Abstract:
An implant system provides motion preservation or stabilization between two spinal vertebrae. An associated instrumentation system is capable of delivering and removing the implants from either the anterior, left lateral or right lateral positions. The instrumentation system also provides instrumentation for delivering the implant end plates into the disc space, adjusting the position of the end plates in situ, compressing end plates into the vertebral bodies, interoperatively determining the height and angulation of bearings, delivering bearings together and then independently connecting them to the end plates. The system provides alternative instrumentation for revising the motion preservation disc from at least three directions. The system further provides alternative instrumentation for converting the motion preservation disc system to an interbody fusion device from at least three directions.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims the benefit of the following:  
         [0002]     U.S. Provisional Application No. 60,720,513, filed Sep. 26, 2005, which carries Applicants&#39; Docket No. MLI-45 PROV and is entitled MODULAR ARTICULATING AND FUSION SPINAL DISC IMPLANT SYSTEM;  
         [0003]     U.S. Provisional Application No. 60/720,514, filed Sep. 26, 2005, which carries Applicants&#39; Docket No. MLI-46 PROV and is entitled UNIVERSAL SPINAL DISC IMPLANT SYSTEM FOR PROVIDING INTERVERTEBRAL ARTICULATION AND FUSION; and  
         [0004]     U.S. Provisional Application No. 60/741,513, filed Nov. 30, 2005, which carries Applicants&#39; Docket No. MLI-50 PROV and is entitled SYSTEM AND METHOD FOR INTERVERTEBRAL IMPLANT DELIVERY AND REMOVAL.  
         [0005]     All of the foregoing are incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION  
       [0006]     1. The Field of the Invention  
         [0007]     The present invention relates generally to spinal orthopedics, and more precisely, to intervertebral implants and related instrumentation.  
         [0008]     2. The Relevant Technology  
         [0009]     Severe back pain can be caused by sa number of different ailments, including spinal stenosis, degenerative disc disease, spondylolisthesis, and the like. Many such ailments can be corrected by controlling or limiting relative motion between the affected vertebrae. Accordingly, a variety of devices including artificial discs and fusion devices have been proposed.  
         [0010]     A variety of instruments have also been proposed for use with such intervertebral devices. These instruments are typically limited to use with one implant configuration and/or one surgical approach. Accordingly, many known instruments are usable only when the indications fit within a relatively narrow set of criteria. Furthermore, the soft tissue damage often caused by operation in the intervertebral disc space may prevent any revision surgery from being carried out along the same approach. Thus, many known instruments are not usable for revision of an existing intervertebral treatment.  
         [0011]     Further, many known instruments are expensive or difficult to manufacture, or are difficult to use. Accordingly, there is a need in the art for instrumentation that remedies these problems.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]     Various embodiments of the present invention will now be discussed with reference to the appended drawings. It is appreciated that these drawings depict only typical embodiments of the invention and are therefore not to be considered limiting of its scope.  
         [0013]      FIG. 1  is a perspective view of an intervertebral disc motion preservation implant in an assembled state.  
         [0014]      FIG. 2  is a perspective view of an adjustable support assembly, a pivot assembly, and an end plate instrument assembly.  
         [0015]      FIG. 3  is a perspective view of a bearing instrument assembly and the pivot assembly shown in  FIG. 2 , and the implant shown in  FIG. 1 .  
         [0016]      FIG. 4  is a top elevation view of the pivot assembly shown in  FIG. 2 .  
         [0017]      FIG. 5  is a perspective view of the end plate instrument assembly and the pivot assembly shown in  FIG. 2 , and two end plates.  
         [0018]      FIG. 6  is a perspective view of the pivot assembly shown in  FIG. 2  and two end plate holders.  
         [0019]      FIG. 7  is a side elevation view of the pivot assembly and end plate holders shown in  FIG. 6 , with hidden parts shown in phantom.  
         [0020]      FIG. 8  is a side elevation view of the distal end of an end plate holder shown in  FIG. 6  and an end plate, with hidden parts shown in phantom.  
         [0021]      FIG. 9  is a side elevation view of the distal end of a spike guard.  
         [0022]      FIG. 10  is a side elevation view of the distal end of the spike guard shown in  FIG. 9  mounted on an end plate.  
         [0023]      FIG. 11  is a perspective view of the distal end a primary spacer.  
         [0024]      FIG. 12  is a side elevation view of the end plate instrument assembly shown in  FIG. 5 , and two end plates.  
         [0025]      FIG. 13  is a perspective view of an intervertebral disc motion preservation implant in a disassembled state.  
         [0026]      FIG. 14  is a perspective view of the distal end of a secondary spacer.  
         [0027]      FIG. 15  is a side elevation view of the distal end of two end plate holders and end plates shown in  FIG. 8 , and two primary spacers shown in  FIG. 12 , and two secondary spacers shown in  FIG. 14 .  
         [0028]      FIG. 16  is a perspective view of the distal end of an angle compressor and an end plate.  
         [0029]      FIG. 17  is a perspective view of the distal end of a bearing holder.  
         [0030]      FIG. 18  is a perspective view of the distal end of the bearing holder shown in  FIG. 17 , attached to the superior bearing and the inferior bearing shown in  FIG. 13 .  
         [0031]      FIG. 19  is a perspective view of the distal end of a height compressor.  
         [0032]      FIG. 20  is a perspective view of the distal end of the bearing holder and bearings shown in  FIG. 18 , attached to the height compressor shown in  FIG. 19 .  
         [0033]      FIG. 21  is a side elevation view of the distal end of the bearing instrument assembly and implant shown in  FIG. 3 .  
         [0034]      FIG. 22  is a perspective view of an alternative bearing guidance assembly, the support assembly, the pivot assembly and the end plate assembly.  
         [0035]      FIG. 23  is an enlarged exploded view an alternative disc motion preservation implant.  
         [0036]      FIG. 24  is a perspective view of a bearing holder, holding the bearing components of the implant of  FIG. 23 .  
         [0037]      FIG. 25  is an enlarged view of an inferior side of a distal end of the bearing holder of  FIG. 24 .  
         [0038]      FIG. 26  is an enlarged view of a superior side of the distal end of the bearing holder of  FIG. 24 .  
