Abstract:
A spinal disc prosthesis comprising: (a) a distal spinal prosthetic comprising at least two separable portions; (b) a proximal spinal prosthetic comprising at least two separable portions, where at least one of the two separable portions of at least one of the distal spinal prosthetic and the proximal spinal prosthetic includes a partial loop appendage at least partially defining a spinal nerve canal.

Description:
RELATED ART 
       [0001]    1. Field of the Disclosure 
         [0002]    The present disclosure relates to orthopaedic implants and, specifically, to spinal implants for use in joint replacement and revision procedures in the treatment of spinal pathologies. The disclosure also pertains to the development of an artificial spinal joint that is designed to be inserted from a minimally invasive approach to the spine. 
         [0003]    2. Brief Discussion of Related Art 
         [0004]    At present, spinal surgery has become the most rapidly growing area in orthopaedics. Previously, patients having disc degeneration would undergo a spinal fusion to offset pain in the neck or lower back. More recently, artificial discs have been developed to replace degenerated discs and facet replacements have been introduced to replace failing facets. Unfortunately, disc replacements have not yet proven to be successful and facet replacements are in their infancy. Most facet replacements are performed using an investigational device exemption (IDE) that includes removal of present facet bones and replacement by a metal facet that is screwed into the vertebral bones. It is hypothesized that these types of replacements will fail dramatically, since the vertebral bodies do not have extensive bone stock and induced torques will loosen these devices. 
         [0005]    Disc replacements and facet replacements are also implanted through an “open” technique, which requires making a large incision along the middle of the back or along the abdomen. The surgeon then cuts and pulls back spinal muscles and tissue to get to the vertebrae and disc space in order to position the implanted devices. These surgical techniques can cause tissue trauma and damage due to muscle, ligament, tendon, bone, and local nerve injury from performing this surgical procedure. This may lead the body to biomechanically rely more on the facet replacements, thereby affecting facet stability. In contrast, the use of minimally invasive surgical techniques has been hypothesized to reduce these negative consequences. 
       INTRODUCTION TO THE INVENTION 
       [0006]    The instant disclosure includes a total spine replacement optionally having both disc and facet replacement using a total joint-type procedure. Initially, minimal bone is resected distally from the upper vertebral body and proximally from the distal vertebral body. Then, the bearing surfaces of the facets are removed from the bone. A distal disc replacement is mounted to the upper vertebral body and a proximal disc replacement is mounted to the lower vertebral body. Both of these disc replacement devices may be multi-piece implants that join together, optionally in the center. Polyethylene materials (such as for bearing surfaces), or other known or developed materials, may then mounted to the proximal and distal devices to replace the degenerated disc. The replacement disc material may be mounted in a fixed orientation or may exhibit mobile bearing characteristics. Polyethylene inserts, or another known or developed material, may also be rigidly attached to the facets as facet replacements. Accordingly, the exemplary embodiments may be utilized to replace one or both of the disc and the facets. 
         [0007]    It is a first aspect of the present invention to provide a spinal disc prosthesis comprising: (a) a distal spinal prosthetic comprising at least two separable portions; and (b) a proximal spinal prosthetic comprising at least two separable portions, where at least one of the two separable portions of at least one of the distal spinal prosthetic and the proximal spinal prosthetic includes a partial loop appendage at least partially defining a spinal nerve canal. 
         [0008]    In a more detailed embodiment of the first aspect, the distal spinal prosthetic includes a first bearing insert mounted to at least one of the at least two separable portions, the first bearing insert including a bearing surface interposing the distal spinal prosthetic and the proximal spinal prosthetic. In yet another more detailed embodiment, at least one of the complementary halves includes a cavity for receiving a projection of the first bearing insert to mount the first bearing insert to at least one of the at least two separable portions. In a further detailed embodiment, at least one of the complementary halves includes a projection received within a cavity of the first bearing insert to mount the first bearing insert to at least one of the at least two separable portions. In still a further detailed embodiment, the partial loop appendage extends from a rear surface of at least one of the distal spinal prosthetic and the proximal spinal prosthetic. In a more detailed embodiment, the partial loop appendage extends from a top surface of at least one of the distal spinal prosthetic and the proximal spinal prosthetic. In a more detailed embodiment, the partial loop appendage extends from a bottom surface of at least one of the distal spinal prosthetic and the proximal spinal prosthetic. In another more detailed embodiment, the partial loop appendage includes a helical portion. In yet another more detailed embodiment, the partial loop appendage extends from a side surface of at least one of the distal spinal prosthetic and the proximal spinal prosthetic. In still another more detailed embodiment, both the distal spinal prosthetic and the proximal spinal prosthetic include at least one partial loop appendage at least partially defining the spinal nerve canal. 
         [0009]    In yet another more detailed embodiment of the first aspect, both the distal spinal prosthetic and the proximal spinal prosthetic include a pair of partial loop appendages at least partially defining the spinal nerve canal. In still another more detailed embodiment, the pair of partial loop appendages of the proximal spinal prosthetic includes an arcuate diameter less than an arcuate diameter of the pair of partial loop appendages of the distal spinal prosthetic. In a further detailed embodiment, interior surfaces of the pair of partial loop appendages of the distal spinal prosthetic provides camming surfaces for exterior surfaces of the pair of partial loop appendages of the proximal spinal prosthetic. In still a further detailed embodiment, the distal spinal prosthetic includes a pair of partial loop appendages at least partially defining the spinal nerve canal. In a more detailed embodiment, the proximally spinal prosthetic includes a pair of partial loop appendages at least partially defining the spinal nerve canal. In a more detailed embodiment, the partial loop appendage includes a facet replacement. In another more detailed embodiment, the proximal spinal prosthetic includes a first bearing insert mounted to at least one of the at least two separable portions, the first bearing insert including a bearing surface interposing the distal spinal prosthetic and the proximal spinal prosthetic. In yet another more detailed embodiment, at least one of the complementary halves includes a cavity for receiving a projection of the first bearing insert to mount the first bearing insert to at least one of the at least two separable portions. 
