Abstract:
An assembly for preparing an intervertebral disc space between a first vertebra and a second vertebra to receive a prosthesis comprises a distractor having a first distraction arm and a second distraction arm. The assembly further includes a first anchoring device attached to both the first distraction arm and the first vertebra and a second anchoring device attached to both the second distraction arm and the second vertebra. In this assembly, the first anchoring device moves independently of the second anchoring device.

Description:
BACKGROUND  
       [0001]     Recently, technical advances in the design of joint reconstructive devices has revolutionized the treatment of degenerative joint disease, moving the standard of care from arthrodesis to arthroplasty. Reconstruction of a damaged joint with a functional joint prosthesis to provide motion and to reduce deterioration of the adjacent bone and adjacent joints is a desirable treatment option for many patients. For the surgeon performing the joint reconstruction, specialized instrumentation and surgical methods may be useful to facilitate precise placement of the prosthesis.  
       SUMMARY  
       [0002]     In one embodiment, an assembly for preparing an intervertebral disc space between a first vertebra and a second vertebra to receive a prosthesis comprises a distractor having a first distraction arm and a second distraction arm. The assembly further includes a first anchoring device attached to both the first distraction arm and the first vertebra and a second anchoring device attached to both the second distraction arm and the second vertebra. In this assembly, the first anchoring device moves independently of the second anchoring device.  
         [0003]     In another embodiment, a method of preparing an intervertebral disc space, between first and second vertebral bodies of a vertebral column, to receive an intervertebral prosthesis comprises fixedly attaching first and second anchoring devices to the first and second vertebral bodies, respectively. The method further comprises attaching a distraction assembly to the first and second anchoring devices, wherein a first arm of the distraction assembly is attached to the first anchoring device and a second arm of the distraction assembly is attached to the second anchoring device. The method also comprises moving the first and second arms of the distraction assembly, in parallel, relative to one another. The method further comprises independently moving the first and second anchoring devices relative to the first and second arms, respectively. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]      FIG. 1  is a sagittal view of a vertebral column having a damaged disc.  
         [0005]      FIG. 2  is a flowchart describing a surgical technique.  
         [0006]      FIG. 3  is an isometric view of an alignment guide according to an embodiment of the current disclosure.  
         [0007]      FIG. 4  is an isometric view of a distractor assembly according to a one embodiment of the current disclosure.  
         [0008]      FIG. 5  is an anchoring device according to an embodiment of the current disclosure.  
         [0009]      FIG. 6  is an anchoring device according to still another embodiment of the current disclosure.  
         [0010]      FIG. 7  is the distractor assembly of  FIG. 4  configured with the anchoring devices of FIGS.  5  an  6 .  
         [0011]      FIG. 8  is the distractor assembly of  FIG. 4  configured with the anchoring devices of FIGS.  5  an  6 .  
         [0012]      FIG. 9  is the distractor assembly of  FIG. 4  configured with the anchoring devices of FIGS.  5  an  6 .  
         [0013]      FIG. 10  is the distractor assembly of  FIG. 4  configured with the anchoring devices of  FIGS. 5 and 6  and the alignment guide of  FIG. 3 .  
         [0014]      FIG. 11  is a front view of a measurement instrument according to one embodiment of the current disclosure.  
         [0015]      FIG. 12  is an environmental view of the distractor assembly of  FIG. 7  and the measurement instrument of  FIG. 11 .  
         [0016]      FIG. 13  is an exploded view of a cutting assembly according to one embodiment of the current disclosure.  
         [0017]      FIG. 14  is an environmental view of the cutting assembly of  FIG. 13  in operation.  
         [0018]      FIG. 15  is an isometric view of a distractor assembly according to a second embodiment of the current disclosure.  
         [0019]      FIG. 16  is an anchoring device according to still another embodiment of the current disclosure.  
         [0020]      FIG. 17  is an environmental view of the distractor assembly of  FIG. 15  coupled with the anchoring device of  FIG. 16 .  
         [0021]      FIG. 18  is an isometric view of a distractor assembly according to still another embodiment of the current disclosure coupled to an anchoring device according to still another embodiment of the current disclosure.  
         [0022]      FIG. 19  is an isometric view of a pair of anchoring devices according to still another embodiment of the current disclosure.  