         [0039]      FIG. 27  is an enlarged view of a superior and an inferior bearing mounted on the distal end of the bearing holder.  
         [0040]      FIG. 28  is an enlarged view of the bearing holder with mounted bearings inserted in the end plate assembly.  
         [0041]      FIG. 29  is a perspective view of a compressor.  
         [0042]      FIG. 30  is an enlarged view of the distal end of the compressor of  FIG. 29 .  
         [0043]      FIG. 31  is a perspective view of a superior feeler gauge.  
         [0044]      FIG. 32  is a perspective view of an inferior feeler gauge.  
         [0045]      FIG. 33  is a perspective view of a fusion block attached to the distal end of the bearing holder of  FIG. 24 .  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0046]      FIG. 1  illustrates an intervertebral disc motion preservation implant  14 . The implant  14  is designed for placement between spinal vertebrae to replace degenerated intervertebral disc material. The implant  14  comprises two end plates  300 , a superior bearing  800 , and an inferior bearing  850 , and two snap fasteners  900 . The end plates  300  are implanted in the vertebral bodies, and the snap fasteners  900  hold the bearings  800 ,  850  in place between the end plates  300 .  
         [0047]     Referring to  FIG. 2 , a perspective view illustrates two end plates  300  and an end plate instrument assembly  16  necessary to hold and guide the end plates  300  during the implantation process. Also shown are a pivot assembly  18  which holds and adjusts the end plate instrument assembly  16 , and an adjustable support assembly  12  which holds the pivot assembly  18 . The end plates  300  and the other implant components may be implanted and removed from any one of three approaches: anterior, left lateral or right lateral. Prior to the implantation procedure, the adjustable support assembly  12  is attached to the operating table on the right or left side, depending upon which approach is to be used.  
         [0048]     After the end plates  300  are implanted, the inferior  850  and superior bearing  800  are inserted between the end plates.  FIG. 3  illustrates a bearing instrument assembly  17  required to insert the bearings. The bearing instrument assembly  17  is supported by the pivot assembly  18 , which in turn is held by the adjustable support assembly  12 .  
         [0049]     The instrumentation illustrated herein is for an implant  14  which has a specific anterior-posterior angle. Implants of differing angulation may be implanted and may require a different configuration of instrumentation. That is, instruments of varying sizes and designs may be necessary to implant an implant of a wider or narrower angle. In addition, the order of the procedure described herein may vary for a different implant.  
         [0050]      FIG. 4  depicts the pivot assembly  18 . The pivot assembly  18  comprises an angle adjustment pivot  100  and a height adjustment pivot  140 . The pivots  100 ,  140  are generally U-shaped and are secured together by two screws  102 . The height adjustment pivot  140  has a body  150  and two arms  152  which extend perpendicularly away from the body  150  and parallel to one another, forming a U-shape. The angle adjustment pivot  100  also has a body  110  and two arms  112  which form a U-shape. A support feature in the form of support assembly ball  114  is located on the outer side of each angle adjustment pivot arm  112 . The adjustable support assembly  12  depicted in  FIG. 2  attaches to the pivot assembly  113  via one of the support assembly balls  114 . Which support assembly ball  114  is used is determined by the surgical approach (anterior, right lateral, or left lateral) and the preference of the surgical personnel.  
         [0051]     An angle adjustment guide arm  116  extends through in opening in the body  110  of the angle adjustment pivot  100 . At the proximal end  118  of the guide arm  116  is an angle adjustment screw  120 . This angle adjustment screw  120  extends through the length of the guide arm  116  and emerges at the distal end  122  of the guide arm  116 , and is capped by an adjustment nut  124 . An angle adjustment gauge  130  appears as a series of numbers on the top side of the body  110 . Also on the top side of the body  110 , an adjustment knob  126  extends through an opening in the body  110  to the top of the angle adjustment guide arm  116 . Tightening the adjustment knob  126  secures the angle adjustment guide arm  116  in place within the angle adjustment pivot  100 . A row of angle guide arm teeth  128  line the distal end  122  of the angle adjustment guide arm  116 .  
         [0052]     A height adjustment guide arm  156  extends through an opening in the body  150  of the height adjustment pivot  140 . At the proximal end  158  of the guide arm  156  is a height adjustment screw  160 . This height adjustment screw  160  extends through the length of the guide arm  156  and emerges at the distal end  162  of the guide arm  156 , and is capped by an adjustment nut  164 . A height adjustment gauge  170  appears as a series of numbers on the top side of the body  150 . Also on the top side of the body  150 , an adjustment knob  166  extends through an opening in the body  150  to the top of the height adjustment guide arm  156 . Tightening the adjustment knob  166  secures the height adjustment guide arm  156  in place within the height adjustment pivot  140 . A row of height guide arm teeth  168  line the distal end  162  of the height adjustment guide arm  156 .  
         [0053]     The instrument assembly  16  and pivot assembly  18  are depicted in  FIG. 5 . Individual components of the instrument assembly  16  are positioned, implemented, and removed throughout the implantation procedure. In the embodiment depicted, the instrument assembly  16  consists of two end plate holders  200 , two spike guards  400 , and two primary spacers  500 . Attached to the distal end of the end plate holders  200  are two end plates  300 . (Additional spacers not depicted in  FIG. 5  are used in the procedure and will be illustrated and described as they are used.)  
         [0054]      FIG. 6  depicts a top-down view of the pivot assembly  18  and its connection to the end plate holders  200 . The two end plate holders  200  are identical to one another; they differ only in orientation during the implantation procedure. Each end plate holder  200  has a distal first end  250  and a proximal second end  260 , connected by a shaft  201 . At the second end  260  of each end plate holder  200  is a connector  240  with an opening  242  and a plurality of connector teeth  248 . One end plate holder is connected to the height adjustment guide arm  156  by fitting the opening  242  over the adjustment nut  164 , and meshing the connector teeth  248  with the height guide arm teeth  168 . The other end plate holder  200  is connected to the angle adjustment guide arm  116  in an identical manner; by fitting the opening  242  over the adjustment nut  124 , and meshing the connector teeth  248  with the angle guide arm teeth  128 . Once the end plate holders  200  are connected to the adjustable guide arms  116 ,  156 , the height of the end plate holders  200  can be adjusted by turning the height adjustment screw  160 , and the angle of the end plate holders  200  can be adjusted by turning the angle adjustment: screw  120 .  
