Abstract:
An intervertebral implant consisting of multiple elements connected by a flexible member and a method of positioning said implant via an operative corridor having an axis oblique to the disc plane. The implant is advanced through the operative corridor by altering the orientation of the first element of the implant such that it is in general alignment with the disc space plane without altering the alignment of the second element of the implant. Upon insertion of the first element into the disc space, the orientation of the second element is altered to be in general alignment with the disc space and the second element is inserted into the disc space.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This non-provisional application claims the benefit of the filing date under 35 USC 119(e) to the commonly owned U.S. Provisional Patent Application Ser. No. 61/009,546, entitled “Spinal Surgical Implant and Relted Methods,” and filed on Dec. 28, 2007, the entire contents of which are incorporated by reference as if set forth herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     This invention relates generally to spine surgery and, in particular, to a surgical implant for separating adjacent spinal vertebrae. 
     II. Discussion of the Prior Art 
     The spinal column is made up of individual vertebrae that provide support for the body and allow spinal movement. Between each vertebra sits a fibrocartilaginous disc that serves as a cushion and allows slight movement of the vertebrae. Spinal fusion procedures are common surgical techniques used to correct problems with displaced, damaged, or degenerated discs due to trauma, disease, or aging. Currently estimates suggest there are approximately 500,000 to 750,000 spinal fusion procedures performed each year in the United States. Generally, spinal fusion procedures involve removing the diseased or damaged disc and inserting one or more intervertebral implants into the resulting disc space. Introducing the intervertebral implant restores the height between adjacent vertebrae, which reduces or eliminates neural impingement and pain commonly associated with a damaged or diseased disc. 
     While various intervertebral implants are currently available in the prior art, there exists a need for an implant that can be inserted when surgical angles are less than optimal due to surgical constraints, the anatomical location of the vertebrae, or when two or more fusions are performed within one surgical corridor. When the surgical angle is less than optimal, the advancing implant may gouge or injure the vertebral endplate as it enters the intervertebral space. Also, it may be necessary for the surgeon to remove a portion of the side of the vertebral body to improve the entry angle into the intervertebral space. This may have the undesirable effect of destabilizing the interbody fusion. The present invention addresses this need. 
     SUMMARY OF THE INVENTION 
     The present invention includes a spinal fusion system for performing spinal fusion between adjacent lumbar vertebrae, including an exemplary spinal fusion implant. In one embodiment, the implant has a generally rectangular shape, with a leading element, a trailing element. The leading element and the trailing element are connected via flexible element. The flexible element allows the trailing element to move relative to the leading element (or vice versa). Thus, trailing element (and/or leading element) may bend from a neutral position in which the trailing element (and/or leading element) is aligned with the longitudinal axis L to a biased position in which the trailing element (and/or the leading element) deviates from the longitudinal axis L. This flexibility allows the implant to adopt various temporary profiles that may be desirable, particularly during insertion. For example, when the operative corridor used to access the disc space is offset or angled relative to the plane of the disc space the implant may transition from the offset access trajectory to the disc space in stages (e.g. the leading element may transition before the trailing element), thus protecting the vertebral endplates during insertion. The flexible element should thus be flexible enough to allow the trailing element to bend appropriately without effecting the overall integrity and strength of the implant. 
     The flexible element may comprise any number of suitable forms including, but not limited to a spring, a textile body, and an elastomeric body. The leading element, trailing element, and flexible element may be formed of a single component. Alternatively, leading element, trailing element, and flexible element may comprise separate components. It will be appreciated that any manner of mechanisms or techniques may be used attach the flexible element to the leading element and trailing element. By way of example only, the flexible element may be attached via mechanical fasteners (e.g. snaps, rivets, screws, pins, etc . . . ), chemical bonding, thermal bonding, adhesives, and molding. 
