Abstract:
Instrumentation for implanting an artificial intervertebral disc includes an inserter/impactor for inserting and removing the static trials and for inserting the artificial intervertebral discs, the inserter/impactor having at least one shaft having a longitudinal axis and a shaft distal end adapted for engagement with the trials and the disc, the shaft distal end further having forward surfaces for engagement with corresponding confronting surfaces of at least one of the baseplates for axial rotationally aligning the at least one of the baseplates with respect to the longitudinal axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    The present application is a continuation application of U.S. patent application Ser. No. 10/282,356 (filed Oct. 29, 2002) entitled “Instrumentation and Methods for use in Implanting an Artificial Intervertebral Disc”, which is a continuing application of U.S. patent application Ser. No. 10/256,160 (filed Sep. 26, 2002) entitled “Artificial Intervertebral Disc Having Limited Rotation Using a Captured Ball and Socket Joint With a Solid Ball and Compression Locking Post”, which is a continuing application of U.S. patent application Ser. No. 10/175,417 (filed Jun. 19, 2002) entitled “Artificial Intervertebral Disc Utilizing a Ball Joint Coupling”, which is a continuing application of U.S. patent application Ser. No. 10/151,280 (filed May 20, 2002) entitled “Tension Bearing Artificial Disc Providing a Centroid of Motion Centrally Located Within an Intervertebral Space”, which is a continuing application of both U.S. patent application Ser. No. 09/970,479 (filed Oct. 4, 2001) entitled “Intervertebral Spacer Device Utilizing a Spirally Slotted Belleville Washer Having Radially Extending Grooves” as well as U.S. patent application Ser. No. 10/140,153 (filed May 7, 2002) entitled “Artificial Intervertebral Disc Having a Flexible Wire Mesh Vertebral Body Contact Element”, the former being a continuing application of U.S. patent application Ser. No. 09/968,046 (filed Oct. 1, 2001) entitled “Intervertebral Spacer Device Utilizing a Belleville Washer Having Radially Extending Grooves” and the latter being a continuing application of both U.S. patent application Ser. No. 09/970,479 (detailed above) as well as U.S. patent application Ser. No. 10/128,619 (filed Apr. 23, 2002) entitled “Intervertebral Spacer Having a Flexible Wire Mesh Vertebral Body Contact Element”, which is a continuing application of both U.S. patent application Ser. No. 09/906,119 (filed Jul. 16, 2001) and entitled “Trial Intervertebral Distraction Spacers” as well as U.S. patent application Ser. No. 09/982,148 (filed Oct. 18, 2001) and entitled “Intervertebral Spacer Device Having Arch Shaped Spring Elements”. All of the above mentioned applications are hereby incorporated by reference herein in their respective entireties.  
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to systems and methods for use in spine arthroplasty, and more specifically to instruments for distracting an intervertebral space, inserting and removing trial artificial intervertebral discs, and inserting, impacting, repositioning, leveling and extracting artificial intervertebral discs, and methods of use thereof.  
         BACKGROUND OF THE INVENTION  
         [0003]    The bones and connective tissue of an adult human spinal column consists of more than twenty discrete bones coupled sequentially to one another by a tri-joint complex that consists of an anterior disc and the two posterior facet joints, the anterior discs of adjacent bones being cushioned by cartilage spacers referred to as intervertebral discs. These more than twenty bones are anatomically categorized as being members of one of four classifications: cervical, thoracic, lumbar, or sacral. The cervical portion of the spine, which comprises the top of the spine, up to the base of the skull, includes the first seven vertebrae. The intermediate twelve bones are the thoracic vertebrae, and connect to the lower spine comprising the five lumbar vertebrae. The base of the spine is the sacral bones (including the coccyx). The component bones of the cervical spine are generally smaller than those of the thoracic spine, which are in turn smaller than those of the lumbar region. The sacral region connects laterally to the pelvis. While the sacral region is an integral part of the spine, for the purposes of fusion surgeries and for this disclosure, the word spine shall refer only to the cervical, thoracic, and lumbar regions.  
           [0004]    The spinal column is highly complex in that it includes these more than twenty bones coupled to one another, housing and protecting critical elements of the nervous system having innumerable peripheral nerves and circulatory bodies in close proximity. In spite of these complications, the spine is a highly flexible structure, capable of a high degree of curvature and twist in nearly every direction.  
           [0005]    Genetic or developmental irregularities, trauma, chronic stress, tumors, and degenerative wear are a few of the causes that can result in spinal pathologies for which surgical intervention may be necessary. With respect to the failure of the intervertebral disc, and the insertion of implants and/or height restorative devices, several methods and devices have been disclosed in the prior art that achieve immobilization and/or fusion of adjacent bones by implanting artificial assemblies in or on the spinal column. More recently, the development of non-fusion implant devices, which purport to permit continued natural movement in the tri-joint complex, have provided great promise as a preferably alternative to fusion devices. The region of the back that needs to be corrected, as well as the individual variations in anatomy, determine the appropriate surgical protocol and implantation assembly. Generally, the preparation of the intervertebral space for the receipt of fusion or non-fusion devices involves removing the damaged disc material and thereafter distracting the adjacent vertebral bones to their appropriate distance apart. Once the proper height of the intervertebral space is restored, the fusion or non-fusion device can be implanted.  
           [0006]    It is an object of the invention to provide instrumentation and methods that enable surgeons to more accurately, easily, and efficiently prepare the intervertebral space and implant fusion or non-fusion devices. Other objects of the invention not explicitly stated will be set forth and will be more clearly understood in conjunction with the descriptions of the preferred embodiments disclosed hereafter.  
         SUMMARY OF THE INVENTION  
         [0007]    The preceding objects are achieved by the invention, which includes static trial artificial intervertebral discs (sometimes referred to herein as a “static trial”), a static trial artificial intervertebral disc holder (sometimes referred to herein as a “static trial holder”), a dynamic trial artificial intervertebral disc (sometimes referred to herein as a “dynamic trial”), an artificial intervertebral disc inserter/impactor (sometimes referred to herein as an “inserter/impactor”), an artificial intervertebral disc repositioner/extractor (sometimes referred to herein as a “repositioner/extractor”), and an artificial intervertebral disc leveler (sometimes referred to herein as a “leveler”).  
           [0008]    More particularly, the systems and methods disclosed herein are intended for use in spine arthroplasty procedures, and specifically for use with the systems and methods described herein in conjunction with the systems and method described in U.S. patent application Ser. No. 10/256,160 (filed Sep. 26, 2002) entitled “Artificial Intervertebral Disc Having Limited Rotation Using a Captured Ball and Socket Joint With a Solid Ball and Compression Locking Post” (hereinafter referred to as “the &#39;160 application”) as well as U.S. patent application Ser. No. 09/906,127 (filed Jul. 16, 2001) entitled “Insertion Tool For Use With Intervertebral Spacers” (hereinafter referred to as “the &#39;127 application”), both applications of which are mentioned above. However, it should be understood that the systems and methods described herein are also suitable for use with other systems and methods without departing from the scope of the invention.  
           [0009]    For example, while the static trials described herein are primarily intended for use in determining the appropriate size of particular embodiments of the artificial intervertebral disc implants described in the &#39;160 application to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space, they can also be used for determining the appropriate size of any other suitably configured orthopedic implant or trial to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space.  
           [0010]    And, for example, while the static trial holder described herein is primarily intended for use in holding, inserting, removing, and otherwise manipulating the static trials described herein, it can also be used for manipulating any embodiment of the trial spacers described in the &#39;127 application (also referred to therein and herein as distraction spacers), and can also be used for manipulating any other suitably configured orthopedic device.  
           [0011]    And, for example, while the dynamic trial described herein is primarily intended for use in distracting an intervertebral space according to the procedures described herein and/or for determining the appropriate size of particular embodiments artificial intervertebral disc implants described in the &#39;160 application to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space, it can also be used for distracting an intervertebral space according to other procedures and/or for determining the appropriate size of any other suitably configured orthopedic implant or trial to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space.  
           [0012]    And, for example, while the inserter/impactor described herein is primarily intended for use in holding, inserting, removing, impacting, extracting, and otherwise manipulating particular embodiments of the artificial intervertebral disc implants described in the &#39;160 application, it can also be used for manipulating any other suitably configured orthopedic implant or trial.  
           [0013]    And, for example, while the repositioners/extractors described herein is primarily intended for use in repositioning and/or extracting and/or otherwise manipulating particular embodiments of the artificial intervertebral disc implants described in the &#39;160 application, it can also be used for manipulating any other suitably configured orthopedic implant or trial.  
           [0014]    And, for example, while the leveler described herein is primarily intended for use in setting the proper position of, and/or otherwise manipulating, particular embodiments of the artificial intervertebral disc implants described in the &#39;160 application, it can also be used for manipulating any other suitably configured orthopedic implant or trial.  
           [0015]    While the instrumentation described herein (e.g., the static trials, static trial holder, dynamic trial, inserter/impactor, repositioners/extractors, and leveler) will be discussed for use with the artificial intervertebral disc of FIGS. 1 g - n , such discussions are merely by way of example and not intended to be limiting of their uses. Thus, it should be understood that the tools can be used with any of the artificial intervertebral discs disclosed in the &#39;160 application, or any other artificial intervertebral disc having (or being modifiable or modified to have) suitable features therefor. Moreover, it is anticipated that the features of the artificial intervertebral disc (e.g., the flat surfaces and accompanying holes) and/or the static trials (e.g., the cylindrical trunks and flat surfaces and accompanying holes) that are used by the tools discussed herein to hold and/or manipulate these devices (such features, it should be noted, were first shown and disclosed in the &#39;160 application and the &#39;127 application) can be applied, individually or collectively or in various combinations, to other trials, spacers, artificial intervertebral discs or other orthopedic devices as stand-alone innovative features for enabling such trials, spacers, artificial intervertebral discs, or other orthopedic devices to be more efficiently and more effectively held and/or manipulated by the tools described herein or by other tools having suitable features. In addition, it should be understood that the invention encompasses artificial intervertebral discs, spacers, trials (static or dynamic), and/or other orthopedic devices, that have one or more of the features disclosed herein, in any combination, and that the invention is therefore not limited to artificial intervertebral discs, spacers, trials, and/or other orthopedic devices having all of the features simultaneously.  
           [0016]    More particularly with regard to the static trials described herein, a plurality of static trials are provided primarily for use in determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size of the artificial intervertebral disc can be implanted) into the distracted intervertebral space (e.g., the artificial intervertebral disc  160  of FIGS. 1 g - n ). Preferably, for each artificial intervertebral disc to be implanted, a plurality of sizes of the artificial intervertebral disc would be available. That is, preferably, a plurality of the same type of artificial intervertebral disc would be available, each of the plurality having a respective width and depth dimension combination that allows it to fit within a correspondingly dimensioned intervertebral space. For example, the plurality of artificial intervertebral discs could include artificial intervertebral discs having widths being either 35 mm or 40 mm, and depths ranging from 14 mm to 18 mm in 1 mm increments, for a total of 10 discs. Accordingly, preferably, each of the plurality of static trials  100  for use with a particular plurality of differently sized artificial intervertebral discs would have a respective width and depth dimension set corresponding to the width and depth of a respective one of the plurality of differently sized artificial intervertebral discs. For example, the plurality of static trials  100  for use with the set of artificial intervertebral discs described for example could include static trials  100  having widths being either 35 mm or 40 mm, and depths ranging from 14 mm to 18 mm in 1 mm increments, for a total of 10 static trials. It should be understood that the artificial intervertebral discs and/or the static trials  100  can be offered in a variety of dimensions without departing from the scope of the invention, and that the dimensions specifically identified and quantified herein are merely exemplary. Moreover, it should be understood that the set of static trials  100  need not include the same number of trials for each artificial intervertebral disc in the set of artificial intervertebral discs, but rather, none, one, or more than one trial can be included in the trial set for any particular artificial intervertebral disc in the set.  
           [0017]    Each of the plurality of static trials preferably further includes features that can be used by the static trial holder (described below), the inserter/impactor (described below), and the repositioners/extractors (described below). With regard to a feature that can be used by the static trial holder, each static trial preferably includes a recess that can be gripped by the opposing semicircular extents of the static trial holder. Preferably, this recess forms an annular groove that establishes a cylindrical trunk between the baseplates of the static trial, such that the baseplates extend as flanges from either end of the cylindrical trunk. Accordingly, preferably, the opposing semicircular extents each have a thickness smaller than the width of the annular groove, and as such fit into the annular groove to grip the cylindrical trunk between them.  
           [0018]    With regard to features that can be used by the inserter/impactor, each static trial (and each artificial intervertebral disc that the trials approximate) preferably includes an anteriorly facing flat surface, flanked by two anteriolaterally facing flat surfaces (one on each side of the anteriorly facing flat surface), and, to provide for holding of the static trial or disc for an anterior insertion approach, a hole spaced from the anteriorly facing flat surface, the hole having a longitudinal axis parallel to the anteriorly facing flat surface. The holding pin of the inserter/impactor fits within the hole, and the angled flat surfaces of the static trial or disc fit against the correspondingly angled flat surfaces of the inserter/impactor, and operation of the inserter/impactor pulls the holding pin toward the flat surface of the inserter/impactor opposite the pin, to rigidly hold the static trial or disc by the baseplate. When the static trial is held in this manner, rotation of the static trial or disc about a longitudinal axis (e.g., in the case of the trials, an axis parallel to the longitudinal axis of the cylindrical trunk) relative to the inserter/impactor is prevented by interference of the corners of the static trial&#39;s or disc&#39;s flat surfaces and the corners of the inserter/impactor&#39;s flat surfaces, similar to the manner in which a wrench holding a nut prevents rotation of the nut relative to the wrench. Further, the holding of the static trial or disc in this manner allows for some repositioning of the static trial or disc in the intervertebral space via rotation of the static trial or disc in either direction about the longitudinal axis of the intervertebral space.  
           [0019]    Preferably, both of the baseplates of the static trial or disc have similarly configured flat surfaces, and both baseplates&#39; flat surfaces fit against the angled flat surfaces of the inserter/impactor to provide for a more secure holding of the static trial or disc by the inserter/impactor. Also preferably, in order to provide for a holding of the static trial or disc for two additional (here, anteriolateral) insertion approaches, each static trial or disc also include two additional holes, one spaced apart from one of the anteriolaterally facing flat surfaces, and the other spaced apart from the other of the anteriolaterally facing flat surfaces. Accordingly, operation of the inserter/impactor can fit the holding pin into either of these two additional holes, and hold the anteriolaterally facing flat surface (the one associated with the hole into which the pin is fit) of the static trial or disc against the flat surface of the inserter/impactor opposite the pin. It should be understood that preferably, in order to facilitate these two additional approaches, the angle separating the anteriorly facing flat surface of the static trial or disc and one of the anteriolaterally facing flat surfaces of the static trial or disc is equal to the angle separating the anteriorly facing flat surface and the other of the anteriolaterally facing flat surfaces.  