     
    
     DETAILED DESCRIPTION  
       [0023]     The present disclosure relates generally to the field of orthopedic surgery, and more particularly to instrumentation and methods for vertebral reconstruction using an intervertebral prosthesis. For the purposes of promoting an understanding of the principles of the invention, reference will now be made to embodiments or examples illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alteration and further modifications in the described embodiments, and any further applications of the principles of the invention as described herein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0024]     Referring first to  FIG. 1 , the numeral  10  refers to a human anatomy having a joint location which in this example includes an injured, diseased, or otherwise damaged intervertebral disc  12  extending between vertebrae  14 ,  16 . The damaged disc may be replaced by an intervertebral disc prosthesis  18  which may be a variety of devices including the prostheses which have been described in U.S. Pat. Nos. 5,674,296; 5,865,846; 6,156,067; 6,001,130 and in U.S. Patent Application Nos. 2002/0035400; 2002/0128715; and 2003/0135277 which are incorporated by reference herein.  
         [0025]     A surgical technique for repairing the damaged joint may be represented, in one embodiment, by the flowchart  20  depicted in  FIG. 2 . Referring first to step  22 , all or a portion of the damaged disc  12  may be excised. This procedure may be performed using an anterior, anterolateral, lateral, or other approach known to one skilled in the art, however, the following embodiments will be directed toward a generally anterior approach. Generally, the tissue removal procedure  22  may include positioning and stabilizing the patient. Fluoroscopic or other imaging methods may be used to assist with vertebral alignment and surgical guidance. Imaging techniques may also be used to determine the proper sizing of the intervertebral prosthesis  18 . In one embodiment, a sizing template may be used to pre-operatively determine the correct prosthesis size. The tissue surrounding the disc space may be retracted to access and verify the target disc space. The area of the target disc may be prepared by removing excess bone, including osteophytes which may have developed, and other tissues which may include portions of the annulus and all or portions of the nucleus pulpous. The tissue removal procedure  22 , which may include a discectomy procedure, may alternatively or additionally be performed after alignment and/or measurement procedures have been taken.  
         [0026]     Proceeding to step  23  of  FIG. 2 , various alignment procedures may be conducted to align the intervertebral space in preparation for the disc prosthesis  18 . The transverse center of the disc space may be determined and marked. Referring now to  FIG. 3 , an alignment guide  30 , comprising an intervertebral portion  32 , may be selected. The intervertebral portion  32  may be selected to permit insertion between the adjacent vertebrae  14 ,  16  with minimal distraction. The alignment guide may further comprise positioning guides  34 ,  36 . In one embodiment, as illustrated in  FIG. 3 , the positioning guides  34 ,  36  may have differing lengths to facilitate easy coupling to subsequent instrumentation.  
         [0027]     Referring now to  FIG. 4 , the alignment step  23  ( FIG. 2 ) continues with the introduction of a distractor assembly  40 . The distractor assembly  40  may include a cross bar member  42  having a securing mechanism  44 . A pair of distracting arms  46  may be attached to the cross bar member  42 . A variety of securing mechanisms  44  may be used to maintain a selected distance between the distracting arms  46  including a ratchet system, clamps, threaded connectors, pins, gripping hardware, or other fasteners may be selected as the means to maintain a selected distance between the distracting arms  46 . At least one of the distracting arms  46  may be movably connected to cross bar member  42  with the securing mechanism  44 . Each of the distracting arms  46  may include attachment mechanisms  48 . In the embodiment of  FIG. 4 , the attachment mechanisms  48  includes pins  50  and hollow recesses  52 . In some embodiments, as shown, the one or more of the walls of the hollow recesses  52  may have elongated openings  53 . The attachment mechanisms  48  may be used to locate, hold, and/or guide anchoring devices as will be described below. The attachment mechanisms  48  may include stops or other features useful for position verification or instrument support.  
         [0028]     Referring now to  FIG. 5 , an anchoring device  60  may include a connecting portion  62 , a pivot mechanism  64 , a vertebral body attachment portion  66 , a restraint pin  67 , a seat  68 , and constraint members  70 . The anchoring device  60  may attach to one of the distracting arms  46  by engaging the pin  50  with the pivot mechanism  64  and by inserting the connecting portion  62  into one of the hollow recesses  52 .  
