Abstract:
A prosthetic spinal implant having a deployable securing mechanism that is deployable into a portion of the vertebral space for affixing the implant between the vertebrae, the securing mechanism having tactile feedback means comprising a surface for transmitting tactile feedback during deployment of the securing mechanism. A spinal implant having deployable securing means that interface with the implant to prevent the deployable securing means from retracting after deployment. An implant that utilizes its resilient properties to provide the user with tactile feedback with which the user may ascertain the position of the securing mechanism. A system and tools for sizing and implanting implants with the aforementioned characteristics.

Description:
RELATED APPLICATIONS  
       [0001]     This application is related to Provisional Application No. 60/825,865, filed Sep. 15, 2006, and Provisional Application No. 60/912,138, filed Apr. 16, 2007, both of which are also incorporated herein by reference in their entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The invention relates to systems and methods for sizing an intervertebral space and placement of an appropriately sized implant therein and, more particularly, to systems and methods for sizing, inserting and securing an implant in the intervertebral space.  
       BACKGROUND OF THE INVENTION  
       [0003]     Joint degeneration is a common problem that can occur in a variety of joints throughout the human body. The condition typically is more prevalent as the skeletal system ages and is often treated with medications and/or physical therapy. These conservative treatments sometimes meet only limited success. If unsuccessful, the patient typically will continue to experience ongoing pain and limited mobility.  
         [0004]     Often the treatment progression leads to a total joint replacement. These replacements have been performed for years in joints such as the hip and the knee. The replacement devices usually comprise some form of a metallic structural component or endplate with an intermediate polyethylene core. It is not unusual for replacements such as these to give 15-20 years of service before requiring some degree of revision.  
         [0005]     In the spine, the surgical treatment of choice has been fusion for the treatment of intervertebral disc degeneration. The spinal intervertebral disc is arguably the most important joint in the spine and is situated between the vertebral bodies. The spinal disc is comprised of a tough outer ring called the annulus, and a jelly-like filling called the nucleus. The belief has been that removing the diseased spinal disc(s) and fusing between affected levels will not make a significant difference in the overall mobility of the spine. However, spinal fusion has proved to cause an increase in degeneration at other vertebral levels that must compensate for the loss of motion at the fused level commonly causing the patient to relapse into more pain and limited mobility.  
         [0006]     Recently, there has been a focus on the use of “motion preservation” implants over implants that promote spinal fusion. These motion preserving implants, in the form of joint replacements in the spine, hope to alleviate many of the problems associated with fusion devices in the spine. Intervertebral disc replacement devices are seen today typically comprising a pair of biocompatible metal plates with a polymer or elastomeric core, or a metal plate articulating on a metal plate.  
         [0007]     Metal on metal implants have a history of failure in long term use, however, precision machining has spawned a reemergence of implants using these materials since it is believed that this change in manufacturing greatly improves the wear. Regardless, the metal implants are radiopaque and continue to frustrate surgeons due to the difficulty in imaging the affected area. Other implants, such as those using a polymer or elastomeric core between metallic plates suffer from the same radiopaque frustrations due to the metal components in addition to the added complexities of design due to the necessity of utilizing a multitude of materials for a single implant.  
         [0008]     The prior art discloses a laundry list of biocompatible materials including metals, ceramics, and polymers, that can be used for the manufacture of these implants, yet historically many of these materials have failed when interfaced together and tested in an articulating joint. There is in particular an extensive history of failure when polymers articulate against polymers in weight bearing artificial joints. Due to this failure history, polymer combinations have naturally been excluded as an acceptable self-articulating material combination for use in weight bearing joint replacements.  
         [0009]     PEEK (poly-ether-ether-ketone), for example, has been suggested as an appropriate material of manufacture for use in implant devices due in large part to its strength, radiolucent nature, and biocompatibility. This is particularly true in structural implants having no articulating component. PEEK on PEEK has been suggested for use in low wear non-weight bearing joints such as in finger joints. However, the prior art has been careful not to suggest self-articulating PEEK on PEEK as a suitable material combination in weight bearing joint replacement devices due to the failure history of biocompatible polymers articulating against themselves.  
       SUMMARY OF THE INVENTION  
       [0010]     Testing in our laboratories however, told a different and unexpected story. In simulated weight bearing artificial joint configurations, PEEK against PEEK performed very favorably. PEEK articulating against PEEK demonstrated exceptional mechanical performance and biocompatibility characteristics required for load bearing artificial joints used in the human body and in other animals. PEEK may also be manufactured in a fiber reinforced form, typically carbon fiber, which also performs favorably against itself and against non-fiber reinforced PEEK.  
         [0011]     Once PEEK was recognized as a viable option for self articulation, it became clear that an entire articulating joint could be made from the material without the need for metallic structural or articulating components. This discovery substantially simplified the nature of weight bearing artificial joint replacement design and great benefits have emerged. A partial list of these benefits include artificial joints that; have less components due to integrating features into the same component that were previously separated due to the need for a plurality of materials to serve the function, will last longer due to favorable wear characteristics, are substantially radiolucent, have a modulus of elasticity closer to the bone tissue they are implanted in, and are ultimately less expensive. It is important to note that less components typically equates to fewer modes of failure, reduced inventory, and simplified manufacturing and assembly. Although less preferred, clearly one may choose to keep the metallic components of an implant system and utilize PEEK on each articulating surface of the artificial joint for a PEEK on PEEK articulation.  
         [0012]     Two piece articulating PEEK on PEEK intervertebral implants have been presented in parent applications by the same inventor. These implants perform exceptionally well for replacement of the spinal nucleus. However, many indications require implants of this nature to also comprise improved restraining features particularly in weight bearing applications.  
         [0013]     For example, there is a need for a simplified radiolucent artificial disc device, with excellent wear characteristics and features that will secure the device to the vertebral endplates or otherwise restrain it between the vertebral bodies. An artificial disc such as this would be particularly useful as a lumbar disc replacement, and even more so as a cervical disc replacement. The cervical disc is much smaller than the lumbar disc as is the space the cervical disc occupies. For at least this reason, a simplified design utilizing fewer parts is beneficial.  
         [0014]     In all cases, the articulating joint surfaces are preferably a combination of PEEK articulating on PEEK, PEEK on carbon reinforced (CR) PEEK, or CR PEEK on CR PEEK. Boney integration of these implants may benefit from prepared osteo-conductive surfaces or coatings described elsewhere in this document.  
         [0015]     It is preferable that the radiolucent implant includes one or more small radiopaque markers which will show on up an X-ray image to assist the surgeon in positioning the implant during surgery. The preferred material for these markers is tantalum. Typically these markers will be encased in predetermined locations in the implant at their periphery. Coatings which show up on imaging as a subtle outline of the implant device may also be used.  
         [0016]     It is also preferable, although not necessary, that the implants disclosed herein include a layer of osteo-conductive or osteo-inductive surfaces or coatings on those implant surfaces in contact with bone or tissue that will assist in securing the implant in a predetermined location. Typically this will occur through boney integration of the bone with the coating or implant surface. Examples of such coatings are hydroxyapatite, calcium phosphates such as tricalcium phosphate, or porous titanium spray.  
         [0017]     The implant devices disclosed herein are particularly suited as intervertebral disc replacements for all or a portion of the natural intervertebral disc. In addition, the securing mechanisms disclosed herein are also suited for other spinal implants, such as vertebral body replacements, spinal cages, and other fusion promoting implants, as well as other known motion preserving implants. The devices have minimal structural parts and are preferably manufactured from specialized materials that are substantially radiolucent such as PEEK or Carbon-Fiber PEEK in both their structural and joint articulating portions.  
         [0018]     Generally, the various systems and methods described herein allow for an implant, such as an artificial disc, to be properly sized, implanted and secured in an intervertebral space with the disc having a bearing interface that preserves motion between the upper and lower vertebrae between which the disc is implanted and secured. In each form described herein, a trial spacer is not only used to assess the size of the intervertebral space so that an appropriately sized disc implant can be selected, it is also used to assist in generating features in the vertebrae and/or end plates thereof (hereinafter “vertebral bodies”) for a securing mechanism that holds and retains the disc implant in the intervertebral space.  
         [0019]     In some forms, the securing mechanism is associated with the implant to be inserted into the intervertebral space therewith. After the disc and securing mechanism are inserted in the intervertebral space, the securing mechanism can be deployed into the preformed features in the adjacent vertebral bodies from the disc implant. In one form, the insertion tool is used to engage the securing mechanism with the preformed features in the intervertebral bodies. In another form, the securing mechanism is actuated directly to engage the securing mechanism with the preformed features of the vertebral bodies.  
         [0020]     In yet another form, the securing mechanism is inserted into the intervertebral space via the trial spacer prior to insertion of the disc implant. In this form, the securing mechanism is actuated directly to be deployed into the features in the adjacent vertebral bodies with the disc implant then inserted into the intervertebral space. Thereafter, the securing mechanism is actuated so as to engage both the implant and the vertebral body for securing the implant in the intervertebral space.  
         [0021]     In any event, the level of restraint required for a particular orthopedic application will vary. This disclosure also describes examples of a variety of securing mechanisms or alternative features suitable for restraining the device in a predetermined location. The securing mechanisms generally possess structure which allow for dynamic fixation of the implant. Instead of relying solely on subsidence or boney ingrowth of the bone around the features of the implant, the securing mechanisms actively engage the bone for immediate and reliable fixation of the implant to the vertebrae. In one embodiment, a rotatable shaft with at least one bone engaging body is disposed on the implant for securing the implant within the intervertebral space. In an undeployed position, the bone engaging body is disposed within the implant body. When the shaft is rotated, the bone engaging body is deployed into the vertebra and thereby fixes the implant to the vertebra to prevent migration of the implant.  
         [0022]     In addition, securing mechanisms according to the present invention may incorporate designs that transmit tactile feedback to the surgeon when the securing mechanism is being operated. As it is very difficult for the surgeon to visually ascertain the position of the implant and its securing features during operation, a surgeon will also use his hands to feel for tactile responses transmitted from the implant and through his tools. In one embodiment, the securing mechanism has a cammed surface for interacting with a corresponding cammed surface to cause the securing mechanism to be biased against the implant to provide resistance against the movement of the securing mechanism that can be felt through the surgeon&#39;s tools. In this manner, the surgeon can easily ascertain when the securing mechanism has been fully extended or deployed. The tactile feedback features of the securing mechanism also prevent the securing mechanism from being over- or under-actuated, i.e. deploying the securing mechanism beyond its intended range of motion, or failing to fully deploy the securing mechanism. This condition may result in improper fixation of the implant and cause damage to the implant, spine, nerves, vascular system, or other tissue in the area around the spine.  
