Patent Publication Number: US-6214005-B1

Title: Spinal column retaining apparatus

Description:
This application is a continuation of co-pending application Ser. No. 09/655,851, filed on Aug. 31, 1996, now U.S. Pat. No. 5,800,433. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to an apparatus for use in retaining vertebrae of a spinal column in a desired spatial relationship. In particular, the present invention relates to an apparatus for use in retaining cervical vertebrae of a human spinal column in a desired spatial relationship. 
     2. Description of the Prior Art 
     There are various known devices for retaining vertebrae of a spinal column in a desired spatial relationship. Certain of such known devices include rods connected to and extending between vertebrae and certain of such known devices include plates connected to and extending between vertebrae. 
     SUMMARY OF THE INVENTION 
     The present invention is an apparatus for retaining first and second vertebrae of a spinal column in a desired spatial relationship. The apparatus includes a longitudinal member positionable along the spinal column. A member connectable with the first vertebra has first and second fastener openings and a portion engageable with the longitudinal member. A first fastener is extendable through the first fastener opening in the member to connect the member with the first vertebra. The first fastener has a first end portion for attachment to the first vertebra and has a longitudinal axis. A second fastener is extendable through the second fastener opening in the member to connect the member with the first vertebra. The second fastener has a first end portion for attachment to the first vertebra and has a longitudinal axis. 
     In accordance with one feature of the present invention, the longitudinal axis of the first fastener and the longitudinal axis of the second fastener converge at an acute angle as viewed in the sagittal plane when the first and second fasteners connect the member with the first vertebra. The apparatus also includes means for connecting the longitudinal member with the second vertebra. 
     In accordance with another feature of the present invention, the member connectable with the first vertebra has a body portion. The member also has a lip portion projecting in a first direction from the body portion of the member. The lip portion of the member is engageable with a surface of the first vertebra facing toward the second vertebra. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The foregoing and other features of the present invention will become more apparent to one skilled in the art upon reading the following description with reference to the accompanying drawings, wherein: 
     FIG. 1 is an elevational view of an apparatus constructed in accordance with the present invention for maintaining a desired spatial relationship between cervical vertebrae of a spinal column; 
     FIG. 2 is a view of the apparatus of FIG. 1, taken along the sagittal plane as indicated by line  2 — 2  of FIG. 1; 
     FIG. 3 is a sectional view taken generally along line  3 — 3  of FIG. 2; 
     FIG. 4 is a sectional view taken generally along line  4 — 4  of FIG. 2; 
     FIG. 5 is a perspective view of a first plate which forms a portion of the apparatus of FIG. 1; 
     FIG. 6 is another perspective view of the plate of FIG. 5; 
     FIG. 7 is a view similar to FIG. 5 of a second plate which forms a portion of the apparatus of FIG. 1; 
     FIG. 8 is another perspective view of the plate of FIG. 7; 
     FIG. 9 is a view similar to FIG. 1 of a modified embodiment of the invention. 
     FIG. 10 is a perspective view of a plate which is constructed in accordance with a second embodiment of the present invention; and 
     FIG. 11 is an enlarged sectional view of a portion of the plate of FIG.  10  and showing a set screw and rod associated with the plate; 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     The present invention relates to an apparatus for use in retaining vertebrae of a spinal column in a desired spatial relationship. As representative of the present invention, FIG. 1 illustrates an apparatus  10  for use in retaining bone portions such as cervical vertebrae V 1  and V 2  of a human spinal column C in a desired spatial relationship. The spinal column C has an axis A which is a vertical axis of the human body. 
     The apparatus  10  includes a pair of surgically implantable rods  12  and  14  (FIGS.  1  and  2 ). The apparatus  10  also includes first and second members or plates  30  and  32  which engage the rods  12  and  14 ; three fasteners  38 ,  40 , and  42  for connecting the first plate with the first vertebra V 1 ; and three fasteners  44 ,  46 , and  48  for connecting the second plate with the second vertebra V 2 . 