     The implant is preferably configured for lateral introduction into the disc space. By way of example, the implant may be particularly advantageous for implanting positioning the implant at L5-S1 via a lateral approach. By way of example only, the operative corridor may be created using any know tissue distraction and/or tissue retraction systems. The skin entry position depends upon individual patient anatomy but should be positioned just superior to the iliac crest. The distal end of the tissue distraction/retraction system may then be advanced at an angle towards the L5-S1 disc space, avoiding the iliac crest and thereafter opened to a final working corridor. After the creation of the operative corridor, the intervertebral space may be prepared via any number of well known preparation tools, including but not limited to kerrisons, rongeurs, pituitaries, and rasps. According to one embodiment, the preparation tools may utilize distal working ends angularly offset from the longitudinal axis of the tool shafts to facilitate entry into the disc space through the angled operative corridor. After preparation is complete, the implant is preferably advanced through the operative corridor in the neutral position (i.e. with leading element and trailing element aligned with the longitudinal axis L and the operative corridor). 
     The flexible element permits the trailing element to move relative to the leading element as the leading element enters the disc space. In this manner, the longitudinal axis L of the implant is permitted to rotate into alignment with the disc space, despite the small height of the disc space relative to the length of the implant and any space constraints in the operative corridor and the implant may be advanced into the disc space without causing damage. 
     According to another embodiment the leading element and trailing element are connected by an articulating element. The articulating element allows the trailing element to move relative to the leading element (or vice versa). The articulating element may be constructed of any suitable biocompatible material, but preferably, comprises the same material as leading element and trailing element. One articulating element preferably attaches to an interior surface of both sidewalls on each side of the implant. By attaching the articulating element to the interior surface of sidewalls the outer dimensions of implant may remain the same. Any number of additional articulation elements within one implant is also contemplated. Intervening members may connect the articulating elements with the leading and trailing ends. The additional articulation elements allow the implant to advance into an intervertebral space at greater and greater angles, depending on the number of articulation elements. 
     In still other embodiments, the leading element and trailing element may be connected via wires or tethers. Additional one or more additional element may be situated between the leading element and the trailing element. Various mechanisms for locking the elements together after insertion are also contemplated. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be more fully understood from the following detailed descriptions taken in conjunction with the accompanying drawings, in which: 
         FIG. 1  is a side view of an implant having a first element and a second element movably connected about the longitudinal axis, according to one embodiment of the present invention; 
         FIG. 2  is a side view of the implant of  FIG. 1  wherein an element of the implant is offset relative to the longitudinal axis, according to one embodiment of the present invention; 
         FIG. 3  is a top view of the implant of  FIG. 1 , according to one embodiment of the present invention; 
         FIG. 4A  is a side view of the implant of  FIG. 1  being inserted to an intervertebral space through an operative corridor having an axis offset from the plane of the intervertebral space; according to one embodiment of the present invention; 
         FIG. 4B  is a side view of the implant of  FIG. 4A  with a first element positioned within and aligned with the plane of the disc space and a second element aligned with the axis of the operative corridor prior to being advanced into the disc space, an operative corridor having an axis offset from the plane of the intervertebral space; according to one embodiment of the present invention; 
         FIG. 5  is a side view of the implant of  FIG. 4A  completely inserted into an intervertebral space, according to one embodiment of the present invention; 
         FIG. 6  is a side view of an implant having a first element and a second element movably connected about the longitudinal axis, according to another embodiment of the present invention; 
         FIG. 6A  is a cross-sectional view of the implant of  FIG. 6 , according to one embodiment of the present invention; 
         FIG. 7  is a top view of the implant in  FIG. 6 , according to one embodiment of the present invention; 
         FIG. 8  is a top cross-sectional view of an implant having multiple elements movably connected about the longitudinal axis, according to another embodiment of the present invention; 
         FIG. 9  is a top view of an implant having multiple elements movably connected about the longitudinal axis, according to yet another embodiment of the present invention; 
         FIG. 10  is a side view of the implant of  FIG. 9 , according to one embodiment of the present invention; 
         FIG. 10A  is a cross-sectional view of the implant of  FIG. 9 , according to one embodiment of the present invention; 