         [0023]     Another aspect of the current invention includes securing mechanisms for an implant having anti-retraction or derotation prevention means. Some securing mechanisms according to the present invention are deployed or extended into the bone by actuating the securing mechanism, for example, by rotating a shaft. However, it is possible for the securing mechanism to retract or derotate back to its undeployed position over time, due to forces exerted on the implant. Thus, to prevent such an event, a securing mechanism may be provided with means to prevent retraction or derotation. In one embodiment, derotation prevention means are provided in the form of a camming surface on the securing mechanism in combination with a corresponding camming surface on the implant. The camming surfaces are disposed to engage or interfere with one another when the securing mechanism is in a fully deployed position to prevent derotation of the securing mechanism. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]     To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which:  
         [0025]      FIG. 1  is a perspective view of an anterior portion of the spine with two implants according to the present invention disposed within the intervertebral spaces;  
         [0026]      FIG. 2  is an anterolateral perspective view of an implant according to the present invention;  
         [0027]      FIG. 3  is a perspective view of one part of a motion preserving implant with a concave articulation surface according to the present invention;  
         [0028]      FIG. 4  is a perspective view of a corresponding part of the motion preserving implant of  FIG. 3  with a convex articulation surface according to the present invention;  
         [0029]      FIG. 5  is an anterolateral perspective view of an implant with securing means according to the present invention implanted within the intervertebral space;  
         [0030]      FIG. 6  is an anterolateral perspective view of an implant with securing means according to the present invention;  
         [0031]      FIG. 6A  is an anterolateral perspective view of an implant component with securing means and inserter tool docking means according to the present invention;  
         [0032]      FIG. 7  is a side view of an implant component with securing means according to the present invention;  
         [0033]      FIG. 8  is an anterolateral perspective view of an implant with a securing mechanism according to the present invention implanted within the intervertebral space;  
         [0034]      FIG. 9  is a perspective view of a bearing surface of an implant component with a securing mechanism according to the present invention;  
         [0035]      FIG. 10  is a perspective view of a securing component in the form of a deployable paddle or cam according to the present invention;  
         [0036]      FIG. 11  is a perspective view of a bearing surface of an implant component with a deployable securing mechanism according to the present invention;  
         [0037]      FIG. 12  is an anterolateral perspective view of an implant with a securing mechanism according to the present invention implanted within the intervertebral space;  
         [0038]      FIG. 13  is a perspective view of an implant with a securing mechanism according to the present invention;  
         [0039]      FIG. 13A  is a perspective view of an implant component with a securing mechanism according to the present invention shown adjacent a vertebra;  
         [0040]      FIG. 14  is an anterolateral perspective view of two implants with a securing mechanism according to the present invention implanted within the intervertebral space;  
         [0041]      FIG. 15  is an anterolateral perspective view of an implant with a securing mechanism according to the present invention;  
         [0042]      FIG. 16  is an anterolateral perspective view of two implants with securing mechanisms according to the present invention implanted within the intervertebral space;  
         [0043]      FIG. 17  is an anterolateral perspective view of two implants with securing mechanisms according to the present invention implanted within the intervertebral space;  
         [0044]      FIG. 18  is an anterolateral perspective view of the implant of  FIG. 17 ;  
         [0045]      FIG. 19  is an anterolateral perspective view of two implants with securing mechanisms according to the present invention implanted within the intervertebral space;  
         [0046]      FIG. 20  is a perspective view of the lower implant member of  FIG. 19 ;  
         [0047]      FIG. 21  is a perspective view of a fastener implemented in the securing mechanism of  FIG. 20 ;  
         [0048]      FIG. 22  is an anterolateral perspective view of two implants with securing mechanisms according to the present invention implanted within the intervertebral space;  
         [0049]      FIG. 23  is an anterolateral perspective view of the implant of  FIG. 22  adjacent a vertebrae having a groove and angled bore formed therein for engaging with the securing mechanism;  
         [0050]      FIG. 24  is a perspective view of the implant of  FIG. 22 ;  
         [0051]      FIG. 25  is an anterolateral perspective view of an implant member with a deflectable stop according to the present invention;  
         [0052]      FIG. 26  is a posterolateral perspective view of a vertebrae with a formed recess for engaging with the deflectable stop of  FIG. 25 ;  
         [0053]      FIG. 27  is an anterolateral perspective view of an implant with a securing mechanism according to the present invention implanted within the intervertebral space;  
         [0054]      FIG. 28  is a perspective view of the implant of  FIG. 27 ;  
         [0055]      FIG. 29  is a perspective view of an implant member of the implant of  FIG. 27 ;  
         [0056]      FIG. 30  is an anterolateral perspective view of a vertebra with a formed recess for interacting with a securing mechanism;  
         [0057]      FIG. 31  is an anterolateral perspective view of two implants with securing mechanisms according to the present invention implanted within the intervertebral space;  
         [0058]      FIG. 32  is a perspective view of a bearing surface of the lower implant member of the implant of  FIG. 31 ;  
         [0059]      FIG. 33  is a top view of a vertebra end plate with grooves formed therein for mating with the securing mechanism of the implant of  FIG. 31 ;  
         [0060]      FIG. 34  is a perspective view of an implant component according to the present invention with a motion limiting component disposed on the articulating surface;  
         [0061]      FIG. 35  is a perspective view of the motion limiting component of  FIG. 34 ;  
         [0062]      FIG. 36  is a perspective view of a corresponding implant component of the implant component of  FIG. 34  with a motion limiting recess;  
         [0063]      FIG. 37  is an anterolateral perspective view of a strut implant according to the present invention implanted within spine;  
         [0064]      FIG. 38  is a lateral perspective view of the implant of  FIG. 37 ;  
         [0065]      FIG. 39  is an anterolateral perspective view of an implant member of the implant of  FIG. 37 ;  
         [0066]      FIG. 40  is bottom perspective view of the implant member of  FIG. 39 ;  
         [0067]      FIG. 41  is a posterolateral perspective view of an artificial disc implant according to the present invention;  
         [0068]      FIG. 42  is a posterolateral perspective view of the upper artificial disc implant member of  FIG. 41 ;  
         [0069]      FIG. 43  is a posterolateral perspective view of the lower artificial disc implant member of  FIG. 41 ;  
         [0070]      FIG. 44  is an anterolateral perspective view of a trial spacer assembly according to the present invention inserted between two adjacent vertebrae;  
         [0071]      FIG. 45  is an anterolateral perspective view of the trial spacer assembly of  FIG. 44  with the upper vertebra hidden for illustration purposes;  
         [0072]      FIG. 46  is an anterolateral perspective view of the trial spacer assembly of  FIG. 44 ;  
         [0073]      FIG. 47  is an anterolateral perspective view of the internal components of the trial spacer of  FIG. 44 ;  
         [0074]      FIG. 48  is an anterolateral perspective view of the components of  FIG. 47  including a spreader device disposed between the vertebrae;  
         [0075]      FIG. 49  is a posterolateral perspective view of the trial spacer internal components of  FIG. 47 ;  
         [0076]      FIG. 50  is a perspective view of the closing device of the trial spacer assembly;  
         [0077]      FIG. 51  is an anterolateral perspective view of the artificial disc implant of  FIG. 41  with the implant inserter;  
         [0078]      FIG. 52  is an anterolateral perspective view of the implant of  FIG. 41  loaded in the inserter of  FIG. 51 ;  
         [0079]      FIG. 53  is an anterolateral perspective view of the implant of  FIG. 41  loaded in the inserter of  FIG. 51  adjacent the intervertebral space prior to insertion;  
         [0080]      FIG. 54  is an anterolateral perspective view of the implant and inserter of  FIG. 53  with the upper arm of the inserter retracted from the implant;  
         [0081]      FIG. 55  is a side view of the implant of  FIG. 41  implanted within the intervertebral space;  
         [0082]      FIG. 56  is an anterolateral perspective view of a trial spacer assembly according to the present invention;  
         [0083]      FIG. 57  is a posterolateral perspective view of the trial spacer assembly of  FIG. 56 ;  
         [0084]      FIG. 58  is a anterolateral perspective view of the trial spacer assembly of  FIG. 56  with the shaft handle removed;  
         [0085]      FIG. 59  is a posterolateral perspective view of the trial spacer assembly of  FIG. 58 ;  
         [0086]      FIG. 60  is an anterolateral perspective view of the shaft handle of the trial spacer assembly of  FIG. 56 ;  
         [0087]      FIG. 61  is an posterolateral perspective view of the shaft handle of the trial spacer assembly of  FIG. 56 ;  
         [0088]      FIG. 62  is an anterolateral perspective view of the trial spacer assembly of  FIG. 56  inserted into the intervertebral space;  
         [0089]      FIG. 63  is an anterolateral perspective view of the trial spacer assembly of  FIG. 56  inserted into the intervertebral space with the handle portion removed;  
         [0090]      FIG. 64  is an anterolateral perspective view of a drill guide according to the present invention;  
         [0091]      FIG. 65  is an anterolateral perspective view of the drill guide of  FIG. 64  inserted over the trial spacer assembly;  
         [0092]      FIG. 66  is an anterior view of the trial spacer and drill guide of  FIG. 65 ;  
         [0093]      FIG. 67  is an anterolateral perspective view of the trial spacer and drill guide of  FIG. 65  with a drill;  
         [0094]      FIG. 68  is an anterolateral perspective view of the trial spacer of  FIG. 67  after the grooves have been drilled and the drill guide is removed;  
         [0095]      FIG. 69  is an anterolateral perspective view of the trial spacer of  FIG. 68  with the cam cutter guide slid over the shaft and a cam cutter prior to cutting cams into the vertebrae;  
         [0096]      FIG. 70  is a perspective view of the cam cutter of  FIG. 69 ;  
         [0097]      FIG. 71  is an anterolateral perspective view of the intervertebral space after the grooves and cams have been cut by the drill and the cam cutter;  
         [0098]      FIG. 72  is an anterolateral perspective view of an artificial disc implant according to the present invention including a securing mechanism in the form of three cam shafts with deployable cam lobe members;  
         [0099]      FIG. 73  is an enlarged anterolateral perspective view of the artificial disc implant of  FIG. 72  with one cam shaft removed to show the retainer members;  
         [0100]      FIG. 74  is lateral view of the implant of  FIG. 72  as implanted in the intervertebral space;  
         [0101]      FIG. 75  is an anterolateral perspective view of the implant of  FIG. 72  with cam members with sharpened edges for cutting into bone when deployed into the vertebra;  
         [0102]      FIG. 76  is an anterolateral perspective view of the implant of  FIG. 75  with the cam members fully deployed;  
         [0103]      FIG. 77  is an anterior perspective view of a trial spacer member according to the present invention inserted into the intervertebral space;  
         [0104]      FIG. 78  is an anterolateral perspective view of a trial spacer member of  FIG. 77  with a drill guide inserted over the trial spacer for drilling offset grooves into the vertebrae for installing cam shafts directly into the vertebrae;  
         [0105]      FIG. 79  is an anterolateral perspective view of a trial spacer member of  FIG. 77  with the cam shafts inserted into the trial spacer for being imbedded in the vertebra prior to insertion of the implant;  
         [0106]      FIG. 80  is an anterolateral perspective view of a trial spacer of  FIG. 79  with the cam shafts imbedded into the offset grooves in the vertebrae;  
         [0107]      FIGS. 81-84  show a sequence from a posterior viewpoint detailing the operation of the cam shafts from an initial resting point on the trial spacer in  FIG. 81  to being cammed up into the vertebrae in  FIGS. 82 and 83 , and being imbedded into the vertebrae in  FIG. 84  so that the trial spacer may be removed and the implant may be inserted;  
         [0108]      FIG. 85  is an anterolateral perspective view of an artificial disc implant according to the present invention with one cam shaft hidden, wherein the cam shafts are first imbedded into the vertebrae before the implant is inserted;  
         [0109]      FIG. 86  is an anterior view of the artificial disc implant of  FIG. 85  wherein the cam shafts have been rotated 90 degrees to secure the implant with respect to the vertebrae;  
         [0110]      FIG. 87  is a posterolateral view of the trial spacer of  FIG. 79  with the cam shaft driver driving one of the cam shafts up into the upper vertebrae, which is hidden for illustration purposes;  
         [0111]      FIG. 88  is a side perspective view of the trial spacer system comprised of a trial spacer assembly, a drill set, and a trial spacer inserter tool;  
         [0112]      FIG. 89  is a posterolateral perspective view of the trial spacer assembly of  FIG. 88 ;  
         [0113]      FIG. 90  is an anterolateral perspective view of the trial spacer assembly of  FIG. 88 ;  
         [0114]      FIG. 91  is an enlarged longitudinal cross-sectional view of the trial spacer assembly of  FIG. 88  with the gripping mechanism of the inserter tool inserted therein;  
         [0115]      FIG. 92  is a side perspective view of the inserter tool of  FIG. 88 ;  
         [0116]      FIG. 93  is an exploded view of the inserter tool of  FIG. 88 ;  
         [0117]      FIG. 94  is a longitudinal cross-sectional view of the inserter tool and trial spacer assembly of  FIG. 88 ;  
         [0118]      FIG. 95  is an anterolateral perspective view of an artificial disc implant according to the present invention with the securing mechanisms fully deployed;  
         [0119]      FIG. 96  is a posterolateral perspective view of a cam shaft securing mechanism according to the present invention illustrating a camming surface;  
         [0120]      FIG. 97  is an anterolateral perspective view of the cam shaft of  FIG. 96  with the head hidden disposed in a test block mimicking a securing mechanism for an implant for illustration of the operation of the cam shaft. The cam shaft is shown in an undeployed position, a partially deployed position, and fully deployed, from left to right;  
         [0121]      FIG. 98  is a posterolateral perspective view of a cam shaft securing mechanism according to the present invention illustrating a flat camming surface;  
         [0122]      FIG. 99  is an anterolateral perspective view of the cam shaft of  FIG. 98  with the head hidden disposed in a test block mimicking a securing mechanism for an implant for illustration of the operation of the cam shaft. The cam shaft is shown in an undeployed position, a partially deployed position, and fully deployed, from left to right;  
         [0123]      FIG. 100  is a posterolateral perspective view of a cam shaft securing mechanism according to the present invention illustrating a dual chamfered camming surface;  
         [0124]      FIG. 101  is an anterolateral exploded view of the artificial disc implant of  FIG. 95 ;  
         [0125]      FIG. 102  is an anterolateral perspective view of an alternate embodiment of a cam shaft securing mechanism according to the present invention;  
         [0126]      FIG. 103  is a side view of an alternate embodiment of a cam shaft securing mechanism according to the present invention illustrating cupped cam members;  
         [0127]      FIG. 104  is a side view of an alternate embodiment of a cam shaft securing mechanism according to the present invention illustrating contoured cam members;  
         [0128]      FIG. 105  is a top view of an alternate embodiment of a cam shaft securing mechanism according to the present invention illustrating contoured cam members;  
         [0129]      FIG. 106  is an anterolateral perspective view of an alternate embodiment of the artificial disc implant according to the present invention;  
         [0130]      FIG. 107  is an inverted anterolateral exploded view of the artificial disc implant of  FIG. 95 ;  
         [0131]      FIG. 108  is a perspective view of the implant inserter tool and artificial disc implant according to the present invention;  
         [0132]      FIG. 109  is an exploded view of the implant inserter tool of  FIG. 108 ;  
         [0133]      FIG. 110  is an enlarged perspective view of the implant and implant inserter tool of  FIG. 108  with the upper disc member and upper housing member of the tool hidden for illustration purposes;  
         [0134]      FIG. 111A  is an enlarged perspective view of the implant and implant inserter tool of  FIG. 108  illustrating the engagement of the implant and inserter tool;  
         [0135]      FIG. 111B  is an enlarged perspective view of the underside of the implant and implant inserter tool of  FIG. 108  illustrating the engagement of the implant and inserter tool;  
         [0136]      FIG. 112A  is a side view of the implant inserter tool of  FIG. 108  illustrating the initial disengaged position of the inserter tool;  
         [0137]      FIG. 112B  is an enlarged side view of the gripping mechanism of the inserter tool of  FIG. 108  illustrating the position of the gripping mechanism in the initial disengaged position;  
         [0138]      FIG. 113A  is a side view of the implant inserter tool of  FIG. 108  illustrating the engaged position of the inserter tool;  
         [0139]      FIG. 113B  is an enlarged side view of the gripping mechanism of the inserter tool of  FIG. 108  illustrating the gripping mechanism in the engaged position. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0140]     In a preferred embodiment, such as illustrated in  FIGS. 1-4 , an artificial disc device  001  comprises an upper shell  100  and lower shell  110 . The upper shell  100  comprises a substantially concave recess portion  120 , and the lower shell  110  comprises a substantially convex portion  130 . Although not preferred, the concave and convex portions may be switched such that the upper shell  100  may alternatively comprise the convex portion  130 .  
