Patent Publication Number: US-11638652-B2

Title: Systems and methods for spinal fusion

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/893,394, filed Feb. 9, 2018, which is a continuation of U.S. patent application Ser. No. 15/291,494, filed Oct. 12, 2016, which is a continuation of U.S. patent application Ser. No. 14/931,351, filed Nov. 3, 2015 (now U.S. Pat. No. 9,486,329), which is a continuation of U.S. patent application Ser. No. 14/193,866, filed Feb. 28, 2014 (now U.S. Pat. No. 9,186,261), which is a continuation of U.S. patent application Ser. No. 12/044,917, filed Mar. 7, 2008 (now U.S. Pat. No. 8,673,005), which claims the benefit of priority from U.S. Provisional Patent Application Ser. No. 60/905,674, filed Mar. 7, 2007, the entire contents of which are all hereby expressly incorporated by reference into this disclosure as if set forth in its entirety herein. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates generally to spinal surgery and, more particularly, to a system and method for spinal fusion comprising a spinal fusion implant of non-bone construction releasably coupled to an insertion instrument dimensioned to introduce the spinal fusion implant into the thoracic region of the spine. 
     II. Discussion of the Prior Art 
     Currently there are nearly 500,000 spine lumbar, thoracic and cervical fusion procedures performed each year in the United States. Such procedures are commonly performed to correct problems, such as chronic back or neck pain, which result from degenerated intervertebral discs or trauma. Generally, spinal fusion procedures involve removing some or the entire diseased or damaged disc, and inserting one or more intervertebral implants into the resulting disc space. Introducing the intervertebral implant serves to restore the height between adjacent vertebrae (“disc height”), which reduces if not eliminates neural impingement commonly associated with a damaged or diseased disc. 
     Autologous bone grafts are widely used as intervertebral implant for thoracic fusion. Autologous bone grafts are obtained by harvesting a section of bone from the iliac crest of the patient and thereafter implanting the article of autologous bone graft to effect fusion. While generally effective, the use of autologous bone grafts suffers certain drawbacks. A primary drawback is the morbidity associated with harvesting the autologous graft from the patient&#39;s iliac crest. Another related drawback is the added surgical time required to perform the bone-harvesting. 
     Allograft bone grafts have been employed with increased regularity in an effort to overcome the drawbacks of autologous bone grafts. Allograft bone grafts are harvested from cadaveric specimens, machined, and sterilized for implantation. While allograft bone grafts eliminate the morbidity associated with iliac crest bone harvesting, as well as decrease the overall surgical time, they still suffer certain drawbacks. A primary drawback is supply constraint, in that the tissue banks that process and produce allograft bone implants find it difficult to forecast allograft given the inherent challenges in forecasting the receipt of cadavers. Another related drawback is that it is difficult to manufacture the allograft with consistent shape and strength characteristics given the variation from cadaver to cadaver. 
     The present invention is directed at overcoming, or at least improving upon, the disadvantages of the prior art. 
     SUMMARY OF THE INVENTION 
     The present invention overcomes the drawbacks of the prior art by providing a spinal fusion system and related methods involving the use of a spinal fusion implant of non-bone construction. The non-bone construction of the spinal fusion implant of the present invention overcomes the drawbacks of the prior art in that it is not supply limited (as with allograft) and does not require harvesting bone from the patient (as with autograft). The spinal fusion implant of the present invention may be comprised of any suitable non-bone composition, including but not limited to polymer compositions (e.g. poly-ether-ether-ketone (PEEK) and/or poly-ether-ketone-ketone (PEKK)), ceramic, metal or any combination of these materials. 
     The spinal fusion implant of the present invention may be provided in any number of suitable shapes and sizes depending upon the particular surgical procedure or need. The spinal fusion implant of the present invention may be dimensioned for use in the cervical and/or lumbar spine without departing from the scope of the present invention. For thoracic fusion, the spinal fusion implant of the present invention may be dimensioned, by way of example only, having a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm. 
