67-69 , body portion  650  has a generally oblong octagonal shape footprint. Located on upper surface  655  and lower surface  657 , body portion  650  has a shoulder  662  defining a cavity  664  and a protrusion  656 . While shoulder  662  is shown as completely enclosing and surrounding cavity  664 , shoulder  662  may only partially surround cavity  664 . Likewise, upper surface  655  and lower surface  657  are shown as completely surrounding protrusions  656 , but it can be appreciated that upper surface  655  and lower surface  657  may only partially surround protrusions  656 . Shoulder  662  and cavity  664  are configured and dimensioned to interface and mate with either protrusion  618  of endcap  602 , or protrusion  656  of another body portion  650 . Protrusion  656  of body portion  650  is configured and dimensioned to interface and mate with either cavity  613  of endcaps  602  or cavity  664  of another body portion  650 . Again, the protrusions may be any contemplated geometric shape. 
     As mentioned above, implant  600  is a stackable implant comprising two endcaps  602 , and, if necessary, at least one body portion  650 . The modularity of implant  600 , allows implant  600  to have a variable height, thereby allowing a surgeon to create an implant sized to appropriately fit the surgical space. In use, once the implant height that will be needed for the surgical procedure is determined, the desired implant can be created from the endcaps and, if necessary, one or more body portions. If a smaller implant is needed, implant  600  may comprise two endcaps  602 . If a larger implant is needed, implant  600  may comprise endcaps  602 , and at least one body portion  650 . Body portions  650  may be the same size or of various sizes. Endcap  602 , and body portion  650  are configured and dimensioned to mate with each other via an interference or similar fit. For further fixation of the endcaps or the endcaps and body portion together, a fixation screw may be threaded into central bore  611 . Additional screws and bores my also be used. 
     Body portion  650  also may include windows  665 ,  666  which can be filled with bone growth inducing substances to further allow for bony ingrowth and to further assist in the fusion of the adjacent vertebrae. Windows  665 ,  666  may also be used to mate with the implant holder to assist with the implantation of the implant. 
     Body portion  650  may also have a threaded bore  658 . Threaded bore  658  is sized to receive an implantation instrument such as a threaded inserter for implantation of the assembled implant  600 . As can best be seen in  FIG. 69 , threaded bore  558  is located on lateral sides  606 ,  608 . This location allows for insertion of implant  600  in a lateral fashion. 
       FIG. 70  shows a perspective view of one embodiment of implant  600  which includestwo endcaps  602  and one body portion  650 . 
     The embodiments disclosed herein are illustrative and exemplary in nature and it will be appreciated that numerous modifications and other embodiments of the implant disclosed may be devised by those skilled in the art.