     The first rod  12  (FIG. 1) is made of a suitable biocompatible material, such as titanium or stainless steel. The first rod  12  has an elongate cylindrical configuration and has a circular cross section taken in a plane extending perpendicular to the longitudinal central axis of the first rod. The first rod  12  has a smooth outer surface. A first end portion of the first rod  12  is formed as a cap  50 . The first rod  12  also has a second end portion  52  opposite from the first end portion  50 . 
     The second rod  14  is identical to the first rod  12 . The second rod  14  has a first end portion which is formed as a cap  54 . The second rod  14  also has a second end portion  56  opposite from the first end portion  54 . The rods  12  and  14  are bendable to a desired configuration to conform to a desired curvature of the spinal column C. The rods  12  and  14  together have sufficient strength and rigidity to maintain the vertebrae V 1  and V 2  in a desired spatial relationship. 
     The rods  12  and  14  have a length which is sufficient to enable the rods to span at least the two vertebrae V 1  and V 2 . The length of the rods  12  and  14  will depend upon the condition to be corrected and the number of vertebrae to be held in a desired spatial relationship relative to each other by the apparatus  10 . If more than two vertebrae are to be held in a desired spatial relationship relative to each other by the apparatus  10 , the rods  12  and  14  would be longer and more than two plates, such as the plates  30  and  32 , may be used. 
     The first plate  30  (FIGS. 5 and 6) is made of a suitable biocompatible material, such as titanium or stainless steel. The first plate  30  includes a main body portion  60 . The main body portion  60  of the first plate  30  has a planar outer side surface  62  for facing anteriorly or away from the first vertebra V 1 . The first plate  30  has an arcuate inner side surface  64  for facing posteriorly or toward the first vertebra V 1 . The inner side surface  64  of the first plate  30  may engage the anterior surface of the first vertebra V 1  when the first plate is connected with the first vertebra as described below. 
     The main body portion  60  of the first plate  30  has a central portion  66  which extends laterally between a first side portion  68  and a second side portion  70  of the first plate. Because the inner side surface  64  of the first plate  30  has an arcuate configuration, the central portion  66  of the first plate is relatively thin (as viewed in a direction from left to right in FIG. 3) as compared to the first side portion  68  and to the second side portion  70 . 
     The main body portion  60  of the first plate  30  also has first and second end portions  72  and  74 . The first end portion  72  of the first plate  30  includes a planar first end surface  76  of the first plate  30 . The second end portion  74  includes a planar second end surface  78  of the first plate  30 . The second end surface  78  extends parallel to the first end surface  76 . 
     A first rod passage  80  is formed in the first side portion  68  of the first plate  30 . The first rod passage  80  is an opening which extends between the first and second end surfaces  76  and  78  of the first plate  30  in a direction parallel to the planar outer side surface  62  of the first plate. The first rod passage  80  is defined by a cylindrical surface  81  and tapered pilot surfaces  83  and  84  at opposite ends of the cylindrical surface  81 . The diameter of the cylindrical surface  81  is slightly greater than the diameter of the first rod  12 , so that the first rod and the first plate  30  can be relatively movable. 
     The second side portion  70  of the first plate  30  is a mirror image of the first side portion  68 . A second rod passage  82  is formed in the second side portion  70  of the first plate  30 . The second rod passage  82  is an opening which extends between the first and second end surfaces  76  and  78  of the first plate  30  in a direction parallel to the planar outer side surface  62  of the first plate. The second rod passage  82  extends parallel to the first rod passage  80 . The second rod passage  82  is defined by a cylindrical surface  85  and tapered pilot surfaces  86  and  87  at opposite ends of the cylindrical surface  85 . The diameter of the second rod passage  82  is the same as the diameter of the first rod passage  80 . The diameter of the cylindrical surface  85  is slightly greater than the diameter of the second rod  14 , so that the second rod and the first plate  30  can be relatively movable. 
