Abstract:
The present invention is directed to an implant that can be placed between two adjacent vertebral bodies using a lateral insertion method. The implant is characterized as having a first end plate and a second end plate which a crossbar spacer therebetween. The crossbar spacer preferably fits within a channel on the inner surfaces of the first end plate and the second end plate, whereby the spacer allows pivots, twisting and/or rotational movement of the spine. The first end plate and the second end plate include a keel extending therefrom, whereby the keel traverses longitudinally between a first lateral side and a second opposed lateral side and is substantially perpendicular to the sagittal plane of the patient&#39;s spine.

Description:
CLAIM OF PRIORITY  
       [0001]     This application claims priority to U.S. Provisional Patent Application No. 60/524,350, filed Nov. 21, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER AND LATERAL IMPLANT METHOD,” which is incorporated herein by reference.  
       CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0002]     This application is related to U.S. Provisional Application No. 60/422,039, filed Oct. 29, 2002, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT AND METHOD,” U.S. patent application Ser. No. 10/684,669, filed Oct. 14, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT AND METHOD,” U.S. Provisional Application No. 60/422,011, filed Oct. 29, 2002, entitled “TOOLS FOR IMPLANTING AN ARTIFICIAL VERTEBRAL DISK AND METHOD,” U.S. patent application Ser. No. 10/685,134, filed Oct. 14, 2003, entitled “TOOLS FOR IMPLANTING AN ARTIFICIAL VERTEBRAL DISK AND METHOD,” U.S. Provisional Application No. 60/422,022, filed Oct. 29, 2002, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER AND METHOD,” U.S. patent application Ser. No. 10/685,011, filed Oct. 14, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH SPACER AND METHOD,” and U.S. Provisional Application No. 60/517,973, filed Nov. 6, 2003, entitled “ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH CROSSBAR SPACER AND LATERAL IMPLANT METHOD,” U.S. patent application Ser. No. ______, filed ______, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT,” (KLYCD-05007US5), U.S. patent application Ser. No. ______, filed ______, entitled “METHOD OF LATERALLY INSERTING AN ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH TRANSLATING PIVOT POINT,” (KLYCD-05007US6), U.S. patent application Ser. No. ______, filed ______, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A CROSSBAR SPACER,” (KLYCD-05008US6), U.S. patent application Ser. No. ______, filed ______, entitled “METHOD OF LATERALLY INSERTING ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A CROSSBAR SPACER,” (KLYCD-05008US7), U.S. patent application Ser. No. ______, filed ______, entitled “LATERALLY INSERTABLE ARTIFICIAL VERTEBRAL DISK REPLACEMENT IMPLANT WITH A SPACER,” (KLYCD-05010US4), all of which are incorporated herein by reference. 
     
    
     FIELD OF ART  
       [0003]     This field of art of this disclosure is directed to an artificial vertebral disk replacement and method.  
       BACKGROUND  
       [0004]     The spinal column is a biomechanical structure composed primarily of ligaments, muscles, vertebrae and intervertebral disks. The biomechanical functions of the spine include: (1) support of the body, which involves the transfer of the weight and the bending movements of the head, trunk and arms to the pelvis and legs, (2) complex physiological motion between these parts, and (3) protection of the spinal cord and nerve roots.  
         [0005]     As the present society ages, it is anticipated that there will be an increase in adverse spinal conditions which are characteristic of aging. For example, with aging comes an increase in spinal stenosis (including, but not limited to, central canal and lateral stenosis), and facet joint degeneration. Spinal stenosis typically results from the thickening of the bones that make up the spinal column and is characterized by a reduction in the available space for the passage of blood vessels and nerves. Facet joint degeneration results from the constant load borne by the facet joints, and the eventual wear that results. Pain associated with both conditions can be relieved by medication and/or surgery.  
         [0006]     In addition, to spinal stenosis, and facet joint degeneration, the incidence of damage to the intervertebral disks is also common. The primary purpose of the intervertebral disk is to act as a shock absorber. The disk is constructed of an inner gel-like structure, the nucleus pulposus (the nucleus), and an outer rigid structure comprised of collagen fibers, the annulus fibrosus (the annulus). At birth, the disk is 80% water, and then gradually diminishes with time, becoming stiff. With age, disks may degenerate, and bulge, thin, herniate, or ossify. Additionally, damage to disks may occur as a result disease, trauma or injury to the spine.  
