Abstract:
A vertebral endplate preparation assembly is disclosed for preparing an endplate of a single vertebral body in a vertebral column to receive an implant. The assembly comprises a datum block for connecting to the single vertebral body, measuring instruments, and a cutting guide attached to the datum block. A cutting instrument is used for preparing the endplate, and an instrument coupling assembly is connected between the cutting instrument and the cutting guide.

Description:
BACKGROUND  
       [0001]     Recently, technical advances in the design of joint reconstructive devices have 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, a vertebral endplate preparation assembly is disclosed for preparing an endplate of a single vertebral body in a vertebral column to receive an implant. The assembly comprises a datum block for connecting to the single vertebral body. From datum block, a measuring instrument or cutting guide may be attached. A cutting instrument is used for preparing the endplate, and an instrument coupling assembly is connected between the cutting instrument and the cutting guide.  
         [0003]     In another embodiment, a datum block is disclosed for attachment to a single vertebral body in a vertebral column. The datum block comprises a bottom surface shaped to conform to an outer surface of the vertebral body and a channel portion shaped to interlock with a bone measuring and preparation fixture. The datum block further comprises a tool connection portion for positioning a distraction tool and an aperture in the bottom surface adapted for inserting a bone fastener into the vertebral body.  
         [0004]     In still another embodiment, a distraction assembly is disclosed for separating a pair of vertebral bodies. The assembly comprises a first handle assembly pivotally connected to a second handle assembly, a first terminal member pivotally connected to the first handle, and a second terminal member pivotally connected to the second handle. The first and second terminals maintain a parallel distraction between the pair of vertebral bodies as the first handle assembly is moved relative to the second handle assembly.  
         [0005]     In still another embodiment, a method of preparing a first vertebral endplate to receive an implant comprises attaching a first datum block to a first vertebral body, attaching a measuring instrument to check the size of the vertebral body, and attaching a cutting guide to the first datum block. The cutting guide including first and second rotary guides between which an alignment bar extends. The method further comprises attaching an instrument coupling assembly to the cutting guide and attaching a cutting instrument, having a cutting head, to the instrument coupling assembly. The first vertebral endplate is shaped to receive the implant.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a side view of a vertebral column having a damaged disc.  
         [0007]      FIG. 2  is a flowchart describing a surgical technique.  
         [0008]      FIG. 3  is an isometric view of an alignment guide according to an embodiment of the current disclosure.  
         [0009]      FIG. 4  is a perspective view of a distractor assembly according to a one embodiment of the current disclosure.  
         [0010]      FIG. 5  is a perspective view of a portion of the distractor assembly of  FIG. 4 .  
         [0011]      FIG. 6  is an environmental view of the distractor assembly of  FIG. 4 .  
         [0012]      FIG. 7  is a perspective view of a cutting assembly according to one embodiment of the current disclosure.  
         [0013]      FIGS. 8-9  are perspective views of an instrument guide according to one embodiment of the current disclosure.  
         [0014]      FIG. 10  is a perspective view of an instrument coupling assembly according to one embodiment of the current disclosure.  
         [0015]      FIG. 11  is an environmental view of the cutting assembly of  FIG. 7 , the instrument guide of  FIGS. 8-9 , and the instrument coupling assembly of  FIG. 10 .  
         [0016]      FIG. 12  is an environmental view of the cutting assembly of  FIG. 7 , the instrument guide of  FIGS. 8-9 , the instrument coupling assembly of  FIG. 10  and the distractor assembly of  FIG. 4 .  
         [0017]      FIGS. 13   a  is an environmental view of the cutting assembly of  FIG. 7 , the instrument guide of  FIGS. 8-9 , and the instrument coupling assembly of  FIG. 10  in a first cutting position.  
         [0018]      FIGS. 13   b  is an environmental view of the cutting assembly of  FIG. 7 , the instrument guide of  FIGS. 8-9 , and the instrument coupling assembly of  FIG. 10  in a second cutting position.  
         [0019]      FIG. 14  is an instrument coupling assembly according to another embodiment of the current disclosure.  
         [0020]      FIG. 15  is a distractor assembly according to another embodiment of the current disclosure. 
     
    
     DETAILED DESCRIPTION  
       [0021]     The present disclosure relates generally to the field of orthopedic surgery, and more particularly to instrumentation and methods for vertebral reconstruction. 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.  