     The spinal fusion implant has a top surface, a bottom surface, an anterior side, a posterior side, a proximal side, and a distal side. The spinal fusion implant of the present invention may be provided in such a shape as to promote the proper kyphotic curvature of the spine. Such shape may be accomplished by varying the angle between the top and bottom contact surfaces of the spinal fusion implant to reflect the desired curvature for the vertebral bodies being fused. The desired angle between said top and bottom surfaces may be accomplished by providing the anterior face of the implant with a greater height than the posterior face of the implant. Thus the top and bottom contact surfaces may not be parallel to one another, but rather they may be angled towards one another at the posterior end and angled away from one another at the anterior end. 
     The spinal fusion implant of the present invention may be provided with any number of additional features for promoting fusion, such as an aperture extending between the upper and lower vertebral bodies which allow a boney bridge to form through the spinal fusion implant of the present invention. Such fusion-promoting aperture may be dimensioned to receive any number of suitable osteoinductive agents, including but not limited to bone morphogenic protein (BMP) and bio-resorbable polymers, including but not limited to any of a variety of poly (D,L-lactide-co-glycolide) based polymers. The spinal fusion implant of the present invention is preferably equipped with one or more lateral openings which aid in visualization at the time of implantation and at subsequent clinical evaluations. 
     The spinal fusion implant of the present invention may be provided with any number of suitable anti-migration features to prevent the spinal fusion implant from migrating or moving from the disc space after implantation. Suitable anti-migration features may include, but are not necessarily limited to, angled teeth formed along the upper and/or lower surfaces of the spinal fusion implant and/or spike elements disposed partially within and partially outside the top and/or bottom surfaces of the spinal fusion implant. Such anti-migration features provide the additional benefit of increasing the overall surface area between the spinal fusion implant of the present invention and the adjacent vertebrae, which promotes overall bone fusion rates. 
     The spinal fusion implant of the present invention may be provided with any number of features for enhancing the visualization of the implant during and/or after implantation into a spinal target site. According to one aspect of the present invention, such visualization enhancement features may take the form of the spike elements used for anti-migration, which 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 may also take any of a variety of suitable shapes, including but not limited to a generally elongated element disposed within the implant such that the ends thereof extend generally perpendicularly from the top and/or bottom surfaces of the implant. The spike elements may each comprise a unitary element extending through upper and lower surfaces or, alternatively, each spike element may comprise a shorter element which only extends through a single surface (that is, does not extend through the entire height of the implant). In any event, when the spike elements are provided having radiodense characteristics and the implant is manufactured from a radiolucent material (such as, by way of example only, PEEK and/or PEKK), the spike elements will be readily observable under X-ray or fluoroscopy such that a surgeon may track the progress of the implant during implantation and/or the placement of the implant after implantation. 