         [0007]     The damage to disks may call for a range of restorative procedures. If the damage is not extensive, repair may be indicated, while extensive damage may indicate full replacement. Regarding the evolution of restoration of damage to intervertebral disks, rigid fixation procedures resulting in fusion are still the most commonly performed surgical intervention. However, trends suggest a move away from such procedures. Currently, areas evolving to address the shortcomings of fusion for remediation of disk damage include technologies and procedures that preserve or repair the annulus, that replace or repair the nucleus, and that advance implants for total disk replacement. The trend away from fusion is driven both by issues concerning the quality of life for those suffering from damaged intervertebral disks, as well as responsible health care management. These issues drive the desire for procedures that are minimally invasive, can be tolerated by patients of all ages, especially seniors, and can be performed preferably on an out patient basis.  
         [0008]     Most recently, there has been an increased interest in total disk replacement technology. A number of artificial disks are beginning to appear in the medical device marketplace. These artificial disks vary greatly in shape, design and functionality. With these devices go tools and methods for insertion between vertebrae thereof. Though currently the most common method of insertion of disk replacement implants is the anterior approach, other surgical procedures, such as the lateral approach, are evolving.  
         [0009]     Accordingly, there is a need in the art for innovation in technologies and methods that advance the art in the area of minimally invasive intervertebral disk replacement. This not only enhances the quality of life for those suffering from the condition, but is responsive to the current needs of health care management. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]      FIG. 1A  is a side perspective view of an embodiment of the assembled implant  100 .  FIG. 1B  is an alternative side perspective view of an embodiment of the assembled implant  100 .  
         [0011]      FIG. 2A  and  FIG. 2B  show perspective views of the first and second inner surfaces of the first end plate and the second end plate of an embodiment of implant  100 .  FIG. 2   c  through  FIG. 2F  show cross-sectional views of the first end plate and the second end plate of an embodiment of implant  100 .  
         [0012]      FIG. 3A  is a perspective view of a spacer of an embodiment of implant  100 .  FIG. 3B  and  FIG. 3   c  are cross-sections of the spacer of an embodiment of implant taken at 90° angles respective to each other.  
         [0013]      FIG. 4A  is a cross-section of an embodiment of implant  100  taken along a plane parallel to the sagittal plane.  FIG. 4B  is a cross-section of an embodiment of implant corresponding to a plane parallel to the location of the coronal plane, or perpendicular to the sagittal plane of the vertebrae after implant  100  has been inserted.  
         [0014]      FIG. 5A  and  FIG. 5B  show perspective views of the first and second inner surfaces of the first end plate and the second end plate of another embodiment of implant  100 .  FIG. 5   c  is a cross-section of the embodiment of implant  100  taken along a plane parallel to the sagittal plane.  FIG. 5D  is a cross-section of the embodiment of implant  100  corresponding to a plane parallel to the location of the coronal plane, or perpendicular to the sagittal plane of the vertebrae after implant  100  has been inserted.  
         [0015]      FIG. 6  is a block diagram showing the method steps for the lateral implantation of an embodiment of the disclosed the disclosed implant. 
     
    
     DETAILED DESCRIPTION  
       [0016]     The following description is presented to enable any person skilled in the art to make and use what is disclosed. Various modifications to the embodiments described will be readily apparent to those skilled in the art, and the principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of what is disclosed and defined by the appended claims. Thus, what is disclosed is not intended to be limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and features disclosed herein. To the extent necessary to achieve a complete understanding of what is disclosed herein, the specification and drawings of all patents and patent applications cited in this application are incorporated herein by reference.  
         [0017]      FIG. 1A  shows an embodiment of implant  100 . The designations, “A” for anterior, “P” for posterior, “RL” for right lateral, and “LL” for left lateral are given in the drawings for spatial orientation. These designations give the relationship of all faces of implant from the superior perspective; i.e. looking down the axis of the spine. Implant  100  has a first end plate, or upper end plate  110  that is configured to mate with a first vertebra, and a second end plate, or lower end plate  120  that is configured to mate with a second vertebra. A third part  130  that sits between the first end plate  110  and the second end plate  120  is also provided. The third part  130  acts as a spacer between the first end plate  110  and the second end plate  120  and facilitates pivotal or rotational and also twisting movement of the first end plate  110  and the second end plate  120 , relative to each other. The third part  130 , the spacer, is dimensioned so that it has a curved or convex upper surface and a curved or convex lower surface, as discussed in more detail below.  