         [0022]     Referring first to  FIG. 1 , the numeral  10  refers to a vertebral column 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 any of 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. 2002/0128715 and 2003/0135277 which are incorporated by reference herein. A longitudinal axis  20  may be generally defined by the vertebral column  10 . A sagittal axis  22  may extend in an anterior posterior direction, and a lateral axis  24  may extend in a transverse direction.  
         [0023]     A surgical technique for repairing the damaged joint may be represented, in one embodiment, by the flowchart  30  depicted in  FIG. 2 . Referring first to step  32 , 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  32  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. Next, 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  32 , which may include a discectomy procedure, may alternatively or additionally be performed after alignment and/or measurement procedures have been taken.  
         [0024]     Proceeding to step  33  of the surgical technique  30  of  FIG. 2 , various orientation and location procedures may be conducted in preparation for implantation of the disc prosthesis  18 . The transverse center of the disc space may be determined and marked. Referring now to  FIG. 3 , a pair of datum blocks  40 ,  42  may be attached directly to the surfaces of the vertebral bodies  14 ,  16 , respectively. The datum block  42  may be substantially similar to datum block  40  and therefore will not be described in detail. Datum block  40  may include a vertebral body attachment aperture  44 , an attachment guide  46 , and tool guides  48 ,  50 . In this embodiment, the attachment guide  46  may be a dove tailed groove, but it is understood that in alternative embodiments, the attachment guide may be either the male or female component of an interlocking assembly such as a dovetailed or T-shaped coupling. The datum block  40  may include a base portion  52  which may be saddle-shaped. The datum block  40  may further include alignment guides  54 ,  56 . The datum blocks  40 ,  42  may be relatively low profile and allow for improved visibility of the surgical site.  
         [0025]     During the orientation procedures of step  2 , the datum block  40  may be centered on the vertebral body  14  by aligning the alignment guides  54 ,  56  with the transverse centering mark. The block  40  is secured to the vertebral body  14  by a fastener, such as a screw (not shown), installed through the attachment aperture  44 . The datum block  40  uses the external anatomy of the individual vertebral body  14  to set up proper location and orientation. The datum block  40  may be used for attaching and/or aligning instrumentation used for distraction, measuring, bone preparation, or prosthesis insertion. Block  42  may be located on vertebral body  16  in substantially the same way as described above for block  40 . With the datum blocks  40 ,  42  attached as disclosed above, the blocks may independently follow the vertebral bodies  14 ,  16 .  
         [0026]     Proceeding to step  34  of the surgical technique  30  of  FIG. 2 , a spreader or distractor assembly  60 , as shown in  FIGS. 4-6 , may be introduced. The distractor assembly  60  may include handles or arms  62 ,  64  connected to cam mechanisms  66 ,  68  by handle joints  70 ,  72 , respectively. Cam mechanisms  66 ,  68  may engage cam sliders  74 ,  76 , respectively, which may in turn, moveably engage terminals  78 ,  80 , respectively. Cam mechanism  66  may be rotatably coupled to cam mechanism  68 , and terminals  78 ,  80  may be pivotally coupled to cam mechanisms  68 ,  66 , respectively.  
         [0027]     In operation, the terminal  78  may engage the tool guide  48 , and the terminal  80  may engage a corresponding tool guide on the datum block  42 . With the distractor assembly  60  engaged, the vertebral bodies  14 ,  16  may be distracted by drawing the arms  62 ,  64  together. As the arms  62 ,  64  are drawn together, the cam mechanisms  66 ,  68  may engage the cam sliders  74 ,  76 , respectively, which may in turn move the terminals  78 ,  80 , respectively. As the terminals  78 ,  80  move apart, a relatively parallel displacement may be maintained between the terminals and correspondingly, between the vertebral bodies  14 ,  16 . The vertebral bodies  14 ,  16  may be placed in tension, providing access to the intervertebral space to allow further discectomy and/or decompression procedures as needed. The arms  62 ,  64  may bend at the handle joints  70 ,  72  to open the operating field. The arms  62 ,  64  may also be locked in the distracted position to maintain the operating field.  
         [0028]     Although the use of only one distractor assembly  60  has been described, it is understood that a second distractor, as shown in  FIG. 6 , may be used. In an alternative embodiment, a similar distractor assembly may have a scissor-style configuration, such that as the arms are drawn apart, the terminals also are drawn apart.  
         [0029]     Referring again to  FIG. 2 , with the datum blocks  40 ,  42  attached to the distracted vertebral bodies  14 ,  16 , the surgical technique  30  may then proceed to step  35 . At step  35 , 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  30 . Measuring the intervertebral space may involve the use of a variety of instrumentation and equipment including, for example, the measurement instrumentation described in U.S. patent application Ser. No. 10/799,835 which is incorporated by reference herein.  