         [0055]     A transparent side view of the proximal end of the end plate holders  200  and the guide arms  116 ,  156  is shown in  FIG. 7 . Fitted into a longitudinal channel  210  in each shaft  201  is a spreader  220 . The spreaders  220  lie on the inside planes of the end plate holders  200  such that the spreaders  220  face one another once the end plate holders  200  are secured to the adjustment arms  116 ,  156 . Each spreader  220  has a lever  222  which lies on the outside of the end plate holder  200 . A rod  226  and lever pin  224  assembly connect the spreader  220  to the lever  222 . When the lever  222  is in the lowered position as in  FIG. 5 , the spreader  220  is extended distally down the channel  210  of the shaft  201 .  
         [0056]     An end plate  300  and its connection to the first end  250  of the end plate holder  200  are illustrated in  FIG. 8 . The end plate  300  has a right lateral end  302 , a left lateral end  304 , an anterior end  306  and a posterior end  308 . The end plate  300  has three pockets  310 , placed on the right lateral end  302 , the left lateral end  304 , and the anterior end  306 . The three pockets  310  are identical in shape and design, only differing in placement on the end plate  300 . Each pocket  310  has two angled corners  312 . If the implant:  14  is to be placed using the anterior approach, as depicted in  FIG. 8 , the end plate holder  200  will be connected to the end plate  300  via the pocket  310  located on the anterior end  306 . Similarly, if the implant  14  is to be placed using a right lateral approach, the end plate holder  200  will be connected via the pocket  300  on the right end  302  and if the implant is to be placed using a left lateral approach, the end plate holder  200  will be connected via the pocket  310  in the left end  304 .  
         [0057]     The first end  250  of the end plate holder  200  comprises an expandable retention interface having two prongs  202 . The two prongs  202  terminate in angled prong tips  204 , which have radius edges  206 . In the embodiment depicted, the anterior approach is used, so the end plate holder  200  is connected to the end plate  300  by placing the two prongs  202  into the pocket  310  on the anterior end  306 . Once the prongs  202  are placed in the pocket  310 , the spreader  220  is extended lengthwise between the two prongs  202 , by lowering the lever  222  illustrated in  FIG. 7 . As the spreader  220  extends, the prong tips  204  are forced apart, and pushed into the outer pocket corners  312 . When the spreader  220  is filly extended, the spreader tip  228  is pushed firmly against the end of the pocket  310 , and the prong tips  204  are forced slightly back, thus seating their rounded edges  206  against the pocket corners  312 . This seating creates a firm connection between the end plate  300  and the end plate holder  200 . The second end plate  300  is connected to the first end  250  of the second end plate holder  200  in an identical manner.  
         [0058]     As seen in  FIG. 8 , each end plate  300  has a plurality of spikes  314 . The spikes  314  comprise hollow, pointed protrusions extending from an exterior surface  316  of the end plate  300 . The spikes  314  are positioned such that they form a ring on the exterior surface  316 , but are set back from the ends  302 - 308  of the end plate  300 , allowing an outer ring of flat surface area between the spikes  314  and the ends  302 - 308 .  
         [0059]     After each of the end plates  300  is attached to the end plate holders  200 , a spike guard  400  is fitted over the exterior surface  316 . As seen in  FIG. 9 , the distal end of each spike guard  400  terminates in a flat, spatula-like cover plate  402  that fits over the exterior surface  316  of the end plate  300 . The inside of the cover plate  402  has grooves  404  into which the centrally located spikes  314  slide as the spike guards  400  are put on. The spike guards  400  are put on to the end plates  300  by sliding them distally parallel to the end plate holders  200  and onto the end plates, allowing the spikes  314  to slide into the grooves  404 , illustrated in  FIG. 10 . The outer surface of the cover plate has two curved notches  406  which come to rest around the spikes  314  nearest the right end  302  and left end  304  of the end plate  300 . These two spikes  314  are not covered, but the outer surface of the cover plate  402  extends higher than the ends of the spikes  314 , so the spikes  314  do not protrude past the cover plate  402 . The cover plate  402  prevents the spikes  314  from snagging or scratching anything prior to implantation, and prevents premature contact between the spikes  314  and the vertebral bodies. The spike guards  400  are composed of a radiolucent material, so that the end plates  300  are visible through radiography during the implantation process. Placement and removal of the spike guards  400  is via handles (not visible in  FIG. 9 ). The spike guard depicted in  FIGS. 9 and 10  is designed for use during an anterior approach implantation. It is appreciated that the shape and placement of the spike guards may differ in alternative embodiments of the invention.  
         [0060]      FIG. 11  depicts the distal end of a primary spacer  500 . The distal end of the primary spacer  500  terminates in a flat, rectangular plate  502 . A shaft  504  connects the plate  502  to a handle at the proximal end (not visible in  FIG. 11 ). Raised edges  506  extend partway up the shaft  504  from the plate  502  toward the proximal end The raised edges  506  have a distal end  508  near the plate  502  and a proximal end  510  partway up the shaft  504 .  
         [0061]      FIG. 12  illustrates the distal ends of the two end plate holders  200  with attached end plates  300 , spike guards  400 , and one primary spacer  500 . Two primary spacers  500  are used in the procedure, but only one is illustrated so that the details of the end plate holder  200  may be seen. Either before or after the spike guards  400  are fitted over the end plates  300 , the two primary spacers  500  are slid in between the end plate holders  200 , as also shown in  FIG. 5 . The first primary spacer  500  is slid parallel to the inner side of the end plate holder  200  such that the raised edges  506  clasp around the lateral edges of the end plate holder  200  and slide inside a lateral groove  212 . When the distal end  508  of the raised edge  506  contacts the end plate  300 , the primary spacer  500  is in place and cannot move distally any more. The plate  502  is in between the two end plates  300 . The other primary spacer  500  is slid into place next to the other end plate holder  200 , and its plate  502  comes to rest between the first plate  502  and the end plate  300 . The primary spacers are radiolucent, so they do not obscure the visibility of the end plates  300  and vertebral bodies during implantation. The number and positioning of spacers may vary with alternative embodiments of the invention.  