     A circular first fastener opening  90  extends through the central portion  66  of the first plate  30 . The first fastener opening  90  has an axis  92  (FIG. 2) which extends perpendicular to the plane of the outer side surface  62  of the first plate  30 . The axis  92  extends in a first direction as indicated by the arrow  94 , that is, from right to left as viewed in FIG. 2, when the first plate  30  is mounted on the first vertebra V 1 . The first direction  94  extends perpendicular to the axes of the rods  12  and  14 . 
     The first fastener opening  90  is partially defined by a larger diameter cylindrical surface  96  (FIG. 6) which extends from the outer side surface  62  of the first plate  30  in a direction into the material of the central portion  66  of the first plate. The cylindrical surface  96  is centered on the axis  92  of the first fastener opening  90 . The first fastener opening  90  is partially defined by a smaller diameter cylindrical surface  98  which extends from the inner side surface  64  of the first plate  30  in a direction into the material of the central portion  66  of the first plate to a location spaced radially inward from the surface  96 . The cylindrical surface  98  is centered on the axis  92  of the first fastener opening  90 . 
     An annular shoulder surface  100  (FIGS. 2 and 6) extends radially (relative to the axis  92 ) between the cylindrical surfaces  96  and  98 . The shoulder surface  100  and the larger diameter cylindrical surface  96  define a recess  102  in the outer side surface  62  of the first plate  30 . 
     The main body portion  60  of the first plate  30  also includes a circular second fastener opening  110  formed at a location adjacent to, but spaced apart from, the first rod passage  80  in the first side portion  68  of the first plate. The second fastener opening  110  extends through both the second end surface  78  of the first plate  30  and the outer side surface  62  of the first plate. 
     The second fastener opening  110  is partially defined by a larger diameter cylindrical surface  112  (FIG. 6) which extends from the outer side surface of the first plate  30  in a direction into the material of the first side portion  68  of the first plate. The cylindrical surface  112  is centered on an axis  114  (FIG. 2) of the second fastener opening  110 . The cylindrical surface  112  is spaced apart from the first rod passage  80 . 
     The second fastener opening  110  is partially defined by a smaller diameter cylindrical surface  116  (FIG. 6) which extends from the inner side surface  64  of the first plate  30  in a direction into the material of the first side portion  68  of the first plate, to a location spaced radially inward from the surface  112 . The cylindrical surface  116  is centered on the axis  114  of the second fastener opening  110 . 
     An annular shoulder surface  118  (FIGS. 3 and 6) extends radially (relative to the axis  114 ) between the cylindrical surfaces  112  and  116 . The shoulder surface  118  and the larger diameter cylindrical surface  112  define a recess  120  in the outer side surface  62  of the first plate  30 . 
     The axis  114  of the second fastener opening  110  extends transverse to the axis  92  of the first fastener opening  90 . Specifically, the axis  114  (FIG. 3) of the second fastener opening  110  converges with the axis  92  of the first fastener opening  90  as viewed in a transverse plane at right angles to the vertical axis A, as can be seen from FIG.  3 . In the illustrated embodiment, the axis  114  converges at an angle of about  100  with the axis  92  as viewed in this transverse plane. 
     The axis  114  of the second fastener opening  110  also converges with the axis  92  of the first fastener opening  90  as viewed in the sagittal plane, as can be seen in FIG.  2 . In the illustrated embodiment, the axis  114  converges at an angle of 45° with the axis  92  as viewed in the sagittal plane. It is contemplated that the angle of convergence as viewed in the sagittal plane could be in the range of from about 30° to about 60°. 
     The main body portion  60  of the first plate  30  also includes a circular third fastener opening  130  formed at a location adjacent to, but spaced apart from, the second rod passage  82  in the second side portion  70  of the first plate. The third fastener opening  130  extends through both the second end surface  78  of the first plate  30  and the outer side surface  62  of the first plate. 
     The third fastener opening  130  is partially defined by a larger diameter cylindrical surface  132  (FIG. 6) which extends from the outer side surface  62  of the first plate  30  in a direction into the material of the second side portion  70  of the first plate. The cylindrical surface  132  is centered on an axis  134  (FIG. 4) of the third fastener opening  130 . The cylindrical surface  132  is spaced apart from the second rod passage  82 . 