         [0018]     The upper end plate  110  has a first outer surface  112  from which a first keel  114  extends with a first set of teeth  115 . In one embodiment, when implant  100  is inserted between vertebrae, the first keel  114  extends longitudinally across the first outer surface  112 , about perpendicular to the sagittal plane of the spine. In another embodiment, the first keel  114  extends longitudinally only partially across the first outer surface  112 , about perpendicular to the sagittal plane of the spine. The teeth in the two embodiments with complete or partial extension of the keel across the first outer surface  112  of the upper end plate  110 , point towards the left lateral face of implant  100  when the embodiment is meant to be put into a slot in a vertebral body from the left lateral approach to the spine. This orientation is shown in  FIG. 1A  and  FIG. 1B , for example. Alternatively, the teeth  115  point towards the right lateral face of implant  100  when the embodiments are meant to be put into a slot in a vertebral body from the right lateral approach to the spine.  
         [0019]     The first outer surface  112  abuts the vertebral body when implant  100  is inserted between vertebrae. The first keel  114  extends into the vertebral body to anchor implant  100  into position, and is perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The first keel  114  in this orientation offers substantial stability during extension and flexion for implant  100  inserted between the vertebrae of a patient. Additionally, the first keel  114  in this embodiment is aligned with and supports the lateral axis of articulation of implant  100  perpendicular to the sagittal plane of the spine. The first inner surface  116  engages the spacer  130  of implant and opposes the second end plate  120 . The first inner surface  116  can form a planar surface that is parallel to the first outer surface  112 , or can form a planar surface that is not parallel to the first outer surface  112 .  
         [0020]     The lower end plate  120  has a second outer surface  122  from which a keel second  124  extends with a second set of teeth  125 . In one embodiment, when implant  100  is inserted between vertebrae, the second keel  124  is about perpendicular to the sagittal plane of the spine. As described above for the first upper end plate  110 , in one embodiment, the second keel  124  extends longitudinally across the second outer surface  122 , while in another embodiment, the second keel  124  extends longitudinally partially across the second outer surface  122 . Similarly, the teeth in the two embodiments with complete or partial extension of the keel across the second outer surface  122  of the lower end plate  120  point towards the left lateral face of implant  100  when the embodiment is meant to be put into a slot in a vertebral body from the left lateral approach to the spine. Alternatively, the teeth  125  point towards the right lateral face of implant  100  when the embodiments are meant to be put into a slot in a vertebral body from the right lateral approach to the spine.  
         [0021]     The second outer surface  122  abuts the vertebral body when implant  100  is inserted. The second keel  124  extends into the vertebral body to anchor implant  100  into position, and is perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The second keel  124  in this orientation offers substantial stability during extension and flexion for implant  100  inserted between the vertebrae of a patient. Additionally, the second keel  124  in this embodiment is aligned with and supports the lateral axis of articulation of implant  100  perpendicular to the sagittal plane of the spine. The second inner surface  126 , engages the spacer  130  of implant and opposes the first end plate  110 . The second inner surface  126  can form a planar surface that is parallel to the second outer surface  122 , or can form a planar surface that is not parallel to the second outer surface  122 .  
         [0022]     The lateral orientation of the first keel  114  and the second keel  124  allow the implant  100  to be inserted into the spine using an advantageous lateral approach as opposed to an anterior or posterior approach. In comparison to a posterior insertion approach in which the spinal nerves can be substantially disturbed, the spinal nerves are bypassed and relatively undisturbed when the implant  100  is inserted laterally between the vertebral bodies from the side of the spine. Although an anterior insertion approach has its benefits, the lateral insertion approach can allow the present implant  100 , and associated implantation tools, to be inserted into the spine with less disturbance of the patient&#39;s internal organs. This can translate into less time and risk associated with preparing the spine for insertion as well as inserting the implant itself into the spine. Further, the laterally oriented first and second keels  114 ,  124  offer substantial stability to the vertebral bodies during extension, flexion and lateral bending of the spine.  
         [0023]     The first inner surface  116  of the first end plate  110  can be parallel to the second inner surface  126  of the second end plate  120  when implant  100  is assembled and is in a neutral position (i.e., the position where the first end plate  110  has not rotated relative to the second end plate  120 ). Alternatively, the first inner surface  116  of the first end plate  110  can be non-parallel to the planar surface of the second inner surface  126  of the second end plate  120  when implant  100  is assembled and in a neutral position. This non-parallel orientation of the first end plate  110  and the second end plate  120  allows the plates to pivot to a greater degree with respect to each other. Additionally, other factors such as the height and position of the spacer  130 , can also be adjusted in order to increase the degree that the first end plate  110  and the second end plate  120  can pivot relative to each other.  