         [0030]     Referring again to  FIG. 2 , the surgical technique  30  may proceed to step  36  for further preparation of the vertebral endplate surfaces. Referring now to  FIG. 7 , to prepare the endplate surfaces to provide a secure seat for the intervertebral prosthesis  18 , a milling or cutting instrument  90  may be provided. In the embodiment of  FIG. 7 , the cutting instrument  90  may comprise a shaft  92  and a cutting head  94  having a cutting surface  96 . A portion of the shaft  92  may include threads  93 .  
         [0031]     The cutting instrument described above for  FIG. 7  is merely one embodiment which may be used with the distractor assembly  60  and the anchoring devices  40 ,  42 . In alternative embodiments, the cutting instrument may 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. The cutting instrument  90  may be substantially similar to one of the cutting instrument embodiments described in the above referenced U.S. patent application Ser. No. 10/799,835.  
         [0032]     Referring now to  FIGS. 8 and 9 , a cutting guide  100  may also be used to prepare the vertebral endplate surfaces. The cutting guide  100  may include a body  102  having a tool interface side  104 , an external side  106 , and a connection portion  108  for interlocking with the attachment guide  46  of the datum block  40 . In this embodiment, the connection portion  108  is a dove tail shaped projection, but other interlocking mechanisms are also suitable. The cutting guide  100  may also include an aperture  110  through which an interlock fastener  112  may extend to secure the interface between the cutting guide  100  and the datum block  40 . The cutting guide  100  may house a set of sealed bearings  114 ,  116  which permit movement of a set of rotary guides  118 ,  120 . A set of cam spindles  122 ,  124  may extend, offset from the center, from the rotary guides  118 ,  120 , respectively, on the external side  106  of the cutting guide  100 . A set of cam spindles  126 ,  128  may extend, offset from the center, from the rotary guides  118 ,  120 , respectively, on the tool interface side  104  of the cutting guide  100 . An alignment bar  130  may extend between the cam spindles  122 ,  124  on the external side  106  of the cutting guide  100 , and a coupling bar  132  may extend between the cam spindles  126 ,  128  on the tool interface side  104 .  
         [0033]     Referring now to  FIG. 10 , an instrument coupling assembly  140  for connecting the cutting guide  100  to the cutting instrument  90  may include an attachment device  142  and a tool positioning device  144 . The attachment device  142  may include forked arms  146 ,  148  and a channel  150  for locking to the coupling bar  132 . The tool positioning device  144  may include channels  152 ,  154  configured to mate with and slide along the forked arms  146 ,  148 , respectively. The tool positioning device  144  may also include a tubular sleeve  156  through which the cutting instrument  90  may extend. The tool positioning device  144  may also include an adjustment dial  158  for adjusting the position of the cutting instrument  90  relative to the tool positioning device  144 . The adjustment dial  158  may be threadedly engaged with the cutting instrument  90 .  
         [0034]     The forked arms  146 ,  148  of the attachment device  142  may include toothed surfaces  160 ,  162  configured to engage a pinion gear  164  extending from the tool positioning device  144 . This rack and pinion system formed by the toothed surfaces  160 ,  162  and gear  164  allow the tool positioning device  144  to move along and lock to the forked arms  146 ,  148 . Connections between the components of the cutting guide  100  and instrument coupling assembly  140  may be secured, as needed, with fasteners such as pins and screws.  
         [0035]     Referring now to  FIGS. 11, 12 ,  13   a,  and  13   b,  based upon the measurements taken in step  35  and the size and profile of the prosthesis  18  to be implanted, the cutting surface  96  may be selected. The cutting instrument  90  with the selected cutting surface  96  may be assembled to the tool positioning device  144  as described above. With the datum block  40  attached to the vertebral body  14 , the cutting guide  100  may be mounted to the datum block  40  as described above. The attachment device  142  may be mounted to cutting guide  100  as described above, and the tool positioning device  144  coupled with the cutting instrument  90  may be mounted to the attachment device  142  also as described above.  
         [0036]     With the attachment device  142  and the tool positioning device  144  interconnected by the gear  164  and the toothed surfaces  160 ,  162 , the depth of the cut made by the cutting head  94  along the longitudinal axis  20  may be adjusted by rotating the pinion gear  164 . Using the adjustment dial  158 , the anterior-posterior placement of the cutting head  94  along the sagittal axis  22  may be adjusted. The proper positioning of the cutting head  94  may be established with known offsets and may be verified with fluoroscopic or other imaging techniques.  