         [0010]    In yet a further detailed embodiment of the first aspect, at least one of the complementary halves includes a projection received within a cavity of the first bearing insert to mount the first bearing insert to at least one of the at least two separable portions. In still another more detailed embodiment, at least one of the distal spinal prosthetic and the proximal spinal prosthetic includes a twisted appendage including a facet interface pad. In a further detailed embodiment, the first bearing insert is a fixed bearing insert with respect to at least one of the at least two separable portions. In still a further detailed embodiment, the first bearing insert is a mobile bearing insert with respect to at least one of the at least two separable portions. 
         [0011]    It is a second aspect of the present invention to provide an intervertebral prosthetic comprising a first spinal implant including a vertebral body portion, the vertebral body portion at least partially replicating the horizontal cross-section of a vertebral body and including a vertebral contacting surface adapted to contact a native vertebral body, the first spinal implant also including a disc portion including a bearing surface, the first spinal implant also including an appendage at least partially defining a spinal nerve conduit. 
         [0012]    In a more detailed embodiment of the second aspect, the first implant includes a pair of appendages at least partially defining a spinal nerve conduit. In yet another more detailed embodiment, the appendage includes a helical portion. In a further detailed embodiment, the appendage includes a twisted portion. In still a further detailed embodiment, the appendage includes a facet replacement portion. In a more detailed embodiment, the vertebral body portion is a separable component from the disc portion. In a more detailed embodiment, the vertebral body portion is fabricated from a metal and the disc portion is fabricated from a polymer. In another more detailed embodiment, the vertebral body portion includes a cavity that receives a projection of the disc portion to mount the vertebral body portion to the disc portion. In yet another more detailed embodiment, the disc portion includes a cavity that receives a projection of the vertebral body portion to mount the vertebral body portion to the disc portion. In still another more detailed embodiment, the vertebral body portion is at least one of glued and cemented to the disc portion. 
         [0013]    It is a third aspect of the present invention to provide an intervertebral implant comprising: (a) a first implant adapted to mate with a first vertebra, where the first implant includes an arm operative to at least partially define a spinal nerve passage; and (b) a second implant adapted to mate with a second vertebra consecutive to the first vertebra, where the second implant includes an appendage operative to cooperate with the arm of the first implant to at least partially define the spinal nerve passage. 
         [0014]    In a more detailed embodiment of the third aspect, the first implant includes a first bearing insert having a first bearing surface interposing the first vertebra and the second vertebra. In yet another more detailed embodiment, the second implant includes a second bearing insert having a second bearing surface interposing the first vertebra and the second vertebra, the second bearing surface adapted to interface with the first bearing surface of the first implant. In a further detailed embodiment, the first implant comprises a first vertebral segment and a first disc segment mounted to one another. In still a further detailed embodiment, the first vertebral segment includes a cavity receiving a projection from the first disc segment to mount the first vertebral segment to the first disc segment. In a more detailed embodiment, the first disc segment includes a cavity receiving a projection from the first vertebral segment to mount the first vertebral segment to the first disc segment. In a more detailed embodiment, the first implant comprises at least two component parts simulating the horizontal cross-section of a vertebral body. In another more detailed embodiment, the at least two component parts comprise complementary halves of a base plate. In yet another more detailed embodiment, the base plate halves are mounted to a bearing insert. In still another more detailed embodiment, the second implant comprises a second vertebral segment and a second disc segment mounted to one another. 
         [0015]    In yet another more detailed embodiment of the third aspect, the first vertebral segment includes a cavity receiving a projection from the first disc segment to mount the first vertebral segment to the first disc segment. In still another more detailed embodiment, the first disc segment includes a cavity receiving a projection from the first vertebral segment to mount the first vertebral segment to the first disc segment. In a further detailed embodiment, the second implant comprises at least two component parts simulating the horizontal cross-section of a vertebral body. In still a further detailed embodiment, the at least two component parts comprise complementary halves of a base plate. In a more detailed embodiment, the base plate halves are adapted to receive a bearing insert. In a more detailed embodiment, the arm of the first implant extends from a rear surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In another more detailed embodiment, the arm of the first implant extends from a top surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In yet another more detailed embodiment, the arm of the first implant extends from a bottom surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. 
         [0016]    In yet further more detailed embodiment of the third aspect, the arm of the first implant extends from a side surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In still another more detailed embodiment, the arm of the first implant includes a helical portion. In a further detailed embodiment, the appendage of the second implant extends from a rear surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In still a further detailed embodiment, the appendage of the second implant extends from a top surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In a more detailed embodiment, the appendage of the second implant extends from a bottom surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In a more detailed embodiment, the appendage of the second implant extends from a side surface a base plate at least partially simulating the horizontal cross-section of a vertebral body. In another more detailed embodiment, the appendage of the second implant includes a helical portion. In yet another more detailed embodiment, the first implant includes a pair of arms operative to at least partially define a pair of spinal nerve passages, and the second implant includes a pair of appendages operative to at least partially define the pair of spinal nerve passages. 
         [0017]    In still a further more detailed embodiment of the third aspect, each of the pair of arms includes at least one of a twisted portion and a helical portion, and each of the pair of appendages includes at least one of a twisted portion and a helical portion. In still another more detailed embodiment, each of the pair of arms includes a helical portion, each of the pair of appendages includes a helical portion, and each of the pair of arms of the first implant includes an arcuate diameter less than an arcuate diameter of the pair of appendages of the second implant. In a further detailed embodiment, the arm includes a facet replacement. In still a further detailed embodiment, the appendage includes a facet replacement. 