         [0024]     The embodiments shown in  FIG. 1   a  and  FIG. 1   b  illustrate the first and second keels  114 , 124 , which include ports  148 , 152 , respectively, that facilitate bone ingrowth. For example, bone from the vertebral bodies can grow thorough the ports  148 , 152 , and aid in securing the first and second keels  114 , 124  and the implant  100  with respect to the vertebral bodies. In addition, surfaces defined by the first and second keels  114 , 124  and the first and second outer surfaces  112 ,  122  of implant  100  can be roughened in order to promote bone ingrowth into these defined surfaces of implant  100 . In another embodiment the ports  148 , 152 , the first and second keels  114 , 124 , and the first and second outer surfaces  112 ,  122  of implant  100  can be coated with materials that promote bone growth such as for example bone morphogenic protein, BMP, or structural materials such as hyaluronic acid, HA, or other substance which promotes growth of bone relative to and into the keel, keel ports, and other external surfaces of the implant  100 .  
         [0025]     When implant  100  is inserted between vertebrae the planar surfaces corresponding to the first and second outer surfaces  112 ,  122  and the first and second inner surfaces  116 ,  126  of the first and second end plates  110 ,  120  lie within, or substantially within, the axial plane of the body of the patient. Similarly, the first and second keels  114 ,  124  are aligned in the axial plane, or perpendicular to the sagittal plane of the vertebrae.  
         [0026]      FIG. 1B  shows an alternative perspective view of implant  100  shown in  FIG. 1A . Again, implant  100  has a first or upper end plate  110  that is configured to mate with a first vertebra and a second or lower end plate  120  that is configured to mate with a second vertebra. The first and second keels  114 , 124  extend into the vertebral bodies to anchor implant  100  into position, and are perpendicular to the median sagittal plane of the spine, in which extension and flexion occur. The first and second keels  114 , 124  in this orientation offer substantial stability during extension and flexion for implant  100  inserted between the vertebrae of a patient. Additionally, the first and second keels  114 , 124  in this embodiment are aligned with and support the axis of articulation of implant  100  defined by an RL to LL orientation. The axis of articulation of implant  100  defined by an RL to LL orientation will be discussed in more detail below. The spacer  130  separates the first end plate  110  from the second end plate  120 . As evidenced from the perspective view of  FIG. 1B , the perimeter shape of the upper and lower end plates  110 , 120  can be configured to correspond to the perimeter shape of a vertebral disk. As will be appreciated by those of ordinary skill in the art, the perimeter shape of the upper end plate  110  and the lower end plate  120  can be the same.  
         [0027]      FIG. 2   a  shows a perspective view of an embodiment of the first inner surface  116  of the first or upper end plate  110  of implant  100 . The first inner surface  116  of the upper end plate  110  has a first socket or first cavity  210  formed therein. In one embodiment, the first socket  210  has a concave hemi-cylindrical surface. In this embodiment, the first socket  210  includes the shallow concave surface  211  with first ends  213 , 215  that are substantially perpendicular to the first inner surface  116 . Also indicated in  FIG. 2   a  are two axes,  217 , 219 . The first upper axis  217  intersects the first upper plate  110  in an RL to LL orientation. The second upper axis  219  is perpendicular to the first upper axis  217 , and intersects the upper plate  110  in an A to P orientation. The first socket  210  allows the first end plate  110  to pivot or rotate on spacer  130 , about a first upper axis  217  that is about perpendicular to the first ends  213 , 215 . The ends  213 , 215  block motion of the spacer  130  about the second upper axis  219 , perpendicular to the first upper axis  217 . In this embodiment, it is noted that the first and second keels  114 , 124  are aligned with and support the first upper axis  217 , which is an axis of articulation for first end plate  110  about the spacer  130  for this embodiment, and is an axis that is about perpendicular to the sagittal plane of the spine.  
         [0028]     As can be seen in  FIG. 2   a , the first socket  210  in this embodiment includes first ends  213 , 215  that have crests  233 , 235  respectively. The crests  233 , 235  project into the first socket  210 . Additionally, concave surface  211  has edges  234 , 236  with crests  237 ,  239 , respectively. The crests  233 ,  235 ,  237 , and  239  allow a loose fit between the spacer  130  and the first socket  210 , which will be disused in more detail below.  