           [0020]    With regard to features that can be used by the repositioners/extractors, each static trial (and each artificial intervertebral disc that the trials approximate) preferably includes at least two holes extending longitudinally into one of the baseplates of the trial or disc from the inwardly facing surface of the baseplate. More than two holes can be used to provide for multiple repositioning/extracting approaches. Preferably, in order for the same repositioning/extracting tool to be used for multiple approaches on the same trial or artificial intervertebral disc, adjacent holes should be separated by the same distance separating other adjacent holes.  
           [0021]    As discussed in greater detail below with regard to the repositioners/extractors, in order to engage two of the holes, each repositioner/extractor has two pins extending in parallel from a central shaft, perpendicular to the longitudinal axis of the central shaft. The pins can be inserted into the holes, and pulling or pushing on the central shaft along its longitudinal axis when the holes are engaged pulls or pushes the static trial or artificial intervertebral disc in the intervertebral space. Further, because two holes are engaged, the static trial or artificial intervertebral disc can be rotated in either direction about a longitudinal axis passing through the intervertebral space, by rotating of the central shaft of the repositioner/extractor about its distal end, about an axis parallel to the longitudinal axes of the pins.  
           [0022]    On each repositioner/extractor, the pins are formed on prongs that extend laterally from the central shaft. The direction of the prongs, and the location of the pins relative to the central shaft, determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Further, the number and location of holes further determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Accordingly, the present invention contemplates a variety of repositioner/extractors, and a variety of holes configurations, to provide the surgeon with a variety of possible surgical approach angles.  
           [0023]    As described in greater detail below, three repositioner/extractors are illustrated and described (symmetric, offset left, and offset right) for example, and, for example, two hole configurations are illustrated and described. A first hole configuration includes the hole configuration described above, that is, three holes on one of the baseplates (e.g., the lower baseplate), the holes being configured so that a first hole is located in the anterior-posterior plane, and the adjacent (second and third) holes are located in respective opposing anteriolateral planes on either side of the first hole. A second hole configuration includes four holes on one of the baseplates (e.g., the upper baseplate), the holes being configured so that first and second holes straddle the anterior-posterior plane, a third hole is located so that the third hole and the first hole straddle one of the opposing anteriolateral planes, and a fourth hole is located so that the fourth hole and the second hole straddle the other of the opposing anteriolateral planes.  
           [0024]    With further regard to the static trial holder described herein, the static trial holder is provided primarily for use in holding, inserting, removing, and otherwise manipulating the static trials described herein. Preferably, the static trial holder has a pair of opposing prongs that open away from one another and close toward one another. Each of the prongs has a semicircular extent and the semicircular extents face one another to define a circular holding enclosure that is useful for capturing the cylindrical trunk of the static trial between them. The prongs are spring biased toward a neutral position such that the holding enclosure is spring biased to a receptive state in which the cylindrical trunk can be snapped into (or out of) the holding enclosure by temporarily placing the holding enclosure in an expanded state (by forcing the cylindrical trunk against the mouth of the enclosure) that allows passage of the cylindrical trunk through the mouth of the enclosure. Once the cylindrical trunk is in the enclosure, the holding enclosure can be placed in a contracted state, or locked, where the trial is more securely held, so that the trial will not escape the holding enclosure as it is experiencing greater forces while being inserted and removed from the intervertebral space. This locking is effected by rotating a sleeve that surrounds the prongs. The bore of the sleeve is configured to press the prongs together when the sleeve is rotated a quarter turn, and to allow them to separate when the sleeve is again rotated a quarter turn (in either direction). The sleeve is biased toward stopping its rotation at either the “locked” or “unlocked” states of the holding enclosure, by the cooperation of recesses on the extension&#39;s outer surface and corresponding spring plungers radially disposed to project from the sleeve&#39;s inner surface. It should be understood that when the static trial is being held (either when the holding enclosure is in its receptive state or in its contracted state), because the semicylindrical extents fit within the annular groove of the static trial, the static trial will not escape from the enclosure along the longitudinal axis of the cylindrical trunk. While the static trial holder is discussed herein as primarily used for manipulating the static trials, it preferably is also useful for manipulating the distraction spacers described in the &#39;127 application, in that the semicircular extents of the pincers preferably also interact with the annular grooves and cylindrical trunks of those distraction spacers in the same manner as described herein.  
           [0025]    With regard to the dynamic trial described herein, the dynamic trial is provided primarily for distracting an intervertebral space according to the procedures described herein and/or for determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space. While the distraction systems and methods described in the &#39;127 application are also useful for distracting an intervertebral space, the dynamic trial is provided as an additional or alternate distraction tool. Further, while the static trials described herein as useful for determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size can be implanted), the dynamic trial is provided as an additional or alternate sizing tool.  
           [0026]    The dynamic trial preferably includes a shaft having a bifurcated trial at a distal end. Each half of the bifurcated trial preferably has on its outwardly facing surface a convex dome that is shaped like the convex dome of the corresponding baseplate of the artificial intervertebral disc that the dynamic trial approximates. The shaft includes an inner shaft portion that centrally divides into upper and lower distal extensions that, from the point of division to their distal ends, are each biased toward positions in which they converge toward one another. The lower distal extension is connected to the lower half of the bifurcated trial, and the upper distal extension is connected to the upper half of the bifurcated trial. Preferably, the upper half is adjustably connected to the upper distal extension by a pivot pin that allows the upper half to rotate about a lateral axis that passes through the longitudinal and lateral center of the bifurcated trial. This axis of rotation allows the upper half, when separating from the lower half, to adjust to the orientation of the upper vertebral bone without causing the bone to hinge relative to the lower vertebral bone. In order to effect the separation of the upper and lower halves, the shaft further includes an outer shaft potion that is translatable adjacent the inner shaft portion, the outer shaft portion having a pin that passes between the distal extensions.  
           [0027]    The outer shaft portion is preferably translatable distally by the forward movement of a control knob near the proximal end of the shaft, and translatable proximally by backward movement of the control knob. As the outer shaft portion is pushed distally, the pin is pushed distally to overcome the bias of the divided extensions to separate them and correspondingly separate the halves of the bifurcated trial. Preferably, markings are provided on the inner shaft portion to quantify the depth (to which the bifurcated trial has been expanded) corresponding to the distance that the outer shaft portion has been translated with respect to the inner shaft portion. It is anticipated that the pushing force required to separate the halves will increase as they separate, due to the compression of the spine seeking to close the intervertebral space and the annulus seeking to prevent the adjacent vertebral discs from separating beyond a certain point. Therefore, to provide a mechanical advantage to the operator in the event that greater distraction is required, but the operator cannot push the control knob farther with unaided human effort, an fine control knob is provided. The fine control knob is preferably threaded onto the proximal end of the inner shaft portion, proximal to the control knob. Thus, rotation of the fine control knob about the longitudinal axis of the inner shaft portion will cause the body of the fine control knob to press against the control knob to move it farther distally. The interference of the threads of the fine control knob-inner shaft portion interface prevents the fine control knob from backing up proximally unless the fine control knob is reverse rotated to effect that result. Finally, the proximal end of the shaft is preferably flanged to serve as a slap hammer for impaction, if necessary for proper positioning of the bifurcated trial, and/or forced extraction of the bifurcated trial.  
           [0028]    With further regard to the inserter/impactor described herein, the inserter/impactor is provided primarily for holding, inserting, repositioning, removing, impacting, extracting, and otherwise manipulating an artificial intervertebral disc (or static trial) having features suitable for being manipulated by the inserter/impactor. Exemplary suitable artificial intervertebral discs are described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by the inserter/impactor, such features include those discussed above as being suitable features on the static trials and artificial intervertebral disc, namely, an anteriorly facing flat surface on the second (e.g., lower) baseplate of the trial or disc, flanked by two anteriolaterally facing flat surfaces (one on each side of the anteriorly facing flat surface), and, to provide for holding of the trial or disc for an anterior insertion approach, a hole spaced from the anteriorly facing flat surface, the hole having a longitudinal axis parallel to the anteriorly facing flat surface.  
           [0029]    The inserter/impactor includes a shaft having a distal end that has angled flat surfaces corresponding to and fittable against the angled flat surfaces of the static trial or artificial intervertebral disc, and a holding pin that extends from the center flat surface along a longitudinal axis of the shaft, the pin having a distal end that bends downward. The holding pin is spring loaded in a central channel of the shaft, so that it is biased toward and against the central flat surface (preferably, the bent end of the pin prevents it from entering the central channel). A flange, mechanically connected to the pin and translating adjacent the shaft, can be pushed distally to overcome the bias of the spring to space the pin away from the central flat surface. In this position, the pin can be inserted in the hole in the baseplate of the artificial intervertebral disc. Releasing the knob allows the spring to pull the pin back, causing the anteriorly facing surface of the baseplate to be held against the central flat surface of the inserter/impactor and the anteriolaterally facing flat surfaces of the artificial intervertebral disc to be held against the other corresponding flat surfaces of the inserter/impactor. A knob on the inserter/impactor can be rotated about the longitudinal axis of the shaft to pull the pin tighter and lock its position to more securely hold the baseplate, and reverse rotated to unlock and loosen the pin.  
           [0030]    When the static trial or artificial intervertebral disc is held in this manner, rotation of the trial or disc about its longitudinal axis relative to the inserter/impactor is prevented by interference of the corners of the trial&#39;s or disc&#39;s flat surfaces and the corners of the inserter/impactor&#39;s flat surfaces, similar to the manner in which a wrench holding a nut prevents rotation of the nut relative to the wrench. Further, the holding of the trial or disc in this manner allows for some repositioning of the trial or disc in the intervertebral space via rotation of the trial or disc in either direction about the longitudinal axis of the intervertebral space.  
           [0031]    Preferably, both of the baseplates of the static trial or disc have similarly configured and oriented flat surfaces, and both baseplates&#39; flat surfaces fit against the angled flat surfaces of the inserter/impactor, to provide for a more secure holding of the static trial or disc by the inserter/impactor.  
           [0032]    Also preferably, in order to provide for a holding of the static trial or disc for two additional (here, anteriolateral) insertion approaches, each static trial or disc also includes two additional holes, one spaced apart from one of the anteriolaterally facing flat surfaces, and the other spaced apart from the other of the anteriolaterally facing flat surfaces. Accordingly, operation of the inserter/impactor can fit the holding pin into either of these two additional holes, and hold the associated anteriolaterally facing flat surface (the one associated with the hole into which the pin is fit) of the static trial or disc against the flat surface of the inserter/impactor opposite the pin. It should be understood that preferably, in order to facilitate these two additional approaches, the angle separating the anteriorly facing flat surface of the static trial or disc and one of the anteriolaterally facing flat surfaces of the static trial or disc is equal to the angle separating the anteriorly facing flat surface and the other of the anteriolaterally facing flat surfaces.  
           [0033]    Also preferably, as shown the baseplates of each of the plurality of static trials are appropriately lordotically angled relative to one another to ease insertion of the static trial or artificial intervertebral disc into the intervertebral space and to mimic how the artificial intervertebral disc will typically be oriented as it is being inserted.  
           [0034]    With further regard to the repositioners/extractors described herein, each repositioner/extractor is provided primarily for repositioning and/or extracting a static trial or artificial intervertebral disc having features suitable for being manipulated by the repositioner/extractor. Exemplary suitable artificial intervertebral discs are described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by each repositioner/extractor, such features include at least two holes extending longitudinally into one of the baseplates of the static trial or artificial intervertebral disc from the inwardly facing surface of the baseplate. More than two holes can be used to provide for multiple repositioning/extracting approaches. Preferably, in order for the same repositioning/extracting tool to be used for multiple approaches on the same trial or artificial intervertebral disc, adjacent holes should be separated by the same distance separating other adjacent holes.  
           [0035]    In order to engage the two holes, each repositioner/extractor has two pins extending in parallel from a central shaft, perpendicular to the longitudinal axis of the central shaft. The pins are spaced to engage the two holes simultaneously, and each pin has a diameter smaller than the diameter of the hole it is to engage. Therefore, the pins can be inserted into the holes, and pulling or pushing on the central shaft along its longitudinal axis when the holes are engaged pulls or pushes the static trial or artificial intervertebral disc in the intervertebral space. Further, because two holes are engaged, the static trial or artificial intervertebral disc can be rotated in either direction about a longitudinal axis passing through the intervertebral space, by rotating of the central shaft of the repositioner/extractor about its distal end, about an axis parallel to the longitudinal axes of the pins. A handle at a proximal end of the central shaft is useful for pushing or pulling on the shaft. A flange adjacent the proximal end of the shaft is useful for impaction (either with a distally directed force or a proximally directed force), if necessary to manipulate the shaft.  
           [0036]    On each repositioner/extractor, the pins are formed on prongs that extend laterally from the central shaft. The direction of the prongs, and the location of the pins relative to the central shaft, determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Further, the number and location of holes further determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Accordingly, the present invention contemplates a variety of repositioner/extractors, and a variety of holes configurations, to provide the surgeon with a variety of possible surgical approach angles.  
           [0037]    With further regard to the leveler described herein, the leveler is provided primarily for establishing a parallel orientation of the baseplates (relative to one another), and/or securing the purchase of the stabilizing spikes, of an artificial intervertebral disc having features suitable for being manipulated by the leveler. Exemplary suitable artificial intervertebral discs are described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by the leveler, such features include suitably formed inwardly facing surfaces of the baseplates of the artificial intervertebral disc.  
           [0038]    More particularly, the leveler includes a shaft having a forked distal end formed by two opposing tongs that are symmetric to one another about a longitudinal axis of the shaft. Each of the tongs has an extent that initially curves laterally outward away from the shaft and from the other tong&#39;s extent, to define a central pocket forward of the shaft between the tongs&#39; extents. Each tong&#39;s extent then resumes a distal direction to become parallel to the shaft and to the other tong&#39;s extent.  
           [0039]    Each tong&#39;s extent has an upper surface and a lower surface. The upper surface is preferably shaped to conform against the inwardly facing surface of a first (e.g., upper) baseplate of an artificial intervertebral disc, and the lower surface is preferably shaped to conform against the inwardly facing surface of a second (e.g., lower) baseplate of the artificial intervertebral disc, so that insertion of the forked distal end of the leveler between the baseplates, with the central pocket of the distal end avoiding the central portion of the artificial intervertebral disc, and with the upper and lower surfaces so engaging the inwardly facing surfaces of the baseplates, causes the baseplates to be placed in parallel orientation with respect to one another. A handle is provided at a proximal end of the shaft for pushing, pulling, and otherwise manipulating the leveler as needed.  