         [0141]     The convex portion  130  comprises a convex articulation surface  131 , and the concave portion  120  comprises a concave articulation surface  121 . It is preferred that the articulation surfaces  121  and  131  have substantially matching geometries or radiuses of curvature although some mismatch of curvature may be desired to provide a combination of rolling and sliding motion to occur between the articulation surfaces  120  and  121 . The geometries may be complex in nature but preferably are ball and socket style. The convex portion  130  and concave portion  120  may extend substantially to the outer perimeter of the shell  100 ,  110  as illustrated in  FIG. 4 , or may be formed, typically with a smaller radius of curvature inward a predetermined distance from the outer perimeter of the shell  100 ,  110 . Each shell  100 ,  110  is preferably manufactured from PEEK or fiber reinforced PEEK or other biocompatible polymer combination or radiolucent material demonstrating very low surface wear in high repetition wear testing.  
         [0142]     The artificial disc device  001  preferably comprises one or more restraint portion(s)  220  or structure located on one or both of the shell members  100 ,  110  to help prevent the shells  100 ,  110  from becoming dislodged or migrating across the boney endplate  141  of the vertebrae  143  after insertion. For example, the restraining portion  220  may be located on one of the shells  100 ,  110  on the endplate facing surface  142  in the form of directional teeth  140 .  
         [0143]     It is preferred that the footprint of the artificial disc device  001  be similar to the footprint of the endplate although generally smaller to fit within the intervertebral space. The endplate facing surfaces  142  are preferably contoured to match the contour of the endplates  141 . For example, if the surgeon prepares the endplates to be flat, it is preferred that the endplate facing surfaces  142  are also flat. Likewise, if the endplates  141  are prepared to be concave, it is preferred that the endplate facing surfaces  142  are similarly convex. It should be noted that endplates  141  that are concave will generally retain the artificial disc device  001  better since the device  001  becomes cupped between the vertebrae.  
         [0144]     Additional restraining features may be needed to assist holding the artificial disc device  001  in the predetermined position. Described in this application are various securing mechanisms, coatings, or surface preparations that can be used on the endplate facing surfaces  142  to restrain an implant.  
         [0145]     An additional embodiment of a restraint is illustrated in the artificial disc device  001  shown in  FIG. 5 . In this embodiment, the surgeon may choose to form a recess  002  in the anterior edge of the facing upper and lower vertebrae to accommodate the restraint boss  200 . The restraint boss  200  is preferably an extended wall or lip from the endplate facing surface  142  and is of a thickness suitable to block further posterior motion. If the recess  002  is suitably formed into a pocket, the restraint boss  200  will also assist in unwanted lateral motion of the shell  100  or  110 . Alternatively, the restraint boss may sit on the anterior bone surface of the vertebral body without the recess  002 . The restraint boss  200  may be included on one or both of the shells  100 ,  110 .  
         [0146]     Upon insertion of the artificial disc device  001 , the restraint boss  200  acts as a stop to the shell  100 ,  110  as it is guided to the predetermined position. The boss  200  also assures the device is unable to migrate posteriorly towards the spinal cord and cause injury. It is preferred the recess  002  is generally the thickness of the boss  200  such that the boss  200  may be generally flush with the anterior surface of the vertebral body  144 .  
         [0147]     The shell  100 ,  110  preferably includes an attachment portion  210  which may be in the form of a boss, hole, post, recess, ridge, flange or other structure for securing of an implant insertion or removal instrument to assist with inserting or removing the implant from the intervertebral space. For example, in the embodiment in  FIG. 6A , the attachment portion  210  comprises a window  211  for insertion of the head of an insertion or removal instrument and connection holes  212  for occupation by deployable pins on each end of the window  211  situated in the instrument.  
         [0148]     As described earlier, the restraint portion  220  on the endplate facing surfaces  142  may be in the form of directional teeth  140  which are angled like saw teeth to encourage eased insertion across the boney endplate  141  and resist anterior migration to help retain the shell members  100 ,  110  in the predetermined location between the intervertebral bodies. The actual form of the restraint portion  220 , i.e. directional teeth  140  or a surface coating, may be found on one or both shell  100 ,  110  members. The restraint portion  220  may include different forms of restraint on each shell  100 ,  110 . In addition, more than one form of restraint may be used on each restraining portion  220 . For example, the shell  100  may include a restraint portion  220  which comprises both directional teeth  140  with an osteo-conductive surface coating such as hydroxyapatite.  
         [0149]     The shell  100 ,  110  may include apertures for the placement of fasteners such as bone screws to secure the shell  100 ,  110  to the endplate  141  after insertion. It is preferable that the fasteners are also manufactured from a radiolucent material such as PEEK, however the surgeon may choose to use fasters made of a biocompatible metal such as from the family of titaniums or stainless steels. It is preferable that these apertures are counter bored when possible to reduce the profile of the screw head outside the periphery of the shell  100 ,  110 . If the device is equipped with a restraint boss  200 , the anterior facing surface of this boss is a preferred location for these apertures  520  wherein the apertures  520  are preferably directed towards the center of the vertebral body.  
         [0150]     In some forms, the restraint boss  200  may be offset to the left or the right as illustrated in  FIG. 16 . In this fashion, the artificial disc device  001  can be utilized at multiple adjacent vertebral levels without interference of an adjacent restraint boss  200 . Similarly, the restraint boss  200  may be contoured to accommodate an adjacent restraint boss  200  through a boss recess  240 . Again, this orientation provides utilization of the artificial disc device at multiple adjacent vertebral levels without interference of an adjacent restraint boss  200 .  FIG. 18  further illustrates this embodiment.  
         [0151]     In other forms, the restraint boss  200  may not be integral to the shell  100 ,  110 . Instead the boss  200  may be configured as a small plate, fastened to the anterior surface of the vertebral body and extending just past the endplate to block back-out of the shell  100 ,  110  and lateral movement of the shell  100 ,  110  if the boss  200  is so equipped with interlocking geometry. Further, the disc device may be blocked from backing out by a broad flexible mesh, preferably made of a polymer such as PEEK, fastened from the anterior surface of one vertebral body to the other.  
         [0152]     In an alternative embodiment, the artificial disc device  001  shown in  FIG. 8  comprises a restraint portion  220  in the form of a deployable paddle  300 . The paddle  300  is housed within one of the shell members  100 ,  110  as illustrated in  FIG. 9 . The paddle  300  may be manufactured from an array of biocompatible materials including but not limited to polymers such as PEEK or metals such as titanium or stainless steel alloys although radiolucent materials are preferred. In a preferred orientation, the paddle  300  is secured within the body of a shell  100 ,  110  by a paddle restraint  310  in this case in the form of a snap joint. The paddle comprises a restraint arm  330  that may be deployed into the endplate  141  of the vertebrae  143  upon rotation of the drive head  320  with the proper instrument. The restraint arm  330  may include a sharpened edge if so desired. The neck portion  340  of the paddle  300  is held by the paddle restraint  310  and is preferably configured with a profile suitable for rotation. The restraint arm  330  may include apertures or slots to encourage bone growth through the restraint arm  330 .  
         [0153]     The endplate facing surface  142  comprises a restraint recess  350  to accommodate the paddle  300  and the restraint arm  330  during implant insertion. Once the disc device  001  is inserted, the restraint arm  330  may be deployed into the endplate to secure the device  001  in the desired location between the vertebrae. Several of the disclosed embodiments may require the surgeon to prepare the vertebral body  144  to accept restraint portions  220  that are intended to become integrated into the bone. In most cases, this preparation involves removing bone and creating restraint access  420  typically in the form of a recess, channel, slot or profile similar to the restraint feature. Obviously, the size of the restraint portion  220  will affect the size of the restraint access  420 . Therefore it is beneficial that restraint portions  220  that interfere with the bone are suitably sized to prevent an oversized restraint access  420  that compromises the vertebrae  143  and risks vertebrae  143  fracture. It is preferable that both the restraint access  420  and restraint portion  220  have radiused edges to reduce stress concentrations in the vertebral body.  
         [0154]     In another alternative embodiment, such as shown in  FIG. 13 , an artificial disc device  001  comprises a restraint portion  220  in the form of an integrated fin  400  extending from the endplate facing surface  142 . The fin  400  may vary in thickness and length as needed to assist in restraining the artificial disc device  001  in a predetermined intervertebral position. The fin  400  may include bone growth apertures  410 , slots, or other structure to facilitate bone growth through the fin and thereby provide additional restraint to the device. Again, the restraint portion  220  may be found on one or both of the shells  100 ,  110 . Alternatively, although the implant is typically inserted from an anterior to posterior approach, the fin  400  may not necessarily be oriented in this same direction. For example, the fin  400  in  FIG. 13A  illustrates a fin  400  that extends laterally across the endplate facing surface  142 . In this embodiment, a restraint access  420  is also cut laterally across the endplate  141 . There is no entry into the restraint access  420  from the peripheral edge of the vertebral body. Therefore, the surgeon may choose to first distract or over stretch the intervertebral space, making room for the addition height of the fin  400  until the fin  400  can fall into the restraint access  420  to secure the implant in the predetermined position. The fin  400  may be equipped with a ramped lead-in wherein the lead-in can be utilized to help distract the vertebrae.  
         [0155]     In an alternative embodiment, the artificial disc device  001  as illustrated in  FIG. 14  may comprise a restraint portion  220  in the form of a fin  400  which accommodates a bone fastener  510  therein. It is preferable that the bone fastener  510  is in the form of a bone screw and is manufactured from a radiolucent material such as PEEK, however the surgeon may choose to use bone fasteners  510  made of a biocompatible metal such as from the family of titaniums or stainless steels. It is preferable that the fastener aperture  520  is counter bored when possible to reduce the profile of the screw head outside the periphery of the shell  100 ,  110 . The fastener aperture  520  may include fastener restraint such as an interference spring to prevent fastener  510  back-out. For example, the fastener aperture  520  may have a groove inscribed therein to house a spring that expands out of the way of the fastener  510  while driving the fastener and closes over the head of the fastener once the head passes the spring.  
         [0156]     An additional alternative embodiment of the artificial disc device  001  is illustrated in  FIGS. 19-21  and comprises a restraint portion  220  in the form of a fin  400  wherein the fin  400  comprises one or more deflectable wall portions  600 . The fin  400  again comprises a fastener aperture  520  to house an expansion fastener  610 . In the preferred form, the expansion fastener  610  comprises a threaded shaft  630 , to drive the fastener  610  down the aperture  520  when rotated, and an expansion shaft  640  to drive apart the deflectable wall portions  600  as the fastener  610  is driven forward. The aperture  520  in this configuration preferably comprises threads  620  to complement the threaded shaft  630 . As the expansion fastener  610  is driven and causes the wall portion  600  to deflect outward a predetermined amount, these wall portions  600  will interfere within the restraint access  420  securely holding the disc device  001  in position. Deflection cuts  650  facilitate the deflection of the wall portion  600  with respect to the fastener block  660 . The deflection cuts  650  may be orientated in different directions wherein, for example, the wall portion may deflect laterally along a vertical plane or laterally along a horizontal plane. Since the disc device  001  will typically be inserted from a generally anterior surgical approach, it is preferred that the fin  400  also be orientated generally anterior to posterior.  
         [0157]     Another embodiment of an artificial disc device  001  is illustrated in  FIGS. 22-24  and comprises a restraint portion  220  in the form of a fin  400 . The fin  400  in this embodiment is preferably laterally offset to one side or the other. The fin  400  preferably comprises an interference portion  710 , typically in the form of a threaded or unthreaded hole or recess. After the shell  100 ,  110  having this feature is inserted into the predetermined position, an alignment instrument (not shown), comprising a drill guide orientated to the implant may be utilized to create a pilot hole  720  through the vertebrae that is directed at the interference portion  710 . A bone fastener  510 , preferably in the form of a bone screw, is then driven into the pilot hole  720 , and in interfering relation with the interference portion  710 , secures the disc device  001  in a predetermined position. The fastener  510  in this embodiment is preferably threaded where it contacts the bone, and may interfere with the fin  400  by threading through it, extending through it, abutting it, or any other interference method. In embodiments wherein a fastener  510  is threaded or otherwise engaged into a deformable implant material, (i.e. an implant manufactured from PEEK), the material itself may serve as adequate protection against fastener  510  back-out.  