         [0029]     Referring now to  FIG. 6 , an anchoring device  80 , which may complementary to the anchoring device  60  may include a connecting portion  82 , a pivot mechanism  84 , a vertebral body attachment portion  86 , a restrait pin  87 , a seat  88 , and constraint members  90 . The anchoring device  80  may attach to one of the distracting arms  46  by engaging the pin  50  with the pivot mechanism  84  and by inserting the connecting portion  82  into one of the hollow recesses  52 . In some embodiments, the anchoring devices may be identical rather than complementary.  
         [0030]     Referring now to  FIG. 7 , the rotation restraint pin  67  of anchoring device  60  is more clearly illustrated. In this embodiment the restraint pins  67 ,  87  may be retractable, but in other embodiments, the restraint pins may be fixed.  
         [0031]     Referring now to  FIGS. 8, 9   a , and  9   b , in this embodiment, the pivot mechanisms  64 ,  84  are “C”-shaped which may permit independent displacement of the anchoring devices  60 ,  80  relative to one another along an axis  90  aligned with the axis of the hollow recess  52 . When using an anterior surgical technique, the axis  90  may be an anterior-posterior axis. Referring to  FIG. 9   b , the “C”-shape of the pivot mechanisms  64 ,  84  may also permit the anchoring devices  60 ,  80  to independently pivot or rotate in a sagittal plane about the pins  50 . In this embodiment, the connecting portions  62 ,  82  may be pulled from the hollow recesses  52 . As the anchoring devices  60 ,  80  pivot independently of each other, the connecting portions  62 ,  82  may be permitted to pivot in and out of the elongated openings  53  of the distracting arms  46 .  
         [0032]     Referring now to  FIG. 10 , the alignment guide  30  may be coupled to the anchoring devices  60 ,  80 . Specifically, in the illustrated embodiment, one set of positioning guides, for example guides  34 , may mate with the constraint portions  90 . Then, the second set of positioning guides  36  may mate with the constraint portions  70 . The differing lengths of the positioning guides  34 ,  36  may allow the surgeon to more easily align the positioning guides with the constraint portions. The constraint portions  70 ,  90  may prevent movement of the alignment guide  30  relative to the anchoring devices  60 ,  80 , respectively.  
         [0033]     With the alignment guide  30  coupled to the anchoring devices  60 ,  80 , the intervertebral portion  32  may be inserted between the vertebral endplates of vertebral bodies  14 ,  16 . Alternatively, the insertion of intervertebral portion  32  between the vertebral endplates may take place before or as the alignment guide  30  is coupled to the anchoring devices  60 ,  80 . The anchoring devices  60 ,  80  may be positioned equidistant from the mid-line center of the intervertebral disc space. Mid-line alignment of the alignment guide  30  may be confirmed, and the sagittal placement of the alignment guide  30  may be assessed with flouroscopic or other imaging techniques. After alignment has been assessed, the alignment guide  30  may be locked in place to either or both of the distractor assembly  40  and the anchoring devices  60 ,  80 . During these alignment procedures, the alignment guide  30  may be generally parallel to the plane of the intervertebral disc space. Additional flouroscopic or other images may be taken throughout the alignment step  23  to verify alignment of the instruments and/or the vertebral bodies.  
         [0034]     With the alignment verified, a hole may be drilled into the caudal vertebral body  16  through the vertebral body attachment portion  66  of the anchoring device  60 . An anchoring fixture  92 , such as a bone screw, may be inserted through the vertebral body attachment portion  66  and into the vertebral body  16  thus firmly locking the seat  68  to the vertebral body  16 . As the anchoring fixture  92  descends through the vertebral body attachment portion  66 , the anchoring fixture  92  may push on the retractable restraint pin  67 , embedding the pin  67  in the vertebral body  16  to prevent rotation of the anchoring device  60  and the subsequent loosening of the anchoring fixture  60  from the vertebral body  16 .  
         [0035]     The seats  68 ,  88  of the anchoring devices  60 ,  80 , respectively, may be adjustable and thus may be raised, lowered, and/or tilted. With the seat  68  locked to the vertebral body  16 , the seat  88  of the cephalad anchoring device  80  may be adjusted to contact the vertebral body  14 , maintaining the alignment guide  30  aligned in a generally anterior-posterior direction. The seat  88  may be adjusted to level the anchoring devices  60 ,  80 , using for example a bubble level (not shown). With the seat  88  in postion, a second hole may be drilled into the cephalad vertebral body  14  through the vertebral body attachment portion  86  of the anchoring device  80 . Another anchoring fixture  94 , such as a bone screw, may be inserted through the vertebral body attachment portion  86  and into the vertebral body  14  thus firmly locking the seat  88  to the vertebral body  14 . As the anchoring fixture  94  descends through the vertebral body attachment portion  86 , the anchoring fixture  94  may push on the retractable restraint pin  87 , embedding the pin  87  in the vertebral body  14  to prevent rotation of the anchoring device  80  the subsequent loosening of the anchoring fixture  80  from the vertebral body  14 . It is understood that in an alternative embodiment, the cephalad anchoring fixture  94  may be placed before the caudal anchoring fixture  92 . With the anchoring fixtures  92 ,  94  in place, the alignment guide  30  may be removed.  