         [0018]    It is a fourth aspect of the present invention to provide a spinal implant comprising: (a) a first platform allowing fixation to a first vertebra; (b) a second platform allowing fixation to a second vertebra immediately following the first vertebra; and (c) a bearing interposing the first platform and the second platform, where at least one of the first platform, the second platform, and the bearing includes an arcuate projection at least partially defining a spinal nerve passageway. 
         [0019]    It is a fifth aspect of the present invention to provide a spinal disc prosthesis comprising: (a) a distal spinal prosthetic comprising a distal base plate and a distal bearing; and (b) a proximal spinal prosthetic comprising a proximal base plate and a proximal bearing, where at least one of the distal spinal prosthetic and the proximal spinal prosthetic includes an appendage at least partially defining a spinal nerve canal. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  is a profile view of an exemplary human spinal column. 
           [0021]      FIG. 2  is an overhead view of a lumber vertebrae. 
           [0022]      FIG. 3  is a profile view of a pair of lumbar vertebrae. 
           [0023]      FIG. 4  is an overhead view of a pair of lumbar vertebrae interposed by a first exemplary spinal implant embodiment of the instant disclosure. 
           [0024]      FIG. 5  a left profile view of the first exemplary spinal implant embodiment between the consecutive lumbar vertebrae of  FIG. 4 . 
           [0025]      FIG. 6  an elevated perspective view from the left front of the first exemplary spinal implant embodiment between the consecutive lumbar vertebrae of  FIG. 4 . 
           [0026]      FIG. 7  a frontal view of the first exemplary spinal implant embodiment between the consecutive lumbar vertebrae of  FIG. 4 . 
           [0027]      FIG. 8  an elevated perspective view from the right front of the first exemplary spinal implant embodiment between the consecutive lumbar vertebrae of a human body. 
           [0028]      FIG. 9  is an elevated perspective view from the right rear of the first exemplary spinal implant embodiment between the consecutive lumbar vertebrae of a human body. 
           [0029]      FIG. 10  is a bottom view of an exemplary proximal component part of the first exemplary spinal implant embodiment. 
           [0030]      FIG. 11  is a top view of an exemplary proximal component part of the first exemplary spinal implant embodiment. 
           [0031]      FIG. 12  is a bottom view of exemplary proximal base plate halves, separated, of the first exemplary spinal implant embodiment. 
           [0032]      FIG. 13  is a bottom view of the exemplary proximal base plate halves of  FIG. 12 , joined. 
           [0033]      FIG. 14  is a bottom view of exemplary proximal insert halves, separated, of the first exemplary spinal implant embodiment. 
           [0034]      FIG. 15  is a right profile view of the exemplary proximal insert halves of  FIG. 14 , joined. 
           [0035]      FIG. 16  a top view of an exemplary distal component part of the first exemplary spinal implant embodiment. 
           [0036]      FIG. 17  is a top view of exemplary distal base plate halves, joined, of the first exemplary spinal implant embodiment. 
           [0037]      FIG. 18  is a top view of exemplary distal base plate halves, separated, of the first exemplary spinal implant embodiment. 
           [0038]      FIG. 19  is a top view of exemplary distal insert halves, separated, of the first exemplary spinal implant embodiment. 
           [0039]      FIG. 20  is a left profile view of the exemplary distal insert halves of  FIG. 19 , joined. 
           [0040]      FIG. 21  is a left profile view of alternate exemplary distal insert halves, joined. 
           [0041]      FIG. 22  is a frontal view of the alternate exemplary distal insert halves of  FIG. 21 . 
           [0042]      FIG. 23  is a top view of an alternate exemplary distal base plate. 
           [0043]      FIG. 24  is a top view of a further alternate exemplary distal base plate. 
           [0044]      FIG. 25  is a left profile view of an alternate exemplary distal component. 
           [0045]      FIG. 26  is a right profile view of two consecutive lumbar vertebrae. 
           [0046]      FIG. 27  is a right profile view of the two consecutive lumbar vertebrae of  FIG. 26  being notched out to accept a spinal implant. 
           [0047]      FIG. 28  is a bottom right lowered perspective view showing the exemplary positioning of a proximal base plate right half with respect to a proximal lumbar vertebra. 
           [0048]      FIG. 29  is a bottom left lowered perspective view showing the exemplary positioning of the proximal base plate right half of  FIG. 28  with respect to both proximal and distal lumbar vertebrae. 
           [0049]      FIG. 30  is a bottom right lowered perspective view showing the exemplary positioning of a proximal base plate left, half with respect to both proximal and distal lumbar vertebrae. 
           [0050]      FIG. 31  is a right profile view showing the exemplary positioning of proximal base plate halves with respect to both proximal and distal lumbar vertebrae. 
           [0051]      FIG. 32  is an elevated perspective view from the left rear showing the exemplary positioning of a distal base plate right half with respect to a distal lumbar vertebra. 
           [0052]      FIG. 33  is a right profile view showing the exemplary positioning of proximal and distal base plate halves with respect to both proximal and distal lumbar vertebrae. 
           [0053]      FIG. 34  is a right profile view showing the exemplary positioning of proximal and distal base plate halves, as well a proximal insert halves, with respect to both proximal and distal lumbar vertebrae. 
           [0054]      FIG. 35  is a right profile view showing the exemplary positioning of proximal and distal base plate halves, as well a proximal and distal insert halves, with respect to both proximal and distal lumbar vertebrae. 