         [0029]      FIG. 2   b  shows a perspective view of an embodiment of the second or lower end plate  120  of implant  100 . The second inner surface  126  of the lower end plate  120  has a second socket or second cavity  240  formed therein. In one embodiment, the second socket  240  has a concave hemi-cylindrical surface. In this embodiment, the second socket  240  includes the shallow concave surface  241  with second ends  243 , 245  that are substantially perpendicular to the second inner surface  126 . Also indicated in  FIG. 2   b  are two axes,  247 , 249 . The first lower axis  247  intersects the first lower plate  120  in an A to P orientation. The second lower axis  249  is perpendicular to the first lower axis  247 , and intersects the lower plate  120  in an RL to LL orientation. As will be described later with respect to the spacer  130 , the second socket  240  allows the second end plate  120  to pivot or rotate on spacer  130 , about the first lower axis  247  that is about perpendicular to the second ends  243 , 245 . The ends  243 , 245  block motion of the spacer  130  about the second lower axis  249 , perpendicular to the first lower axis  247 . In this embodiment, it is noted that the second lower axis  249  is about parallel with first upper axis  217 . As previously mentioned, the first and second keels  114 , 124  are aligned with and support the first upper axis  217 , which is an axis of articulation of the upper end plate  110  about the spacer  130  for this embodiment, and is an axis that is about perpendicular to the sagittal plane of the spine, as is second lower axis  249 . Further, the first lower axis  247  is an axis of articulation of the lower end plate  120  about the spacer  130 , and the first lower axis  247  is perpendicular to the first upper axis  217 .  
         [0030]     The fit of the spacer in the first socket  210  and the second socket  240  can be loose so that the spacer allows the first end plate  110  to be able to twist somewhat relative to the second plate  120 . This twisting action would generally be about an axis that is perpendicular to the first and second inner surfaces  116 , 126  of the first and second end plates  110 , 120 , respectively. Thus, implant  100  of this embodiment allows the spine to have movement in three orthogonal degrees of freedom, namely (1) forward and backward bending movement, (2) lateral side-to-side bending, and (3) twisting movement. It is to be understood that the second socket  240  in the lower end plate  120  can also have the same design as the first socket  210  in the upper end plate  110  with an increase in the amount of twisting movement afforded by implant  100 . As is noted previously herein, loose fit generally between one or both of first socket  210  and second socket  240  and the spacer  130  can allow for twisting motion. Further the spacer  130  can also be made with crests on the curved surfaces and on the ends in order to afford similar twisting motion. In other embodiments, the fit can be tighter in order to restrict such twisting action.  
         [0031]     Turning now to  FIG. 2   c  through  FIG. 2   f , the cross-sections of the upper and lower end plates  110 , 120  of an embodiment of implant  100  are shown.  FIG. 2   c  illustrates the first dimension  212  of the first socket  210 , and  FIG. 2   d  illustrates the second dimension  214  of the first socket  210 . The first dimension  212  and the second dimension  214  of the first socket  210  are perpendicular to each other.  FIG. 2   e  illustrates that the first dimension  242  of the second socket  240 , and  FIG. 2   f  illustrates the second dimension  244  of the second socket  240 . The first dimension  242  and the second dimension  244  of the second socket  240  are perpendicular to each other.  FIGS. 2   c  and  2   e  are a cross-section taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body after implant was inserted.  FIG. 2   d  and  FIG. 2   f  are a cross-section taken along a plane that would correspond to a plane that is parallel to the frontal (coronal) plane of the body after implant  100  was inserted.  
         [0032]     For one embodiment, relative dimensions of the first and second sockets  210 , 240  are indicated in  FIG. 2   c  through  FIG. 2   f . As previously discussed, the first and second outer surfaces  112 , 122  of the first and second end plates  110 , 120  are configured to contact vertebral bodies when implant  100  is inserted between vertebrae. The first and second outer surfaces  112 , 122  have first and second keels  114 , 124  that extend into the vertebral body when implant  100  is inserted between vertebrae. The first and second inner surfaces  116 , 126  of the upper and lower end plates  110 , 120  have first and second sockets  210 , 240  formed therein.  
         [0033]     In  FIG. 2   c , the first socket  210  has a first dimension  212 . In the first dimension  212 , the first socket  210  is concave such that it is curved like the inner surface of a cylinder. In  FIG. 2   d , the second dimension  214  is in the form of a trough or “flattened-U” with a previously indicated concave bottom surface  211  and two ends or sidewalls  213 ,  215 . As shown in  FIG. 2   d , the ends or sidewalls  213 ,  215  are parallel to each other and perpendicular to the bottom surface  211 . However, as will be appreciated by those of ordinary skill in the art, the ends or sidewalls  213 ,  215  can be formed at an angle relative to each other without departing from the scope of what is disclosed.  
         [0034]     In  FIG. 2   e , the second socket  240  has a first dimension  242 . The first dimension  242  is in the form of a trough or “flattened-U” with a bottom concave surface  241  and two ends or sidewalls  243 , 245 . As shown in  FIG. 2   f , the ends or sidewalls  243 ,  245  are parallel to each other and perpendicular to the bottom surface  241 . However, as will be appreciated by those of ordinary skill in the art, the ends or sidewalls  243 ,  245  can be formed at an angle relative to each other without departing from the scope of what is disclosed. In  FIG. 2   f , the second dimension  242  of the second socket  240  is concave such that it is curved like the inner surface of a cylinder.  