         FIG. 11  is a top view of the implant of  FIG. 9 , wherein the multiple elements are coupled in a locked position, according to one embodiment of the present invention; 
         FIG. 11A  is a cross-sectional view of the implant of  FIG. 11 ; according to one embodiment of the present invention; 
         FIG. 12  is a side view of the implant of  FIG. 11 , according to one embodiment of the present invention; 
         FIG. 13  is a side view of an implant having a first element and a second element movably connected about the longitudinal axis, according to still another embodiment of the present invention; 
         FIG. 14 , is a side view of the implant of  FIG. 13  wherein an element of the implant is offset relative to the longitudinal axis, according to one embodiment of the present invention; and 
         FIG. 15  is a side view of the implant of  FIG. 13 , wherein first and second elements are aligned with the longitudinal axis of the implant and are drawn tight together after positioning within an intervertebral disc space, according to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below for the purposes of understanding the principles of the invention. No limitation of the scope of the invention is therefore intended. In the interest of clarity, not all features of an actual implementation are described in this specification. It will be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The invention disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
     With reference to  FIG. 1-3 , there is shown an example embodiment of an implant  10  for positioning within the intervertebral disc space between adjacent vertebral bodies of a spine. The implant  10 , when deposited in the disc space, facilitates spinal fusion and alleviates pain by restoring the disc space to a desired height while natural bone growth occurs through and/or past the implant  10 . Over time the bone growth results in the formation of a boney bridge between the adjacent vertebral bodies. The implant  10  is particularly adapted for introduction into the disc space via a lateral (trans-psoas) approach to the spine. The implant may nevertheless be introduced through any of a variety of other approaches (depending on the implant size), including posterior, anterior, antero-lateral, and postero-lateral approaches, without departing from the scope of the present invention. The implant  10  includes a longitudinal axis L, a leading element  12 , a trailing element  16 , and a flexible element  14  extending along the longitudinal axis L. The flexible element  14  is situated between the leading element  12  and trailing element  16  along the longitudinal axis L and connects the leading element  12  with the trailing element  16 . 
     The implant  10  may be provided in any number of sizes by varying one or more of the implant height, width, and length. By way of example only, the implant may be provided with a length dimension ranging from 30 mm to 60 mm. By way of further example, the implant may be provided with a width dimension ranging from 15 mm to 22 mm. By way of still further example, the implant may be provided with a height dimension ranging from 5 mm to 20 mm. The size ranges described, by way of example only, are generally appropriate for implantation into the lumbar region of the spine. The dimensions of the implant may be altered according to proportions of the particular patient. Further variation of the implant dimensions may be implemented to produce implants generally appropriate for implantation into either of the thoracic spine and the cervical spine. 
     The leading element  12  and trailing element  16  may be of bone or non-bone construction. By way of example, the leading element  12  and trailing element  16  may be cut and shaped from a suitable allograft bone. Preferably, the allograft source comprises a donor femur, however, it will be appreciated that any suitable bone may be used. Alternatively, the leading element  12  and trailing element  16  may be comprised of any suitable bio-compatible material including, but not limited to, polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK) or any combination of PEEK and PEKK), and metals (e.g. titanium). 
     The leading element  12  has a top surface  18 , a bottom surface  20 , opposing sidewalls  22  (which comprise an anterior side and a posterior side when the implant is positioned in the disc space), a distal end  24 , and a proximal end  26 . The trailing element  16  has a top surface  28 , a bottom surface  30 , opposing sidewalls  32  (which comprise an anterior side and a posterior side when the implant is positioned in the disc space), a distal end  34 , and a proximal end  36 . Though not shown, it will be appreciated that the opposing side walls  22 ,  32  may be dimensioned with differing heights in order to promote the natural curvature of the spine. That is, by way of example, the sidewalls  22 ,  32  may be dimensioned such that the sidewalls comprising the anterior side when the implant is positioned in the disc space have a greater height than the sidewalls comprising the posterior side, thus restoring the lordotic curvature of the lumbar (and cervical) spine. Alternatively, the sidewalls  22 ,  32  may be dimensioned such that the sidewalls comprising the anterior side when the implant is positioned in the disc space have a lesser height than the sidewalls comprising the posterior side, thus restoring the kyphotic curvature of the thoracic spine. The top surfaces  18 ,  28  and bottom surfaces  20 ,  30  may be provided in any number of suitable surface contours, including but not limited to generally planar, concave, and/or convex. 