     The third fastener opening  130  is partially defined by a smaller diameter cylindrical surface  136  (FIG. 6) which extends from the inner side surface  64  of the first plate  30  in a direction into the material of the second side portion  70  of the first plate, to a location spaced radially inward from the surface  32 . The cylindrical surface  136  is centered on the axis  134  of the third fastener opening  130 . 
     An annular shoulder surface  138  (FIGS. 3 and 6) extends radially (relative to the axis  134 ) between the cylindrical surfaces  132  and  136 . The shoulder surface  138  and the larger diameter cylindrical surface  132  define a recess  140  in the outer side surface  62  of the first plate  30 . 
     The axis  134  (FIG. 3) of the third fastener opening  130  is coplanar with the axis  114  of the second fastener opening  110 . The axis  134  of the third fastener opening  130  extends transverse to the axis  92  of the first fastener opening  90 . Specifically, the axis  134  of the third fastener opening  130  converges with the axis  92  of the first fastener opening  90  as viewed in a transverse plane at right angles to the vertical axis A, as can be seen from FIG.  3 . In the illustrated embodiment, the axis  134  converges with the axis  92  at an angle of 10° as viewed in this transverse plane. 
     The axis  134  of the third fastener opening  130  also converges with the axis  92  of the first fastener opening  90  as viewed in the sagittal plane, as can be seen from FIG.  2 . In the illustrated embodiment, the axis  134  converges with the axis  92  at an angle of 45° as viewed in the sagittal plane. It is contemplated that this angle of convergence as viewed in the sagittal plane could be in the range of from about 30° to about 60°. 
     The first plate  30  includes a lip portion or lip  150  which is formed as one piece with the main body portion  60  of the first plate. The lip  150 , best seen in FIGS. 2 and 5, projects from the second end portion  74  of the main body portion  60  of the first plate  30 . The lip  150  projects in the first direction  94  (FIG. 2) when the first plate  30  is mounted on the first vertebra V 1 . 
     The lip  150  has a planar configuration as viewed in the first direction  94 , for example, as seen in FIG.  2 . The lip  150  has an arcuate configuration, as can be seen in FIG. 5, when viewed in a direction parallel to the plane of the outer side surface  62  of the first plate  30 . The arcuate configuration of the lip  150  generally follows the arcuate configuration of the inner side surface  64  of the main body portion  60  of the first plate  30 . The lip  150  extends continuously between the first and second side portions  68  and  70  of the first plate  30 . Alternatively, the lip  150  may be discontinuous at one or more locations along the width of the plate  30 . 
     The lip  150  has an outer end surface  152  (FIG. 2) which is formed as an extension of the second end surface  78  of the main body portion  60  of the first plate  30 . An opposite inner end surface  154  (FIGS. 2 and 5) of the lip  150  extends parallel to the outer end surface  152 . The lip  150  also has an inner side surface  156  which extends between the inner and outer end surfaces  154  and  152  of the lip  150 . 
     The second and third fastener openings  110  and  130  extend partially through the lip  150 . The second fastener opening  110 , as can be seen in FIG. 2, extends through the corner between, or intersection of, the lip  150  and the main body portion  60  of the first plate  30 . The third fastener opening  130  also extends through the corner between, or intersection of, the lip  150  and the main body portion  60  of the first plate  30 . 
     The second plate  32  (FIG. 7) is generally similar in configuration to the first plate  30  (FIG.  5 ). The second plate  32  (FIG. 7) is configured, however, so that the head ends of fasteners received in certain fastener openings in the second plate are engageable with the rods  12  and  14  disposed in rod passages in the second plate. This engagement can block movement of the second plate  32  relative to the rods  12  and  14 , in a manner described below. 
     The second plate  32  includes a main body portion  160  which has a planar outer side surface  162  for facing anteriorly or away from the vertebra V 2 . The main body portion  160  also has an arcuate inner side surface  164  for facing posteriorly or toward the second vertebra V 2 . The inner side surface  164  of the second plate  32  may engage the anterior surface of the second vertebra V 2  when the second plate is connected with the second vertebra as described below. 