           [0040]    When the artificial intervertebral disc is inserted into the intervertebral space, its baseplates will typically be lordotically angled with respect to one another. The leveler can be applied to the artificial intervertebral disc to bring the baseplates parallel to one another. The forked distal end of the leveler is inserted so that the tongs&#39; extents are placed between the inwardly facing surfaces of the baseplates, and so that the central pocket of the leveler avoids that portion of the artificial intervertebral disc that joins the baseplates. As the leveler is inserted, the tongs act as wedges to force the posterior portions of the baseplates away from one another. Accordingly, as the posterior portions are being separated, the stabilizing spikes on the outwardly facing surfaces of the baseplates find or secure their purchase in the hard bone of the outer ring of the vertebral body endplates. When the forked distal end is fully seated, the extents of the tongs hold the baseplates parallel to one another, and so that the spikes are fully engaged in the endplates. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]    [0041]FIGS. 1 a - f  show front (FIG. 1 a ), side (FIG. 1 b ), perspective (FIG. 1 c ), top (FIG. 1 d ), bottom cutaway (FIG. 1 e ) and top cutaway (FIG. 1 f ) views of a static trial of the present invention  
         [0042]    [0042]FIGS. 1 g - n  show front (FIG. 1 g ), side cutaway (FIG. 1 h ), top (FIG. 1 i ), side cutaway (FIG. 1 j ), bottom cutaway (FIG. 1 k ), top cutaway (FIG. 1 l ), bottom perspective (FIG. 1 m ), and top perspective (FIG. 1 n ) views of an exemplary artificial intervertebral disc of the present invention.  
         [0043]    [0043]FIGS. 2 a - k  show top (FIG. 2 a ), side (FIG. 2 b ), perspective (FIG. 2 c ), disassembly (FIG. 2 d - j ), and side cutaway (FIG. 2 k ) views of a static trial holder of the present invention.  
         [0044]    [0044]FIGS. 3 a - d  show side (FIG. 3 a ), top (FIG. 3 b ), side cutaway (FIG. 3 c ), and perspective (FIG. 3 d ) views of a dynamic trial of the present invention.  
         [0045]    [0045]FIGS. 4 a - d  show side (FIG. 4 a ), top (FIG. 4 b ), side cutaway (FIG. 4 c ), and perspective (FIG. 4 d ) views of an inserter/impactor of the present invention.  
         [0046]    [0046]FIGS. 4 e - h  show side (FIG. 4 e ), top (FIG. 4 f ), side cutaway (FIG. 4 g ), and perspective (FIG. 4 h ) views of an inserter/impactor of the present invention holding a static trial of the present invention.  
         [0047]    [0047]FIGS. 4 i - j  show top views of an inserter/impactor of the present invention holding a static trial of the present invention in two alternative ways.  
         [0048]    [0048]FIGS. 4 k - n  show side (FIG. 4 k ), top (FIG. 4 l ), side cutaway (FIG. 4 m ), and perspective (FIG. 4 n ) views of an inserter/impactor of the present invention holding an exemplary artificial intervertebral disc of the present invention.  
         [0049]    [0049]FIGS. 4 o - p  show top views of an inserter/impactor of the present invention holding an exemplary artificial intervertebral disc of the present invention in two alternative ways.  
         [0050]    [0050]FIGS. 5 a - c  show side (FIG. 5 a ), top (FIG. 5 b ), and perspective (FIG. 5 c ) views of a symmetric repositioner/extractor of the present invention.  
         [0051]    [0051]FIGS. 5 d - f  show side (FIG. 5 d ), top (FIG. 5 e ), and perspective (FIG. 5 f ) views of an offset left repositioner/extractor of the present invention.  
         [0052]    [0052]FIGS. 5 g - i  show side (FIG. 5 g ), top (FIG. 5 h ), and perspective (FIG. 5 i ) views of an offset right repositioner/extractor of the present invention.  
         [0053]    [0053]FIGS. 5 j - l  show side (FIG. 5 j ), top (FIG. 5 k ), and perspective (FIG. 5 l ) views of an alternative offset left repositioner/extractor of the present invention.  
         [0054]    [0054]FIGS. 5 m - o  show side (FIG. 5 m ), top (FIG. 5 n ), and perspective (FIG. 5 o ) views of an alternative offset right repositioner/extractor of the present invention.  
         [0055]    [0055]FIGS. 5 p - u  show exemplary various possible repositioner/extractor approach angles with a three hole configuration of the present invention.  
         [0056]    [0056]FIGS. 5 v - dd  show exemplary various possible repositioner/extractor approach angles with a four hole configuration of the present invention.  
         [0057]    [0057]FIGS. 6 a - d  bottom (FIG. 6 a ), side (FIG. 6 b ), front (FIG. 6 c ), top partial perspective (FIG. 6 d ), and bottom partial perspective (FIG. 6 e ) views of a leveler of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0058]    While the invention will be described more fully hereinafter with reference to the accompanying drawings, it is to be understood at the outset that persons skilled in the art may modify the invention herein described while achieving the functions and results of the invention. Accordingly, the descriptions that follow are to be understood as illustrative and exemplary of specific structures, aspects and features within the broad scope of the invention and not as limiting of such broad scope. Like numbers refer to similar features of like elements throughout.  
         [0059]    A preferred embodiment of a static trial of the present invention, and a preferred embodiment of an artificial intervertebral disc of the present invention, both for use with the instrumentation of the present invention, will now be described.  
         [0060]    Referring now to FIGS. 1 a - f , a static trial of the present invention is shown in front (FIG. 1 a ), side (FIG. 1 b ), perspective (FIG. 1 c ), top (FIG. 1 d ), bottom cutaway (FIG. 1 e ) and top cutaway (FIG. 1 f ) views. Referring now to FIGS. 1 g - n , an artificial intervertebral disc of the present invention is shown in front (FIG. 1 g ), side cutaway (FIG. 1 h ), top (FIG. 1 i ), side cutaway (FIG. 1 j ), bottom cutaway (FIG. 1 k ), top cutaway (FIG. 1 l ), bottom perspective (FIG. 1 m ), and top perspective (FIG. 1 n ) views.  
         [0061]    It should be understood that the illustration and reference herein to the artificial intervertebral disc shown in FIGS. 1 g - n  is merely to show an example of one type of artificial intervertebral disc that is contemplated by, encompassed by, and suitable for use with, the present invention, and that such illustration and reference herein is not meant to limit the scope of the present invention or limit the uses of the present invention. Rather, any other artificial intervertebral disc (or any other orthopedic device) having suitable features for being manipulated by the instrumentation and methods described herein are contemplated by the present invention. Indeed, the features suitable for manipulation (e.g., angled flat surfaces with adjacent holes) are encompassed by the present invention, regardless of to what orthopedic device they may be applied. Other exemplary suitable artificial intervertebral discs include, but are not limited to, the artificial intervertebral discs described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). It should be noted that, as can be seen from FIGS. 1 g - n , that the artificial intervertebral disc shown in FIGS.  1   g - n  has features similar to those of these other suitable artificial intervertebral discs of the &#39;160 application, and it should be understood that such similar features are structurally and functionally as described in the &#39;160 application. Such similar features include an inwardly facing surface  164   a  of the upper baseplate  164   a , and a convex structure  162  on the lower baseplate  168   b , the convex structure  162  having an inwardly facing surface  164   b.    
         [0062]    And, while the instrumentation described herein (e.g., the static trials, static trial holder, dynamic trial, inserter/impactor, repositioners/extractors, and leveler) will be discussed for use with the artificial intervertebral disc of FIGS. 1 g - n , such discussions are merely by way of example and not intended to be limiting of their uses. Thus, it should be understood that the tools can be used with any of the artificial intervertebral discs disclosed in the &#39;160 application, or any other artificial intervertebral disc having (or being modifiable or modified to have) suitable features therefor. Moreover, it is anticipated that the features of the artificial intervertebral disc (e.g., the flat surfaces and accompanying holes) and/or the static trials (e.g., the cylindrical trunks and flat surfaces and accompanying holes) that are used by the tools discussed herein to hold and/or manipulate these devices (such features, it should be noted, were first shown and disclosed in the &#39;160 application and the &#39;127 application) can be applied, individually or collectively or in various combinations, to other trials, spacers, artificial intervertebral discs or other orthopedic devices as stand-alone innovative features for enabling such trials, spacers, artificial intervertebral discs, or other orthopedic devices to be more efficiently and more effectively held and/or manipulated by the tools described herein or by other tools having suitable features. In addition, it should be understood that the invention encompasses artificial intervertebral discs, spacers, trials (static or dynamic), and/or other orthopedic devices, that have one or more of the features disclosed herein, in any combination, and that the invention is therefore not limited to artificial intervertebral discs, spacers, trials, and/or other orthopedic devices having all of the features simultaneously.  
         [0063]    A plurality of static trials  100  are provided primarily for use in determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size of the artificial intervertebral disc can be implanted) into the distracted intervertebral space (e.g., the artificial intervertebral disc  160  of FIGS. 1 g - n ). Preferably, for each artificial intervertebral disc to be implanted, a plurality of sizes of the artificial intervertebral disc would be available. That is, preferably, a plurality of the same type of artificial intervertebral disc would be available, each of the plurality having a respective width and depth dimension combination that allows it to fit within a correspondingly dimensioned intervertebral space. For example, the plurality of artificial intervertebral discs could include artificial intervertebral discs having widths being either 35 mm or 40 mm, and depths ranging from 14 mm to 18 mm in 1 mm increments, for a total of 10 discs. Accordingly, preferably, each of the plurality of static trials  100  for use with a particular plurality of differently sized artificial intervertebral discs would have a respective width and depth dimension set corresponding to the width and depth of a respective one of the plurality of differently sized artificial intervertebral discs. For example, the plurality of static trials  100  for use with the set of artificial intervertebral discs described for example could include static trials  100  having widths being either 35 mm or 40 mm, and depths ranging from 14 mm to 18 mm in 1 mm increments, for a total of 10 static trials. It should be understood that the artificial intervertebral discs and/or the static trials  100  can be offered in a variety of dimensions without departing from the scope of the invention, and that the dimensions specifically identified and quantified herein are merely exemplary. Moreover, it should be understood that the set of static trials  100  need not include the same number of trials for each artificial intervertebral disc in the set of artificial intervertebral discs, but rather, none, one, or more than one trial can be included in the trial set for any particular artificial intervertebral disc in the set.  
         [0064]    Each of the static trials (the static trial  100  shown is exemplary for all of the static trials in the plurality of static trials; preferably the static trials in the plurality differ from one another only with regard to overall dimensions as described above) includes at least one feature that can be gripped by a tool. Suitable tools include, but are not limited to, the static trial holder  200  described below, the inserter/impactor  400  described below, and the repositioners/extractors  510 ,  520 ,  530 ,  540  described below. Specifically, the static trial  100  includes a recess  102  that can be gripped by the opposing semicircular extents  216   a - b  of the static trial holder  200 . Preferably, this recess  102  forms an annular groove  104  that establishes a cylindrical trunk  106  between the upper and lower baseplates  108   a - b  of the static trial  100 , such that the baseplates  108   a - b  extend as flanges  110   a - b  from either end of the cylindrical trunk  106 . Accordingly, preferably, the opposing semicircular extents  216   a - b  each have a thickness smaller than the width of the annular groove  104 , and as such fit into the annular groove  104  to grip the cylindrical trunk  106  between them.  
         [0065]    In some embodiments, while not shown in FIGS. 1 a - f , it is also preferable that the annular groove  104  radially widen outwardly, such that the walls  112  of the annular groove  104  are tapered toward one another with the increasing depth of the groove  104 , such that the floor  114  of the groove  104  is more narrow than the opening  116  of the groove  104 . Accordingly, preferably, in such embodiments, each semicircular extent  216   a - b  correspondingly radially widens outwardly, such that the thinner portion of the extent  216   a - b  fits closer to the floor  114  of the annular groove  104 , so that the tapered surfaces of the extents  216   a - b  compress against the tapered walls  112  of the annular groove  104  when the static trial  100  is gripped by the static trial holder  200 . This taper locking provides for a secure grip so that the static trial  100  can be manipulated accurately and efficiently.  
         [0066]    In some embodiments, while not shown in FIGS. 1 a - f , it is also preferable that the floor of the annular groove  104  of the cylindrical trunk  106  be ridged (e.g., have ridges that run parallel to the longitudinal axis of the cylindrical trunk), and the surfaces of the semicircular extents  216   a - b  of the static trial holder  200  that compress against the floor of the annular groove  104  when the static trial holder  200  grips the static trial  100  be correspondingly provided with ridges. The interlocking of the ridges of the static trial  100  with the ridges of the static trial holder  200  when the static trial  100  is gripped prevents rotation of the static trial  100  about the longitudinal axis of the cylindrical trunk  106  with respect to the static trial holder  200 .  
         [0067]    Additionally with regard to features that can be gripped by a tool, each of the static trials includes at least one feature that can be gripped by a tool that preferably is also used to grip the artificial intervertebral disc that the trial approximates. Suitable tools that can grip both the trial and the artificial intervertebral disc include, but are not limited to, the inserter/impactor  400  described below. Specifically, for being gripped by the inserter/impactor  400 , each static trial  100  and artificial intervertebral disc  160  includes an anteriorly facing flat surface  120   b , 180   b , flanked by two anteriolaterally facing flat surfaces  120   a , 180   a  and  120   c , 180   c  (one on each side of the anteriorly facing flat surface  120   b , 180   b ), and, to provide for holding of the static trial  100  or disc  160  for an anterior insertion approach, a hole  122   b , 182   b  spaced from the anteriorly facing flat surface, the hole  122   b , 182   b  having a longitudinal axis parallel to the anteriorly facing flat surface  120   b , 180   b.    