           [0055]      FIG. 36  is an elevated perspective view from the right rear showing the exemplary positioning of proximal and distal base plate halves, as well a proximal and distal insert halves, with respect to both proximal and distal lumbar vertebrae. 
           [0056]      FIG. 37  is a right profile view showing the exemplary positioning of proximal and distal base plate halves, as well a proximal and distal insert halves, with respect to both proximal and distal lumbar vertebrae as well as the spinal column nerves extending through a right side opening defined by the spinal implant. 
           [0057]      FIG. 38  is an elevated perspective view from the right front showing the exemplary positioning of proximal and distal base plate halves, as well a proximal and distal insert halves, with respect to both proximal and distal lumbar vertebrae as well as the spinal column nerves extending through a right side opening defined by the spinal implant. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    The exemplary embodiments of the present disclosure are described and illustrated below to encompass spinal prosthetics and associated methods of fabricating and implanting spinal prosthetics. Of course, it will be apparent to those of ordinary skill in the art that the embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present disclosure. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present disclosure. For example, while the exemplary embodiments are described with respect to lumbar spinal implants, those skilled in the art will understand that the following aspects of the disclosure encompass all spinal implants, including, but not limited to, cervical spinal implants. 
         [0059]    As shown in  FIG. 1 , the human spinal column  10  is comprised of a series of thirty-three stacked vertebrae divided into five regions. The cervical region includes seven vertebrae  12 , known as C 1 -C 7 , the thoracic region includes twelve vertebrae  14 , known at T 1 -T 12 , the lumbar region contains five vertebrae  16 , known as L 1 -L 5 , the sacral region is comprised of five vertebrae  18 , known as S 1 -S 5 , and the coccygeal region contains four vertebrae  20 , known as Co 1 -Co 4 . 
         [0060]      FIG. 2  shows an exemplary lumbar vertebra  16 . Although lumbar vertebrae  16  vary somewhat according to location, these vertebrae share many features in common with most other vertebrae. Each vertebra  16  includes a vertebral body  22  and pedicles  24  that extend from each side of the vertebral body  22  to form a vertebral arch  26 . At the posterior end of each pedicle  24 , the vertebral arch  26  transitions into laminae  28 . The laminae  28  fuse with each other to form a spinous process  30  that allow for muscle and ligamentous attachment. 
         [0061]    Two transverse processes  32  thrust laterally outward from each side of the junction of the pedicle  24  with the lamina  28 . The transverse processes  32  serve as levers for the attachment of muscles to the vertebrae  16 . Four articular processes, two superior  34  and two inferior  36 , also rise from the junctions of the pedicles  24  and the laminae  28 . The superior articular processes  34  are sharp oval plates of bone rising upward on each side from the union of the pedicle  24  with the lamina  28 . The inferior processes  36  are oval plates of bone that extend in an inferior direction on each side. Both processes  34 ,  36  include facets, with the superior articular facet  38  facing upward or superiorly, while the inferior articular facet faces downward or inferiorly. 
         [0062]    As shown in  FIG. 3 , when adjacent lumbar vertebrae  16  are aligned, the facets  38 , which are capped with smooth articular cartilage, interlock to form a facet joint, commonly referred to as a zygapophysial joint. The facet joint is composed of a superior half and an inferior half. The superior half is formed by the vertebral level below the joint, and the inferior half is formed by the vertebral level above the joint. For example, in the L 3 -L 4  facet joint, the superior portion of the joint is formed by a bony structure on the L 4  vertebra (e.g., a superior articular surface and supporting bone on the L 4  vertebra), and the inferior portion of the joint is formed by a bony structure on the L 3  vertebra (e.g., an inferior articular surface and supporting bone on the L 3  vertebra). As also shown in  FIG. 3 , an intervertebral disc  42  located between each pair of vertebrae  16  permits relative movement between the vertebral bodies  22 . Thus, the structure and alignment of the vertebrae  16  permit a range of movement relative to each other. 
         [0063]    Referencing  FIGS. 4-9 , a first exemplary lumbar spinal implant  100  includes a proximal component  102  and a complimentary distal component  104  cooperating to provide a lumbar disc replacement prosthetic. The proximal component  102  includes a two-piece base plate  106 ,  108  and a two-piece insert  110 ,  112  mounted to the base plate  106 ,  108 . In exemplary from, the base plate comprises substantially mirror image halves  106 ,  108  that are joinable by way of a locking system. It should be understood, however, that the proximal component  102  and the distal component  104  may each comprise a single part or a compilation of three or more complimentary parts. 
         [0064]    Referring to  FIGS. 10-13 , each proximal plate half  106 ,  108  includes a substantially planar top surface  130  that is generally operative to cross-sectionally duplicate the vertebral body  22  (See e.g.,  FIG. 28 ) against which it is mounted. As will be discussed hereafter, the vertebral body  22  is resurfaced in preparation for receiving the proximal plate halves  106 ,  108 . For purposes of explanation only, each plate half  106 ,  108  includes a continuous perimeter  132  comprising a front face  134  arcuately transitioning to a side face  136 , with a projecting ledge  138 , that transitions into a rear face  140 . Both the front face  134  and the rear face  140  transition at generally a right angle to an engagement face  142 , where the engagement face  142  of each plate half  106 ,  108  abuts the other. A bottom surface  131  of each plate half  106 ,  108  includes a lateral groove  146  for receiving a projection  160  (see  FIG. 15 ) from one of the proximal inserts  110 ,  112 . In this exemplary embodiment, the groove  146  exhibits an inverted T-shape cross-section to receive the T-shape projection  160  of the inserts  110 ,  112 . It is also within the scope of the disclosure to utilize other shaped grooves such as, without limitation, dove-tail grooves, block grooves, and tapered grooves. 