         [0062]     The pivot assembly  18  and attached instrument assembly  16  are now ready to be positioned for the implantation procedure. Referring to  FIGS. 2 , and  4 , the pivot assembly  18  is attached to the adjustable support assembly  12  via one of the two support assembly balls  114 . The support assembly  12  is adjusted so that the pivot assembly  18  and the instrument assembly  16  are supported over the patient in a position appropriate to the approach chosen (anterior, right lateral, or left lateral). The instrument assembly  16  is positioned so that the end plates  300  covered with the protective spikes guards  400  are placed between the vertebral bodies. Radiography is employed to observe the positioning of the end plates. At this point, the surgical personnel select the components of the disc implant  14 . The radiolucent spike guards  400  allow the surgical personnel to see the end plates  300  in position relative to the vertebral bodies, and the personnel can determine which size, thickness and angle of bearings  800 ,  850  should be used.  
         [0063]      FIG. 13  displays an exploded side view of disc implant  14 . The superior bearing  800  has a superior bearing surface  802  in which is an indented cup  810 . The inferior bearing  850  has an inferior bearing surface  852 , from which protrudes a dome  860 . When the bearings  800 ,  850  are held in place between the two end plates  300 , the cup  810  fits over the dome  860 , and the superior bearing surface  802  is in contact with the inferior bearing surface  852 . The snap fasteners  900  connect the bearings  800 ,  850  to the end plates  300  by fitting into snap ports  330  on the end plates  300 , and into troughs  804 ,  854  on the bearings  800 ,  850 .  
         [0064]     All pieces—end plates  300 , the inferior bearing  850 , the superior bearing  800  and the snap fasteners  900  are made in three sizes, where size refers to the area of the component, which will correspond to the area of the vertebral bodies where the disc implants are implanted. The superior bearings  800  are made in a variety of thicknesses, to match the height of the intervertebral space. The inferior bearings  850  are made in a variety of angles, in which the height of the posterior end of the inferior bearing is greater than the height of the anterior end of the inferior bearing, to match the angle of the intervertebral space. If deemed necessary, the end plates  300  can be removed and alternate, differently sized end plates  300  substituted for them.  
         [0065]     Referring back to  FIG. 6 , the adjustment screws  160 ,  120  on the guide arms  156 ,  116  allow for height and angle adjustment control at the second ends  260  of the end plate holders  200  while the first ends  250  are inserted in the intervertebral space. The height adjustment screw  160  at the second end  260  of the end plate holder  200  can be turned in either direction, raising or lowering the first end  250  of the end plate holder  200 , until the end plate  300  is correctly positioned in the intervertebral space. The height measurement gauge  170  is read on the height adjustment guide arm  156  and the superior bearing  800  matching that height is selected. Similarly, the angle adjustment screw  120  at the second end  260  of the other end plate holder  200  can be turned, changing the anterior-posterior angle of the first end  250  of the other end plate holder  200 , until the end plate  300  is correctly positioned. The angle measurement gauge  130  is read on the angle adjustment guide arm  116  and the inferior bearing  850  matching that angle is selected.  
         [0066]     An alternate method for determining the correct size of end plates  300  and bearings is to have a group of samples which duplicate the size, thickness and angles of the end plates and bearings. These sample components are each mounted on a shaft to allow temporary insertion into the intervertebral space, to determine if the size, thickness and angle of the components are correct. A sample has the same dimensions as the two end plates, the inferior and superior bearings, and the snap fittings do when they are fitted together as they would be in the intervertebral space. Instead of temporarily inserting and removing the actual end plates and bearings to check for the proper configuration, the samples can be inserted and removed to determine the proper choice for each component.  
         [0067]     Once the correct disc implant  14  components are chosen, the final position of the end plates  300  is adjusted. Radiography is used to see where the end plates  300  and more specifically the spikes  314  will fit against the vertebral bodies. The angle adjustment screw  120  is turned to place the end plate holder  200  and end plate  300  at the proper angle. The height adjustment screw  160  is turned to raise or lower the other end plate holder  200  and end plate  300 . Once the correct angle and height are determined, the adjustment knob  126  is tightened to lock the angle adjustment guide arm  116  in place, and the adjustment knob  166  is tightened to lock the height adjustment guide arm  156  in place.  
         [0068]     With the end plate holders  200  now locked in place at the correct height and angle, the spike guards  400  are removed, allowing the now exposed spikes,  314  to engage against the surface of the vertebral bodies. Secondary spacers  550  are inserted between the primary spacers  500 . This action pushes the end plates  300  cephalic-caudally away from one another, and presses the spikes  314  into the vertebral bodies.  FIG. 14  illustrates the distal end of an individual secondary spacer  550 . The secondary spacer  550  terminates in a paddle-like plate  552  that is thicker than the plate  502  of the primary spacer  500 . A shaft  554  connects the plate  552  to a handle (not visible in  FIG. 14 ). Partway up the shaft  554  in a proximal direction from the plate  552 , a pair of rails  556  are on either side of the shaft  554 . The rails  556  have squared edges  558  which extend out from the shaft  554 .  
         [0069]      FIG. 15  illustrates the distal end of instrument assembly  16 , including end plate holders  200 , and primary and secondary spacers  500 ,  550 . The end plate holders  200  are holding two end plates  300 . The secondary spacers  550  are inserted one at a time into the space between the two primary spacers  500 . As the secondary spacer  550  is moved into place, the edges  558  of the rails  556  slide into the lateral grooves  212  on the end plate holder  200 . The secondary spacer  550  is slid distally until the rails  556  contact a proximal end  510  of the raised edges  506  of the primary spacer  500 , preventing the secondary spacer  550  from sliding any further. The plate  552  is now positioned next to the plate  502  of the primary spacer  500 , and the primary spacer  500  is sandwiched between the end plate holder  200  and the secondary spacer  500 . The other secondary spacer  550  is inserted in the same fashion onto the opposite primary spacer  500  and end plate holder  200 . The action of inserting the secondary spacers  550  pushes the spikes  314  into the vertebral bodies, thus firmly seating the exterior surfaces  316  of the end plates  300  against the surface of the vertebral bodies.  