         [0068]    The holding pin  408  of the inserter/impactor  400  fits within the hole  122   b , 182   b , and the angled flat surfaces  120   a - c , 180   a - c  of the static trial  100  or disc  160  fit against the correspondingly angled flat surfaces  420   a - c  of the inserter/impactor  400 , and operation of the inserter/impactor  400  pulls the holding pin  408  toward the flat surface  120   b , 180   b  of the inserter/impactor  400  opposite the pin  408 , to rigidly hold the static trial  100  or disc  160  by the structure of the static trial  100  or disc  160  having the hole  122   b , 182   b  (e.g., the baseplate  108   b , 168   b ). When the static trial  100  or disc  160  is held in this manner, rotation of the static trial  100  or disc  160  about a longitudinal axis (of the static trial  100  or disc  160 ) relative to the inserter/impactor  400  is prevented by interference of the corners of the static trial&#39;s  100  or disc&#39;s  160  flat surfaces  120   a - c , 180   a - c  and the corners of the inserter/impactor&#39;s  400  flat surfaces  420   a - c , similar to the manner in which a wrench holding a nut prevents rotation of the nut relative to the wrench. Further, the holding of the static trial  100  or disc  160  in this manner allows for some repositioning of the static trial  100  or disc  160  in the intervertebral space via rotation of the static trial  100  or disc  160  in either direction about the longitudinal axis of the intervertebral space.  
         [0069]    Preferably, both of the baseplates of the static trial  100  or disc  160  have similarly configured flat surfaces. For example, the lower baseplate&#39;s  108   b , 168   b  flat surfaces  120   a - c , 180   a - c  have similarly configured and similarly oriented counterpart flat surfaces  120   d - f , 180   d - f  on the upper baseplate  108   a , 168   a . Further preferably, both baseplates&#39;  108   a - b , 168   a - b  flat surfaces  120   a - f , 180   a - f  face the angled flat surfaces  420   a - c  of the inserter/impactor  400  when the static trial  100  or disc  160  is held by the inserter/impactor  400 . For example, as discussed below with regard to the inserter/impactor  400 , in an anterior approach for the trial  100  (as shown in FIGS. 4 e - h ),  120   a  and  120   d  facing  420   a ,  120   b  and  120   e  facing  420   b , and  120   c  and  120   f  facing  420   c , and in an anterior approach for the disc  160  (as shown in FIGS. 4 k - n ),  180   a  and  180   d  facing  420   a ,  180   b  and  180   e  facing  420   b , and  180   c  and  180   f  facing  420   c.    
         [0070]    It should be noted that preferably, when the static trial  100  is held by the inserter/impactor  400 , the flat surfaces  120   a - c  and the counterpart flat surfaces  120   d - f  are tightly held against the angled flat surfaces  420   a - c  of the inserter/impactor  400  as described above. It is also preferable that the baseplates  108   a - b  of each of the plurality of static trials  100  be appropriately lordotically angled relative to one another to ease insertion of the static trial  100  into the intervertebral space and to mimic how the artificial intervertebral disc  160  will typically be oriented as it is being inserted using the inserter/impactor  400 , and to ease insertion of the static trial  100  into the intervertebral space. While not shown in FIGS. 1 a - f , in some embodiments, when the static trials  100  are formed in such a lordotically oriented configuration, it is preferable that the flat surfaces  120   d - f  on the first (e.g., upper) baseplate  108   a  be parallel to the flat surfaces  120   a - c  of the second (e.g., lower) baseplate  108   b  in the static trial&#39;s  100  appropriately lordotically oriented configuration, so that when the static trial  100  is held tightly by the inserter/impactor  400 , the flat surfaces  120   a - f  are flush with the flat surfaces  420   a - c  of the inserter/impactor  400  even though the baseplates  108   a - b  are lordotically angled with respect to one another.  
         [0071]    By contrast, preferably, when the artificial intervertebral disc  160  is held by the inserter/impactor  400 , the flat surfaces  180   a - c  are tightly held against the angled flat surfaces  420   a - c  of the inserter/impactor  400  as described above, but the counterpart flat surfaces  180   d - f  are loosely held against the angled flat surfaces  420   a - c  of the inserter/impactor  400 . As such, the structure of the artificial intervertebral disc  160  having the counterpart flat surfaces  180   d - f  (e.g., the upper baseplate  168   a ) is able to angulate and rotate to a limited extent relative to the structure of the artificial intervertebral disc  160  having the flat surfaces  180   a - c . This permits the artificial intervertebral disc  160  to adjust to the intervertebral space (e.g., to the angulation of the adjacent vertebral endplates, defining the intervertebral space, relative to one another) as it is being inserted thereinto. That is, typically, the adjacent vertebral endplates will be lordotically angled with respect to one another as a result of the intervertebral space being prepared and distracted. As the artificial intervertebral disc  160  is then inserted into the intervertebral space using the inserter/impactor  400 , then, the baseplates  168   a - b  will be permitted to lordotically angle with respect to one another to squeeze into the intervertebral space.  
         [0072]    Also preferably, in order to provide for a holding of the static trial  100  or disc  160  for two additional (here, anteriolateral) insertion approaches, each static trial  100  or disc  160  also includes two additional holes  122   a , 182   a  and  122   c , 182   c , one (e.g.,  122   a , 182   a ) spaced apart from one of the anteriolaterally facing flat surfaces (e.g.,  120   a , 180   a ), and the other (e.g.,  122   c , 182   c ) spaced apart from the other of the anteriolaterally facing flat surfaces (e.g.,  120   c , 180   c ). Accordingly, operation of the inserter/impactor  400  can fit the holding pin  408  into either of these two additional holes  122   a , 182   a  or  122   c , 182   c , and hold the associated anteriolaterally facing flat surface (the one associated with the hole into which the pin  408  is fit) of the static trial  100  or disc  160  against the flat surface of the inserter/impactor  400  opposite the pin  408 . For example, as discussed below with regard to the inserter/impactor  400 , in a first anteriolateral approach for the trial  100  (as shown in FIG. 4 i ),  120   a  and  120   d  facing  420   b ,  120   b  and  120   e  not confronted, and  120   c  and  120   f  facing  420   a , and a first anteriolateral approach for the disc  160  (as shown in FIG. 4 o ),  180   a  and  180   d  facing  420   b ,  180   b  and  180   e  not confronted,  180   c  and  180   f  facing  420   a . And, for example, as discussed below with regard to the inserter/impactor  400 , in a second anteriolateral approach for the trial  100  (as shown in FIG. 4 j ),  120   a  and  120   d  facing  420   c ,  120   b  and  120   e  facing  420   a,  and  120   c  and  120   f  not confronted, and a second anteriolateral approach for the disc  160  (as shown in FIG. 4 p ),  180   a  and  180   d  facing  420   c ,  180   b  and  180   e  facing  420   a ,  180   c  and  180   f  not confronted.  
         [0073]    It should be understood that preferably, in order to facilitate these additional approaches, the angle separating the anteriorly facing flat surface of the static trial  100  or disc  160  and one of the anteriolaterally facing flat surfaces of the static trial  100  or disc  160  is equal to the angle separating the anteriorly facing flat surface and the other of the anteriolaterally facing flat surfaces. Preferably, the surfaces are angled with respect to one another at an angle of 33.4 degrees.  
         [0074]    It should also be understood that the inclusion of additional adjacent angulated surfaces (or placing the angulated surfaces in other locations on the trial or disc), and/or including corresponding holes adjacent to such surfaces, can provide the surgeon with additional approaches, e.g., other anteriolateral approaches, directly lateral approaches, posteriolateral approaches, and/or directly posterior approaches. For example, a trial or disc can have angled surfaces (and corresponding holes) along the entire perimeter of one or both of the baseplates, and thus enable the surgeon to engage the trial or disc from a number of angles, including anterior, posterior, lateral, anteriolateral, and posteriolateral angles.  
         [0075]    Additionally with regard to features that can be gripped by a tool, each of the static trials includes at least one feature that can be gripped by a tool that preferably is also used to grip the artificial intervertebral disc that the trial approximates. Suitable tools that can grip both the trial and the artificial intervertebral disc include, but are not limited to, the repositioners/extractors  500 ,  510 ,  520 ,  530 ,  540  described below. Specifically, for being gripped by the repositioners/extractors, each static trial  100  and artificial intervertebral disc  160  includes at least two holes extending longitudinally into one of the baseplates of the static trial  100  or artificial intervertebral disc  160  from the inwardly facing surface of the baseplate. More than two holes can be used to provide for multiple repositioning/extracting approaches. Preferably, in order for the same repositioning/extracting tool to be used for multiple approaches on the same trial or artificial intervertebral disc, adjacent holes should be separated by the same distance separating other adjacent holes.  
         [0076]    As discussed in greater detail below with regard to the repositioners/extractors  500 ,  510 ,  520 ,  530 ,  540 , in order to engage two of the holes, each repositioner/extractor has two pins extending in parallel from a central shaft, perpendicular to the longitudinal axis of the central shaft. The pins are spaced to engage the two holes simultaneously, and each pin has a diameter smaller than the diameter of the hole it is to engage. Therefore, the pins can be inserted into the holes, and pulling or pushing on the central shaft along its longitudinal axis when the holes are engaged pulls or pushes the static trial or artificial intervertebral disc in the intervertebral space. Further, because two holes are engaged, the static trial or artificial intervertebral disc can be rotated in either direction about a longitudinal axis passing through the intervertebral space, by rotating of the central shaft of the repositioner/extractor about its distal end, about an axis parallel to the longitudinal axes of the pins. A handle at a proximal end of the central shaft is useful for pushing or pulling on the shaft. A flange adjacent the proximal end of the shaft is useful for impaction (either with a distally directed force or a proximally directed force), if necessary to manipulate the shaft.  
         [0077]    On each repositioner/extractor, the pins are formed on prongs that extend laterally from the central shaft. The direction of the prongs, and the location of the pins relative to the central shaft, determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Further, the number and location of holes further determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Accordingly, the present invention contemplates a variety of repositioner/extractors, and a variety of holes configurations, to provide the surgeon with a variety of possible surgical approach angles.  
         [0078]    As described in greater detail below, three repositioner/extractors are illustrated and described (symmetric, offset left, and offset right) for example, and, for example, two hole configurations are illustrated and described. Referring again to FIGS. 1 a - n , a first hole configuration includes the hole configuration described above, that is, three holes on one of the baseplates (e.g., the lower baseplate  108   b , 168   b ), the holes being configured so that a first hole  122   b , 182   b  is located in the anterior-posterior plane, and the adjacent (second  122   a , 182   a  and third  122   c , 182   c ) holes are located in respective opposing anteriolateral planes on either side of the first hole  122   b , 182   b . (This hole configuration is also shown in FIGS. 5 p - u , each of which shows a top cutaway view of the artificial intervertebral disc  160  of FIGS. 1 g - n , showing its lower baseplate  168   b , having the first hole configuration, engaged by one of the repositioners/extractors  500 , 510 , 520 . Each view of the lower baseplate  168   b  shows the first hole  182   b , the second hole  182   a , and the third hole  182   c  of the first hole configuration.)  
         [0079]    Referring again to FIGS. 1 a - n , a second hole configuration includes four holes on one of the baseplates (e.g., the upper baseplate  108   a , 168   a ), the holes being configured so that first (e.g.,  130   c , 190   c ) and second (e.g.,  130   b , 190   b ) holes straddle the anterior-posterior plane, a third hole (e.g.,  130   d , 190   d ) is located so that the third hole and the first hole straddle one of the opposing anteriolateral planes, and a fourth hole (e.g.,  130   a , 190   a ) is located so that the fourth hole and the second hole straddle the other of the opposing anteriolateral planes. (This hole configuration is also shown in FIGS. 5 v - dd , each of which shows a bottom cutaway view of the artificial intervertebral disc of FIGS. 1 g - n , showing its upper baseplate  168   a , having the second hole configuration, engaged by one of the repositioners/extractors  500 , 510 , 520 . Each view of the upper baseplate shows the first hole  190   c , the second hole  190   b , the third hole  190   d , and the fourth hole  190   a , of the second hole configuration.)  
         [0080]    It should be understood that configurations having more or fewer holes, and in a variety of locations, are contemplated by the invention, and the detailed descriptions of only two hole configurations is not meant to limit the invention to only these two configurations. Importantly, the invention encompasses using a hole or any number of holes, bored at any suitable angle, whether parallel to other holes or not, in any number of locations on a spacer, a trial or an artificial intervertebral disc (not limited to locations on the baseplates), for purposes of enabling the spacer, trial, or disc to be gripped by a manipulation instrument (not limited to a repositioner/extractor) that engages the hole, and/or to enable the surgeon to work from a variety of approaches. For example, as described in more detail below, the first and second hole configurations described herein, in cooperation with the repositioner/extractors, provide the surgeon with the ability to work from a directly anterior approach, as well as several anteriolateral approaches. It should be understood that additional hole configurations can enable the surgeon to work from a directly posterior approach, posteriolateral approaches, directly lateral approaches, or anteriolateral approaches that are different that those illustrated. For example, the placement of one or more suitably spaced holes (or the addition of one or more holes) on the posterior edge, and/or one or both of the lateral edges of one or both of the baseplates, would enable the surgeon to use the repositioner/extractors of the present invention to achieve such approaches.  
         [0081]    Thus, it can be seen that each of the repositioner/extractors can be used in more than one manner depending on the tool desired and the approach desired. These manners are described in greater detail below and illustrated in FIGS. 5 p - dd  with regard to the detailed description of the repositioners/extractors.  
         [0082]    Also preferably, the baseplates  108   a - b  of each of the plurality of static trials  100  preferably has a convex dome  124   a - b  on its outwardly facing surface  126   a - b  that is shaped like the convex dome  184   a - b  on the outwardly facing surface  186   a - b  of the corresponding baseplate  168   a - b  of the artificial intervertebral disc  160  that the static trial  100  approximates. Preferably, each convex dome  124   a - b  is smooth, rather than having a porous coating that is preferred for the convex domes  184   a - b  of the artificial intervertebral disc  160 , and each outwardly facing surface  126   a - b  does not have stabilizing spikes such as the stabilizing spikes  188   a - b  on the outwardly facing surfaces  186   a - b  of the artificial intervertebral disc  160 . The omission of these device stabilizing and bone ingrowth encouraging structures and surfaces on the static trials  100  enables the surgeon to test the size of the artificial intervertebral disc  160  to be implanted without traumatically engaging the vertebral body endplates.  
         [0083]    Accordingly, the surgeon can prepare and distract the intervertebral space, and then insert and remove at least one of the static trials (or more, as necessary) to find the size that is most appropriate for the intervertebral space.  
         [0084]    A preferred embodiment of a static trial holder of the present invention will now be described.  
         [0085]    Referring to FIGS. 2 a - c  and  2   k , a static trial holder of the present invention is shown in side (FIG. 2 a ), top (FIG. 2 b ), perspective (FIG. 2 c ), and side cutaway (FIG. 2 k ) views. In addition, referring to FIGS. 2 d - f , a sleeve of the static trial holder is shown in side cutaway (FIG. 2 d ), front (FIG. 2 e ), and back (with partial cutaway) (FIG. 2 f ) views. In addition, referring to FIGS. 2 g - i , an extension of the static trial holder is shown in top (FIG. 2 g ), proximal cutaway (FIG. 2 h ), side (FIG. 2 i ), and distal cutaway (FIG. 2 j ) views.  