         [0158]     In an alternative embodiment, a shell  100 ,  110  is illustrated in  FIG. 25  comprising a restraint portion  220  in the form of a deflectable stop  800 . The deflectable stop  800  is preferably integrated into the endplate facing surface  142  adjacent the posterior end of the shell  100 ,  110 . In the undeflected orientation and from this point of integration, the deflectable stop  800  gradually extends anterior and away from the endplate facing surface  142 . As the shell  100 ,  110  is inserted between the vertebrae, the deflectable stop  800  may deflect into the stop recess  810  as the shell passes over the complementary profiled restraint access  420  created by the surgeon as illustrated in  FIG. 26 . Once the shell  100 ,  110  is positioned in its predetermined location, the deflectable stop  800 , and the restraint access  420  are aligned such that the stop  800  will spring back into the restraint access  420  securely retaining the shell  100 ,  110  in position.  
         [0159]     Similarly, and in a further alternative embodiment, an artificial disc device  001  is illustrated primarily in  FIGS. 27-29  comprising a restraint portion in the form of a deflectable capture  900  preferably integrated into the endplate facing surface  142  adjacent the posterior end of the shell  100 ,  110 . An interlock key  910 , comprising a bone boss  930  and a connection pod  940  with interlock structure complementary to the interlock key  910 , is situated in a preformed restraint access  420  such as shown in  FIG. 30 . As the shell  100 ,  110  is inserted across the vertebral endplate  141 , the deflection arms  960  are pushed open by the connection pod  940  until the pod  940  is seated in the pod canal  950  and the deflection arms  960  are able to spring back into a pod  940  locking position. The pod canal  950  may include complementary structure, such as a tongue and groove arrangement  920 , to secure the pod  940  to the shell  100 ,  110 .  
         [0160]     Another alternative embodiment is illustrated in  FIG. 31  wherein an artificial disc device  001  comprises a restraint portion  220  in the form of a fixed fin  400 , and an insertable locking fin  1000 . Restraint access  420  is formed in the vertebral endplate  141  complementing the position of the fixed fin  400  and the locking fin  1000  on the shell  100 ,  110  as illustrated in  FIG. 33 . The shell  100 ,  110  is inserted, with the locking fin  1000  removed, to its predetermined position between the intervertebral endplates. The locking fin  1000  preferably comprises a friction fit interlocking architecture such as tongue and groove with the shell  100 ,  110  to secure the locking fin to the shell  100 ,  110  and restrict back-out. The locking fin  1000  and the fixed fin  400  are orientated non-parallel to each other such that once the locking fin  1000  is inserted, the corresponding shell is restrained to the desired position on the endplate  141 .  
         [0161]     The artificial disc device  001  can take a form of a non-constrained articulating joint wherein the device  001  has no built in features to limit motion between the articulation surfaces  121  and  131 . In some cases, this can be problematic if the anatomy of the user, by hard or soft tissue, does not perform this function since it is possible that a shell  100 ,  110  can dislocate off the other shell  100 ,  110  and potentially become jammed. In addition, excessive unnatural motion at the device  001  may cause injury to the user. For these reasons it may be advantageous to limit the motion occurring between the articulation surfaces  121  and  131 .  
         [0162]     The artificial disc device may include a motion-limiting portion. In the shell  110  embodiment shown in  FIG. 36 , this motion-limiting portion is in the form of a motion-limiting stop  1100  that is a protruding surface discontinuous with the curvature of the convex articulating surface  131 . Alternately, the stop may instead be formed on the shell  100 , or on both shells  100 ,  110 . As one shell articulates against the other, the stop will limit the freedom of motion that can occur.  
         [0163]     The motion limit portion may take numerous forms. For example, one of the shells  100 ,  110  may comprise a limiter holder  1120  to house a limit post  1130 . Alternatively the limit post  1130  may be integrated into the articulating surface of the shell  100 ,  110 . The limit post  1130  extends into a limit recess  1110  preferably bound by a limit wall  1140 . As the shells  100 ,  110  articulate against each other, interference between the limit post  1130  and the limit wall  1140  limit the motion that can occur between the shells  100  and  110 . Clearly, by adjusting the shape and/or size of the limit recess  1110 , motion can be limited in varying amounts in different directions. For example, motion can be limited to 10 degrees of flexion but only 5 degrees of lateral bending at the joint.  
         [0164]     The artificial disc device  001  may be configured for use when all or a portion of the vertebral body  144  is removed such as in a corpectomy surgery. As seen in  FIGS. 37 and 38 , the majority of a vertebral body  144  is removed and replaced with a vertebral strut  1200 . The strut  1200  comprises any combination of convex articulation surfaces  131  and/or concave articulation surfaces  121 . In addition, the body of the strut  1200  preferably comprises fastener apertures  520  to house bone fasteners  510  (not shown) secured into the remaining bone  1210  of the vertebrae  143  securing the vertebral strut  1200  in the predetermined position. Complementary shells  100 ,  110  articulate with the vertebral strut  1200 . The vertebral strut may also comprise apertures for boney ingrowth or other osteo-conductive coatings or surfaces.  
         [0165]      FIG. 41  shows an artificial disc implant  1310  having an upper component or member  1312  and a lower component or member  1314  with the members  1312  and  1314  having a bearing interface  1316  therebetween that allows the members  1312  and  1314  to shift or articulate relative to each other when implanted and secured in an intervertebral space. The bearing interface  1316  can be in the form of a concave recess  1318  formed in the inner or lower surface  1320  of the upper disc member  1312  ( FIG. 42 ), and a convex dome  1322  that projects up from inner or upper surface  1324  of the lower disc member  1314  ( FIG. 43 ). Manifestly, the orientation of the bearing interface  1316 , and specifically the concave recess  18  and convex dome  1322  can be reversed such that the recess  18  would be formed on the lower implant member  1314  while the dome  1322  would be formed on the upper member  1312 . Preferably, the radius of curvature of the concave recess  1318  and convex dome  1322  are the same for smooth sliding engagement therebetween, although differences in the radius of curvature can also be utilized if desired.  
         [0166]     Preferably, both the upper and lower disc members  1312  and  1314  are formed of a PEEK (polyetheretherketone) material which has been found to provide the disc implant  1310  with excellent strength and wear characteristics that are desirable for a joint that is intended for motion preservation such as the artificial disc implants described herein.  
         [0167]     Referring to  FIG. 44 , a trial spacer assembly  1326  is shown that includes a forward, trial spacer portion  1328  that is inserted into the intervertebral space  1330  between adjacent, upper and lower vertebral bodies  1332  and  1334 . The trial spacer portion  1328  has a generally tongue-shaped configuration including a rounded distal end  1336  and generally flat upper and lower surfaces  1338  and  1340 , as best seen in  FIGS. 45 and 46 . The outer surfaces of the trial spacer portion  1328  present a generally smooth, continuous periphery of the trial spacer portion  1328  for smooth insertion thereof into the intervertebral space  1330 . This smooth tongue configuration for the trial spacer portion  1328  substantially corresponds to the peripheral configuration of the disc implant  1310  less the integrated securing mechanism thereof, as will be described hereinafter.  
         [0168]     The forward trial spacer portion  1328  is connected to an enlarged rear portion  1342  that remains outside the intervertebral space  1330  after the trial spacer portion  1328  is fully inserted therein, as shown in  FIG. 44 . The trial spacer portion  1328  and rear portion  1342  have a hollow interior with the rear portion  1342  having a generally rectangular box-like configuration. As shown, there is a transverse shoulder surface  1343  between the trial spacer portion  1328  and rear portion  1342  that acts as a stop to engage the vertebral bodies  1332  and  1334  with the trial spacer portion  1328  fully inserted into the intervertebral space  1330 .  
         [0169]     The hollow portion of the tongue  1328  contains a pair of plates  1344  and  1346  with the upper plate  1344  including several upstanding posts  1348  and the lower plate  1346  including several depending posts  1350  corresponding in positioning to the posts  1348 , as can be seen in  FIGS. 47-49 . The posts  1348  and  1350  are used to form correspondingly spaced openings in the facing surfaces of the vertebral bodies  1332  and  1334 . As shown, the posts  1348  and  1350  have blunt end surfaces, although other configurations for these ends can also be used to ease driving of the posts  1348  and  1350  into the bone surfaces.  
         [0170]     Referring to  FIG. 47 , the upper plate  1344  includes raised side platform portions  1352  each having three posts  1348  equally spaced therealong and upstanding therefrom. A central ramp portion  1354  is recessed from the raised side portions  1352  at its rear end and extends at an incline upwardly and forwardly toward the forward end  1382  of the upper plate  1344 . Intermediate vertical wall portions  1356  extend along either side of the ramp portion  1354  to interconnect the ramp portion  1354  and the side platform portions  1352  of the upper plate  1344 . The lower plate  46  has a similar configuration to the upper plate  1344  in that it also has lowered, side platform portions  1358  that each include three posts  1350  equally spaced therealong and depending therefrom. A central ramp portion  1360  extends between the side portions  1358  and is raised at its rearward end and extends at an incline downwardly and forwardly toward the forward end  1384  of the lower plate  1346 . Intermediate vertical wall portions  1352  interconnect the side platform portions  1358  and the central ramp portion  1360 .  
         [0171]     The corresponding platform portions  1352  and  1358  of the plates  1344  and  1346  cooperate to form a wedge-shape elongate openings or channels  1367  and  1369  by way of their facing inclined surfaces  1364  and  1366 . More specifically, the corresponding wall portions  1356  and  1362  and the inclined surfaces  1364  and  1366  cooperate to form wedge-shaped side channels  1367  and  1369  which are used to drive the plates  1344  and  1346  apart for creating the indentations or pocket openings in the vertebral bodies, as described further hereinafter.  
         [0172]     Referring to  FIG. 48 , in addition to the upper and lower plates  1344  and  1346 , the internal components of the trial spacer assembly  1326  include a spreader device  1368 , and a generally block-shaped, closing device  1370  shown in their compact or insertion/removal configuration. Referring to  FIG. 50 , the closing wedge device  1370  has upper and lower projecting arms  1372  and  1374  including inclined facing surfaces  1376  and  1378 , respectively. The surfaces  1376  and  1378  cooperate to form a V-shaped opening  1380 . In the insertion configuration, the closing device  1370  has the ramp portions  1354  and  1360  of the plates  1344  and  1346  fully received in the V-shaped opening  1380  with the surfaces  1376  and  1378  fully engaged on the ramp portions  1354  and  1360 , as shown in  FIGS. 48 and 49 . In this manner, the plates  1344  and  1346  are held together with the respective forward ends  1382  and  1384  in engagement, as is best seen in  FIG. 49 .  
         [0173]     The spreader device  1368  has an enlarged rear, box-shaped portion  1386  that fits in the hollow space defined by a box-shaped portion  1342  of the trial spacer assembly  1326 . The spreader device  1368  also includes forwardly projecting arms  1388  and  1390  laterally spaced so that the wedge device  1370  fits therebetween, as can be seen in  FIGS. 48 and 49 . As best seen in  FIG. 48 , the arms  1388  and  1390  have a wedge configuration so that they fit into the corresponding wedge channels  1367  and  1369  formed on either side of the plates  1344  and  1346 . In this regard, each of the wedge arms  1388  and  1390  have inclined surfaces  1392  and  1394  that extend from their rear ends at the portion  1386  and taper down toward each other at their forward ends in the channels  1367  and  1369 .  
         [0174]     Accordingly, to drive the plates  1344  and  1346  apart, the spreader device  1368  and wedge device  1370  are moved in opposite directions with the wedge device  1370  being advanced forwardly so that the inclined surfaces  1392  and  1394  cam against the corresponding plate inclined surfaces  1364  and  1366  to drive the upper plate  1344  in an upward direction toward the vertebral body  1332  and the lower plate  1346  downwardly toward the vertebral body  1334 . The rear portion  1386  of the spreader device  1368  has a window opening  1396  to allow the closing device  1370  to fit therethrough so that as the spreader device  1368  is advanced, the wedge device  1370  can be retracted off of the ramp portions  1354  and  1360  of the plates  1344  and  1346  and through the window opening  1396  to allow the plates  1344  and  1346  to be spread apart. In addition, the trial spacer portion  1328  is provided with through openings  1398  so that the posts  1348  and  1350  can be driven therethrough and into the facing surfaces of the vertebral bodies  1332  and  1334 . As can be seen in  FIG. 45 , openings  1398  are shown in the upper portion of the trial spacer portion  1328  through which the upper posts  1350  are driven. Similar openings are provided in the lower portion of the trial spacer portion  1328  for the lower posts  1350 .  
         [0175]     To remove the trial spacer portion  1328  from the intervertebral space  1330 , the trial spacer assembly  1326  is shifted back from its spread or expanded configuration to its insertion/removal or compact configuration with the plates  1344  and  1346  held together with the closing device  1370 . For this purpose, the operation of the spreader device  1368  and the closing device  1370  is reversed with the closing device  1370  being advanced forwardly through the window opening  1396  of the spreader device  1368  and the spreader device  1368  being retracted rearwardly until the plate ends  1382  and  1384  are brought together as shown in  FIG. 49  with the surfaces  1376  and  1378  of the closing device  1370  once more fully engaged on the ramp surfaces  1354  and  1360 . As the trial spacer assembly  1326  is shifted back to its compact configuration, the posts  1348  and  1350  are retracted back through their corresponding openings  1398  in the trial spacer portion  1328  and into the hollow space therein.  