     The leading element  12  and/or trailing element  16  may also include anti-migration features designed to increase the friction between the implant  10  and the adjacent contacting surfaces of the vertebral bodies. Such anti-migration features may include ridges or teeth  38  provided along the top surfaces  18 ,  28  and/or bottom surface  20 ,  30 . Additional anti-migration features may also include one or more spike elements  40  disposed at various locations along the implant  10 . In one embodiment, the implant  10  includes a total of 4 spike elements  40  extending through the upper surfaces  18 ,  28  and the lower surfaces  20 ,  30 . Spike elements  40  may be positioned near the “corners” of the implant  10  where the distal end  24  of leading element  12  meets sidewalls  22  and the proximal end  36  of trailing element  16  meets sidewalls  32 . The spike elements  40  may be manufactured from any of a variety of suitable materials, including but not limited to a metal, ceramic, and/or polymer material, preferably having radiopaque characteristics. The spike elements  40  may also take any of a variety of suitable shapes, including but not limited to a generally elongated element disposed within the implant  10  such that the ends thereof extend generally perpendicularly from the upper  18 ,  28  and/or lower surfaces  20 ,  30 . When the spike elements  40  are provided having radiodense characteristics and the leading and trailing elements  12 ,  16  are manufactured from a radiolucent material (such as, by way of example only, PEEK and/or PEKK), the spike elements  40  will be readily observable under X-ray or fluoroscopy such that a surgeon may track the progress of the implant  10  during implantation and/or the placement of the implant  10  after implantation. 
     The implant  10  may be configured with one or more fusion apertures  42 . Preferably, each of leading element  12  and trailing element  16  include a fusion aperture  42  extending in a vertical fashion through the top surface  18 ,  28  and bottom surface  20 ,  30 , respectively. The fusion apertures  42  function primarily as an avenue for bony fusion between adjacent vertebrae. The fusion apertures  42  may be provided in any of a variety of suitable shapes, including but not limited to the generally rectangular shape best viewed in  FIG. 3 , or a generally circular, oblong and/or triangular shape or any combination thereof. The spinal fusion implant  10  may have a plurality of visualization apertures  44  which allow a clinician to make visual observations of the degree of bony fusion un-obscured by the sidewalls  22 ,  32  of the implant  10  to facilitate further diagnosis and treatment. Preferably, each of leading element  12  and trailing element  16  include at least one visualization aperture  44 . Visualization apertures may be provided in any of a variety of suitable shapes, including but not limited to the generally oblong shape best viewed in  FIGS. 1-2 , or a generally circular, rectangular and/or triangular shape or any combination thereof. 
     Fusion between the adjacent vertebrae may be facilitated or augmented by introducing or positioning various osteoinductive materials within the fusion apertures  42  and/or adjacent to the spinal fusion implant  10 . Such osteoinductive materials may be introduced before, during, or after the insertion of the implant  10 , and may include (but are not necessarily limited to) autologous bone harvested from the patient receiving the spinal fusion implant  10 , bone allograft, bone xenograft, any number of non-bone implants (e.g. ceramic, metallic, polymer), bone morphogenic protein, and bio-resorbable compositions, including but not limited to any of a variety of poly (D,L-lactide-co-glycolide) based polymers. 
     The leading element  12  and the trailing element  14  are connected via flexible element  14 . Flexible element  14  allows the trailing element  16  to move relative to the leading element  12  (or vice versa). Thus, trailing element  16  (and/or leading element  12 ) may bend from a neutral position in which the trailing element  16  (and/or leading element  12 ) is aligned with the longitudinal axis L to a biased position in which the trailing element (and/or the leading element  12 ) deviates from the longitudinal axis L by and angle α. This flexibility allows the implant  10  to adopt various temporary profiles that may be desirable. By way of example, when the operative corridor used to access the disc space is offset or angled relative to the plane of the disc space (due to, for example, one or more anatomical and procedural constraints or considerations) the implant  10  may transition from the offset access trajectory to the disc space in stages (e.g. the leading element  12  may transition before the trailing element  16 ), thus protecting the vertebral endplates during insertion. The flexible element  14  should thus be flexible enough to allow the trailing element  16  to bend appropriately without effecting the overall integrity and strength of the implant  10 . 