     The spinal implant of the present invention may be introduced into a spinal target site through the use of any of a variety of suitable instruments having the capability to releasably engage the spinal implant. In a preferred embodiment, the insertion instrument permits quick, direct, accurate placement of the spinal implant of the present invention into the intervertebral space. According to one embodiment, the insertion instrument includes a threaded engagement element dimensioned to threadably engage into a receiving aperture formed in the spinal fusion implant of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many advantages of the present invention will be apparent to those skilled in the art with a reading of this specification in conjunction with the attached drawings, wherein like reference numerals are applied to like elements and wherein: 
         FIG.  1    is a perspective view of a spinal fusion system of the present invention, including a thoracic fusion implant releasably coupled to an insertion instrument, according to one embodiment of the present invention; 
         FIG.  2 - 4    is a perspective view of the thoracic fusion implant of  FIG.  1   , illustrating (among other things), a fusion aperture extending between top and bottom surfaces, a plurality of visualization apertures extending through the side walls, and a variety of anti-migration features, according to one embodiment of the present invention; 
         FIG.  5    is a top view of the thoracic fusion implant of  FIG.  1   , illustrating (among other things) the fusion aperture and the anti-migration features, according to one embodiment of the present invention; 
         FIG.  6    is a side view of the thoracic fusion implant of  FIG.  1   , illustrating (among other things) the visualization aperture, the anti-migration features, and a receiving aperture for releasably engaging the insertion instrument of  FIG.  1   , according to one embodiment of the present invention; 
         FIG.  7    is an end view of the thoracic fusion implant of  FIG.  1   , illustrating (among other things) the receiving aperture formed in the proximal end and the anti-migration features, according to one embodiment of the present invention; 
         FIG.  8    is an end view of the thoracic fusion implant of  FIG.  1   , illustrating the distal end and the anti-migration features, according to one embodiment of the present invention; 
         FIG.  9    is a perspective view of the insertion instrument of  FIG.  1    in a fully assembled form, according to one embodiment of the present invention; 
         FIG.  10    is an enlarged perspective view of the distal region of the insertion instrument of  FIG.  1   , according to one embodiment of the present invention; 
         FIG.  11    is a perspective exploded view of the insertion instrument of  FIG.  1   , illustrating the component parts of the insertion instrument according to one embodiment of the present invention; and 
         FIG.  12    represents a flourographic image of the implant and is a side view illustrating the “enhanced visualization” feature of the present invention as employed within a thoracic fusion implant according, to one embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course 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 fusion implant system disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIG.  1    illustrates, by way of example only, a spinal fusion system  5  for performing spinal fusion between adjacent thoracic vertebrae, including an exemplary spinal fusion implant  10  and an exemplary insertion instrument  20  provided in accordance with the present invention. The spinal fusion implant  10  may be comprised of any suitable non-bone composition having suitable radiolucent characteristics, 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. The spinal fusion implant  10  of the present invention may be dimensioned, by way of example only, having a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm. 
     As will be described in detail below, the insertion instrument  20  is configured to releasably maintain the exemplary spinal fusion implant  10  in the proper orientation during insertion into a thoracic disc space and thereafter release to deposit the implant  10 . The exemplary spinal fusion implant  10 , having been deposited in the disc space, facilitates spinal fusion restoring and maintaining a desired disc height as natural bone growth occurs through and/or past the implant  10 , resulting in the formation of a boney bridge extending between the adjacent vertebral bodies. The implant  10  is particularly suited for introduction into the disc space via a lateral (trans-psoas) approach to the spine, but may be introduced in any of a variety of approaches, such as posterior, anterior, antero-lateral, and postero-lateral, without departing from the scope of the present invention (depending upon the sizing of the implant  10 ). 
       FIGS.  2 - 8    depict an example embodiment of the spinal fusion implant  10 . The spinal fusion implant  10  has a top surface  31 , a bottom surface  33 , an anterior side  52 , a posterior side  14 , a proximal side  22 , and a distal side  16 . The generally D-shaped circumference of implant  10 , shown by way of example only, is configured for placement in the thoracic spine. Preferably the anterior side  52  is dimensioned with a length than that of the posterior side  14 . This may be accomplished, by way of example, by providing a large radius of curvature of the corners between the anterior side  52  and the distal and proximal ends  16  and  22 , by angling the distal and proximal ends  16  and  22  such that they converge towards each other proximate the anterior side  52 , or a combination of both. By way of example only the radius of the corners proximate the anterior side  52  may be approximately 0.25 inch (¼ inch) while the radius of the corners proximate the posterior side  14  may be approximately 0.06 inch ( 1/16 inch). Optionally, to promote the natural kyphotic curvature of the thoracic region of the spine, the posterior side  14  may be dimensioned at a height greater than that of the anterior side  52 . This dimensioning allows for the upper  31  and lower surfaces  33  to converge toward one another at the anterior end, thereby forcing the fusing vertebrae to conform to the proper kyphotic curvature. The kyphotic curvature requirements may vary by patient, but the implant angle will likely lie in the range between 1.degree. and 20.degree., with one example embodiment having and angle of 10.degree. In one embodiment, the top and bottom surfaces  31 ,  33  are generally flat across. However, it can be appreciated by one skilled in the art that the top and bottom surfaces  31 ,  33  may be provided in any number of suitable shapes, including but not limited to concave and/or convex. When provided as convex shapes, the top and bottom surfaces  31 ,  33  may better match the natural contours of the vertebral end plates. 