         [0035]     As previously mentioned,  FIG. 2   c  and  FIG. 2   d  are oriented to illustrate that the first dimension  212  shown in  FIG. 2   c  and the second dimension  214  shown in  FIG. 2   d  are perpendicular to each other, while  FIG. 2   e  and  FIG. 2   f  illustrate that the first dimension  242  is perpendicular to second dimension  244 . Further, the curved first dimension  212  of  FIG. 2   c  is oriented perpendicularly to the curved second dimension  244  of  FIG. 2   f , while the trough dimension  214  of  FIG. 2   d  is oriented perpendicularly to the trough dimension  242  of  FIG. 2   e . It is noted that in  FIGS. 2   c  through  2   f  that the first inner and second inner surfaces  116 , 126  of the first and second plates  110 , 120  are not parallel as shown in  FIG. 1   a  and  FIG. 1   b , for example. In  FIGS. 2   c  through  2   f  the surfaces slope away from the first and second sockets  210 , 240 , respectively, in order to provide for a larger range of motion between the first and second plates.  
         [0036]     In  FIG. 3   a , the spacer  130  is depicted in perspective view. The spacer  130  is dimensioned so that it has a curved or convex upper surface  310  and a curved or convex lower surface  320 , respectively, corresponding with the opposing concave surfaces in the upper end plate  110  and the lower end plate.  
         [0037]     As shown in  FIG. 3   a , the curved upper surface  310  is bordered along its curved edge by a pair of first sides  312 ,  314  that are parallel to each other and along its flat edge by a pair of second sides  316 ,  318  that are parallel to each other and perpendicular to the pair of first sides  312 ,  314 . The orientation of the pair of first sides  312 ,  314  to the pair of second sides  316 ,  318  is such that the curved upper edges  322 ,  324  of the first sides  312 ,  314  extend toward the ends of the flat edges  321 ,  323  of the pair of second sides  316 ,  318 . The curved lower edges  326 ,  328  extend to meet the ends of the flat edges  325 ,  327  of the first sides  312 ,  314 .  
         [0038]      FIG. 3   b  and  FIG. 3   c  show cross-sections of the spacer  130 , shown in  FIG. 3   a . The cross-section of  FIG. 3   b  is taken at a 90° angle from the cross-section shown in  FIG. 3   c .  FIG. 3   b  is taken through a plane parallel to the ends  312 ,  314  and  FIG. 3   c  is taken through a plane parallel to ends  316 ,  318 . The spacer  130  has a concave upper surface  310  and a concave lower surface  320  and pairs of parallel sides  312 ,  314  and  314 ,  318 .  
         [0039]      FIG. 4   a  and  FIG. 4   b  show sections for an embodiment of implant  100 .  FIG. 4   a  shows a cross-section of implant  100  in its assembled condition taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body of a patient after implant  100  was inserted.  FIG. 4   b  shows a cross-section of implant  100  in its assembled condition taken at 90° from the cross-section shown in  FIG. 4   a , which is parallel to the frontal (coronal) plane, or perpendicular to the sagittal plane of the body of a patient after implant  100  was inserted. The implant  100  has a first upper end plate  110  that is configured to mate with a first vertebra and a second lower end plate  120  that is configured to mate with a second vertebra. The spacer  130  sits between the upper end plate  110  and the lower end plate  120 . As previously mentioned, the first upper axis  217  is an axis of articulation for first end plate  110  about the spacer  130  for this embodiment, while the first lower axis  247  is an axis of articulation of the lower end plate  120  about the spacer  130 . Further, first upper axis  217  is perpendicular to the first lower axis  247 .  FIG. 4   a , in particular, indicates how the first and second keels,  114 , 124 , are aligned with and support the lateral axis of articulation defined by the first upper axis  217 . The first and second keels  114 , 124  in this orientation offers substantial stability during extension and flexion for implant  100  inserted between the vertebrae of a patient. As in all of the embodiments described herein, the keels are about perpendicular to the sagittal plane of the body of a patient and suitable for lateral insertion into the spine of a patient.  
         [0040]      FIG. 5   a  through  FIG. 5   c  show representations for an another embodiment of implant  100 .  FIG. 5   a  and  FIG. 5   b  show the first and second inner surfaces,  116 , 126 , of the first and second endplates of another embodiment of implant  100 . It should be noted that this additional embodiment of Implant  100  has the features described previously described for  FIG. 2   a  and  FIG. 2   b . Similarly,  FIG. 5   c  and  FIG. 5   d  are sections that are analogous to the sections of a first embodiment shown for  FIG. 4   a  and  FIG. 4   b , respectively.  