         [0176]     After the trial spacer assembly  1326  is utilized as described above to form openings or indentations  1398  in the facing surfaces of the vertebral bodies  1332  and  1334 , the implant  1310  is inserted into the intervertebral space  1330  via inserter tool  1400 . The inserter tool  1400  has an elongate shaft  1402  and an enlarged head  1404  at its end in which it carries the disc implant  1310  for insertion thereof. Shaft  1402  and the head  1404  are formed by an upper elongate tool member  1406  and a lower elongate tool member  1408  having shaft portions  1410  and  1412 , respectively, and an associated head portion  1414  and  1416  at their respective ends. The upper and lower tool members  1406  and  1408  are able to slidingly reciprocate relative to each other for removal of the disc  1310  from the intervertebral space  1330 , as will be described more fully hereinafter.  
         [0177]     As shown in  FIG. 51 , the tool head  1404  has a forward opening  1318  between upper and lower plate portions  1420  and  1422  of the respective upper and lower head portions  1414  and  1416 . The opening  1418  between the plate portions  1420  and  1422  is sized to receive the implant  1310  therein. In this regard, each plate portion  1420  and  1422  has respective side slots  1424  and  1426  formed therein. The slots  1424  and  1426  allow the securing mechanism, in the form of upstanding posts  1428  that are integral with and project up from the upper disc member  1312 , and depending posts  1430  that are integral with and project downwardly from the lower disc member  1314 , to fit therein. The slots  1424  and  1426  are defined by side prongs that extend along either side of a central projection of each of the tool member head portions  1414  and  1416 . More specifically, the upper head portion  1414  has side prongs  1432  on either side of central projection  1434 , and the lower head portion  1416  has side prongs  1436  on either side of central projection  1438 . The posts  1428  are formed in two rows of three equally spaced posts  1428  on either side of the upper disc member  1312 , and the lower posts  1430  are formed similarly in two rows of three equally spaced lower posts  1430  on lower disc member  1314  so that the posts  1428  and  1430  correspond to the spacing and positioning of the posts  1348  or  1350  of the plates  1344  and  1346 , and the openings  1398  that they form in the vertebral bodies  1332  and  1334 .  
         [0178]     As shown in  FIG. 51 , the implant  1310  is arranged so that the straight upper and lower ends  1438  and  1440  thereof are facing rearwardly so that they abut against the shoulder abutment walls  1442  and  1444  at the rear end of the disc receiving opening  1418  in the tool head  1404 . In this regard, the upper and lower actuator ends  1445  and  1447  are arranged forwardly so as to be at the trailing end of the disc implant  1310  as it is inserted into the tool head opening  1418 . So that the upper plates  1420  and  1422  substantially match the configuration of the upper and lower disc members  1312  and  1314 , the prongs  1432  and  1436  do not extend as far forwardly as the adjacent central projection  1434  and  1438 , respectively. In addition, the peripheral edges of the side prongs  1432  and  1436  and the respective central projections  1434  and  1438  have an actuate chamfer to match that of the ends  1445  and  1447  of the disc members  1312  and  1314 , respectively. In this manner, with the disc  1310  fully received in the tool head opening  1418  as shown in  FIG. 52 , the projecting ends  1445  and  1447  of the disc implant  1310  present a substantially smooth, continuous surface in combination with the corresponding, adjacent edges of the prongs  1432  and  1436  and central projections  1434  and  1438 .  
         [0179]     Referring to  FIG. 52 , the implant posts  1428  and  1430  are received in the respective slots  1424  and  1426 . As shown, the rearmost posts  1428  abut against the end of the slots  1424  with the upper and lower disc member ends  1439  and  1440  engaged against the shoulder walls  1442  and  1444  with the disc implant  1310  fully received in the tool head opening  1418 . Similarly, the rearmost lower posts  1430  are engaged at the end of lower slots  1426  with the upper and lower disc ends  1439  and  1440  engaged against the shoulder walls  1442  and  1444  with the disc implant  1310  fully received in the tool head opening  1418 . As shown, the spacing the plates  1420  and  1422  is such that with the posts  1428  and  1430  received in the slots  1424  and  1426 , the upper ends of the posts  1428  and  1430  will be substantially flush with the top and bottom surfaces  1446  and  1448  of the plate portion  1420  and  1422 , respectively. In this manner, the disc implant  1310  is smoothly inserted into the intervertebral space  1330  with the inserter tool  1400 . Also, the inserter tool plates  1420  and  1422  are spaced so as to distract the vertebral bodies  1332  and  1334  apart for fitting the disc implant  1310  therebetween. In other words, the spacing between the surfaces  1446  and  1448  of the respective plates  1420  and  1422  is slightly greater than the spacing between the surfaces  1338  and  1340  of the trial spacer portion  1328  of the trial spacer assembly  1326 . This allows the disc posts  1428  and  1430  to be fit into the openings  1398 .  
         [0180]     More specifically, the upper and lower tool members  1406  and  1408  preferably include respective, laterally extending stop members  1450  and  1452  that are spaced slightly rearwardly of the rear ends of the slots  1424  an  1426 . The tool  1400  is advanced forwardly to fit the tool head  1404  and artificial disc  1310  carried thereby into the intervertebral space  1330 . The tool  1404  continues to be advanced forwardly until the stops  1450  and  1452  abut against the vertebral bodies  1332  and  1334  to provide the user an indication that the tool head  1404  and the artificial disc  1310  carried thereby are fully received in the intervertebral space  1330 . With the stops  1450  and  1452  engaged against the respective vertebral bodies  1332  and  1334 , the posts  1428  and  1430  are now properly aligned with the pocket openings  1398  formed in each of the vertebral bodies  1332  and  1334 .  
         [0181]     As previously mentioned, the tool members  1406  and  1408  are slidable relative to each other so that one of the members  1406  and  1408  can be retracted while the other member  1406  or  1408  remains in its advanced position with the corresponding stop  1450  or  1452  engaged against the corresponding vertebral body  1332  or  1334 . As shown in  FIG. 54 , upper tool member  1406  is retracted while the lower tool member  1408  remains in its advanced position with the stop  1452  thereof engaged against the vertebral body  1334 . With the plate  1420  retracted out from the intervertebral space  1330 , the distracted vertebral body  1332  will shift down toward the vertebral body  1334  causing the posts  1428  of the disc upper member  1312  to be received in the corresponding preformed pocket openings  1398  in the vertebral body  1332 . Thereafter, the lower tool member  1408  is retracted to pull the plate member  1422  out from the intervertebral space  1330  so that the posts  1430  can fall into the corresponding preformed pocket openings  1398  formed in the vertebral body  1334 , as shown in  FIG. 55 . With the disc implant  1310  secured to the vertebral bodies  1332  and  1334  in the intervertebral space  1330  therebetween via the fitting of the posts  1428  and  1430  into the pocket openings  1398 , the risk that the disc  1310  will be extruded out from the intervertebral space  1330  is substantially minimized as the vertebral bodies  1332  and  1334  move relative to each other via the bearing interface  16  between the secured upper and lower disc members  1312  and  1314 .  
         [0182]     In the next trial spacer and disc implantation and securing system, a trial spacer assembly  1450  as shown in  FIG. 56  is employed. The trial spacer assembly  1450  also is utilized to form features in the vertebral bodies  1334  and  1336  for receipt of the securing mechanism that is associated with the artificial disc implant  1452  ( FIG. 52 ). The disc implant  1452  only varies from the disc implant  1310  in the securing mechanism employed so that the common features between the disc implants  1310  and  1452  will not be described in detail hereinafter.  
         [0183]     The trial spacer assembly  1450  has a forward, trial spacer portion  1454  that has an outer, peripheral configuration substantially matching that of the disc implant  1452  less the securing mechanism thereof. The trial spacer assembly  1450  also includes a rearwardly extending shaft portion  1456 . The trial spacer assembly  1450  is formed from two components. As shown in  FIG. 58 , the main trial spacer member  1458  includes a head trial spacer portion  1460  and a rearwardly extending shaft portion  1462 . The shaft portion  1458  has an elongate lower groove  1464  formed along its entire length, and the head portion  1460  also includes an elongate lower groove  1466  aligned with the shaft groove  1464 , as shown in  FIG. 58 . In addition, the head portion  1460  has a pair of upper grooves  1468  and  1470  on either side thereof. The grooves  1464 - 1470  are used to form features in the vertebral bodies  1332  and  1334  for receipt of the securing mechanism of the disc implant  1452 , as described more fully hereinafter.  
         [0184]     The second component of the trial spacer assembly  1450  is a head cover and handle member  1472 . The member  1472  includes a head cover portion  1474  that consists of a laterally extending, rear flange portion  1474  from which a central lower prong  1476  and a pair of upper prongs  1478  extend forwardly. Shaft handle portion  1480  extends rearwardly from the flange portion  1474  and has a hollow throughbore  1482  extending therethrough opening to the flange portion  1474 , as seen in  FIGS. 60 and 61 .  
         [0185]     The trial spacer assembly  1450  is assembled by sliding the head cover and handle member  1472  over the trial spacer member  158  with the shaft portion  1462  fitting into the throughbore  1482  and the prongs  1476  and  1478  fitting into the corresponding grooves  1466 - 1470  of the trial spacer head portion  1460 . Referring to  FIG. 56 , the throughbore  1482  has a generally D-shaped configuration so that the shaft portion  1462  is non-rotatably received therein. Further, as can be seen in  FIG. 57 , the prongs  1476  and  1478  fit into the corresponding grooves  1466 - 1470  such that the outer, peripheral surface of the trial spacer portion  1454  has no sharp or discontinuous surfaces that might otherwise gouge the vertebral bodies  1332  and  1334  during insertion of the trial spacer portion  1454  into the intervertebral space  1330 . Also, the trial spacer portion  1460  is provided with three laterally extending stop members including central, upper stop member  1484  that extends laterally between the upper grooves  1468  and  1470 , and side, lower stop members  1486  that extend laterally on either side of the central lower groove  1466  with all three stop members  1484  and  1486  being adjacent the rear end of the trial spacer portion  1460 .  
         [0186]      FIG. 62  shows the trial spacer portion  1454  inserted into the intervertebral space  1330  between adjacent vertebral bodies  1332  and  1334  for assessing the size of the intervertebral space  1330  so as to be able to accurately select an appropriately sized artificial disc  1452  for implantation therein. As shown in  FIG. 62 , the trial spacer portion  1454  is fully received in the intervertebral space  1330  with the stops  1484  and  1486  engaged against the vertebral bodies  1332  and  1334  and the shaft portion  1462  extending outside the intervertebral space  1330  and away therefrom. Thereafter, the head cover and handle member  1472  are slid off and removed from the trial spacer member  1458  leaving the grooved trial spacer portion  1460  in the intervertebral space  1330  with the shaft portion  1462  extending rearwardly therefrom, as shown in  FIG. 63 .  
         [0187]     At this point, the trial spacer member  1458  is used in cooperation with a drill guide  1488  for drilling grooves in the vertebral bodies  1332  and  1334  at the facing surfaces thereof. Referring to  FIG. 64 , the drill guide  1488  has a triangular-block body  1490  with a pair of upper throughbores  1492  extending through the body  1490 , and an irregularly-shaped, enlarged central throughbore  1494  between and below the upper, side throughbores  1492 . The enlarged, central throughbore  1494  is sized so that the drill guide  1488  can be slid along the trial spacer member  1458  with the shaft portion  1462  fitting in the upper portion of the central throughbore  1494 , as shown in  FIG. 65 . Referring next to  FIG. 66 , it can be seen that the upper side throughbores  1492  are aligned with the upper grooves  1468  and  1470  in the trial spacer portion  1460  to cooperate therewith in guiding a drill  1496  ( FIG. 67 ) for cutting grooves in the upper vertebral body  1332 . Similarly, the lower portion of the central throughbore  1494  of the drill guide  1488  cooperates with the lower groove  1464  in the shaft portion  1462  and lower groove  1466  in the trial spacer portion  1460  to form an opening through which the drill bit  1496  is guided for cutting a groove in the lower vertebral body  1334 .  FIG. 68  shows the pair of upper grooves  1498  formed along either side of the facing surface of the vertebral body  1332  and the lower groove  1500  formed centrally in the facing surface of the lower vertebral body  1334  with the drill guide  1488  removed from the shaft portion  1462  for purposes of illustrating the grooves  1490  and  1500 .  
         [0188]     Next, a cam cutter  1502  is advanced through the bores  1492  and  1494  in a manner similar to the drill bit  1496 . The cam cutter  1502  has a reduced size, radially offset cutting end  1504  including several cutting blade portions  1506 , and a counter bore cutting portion  1508  at the rear thereof. An enlarged shaft  1510  extends rearwardly from adjacent to the counter bore cutting portion  1508 . The shaft  1510  is sized to fit into the openings through the drill guide  1488  formed in cooperation with the trial spacer member  1458 , as previously described with respect to the drill bit  1496 .  FIG. 70  is a view of the cam cutter  1502  showing the bell-shaped configuration of the cutting blade portions  1506  and counter bore cutting blade portion  1508 . The cam cutter  1502  is operable to cut radially enlarged recesses  1512  in the grooves  1498  and  1500  as well as enlarged counter bore portion  1514  at the rear end of the grooves  1498  and  1500 . Alternately, the drill bit  1496  can be provided with a stepped configuration to form the counter bore  1514  simultaneously with the drilling of the grooves  1498  and  1500 . Similarly, the cam cutter  1502  can be avoided altogether if the securing mechanism for the artificial disc implant  1452  is provided with cutting-type cams, as will be described hereinafter.  