         [0065]    Each proximal plate half  106 ,  108  also includes an arm  150  proximally extending from the projecting ledge  138 . Each arm  150  proximate the ledge  138  includes a rectangular cross-section (having front, back, and opposing sides), that transitions into a hood-shape with the width of the sides decreasing and the width of the front and rear sides increasing. The arms  150 , extending from the ledges  138 , exhibit a mild spiral  152  that terminates at a rounded end  154 . The spiral  152  arcs rearward (away from the rear face  140 ) and inward (away from the side face  136 ) to terminate proximate the inferior processes  36  of the vertebrae to which it is mounted. The spiral  152  is adapted to at least partially define an opening for egress of nerves exiting the spinal column between the vertebrae. As will be discussed in more detail hereafter, the distal component  104  also include arms that cooperate with the arms  150  of the proximal component  102  to define opposing lateral openings through which nerves exiting the spinal column may pass between the vertebrae. 
         [0066]    Referring to  FIGS. 14 and 15 , each proximal insert half  110 ,  112  cooperates to provide a flexible bushing interposing the plate halves  106 ,  108  and the distal component  104 . As discussed briefly beforehand, each insert half  110 ,  112  includes a T-shape projection  160  that is received within a corresponding groove  146  of one of the plate halves  106 ,  108 . This projection  160  extends from a substantially planar top surface  162  that abuts a bottom surface  131  of each half  106 ,  108 . Depending upon the overall size and shape of the insert halves  110 ,  112 , each half may exhibit a front face  164 , arcuately transitioning to a side face  166  that transitions into a rear face  168 . Both the front face  164  and the rear face  168  transition at generally a right angle to an engagement face  170 , where the engagement face  170  of each insert half  110 ,  112  abuts the other. 
         [0067]    In this exemplary embodiment, the insert halves  110 ,  112  cooperate to form a generally dome-shaped bearing surface  172 . As will be discussed in more detail hereafter, alternative shaped bearing surfaces may be utilized such as, without limitation, flat horizontal surfaces, concave surfaces, sloped flat surfaces, and sloped arcuate surfaces. This bearing surface  172  provides a surface that rides upon the bearing surface(s) of the distal component  104 . In this exemplary embodiment, the apex of the domed bearing surface  172  is proximate the engagement face  170 , however, it is also within the scope of the disclosure to include an apex within the middle of the insert, posterior of the center of the insert, anterior of the center of the insert, lateral or medial of the center of the insert. In exemplary from, the insert halves comprise substantially mirror image halves  110 ,  112  that are joinable by way of a locking system. 
         [0068]    Referencing  FIGS. 16-18 , the exemplary distal component  104  includes a two-piece base plate  186 ,  188  and a two-piece insert  190 ,  192  mounted to the base plate  186 ,  188 . In exemplary from, the base plate halves  186 ,  188  comprises substantially mirror image portions at are joinable by way of a locking system similar to that of the base plate  106 ,  108  of the proximal component  102 . 
         [0069]    Each distal plate half  186 ,  188  includes a substantially planar bottom surface that is generally operative to cross-sectionally duplicate the vertebral body  22  (See e.g.,  FIGS. 32 and 33 ) against which it is mounted. For purposes of explanation only, each plate half  186 ,  188  includes this bottom surface and a continuous perimeter  202  comprising a front face  204  arcuately transitioning to a side face  206  that transitions into a rear face  208 . Both the front face  204  and the rear face  208  transition at generally a right angle to an engagement face  212 , where the engagement face  212  of each plate half  186 ,  188  abuts the other. A top surface  214  of each half  186 ,  188  includes a lateral groove  216  for receiving a T-shape projection  230  of one of the distal inserts  190 ,  192 . In this exemplary embodiment, the groove  216  exhibits a T-shape cross-section to receive the T-shape projection  230  of the inserts  190 ,  192 . It is also within the scope of the disclosure to utilize other shaped grooves such as, without limitation, dove-tail grooves, block grooves, and tapered grooves. 
         [0070]    Each distal plate half  186 ,  188  also includes an arm  240  proximally extending from the rear face  208 . Each arm  240 , proximate the rear face  208 , includes a rectangular cross-section (having front, back, and opposing sides), that transitions into a hood-shape with the width of the sides slightly decreasing and the width of the front and rear sides increasing. Each arm  240  exhibits a mild spiral  242  that terminates at a rounded end  244 . The spiral  242  arcs rearward (away from the rear face  208 ) and inward (away from the side face  206 ) to terminate proximate the inferior processes  36  of the vertebrae above which it is mounted (see  FIG. 5 ). The spiral  242  is adapted to cooperate with the spiral  152  of the proximal component  102  to define an opening  250  (see e.g.,  FIGS. 33-35 ) for egress of nerves exiting the spinal column between the vertebrae. 
         [0071]    In exemplary form, plate halves  106 ,  108 ,  186 ,  188  may be fabricated from any surgical grade metal or metal alloy, plastic, ceramic, or any combination of the foregoing. In this first exemplary embodiment, however, the plate halves  106 ,  108 ,  186 ,  188  are fabricated from titanium or a titanium alloy. 
         [0072]    Referring to  FIGS. 19 and 20 , each distal insert half  190 ,  192  cooperates to provide a bushing interposing the plate halves  186 ,  188  and the proximal component  102 . As discussed briefly beforehand, each distal insert half  190 ,  192  includes a T-shape projection  230  that is received within a corresponding groove  216  of one of the distal plate halves  186 ,  188 . This projection  230  extends from a substantially planar surface  252  that abuts a bottom surface of each distal plate half  186 ,  188 . Depending upon the overall shape of the distal insert halves  190 ,  192 , each half may exhibit a front face  264 , arcuately transitioning to a side face  266  that transitions into a rear face  268 . Both the front face  264  and the rear face  268  transition at generally a right angle to an engagement face  270 , where the engagement face  270  of each insert half  190 ,  192  abuts the other when the halves are joined. 