     The flexible element  14  may comprise any number of suitable forms for providing the desired flexibility to the implant  10 . By way of example, flexible element  14  may comprise any one or a combination of, but not limited to a spring, a textile body (constructed, for example, via one or more of embroidery, weaving, three-dimensional weaving, knitting, three-dimensional knitting, injection molding, compression molding, cutting woven or knitted fabrics, etc.), and an elastomeric body. According to one embodiment, leading element  12 , trailing element  16 , and flexible element  14  may be formed of a single component. According to one example of such an embodiment, the entire implant  10  may be formed of polymer material (e.g. PEEK) and a central portion of the component may be machined in a manner that provides the necessary flexibility. Alternatively, leading element  12 , trailing element  16 , and flexible element  14  may comprise separate components. It will be appreciated that any manner of mechanisms or techniques may be used attach the flexible element  14  to the proximal end  26  of leading element  12  and distal end  34  of trailing element  16 , respectively. By way of example only, flexible element  14  may be attached via mechanical fasteners (e.g. snaps, rivets, screws, pins, etc . . . ), chemical bonding, thermal bonding, adhesives, and molding. 
     As mentioned above, the implant  10  is configured for lateral introduction into the disc space. A lateral approach to the disc space can be highly advantageous over other approaches to the spine. However, the iliac crest of the pelvis generally lies lateral to the L5-S1 disc space making a lateral approach to this spinal level (and thus the advantages that accompany a lateral approach) difficult to achieve in practice. According to one clinical utilization, set forth by way of example only, the implant  10  may be employed to advantageously access and fuse the L5-S1 disc space from a lateral approach, as will now be described. With the patient properly situated on the surgical table (preferably in the lateral decubitus position) an operative corridor is created to the L5-S1 disc space from a skin entry position located superior to L5-S1. By way of example only, the operative corridor may be created using any know tissue distraction and/or tissue retraction systems  46 , such as, by way of example only, the tissue distraction and retraction assemblies shown and described in the commonly owned U.S. Pat. No. 7,207,949, the entire contents of which is incorporated by reference into this disclosure as if set forth fully herein. The skin entry position depends upon individual patient anatomy but should be positioned just superior to the iliac crest. The distal end of the tissue distraction/retraction system  46  may then be advanced at an angle towards the L5-S1 disc space, avoiding the iliac crest. Once the distraction/retraction system  46  reaches the L5-S1 disc space, the operative corridor may be expanded by spreading the distraction/retraction system  46  to a final working configuration. Alternatively, the distraction/retraction assembly may be advanced straight to the spine from the skin entry position, and thereafter adjusted to position the distal end of the distraction/retraction system (and thus the operative corridor) adjacent to the L5-S1 disc space. 
     After the creation of the operative corridor, the intervertebral space may be prepared via any number of well known preparation tools, including but not limited to kerrisons, rongeurs, pituitaries, and rasps. According to one embodiment, the preparation tools may utilize distal working ends angularly offset from the longitudinal axis of the tool shafts to facilitate entry into the disc space through the angled operative corridor. After preparation, an insertion instrument  48  is utilized to advance the implant  10  through the operative corridor and into the intervertebral space. As illustrated in  FIG. 4A , the implant  10  is preferably advanced through the operative corridor in the neutral position (i.e. with leading element  12  and trailing element  16  aligned with the longitudinal axis L). 
     As illustrated in  FIG. 4B , the flexible element  14  permits the trailing element  16  to move relative to the leading element  12  as the leading element  12  enters the disc space. In this manner, the longitudinal axis L of the implant is permitted to rotate into alignment with the disc space, despite the small height of the disc space relative to the length of the implant and any space constraints in the operative corridor. The implant  10  may thus be advance into the disc with a reduced risk of gouging or otherwise injuring the vertebral endplates and without requiring a portion of the vertebral body be removed to improve the entry angle into the intervertebral space. The insertion instrument  48  may utilize any number of suitable means for engaging the trailing element  16  of implant  10 . To facilitate insertion of the implant  10 , the insertion instrument  48  may utilize an angularly offset distal head and/or a flexible shaft. Once the entire implant  10  is inserted into the prepared space and resumes a generally neutral position, the implant  10  is released from the insertion instrument  48 , the tissue distraction/retraction system  46  removed, and the operative corridor closed, as depicted in  FIG. 5 . As previously mentioned, additional materials may be included in the procedure before, during or after the insertion of the spinal fusion implant  10  to aid the natural fusion of the targeted spinal level. 