         [0070]     With the end plates  300  implanted in the vertebral bodies, the primary spacers  500  and secondary spacers  550  are removed. Removal is accomplished by grasping the handles of the spacers  500 ,  550  and pulling them proximally until they are free of the instrument assembly  16 .  
         [0071]     Referring back to  FIG. 3 , the bearing instrument assembly  17  used to place the bearings  800 ,  850  between the implanted end plates  200  is depicted. This assembly is supported by the pivot assembly  18 , and comprises the end plate holders  200 , an angle compressor  650 , a height compressor  600 , and a bearing holder  700 . At the distal end of the instrumentation set is the intervertebral disc motion preservation implant  14 , which comprises the two end plates  300 , an inferior bearing  800 , a superior bearing  850 , and two snap fasteners  900 , as illustrated in  FIG. 10 . The instruments which comprise instrument assembly  17  are assembled in the following order: the angle compressor  650  is inserted between the end plate holders  200 ; the bearings  800 ,  850  are attached to the bearing holder  700 ; the height compressor  600  is attached to the bearing holder  700 ; and the bearing holder  700  (with attached height compressor  600  and bearings  800 ,  850 ) is inserted between the end plate holders  200 .  
         [0072]      FIG. 16  depicts the distal end of one angle compressor  650  with one end plate holder  200  and one end plate  300 . The angle compressor  650  is comprised of a handle at the proximal end (not visible in  FIG. 14 ), a shaft  654 , and two prongs  652 . The shaft  654  has raised edges  658  which extend perpendicularly from the shaft  654  and bend to form an L-shape. At the distal end of the shaft  654  are the prongs  652  which each terminate in an angled ramp  662 . Partway up the shaft  654  in a proximal direction are a pair of rails  656 . The L-shaped rails  656  extend in the opposite direction from the raised edges  658 . The angle compressor  650  is slid onto the end plate holder  200  which is attached to the angle guide arm  116  as seen in  FIG. 6 . The raised edges  658  slide into the lateral grooves  212  on either side of the end plate holder  200 . The angle compressor  650  is slid distally down the length of the end plate holder  200  until the distal ends  660  of the raised edges  658  contact the end plate  300 . The prongs  652  lie on either side of the snap port  330  of the end plate  300 .  
         [0073]     The inferior side of the distal end of bearing holder  700  is illustrated in  FIG. 17 . The bearing holder  700  has two handles  734  at the proximal end (visible in  FIG. 3 ), and a shaft  704  which terminates at its distal end all an intersection with a body  710 . Along each lateral side of the shaft  704  is a camming channel  730  with undulating edges  732 . The body  710  extends distally and splits into two prongs  702 . The body  710  and prongs  702  are generally flat and fork-like in shape, with a superior side  716  and an inferior side  718 . Where the body  710  originates at the base of the shaft  704  are two shoulders  706 , one on each lateral side of the shaft  704 . Each shoulder  706  extends perpendicularly from the body  710  in both directions. On each side of each shoulder is a slot  708  which lies parallel to the prongs  702  and is open to the inside of the shoulder  706  adjacent to the shaft  704 . At the base of each shoulder  706 , and between the slot  708 , and the body  710 , is a slanted edge  720 .  
         [0074]     Where the two prongs  702  meet at the base of the body  710  is a locking key  712  with two teeth  728 . The locking key  712  is mounted on the end of a pin  722  that extends from the proximal end of the shaft to the distal end, and is enclosed in a channel  724 . At the proximal end of the bearing holder  700 , the pin  722  emerges from the channel  724  and is capped by an adjustment nut  726  (seen in  FIG. 3 ). When the adjustment nut  726  is turned, the pin  722  and the locking key  712  turn.  
         [0075]      FIG. 18  depicts a superior side view of superior bearing  800  and an inferior bearing  850  mounted on the bearing holder  700 . In the embodiment depicted, the bearings  800 ,  850  are mounted in the anterior position; however they can also be mounted in either of the lateral positions, depending upon which surgical approach is used. Prior to mounting, the snap fasteners  900  are snapped onto the bearings  800 ,  850 . The superior bearing  800  is mounted on the superior side  716  of the bearing holder  700 . The superior bearing  800  is placed parallel to and adjacent to the body  710 , with the cup  810  surrounded by the prongs  702 . Anterior faceted edges  806  of the superior bearing  800  are flush against the slanted edges  720  of the shoulders  706 . One tooth  728  of the locking key  712  protrudes into the anterior instrument port  816 . Simultaneously, the inferior bearing  850  is placed on the inferior side  718  of the bearing holder  700 , parallel to and adjacent to the body  710  and with the prongs  702  surrounding the dome  860 . Anterior faceted edges  856  of the inferior bearing  850  are flush against the slanted edges  720  of the shoulders  706 , and the other tooth  723  of the locking key  712  is protruding through the anterior instrument port  866 . With both bearings  800 ,  850  held thus, the adjustment nut  726  is turned. The pin  722  and locking key  712  turn, and the teeth  728  on the locking key  712  engage and tighten down on the edges of the instrument ports  816 ,  866 . The bearings  800 ,  850  are thus locked in place on the bearing holder  700 . The inferior bearing surface  852  and the superior bearing surface  802  are adjacent to one another, with the dome  860  encircled by the cup  810  (not visible in  FIG. 18 ).  
         [0076]      FIG. 19  illustrates the distal end of the height compressor  600 . At the proximal end is a handle (not visible in  FIG. 19 ). The height compressor  600  has a shaft  604  with two prongs  602  at its distal end  610 . Each prong  602  terminates in an angled ramp  612 . On either lateral side of the shaft  604  is a raised edge  608 , which extends perpendicularly from the shaft  604  and bends to form an L-shape. Slightly above the distal end  610  of the shaft  604  is a pair of rails  606 , with one rail  606  located on each raised edge  608 . A second pair of rails  606  is located some distance proximally along the shaft  604 , one on each raised edge  608 .  
         [0077]     The bearing holder  700  with attached bearings  800 ,  850 , and a height compressor  600  are shown in  FIG. 20 . The height compressor  600  is connected to the bearing holder  700  by sliding the height compressor  600  parallel to the bearing holder  700  in the distal direction, on the superior side  716 , allowing the rails  606  to clasp the camming channel  730  on each side of the bearing holder  700 . As the height compressor  600  slides, the prongs  602  slide into the slots  708  on the bearing holder  700 . The height compressor  600  is slid distally until the rails  606  contact the shoulders  706  of the bearing holder  700 . At this point the height compressor  600  cannot slide distally any farther and the prongs  602  encircle the snap fastener  900  on the superior bearing  800 . The raised edges  608  are facing outward.  