         [0041]      FIG. 5   a  shows a perspective view of an embodiment of the first inner surface  116  of the first or upper end plate  110  of implant  100 . The first inner surface  116  of the upper end plate  110  has a first socket or first cavity  210  formed therein. In the embodiment of  FIG. 5   a , the first socket  210  has a concave hemispherical surface. Indicated in  FIG. 5   a  are two axes,  217 , 219 . The first upper axis  217  intersects the first upper plate  110  in an RL to LL orientation. The second upper axis  219  is perpendicular to the first upper axis  217 , and intersects the upper plate  110  in an A to P orientation. The two axes intersect at first, or upper point  119 . The first socket  210  allows the first end plate  110  to pivot or rotate on spacer  130  about the first point  119 .  FIG. 5   b  shows a perspective view of an embodiment of the second inner surface  126  of the second or lower end plate  120  of implant  100 . The second inner surface  126  of the lower end plate  120  has a second socket or first cavity  240  formed therein. In the embodiment of  FIG. 5   b , the second socket  240  has a concave hemispherical surface. Indicated in  FIG. 5   b  are two axes,  247 , 249 . The first lower axis  247  intersects the second, or lower plate  120  in an RL to LL orientation. The second lower axis  249  is perpendicular to the first upper axis  247 , and intersects the lower plate  120  in an A to P orientation. The two axes intersect at second, or lower point  121 . The second socket  240  allows the second lower end plate  120  to pivot or rotate on spacer  130 , about the lower point  121 .  
         [0042]     In the alternative embodiment shown in  FIG. 5   a  and  FIG. 5   b , it is noted that the first and second keels  114 , 124  are aligned with and support the first and second points and  119 ,  121 , which are an points of articulation for first end plate  110  and the second end plate, respectively about the spacer  130  for this embodiment. The keels are oriented so as to be about perpendicular to the sagittal plane of a patient when the implant is inserted using a lateral approach.  
         [0043]      FIG. 5   c  shows a cross-section of implant  100  in its assembled condition taken along a plane that would correspond to a plane that is parallel to the median sagittal plane of the body of a patient after implant  100  was inserted.  FIG. 5   d  shows a cross-section of implant  100  in its assembled condition taken at 90° from the cross-section shown in  FIG. 5   c ., which is parallel to the frontal (coronal) plane, or perpendicular to the sagittal plane of the body of a patient after implant  100  was inserted. The implant  100  has a first upper end plate  110  that is configured to mate with a first vertebra and a second lower end plate  120  that is configured to mate with a second vertebra. The spacer  130  sits between the upper end plate  110  and the lower end plate  120 . As previously mentioned, the first and second upper axes  217 , 219  define a first point of articulation for first end plate  110  about the spacer  130  for this embodiment, while the first and second lower axes  247 , 249  define a second point of articulation of the lower end plate  120  about the spacer  130 .  FIG. 5   c  and  FIG. 5   d  indicate how the first and second keels,  114 , 124 , are aligned with and support the first and second points of articulation  119 , 121 . The first and second keels  114 , 124  in this orientation offer substantial stability during extension and flexion for implant  100  inserted between the vertebrae of a patient.  
         [0044]     It is to be understood that the embodiments of the disclosed implant can be made of medical grade titanium, stainless steel or cobalt chrome. Other materials that have appropriate structural strength and that are suitable for implantation into a patient can also be used.  
         [0045]     Alternatively, the spacer  130  can be made out of a polymer, and more specifically, the polymer is a thermoplastic with the other components made of the materials specified above. Still more specifically, the polymer is a polyketone known as polyetheretherketone (PEEK). Still more specifically, the material is PEEK  450 G, which is an unfilled PEEK approved for medical implantation available from Victrex of Lancashire, Great Britain. (Victrex is located at www.matweb.com or see Boedeker www.boedeker.com). Other sources of this material include Gharda located in Panoli, India (www.ghardapolvmers.com). The spacer  130  can be formed by extrusion, injection, compression molding and/or machining techniques. This material has appropriate physical and mechanical properties and is suitable for carrying and spreading the physical load between the spinous process. Further in this embodiment, the PEEK has the following additional approximate properties:  
                                                   Property   Value                           Density   1.3 g/cc           Rockwell M    99           Rockwell R   126           Tensile Strength    97 Mpa           Modulus of Elasticity   3.5 Gpa           Flexural Modulus   4.1 Gpa                      
 
         [0046]     It should be noted that the material selected may also be filled. For example, other grades of PEEK are also available and contemplated, such as 30% glass-filled or 30% carbon-filled, provided such materials are cleared for use in implantable devices by the FDA, or other regulatory body. Glass-filled PEEK reduces the expansion rate and increases the flexural modulus of PEEK relative to that which is unfilled. The resulting product is known to be ideal for improved strength, stiffness, or stability. Carbon-filled PEEK is known to enhance the compressive strength and stiffness of PEEK and lower its expansion rate. Carbon-filled PEEK offers wear resistance and load carrying capability.  