         [0086]    The static trial holder  200  is provided primarily for use in holding, inserting and removing the static trials described herein, or distraction spacers having suitable features therefor, such as the distraction spacers disclosed in the &#39;127 application.  
         [0087]    More specifically, the static trial holder  200  includes a handle  202 , an extension  204 , and a sleeve  206 . As shown in FIG. 2 k , the handle  202  and the extension  204  are fixed to one another (preferably by the distal end of the handle  202  being fixed to the proximal end of the extension  204 ) to form a shaft  208 . The sleeve  206  surrounds the extension  204  and is rotatable with respect to the handle  202  and the extension  204  about the longitudinal axis of the shaft  208 . The handle  202  preferably has an flange  232  at its proximal end for use in applying a distally or proximally directed force to get the static trial  100  (or distraction spacer) into or out of the intervertebral space, and/or for use in helping the surgeon rotate the sleeve  206  with respect to the extension  204  (by gripping the flange  232  and the control knob  219  described below).  
         [0088]    The distal end of the extension  204  forms a contractable and expandable holding enclosure  210  in that the distal end is divided at a fulcrum  212  into two prongs  214   a - b , each of which terminates in a semicircular extent  216   a - b , each of which has a tapered end  215   a - b . The extents  216   a - b  are oriented such that the tapered ends  215   a - b  face one another to define a radially inwardly tapering mouth  213 , and such that the semicircular openings oppose one another to define the holding enclosure  210 . The prongs  214   a - b  are spring biased toward a neutral position (preferably by the formation of the fulcrum  212  in combination with the strength of the material of which the extension  204  is made) such that the holding enclosure  210  is spring biased to a receptive state (described below), but the prongs  214   a - b  can be brought together to contract the holding enclosure  210  to a contracted state, (described below) or the prongs  214   a - b  can be further separated to expand the holding enclosure  210  to an expanded state (described below).  
         [0089]    When the holding enclosure  210  is in the receptive state, the width of the mouth  213  of the holding enclosure  210  does not accommodate the diameter of the cylindrical trunk  106  of the static trial  100  (or distraction spacer) for passage therethrough. However, from this receptive state, the mouth  213  can be temporarily widened (placing the holding enclosure  210  in its expanded state) to accommodate the diameter (for passage of the cylindrical trunk  106  through the mouth  213 ), if a sufficient force is applied to overcome the neutral position bias of the prongs  214   a - b  and thus widen the mouth  213 . (Preferably, there is enough space between the outer surfaces of the prongs  214   a - b  and the inner surface of the bore  218  of the sleeve, when the prongs  214   a - b  are in their neutral position, so that the prongs  214   a - b  can be separated without interference.) The sufficient force can be applied by pressing the cylindrical trunk  106  against the tapered ends  215   a - b  of the mouth  213 , in that the separating force component of the radially inward force of the pressing will be applied to the semicircular extents  216   a - b  by the taper of the tapered ends  215   a - b . Because the holding enclosure  210  is biased toward the receptive state, after the cylindrical trunk  106  is passed through the mouth  213  and into the holding enclosure  210 , the holding enclosure  210  will return to its receptive state in which the width of the mouth  213  does not allow passage of the cylindrical trunk  106  without the sufficient force. Preferably, the force required to widen the mouth  213  is greater than gravity and/or the greatest force that will be experienced by moving the static trial holder  200  prior to placing the holding enclosure  210  in the contracted state. Therefore, once the cylindrical trunk  106  is in the holding enclosure  210 , even before the holding enclosure  210  is placed in its contracted state, the cylindrical trunk  106  will not escape the holding enclosure  210  as the static trial holder  200  is oriented with the holding enclosure  210  downward, or is moved about.  
         [0090]    It should be understood that when the static trial  100  (or distraction spacer) is being held (either when the holding enclosure  210  is in its receptive state or in its contracted state discussed below), because the semicylindrical extents  216   a - b  fit within the annular groove  104  of the static trial  100  (or distraction spacer), the static trial  100  (or distraction spacer) will not escape from the enclosure along the longitudinal axis of the cylindrical trunk  106 . That is, as noted above, the recess  102  of each static trial  100  (or distraction spacer) forms an annular groove  104  that establishes the cylindrical trunk  106  between the baseplates of the static trial (or distraction spacer), such that the baseplates extend as flanges from either end of the cylindrical trunk  106 . Accordingly, preferably, the opposing semicircular extents each have a thickness smaller than the width of the annular groove  104 , and as such fit into the annular groove  104  to grip the cylindrical trunk  106  between them.  
         [0091]    In some embodiments, while not shown in FIGS. 1 a - f  or FIGS. 2 a - k , it is preferable that the annular groove  104  radially widen outwardly, such that the walls of the annular groove  104  taper toward one another with the increasing depth of the groove, such that the floor of the groove is more narrow than the opening  116  of the groove. Accordingly, preferably, in such embodiments, each semicircular extent  216   a - b  correspondingly radially widens outwardly, such that the thinner portion of the extent  216   a - b  fits closer to the floor of the annular groove  104 , so that the tapered surfaces  215   a - b  of the extents  216   a - b  compress against the tapered walls of the annular groove  104  when the static trial  100  is gripped by the static trial holder  200 . This taper locking provides for a secure grip so that the static trial  100  can be manipulated accurately and efficiently.  
         [0092]    In some embodiments, while not shown in FIGS. 1 a - f  or FIGS. 2 a - k , it is also preferable that the floor of the annular groove  104  of the cylindrical trunk  106  be ridged (e.g., have ridges that run parallel to the longitudinal axis of the cylindrical trunk), and the surfaces of the semicircular extents  216   a - b  of the static trial holder  200  that compress against the floor of the annular groove  104  when the static trial holder  200  grips the static trial  100  be correspondingly provided with ridges. The interlocking of the ridges of the static trial  100  with the ridges of the static trial holder  200  when the static trial  100  is gripped prevents rotation of the static trial  100  about the longitudinal axis of the cylindrical trunk  106  with respect to the static trial holder  200 .  
         [0093]    In order to more tightly hold the static trial  100  (or distraction spacer) for manipulation of the static trial  100  (or distraction spacer) during surgical procedures in which greater forces will be experienced by the static trial  100  (or distraction spacer) and the static trial holder  200 , the holding enclosure  210  can be placed in a contracted state. The holding enclosure  210  can be considered “unlocked” in its receptive or expanded states, and “locked” in its contracted state, with respect to the nature of the hold that the static trial holder  200  potentially can have or has on the cylindrical trunk  106 . Preferably, when the holding enclosure  210  is locked, a force greater than that which is applicable by an unaided surgeon or nurse (i.e., that which can be applied to remove the cylindrical trunk  106  from the holding enclosure  210  when the holding enclosure  210  is in its receptive state), and greater than that which will be experienced by the static trial  100  (or distraction spacer) and the static trial holder  200  during surgical procedures) would be required to pull the cylindrical trunk  106  out of the holding enclosure  210 . The placement of the holding enclosure  210  in its locked state or unlocked state is effected by operation of a holding assembly that includes the extension  204  and the sleeve  206  and the manner in which they are configured and interact.  
         [0094]    More particularly, the prongs  214   a - b  can be brought together, to lock the holding enclosure  210 , by a rotation of the sleeve  206  with respect to the handle  202  and the extension  204  about the longitudinal axis of the shaft  208 . A rotation control knob  219  is provided to ease the rotation of the sleeve  206 . As shown in FIGS. 2 g  and  2   i - j  in view of FIGS. 2 d - e , the bore  218  of the sleeve  206  (shown in cutaway in FIG. 2 e ) defines a cross-section that has a width  220  that is greater than its depth  222 . Further as shown in those figures, the prongs  214   a - b  when separated (shown in cutaway in FIG. 2 j ) define a cross-section having a width  224  that is greater than its depth  226 , the width  224  and depth  226  of the prongs&#39; cross-section being closely accommodated by the width  220  and depth  222  of the bore&#39;s cross-section. When the prongs  214   a - b  are together, the width of prongs&#39; cross-section is closely accommodated by the depth  222  of the bore&#39;s cross-section. Thus, when the sleeve  206  is rotated with respect to the extension  204 , the sides of the bore defining the depth  222  of its cross-section bear against the sides of the prongs  214   a - b  defining the width of their cross-section.  
         [0095]    It should be noted that in order to ease the rotation of the sleeve  210  so that the side of the bore  218  can bear against the sides of the prongs  214   a - b , the corners of the bore  218  are radiused, and at least the sides (that face away from one another) of the prongs  214   a - b  are curved. Preferably, as shown, the prongs  214   a - b  when separated define a partial cylindrical cross-section. The effect of the bearing (of the sides of the bore  218  against the sides of the prongs  214   a - b ) is borne by the space between the prongs  214   a - b , so that the space narrows and the prongs  214   a - b  are brought toward one another until they are accommodated within the bore&#39;s depth  222 . The bringing together of the prongs  214   a - b  brings the semicircular extents  216   a - b  together to place the holding enclosure  210  into its contracted state, locking it.  
         [0096]    Preferably, the sleeve  206  is biased toward establishing the holding enclosure  210  in either an unlocked position or a locked position. Stated alternatively, when the holding enclosure  210  is unlocked (or locked), the force required to begin rotation of the sleeve  206  is greater than the force required to continue rotating the sleeve  206  once rotation has begun. And, as the sleeve  206  is rotated toward a position that will unlock (or lock), the holding enclosure  210 , it is biased toward stopping its rotation at that upcoming position. Stated alternatively, as the sleeve  206  is being rotated, the force required to rotate the sleeve  206  past that upcoming position is greater than the force that is required to rotate it prior to reaching that upcoming position.  
         [0097]    This biasing of the sleeve  206  toward positions that will either unlock or lock the holding enclosure  210  is effected by the inclusion of at least one spaced recess  228  on the outer surface of the extension  204 , and at least one radial bore  230  through the wall of the sleeve  206  (preferably through the rotation control knob  219  as shown), which bores  230  each have secured therein a spring plunger (not shown) (it should be understood that functionally equivalent devices can also be used in place of a spring plunger). Preferably, each recess  228  is associated with a respective cooperating bore  230  and spring plunger. When a given bore  230  (and spring plunger) is aligned with its associated recess  228 , the sleeve  206  is in a position at which the holding enclosure  210  is either unlocked or locked. Each of the spring plungers is biased radially inwardly from the inner surface of the sleeve  206 , and as such presses against the outer surface of the extension  204  as the sleeve  206  is being rotated. Thus, when a recess  230  is presented to the spring plunger, it plunges into the recess  230 , stopping the rotation of the sleeve  206 . In order to restart (or continue) rotation of the sleeve  206 , the bias of the spring plunger must be overcome when the restarting (or continuing) rotational force is applied. In order to lower the overcoming force required to restart or continue the rotation, the end of the spring plunger is preferably convexly curvate, and the recess is concavely curvate. Preferably, four recesses  228  and bores  230  (and spring plungers) are provided, each pair representing one of four quarter-turn rotated positions of the sleeve  206 . At each position of the sleeve  206 , all four plungers plunge into the recesses  228 , securing the sleeve  206  at that position until a sufficient force is applied to overcome their plunging bias.  
         [0098]    Accordingly, the static trials  100  of the invention (or distraction spacers such as those disclosed in the &#39;127 application) can be held and manipulated with the static trial holder  200 . Holding the handle  202  of the static trial holder  200  in one hand, an operator can push the cylindrical trunk  106  of the static trial  100  (or the distraction spacer) against the mouth  213  of the holding enclosure  210  with enough force to temporarily expand the mouth  213  to a width that will accommodate the diameter of the cylindrical trunk  106  for passage through the mouth  213 . The radially inward tapering of the sides of the mouth  213  (the facing ends  215   a - b  of the semicircular extents  216   a - b  of the prongs  214   a - b ) facilitates this insertion. Once the cylindrical trunk  106  has passed into the holding enclosure  210 , the operator can let go of the static trial  100  (or distraction spacer) because the prongs  214   a - b  will be overcome by their bias toward their neutral state and thus hold the static trial  100  in the holding enclosure  210  to prevent the static trial  100  from falling out or slipping out as the static trial holder  200  is moved with the static trial  100  prior to closing (e.g., locking) the holding enclosure  210 . (When the static trial  100  (or distraction spacer) is being held in this manner, and the holding enclosure  210  is unlocked, the static trial  100  can be removed from the holding enclosure  210  by a pulling of the static trial  100  through the mouth  213  of the holding enclosure  210  with a force required to again temporarily overcome the bias of the prongs  214   a - b  toward their neutral state, to separate them and make the width of the mouth  213  accommodate the diameter of the cylindrical trunk  106 .)  
         [0099]    Once the operator is ready to lock the holding enclosure  210 , while still gripping the handle  202  of the static trial holder  200 , he rotates the rotation control knob  219  either clockwise or counterclockwise to move the sleeve  206  to the next quarter-turn position. If the rotation control knob  219  is rotated with enough force to cause the spring plungers in the bores  230  to back out of the recesses  228 , the sleeve  206  will rotate as desired. Once the sleeve  206  has reached the next quarter-turn position, the spring plungers will find the recesses  228  associated with that position, and plunge into the recesses  228  to snap the sleeve  206  into the proper position. As the sleeve  206  rotates, the sides of the sleeve&#39;s bore&#39;s inner surface bear against the curved outer surfaces of the prongs  214   a - b  to push the prongs  214   a - b  together so that they are accommodated by the depth  222  of the bore  218 . When the prongs  214   a - b  are pressed against one another and held in that closed position by the maintenance of the sleeve  206  in the new position (maintained by the spring plungers in the recesses  228 ), the semicircular extents  216   a - b  move toward one another and are correspondingly maintained together about the cylindrical trunk  106 . When the prongs  214   a - b  are held in this manner, the cylindrical trunk  106  cannot be removed through the mouth  213  of the now-tighter (e.g., locked) holding enclosure  210  without the application of forces preferably greater than will be encountered when inserting and removing the static trial  100  from the intervertebral space during the surgical procedures. Once the static trial  100  has been inserted and removed from the intervertebral space (or the distraction spacer has been inserted and removed from the intervertebral space after being used to distract the space), the operator can lock the holding enclosure  210  by rotating the sleeve  206  another quarter turn (in either the clockwise or the counterclockwise direction). Again, if the rotation control knob  219  is rotated with enough force to cause the spring plungers to back out of the recesses  228 , the sleeve  206  will rotate as desired. Once the sleeve  206  has reached the next quarter-turn position, the spring plungers will find the recesses  228  associated with that position, and plunge into the recesses  228  to snap the sleeve  206  into the proper position. As the sleeve  206  rotates, the sides of the sleeve&#39;s bore&#39;s inner surface move away from the curved outer surfaces of the prongs  214   a - b  and allow the prongs  214   a - b  to separate (under their own bias toward the neutral position) as they are accommodated by the width  220  of the bore  218 . When the prongs  214   a - b  are separated and allowed to remain in that position by the maintenance of the sleeve  206  in the new position (maintained by the spring plungers in the recesses  228 ), the semicircular extents  216   a - b  are separated from one another and hold the cylindrical trunk  106  against falling or slipping out. That is, the cylindrical trunk  106  can be removed by the operator if the operator applies a sufficient force to widen the mouth  213  of the holding enclosure  210  enough to let the cylindrical trunk  106  pass through the mouth  213 . Once the static trial  100  (or distraction spacer) is removed, another one can be inserted and manipulated if required.  