         [0078]     After the height compressor  600  is connected to the bearing holder  700 , these two instruments and the attached bearings  800 ,  850  are inserted as a set between the end plate holders  200 , as seen in  FIG. 3 . The angle compressor  650  is already in place, connected to one end plate holder  200 , as seen in  FIG. 16 . The distal ends of the bearing holder  700  and the height compressor  600 , with the attached bearings  800 ,  850  are inserted between the end plate holders  200 , oriented so that the height compressor  600  is slid in next to the end plate holder  200  which is suspended from the height adjustment arm  156  (seen in  FIG. 6 ).The height compressor  600 , bearing holder  700  and bearings  800 ,  850  are slid in a distal direction parallel to the end plate holders  200 . As the instruments are slid in, the rails  656  of the angle compressor  650  slide into the camming channels  730  on the bearing holder  700 , and the prongs  652  slide into the slots  708 . Simultaneously, the raised edges  608  of the height compressor  600  clasp the lateral grooves  212  of the end plate holder  200 . The instrument set is slid distally until the shoulders  706  of the bearing holder  700  contact the end plates  300 . At this point, the instrument set cannot slide in any farther and the prongs  652  of the angle compressor  650  encircle the snap fastener  900  between the end plate  300  and the inferior bearing  850 .  
         [0079]     All components of the intervertebral disc motion preservation implant  14  are now in position between the vertebral bodies.  FIG. 211  illustrates the implant  14  held in place by the end plate holders  200  and bearing holder  700 . To attach the bearings  800 ,  850  to the end plates  200  the height and angle compressors  600 ,  650  are removed, one at a time, in either order. The height compressor  600  is removed by grasping the handle and pulling it proximally. As the height compressor  600  slides out, the rails  606  slide proximally along the camming channels  730  of the bearing holder  700 . As the height compressor  600  is removed, the prongs  602  are slid out from between the end plate  300  and the superior bearing  800 . Just when the prongs  602  reach the point where they are no longer between the end plate  300  and the superior bearing  800 , the rails  606  slide over a widening in the undulating edges  732  of the camming channels  730 . This forces the bearing holder  700  slightly closer to compressor  600 , and therefore closer to the end plate holder  200 . Since the prongs  602  of the height compressor  600  are no longer between the end plate  200  and the superior bearing  800 , the additional force snaps the snap fastener  900  on the bearing  800  into place in the snap port  330  on the end plate  200 .  
         [0080]     The angle compressor  650  is removed in the same way. The angle compressor  650  is removed by grasping the handle and pulling it proximally. As the angle compressor  650  slides out, the rails  656  slide proximally along the camming channels  730  of the bearing holder  700 . As the angle compressor  650  is removed, the prongs  652  are slid out from between the end plate  300  and the inferior bearing  850 . Just when the prongs  652  reach the point where they are no longer between the end plate  300  and the inferior bearing  850 , the rails  656  slide over a widening in the undulating edges  732  of the camming channels  730 . This forces the bearing holder  700  slightly closer to compressor  650 , and therefore closer to the end plate holder  200 . Since the prongs  652  of the angle compressor  650  are no longer between the end plate  200  and the inferior bearing  850 , the additional force snaps the snap fastener  900  on the bearing  850  into place in the snap port  330  on the end plate  200 . The adjustment null.  726  on the bearing holder  700  is turned, so the teeth  728  disengage from the instrument ports  816 ,  866 . All components of the intervertebral implant  14  are now in place between the end plates  200 .  
         [0081]     Referring to  FIGS. 3 and 8 , the bearing holder  700  is removed by grasping its handles  734  and pulling it proximally between the end plate holders  200  until it is free of the end plate holders  200  and the pivot assembly  18 . Each end plate holder  200  is disengaged from its end plate  300  by raising the lever  222 . Raising the lever  222  retracts the spreader  220 , and the prongs  202  are loosened within the pocket  310 . The end plate holder  200  can now be removed by pulling it proximally away from the end plate  200 . Thus all of the instrument assembly  17  is removed from the patient.  
         [0082]     Should removal of the implant  14  or replacement of any of its constituent components be required, such procedure may be carried out in any of the three approaches; anterior, right lateral, or left lateral, regardless of which approach was used during the initial implantation. To remove any component, first each end plate holder  200  is connected to the pivot assembly  18 , as seen in  FIG. 6 , with the lever  222  in the lowered position. The prongs  202  are guided into the pocket  310  of the end plate  300 , and the lever  222  is raised. The spreader  220  moves distally, and the prongs  202  are spread into the pocket corners  312 . With the end plate holders  200  now connected to the end plates  300 , the bearing holder  700  is inserted between the end plate holders  200 , The bearing holder  700  is oriented so that the superior side  716  is facing the end plate holder  200  which is connected to the height adjustment guide arm  156 , and the inferior side  718  is facing the end plate holder  200  which is connected to the angle adjustment guide arm  116 . As the bearing holder  700  is inserted, the prongs  702  will slide between the bearings  800 ,  850  such that the prongs  702  lie on either side of the dome  860 . When the prongs  702  are in place, the adjustment nut  726  is turned, so that the teeth  728  engage in the instrument ports  816 ,  866 , and the bearings  800 ,  850  are locked to the bearing holder  700 .  
         [0083]     Next, the compressors  600 ,  650  are inserted in either order. The height compressor  600  is slid distally along the end plate holder  200  which is connected to the height adjustment guide arm  156 , so that the raised edges  608  slide into and along the lateral groove  212 . As the compressor is slid distally along the end plate holder, the rails  606  slide over the undulating edges  732  and into the camming channel  730 . When the ramps  612  on the prongs  602  slide in between the end plate  300  and the superior bearing  800 , their intrusion will pry the snap fastener  900  apart from the snap port  330 . The angle compressor  650  is then slid distally along the end plate holder  200  which is connected to the angle adjustment guide arm  116 , so that the raised edges  658  slide into and along the lateral groove  212 , and the rails  656  slide along the camming channel  730 . When the ramps  662  on the prongs  652  slide in between the end plate  300  and the inferior bearing  850 , their intrusion will pry the snap fastener  900  apart from the snap port  330 .  