         [0189]     Referring to  FIG. 72 , the securing mechanism of the disc implant  1452  takes the form of upper cam shafts  216  secured on either side of upper disc implant member  1518 , and lower cam shaft  1520  secured centrally to the lower disc implant member  1522 . To hold the cam shafts  1516  and  1520  to the respective disc members  1518  and  1522 , each is provided with a plurality of spaced upwardly open, U-shaped retainer members  1524 . The retainer members  1524  have upwardly extending arms  1526  that are spaced from each other so that the shaft portion  1528  of the cam shafts  1516  and  1520  will be received by a friction fit therebetween. In this regard, the preferred PEEK material from which the disc members  1518  and  1522  including the retainer members  1524  thereof are formed will provide the arms  1526  with sufficient strength and resiliency to provide a secure friction fit with the shaft portions  1528  snap-fit therebetween while allowing for the shaft portions to be rotated to secure the disc members  1518  and  1522  to the corresponding vertebrae  1332  and  1334 .  
         [0190]     More specifically, the cam shafts  1516  and  1522  each include several cam lobe members  1530  spaced along the length thereof and a proximate disc indicator member  1532  adjacent drive head  1534 . Initially, the cam shafts  1516  and  1520  are oriented 1480 degrees from their orientation shown in  FIG. 72  for insertion of the artificial disc  1452  into the intervertebral space  1330  with the cam shafts  1516  and  1520  received in the corresponding grooves  1498  and  1500  of the vertebral bodies  1332  and  1334 . In this regard, the cam lobes  1530  are rotated down into recessed slots  1536  formed in the upper surface of the upper disc member  1518 . Rotating the cam shafts  1516  and  1520  via the hex drive heads  1534  thereof by 1480 degrees from their insertion orientation to their secured orientation shifts the cam lobes  1530  into the recesses  1512  cut into the vertebral body grooves  1498  and  1500 , as shown in  FIG. 74 . In this manner, the artificial disc implant  1452  is secured in the intervertebral space  1330  against extrusion out therefrom during articulation of the upper and lower disc members  1518  and  1522  relative to each other as the upper and lower vertebrae  1332  and  1334  shift via the arcuate bearing interface formed between the members  1518  and  1522 . The disc indicator member  1532  is sized to be received in the counter bore portion  1514  of the grooves  1498  and  1500 . The disc member  1532  can be provided with a pair of diametrically opposite notches  1538  about its periphery that cooperate with a raised nub  1540  on the disc member  1518  so that the user is provided with a tactile indication that the cam shafts  1516  and  1520  have been rotated by 1480 degrees from their insertion orientation to shift the cam lobes  1530  so that they are substantially fully received in the groove recesses  1512 .  
         [0191]      FIGS. 75 and 76  show alternative upper cam shafts  1542  and an alternative lower cam shaft  1544 . In this form, the cam members  1546  have more of a flat mushroom-like configuration with sharp corner edges  1548  for cutting into the vertebral bodies  1332  and  1334 . In this manner, the separate cam cutter  1502  need not be used for cutting the recesses  1512  in the vertebral body grooves  1498  and  1500 . Also, it can be seen that the drive head  1534  can have a cruciform drive recess  1550  rather than having the hex drive configuration of the drive head  1534 .  
         [0192]     The next trial spacer and artificial disc implantation and securing system is similar to the previous system except that the securing mechanism is not associated with the artificial disc as it is inserted into the intervertebral space  1330 , but rather is first inserted into the preformed features formed in the vertebral bodies  1332  and  1334  and thereafter deployed therefrom to interconnect the vertebral bodies and the artificial disc implant  1552  ( FIG. 85 ). Referring to  FIG. 77 , a trial spacer member  1554  is shown having upper side grooves  1556  in the forward head portion  1557  thereof and a lower central groove  1558  that extends in the rear shaft portion  1560  thereof as well as in the forward head portion  1557 . The cover and handle member for the trial spacer member  1554  is not shown for illustration purposes but otherwise is similar to the previously described cover and handle member in that it is configured to ensure that the forward trial spacer portion including the grooved head portion  1557  can be inserted smoothly into the intervertebral space  1330  without gouging the vertebral bodies  1332  and  1334 .  
         [0193]     As shown in  FIG. 78 , the shaft member  1560  receives a drill guide  1562  thereon which has throughbores  1563  that are slightly offset from the corresponding grooves  1556  and  1558  of the trial spacer member  1554 . Accordingly, drill  1565  is guided through the bores  1563  to drill grooves  1569  into the vertebral body  1332  that are slightly offset upwardly from the upper grooves  1556  of the trial spacer member and a groove  1569  into the vertebral body  1334  that is slightly offset downwardly from the lower groove  1558  of the trial spacer member  1554 .  
         [0194]     Next, cam shafts  1567  are inserted into the intervertebral space  1330  guided by the grooves  1556  and  1558  of the trial spacer member  1554 , and then they are rotated and cammed up into the offset grooves  1569  formed in the upper vertebral body  1332  and down into the offset groove  1569  formed in the lower vertebral body  1334 , as shown in  FIGS. 79 and 80 . The camming action of the cam shafts  1567  is shown in  FIGS. 81-84 .  
         [0195]     In  FIG. 81 , a cam shaft  1567  is shown from a posterior viewpoint in its initial position resting in the groove  1556  of the trial spacer member  1554 . The head of the cam shaft is engaged by the drive tool  1570  having an eccentric cam  1573  ( FIG. 87 ) for camming against an anterior platform or ledge  1555  ( FIGS. 77 and 79 ) on the trial spacer member  1554 . The cam shafts  1567  are cammed at both their distal shaft ends  1568  as shown in  FIGS. 81-85  and  87 , as well as at their proximate ends where they interface with drive tool  1570 . In  FIG. 82 , the drive tool  1570  has been rotated clockwise 90 degrees along the anterior platform  1555  of the trial spacer member  1554 . This causes the cam shaft  1567  to rotate 90 degrees and the cam lobes  1572  begin to engage and imbed themselves the upper vertebra. In  FIG. 83 , the cam shaft  1567  is shown fully rotated 180 degrees from its initial position in  FIG. 81 . At this point, the cam lobes  1572  are embedded into the vertebra, and are held in place due to the frictional engagement between the cam lobes  1572  and the bone. Finally, the driver  1570  may be removed, as is shown in  FIG. 84 . Once the cam shafts  1567  have been fully rotated 180 degrees, the cam lobes  1572  are completely removed from the body of the trial spacer member  1554 . Thus, the trial spacer  1554  may be removed.  
         [0196]     With the cam shafts  1567  rotated as shown in  FIG. 84  so that the sharp cam lobes  1572  thereof are rotated up (or down) into the vertebral bodies via a cutting action generated by the cams during such rotation, the disc implant  1552  is then inserted into the intervertebral space  1330 . As shown in  FIG. 85 , the upper disc member  1564  has spiral cutouts  1566  in the upper surface thereof so that rotating the cam shafts  1562  again causes the cam lobes  1572  to be engaged in both the grooves of the vertebral bodies  1332  and  1334  as well as tightly engaged or embedded into the raised ribs  1571  defining the spiral cutouts  1566  so that the implant  1552  is securely held and retained in the intervertebral space  1330  during articulation thereof.  
         [0197]     In another form, a trial spacer system  1600  is shown in  FIG. 88  is employed for sizing and preparing an implantation site for an implant. The trial spacer system  1600  includes a trial spacer assembly  1750 , a drill set  1900 , and an insertion tool  1902 . As in the embodiment disclosed in  FIG. 56 , the trial spacer assembly  1750  is utilized to form features in the vertebral bodies  1330 ,  1332  for receipt of the securing mechanism that is associated with the artificial disc implant  1752 . A principal difference between the trial spacer assembly  1450  of  FIG. 56  and the present trial spacer assembly  1750  is that present assembly eliminates the shaft portion  1462  and integrates the drill guide  1488  together with the trial spacer portion  1454 . Additional features that vary from the previous embodiment of the trial spacer assembly  1450 , including the insertion tool  1902 , will be described below.  
         [0198]     The trial spacer assembly  1750  generally has a forward trial spacer portion  1754  for insertion into the intervertebral space  1330  and rearward drill guide  1788  integrated with the forward trial spacer portion  1754 . The forward trial spacer portion  1754  varies little from the previously described embodiment in  FIG. 56 , and therefore will not be described in full detail here. However, one feature notably different in geometry from the previous embodiment is the upper stop member  1784 , shown in  FIG. 89  located on the upper surface of the trial spacer portion between the upper grooves  1768 ,  1770 . In addition, both the upper grooves  1768 ,  1770  and the lower groove  1766  have a rearward counterbored portion  1904  for accommodating drill bits  1930 ,  1932 ,  1934  having a forward cutting portion  1806  and a rearward counterbored portion  1808 . Also, the upper and lower faces  1906 ,  1908  of the trial spacer portion  1754  may be skewed with respect to one another to mimic the lordotic angle of the spine to improve the fit of the trial spacer  1754 . Preferably, the angle between the upper and lower faces  1906 ,  1908  is about 5 degrees. The trial spacer assembly  1750  is preferably made with titanium or stainless steel. In addition, the assembly is preferably colorized using an anodization process, such that different sized trial spacer assemblies are color coded for ease of identification.  
         [0199]     The drill guide portion  1788  of the of the trial spacer assembly  1750  is similar from the drill guide  1488  of  FIG. 64 , except for a few notable features. For instance, the present drill guide portion  1788  replaces the irregularly-shaped throughbore  1494  with a lower throughbore  1794  similar in diameter to the upper throughbores  1792 , as shown in  FIG. 90 . As shown in  FIG. 91 , the lower throughbore  1794  has an annular recessed portion  1910  for accepting the gripping mechanism  1912  of the insertion tool  1902  to allow the tool  1902  to securely attach to the trial spacer assembly  1750 . Now referring to  FIG. 90 , the drill guide portion  1788  has a rear face  1914  wherein each throughbore  1792 ,  1794  terminates. On the face  1914  adjacent to the lower throughbore  1794  are a set of three recesses  1916 ,  1918  for providing three positions at which the inserter tool  1902  may engage the trial spacer assembly  1750 . Each recess  1916 ,  1918  is sized to mate with a single corresponding guide pin  1920  on the barrel  1922  of the inserter tool  1902 . When the middle recess  1916  is engaged by the pin  1920  of the inserter tool  1902  (as in  FIG. 91 ), the trial spacer assembly  1750  is held at a neutral angle, with the vertical axis (denoted with a “v”) of the assembly parallel with the vertical axis of the inserter tool  1902 . The two remaining recesses  1918  to either side of the middle recess  1916  allow the user to grip the trial spacer assembly  1750  at 45 or −45 degrees with respect to the vertical axis. This allows the surgeon to manipulate the trial spacer  1750  in multiple positions, and gives the tool  1902  greater flexibility. Accordingly, the tool  1902  has a plurality of relative positions between the tool barrel  1922  and the trial spacer assembly  1750 . The drill guide portion  1788  also defines a lateral bore  1924  for providing a point of reference for the surgeon when viewing the trial spacer  1750  using fluoroscopy to help position the assembly  1750  once inserted into the patient&#39;s body. A bore  1924  is used because the trial spacer assembly  1750  is preferably made out of stainless steel or titanium.  
         [0200]     Now referring to  FIG. 88 , each drill bit  1930 ,  1932 ,  1934  of the set  1900  has identical cutting surfaces  1806 ,  1808  on the forward end of the shaft  1928 . The forward cutting portion  1806  consists of a cutting surface at the tip of the bit  1796  suitable for cutting an elongate groove  1498  in the vertebra  1332 ,  1334  for the forward portion of the securing mechanism of the implant  1752 . At the rear end of the first cutting portion  1806  begins the counterbore cutting portion  1808  for creating a counterbore in the vertebra to provide clearance for the head of the securing mechanism.  
         [0201]     Each drill bit  1796  has a collar  1926  for providing an abutment surface to restrict the distance the bit  1796  may be inserted into the trial spacer assembly  1750 . The collar  1926  is an enlarged portion of the drill bit shaft  1928  and abuts the rear face  1914  of the trial spacer assembly  1750  when the drill bit  1796  is fully inserted. This keeps the surgeon from unintentially drilling too far and damaging surrounding tissue, bone, nerves, and other vital areas.  
         [0202]     As shown in  FIG. 88 , the drill set  1900  is comprised of three drill bits  1930 ,  1932 ,  1934  having shafts  1928  of differing lengths. The length of each shaft  1928  is different so the bits  1930 - 34  may be left in the drill guide  1788  and used sequentially, from shortest to longest, without interfering with the drill. The first and shortest bit  1930  is used to create the first groove  1798  in the upper vertebra  1332 , the second and intermediate bit  1932  to create the second groove  1798  in the upper vertebra  1332 , and the third and longest bit  1934  to create the groove  1800  in the lower vertebra  1334 . This way, the first and second drill bits  1930 ,  1932  need not be removed from the trial spacer assembly  1750  prior to insertion of the third drill bit  1934 . Once the first and second drills have cut grooves  1798  into the upper vertebra  1332 , they remain in place to act as placeholders in the newly formed grooves  1798 . In this manner, the drill bits  1900  help to secure the trial spacer  1750  in place to prevent movement of the trial spacer assembly  1750  with respect to the vertebrae  1332 ,  1334  while the other grooves are being cut and while the inserter tool  1902  is being removed. Advantageously, no other fixation means, such as bone screws, are necessary to secure the trial spacer  1750  to the vertebrae  1332 ,  1334 .  