         [0036]     Referring again to the surgical technique  20  of  FIG. 2 , at step  24 , distraction may be performed using the distractor assembly  40  (of  FIG. 4 ). With the distractor arms  52 , attached to the vertebral bodies  14 ,  16  by the anchoring devices  80 ,  60  respectively, the arms  52  may be moved apart placing the vertebral bodies  14 ,  16  in tension and providing access to the intervertebral space to allow further discectomy and/or decompression procedures as needed. During the distraction, the distractor arms  52  may remain relatively parallel. The securing mechanism  44  may be applied to maintain the vertebral bodies  14 ,  16  in the desired distracted position.  
         [0037]     As the distraction is performed, the connecting portions  62 ,  82  may remain inside the hollow recesses  52  thereby causing the adjacent endplates of vertebral bodies  14 ,  16  to remain relatively parallel. Alternatively, during distraction the connecting portions  62 ,  82  may be pulled from the hollow recesses  52 , and the anchoring devices  60 ,  80  may pivot about pins  50  (as described above) allowing independent movement of the vertebral bodies  14 ,  16 . In some embodiments, the rotation of the vertebral bodies  14 ,  16  may be constrained to a transversely centered sagittal plane. In other embodiments, the vertebral bodies  14 ,  16  may rotate in parallel sagittal planes. The independent movement may permit independent preparation of the endplates of vertebral bodies  14 ,  16  as will be described in detail below. Examples of alternative embodiments which permit full or partial independent movement will also be described below.  
         [0038]     With the vertebral bodies  14 ,  16  distracted and the anchoring devices  60 ,  80  attached to the vertebral bodies  14 ,  16 , the surgical technique  20  may then proceed to step  25 . At step  25 , measurements, such as a depth measurement, may be performed at the disc site to determine the proper sizing of instrumentation and devices to be used throughout the remainder of the surgical technique  20 .  
         [0039]     Referring now to  FIGS. 11 and 12 , the measurement step  25  ( FIG. 2 ) may involve the use of a variety of instrumentation including, for example, a measurement instrument  100  which may assist in the selection of appropriately sized tools to perform subsequent operations such as endplate preparation. In this embodiment, the measurement instrument  100 , which includes a shaft  102  extending between an indicator portion  106  and a probe portion  108 , may movably or fixedly fasten to one of the anchoring devices  60 ,  80 . The probe portion  108  may travel through the intervertebral disc space to provide a depth measurement. In this embodiment, the indicator portion  106  may indicate the distance from a point, such as an anterior edge  110  of the intervertebral disc space to the posterior margin  102  of the disc space. The indicator portion  106  may magnify the distance traveled by the probe portion  108  providing a measurement which can be used to determine the proper sizing of subsequently used instruments.  
         [0040]     Referring again to  FIG. 2 , the surgical technique  20  proceeds to step  26  for further preparation of the vertebral endplate surfaces. Referring now to  FIG. 13   a - 13   b , to prepare the endplate surfaces to provide a secure seat for the intervertebral prosthesis  18 , a cutting instrument may be provided. In the embodiment of  FIG. 13   a , the cutting instrument  120  may comprise several component parts including an exterior shaft portion  122 , an internal shaft portion  124 , a cutting head  126 , and a cutting device  128 . The internal shaft portion  124  may extend through the exterior shaft portion  122  to engage the cutting head  126 . The cutting device  128  may be attached to the cutting head  126 . The cutting device  128  may have an abrasive surface  130  which can include blades, teeth, a roughened coating or any other surface capable of cutting, abrading, or milling the vertebral endplates. The cutting instrument  120  may include a variety of other components (not shown) such as rivets, bearings, gears, and springs which may be used to assemble the components  122 - 128  to each other and provide movement to the cutting device  128 .  