         [0073]    In this exemplary embodiment, the distal insert halves  190 ,  192  cooperate to form a concaved bearing surface  272 . As will be discussed in more detail hereafter, alternative shaped bearing surfaces may be utilized such as, without limitation, flat horizontal surfaces, convex surfaces, sloped flat surfaces, and sloped arcuate surfaces. This bearing surface  272  provides a surface that rides against the bearing surface(s) of the proximal component  102 . In exemplary from, the insert halves comprise substantially mirror image halves  190 ,  192  that are joinable by way of a locking system analogous to the locking system of the proximal insert halves  110 ,  112 . 
         [0074]    In exemplary form, the insert halves  110 ,  112 ,  190 ,  192  may be fabricated from any surgical grade metal or metal alloy, plastic, rubber, gel, ceramic, or any combination of the foregoing. In this first exemplary embodiment, however, the insert halves  110 ,  112 ,  190 ,  192  are fabricated from high molecular weight polyethylene. 
         [0075]    The foregoing exemplary insert halves  110 ,  112 ,  190 ,  192  and plate halves  106 ,  108 ,  186 ,  188  include projections  114  and corresponding cavities  116  utilized to friction fit and lock the halves together in a proper orientation. Alternatively, the insert halves  110 ,  112 ,  190 ,  192  and plate halves may  106 ,  108 ,  186 ,  188  be formed together a unitary piece or each fabricated from two or more component parts. In addition, or in the alternative, the insert halves  110 ,  112 ,  190 ,  192  and plate halves  106 ,  108 ,  186 ,  188  may be cemented, glued, screwed, or otherwise fastened together. 
         [0076]    Referring to  FIGS. 21-24 , an alternate exemplary distal component includes a single piece insert  306  repositionably mounted to a single piece distal base plate  308 . In this alternate exemplary component  304 , the insert  306  includes a frustaconical projection  304  extending from its underside that is adapted to be received within cavity  310  formed within a top surface  312  of the distal base plate  308 . In exemplary form, the cavity  310  may be frustaconical to allow for rotational movement of the insert  306  with respect to the base plate  308 . In a further exemplary distal base plate  308 ′, the cavity comprises a longitudinal trench  314  extending partially from front to back and having sidewalls  316  that are tapered to approximate the angled nature of the frustaconical projection  304 . This longitudinal trench  314  allows the insert  306  to move forward and backward, as well as rotate, thereby providing two degrees of movement. 
         [0077]    Similar to the distal insert halves  190 ,  192  discussed as part of the first exemplary embodiment, the single piece insert  306  includes a dished bearing surface  318  on which a proximal insert would ride. The underside  320  is generally planar and adapted to sit upon a substantially planar top surface  322  of the distal base plate  308 . Those skilled in the art will understand that the precise shape of the bearing surface  318  may be modified. For example, the bearing surface  318  may be flat horizontal surfaces, concave surfaces, sloped flat surfaces, and sloped arcuate surfaces. 
         [0078]    Similar to the two-piece base plate  186 ,  188  halves discussed as part of the first exemplary embodiment, the single piece base plate  308  includes a pair of spaced apart arms  330  proximally extending from the rear face  332 . Each arm  330 , proximate the rear face  332 , includes a rectangular cross-section (having front, back, and opposing sides), that transitions into a hood-shape with the width of the sides slightly decreasing and the width of the front and rear sides increasing. Each arm  330  exhibits a mild spiral  334  that terminates at a rounded end  336 . The spiral  334  arcs rearward (away from the rear face  332 ) and inward (away from the side face  338 ) to terminate proximate the inferior processes  36  of the vertebrae above which it is mounted (see  FIG. 5 ). The spiral  334  is adapted to cooperate with the spiral of a proximal component to define an opening (see e.g.,  FIGS. 33-35 ) for egress of nerves exiting the spinal column between the vertebrae. 
         [0079]    Referring to  FIG. 25 , it is further within the scope of the disclosure for a base plate  350  to include a dished cavity  352 . In such a circumstance, a bearing insert  354  may include a dome-shaped projection  356  that has a diameter and depth less than that of the dished cavity  352 . In this alternate exemplary embodiment, the insert  354  has at least three degrees of freedom with respect to the base plate  350 : (1) movement forward and backward; (2) movement from side to side; and, (3) rotational movement. 
         [0080]    An exemplary surgical procedure for effectuating a spinal implant making use of one or more of the exemplary embodiments will now be discussed. 
         [0081]    Initially, it is expected that the patient be placed prone on an operating table with all appropriate pressure points padded. Using C-arm fluoroscopy, both in anterior-posterior Ferguson and lateral directions, the pedicles immediately above and below the disc space are marked out on the skin surface with a linear pedicle-to-pedicle line. A linear skin incision is made from the pedicle-to-pedicle line as previously marked out. A K-wire is then passed to dock over the inferior articulating facet of the superior level, followed by insertion of a series of progressively larger tapered dilators that are operative provide an ever increasing exposure gap between otherwise adjacent muscle. A final visualization tube is then deployed to visualize the spinal facet joint, lateral lamina, and pars interarticularis. In exemplary form, the visualization tube is secured to a malleable arm attached to the operating table for holding the visualization tube in a secure position relative to the patient. Thereafter, anterior-posterior and lateral X-rays are taken to confirm the visualization tube placement. 