         [0203]     Now referring  FIG. 92 , the trial spacer inserter  1902  comprises a gripping assembly  1912  connected by a barrel  1922  to a handle  1936  and an actuator in the form of a trigger  1938 . As shown in  FIGS. 93 and 94 , the handle  1936 , preferably made of a polymer, such as Radel®, has a partially hollow interior including an annular recess  1940  for accepting a downwardly extending handle shaft  1942  having a threaded recess  1944  at the bottom. A fastener  1946  affixes the handle  1936  to the downwardly extending handle shaft  1942  by threading the fastener  1946  into the threaded end  1944 . The handle shaft  1942  is welded or otherwise integrated into the yoke housing  1948  of the inserter  1902 . The trigger  1938  is attached to an elongate trigger link  1950  at the link&#39;s lower end with two pins  1952 . The trigger link  1950  is disposed partially within the interior of the handle  1936  and pivots about a hinge pin  1954  which protrudes through the trigger link  1950  and is captured within the handle  1936 . At its upper end, the trigger link  1950  has an actuating head portion  1956  for actuating the gripping mechanism  1912 .  
         [0204]     Specifically, the head portion  1956  of the trigger link  1950  directly engages the yoke  1958  to move it within the yoke housing  1948  to actuate the gripping mechanism. The yoke  1958  is a cylindrical body having a bore  1960  for accepting the head portion  1956  of the trigger link  1950  and is directly propelled thereby. The yoke  1958  is attached to the push rod  1962  at the rear portion of the yoke&#39;s forward end. A spring  1964  disposed between the yoke  1958  and the internal end wall of the yoke housing  1948  provides a biased resistance to the trigger  1938  when the yoke  1958  is actuated by the trigger link  1950 .  
         [0205]     The yoke housing  1948  is connected to the barrel  1922 , which defines an internal bore  1960  for guiding the push rod  1962  through the barrel  1922 . The push rod  1962  is preferably made of a flexible material, such as Nitinol. The push rod  1962  extends through the internal bore  1960  within the barrel  1922  from the yoke  1958  to the gripping mechanism  1912 . The gripping mechanism  1912  includes a wedge shaped plunger  1966  connected to the push rod  1962  and an expandable flared end  1968 . The flared end  1968  has a plurality of flexible tabs  1970  each having a protrusion  1972  at the forward end of the tab  1970  for engaging the recessed portion  1910  within the lower throughbore  1794  of the trial spacer assembly  1750  as shown in  FIG. 91 . The tabs  1970  also have a stabilizing ridge  1974  for engaging the internal surface of the lower throughbore  1974  to further stabilize the trial spacer assembly  1750  to prevent unwanted movement between the assembly  1750  and the inserter tool  1902 . The flared end  1968  is sized to fit within the lower throughbore  1794  when the plunger  1966  is not retracted. The flexible tabs  1970  are splayed radially outwards by the wedge-shaped plunger  1966  when the plunger  1966  is pulled inwards towards the rear. When the plunger  1966  is retracted, the flexible tabs  1970  engage the internal surfaces of the lower throughbore  1794 .  
         [0206]     The barrel  1922  includes an insertion guide  1976  disposed on the barrel  1922  near the gripping mechanism  1912  for abutting the rear face  1914  of the drill guide portion  1788  to prevent inserting the barrel  1922  too far into the lower throughbore  1794 . In addition, the insertion guide  1976  comprises a guide pin  1920  as described above for engaging the recesses  1916 ,  1918  in the rear face  1914  of the drill guide portion  1788  to increase maneuverability and stability of the trial spacer assembly  1750 .  
         [0207]     A solid cylindrical end cap  1978  at the rear end of the tool  1902  is connected to the yoke housing  1948  to provide a contact surface for the surgeon to strike during insertion of the trial spacer assembly  1750 .  
         [0208]     In operation, the gripping mechanism  1912  is inserted into the lower throughbore  1794  of the trial spacer assembly  1750  with the trigger  1938  depressed to push the plunger  1966  forward to disengage the flexible tabs  1970  of the gripping mechanism  1912 . Once the inserter end is fully inserted into the trial spacer assembly  1750 , the trigger  1938  is released, causing the plunger  1966  to be pulled back and splaying the flexible tabs radially outward. The flexible tabs  1970  are forced into gripping engagement with the internal surfaces of the lower throughbore  1794 , and the guiding pin  1920  engages one of the recesses  1916 ,  1918  in the rear face  1914  of the drill guide portion  1788  for providing additional stability and control. The trial spacer  1750  is then inserted into the intervertebral space  1330 . If the spacer  1750  is the appropriate size, the surgeon will then prepare the vertebrae  1332 ,  1334  for the implant  1752 . While continuing to hold the trial spacer assembly  1750  in place with the trial spacer inserter  1902 , the first drill bit  1930  is affixed to the drill, and then inserted into one of the upper throughbores  1792  of the trial spacer assembly  1750 . The first groove  1798  is drilled. While the drill bit  1930  is still fully within the trial spacer assembly  1750 , the drill bit  1930  is released from the drill and left in place. Next, the second intermediate drill bit  1932  is attached to the drill and the second upper groove  1798  is then drilled. Again, the second drill bit  1932  is left in place. The inserter  1902  is then removed from the trial spacer assembly  1750 . This is done by pulling the trigger  1938  to disengage the gripping mechanism  1912  and pulling the inserter  1902  away. The inserter tool  1902  is then removed and the lower groove  1800  is drilled, using the third and longest drill bit  1934 . Once all of the grooves have been drilled, all three of the drill bits  1930 - 34  are removed by hand. In a preferred embodiment, the cam cutting step described in  FIGS. 69-71  is omitted because the artificial disc implant  1752  is provided with cutting-type cams  1846  as previously described. Then, to remove the trial spacer assembly  1750 , the insertion tool  1902  is reinserted into the lower throughbore  1794 , the trigger  1938  is released to grip the trial spacer assembly  1750 , and the assembly  1750  is pulled out using the insertion tool  1902 . The surgical site is then preferably irrigated in preparation for insertion of the implant  1752 .  
         [0209]     The artificial disc implant  1752  of the present embodiment varies in only a few respects compared with the artificial disc implant shown in  FIGS. 72-76 . For instance, the present embodiment has a different form of disc indicator member  232 . The following embodiments provide tactile feedback regarding the position of the securing mechanism to the surgeon as the securing mechanism is deployed. Because the bone is relatively soft compared to the projections being deployed into the bone, the bone provides little resistance to the projections as they are deployed into the bone. Therefore, it is important to provide the surgeon with tactile feedback so that he does not over or under deploy the projections, causing the implant  1752  to be improperly affixed to the bone. In addition, it is important to provide the securing mechanism with positive retraction blocking structure. Because the vertebral bone provides only a limited amount of resistance to the deployable projections, the projections may be prone to retract, derotate, or otherwise begin to return to their original undeployed position over time. Thus, retraction blocking structures are provided on the disc implant  1752  to avoid this condition.  
         [0210]     The securing mechanism may take many forms. In one embodiment according to  FIG. 96 , the securing mechanism takes the form of a cam shaft  1816 . The cam shaft  1816  has a radially extending cam projection  1979  including a tactile feedback creating surface in the form of a wedge-shaped camming surface  1980  adjacent the drive head  1834 . The camming surface  1980  frictionally engages a corresponding camming surface  1982  disposed on the adjacent retainer member  1824  shown in  FIG. 97  (in a test block for demonstrative purposes with heads  1834  of the cam shafts  1816  hidden) as the cam shaft  1816  is rotated from its undeployed starting position (on left side of  FIG. 97 ), to a partially deployed position, and then to its fully deployed position 180 degrees from its starting position. The camming surfaces  1980  and  1982  are inclined relative to the longitudinal axis  1981  so that as the camming surfaces  1980 ,  1982  engage and cam against each other, the cam shaft  1816  is shifted axially towards the anterior direction (as installed in the spine).  
         [0211]     This frictional interaction between the camming surfaces  1980 ,  1982  and a biasing force exerted by the retainer members  1824  on the cam shaft  1816  caused by the deformation of the retainer members  1824  provides tactile feedback to the surgeon. The deformation of the retainer members is preferably elastic, such that the retainer members  1824  will return to their original shape when the cam shaft  1816  is in its fully deployed position. Alternatively, the deformation could be plastic, wherein the retainer members  1824  undergo some irreversible deformation. This is acceptable when the securing mechanism is not deployed and retracted repeatedly.  
         [0212]     Once the cam shaft  1816  is turned a full 180 degrees, the cam shaft camming surface  1980  snaps into a recess  1984  formed in the adjacent retainer member  1824 , due to the biasing force exerted on the cam shaft  1816  by the flexed retainer members  1824 . The recess  1984  and cam shaft camming surface  1980  is formed such that the camming surface  1980  becomes trapped in the recess  1984  and blocks derotation of the cam shaft  1816 . More specifically, the cam projection  1979  has a straight, trailing edge surface  1983  that is turned toward the straight edge surface  1985  of recess  1984 . Once the trailing edge surface  1983  clears the recess surface  1985 , the cam surface  1980  will have traveled past the corresponding camming surface  1982  so that the cam surfaces  1980  and  1982  are disengaged from one another. This removes the axial biasing force that their camming engagement generates, so that the cam projection  1979  travels or snaps axially back into the recess  1984 . In this orientation, the flat edge surfaces are in confronting relation to each other so that the cam projection  1979  can not be moved back out of the recess  1984 .  
         [0213]     Now referring to  FIGS. 98 and 99 , another embodiment of the securing mechanism for providing tactile feedback to the surgeon and preventing retraction of the securing mechanism is disclosed. The cam shaft  1816  has a flat camming surface  1986  adjacent the drive head  1834 . As shown in  FIG. 99  (in a test block arrangement similar to  FIG. 97 ), the flat camming surface  1986  frictionally engages a corresponding camming surface  1988  formed in the adjacent retainer member  1824 . The camming surfaces  1986 ,  1988  operate similarly to the wedge shape camming surface  1980  and corresponding camming surface  1982 , except that instead of biasing the cam shaft  1816  axially, they bias the cam shaft  1816  generally vertically. As the cam shaft  1816  is rotated from its starting position to the fully deployed position (at 180 degrees from its undeployed starting position), the flat camming surface  1986  of the cam shaft  1816  engages the corresponding camming surface  1988  of the retainer member  1824 . This pushes the cam shaft  1816  generally upward away from the retainer members  1824 , which biases the cam shaft  1816  against the upwardly extending arm  1826  of the retaining members  1824 , providing tactile feedback to the surgeon in the form of increased resistance to the rotation of the cam shaft  1816  until the shaft is almost turned a full 180 degrees. The resistance dissipates quickly as the camming surfaces begin to disengage each other. In fact, the deformation of the retaining members  1824  may help to propel the cam shaft into a fully deployed position. This propulsion and dissipation of resistance constitutes additional tactile feedback which varies during the deployment of the securing mechanism and informs the surgeon that the cam members  1846  are fully deployed. Once the cam shaft  1816  is turned a full 180 degrees, the flat camming surface  1986  snaps into a recess  1990  formed in the adjacent retainer member  1824 , due to the generally vertical biasing force exerted by the flexed retainer members  1824 . The recess  1990  and cam shaft camming surface  1986  are formed such that the camming surface  1986  becomes trapped in the recess  1990  and prevents derotation of the cam shaft  1816 .  
         [0214]     More specifically, the cam projection  1987  has a straight, trailing edge surface  1989  that is turned toward the straight edge surface  1991  of recess  1990 . Once the trailing edge surface  1989  clears the recess surface  1991 , the cam surface  1986  will have traveled past the corresponding camming surface  1988  so that the cam surfaces  1986  and  1988  are disengaged from one another. This removes the vertical biasing force that their camming engagement generates, so that the cam projection  1987  travels or snaps axially down into the recess  1990 . In this orientation, the straight edge surfaces  1989 ,  1991  are in confronting relation to each other so that the cam projection  1987  can not be moved back out of the recess  1990 .  
         [0215]     In another form shown in  FIGS. 100 and 101 , the cam shaft  1816  has a dual chamfered camming surface  1992  for providing tactile feedback to the surgeon and preventing derotation of the cam shaft  1816 . In this embodiment, a chamfered surface  1994  for providing resistive feedback during deployment of the cam lobes  1846  is provided on one side of the camming surface  1992 , which is engaged when the cam shaft  1816  is rotated in a clockwise direction. Another chamfered surface  1996  is provided on the other side of the camming surface  1992  for providing resistive feedback during retraction of the cam lobes  1846 , which is engaged when the cam shaft  1816  is rotated in a counterclockwise direction. Like the embodiments described directly above, the camming surface  1992  engages a corresponding generally concave camming surface  1998  formed in the adjacent retainer member  1824 . The corresponding camming surface  1998  is formed such that the chamfered camming surface  1992  adjacent the drive head engages the corresponding camming surface  1998  causing the cam shaft  1816  to bias against the retainer members  1824  and provide tactile or resistive feedback as described above. Unlike the embodiments above, the cam  1816  may be manually retracted by turning the cam shaft  1816  back 180 degrees in the counterclockwise direction. This is desirable if the surgeon wishes to adjust the implant  1752  or prepare the implantation site further. Over-rotation and rotation in the wrong direction is prevented by leaving a raised surface  2000  on the opposite side of the corresponding camming surface  1998  such that it is virtually impossible to turn the cam shaft  1816  in the wrong direction due to interference between the camming surface  1992  on the cam  1816  and the raised surface  2000 .  