         [0041]     The components  122 - 128  of the cutting instrument  100  may be constructed to simplify cleaning, promote sterility, enhance reliability, and shorten assembly and surgical time. In one embodiment, the cutting head  1206  may be a single piece of molded polymer. In the embodiment of  FIG. 13   a , the use of bearings and other components capable of corrosion or susceptible to wearing out easily may be reduced or eliminated. The cutting head  126  may be disposable which can simplify the cleaning of the cutting instrument  120  and may promote sterility in the surgical field. The internal shaft portion  122 , which may include an integrated pinion gear, may be disposable to minimize wear on other sensitive components such as gear trains, increasing the reliability of the instrument  120 . The use of a pinion shaft as the internal shaft portion  122  may also eliminate bearings and other drive train components which improves the reliability and simplifies cleaning of the cutting instrument  120 . The cutting device  128  may be a one-piece metal injection molded cutter having the cutting surface  130  formed on one side and gear teeth  132  integrated into the opposite side to minimize the profile. This integrated embodiment of the cutting device  128  may also promote reliability and sterility.  
         [0042]     Referring now to  FIG. 14 , based upon the measurements taken in step  25  and the size and profile of the prosthesis  18  to be implanted, the cutting device  128  may be selected. The cutting instrument  120  may be assembled, as described above, using the selected cutting device  128 . With the anchoring devices  60 ,  80  attached to the distracting arms  46 , the cutting instrument  120  may be mounted to one of the anchoring devices  60 ,  80  such that the cutting device  128  is positioned adjacent to one the vertebral endplates  14 ,  16 . The proper positioning of the cutting device  128  may be established with known offsets and may be verified with fluoroscopic or other imaging techniques. In operation, a power source (not shown) may be provided to the cutting instrument  120  to drive the internal shaft portion  124 . The internal shaft portion may directly or indirectly drive the cutting head  126  thereby actuating the cutting device  128 . The actuated cutting device  128  causes the cutting surface  130  to shape the selected vertebral endplate. The cutting device  128  or cutting surface  130  may be shaped such that the profile that it creates in the vertebral endplate matches the profile of the selected intervertebral prosthesis  18  to create a secure seat for the prosthesis. After the first endplate is prepared, the cutting instrument  120  may be mounted to the other of the anchoring devices  60 ,  80  with the cutting device  128  positioned adjacent to the other of the vertebral endplates  14 ,  16 . The cutting instrument  130  may again be powered, this time to shape the second endplate. In this embodiment, as described above, the anchoring devices  60 ,  80  may remain fixedly aligned to the vertebral bodies and rotatably connected to distracting arms  46 . As such, the vertebral bodies  14 ,  16  may be permitted to rotate independently of each other and therefore, the endplate preparation procedure  26  permits each of the vertebral bodies to be shaped independently.  
         [0043]     The cutting instrument described above for  FIG. 13   a  is merely one embodiment which may be used with the distractor assembly  40  and the anchoring devices  60 ,  80 . In alternative embodiments, the cutting device  128  maybe include a burr or other cutting surfaces known in the art. The cutting instrument may also include a telescoping shaft to permit lengthening of the cutting instrument. In some embodiments such as  FIG. 13   b , the cutting instrument  134  may be comprised largely of reusable components capable of being sterilized, such as by an autoclave. In this embodiment, a cutting head  136  may have a higher profile to accommodate a press-fit gear and other gear train components.  
         [0044]     Referring again to  FIG. 2 , after the vertebral endplates are prepared, the cutting instrument  120  or  134  may be removed from the anchoring device  60  or  80  in preparation for implanting the intervertebral prosthesis  18  at step  27 . With the cutting instrumentation removed, the intervertebral prosthesis  18  may be inserted into the prepared space using any of a variety of insertion methods. In some embodiments, the anchoring devices  60 ,  80  may be used to guide prosthesis insertion instrumentation. After the prosthesis  18  is implanted, the tension on the distractor assembly  40  may be released. The anchoring fixtures  92 ,  94  may be removed form the vertebral bodies  16 ,  14  respectively, permitting the distractor assembly  40  to be removed. With all instrumentation removed from the disc site, the wound may be closed.  