         [0100]    Accordingly, the static trial holder  200  can be used to insert and remove the distraction spacers of the &#39;127 application to distract the intervertebral space as described in the &#39;127, and thereafter (or during the distraction) hold to insert and remove the static trials  100  to find the appropriate size of artificial intervertebral disc to be implanted.  
         [0101]    A preferred embodiment of a dynamic trial of the present invention will now be described.  
         [0102]    Referring now to FIGS. 3 a - d , a dynamic trial of the present invention is shown in top (FIG. 3 a ), side (FIG. 3 b ), side cutaway (FIG. 3 c ) and perspective (FIG. 3 d ) views.  
         [0103]    The dynamic trial  300  is provided primarily for distracting an intervertebral space according to the procedures described herein and/or for determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size can be implanted) into the distracted intervertebral space. While the distraction systems and methods described in the &#39;127 application are also useful for distracting an intervertebral space, the dynamic trial  300  is provided as an additional or alternate distraction tool. Further, while the static trials described herein as useful for determining the appropriate size of an artificial intervertebral disc to be implanted (or whether a particular size can be implanted), the dynamic trial  300  is provided as an additional or alternate sizing tool.  
         [0104]    More specifically, the dynamic trial  300  includes a shaft  302  having a bifurcated trial  304  at a distal end of the shaft  302 . The trial  304  has an exterior that is preferably formed like the artificial intervertebral disc that it is meant to approximate. Accordingly, each half  306   a - b  of the bifurcated trial  304  has on its outwardly facing surface a convex dome  308   a - b  that is shaped like the convex dome of the corresponding baseplate of the artificial intervertebral disc that the dynamic trial  300  approximates (e.g., the convex domes  184   a - b  of the baseplates  168   a - b  of the artificial intervertebral disc  160  of FIGS. 1 g - n ). Preferably, each convex dome  308   a - b  is smooth, rather than having a porous coating that is preferred for the convex domes  184   a - b  of the artificial intervertebral disc  160 , and each half  306   a - b  does not have stabilizing spikes such as the stabilizing spikes  188   a - b  on the outwardly facing surfaces  186   a - b  of the artificial intervertebral disc  160 . The omission of these device stabilizing and bone ingrowth encouraging structures and surfaces on the dynamic trial  300  enables the surgeon to test the size of the artificial intervertebral disc  160  to be implanted without invading the vertebral body endplates. The shaft  302  includes an inner shaft portion  310  that centrally divides at a fulcrum  311  into upper and lower distal extensions  312   a - b . The lower distal extension  312   b  is fixed to the upper distal extension  312   a  at the fulcrum  311 , preferably by screws  313   a - b  that are plug welded in place. Preferably, as shown, at least the most proximal screw  313   b  extends above the top surface of the upper distal extension  312   a  to serve as a backup stop to prevent extreme forward movement of the control knob  318  that is operated to separate the distal extensions  312   a - b  (described below).  
         [0105]    From the point of division to their distal ends, each of the upper and lower distal extensions  312   a - b  are spring biased (preferably by the formation of the fulcrum  311  in combination with the strength of the material of which the extensions  312   a - b  are made, although the use of other types of springs is contemplated by the present invention) toward positions in which they converge toward one another (in the figures, the extensions  312   a - b  are shown in these positions). The lower distal extension  312   b  is connected (preferably fixed as shown) to the lower half  306   b  of the bifurcated trial  304 , and the upper distal extension  312   a  is connected to the upper half  306   a  of the bifurcated trial  304 . Preferably, as shown, the upper half  306   a  is adjustably connected to the upper distal extension  312   a  by a pivot pin  315  that allows the upper half  306   a  to rotate about a lateral axis that passes through the longitudinal and lateral center of the bifurcated trial  304 . This axis of rotation allows the upper half  306   a , when separating from the lower half  306   b , to adjust to the orientation of the upper (adjacent) vertebral bone without causing the bone to hinge relative to the lower vertebral bone (the bone adjacent the lower half  306   b ).  
         [0106]    In order to effect the separation of the upper and lower halves  306   a - b , the shaft  302  further includes an outer shaft potion  314  that is longitudinally translatable adjacent the inner shaft portion  310 . The outer shaft portion  314  preferably straddles the inner shaft portion  310  as shown, and includes a pin  316  that passes between the distal extensions  312   a - b . The outer shaft portion  314  is preferably translatable distally by the forward movement of a control knob  318  near the proximal end of the shaft  302 , and translatable proximally by backward movement of the control knob  318 . That is, when the control knob  318  is pushed distally, the outer shaft portion  314  is moves distally, and accordingly the pin  316  moves distally. If the pushing force is great enough to overcome the bias of the divided extensions  312   a - b  (their bias toward one another), the divided extensions  312   a - b  will separate as the pin  316  moves between them (to make room for the pin  316 ). The separation of the extensions  312   a - b  will correspondingly separate the halves  306   a - b  of the bifurcated trial  304 . It should be understood that preferably, if the control knob  318  is released, the bias of the divided extensions  312   a - b  will press against the pin  316 , causing the pin  316  (and correspondingly the outer shaft portion  314  and the control knob  318 ) to move proximally to allow the divided extensions  312   a - b  to return to their biased position, which will bring the halves  306   a - b  of the trial  304  back together so they can be removed from the intervertebral space. Preferably, markings  320  are provided on the inner shaft portion  310  (preferably on its top surface so that the surgeon can more easily see the markings  320 ) to quantify the depth (to which the bifurcated trial  304  is expanded) corresponding to the distance that the outer shaft portion  314  is translated with respect to the inner shaft portion  310 .  
         [0107]    It is anticipated that the pushing force required to separate the halves  306   a - b  will increase as they separate, due to the compression of the spine seeking to close the intervertebral space and the annulus seeking to prevent the adjacent vertebral discs from separating beyond a certain point. Therefore, to provide a mechanical advantage to the operator in the event that greater distraction is required, but the operator cannot push the control knob  318  farther with unaided human effort, an fine control knob  322  is provided. The fine control knob  322  is preferably threaded onto the proximal end of the inner shaft portion  310 , proximal to the control knob  318 . Thus, rotation of the fine control knob  322  about the longitudinal axis of the inner shaft portion  310  will cause the body of the fine control knob  322  to press against the control knob  318  to move it farther distally. The interference of the threads of the fine control knob-inner shaft portion interface prevents the fine control knob  322  from backing up proximally unless the fine control knob  322  is reverse rotated to effect that result.  
         [0108]    Preferably, as shown, the proximal end  324  of the shaft  302  is preferably flanged to serve as a slap hammer for impaction (by hitting the proximal end  324  with a mallet with a distally directed force, e.g.), if necessary for proper positioning of the bifurcated trial  304 , and/or forced extraction of the bifurcated trial  304  (by hitting the flange of the proximal end  324  with a mallet with a proximally directed force, e.g.).  
         [0109]    Accordingly, the dynamic trial  300  can be used as an additional or alternative distracting tool (e.g., to the distraction spacers), and/or as an alternative or additional sizing tool (e.g., to the static trials). As an example of a use for the dynamic trial  300  as an alternative or additional distraction tool and an alterative sizing tool, once the intervertebral space is distracted to (or, without distraction, is at) a depth that is at least equal to the depth of the closed bifurcated trial  304 , the bifurcated trial  304  of the dynamic trial  300  can be inserted into the intervertebral space. (If the intervertebral space must be distracted initially because it starts out more shallow than the depth of the closed bifurcated trial  304 , the distraction spacers of the &#39;127 application and the methods disclosed therein can be used, e.g.) The control knob  318  and/or fine control knob  322  can be operated to separate the halves  306   a - b  of the bifurcated trial  304  to distract the space as clinically appropriate. Because the bifurcated trial  304  is shaped externally to approximate the artificial intervertebral disc to be implanted (e.g., the artificial intervertebral disc  160 ), and because the pivoting of the upper half  306   a  of the bifurcated trial  304  allows the halves  306   a - b  to appropriately lordotically orient themselves, when the surgeon determines the intervertebral space to be distracted to its proper dimension (based on how much compression is being experienced on the dynamic trial  300  and how tight the annulus is), he can read the markings  320  on the shaft  302  to determine what size of artificial intervertebral disc  160  is suitable for the dimensioned intervertebral space. A subsequent bringing together of the halves  306   a - b  and a removal of the dynamic trial  300  can then be followed by insertion of the appropriately sized artificial intervertebral disc  160  (e.g., in a manner described below with regard to the inserter/impactor  400 ).  
         [0110]    As an example of a use for the dynamic trial  300  as an alternative distraction tool and an additional sizing tool, after the surgeon has initially distracted the intervertebral space (preferably with the distraction spacers of the &#39;127 application), and applied one or more of the static trials  100  to the intervertebral space to determine the appropriate size of the artificial intervertebral disc to be implanted (e.g., the artificial intervertebral disc  160 ), the surgeon can apply the dynamic trial  300 , expand it to the size of the static trial  100  that was determined to be the appropriate size for the intervertebral space, and then further open the dynamic trial  300  for a final sizing. An example of a final sizing that would be useful would be to test the amount of farther distraction that is clinically possible, without having to remove and replace static trials  100  when the compression force of the spine and the tension force of the annulus are at their higher levels. Also, the surgeon may wish to distract the space slightly more than the size of the appropriately sized static trial  100  or artificial intervertebral disc  160 , so that the artificial intervertebral disc  160  can be more easily inserted after removal of the static  100  or dynamic trial  300  results in a compressive settling of the intervertebral space. The surgeon may also wish to distract the space slightly more than the size of the appropriately sized static trial  100  or artificial intervertebral disc  160 , to prepare it for easy insertion of the artificial intervertebral disc  160  to be implanted, with consideration for the height of the stabilizing spikes  188   a - b  on the outwardly facing surfaces  186   a - b  of the baseplates  168   a - b  of the artificial intervertebral disc  160 . While the artificial intervertebral disc  160  having the spikes  188   a - b  can be implanted without the additional distraction, some surgeons may find such additional distraction useful or desirable for a particular case.  
         [0111]    A preferred embodiment of an inserter/impactor of the present invention will now be described.  
         [0112]    Referring now to FIGS. 4 a - d , an inserter/impactor of the present invention is shown in side (FIG. 4 a ), top (FIG. 4 b ), side cutaway (FIG. 4 c ) and perspective (FIG. 4 d ) views. FIGS. 4 e - h  show side (FIG. 4 e ), top (FIG. 4 f ), side cutaway (FIG. 4 g ), and perspective (FIG. 4 h ) views of an inserter/impactor of the present invention holding a static trial of the present invention. FIGS. 4 i - j  show top views of an inserter/impactor of the present invention holding a static trial of the present invention in two alternative ways. FIGS. 4 k - n  show side (FIG. 4 k ), top (FIG. 4 l ), side cutaway (FIG. 4 m ), and perspective (FIG. 4 n ) views of an inserter/impactor of the present invention holding an exemplary artificial intervertebral disc of the present invention. FIGS. 4 o - p  show top views of an inserter/impactor of the present invention holding an exemplary artificial intervertebral disc of the present invention in two alternative ways.  
         [0113]    The inserter/impactor  400  is provided primarily for holding, inserting, repositioning, removing, impacting, extracting, and otherwise manipulating an artificial intervertebral disc having features suitable for being manipulated by the inserter/impactor. (However, it can also be used to hold, insert, reposition, remove, impact, extract, and otherwise manipulate the static trials  100  as described above, as well as any other orthopedic device having suitable features therefor.) Exemplary suitable artificial intervertebral discs include, but are not limited to, the artificial intervertebral disc  160  described herein and the artificial intervertebral discs described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by the inserter/impactor  400 , such features include those discussed above as being suitable features on the static trials  100  and disc  160 , namely, an anteriorly facing flat surface on the second (e.g., lower) baseplate of the trial or disc, flanked by two anteriolaterally facing flat surfaces (one on each side of the anteriorly facing flat surface), and, to provide for holding of the trial or disc for an anterior insertion approach, a hole spaced from the anteriorly facing flat surface, the hole having a longitudinal axis parallel to the anteriorly facing flat surface.  
         [0114]    More particularly, the inserter/impactor  400  includes a shaft  402  having a distal end  404  that has angled flat surfaces  420   a - c  corresponding to and fittable against angled flat surfaces of the static trial (e.g., the surfaces  120   a - c  of the static trial  100 ) or artificial intervertebral disc (e.g., the surfaces  180   a - c  of the artificial intervertebral disc  160 ) to be implanted. For example, in an anterior approach for the trial  100  (as shown in FIGS. 4 e - h ),  120   a  and  120   d  facing  420   a ,  120   b  and  120   e  facing  420   b , and  120   c  and  120   f  facing  420   c , and in an anterior approach for the disc  160  (as shown in FIGS. 4 k - n ),  180   a  and  180   d  facing  420   a ,  180   b  and  180   e  facing  420   b , and  180   c  and  180   f  facing  420   c.    
         [0115]    Further, the inserter/impactor  400  includes a holding pin  408  that extends from the center flat surface  420   b  along a longitudinal axis of the shaft  402 , the pin  408  having a distal end  410  that bends downward. The holding pin  408  is spring loaded (by a spring  409 ) in a central channel of the shaft  402 , so that it is biased toward and against the central flat surface  420   b  (preferably, the bent end  410  of the pin  408  prevents it from entering the central channel).  