     The exemplary spinal fusion implant  10  also preferably includes anti-migration features designed to increase the friction between the spinal fusion implant  10  and the adjacent contacting surfaces of the vertebral bodies so as to prohibit migration of the spinal fusion implant  10  after implantation. Such anti-migration features may include ridges  6  provided along the top surface  31  and/or bottom surface  33 . Additional anti-migration features may also include a spike element  7  disposed within the proximal region of the implant  10 , a spike element  8  disposed within the distal region of the implant  10 , and a pair of spike elements  9  disposed within the central region of the implant  10 , one on the posterior side  14  and one on the anterior side  52 . Thus, in a preferred embodiment, posterior side  14  is imbued with  3  spike elements  7 ,  8 ,  9 , situated one at each end and the center, while the anterior side  52  is situated with a single spike element, situated near the center. This triangular arrangement of spike elements  7 ,  8 ,  9 , is adopted for placement in the thoracic spine where the anterior portion of the vertebral body narrows sharply and is in clear proximity to the great vessels. Spike elements  7 ,  8 ,  9  may extend from the top surface  31  and/or bottom surface  33  within the respective proximal, distal and central regions of the implant  10 . The spike elements  7 ,  8 ,  9  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  7 ,  8 ,  9  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 and/or lower surfaces  31 ,  33  of the implant  10 . As best appreciated in  FIGS.  6 - 8   , the spike elements  7 ,  8 ,  9  may each comprise a unitary element extending through top and bottom surfaces  31 ,  33 . Alternatively, each spike element  7 ,  8 ,  9  may comprise a shorter element which only extends through a single surface  31 ,  33  (that is, does not extend through the entire height of the implant  10 ). In any event, when the spike elements  7 ,  8 ,  9  are provided having radiodense characteristics and the implant  10  is manufactured from a radiolucent material (such as, by way of example only, PEEK and/or PEKK), the spike elements  7 ,  8 ,  9  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 spinal fusion implant  10  of the present invention may be provided with any number of additional features for promoting fusion, such as an aperture  2  extending between the upper and lower vertebral bodies which allow a boney bridge to form through the spinal fusion implant  10 . According to a still further aspect of the present invention, this fusion may be facilitated or augmented by introducing or positioning various osteoinductive materials within aperture  2  and/or adjacent to the spinal fusion implant  10 . Such osteoinductive materials may be introduced before, during, or after the insertion of the exemplary spinal fusion 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 large fusion aperture  2  of the implant  10  may be provided in any of a variety of suitable shapes, including but not limited to the generally hourglass shape best viewed in  FIG.  5   , or a generally, rectangular, circular, oblong and/or triangular shape or any combination thereof. The preferred hourglass shape, shown in  FIG.  5   , maximizes the open area for boney growth through the implant  10  while still providing added support and contact surface area along the ends and enter of the implant. 