         [0045]     Referring now to  FIG. 15 , in an alternative embodiment, a distractor assembly  140  may be used to distract vertebral bodies  14 ,  16 . The distractor assembly  140  may include a cross bar member  142  having a securing mechanism  144 . A pair of distracting arms  146  may be attached to the cross bar member  142 . A variety of securing mechanisms  144  may be used to maintain a selected distance between the distracting arms  146  including a ratchet system, clamps, threaded connectors, pins, gripping hardware, or other fasteners may be selected as the means to maintain a selected distance between the distracting arms  146 . At least one of the distracting arms  146  may be movably connected to cross bar member  142  with the securing mechanism  144 . Each of the distracting arms  146  may include attachment mechanisms  148 . In the embodiment of  FIG. 15 , the attachment mechanisms  148  include hollow cavities  152 . In some embodiments, as shown, the distracting arms  146  may have relatively flat end portions  153 , but in alternative embodiments, the end portions may be angled or curved. The attachment mechanisms  148  may be used to locate, hold, and/or guide anchoring devices as will be described below. The attachment guides  148  may include stops or other features useful for position verification or instrument support.  
         [0046]     Referring now to  FIG. 16-17 , an anchoring device  160  may include a connecting portion  162 , a vertebral body attachment portion  166 , a seat  168 , and constraint portions  170 . The anchoring device  160  may attach to one of the distracting arms  46  by inserting the connecting portion  162  into one of the hollow cavities  152 . An opposing anchoring device  180  having the same or similar features anchoring device  160  including an attachment portion  186  may be attached to the other of the distracting arms  146 .  
         [0047]     The anchoring devices  160 ,  180  may be of a configuration which attaches to the vertebral bodies  14 ,  16  and permits independent movement of the vertebral bodies  14 ,  16  in the sagittal plane while maintaining alignment of the vertebral bodies  14 ,  16  in the transverse and coronal planes. The independent movement may permit independent preparation of the endplates of vertebral bodies  14 ,  16  as will be described in detail below. Examples of alternative embodiments which permit full or partial independent movement will also be described below.  
         [0048]     With the anchoring devices  160 ,  180  connected to the distractor assembly  140  as described above, movement of the vertebral bodies  14 ,  16  in the sagittal plane may be permitted. As movement occurs, the anchoring devices  160 ,  180  may maintain a fixed alignment with the vertebral bodies  16 ,  14 . In this embodiment, movement of the attachment portions  166 , 186  within the hollow cavities  152  may permit independent displacement of the anchoring devices  60 ,  80  relative to one another along an axis  190  in the sagittal plane. When using an anterior surgical technique, the axis  190  may be an anterior-posterior axis. Using this alternative distractor assembly  140  and anchoring devices  160 ,  180 , the operations of alignment, distraction, measurement, endplate preparation, and implantation may proceed in a fashion similar to that described above in surgical technique  20 . In this embodiment, however, the vertebral bodies  14 ,  16  may be constrained from pivotal movement in the sagittal plane, resulting in a parallel distraction of the vertebral bodies.  
         [0049]     A variety of alternative anchoring devices with alternative means for attaching to a distractor assembly may be selected which permit at least some movement of the vertebral bodies  14 ,  16  in a single plane, such as a sagittal plane. In some embodiments, the connection between the distractor assembly and the anchoring devices may be selectably fixed, pivotable, or movable in a linear direction.  
         [0050]     Referring now to  FIG. 18 , in still another embodiment, a distractor assembly  200  and anchoring devices  210 ,  212  may be movably connected by a connector  214 . The connector  214  may permit rotational movement or linear movement in a single plane, such as a sagittal plane.  
         [0051]     Referring now to  FIG. 19 , in still another embodiment, a pair of anchoring devices  220 ,  222  may be connected to vertebral bodies  14 ,  16 , respectively. The anchoring devices  220 ,  222  may include vertebral body attachment apertures  224 ,  226  and may further include connection portions  228 ,  230 . The connection portions  228 ,  230  may be used for attaching and/or aligning instrumentation used for measuring, bone preparation, or prosthesis insertion. The anchoring devices  220 ,  222  may permit independent movement of the vertebral bodies  14 ,  16  during preparation of the intervertebral site.  
         [0052]     Although only a few exemplary embodiments of this invention have been described in detail above, those skilled in the art will readily appreciate that many modifications are possible in the exemplary embodiments without materially departing from the novel teachings and advantages of this invention. Accordingly, all such modifications are intended to be included within the scope of this invention as defined in the following claims. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents, but also equivalent structures.