     Alternative example embodiments of implants capable of insertion into the L5-S1 disc space via a lateral surgical approach as described above, are illustrated, by way of example only, in  FIGS. 6-13 . The alternate embodiments illustrated by way of example, in  FIGS. 6-13  are similar to the implant  10  such that repeat discussion of common elements is unnecessary and common elements are numbered accordingly. With reference to  FIGS. 6-8 , implant  110  includes leading element  12  and trailing element  16 . Rather than the flexible member  14  of implant  10 , however, the leading element  12  and trailing element  16  are connected by an articulating element  50 . The articulating element  50  allows the trailing element  16  to move relative to the leading element  12  (or vice versa). Thus, trailing element  16  (and/or leading element  12 ) may bend from the neutral position in which the trailing element  16  (and/or leading element  12 ) is aligned with the longitudinal axis L to a biased position in which the trailing element (and/or the leading element  12 ) deviates from the longitudinal axis L. Implant  110  may thus adopt various temporary profiles prior to and during insertion into the disc space. The articulating element  50  may be constructed of any suitable biocompatible material, but preferably, comprises the same material as leading element  12  and trailing element  16 . As illustrated, one articulating element  50  preferably attaches to an interior surface of both sidewalls  22  and  32  on each side of the implant. By attaching the articulating element  50  to the interior surface of sidewalls  22 ,  32  the outer dimensions of implant  110  may remain the same or similar to implant  10 , however, it will be appreciated that the articulating element  50  may also be attached along the outer surface of sidewalls  22 ,  32 . 
     As best viewed in  FIG. 6A , articulating elements  50  are attached to the leading element  12  and trailing element  16  with fasteners  52 . In the illustrated embodiment, fasteners  52  comprise cylindrical pins inserted through both the articulating element  50  and the leading element  12  or trailing element  16 . Alternatively, it will be appreciated that fasteners  52  may comprise any suitable connector, such as, for example, a post extending from articulating element  50  into a corresponding aperture on leading element  12  or trailing element  16 , or vice versa.  FIG. 8  is a cross-sectional view of an implant  210  according to another example embodiment. Implant  210  is identical to implant  110  except that the length of at least one of the leading element  12  and trailing element  16  is shortened and at least one intervening member  54  is situated between leading element  12  and trailing element  16  on each side of the implant  210 . As shown, the implant  210  includes three intervening members  54  on each side. For each intervening member  54  added to implant  210  an additional articulating element  50  is also added. Thus, the implant  210  as pictured utilizes four articulating elements  50  on each side of the implant. Decreasing the length of the leading element  12  and trailing element  16  and adding articulating elements  50  and intervening members  54  increases the overall offset angle (of the surgical corridor relative to the plane of the disc space) from which the implant  210  may be safely implanted into the disc space. 
     Turning now to  FIGS. 9-12 , an example implant  310  is illustrated. Implant  310  includes a leading element  12 , a trailing element  16 , and a central element  56 . Central element  56  includes a top surface  58 , a bottom surface  60 , opposing sidewalls  62  (which comprise an anterior side and a posterior side when the implant  310  is positioned in the disc space), a distal end  64 , and a proximal end  66 . The leading element  12 , trailing element  16 , and central element  56  are loosely connected in an initial position via at least one wire  68  (and preferably, at least two wires  68  are utilized, as depicted herein) fixed to leading element  12  and passing through central element  56  and trailing element  16 , exiting from the proximal end  36  of trailing element  16 . The wires  68  may be formed of any suitable material having flexibility enough to allow central element  56  and trailing element  16  to move relative to leading element  12  and each other. Preferably, wire  68  will also provide enough stiffness so that movement between the elements is controlled and not floppy. This controlled movement facilitates initial placement of the leading element  12  within the disc space. By way of example only, the wires  68  may be formed of nitanol or other similar metals. The leading, central, and trailing elements  12 ,  56 , and  16  are further configured to interlock with one another upon final insertion of the implant  310  within the disc space. To accomplish this, central element  56  includes a male snap connector  70  extending from proximal end  66  and a female snap receptacle  72  formed within distal end  64 . Extending from proximal end  26 , leading element  12  includes a male snap connector  74  complementary to the female snap receptacle  72  of central element  56 . Trailing element  16  includes a female snap receptacle  76  within distal end  34 . 