     The spinal fusion implant  10  of the present invention is preferably equipped with one or more visualization apertures  4  situated along the anterior  14  and posterior  52  sides, which aid in visualization at the time of implantation and at subsequent clinical evaluations. The plurality of visualization apertures  4  will allow a clinician to make visual observations of the degree of bony fusion un-obscured by the anterior  14  or posterior sides  52 . Specifically, based on the generally radiolucent nature of the implant  10 , the visualization apertures  4  provide the ability to visualize the interior of the implant  10  during X-ray and/or other suitable imaging techniques which are undertaken from the side (or “lateral”) perspective of the implant  10  (e.g. images taken from anterior/posterior position where the implant is inserted in a preferred position from a lateral approach). If fusion has taken place, the visualization apertures  4  will provide a method for the surgeon to make follow up assessments as to the degree of fusion without any visual interference from the spinal fusion implant  10 . Further, the visualization apertures  4  will provide an avenue for cellular migration to the exterior of the spinal fusion implant  10 . Thus, the spinal fusion implant  10  will serve as additional scaffolding for bone fusion on the exterior of the spinal fusion implant  10 . The visualization apertures  4  may be provided in any of a variety of suitable shapes, including but not limited to the generally oblong shape best viewed in  FIG.  6   , or a generally circular, rectangular and/or triangular shape or any combination thereof. 
     The spinal fusion implant  10  may be provided with any number of suitable features for engaging the insertion instrument  20  without departing from the scope of the present invention. As best viewed in  FIG.  7   , one engagement mechanism involves providing a threaded receiving aperture  12  in the proximal sidewall  22  of the spinal fusion implant  10  of the present invention. The threaded receiving aperture  12  is dimensioned to threadably receive a threaded connector  24  on the insertion instrument  20  (as will be described in greater detail below). The receiving aperture  12  extends inwardly from the proximal side  22  in a generally perpendicular fashion relative to the proximal side  22 . Although shown as having a generally circular cross-section, it will be appreciated that the receiving aperture  12  may be provided having any number of suitable shapes or cross-sections, including but not limited to rectangular or triangular. In addition to the receiving aperture  12 , the spinal fusion implant  10  is preferably equipped with a pair of grooved purchase regions  60 ,  61  extending generally horizontally from either side of the receiving aperture  12 . The grooved purchase regions  60 ,  61  are dimensioned to receive corresponding distal head ridges  62 ,  63  on the insertion instrument  20  (as will be described in greater detail below), which collectively provide an enhanced engagement between the implant  10  and the insertion instrument  20 . 
       FIGS.  9 - 11    detail the exemplary insertion instrument  20  according to one embodiment of the invention. The exemplary insertion instrument  20  includes an elongated tubular element  28  and an inserter shaft  44 . The elongated tubular element  28  is constructed with a distal head  26  at its distal end, distal head ridges  62 ,  63  on the distal end of the distal head  26 , a thumbwheel housing  38  at its proximal end and a handle  42  at its proximal end. The elongated tubular element  28  is generally cylindrical and of a length sufficient to allow the device to span from the surgical target site to a location sufficiently outside the patient&#39;s body so the handle  42  and the thumbwheel housing  38  can be easily accessed by a clinician or a complimentary controlling device. 
     The elongated tubular element  28  is dimensioned to receive a spring  46  and the proximal end of the inserter shaft  44  into the inner bore  64  of the elongated tubular element  28 . The inserter shaft  44  is dimensioned such that the threaded connector  24  at the distal end of the inserter shaft  44  just protrudes past the distal head ridges  62 ,  63  to allow engagement with the receiving aperture  12  of the spinal fusion implant  10 . It should be appreciated by one skilled in the art that such a construction allows the inserter shaft  44  to be able to rotate freely within the elongated tubular element  28  while stabilized by the spring  46  to reduce any slidable play in the insertion instrument  20 . 
     The handle  42  is generally disposed at the proximal end of the insertion instrument  20 . The handle  42  is fixed to the thumbwheel housing  38  allowing easy handling by the clinician. Because the handle  42  is fixed the clinician has easy access to the thumbwheel  34  and can stably turn the thumbwheel  34  relative to the thumbwheel housing  38 . Additionally, the relative orientation of the thumbwheel housing  38  to the handle  42  orients the clinician with respect to the distal head  26  and distal head ridge  62 . By way of example, the thumbwheel housing  38  holds a thumbwheel  34 , a set screw  32 , and a spacer  36 . The inserter shaft  44  is attached to the thumbwheel  34  and is freely rotatable with low friction due to the spacer  36 . One skilled in the art can appreciate myriad methods of assembling a housing similar to the above described. 