         [0084]     The bearings  800 ,  850  are now free from the end plates  300 , and attached to the bearing holder  700 . The bearing holder  700  with the attached hearings  800 ,  850 , and the compressors  600 ,  650  are removed simultaneously, by grasping their handles and pulling them proximally out from between the end plate holders  200 . At this juncture new bearings  800 ,  850  may be inserted in the same manner as described previously.  
         [0085]     An alternative embodiment of the invention is illustrated in  FIGS. 22-33 . This embodiment uses many of the same instruments as described for the previous embodiment, and is configured to implant the implant  14 , a fusion block, or an alternative implant. The alternative embodiment comprises alternative bearing placement guidance instrumentation, and compression instrumentation.  
         [0086]     Referring to  FIG. 22 , the support assembly  12 , pivot assembly  18  and end plate assembly  16  are shown with an alternative bearing guidance assembly  1017 , an alternative implant  1014 , and a compressor  1600 . The bearing guidance assembly  1017  comprises a bearing holder  1700  with guidance features. The implant  1014  comprises two end plates  1300 , a superior bearing  1800 , an inferior bearing  1850 , and two snap fasteners  1900 . The bearing holder  1700  holds and guides the superior and inferior bearings  1800 ,  1850  as they are inserted between the end plates  1300 . The compressor  1600  provides compressive force to the end plates  1300 , pushing them toward the bearings  1800 ,  1850  causing the snap fasteners  1900  to engage to the end plates  1300 , thus connecting the end plates  1300  to the bearings  1800 ,  1850 . The compression instrumentation also includes feeler gauges (not shown in  FIG. 22 ) which test the snap fastener connection. Although the alternative implant  1014  is depicted in  FIGS. 22-28 , the alternative bearing guidance assembly  1017  could also be used to place the implant  14 , or a fusion block.  
         [0087]     Referring to  FIG. 23 , an enlarged exploded view of the alternative disc motion preservation implant  1014  is depicted. Each end plate  1300  has a snap port  1330 . The superior bearing  1800  has a trough  1804  on its superior side, and the inferior bearing  1850  has a trough  1854  on its inferior side. The snap fasteners  1900  connect the end plates to the superior and inferior bearings when all components of the implant are snapped together. Prior to implantation, one snap fastener  1900  is snapped into the trough  1804  on the superior bearing  1800 , and similarly the second snap fastener  1900  is snapped into the trough  1854  on the inferior bearing  1850 .  
         [0088]      FIG. 24  depicts the bearing holder  1700 , holding the superior and inferior bearings  1800 ,  1850 . A snap fitting  1900  is attached to each bearing  1800 ,  1850 . The superior bearing  1800  is held on a superior side  1716  of the bearing holder  1700 , and the inferior bearing  1850  is held on an inferior side  1718 . The bearing holder  1700  has two handles  1734  at the proximal end, and a shaft  1704  which terminates at its distal end at an intersection with a body  1710 . Along a portion of each lateral side of the shaft  1704  is guide rail  1730 , which extend perpendicularly from the shaft  1704  on the inferior side  1718 . Near the distal end of the shaft  1704 , a pair of slider arms  1732  extends from the superior side  1716 , holding a slider link  1736 . An inferior feeler gauge  2050  is slidably engaged on the shaft  1704  of the bearing holder  1700 .  
         [0089]     Referring to  FIG. 25 , an enlarged view of the inferior side  1718  of distal end of the bearing holder  1700  is shown. At the end of the shaft  1704 , the body  1710  extends distally and splits into two prongs  1702 . The body  1710  and prongs  1702  are generally flat and fork-like in shape. Where the body  1710  originates at the base of the shaft  1704  are two stops  1708 , one on each lateral side of the shaft  1704 , which protrude perpendicularly from the shaft on the inferior side  1718 . Distal from the stops  1708 , where the two prongs  1702  extend from the body  1710 , are two shoulders  1706 , one on each lateral side of the body  1710 . Each shoulder  1706  extends perpendicularly from the body  1710  in both superior  1716  and inferior  1718  directions.  
         [0090]     Where the two prongs  1702  meet at the base of the body  1710  is a locking key  1712  with two teeth  1728 . The locking key  1712  is mounted on the end of a pin  1722  that extends from the proximal end of the shaft to the distal end, and is enclosed in a channel  1724 . At the proximal end of the bearing holder  1700 , the pin  1722  emerges from the channel  1724  and is capped by an adjustment nut  1726  (seen in  FIG. 23 ). When the adjustment nut  1726  is turned, the pin  1722  and the locking key  1712  turn.  
         [0091]     Referring to  FIG. 26 , an enlarged view of the superior side  1716  of the distal end of the bearing holder is shown. Just proximal to the body  1710 , a slider arm  1732  is linked to each side of the shaft  1704 . Extending between the ends of the arms  1732  is the slider link  1736 , which has a guide rail  1740  at each of its lateral ends. The guide rails  1740  are configured to grip the lateral edges of the end plate holders  1200  as the bearings  1800 ,  1850  are inserted or withdrawn, thus guiding the bearings in between the end plates  1300 .  
         [0092]     Referring to  FIG. 27 , an enlarged view shows the bearings  1800 ,  1850  mounted on the distal end of the bearing holder  1700 . The bearings  1800 ,  1850  are mounted on the bearing holder  1700  in the same manner as described previously for the bearings  800 ,  850  and the bearing holder  700 .  
         [0093]     Referring to  FIG. 28 , the bearing holder  1700  with mounted bearings  1800 ,  1850  is shown inserted between the end plate holders  200  and the end plates  1300 . The bearing holder  1700  and bearings  1800 ,  1850  are slid in between the proximal ends of end plate holders  200  as they are held in the pivot assembly  18 . As the bearing holder  1700  is slid distally, the guide rails  1730  are maneuvered so that they clasp the edges of the inferior end plate holder  200 . Similarly, the guide rails  1740  clasp the edges of the superior end plate holder  200 . With the guide rails  1730 ,  1740  thus engaged, the bearings  1800 ,  1850  are able to slide in between the end plates  1200  with a minimum of lateral movement and adjustment. When the bearings  1800 ,  1850  reach the end plates  1200 , the shoulders  1706  of the bearing holder  1700  contact the end plates  1300 , preventing any further distal movement, and lining the bearings  1800 ,  1850  up so that the snap fasteners  1900  will correctly engage with the end plates  1300  when compressed.  