         [0116]    A flange  411 , mechanically connected to the pin  408  and translating adjacent the shaft  402 , can be pushed distally to overcome the bias of the spring  409  to space the pin  408  away from the central flat surface  420   b.  In this position, the pin  408  can be inserted in the hole  120   b , 180   b  in the baseplate  108   b , 168   b  of the static trial  100  or artificial intervertebral disc  160 . Releasing the flange  411  allows the spring  409  to pull the pin  408  back, causing the anteriorly facing surface  120   b , 180   b  of the baseplate  108   b   168   b  to be held against the central flat surface  420   b  of the inserter/impactor  400  and the anterioloaterally facing flat surfaces  120   a,c , 180   a,c  of the static trial  100  or artificial intervertebral disc  160  to be held against the other corresponding flat surfaces  420   a,c  of the inserter/impactor  400 . A knob  412 , threaded on the shaft  402 , can be rotated about the longitudinal axis of the shaft  402  to push the flange  411  farther proximally, to pull the pin  409  tighter and therefore lock its position (the interference of the threads of the knob-shaft interface prevents the knob  412  from moving distally unless the knob  412  is reverse rotated to effect that result) to more securely hold the baseplate  108   b , 168   b , and reverse rotated to unlock and loosen the pin  409 .  
         [0117]    When the static trial  100  or disc  160  is held in this manner, rotation of the static trial  100  or disc  160  about a longitudinal axis (of the static trial  100  or disc  160 ) relative to the inserter/impactor  400  is prevented by interference of the corners of the static trial&#39;s  100  or disc&#39;s  160  flat surfaces  120   a - c , 180   a - c  and the corners of the inserter/impactor&#39;s  400  flat surfaces  420   a - c , similar to the manner in which a wrench holding a nut prevents rotation of the nut relative to the wrench. Further, the holding of the static trial  100  or disc  160  in this manner allows for some repositioning of the static trial  100  or disc  160  in the intervertebral space via rotation of the static trial  100  or disc  160  in either direction about the longitudinal axis of the intervertebral space.  
         [0118]    Preferably, both of the baseplates of the static trial  100  or disc  160  have similarly configured flat surfaces. For example, the lower baseplate&#39;s  108   b , 168   b  flat surfaces  120   a - c , 180   a - c  have similarly configured and similarly oriented counterpart flat surfaces  120   d - f , 180   d - f  on the upper baseplate  108   a , 168   a . Further preferably, both baseplates&#39;  108   a - b , 168   a - b  flat surfaces  120   a - f , 180   a - f  face the angled flat surfaces  420   a - c  of the inserter/impactor  400  when the static trial  100  or disc  160  is held by the inserter/impactor  400 . For example, in an anterior approach for the trial  100  (as shown in FIGS. 4 e - h ),  120   a  and  120   d  facing  420   a ,  120   b  and  120   e  facing  420   b , and  120   c  and  120   f  facing  420   c , and in an anterior approach for the disc  160  (as shown in FIGS. 4 k - n ),  180   a  and  180   d  facing  420   a ,  180   b  and  180   e  facing  420   b , and  180   c  and  180   f  facing  420   c.    
         [0119]    It should be noted that preferably, when the static trial  100  is held by the inserter/impactor  400 , the flat surfaces  120   a - c  and the counterpart flat surfaces  120   d - f  are tightly held against the angled flat surfaces  420   a - c  of the inserter/impactor  400  as described above. It is also preferable that the baseplates  108   a - b  of each of the plurality of static trials  100  be appropriately lordotically angled relative to one another to ease insertion of the static trial  100  into the intervertebral space and to mimic how the artificial intervertebral disc  160  will typically be oriented as it is being inserted using the inserter/impactor  400 , and to ease insertion of the static trial  100  into the intervertebral space. While not shown in FIGS. 1 a - f , in some embodiments, when the static trials  100  are formed in such a lordotically oriented configuration, it is preferable that the flat surfaces  120   d - f  on the first (e.g., upper) baseplate  108   a  be parallel to the flat surfaces  120   a - c  of the second (e.g., lower) baseplate  108   b  in the static trial&#39;s  100  appropriately lordotically oriented configuration, so that when the static trial  100  is held tightly by the inserter/impactor  400 , the flat surfaces  120   a - f  are flush with the flat surfaces  420   a - c  of the inserter/impactor  400  even though the baseplates  108   a - b  are lordotically angled with respect to one another.  
         [0120]    By contrast, preferably, when the artificial intervertebral disc  160  is held by the inserter/impactor  400 , the flat surfaces  180   a - c  are tightly held against the angled flat surfaces  420   a - c  of the inserter/impactor  400  as described above, but the counterpart flat surfaces  180   d - f  are loosely held against the angled flat surfaces  420   a - c  of the inserter/impactor  400 . As such, the structure of the artificial intervertebral disc  160  having the counterpart flat surfaces  180   d - f  (e.g., the upper baseplate  168   a ) is able to angulate and rotate to a limited extent relative to the structure of the artificial intervertebral disc  160  having the flat surfaces  180   a - c . This permits the artificial intervertebral disc  160  to adjust to the intervertebral space (e.g., to the angulation of the adjacent vertebral endplates, defining the intervertebral space, relative to one another) as it is being inserted thereinto. That is, typically, the adjacent vertebral endplates will be lordotically angled with respect to one another as a result of the intervertebral space being prepared and distracted. As the artificial intervertebral disc  160  is then inserted into the intervertebral space using the inserter/impactor  400 , then, the baseplates  168   a - b  will be permitted to lordotically angle with respect to one another to squeeze into the intervertebral space.  
         [0121]    Also preferably, in order to provide for a holding of the static trial  100  or disc  160  for two additional (here, anteriolateral) insertion approaches, each static trial  100  or disc  160  also includes two additional holes  122   a , 182   a  and  122   c , 182   c , one (e.g.,  122   a , 182   a ) spaced apart from one of the anteriolaterally facing flat surfaces (e.g.,  120   a , 180   a ), and the other (e.g.,  122   c , 182   c ) spaced apart from the other of the anteriolaterally facing flat surfaces (e.g.,  120   c , 180   c ). Accordingly, operation of the inserter/impactor  400  can fit the holding pin  408  into either of these two additional holes  122   a , 182   a  or  122   c , 182   c , and hold the associated anteriolaterally facing flat surface (the one associated with the hole into which the pin  408  is fit) of the static trial  100  or disc  160  against the flat surface of the inserter/impactor  400  opposite the pin  408 . For example, as discussed below with regard to the inserter/impactor  400 , in a first anteriolateral approach for the trial  100  (as shown in FIG. 4 i ),  120   a  and  120   d  facing  420   b ,  120   b  and  120   e  not confronted, and  120   c  and  120   f  facing  420   a , and a first anteriolateral approach for the disc  160  (as shown in FIG. 4 o ),  180   a  and  180   d  facing  420   b ,  180   b  and  180   e  not confronted,  180   c  and  180   f  facing  420   a . And, for example, as discussed below with regard to the inserter/impactor  400 , in a second anteriolateral approach for the trial  100  (as shown in FIG. 4 j ),  120   a  and  120   d  facing  420   c ,  120   b  and  120   e  facing  420   a , and  120   c  and  120   f  not confronted, and a second anteriolateral approach for the disc  160  (as shown in FIG. 4 p ),  180   a  and  180   d  facing  420   c ,  180   b  and  180   e  facing  420   a ,  180   c  and  180   f  not confronted.  
         [0122]    It should be understood that preferably, in order to facilitate these additional approaches, the angle separating the anteriorly facing flat surface of the static trial  100  or disc  160  and one of the anteriolaterally facing flat surfaces of the static trial  100  or disc  160  is equal to the angle separating the anteriorly facing flat surface and the other of the anteriolaterally facing flat surfaces. Preferably, the surfaces are angled with respect to one another at an angle of 33.4 degrees.  
         [0123]    It should also be understood that the inclusion of additional adjacent angulated surfaces (or placing the angulated surfaces in other locations on the trial or disc), and/or including corresponding holes adjacent to such surfaces, can provide the surgeon with additional approaches, e.g., other anteriolateral approaches, directly lateral approaches, posteriolateral approaches, and/or directly posterior approaches. For example, a trial or disc can have angled surfaces (and corresponding holes) along the entire perimeter of one or both of the baseplates, and thus enable the surgeon to engage the trial or disc from a number of angles, including anterior, posterior, lateral, anteriolateral, and posteriolateral angles.  
         [0124]    The inserter/impactor  400  further includes at a proximal end a cap  414  for use as an impact surface if the trial  100  or disc  160  must be impacted further into the intervertebral space after insertion, or forcibly extracted from the intervertebral space. A mallet can be used to strike the cap  414  (in a distal direction for impaction, or in a proximal direction (using the flange of the cap  414 ) for extraction). It should be noted a striking of the cap  414  will translate the striking force to the baseplates through the shaft  402  and the flat surfaces, but will not damage the holding pin  408  because the holding pin  408  is spring loaded in the central channel and thus buffered from the striking force thereby.  
         [0125]    Accordingly, the inserter/impactor  300  can be used to grip either the static trials or the artificial intervertebral disc to be implanted, and hold the same during insertion and/or removal of the same, and is useful for a variety of surgical approach angles.  
         [0126]    Preferred embodiments of a repositioner/extractor of the present invention will now be described.  
         [0127]    Referring now to FIGS. 5 a - c , a symmetric repositioner/extractor of the present invention is shown in side (FIG. 5 a ), top (FIG. 5 b ), and perspective (FIG. 5 c ) views. And referring now to FIGS. 5 d - f , an offset left repositioner/extractor of the present invention is shown in side (FIG. 5 d ), top (FIG. 5 e ), and perspective (FIG. 5 f ) views. And referring now to FIGS. 5 g - i , an offset right repositioner/extractor of the present invention is shown in side (FIG. 5 g ), top (FIG. 5 h ), and perspective (FIG. 5 i ) views. And referring now to FIGS. 5 j - l , an alternative offset left repositioner/extractor of the present invention is shown in side (FIG. 5 j ), top (FIG. 5 k ), and perspective (FIG. 5 l ) views. And referring now to FIGS. 5 m - o , an alternative offset right repositioner/extractor of the present invention is shown in side (FIG. 5 m ), top (FIG. 5 n ), and perspective (FIG. 5 o ) views.  
         [0128]    Each repositioner/extractor is provided primarily for repositioning and/or extracting a static trial or artificial intervertebral disc having features suitable for being manipulated by the repositioner/extractor. Exemplary suitable artificial intervertebral discs are described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by each repositioner/extractor, such features include at least two holes extending longitudinally into one of the baseplates of the static trial or artificial intervertebral disc from the inwardly facing surface of the baseplate. More than two holes can be used to provide for multiple repositioning/extracting approaches. Preferably, in order for the same repositioning/extracting tool to be used for multiple approaches on the same trial or artificial intervertebral disc, adjacent holes should be separated by the same distance separating other adjacent holes.  
         [0129]    In order to engage the two holes, each repositioner/extractor has two pins extending in parallel from a central shaft, perpendicular to the longitudinal axis of the central shaft. The pins are spaced to engage the two holes simultaneously, and each pin has a diameter smaller than the diameter of the hole it is to engage. Therefore, the pins can be inserted into the holes, and pulling or pushing on the central shaft along its longitudinal axis when the holes are engaged pulls or pushes the static trial or artificial intervertebral disc in the intervertebral space. Further, because two holes are engaged, the static trial or artificial intervertebral disc can be rotated in either direction about a longitudinal axis passing through the intervertebral space, by rotating of the central shaft of the repositioner/extractor about its distal end, about an axis parallel to the longitudinal axes of the pins. A handle at a proximal end of the central shaft is useful for pushing or pulling on the shaft. A flange adjacent the proximal end of the shaft is useful for impaction (either with a distally directed force or a proximally directed force), if necessary to manipulate the shaft.  
         [0130]    On each repositioner/extractor, the pins are formed on prongs that extend laterally from the central shaft. The direction of the prongs, and the location of the pins relative to the central shaft, determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Further, the number and location of holes further determine the angle or angles of surgical approach for which a particular repositioner/extractor can be used. Accordingly, the present invention contemplates a variety of repositioner/extractors, and a variety of holes configurations, to provide the surgeon with a variety of possible surgical approach angles.  
         [0131]    For example, three repositioner/extractors are illustrated, and, for example, two hole configurations are illustrated.  
         [0132]    The first, symmetric, repositioner/extractor  500 , shown in FIGS. 5 a - c , includes a shaft  502  having a distal end that is symmetrically divided into two prongs  504   a - b , each of the prongs having a pin  506   a - b  extending upwardly and parallel to the pin on the other prong. The second and third, left offset and right offset, repositioners/extractors  510 , 520 , shown in FIGS. 5 d - f  and  5   g - i , respectively, each include a shaft  512 , 522  having a distal end that bends diagonally laterally, the left offset distal end  514  bending in one direction (e.g., to the left), the right offset distal end  524  bending in an opposite direction (e.g., to the right). The distal end of each of the second and third repositioners/extractors  510 , 520  has two pins  516   a - b , 526   a - b  serially spaced on the bent portion, and each of the pins extends upwardly and parallel to the other pin. (As shown in FIGS. 5 j - l  and  5   m - o , alternative embodiments  530 , 540  of the second and third, left offset and right offset, repositioners/extractors each include a shaft  532 , 542  having a distal end that has a straight prong  534   a , 544   a  and a curved lateral prong  534   b , 544   b , where the curved lateral prong  534   b  extends in one direction (e.g., left) for the alternative left offset repositioner/extractor  530 , and where the curved lateral prong  544   b  extends in an opposite direction (e.g., right) for the alternative right offset repositioner/extractor  540 . Each of the prongs  534   a - b , 544   a - b  has a pin  536   a - b , 546   a - b  extending upwardly and parallel to the pin on the other prong. The alternative repositioners/extractors  530 , 540 , each having a space between the pins  536   a,b , 546   a,b , provides for avoidance of any structures on the static trial or artificial intervertebral disc that may be present between the holes.) On each of the repositioners/extractors  500 ,  510 ,  520 ,  530 ,  540 , the pins are spaced so that they simultaneously each fit into a respective one of the two adjacent holes in the baseplate of the static trial or artificial intervertebral disc. Each of the repositioners/extractors  500 ,  510 ,  520 ,  530 ,  540  has a handle  508 ,  518 ,  528 ,  538 ,  548  at a proximal end of the central shaft which is useful for pushing or pulling on the shaft, and a flange  509 ,  519 ,  529 ,  539 ,  549  adjacent the proximal end of the shaft that is useful for impaction (either with a distally directed force or a proximally directed force), if necessary to manipulate the shaft.  