     The distal head ridges  62 ,  63  are dimensioned to fit slidably into the purchase regions  60 ,  61  with low friction to allow accurate engagement of the threaded connector  24  to the receiving aperture  12  of the spinal fusion implant  10 . In the presented embodiment, the outer dimension of the threaded connector  24  is smaller than the largest outer dimension of the distal head  26  and elongated tubular element  28 . Alternatively, other methods of creating a gripping surface are contemplated including but not limited to knurling or facets. 
     In order to use the system to perform a spinal fusion procedure, the clinician must first designate the appropriate implant size (and optionally, angulation). After the spinal fusion implant  10  is chosen, the distal head ridges  62 ,  63  of the inserter shaft  44  are inserted into the purchase regions  60 ,  61  of the spinal fusion implant  10 . At that time the spinal fusion implant  10  and insertion instrument  20  are slidably engaged with one another. Before the clinician can manipulate the combined spinal fusion implant  10  and insertion instrument  20 , they must be releasably secured together. In order to secure the spinal fusion implant  10  onto the threaded connector  24  of the inserter instrument  20 , the clinician employs the thumbwheel  34  to rotate the inserter shaft  44  and threaded connector  24 . The rotation of the threaded connector  24  will releasably engage the receiving aperture  12  of the spinal fusion implant  10  and stabilize the insertion instrument  20  relative to the spinal fusion implant  10 . 
     A clinician can utilize the secured system in either an open or minimally invasive spinal fusion procedure. In either type of procedure, a working channel is created in a patient that reaches the targeted spinal level. After the creation of that channel, the intervertebral space may be prepared via any number of well known preparation tools, including but not limited to kerrisons, rongeurs, pituitaries, and rasps. After preparation, the insertion instrument  20  is used to place a spinal fusion implant  10  into the prepared intervertebral space. Once the implant  10  is inserted into the prepared space, the implant  10  is released from the insertion instrument  20  by rotating the thumbwheel  34  to disengage the threaded connector  24  from the receiving aperture  12 . This motion removes the compressive force on the purchase regions  60 ,  61  between the distal head  26  and the distal head ridges  62 ,  63  of the spinal fusion implant  10  and allows the insertion instrument to be slidably removed from the implant  10 . After the threaded connector  24  is disengaged from the implant  10 , the insertion instrument  20  is removed from the working channel and the channel is closed. 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. 
     The enhanced visualization features of the implant  10  is explained in greater detail with reference to  FIG.  12   , illustrating the implant  10  dimensioned particularly for use in a lateral approach having (by way of example only) a width ranging between 15 and 20 mm, a height ranging between 6 and 16 mm, and a length ranging between 20 and 45 mm. Furthermore,  FIG.  12    illustrates the implant  10  from a side perspective clearly showing the location of the spike elements  7 ,  8 ,  9  relative to the implant  10  and the visualization apertures  4 . 
     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 by the appended claims. 
     For example, while described herein primarily with reference to the thoracic spinal surgery, it is to be readily appreciated that the spinal fusion implants of the present invention may be suitable for accomplishing fusion in the cervical or lumbar spine without departing from the scope of the present invention. It should be noted that implants designed for the cervical and lumbar regions may be composed in a similar manner, but having a lordosis-promoting shape, rather than the kyphosis promoting shape described above. Specifically, the anterior side may be dimensioned to have a height greater than the posterior side. Those implants  10  designed to be inserted into the cervical region may be very similar to those to be inserted into the thoracic region, albeit smaller, while those designed for the lumbar region may be larger. Moreover, it is to be readily appreciated that the insertion tools described herein may be employed with implants of any number of suitable constructions, including but not limited to metal, ceramic, plastic or composite. 
     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.