         [0094]     Referring to  FIG. 29 , a compressor  1600  is shown. The compressor  1600  has a handle  1602 , a compression lever  1604 , a shaft  1606  and at the distal end of the shaft  1606 , a pair of tongs  1608 . When the compressor  1600  is implemented, the tongs  1608  push the end plates  1300  toward the bearings  1800 ,  1850 , providing force so the snap fasteners  1900  snap into the snap ports  1330  on the end plates  1300 .  
         [0095]     Referring to  FIG. 30 , an enlarged view of the distal end of the compressor  1600  is shown. Extending lengthwise along the shaft  1606  is a pull bar  1610 , which is pivotably connected at its proximal end to the compression lever  1604 , and is pivotably connected at its distal end to the tongs  1608 . The tongs  1608  are pivotably connected to a pair of cross links  1612 , which are pivotably connected to the distal end of the shaft  1606 . When the compression lever  1604  is pulled toward the handle  1602 , the pull bar  1610  moves distally parallel to the shaft  1606 , and the tongs  1608  are forced together.  
         [0096]     Returning to  FIG. 22 , the end plate assembly  16  and the bearing guidance assembly  1017  are shown, with the compressor  1600  grasping the end plate holders  200 . The compressor  1600  is placed so that each tong  1608  is adjacent to the shaft  201  of each end plate holder  200 . The compression lever  1604  is raised, thus extending the pull bar  1610  and pulling the tongs  1608  together, which push the end plate holders  200  with the attached end plates  1300  together. The snap fasteners  1900 , which are already engaged in the troughs on the bearings  1800 ,  1850 , are pushed into the snap ports  1330  on the end plates  1300 .  
         [0097]     Referring to  FIG. 31 , a superior feeler gauge  2000  is shown. The superior feeler gauge  2000  has a handle  2002  and a wide shaft  2004  with guide rails  2006  on each lateral side of the shaft  2004 . The shaft  2004  terminates at a tang  2008  which extends distally from the distal end of the shaft  2004 .  
         [0098]     Referring to  FIG. 32 , the inferior feeler gauge  2050  is shown. The inferior feeler gauge  2050  has a handle  2052 , a shaft  2054 , and a body  2060 . Guide rails  2056  line each lateral edge of the body  2060 , and they enable the gauge  2050  to be slidably engaged to the bearing holder  1700 . At the distal end of the body  2060 , a tang  2058  extends distally from the body  2060 .  
         [0099]     The feeler gauges  2000 ,  2050  are used to test if the snap fasteners  1900  have properly snapped to the end plates  1300  following compression. The compressor  1600  is removed from the instrument assembly  1017 , and the superior feeler gauge  2000  is inserted between the end plate holders  200  and the bearing holder  1700 . The inferior feeler gauge  2050  is already engaged on the bearing holder  1700 , as seen in  FIG. 24 . The superior feeler gauge  2000  is inserted on the superior side  1716  of the bearing holder  1700 , so that its guide rails  2006  clasp the edges of the superior bearing holder  200 . The gauge  2000  is slid distally until its tang  2008  slides in between the superior end plate  1300  and the superior bearing  1800 . If the snap connection between the end plate  1300  and the bearing  1800  has been successfully made, the tang  2008  will not be able to slide between the snap fastener  1900  and the end plate  1300 . If, however, the snap fastener  1900  has failed to engage with the snap port  1330  on the end plate  1300 , the tang  2008  will continue to slide distally until it lies between the snap fastener  1900  and the end plate  1300 .  
         [0100]     Similarly, the inferior feeler gauge  2050  is slid distally until its tang  2058  slides in between the inferior end plate  1300  and the inferior bearing  1850 . If the snap connection between the end plate  1300  and the bearing  1850  has been successfully made, the tang  2058  will not be able to slide between the snap fastener  1900  and the end plate  1300 . If, however, the snap fastener  1900  has failed to engage with the snap port  1330  on the end plate  1300 , the tang  2058  will continue to slide distally until it lies between the snap fastener  1900  and the end plate  1300 .  
         [0101]     If either snap fastener  1900  has failed to engage with its corresponding end plate  1300 , the feeler gauges  2000 ,  2050  are slid proximally, and the compressor  1600  is realigned with the end plate holders  200 . Compression is again attempted, and re-tested with the feeler gauges until both snap fasteners  1900  are snapped in place on the end plates  1300 .  
         [0102]     Referring to  FIG. 33 , a fusion block  2100  is shown attached to the distal end of the bearing holder  1700 . When fusion instead of motion preservation is desired, the fusion block  2100  may be inserted in between two end plates  1300  in the intervertebral space, using the same bearing delivery methods as described previously. The fusion block  2100 , with two snap fasteners  1900  snapped onto each of its two snap ports  2130 , is locked on the end of the bearing holder  1700  using the locking key  1712  mechanism. The fusion block  2100  and snap fasteners  1900  are inserted between the end plates  1300 , and snapped to the end plates  1300  using the compressor  1600 .  
         [0103]     It is appreciated that the bearing set  1800 ,  1850  and the fusion block  2100  are interchangeable, using the same instrumentation and implantation methods. If a motion preservation implant has been implanted, but a change to fusion is desired, the patient may be reopened, and the original implant removed with the instrumentation described above. A fusion block may then be implanted with the same instrumentation. If fusion is to be replaced with a motion preservation implant, the procedure may be reversed. It is also appreciated that all procedures described above may be carried out from an anterior approach, a right lateral approach, or a left lateral approach. Scar tissue buildup may be reduced by carrying out any revisions by a different approach, e.g., original implantation from an anterior approach and revision from a left or right lateral approach, or vice versa.  
         [0104]     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. It is appreciated that various features of the above-described examples can be mixed and matched to form a variety of other alternatives. As such, the described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.