     To insert the implant  310 , an operative corridor is created as described above. After the leading end  12  is directed to the disc space, the implant advanced all the way into the disc space with the aid of an insertion instrument. Similar to the implants described above, the flexible nature of the wires  68  allows the implant  310  to transition from the offset operative corridor into alignment with the disc space in stages. After the implant is completely advanced into the disc space, the wires  68 , which are fixed to leading element  12  may be pulled away from the disc space while pressure is applied to the trailing element  16  in a direction towards the disc space. This combined action draws the leading element and central element together, such that snap connector  74  engages in snap receptacle  72 , locking the leading element  12  and central element  56  together. The central element  56  and trailing element  16  will also be drawn together such the snap connector  70  engages in snap receptacle  76 , locking central element  56  and trailing element  16  together. Once the implant  310  is locked together within the disc space, the wires  68  extending from trailing element  16  may be removed. This may be accomplished, for example, simply by cutting the exposed portion of wires  68 , or any number of other suitable methods.  FIGS. 9-10  illustrate the implant  310  prior to locking the leading element  12 , central element  56 , and trailing element  16  together, while  FIGS. 11-12  depict the implant in its final locked position. 
       FIGS. 13-15  depict yet another example embodiment of an implant  410  according to the present invention. Implant  410  comprises leading element  12  and trailing element  16 . Leading element  12  and a trailing element  16  are loosely connected by an embroidered tether  78  fixed to leading element  12  and passing through trailing element  16 . It will be appreciated that any number of suitable tethers other than the embroidered tether described may be utilized. By way of example only, the tether may be comprised of wire similar to wires  68  described above. The proximal side  26  of leading element  12  and distal side  34  of trailing element  16  are configured with complementary articulating surfaces  80  and  82 , respectively. By way of example, articulating surface  80  of leading element  12  comprises a convex extension of sidewalls  22  while the articulating surface  82  of trailing element  16  comprises a concave depression in sidewalls  32 . Alternatively, articulating surface  80  could be a concave depression and articulating surface  82  could be a convex extension. The complementary articulating surfaces  80 ,  82 , together with the loose connection provided by tether  78  permit the leading element  12  and trailing element  16  to move relative to each other, and again, like the implants described above, allows implant  410  to transition from alignment in an operative corridor to alignment with the disc space in stages when the disc space is angularly offset form the operative corridor. To deliver implant  410  through the offset operative corridor, the leading end  12  is advanced through the corridor until reaching the disc space. The orientation of the leading element is transitioned into alignment with the disc space and leading element  12  is positioned therein. Initially, the leading implant  410  may be held slightly rigid to facilitate initial positioning of the leading element  12  in the disc space by pulling tether  78  and applying pressure to trailing element  16  with the aid of an insertion instrument. Thereafter, providing slack to the tether  78  allows the trailing element  16  to move relative to the leading element  12  such that the implant can again align with the disc space in stages. After the implant is fully positioned within the disc space, the tether  78  may again be pulled while providing force in the opposite direction with the insertion tool. This draws the leading element  12  and trailing element  16  tightly together and the tether  78  may be tied or otherwise fixed at the proximal end  36  of trailing element  16  to maintain the elements  12 ,  16  in snug configuration. The excess tether  78  may be removed. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined herein. By way of example only, the description illustrates the use and implantation of implants into the L5-S1 disc space via a lateral approach. It will be appreciated however, that numerous situations may arise where it is desirable to deliver an intervertebral implant through an operative corridor aligned obliquely to the disc space, and the invention is not intended to be limited to the L5-S1 disc space.