         [0133]    As noted above, the repositioner/extractor that is appropriate or desired for a given case depends at least in part on the configuration of the holes in the baseplates. Two hole configurations are disclosed, as examples of suitable configurations, although other configurations are possible and contemplated by the present invention. A first hole configuration includes three holes on one of the baseplates, the holes being configured so that a first hole is located in the anterior-posterior plane, and the adjacent (second and third) holes are located in respective opposing anteriolateral planes on either side of the first hole. This hole configuration is shown in FIGS. 5 p - u , each of which shows a top cutaway view of the artificial intervertebral disc of FIGS. 1 g - n , showing its lower baseplate, having the first hole configuration, engaged by one of the repositioners/extractors  500 , 510 , 520 . Each view of the lower baseplate shows the first hole  550 , the second hole  552 , and the third hole  554  of the first hole configuration.  
         [0134]    A second hole configuration includes four holes on one of the baseplates, the holes being configured so that first and second holes straddle the anterior-posterior plane, a third hole is located so that the third hole and the first hole straddle one of the opposing anteriolateral planes, and a fourth hole is located so that the fourth hole and the second hole straddle the other of the opposing anteriolateral planes. This hole configuration is shown in FIGS. 5 v - dd , each of which shows a bottom cutaway view of the artificial intervertebral disc of FIGS. 1 g - n , showing its upper baseplate, having the second hole configuration, engaged by one of the repositioners/extractors  500 , 510 , 520 . Each view of the upper baseplate shows the first hole  560 , the second hole  562 , the third hole  564 , and the fourth hole  566 , of the second hole configuration.  
         [0135]    It should be understood that configurations having more or fewer holes, and in a variety of locations, are contemplated by the invention, and the detailed descriptions of only two hole configurations is not meant to limit the invention to only these two configurations. Importantly, the invention encompasses using a hole or any number of holes, bored at any suitable angle, whether parallel to other holes or not, in any number of locations on a spacer, a trial or an artificial intervertebral disc (not limited to locations on the baseplates), for purposes of enabling the spacer, trial, or disc to be gripped by a manipulation instrument (not limited to a repositioner/extractor) that engages the hole, and/or to enable the surgeon to work from a variety of approaches. For example, as described in more detail below, the first and second hole configurations described herein, in cooperation with the repositioner/extractors, provide the surgeon with the ability to work from a directly anterior approach, as well as several anteriolateral approaches. It should be understood that additional hole configurations can enable the surgeon to work from a directly posterior approach, posteriolateral approaches, directly lateral approaches, or anteriolateral approaches that are different that those illustrated. For example, the placement of one or more suitably spaced holes (or the addition of one or more holes) on the posterior edge, and/or one or both of the lateral edges of one or both of the baseplates, would enable the surgeon to use the repositioner/extractors of the present invention to achieve such approaches.  
         [0136]    As noted above, and referring now to FIGS. 5 p - dd , it can be seen that each of the repositioner/extractors can be used in more than one manner depending on the tool desired and the approach desired. For example, with reference to FIGS. 5 p - q , regarding the first hole configuration (three holes in one of the baseplates), the symmetric repositioner/extractor  500  can be used in either of two anteriolateral approaches (see FIGS. 5 p - q ). That is, the symmetric repositioner/extractor&#39;s shaft  502  can be inserted into the wound from either of the two anteriolateral approaches, and the pins  506   a - b  can be inserted into the first  550  and second  552  holes (for one of the two anteriolateral approaches) (FIG. 5 p ) or the first  550  and third  552  holes (for the other of the two anteriolateral approaches) (FIG. 5 q ) of the first hole configuration.  
         [0137]    Also, for example, with reference to FIGS. 5 r - u , regarding the first hole configuration, each of the left offset repositioner/extractor  510  and the right offset repositioner/extractor  520  can be used in either a directly anterior approach (FIGS. 5 r,t ) or a respective anteriolateral approach (FIGS. 5 s,u ). That is, the right offset repositioner/extractor&#39;s shaft  522  can be inserted into the wound from a direct anterior approach, and the right offset repositioner/extractor&#39;s pins  526   a - b  can then be placed into the first  550  and second  552  holes of the first hole configuration (FIG. 5 r ). And, the right offset repositioner/extractor&#39;s shaft  522  can be inserted into the wound from an anteriolateral approach, and the right offset repositioner/extractor&#39;s pins  526   a - b  can then be placed into the first  550  and third  554  holes of the first hole configuration (FIG. 5 s ). And, the left offset repositioner/extractor&#39;s shaft  512  can be inserted into the wound from a direct anterior approach, and the left offset repositioner/extractor&#39;s pins  516   a - b  can then be placed into the first  550  and third  554  holes of the first hole configuration (FIG. 5 t ). And, the left offset repositioner/extractor&#39;s shaft  512  can be inserted into the wound from an anteriolateral approach, and the left offset repositioner/extractor&#39;s pins  516   a - b  can then be placed into the first  550  and second  552  holes of the first hole configuration (FIG. 5 u ). It should be noted that the alternate left offset  530  and alternate right offset  540  repositioners/extractors can also fit into the holes of the first hole configuration in the same manner as described here with regard to the left offset  510  and right offset  520  repositioners/extractors.  
         [0138]    Also, for example, with reference to FIGS. 5 v - dd , regarding the second hole configuration (four holes in one of the baseplates), the symmetric repositioner/extractor  500  can be used in a directly anterior approach (FIG. 5 v ), and either of two anteriolateral approaches (FIGS. 5 w - x ). That is, the symmetric repositioner/extractor&#39;s shaft  502  can be inserted into the wound from a directly anterior approach, and the pins  506   a - b  can be inserted into the first  560  and second  562  holes of the second hole configuration (FIG. 5 v ). And, the symmetric repositioner/extractor&#39;s shaft  502  can be inserted into the wound from either of the two anteriolateral approaches, and the pins  506   a - b  can be inserted into the first  560  and third  564  holes (for one of the two anteriolateral approaches) (FIG. 5 w ) or the second  562  and fourth  566  holes (for the other of the two anteriolateral approaches) (FIG. 5 x ) of the second hole configuration.  
         [0139]    Also, for example, with reference to FIGS. 5 y - dd , regarding the second hole configuration, each of the left offset repositioner/extractor  510  and the right offset repositioner/extractor  520  can be used in any of three respective anteriolateral approaches. That is, the right offset repositioner/extractor&#39;s shaft  522  can be inserted into the wound from any of its three possible anteriolateral approaches, and the right offset repositioner/extractor&#39;s pins  526   a - b  can then be placed into the first  560  and second  562  holes (FIG. 5 y ) (for a first of the three anteriolateral approaches), the first  560  and third  564  holes (FIG. 5 z ) (for a second of the three anteriolateral approaches), or the second  562  and fourth  566  holes (FIG. 5 aa ) (for a third of the three anteriolateral approaches). And, the left offset repositioner/extractor&#39;s shaft  512  can be inserted into the wound from any of its three possible anteriolateral approaches, and the left offset repositioner/extractor&#39;s pins  516   a - b  can then be placed into the first  560  and second  562  holes (FIG. 5 bb ) (for a first of the three anteriolateral approaches), the first  560  and third  564  holes (FIG. 5 cc ) (for a second of the three anteriolateral approaches), or the second  562  and fourth  566  holes (FIG. 5 dd ) (for a third of the three anteriolateral approaches). It should be noted that the alternate left offset  530  and alternate right offset  540  repositioners/extractors can also fit into the holes of the second hole configuration in the same manner as described here with regard to the left offset  510  and right offset  520  repositioners/extractors.  
         [0140]    It should be noted from the illustrations in FIGS. 5 p - dd  that the anteriolateral approaches are at a variety of angles relative to the anterior-posterior plane, and further that the illustrated angles are merely exemplary. That is, the invention encompasses additional approach angles, in that such additional approach angles are possible by (as described above) adding or deleting holes, and/or changing the location of holes, and/or changing the spacing between holes (in conjunction with changing the spacing between pins), and/or changing the angle at which the offset repositioner/extractors&#39; pins are placed relative to one another and to the shaft of such repositioner/extractors.  
         [0141]    As discussed above, once the pins are established in the two adjacent holes, manipulating the shaft of the repositioner/extractor will reposition the static trial or artificial intervertebral disc in the intervertebral space and/or extract it from the intervertebral space. The use of more than one pin (versus one pin) enables the static trial or artificial intervertebral disc to be rotated in either direction about a longitudinal axis passing through the intervertebral space.  
         [0142]    A preferred embodiment of a leveler of the present invention will now be described.  
         [0143]    Referring now to FIGS. 6 a - e , a leveler of the present invention is shown in bottom (FIG. 6 a ), side (FIG. 6 b ), front (FIG. 6 c ), top partial perspective (FIG. 6 d ), and bottom partial perspective (FIG. 6 e ) views. More particularly, FIG. 6 d  shows a top perspective view of the distal end of the leveler, and FIG. 6 e  shows a bottom perspective view of the distal end of the leveler.  
         [0144]    The leveler is provided primarily for establishing a parallel orientation of the baseplates (relative to one another), and/or securing the purchase of the stabilizing spikes, of an artificial intervertebral disc having features suitable for being manipulated by the leveler. Exemplary suitable artificial intervertebral discs are described in the &#39;160 application with regard to FIGS. 8 a - y ,  9   a - t ,  10   a - t ,  11   a - j , and  12   a - o  thereof and by the accompanying descriptions therefor (e.g., embodiments identified as the first, second, third, fourth, and fifth preferred embodiments of the fourth embodiment family, etc.). Regarding the features suitable for being manipulated by the leveler, such features include suitably formed inwardly facing surfaces of the baseplates of the artificial intervertebral disc.  
         [0145]    More particularly, the leveler  600  includes a shaft  602  having a forked distal end formed by two opposing tongs  604   a - b  that are symmetric to one another about a longitudinal axis of the shaft  602 . Each of the tongs  604   a - b  has an extent that initially curves laterally outward away from the shaft  602  and from the other tong&#39;s extent, to define a central pocket  606  forward of the shaft  602  between the tongs&#39; extents. Each tong&#39;s extent then resumes a distal direction to become parallel to the shaft  602  and to the other tong&#39;s extent.  
         [0146]    Each tong&#39;s extent has an upper surface  608   a - b  and a lower surface  610   a - b . The upper surface  608   a - b  is preferably shaped to conform against the inwardly facing surface of a first (e.g., upper) baseplate of an artificial intervertebral disc, and the lower surface  610   a - b  is preferably shaped to conform against the inwardly facing surface of a second (e.g., lower) baseplate of the artificial intervertebral disc, so that insertion of the forked distal end of the leveler  600  between the baseplates, with the central pocket  606  of the distal end avoiding the central portion of the artificial intervertebral disc, and with the upper  608   a - b  and lower surfaces  610   a - b  so engaging the inwardly facing surfaces of the baseplates, causes the baseplates to be placed in parallel orientation with respect to one another.  
         [0147]    More particularly, for example for use with the exemplary artificial intervertebral disc of FIGS. 1 g - n , the upper surface  608   a - b  of each extent is flat, except for a tapered section  612   a - b  at the distal tip of the extent, which tapered section narrows the tip, and the lower surface  610   a - b  of each extent is curved to form opposing concave contours  614   a - b  that are cooperatingly shaped to conform against the inwardly facing surface of the convex structure of the artificial intervertebral disc.  
         [0148]    The preferred use of the leveler  600  is as follows. As discussed above, once the intervertebral space has been prepared and distracted to a dimension that will accept the artificial intervertebral disc to be implanted, the artificial intervertebral disc  160  is engaged at its lower baseplate  168   b  by the inserter/impactor  400  discussed above. During insertion (and, if necessary, impaction) of the artificial intervertebral disc  160  into the intervertebral space, the upper baseplate  168   a  remains free to angulate with respect to the lower baseplate  168   b , so that the angulation of the baseplates conforms to the angulation of the intervertebral space as the artificial intervertebral disc is being inserted thereinto. Typically, the endplates of the prepared and distracted intervertebral space will be lordotically angled with respect to one another, due to the use of the static trials  100  as described above, which are formed to have a lordotic taper as discussed above. Thus, when the artificial intervertebral disc is inserted into the intervertebral space, its baseplates will be lordotically angled with respect to one another. Once the artificial intervertebral disc  160  is inserted, the inserter/impactor  400  can be disengaged, and the repositioner/extractors  500 ,  510 ,  520 ,  530 ,  540  discussed above can be applied to the artificial intervertebral disc, if necessary to achieve a more optimal positioning.  
         [0149]    Once the positioning is established, the leveler  600  is preferably applied to the artificial intervertebral disc  160 . The forked distal end of the leveler  600  is inserted so that the extents  604   a - b  are placed between the inwardly facing surface  164   a  of the upper baseplate  168   a  and the inwardly facing surface  164   b  of the convex structure  162  on the lower baseplate  168   b , and so that the central pocket  606  of the leveler  600  avoids the ball-and-socket joint of the artificial intervertebral disc  160 . If the baseplates are lordotically angled with respect to one another, the tapered sections  612   a - b  of the upper surfaces  608   a - b  of the forked distal end will be approximately parallel to, and will first encounter, the angled inwardly facing surface  164   a  of the upper baseplate  168   a . At the same time, the concave contours  614   a - b  of the lower surfaces  610   a - b  will accommodate the inwardly facing surface  164   b  of the convex structure  162  on the lower baseplate  168   b . As the tapered sections  612   a - b  press against the inwardly facing surface  164   a  of the upper baseplate  168   a , and the concave contours  614   a - b  slip into place against the inwardly facing surface  164   b  of the convex structure  162  on the lower baseplate  168   b , the tapers  612   a - b  will function as wedges to force the posterior portion of the upper baseplate  168   a  away from the posterior portion of the lower baseplate  168   b . Accordingly, as the posterior portions are being separated, the stabilizing spikes  188   a - b  on the outwardly facing surfaces  186   a - b  of the baseplates  168   a - b  find or secure their purchase in the hard bone of the outer ring of the vertebral body endplates. When the forked distal end is fully seated (stops  616   a - b  are provided to butt up against the anterior portions of the baseplates  168   a - b  to prevent the forked distal end from being inserted too far), the extents of the tongs  604   a - b  hold the baseplates  168   a - b  parallel to one another, and so that the spikes  188   a - b  are fully engaged in the endplates. The surgeon then slips the leveler  600  out from between the baseplates  168   a - b , and out from the wound and completes the procedure. A handle  618  is provided at a proximal end of the shaft  602  for pushing, pulling, and otherwise manipulating the leveler  600  as needed.  
         [0150]    While there has been described and illustrated specific embodiments of instrumentation, it will be apparent to those skilled in the art that variations and modifications are possible without deviating from the broad spirit and principle of the invention. The invention, therefore, shall not be limited to the specific embodiments discussed herein.