         [0216]     The cam shafts  1816 , cam members, lobes, or fins  1846  may take on different geometries and orientations to improve performance of the securing mechanism. For example, the camming fins may include serrations  2002 , as shown in  FIG. 102 , divots, or recesses  2002  to promote boney ingrowth. The serrations  2002  may also help to cut the bone when the cam  1816  is rotated. In addition, the camming fins  1846  may be cupped or slanted, as shown in  FIG. 103 , to further promote anchoring of the implant  1752  to the vertebrae  1332 ,  1334 . In a preferred embodiment, the camming fins  1846  are cupped about 8 degrees. Further, as shown in  FIGS. 104 and 105 , the camming fins  1846  may have an outside contour, such that shape or size of the cam fins  1846  varies from one end of the cam shaft  1816  to the other. The contour may match the profile of the endplates to take advantage of the softer bone in the center of the vertebrae  1332 ,  1334  as opposed to the harder-denser bone at the periphery of the vertebrae  1332 ,  1334 . Further, the cam shafts  1816  may have any number of cam members  1846 . In a preferred embodiment, each cam shaft  1816  may have between three and five cam members  1846 . Larger implants may have five members  1846  per cam shaft  1816 , while smaller implants may have only three. The cam shafts  1816  are preferably made from titanium or stainless steel, and may be coated with a bone-growth promoting substance, such as hydroxyapatite, tricalcium phosphates, or calcium phosphates.  
         [0217]     Cam members  1846  that cut or imbed themselves into the bone provide advantages over other securing mechanisms. For instance, securing mechanisms that use static projections such as spikes and keels may rely on the subsidence of the bone around the securing mechanism to secure the implant. Static securing mechanisms are less desirable because they may not properly secure the implant to the bone until the bone begins to subside around the securing mechanism. Thus, the implant may tend to migrate prior to bone subsidence. However, dynamic securing mechanisms like cam members  1846  with cutting surfaces  1848  actively cut into or imbed themselves into the bone, instead of relying on the subsidence of the bone. In this manner, dynamic securing mechanisms create a much more reliable and stable connection between the implant  1752  and the vertebra  1332 ,  1334 . These benefits translate into a more robust and reliable implant  1752 , which means quicker recovery times and increased mobility for the patient.  
         [0218]     In another form, the cam shafts  1816  on the upper disc implant member  1818  may be disposed at converging or diverging angles, such as shown in  FIG. 106 . This orientation prevents migration of the implant  1752  not only in an anterior/posterior direction, but also substantially in the lateral direction as well. Naturally, the lower disc implant member  1822  may employ such a configuration.  
         [0219]     It should be noted that the cam shafts  1816  provide certain advantages over other securing mechanisms, such as screws. For instance, screws do not provide a significant level of tactile feedback. It is very difficult for a surgeon to determine how far a screw has been turned, and therefore he may over- or under-rotate the screw, increasing the risk of implant migration and failure. In addition, metal screws may damage the implant if over-tightened. If the implant is made of a relatively soft material, such as PEEK, the metal screws will easily strip and damage the implant if over-tightened. Moreover, a surgeon is more likely to over-tighten a screw housed within a polymer because the screw is so much harder than the polymer that he will not be able to feel when the screw has been over-tightened. To alleviate this problem, the implant  1752  may be fabricated with a metal portion for housing the screw combined with a polymer, but this greatly increases the difficulty in manufacturing the implant  1752 , as well as its cost, and is therefore less desirable. In addition, over-rotation of a screw may advance the screw beyond its intended range of motion, and may cause it to protrude from the implant and cause damage to vital areas in and around the spine. Because the cams do not advance or retreat as they are rotated, there is no danger that the cams  1846  will be accidentally projected into other vital areas.  
         [0220]     The disc implant  1752  according to the present embodiment has docking features for attaching with the implant insertion tool  2008 , as shown in  FIGS. 101, 107 , and  108 . The lower disc implant member  1822  has a shelf-like platform  2006  along its rear face on either side of the cam shaft  1816  for providing a contact surface for the implant insertion tool  2008 . Similarly, the upper disc implant member  1818  has a shelf  2010  on its anterior face between the two upper cam shafts  1816  for providing a contact surface for the insertion tool  2008 . The internal facing surfaces  1620  of both disc members  1818 ,  1822  each have a pair of generally rectangular recesses  2012  disposed therein to accept the gripping members  2014  of the insertion tool  2008 . These docking features are advantageous because the insertion tool  2008  manipulates the implant  1752  substantially within the overall footprint of the implant  1752 . This prevents trauma to the surrounding tissue and bone during insertion of the implant  1752  and removal of the inserter  2008  after the implant  1752  is inserted.  
         [0221]     An insertion tool  2008  according to the present invention is shown in  FIGS. 108-113B . The insertion tool  2008  is generally comprised of a handle portion  2016 , an actuator, and a gripping mechanism  2020 . Specifically, the handle portion  2016  is attached to a handle shaft  2022 . The handle shaft  2022  has an annular bore  2024  therethrough for slidingly housing the push rod  2026 . An actuator in the form of a cam lever  2018  with opposed camming surfaces is attached to the handle shaft  2022  and push rod  2026  with a pin connection  2030  extending between the camming surfaces  2028  and through opposed openings  2032  in the handle shaft  2022  and a bore  2034  in the push rod  2026 . The handle shaft  2022  is attached at its forward end to upper and lower housing members  2036 ,  2038  which house the gripping mechanism  2020 . A rear spring  2040  surrounds push rod  2026  and is biased between a collar  2042  on the handle shaft  2022  and the prong holder  2044 . The prong holder  2044  is a rectangular shaped block with four L-shaped recesses  2046  (see  FIG. 110 ), two on the upper face and two on the lower face for capturing the L-shaped anchoring ends  2048  of four prongs  2050 ,  2052 . The prong holder  2044  has a cylindrical bore  2054  extending between the front and rear face for allowing the push rod  2026  to pass therethrough. The end of the push rod  2026  extends through a forward spring  2056 , which is captured between the prong holder  2044  and a compression block  2058 , which is attached to the end of the push rod  2026 . The compression block  2058  is a rectangular block having an aperture in the rear face for attaching to the push rod  2026 . In addition, the block  2058  has a pair of vertically aligned bores  2060  extending laterally through the side walls of the block  2058  for holding two pins  2062  operable to actuate the prongs  2050 ,  2052  into a disengaged position by temporarily deforming the prongs  2050 ,  2052  between the two pins.  
         [0222]     The gripping mechanism  2020  includes two upper and two lower flexible prongs  2050 ,  2052  which operate in tandem with upper and lower tabs  2064 ,  2066  for gripping and holding the disc implant  1752  (shown in  FIG. 111A -B). The prongs  2050 ,  2052  are made with a thin rectangular stainless steel shafts having a series of bends  2068 ,  2072 . The upper prongs  2050  generally extend along the longitudinal axis of the insertion tool  2008  and have a series of two upward sloping bends  2068  so that the implant gripping end  2070  of the prong  2050  is vertically higher than the anchor end disposed in the prong holder  2044 . The lower prongs  2052  are shaped in a similar manner, except that they have a series of two downward sloping bends  2072  so that the implant gripping end  2070  of the prong  2052  is vertically lower than the anchor end  2048  disposed in the prong holder  2044 . The upper and lower prongs  2050 ,  2052  are paired adjacent each other and opposite the other pair along the outer lateral edges of the housing, such that the shaft  2026  and compression block  2058  may translate between the sets of prongs  2050 ,  2052 . The upper and lower housing members  2036 ,  2038  have guide surfaces  2074  formed in the internal surfaces for guiding and securing the prongs  2050 ,  2052  to prevent them from becoming misaligned. The gripping ends  2070  of the prongs  2050 ,  2052  have an L-shape for being inserted into the recesses  2012  of the disc implant  1752 .  
         [0223]     In operation, the implant inserter tool prongs  2050 ,  2052  are movable in vertical and longitudinal directions to engage and disengage the disc implant  1752 . In the initial disengaged position shown in  FIG. 112A -B, the lever  2018  is in a released position. The compression block  2058  is pushed forward by the push rod  2026 . The two opposed pins  2062  extending through the compression block  2058  are pushed over the sloping bends  2068 ,  2072  in the prongs  2050 ,  2052 , which locally deform the prongs  2050 ,  2052  and forces the gripping ends  2070  of the prongs  2050 ,  2052  together, effectively lowering the gripping ends  2070  of the upper prongs  2050  and raising the gripping ends  2070  of the lower prongs  2052 . In this manner, the forward portion of the inserter tool  2008  may be inserted between the upper and lower disc implant members  1818 ,  1822 . To engage the implant  1752 , the lever  2018  is pressed forwards, as shown in FIGS.  113 A-B. This causes the push rod  2026  to pull the compression block  2058  rearwards. The opposed pins  2062  are thereby removed from the sloped portions  2068 ,  2072  of the prongs  2050 ,  2052 , which allows the prongs  2050 ,  2052  to return to their original unflexed shape. In this manner, the gripping ends  2070  will spread vertically apart and engage the gripping recesses  2012  of the disc implant  1752 . To provide a counteracting moment against the force imparted by the prongs  2050 ,  2052  on the implant  1752 , tabs  2064 ,  2066  disposed on the forward ends of the housing members  2036 ,  2038  engage the implant  1752  on the shelves  2006 ,  2010  disposed on the rear portions of the disc members  1818 ,  1822 , as shown in  FIG. 111 . In addition, as the lever  2018  is pushed forward, the compression block  2058  biases against the forward spring  2056 , causing the prong holder  2044  to be biased rearwards against the rearward spring  2040 . This causes the prong holder  2044  and the prongs  2050 ,  2052  to translate rearwards to pull the implant  1752  tight against the forward face of the housing members  2036 ,  2038 . The limited range of motion of the lever  2018  prevents damage to the implant  1752  that may be caused by over-tightening the gripping mechanism  2020 .  
         [0224]     Once the implant  1752  is secured to the inserter  2008 , the disc implant  1752  is then inserted into the intervertebral space  1330 . The position of the implant  1752  may be determined using fluoroscopy to view the orientation of the implant  1752 . Tantalum markers disposed in the frontal face of both the upper and lower disc members  1818 ,  1822  allow the surgeon to identify the position of the insertion end of the implant  1752 . In addition, the cam shafts  1816 , which are also radiopaque when made out of titanium or stainless steel, may be used to determine the orientation of the implant  1752 . After the surgeon has placed the implant  1752  in the desired position, he releases the implant  1752  by lifting the lever  2018 . The prongs  2050 ,  2052  are pushed forward and retracted vertically inwards, which releases the implant  1752 . The surgeon then secures the implant  1752  in place by actuating the securing mechanism. Specifically, the surgeon turns each of the cams  1816  180 degrees using a driver, thereby deploying the cam members  1846  into the bone of the upper and lower vertebrae  1332 ,  1334 . The surgeon can feel the resistance provided by the interaction between the camming surfaces of the cam shafts  1816  and the retainer member  1824  while deploying the cam members  1846 . In this manner, he can determine when the cam members  1846  have been fully deployed. In addition, the camming surfaces of the cam shafts  1816  and the retainer members  1824  will prevent the cams  1816  from derotating and allowing the implant  1752  to migrate.  
         [0225]     In other forms of the invention, the implant  1752  may comprise a pharmacological agent used for treating various spinal conditions, including degenerative disc disease, spinal arthritis, spinal infection, spinal tumor and osteoporosis. Such agents include antibiotics, analgesics, anti-inflammatory drugs, including steroids, and combinations thereof. Other such agents are well known to the skilled artisan. These agents are also used in therapeutically effective amounts. Such amounts may be determined by the skilled artisan depending on the specific case.  
         [0226]     The pharmacological agents, if any, are preferably dispersed within the implant  1752  for in vivo release. The pharmacological agents may be dispersed in the spacer by adding the agents to the implant  1752  when it is formed, by soaking a formed implant  1752  in an appropriate solution containing the agent, or by other appropriate methods known to the skilled artisan. In other forms of the invention, the pharmacological agents may be chemically or otherwise associated with the implant  1752 . For example, the agents may be chemically attached to the outer surface of the implant  1752 .  
         [0227]     Although the securing mechanisms and insertion tools have been described with reference to a disc replacement implant, the securing mechanisms and tools may be easily adapted for use with other artificial implants, such as fusion promoting implants, including vertebral body replacements, spinal cages, and the like. In addition, the invention described herein may also be applied to other motion preserving implants, such as those with articulating surfaces, including nucleus replacement implants. Moreover, the securing mechanisms, insertion tools, and methods described herein may be implemented in other weight-bearing joint implants, such as ankle, knee, or hip joint implants.  
         [0228]     While the invention has been described with respect to specific examples including presently preferred modes of carrying out the invention, those skilled in the art will appreciate that there are numerous variations and permutations of the above described systems and techniques that fall within the spirit and scope of the invention as set forth in the claims.