         [0037]     As shown in  FIG. 12 , the distractor assembly  60  may remain in place during the cutting procedures. The arms of the distractor assembly  60  may break away from the surgical site to provide more space to the surgeon. If desired, more than one distractor assembly may be used to maintain the disc space.  
         [0038]     In operation, a user may cause the cutting instrument  90  to travel a relatively circular path predetermined by the relationship between the centers of the rotary guides  118 ,  120  and the location of the cam spindles  126 ,  128 , respectively. As shown in  FIG. 13   a,  when the cam spindles  126 ,  128  are rotated to a position directly above the center of the rotary guides,  118 ,  120 , respectively, the cutting head  94  may be in an uppermost position in its circular path. As shown in  FIG. 13   b,  when the cam spindles  126 ,  128  are rotated to a position directly below the center of the rotary guides,  118 ,  120 , respectively, the cutting head  94  may be in a lowermost position in its circular path. As the cutting instrument  90  travels its path, the cutting surface  96  may be powered to cut, mill, or otherwise shape the vertebral body  14 . The rotary guides  118 ,  120  may be rotated by driving shaft  92  of the cutting instrument  90 , driving the alignment bar  130 , driving one or both of the cam spindles  118 ,  120 , directly, or any other method of driving the cutting head  94  through its predetermined path as may be appreciated by one skilled in the art. The path of the cutting head  94  may be adjusted by adjusting the adjustment dial  158  to raise or lower the cutting instrument  90  relative to the vertebral bodies  14 ,  16 .  
         [0039]     The cutting surface  96  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  90  may be mounted to the datum block  42  with the cutting surface  96  positioned adjacent to the endplate of the vertebral body  16 . The cutting instrument  90  may again be powered, this time to shape the endplate of vertebral body  16 . If multi-level surgical procedures, involving more than one intervertebral disc location, are required, the use of datum block allows bridging across several disc spaces without removing and resetting instrumentation. As described above, the datum blocks  40 ,  42  may be independently fixed and aligned with their respective vertebral bodies. As such, the vertebral bodies  14 ,  16  may be permitted to move independently of each other and therefore, the endplate preparation procedure may permit each of the vertebral bodies to be shaped independently. In one embodiment, the datum blocks  40 ,  42  may move independently in any direction so as to permit the best access and apply the least amount of stress to the system. In an alternative embodiment, the datum blocks  40 ,  42  may permit 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.  
         [0040]     Referring again to  FIG. 2  at step  37 , after the vertebral endplates are prepared, the cutting instrument  90 , the cutting guide  100 , and the instrument coupling assembly  140  may be removed from the datum block  40  in preparation for implanting the intervertebral prosthesis  18 . 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 datum blocks  40 ,  42  may be used to guide prosthesis insertion instrumentation. After the prosthesis  18  is implanted, the tension on the distractor assembly  60  may be released. The datum blocks  40 ,  42  may be removed form the vertebral bodies  14 ,  16  respectively. With all instrumentation removed from the disc site, the wound may be closed.  
         [0041]     Referring now to  FIG. 14 , in an alternative embodiment, an instrument coupling assembly  180  for connecting the cutting guide  100  to the cutting instrument  90  may include an attachment device  182  and a tool positioning device  184  connected by a hinge joint  186 . The attachment device  182  may include a channel  188  for locking to the coupling bar  132 . The tool positioning device  184  may include a tubular sleeve  190  through which the cutting instrument  90  may extend. The tool positioning device  184  may also include an adjustment dial  192  for adjusting the position of the cutting instrument  90  relative to the tool positioning device  184 . The adjustment dial  192  may be threadedly engaged with the cutting instrument  90 . The hinge joint  186  may pivot to allow angular displacement between the cutting instrument  90  and the attachment device  182 .  
         [0042]     Referring now to  FIG. 15 , in an alternative embodiment a distractor assembly  200  may be used to distract the vertebral bodies  14 ,  16  in parallel alignment. The distractor assembly  200  may include pivotally connected handles  202 ,  204 . The handles  202 ,  204  may be connected by hinges  206 ,  208  to legs  210 ,  212 , respectively. The legs  210 ,  212  may be slideably connected to a cross-bar mechanism  214 . The distractor assembly  200  may perform substantially the same type of vertebral body distraction as described above for distractor assembly  60 .  
         [0043]     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. It is understood that one skilled in the art may omit or add minor steps to the described procedures and that such expanded or abbreviated methods are intended to be included within the scope of this invention. 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.