         [0047]     The spacer can also be comprised of polyetherketoneketone (PEKK). Other material that can be used include polyetherketone (PEK), polyetherketoneether-ketoneketone (PEKEKK), and polyetheretherketoneketone (PEEKK), and, generally, a polyaryletheretherketone. Further, other polyketones can be used as well as other thermoplastics.  
         [0048]     Reference to appropriate polymers that can be used in the spacer can be made to the following documents, all of which are incorporated herein by reference. These documents include: PCT Publication WO 02/02158 A1, dated Jan. 10, 2002, entitled “Bio-Compatible Polymeric Materials;” PCT Publication WO 02/00275 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials;” and, PCT Publication WO 02/00270 A1, dated Jan. 3, 2002, entitled “Bio-Compatible Polymeric Materials.” 
         [0049]     In operation, implant  100  enables a forward bending movement and a rearward bending movement by sliding the upper end plate  110  forward and backward over the spacer  130  relative to the lower end plate  120 . This movement is shown as rotation about the axis  217  in  FIG. 4   a  and  FIG. 4   c.    
         [0050]     The implant  100  enables a right lateral bending movement and a left lateral bending movement by sliding the lower end plate  120  side-to-side over the spacer  130  relative to upper end plate  110 . This movement is shown as rotation about the axis  219  in  FIG. 4   b  and  FIG. 4   d . Additionally, with a loose fit between the first end plate, the second end plate and the spacer, rotational or twisting motion along an axis that is along the spine and perpendicular to the first and second plates is accomplished.  
         [0051]      FIG. 6  is a block diagram showing the basic steps of the method of laterally inserting the implant  100 . First the spine is exposed through a lateral access  610 , then the intervertebral disk is removed if necessary laterally  620 . The implant is then inserted laterally  630  between two vertebrae and the wound is closed  640 . This procedure can be followed for either a left lateral approach or right lateral approach. For a left lateral approach, the teeth  115 , 125  of upper and lower keels  114 ,  124  would be pointed towards the left lateral face of the device in order to aid in retaining implant  100  in place. For a right lateral approach, the teeth would point towards the right lateral face of the device.  
         [0052]     Additional steps, such as cutting channels into the vertebral bodies to accept the first and second keels  114 , 124  of the first and second end plates  110 , 120  and assembling implant  100  by inserting the spacer  130  between the upper and lower end plates  110 , 120  prior to installation can also be performed without departing from the scope of what is disclosed.  
         [0053]     It is to be appreciated that although the first and second plates are depicted as having concave cavities and the spacer is depicted as having two convex surfaces that are oriented about perpendicular to each other, that other embodiments the disclosed implant can have other configurations. For example, the first and second plates can have convex protrusions, such as, for example, cylindrical protrusions that are shaped to mate with concave surfaces of a spacer, with the concave surfaces of the spacer oriented about perpendicular to each other. In this embodiment, the convex protrusions of the first and the second plates could preferably each have a pair of parallel side walls that would act as the side walls in the depicted embodiments in order to block motion of the spacer. Also, it is to be appreciated that in still another embodiment, the spacer can have upper and lower truncated convex spherical surfaces with two pairs of side walls, instead of cylindrical surfaces with side walls, and be in the scope and spirit of what is disclosed herein. In this embodiment, each of the first and second plates would have truncated concave spherical surfaces with a pair of side walls. In still a further embodiment, each of the first and second plates could have spherical protrusions with a pair of side walls and the spacer could have first and second spherical concave surfaces with two pairs of side walls joining the first and second spherical concave surfaces. Still alternatively, the first end plate can have a concave surface and blocking side walls and the mating portion of the spacer can be convex with the second plate having a convex protrusion with the mating portion of the spacer, or being concave, with blocking side walls.  
         [0054]     What has been disclosed herein has been provided for the purposes of illustration and description. It is not intended to be exhaustive or to limit what is disclosed to the precise forms described. Many modifications and variations will be apparent to the practitioner skilled in the art. What is disclosed was chosen and described in order to best explain the principles and practical application of the embodiments described herein, thereby enabling others skilled in the art to understand the various embodiments and various modifications that are suited to the particular use contemplated. It is intended that the scope of what is disclosed be defined by the following claims and their equivalence.