         [0082]    Referring to  FIG. 26 , with appropriate visualization and illumination (operating microscope, loupes, headlight, etc.) a drill, osteotome, or rongeur is used to resect the facet joint and the superior articulation of the inferior level to expose the disc space. After a complete facetectomy is completed, dissection is performed to expose the lateral dural edge, the traversing nerve root, and the disc space lateral thereto. A nerve root retractor is positioned and utilized to retract the dura and nerve medially and further expose the disk space laterally. A knife is thereafter used to create an annulotomy and initial discectomy is performed using rongeurs and scrapers. The interbody space is then sequentially dilated with in increasingly sized interbody spreaders under fluoroscopic guidance to assess the size of the disc space and total available height for the implant. The blunted edges of the spreaders will also decorticate the cartilaginous end plate, but leave the bony endplate of the vertebral bodies to eventually hold the implant. Any fragment of disc material not decorticated by the spreaders is removed with a pituitary rongeur or forceps. 
         [0083]    Referencing  FIG. 27 , after the disc material is removed, the resulting vertebrae  400 ,  402  need to be prepared to accept the plate halves  106 ,  108 ,  186 ,  188 . In exemplary form, a series of jigs (not shown) are mounted to the vertebrae in order to make horizontal and vertical cuts to form cut-outs within the anterior portion of the vertebral body for each vertebrae  400 ,  402 . After the jigs are secured, a cutting tool is utilized to make straight horizontal and vertical cuts in to the vertebral body. Depending upon the precise jigs used, the vertical cuts may precede the horizontal cuts or vice versa. At the termination of the cutting, the vertebrae  400 ,  402  include generally planar horizontal adjacent surfaces that face one another. However, a portion of the posterior vertebral body is retained in order to provide a flange against which the plate halves  106 ,  108 ,  186 ,  188  are positioned. A series of trialers is thereafter used, to determine the appropriate implant size, followed by implantation of the artificial joint (implant). 
         [0084]    Next, articulating trials (not shown) are used, under fluoroscopic imaging, to determine the appropriate implant size, the ideal thickness, and the ideal pivot point of the implant. If the subject, pre-operative, was compressed more medial, the pivot point would be made more medial to provide medial stability. If the subject, pre-operative, was compressed more lateral, the pivot point would be made more lateral to provide lateral stability. If the subject, pre-operative, was compressed more anterior, the pivot point would be made more anterior to provide anterior stability. If the subject, pre-operative, was compressed more posterior, the pivot point would be made more posterior to provide posterior stability. If the subject is restricted in internal/external rotation, then a mobile bearing articulating surface insert might be used to all greater rotational freedom. In addition, if the surgeon determines it is best for the subject have rotational and translational freedom, then a total freedom replacement could be used to allow the subject freely rotate and translated. Finally, if minimal rotation, translation or rotation and translation are required for a subject, then the articulating surface insert could have limited rotation and translation. Following trial fitting, implantation of the appropriate implant  100  may occur. 
         [0085]    Referring to  FIGS. 28-33 , implantation of the artificial spinal joint includes initially placing the plate halves  106 ,  108 ,  186 ,  188  of the implant  100  into a holder (not shown) that includes a handle to be impacted with a mallet to place the plate halves into the disc space. Because the plate halves  106 ,  108 ,  186 ,  188  are without the polyethylene insert halves  110 ,  112 ,  190 ,  192  initially, it is easier to put into the plate halves into the disc space. In this exemplary embodiment, the proximal plate halves  106 ,  108  are positioned so that the rear face  140  abuts the flange of the posterior portion of the vertebral body of the vertebra  400 , while the top surface  130  abuts the distal planar cut-out surface of the vertebral body. Similarly, the distal plate halves  186 ,  188  are positioned so that the rear face  208  abuts the flange of the posterior portion of the vertebral body of the vertebra  402 , while the bottom planar surface abuts the proximal planar cut-out surface of the vertebral body. These plate halves  106 ,  108 ,  186 ,  188  are then impacted in a posterior oblique fashion under fluoroscopic guidance in order to position and lock the plate halves together using the locking system. 
         [0086]    In exemplary form, the locking system may comprise two or more corresponding cavities  116  in the plate halves  106 ,  108 ,  186 ,  188  adapted to receive and retain a bolt  114  (threaded or smooth) operative to join and retain the corresponding plate halves. Alternatively, the locking system may include cavities in each of the plate halves  106 ,  108 ,  186 ,  188 , that receive through rods to couple the plate halves together. Exemplary male and female retainers  114 ,  116  are well known to those skilled in the art. Specifically, the male projections  114  may include spline cylinders extending perpendicularly from the plate halves  106 ,  108 ,  186 ,  188  that are received within cylindrical openings  116  in the opposite/corresponding plate halves  106 ,  108 ,  186 ,  188  that are slightly smaller in diameter than the diameter of the spline cylinders. Exemplary locking systems may be fabricated from any combination of biologically acceptable materials including, without limitation, metals (titanium, stainless steel, etc.), ceramics, and plastics (high molecular weight polyethylene, polypropylene, etc.). Subsequent to the plate halves being positioned and locked together, the polyethylene insert halves  110 ,  112 ,  190 ,  192  are properly placed into the disc space. 
         [0087]    Referring to  FIGS. 34-36 , each of the polyethylene insert halves  110 ,  112 ,  190 ,  192  are impacted into position to align each projection  160 ,  230  with its corresponding groove  146 ,  216  to position the insert halves within the center of each plate halve, thereby spreading the proximal plate halves  106 ,  108  from the distal plate halves  186 ,  188  to distract the disc space and restore height. Alternate shaped projections  160 ,  230  and grooves  146 ,  216  may be utilized so that the inserts can be simply impacted into the interspace between the plate halves  106 ,  108 ,  186 ,  188  in a posterior oblique fashion under fluoroscopic guidance so that the insert halves  110 ,  112 ,  190 ,  192  simply snap into the plate halves when the insert halves are in their proper position. In addition, the insert halves  110 ,  112 ,  190 ,  192  may include a separate locking system for securing the insert halves to one another. 
         [0088]    In exemplary form, the locking system may comprise two or more corresponding cavities in the insert halves  110 ,  112 ,  190 ,  192  adapted to receive and retain a threaded bolt operative to join and retain the corresponding insert halves. Alternatively, the locking system may comprise one or more male projections  114  extending from one of the insert halves  110 ,  112 ,  190 ,  192 , while the other corresponding insert halve  110 ,  112 ,  190 ,  192  includes corresponding female cavities  116  to receive the male projections so that coupled engagement occurs when the male projection is received within the female cavity. Exemplary male and female retainers are well known to those skilled in the art. Specifically, the male projections may include spline cylinders extending perpendicularly from the insert halves  110 ,  112 ,  190 ,  192  that are received within cylindrical openings in the opposite/corresponding insert halves  110 ,  112 ,  190 ,  192  that are slightly smaller in diameter than the diameter of the spline cylinders. Exemplary locking systems may be fabricated from any combination of biologically acceptable materials including, without limitation, metals (titanium, stainless steel, etc.), ceramics, and plastics (high molecular weight polyethylene, polypropylene, etc.). 
         [0089]    Referencing  FIGS. 37 and 38 , if any portion of the implant  100  is not in the correct position or if revision is needed, a handle (not shown) can be reattached to the plate halves or insert halves to facilitate reposition or revision. Once the final placement of the implant is completed, a vertebral body screw (not shown) is placed into the eyelets of both plates to hole them in place. However, these screws have cancellous purchase and are not strong enough to permanently hold the implants in place by themselves. A facet joint attachment is then chosen based on the distance between the holding threads of the plate halves  106 ,  108 ,  186 ,  188 , which has an opening for placement of a pedicle screw which is strong enough to hold the implant in place permanently. This joint connects to the plate halves  106 ,  108 ,  186 ,  188  by the holding threads, screwed on, and different sizes allow for anatomic variations of the pedicle to disc space distance. Final tightening is then performed of all screws with a torque wrench. The wound is then inspected, with decompression of the neural elements verified using a Woodson dental tool or other surgical probe. 
         [0090]    In an alternate exemplary embodiment, the bottom surfaces  131  of the plate halves  106 ,  108 ,  186 ,  188  may be cemented or press-fit onto the adjacent vertebrae bone. Alternatively, the halves may be mounted to the adjacent vertebrae bone using surgical screws or other fastening devices. It is also within the scope of the present disclosure to incorporate a bottom surface  131  of the plate halves  106 ,  108 ,  186 ,  188  that is textured and provides for an improved bonding surface when using at least one of cement and bone ingrowth material. 
         [0091]    While the foregoing exemplary embodiment has been described with the inserts  110 ,  112 ,  190 ,  192  including a projection that is received within a groove of one of the plate halves  106 ,  108 ,  186 ,  188 , it is also within the scope of the disclosure for the plate halves to each include a projection that is received within a groove of one of the inserts  110 ,  112 ,  190 ,  192 . Those skilled in the art will certainly understand the interchangeability of the groove  146 ,  216  and corresponding projection  160 ,  230  in the foregoing exemplary embodiments. In addition, the grooves  146 ,  216  need not be oriented laterally, but instead may be oriented from front to back. 
         [0092]    In exemplary form, the lumbar spinal implant  100  is sized or scaled to match a patient&#39;s vertebrae. In other words, while the general shape of an L5 vertebra, for example, is the same for human beings, anatomical considerations and range of motion for each patient warrant sizing or scaling the implant to match the vertebrae of the patient. Likewise, the spinal implants  100  are shaped according to the location of the disc replacement. Because the disc size and, shape of a cervical disc is not identical to the size and shape of a lumbar disc within the same patient, the exemplary implants may be sized and shaped based upon the intended location of use. Moreover, the articulating surfaces may be sized to be gender and/or ethnic specific. 
         [0093]    By way of example, and not limitation, the present embodiments are also amendable for future revision surgery where one or more of the inserts would be replaced without replacing the base plate halves. In this manner, minimally invasive surgery would be an practical alternative to replace the bearing inserts. 
         [0094]    It is also within the scope of the disclosure that the base plates be fabricated from only one or more than two component parts. While some of the foregoing embodiments show base plates comprising complementary halves, these same components may be fabricated as a unitary structure or fabricated from three or more pieces, not necessarily substantially the same size. Along these same lines, the base plates may vary in thickness (distance between top and bottom surfaces) depending upon the disc to be replaced. 
         [0095]    It is also within the scope of the present disclosure for the distal inserts  190 ,  192  to exhibit a domed shape, while the proximal inserts  110 ,  112  exhibit a concave shape. Along these same lines, the thickness and other shape features are interchangeable between the proximal and distal inserts of the present disclosure. 
         [0096]    If each base plate is one piece, it can be attached to the bone either from the lateral direction, medial direction and/or the frontal direction. Alternatively, if the base plate is two or three pieces, it could be attached to the bone from the lateral direction, medial direction and/or the frontal direction or from multiple directions. 
         [0097]    It is further within the scope of the disclosure for the respective base plate halves and insert halves to be fabricated as a unitary structure. In other words, the base plate would embody the any mobile bearing features of the insert and the vertebra bone would be contoured to accommodate this increased range of motion. 
         [0098]    Following from the above description and disclosure summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the inventions disclosed herein are not limited to any precise embodiment and that changes may be made to any such embodiment without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.