     The main body portion  160  has a central portion  166  which extends laterally between a first side portion  168  and a second side portion  170  of the second plate  32 . Because the inner side surface  164  of the second plate  32  has an arcuate configuration, the central portion  166  of the second plate  32  is relatively thin (as viewed in a direction from left to right in FIG. 4) as compared to the first side portion  168  and to the second side portion  170 . 
     The main body portion  160  of the second plate  32  also has first and second end portions  172  and  174 . The first end portion  172  of the second plate  32  includes a planar first end surface  176  of the second plate. The second end portion  174  of the second plate  32  includes a planar second end surface  178  of the second plate. The second end surface  178  extends parallel to the first end surface  176 . 
     A first rod passage  180  is formed in the first side portion  168  of the second plate  32 . The first rod passage  180  is an opening which extends between the first and second end surfaces  176  and  178  in a direction parallel to the planar outer side surface  162  of the second plate  32 . The first rod passage  180  is defined by a cylindrical surface  181  and tapered pilot surfaces  183  and  184  at opposite ends of the cylindrical surface  181 . The diameter of the cylindrical surface  181  is slightly greater than the diameter of the first rod  12 . 
     A second rod passage  182  is formed in the second side portion  170  of the second plate  32 . The second rod passage  182  is an opening which extends between the first and second end surfaces  176  and  178  in a direction parallel to the planar outer side surface  162  of the second plate  32 . The second rod passage  182  extends parallel to and has the same diameter as first rod passage  180 . The second rod passage  182  is defined by a cylindrical surface  185  and tapered pilot surfaces  186  and  187  at opposite ends of the cylindrical surface  185 . The diameter of the cylindrical surface  185  is slightly greater than the diameter of the second rod  14 . 
     A circular first fastener opening  190  extends through the central portion  166  of the second plate  32 . The first fastener opening  190  has an axis  192  (FIGS. 2 and 4) which extends perpendicular to the plane of the outer side surface  162  of the second plate  32 . The axis  192  extends in the first direction  94  when the second plate  32  is mounted on the second vertebra V 2 . 
     The first fastener opening  190  is partially defined by a larger diameter cylindrical surface  196  (FIG. 8) which extends from the outer side surface  162  of the second plate  32  in a direction into the material of the central portion  166  of the second plate. The cylindrical surface  196  is centered on the axis  192  of the first fastener opening  190 . The first fastener opening  190  is partially defined by a smaller diameter cylindrical surface  198  which extends from the inner side surface  164  of the second plate  210  in a direction into the material of the central portion  166  of the second plate, to a location spaced radially inward from the surface  196 . The cylindrical surface  198  is centered on the axis  192  of the first fastener opening  190 . 
     An annular shoulder surface  200  (FIGS. 2 and 8) extends radially (relative to the axis  192 ) between the cylindrical surfaces  196  and  198 . The shoulder surface  200  and the larger diameter cylindrical surface  196  define a recess  202  in the outer side surface  162  of the second plate  32 . 
     The main body portion  160  of the second plate  32  also includes a circular second fastener opening  210  formed at a location adjacent to and intersecting the first rod passage  180  in the first side portion  168  of the second plate. The second fastener opening  210  extends through both the second end surface  178  of the second plate  32  and the outer side surface  162  of the second plate. 
     The second fastener opening  210  is partially defined by a larger diameter cylindrical surface  212  (FIG. 8) which extends from the outer side surface  262  of the second plate  32  in a direction into the material of the first side portion  168  of the second plate. The cylindrical surface  212  is centered on an axis  214  (FIGS. 2 and 4) of the second fastener opening  210 . The cylindrical surface  212  intersects the cylindrical surface  181  which defines the first rod passage  180 . Thus, the second fastener opening  210  overlaps a portion of the first rod passage  180 . 
     The second fastener opening  210  is partially defined by a smaller diameter cylindrical surface  216  which extends from the inner side surface  264  of the second plate  32  in a direction into the material of the first side portion  168  of the second plate, to a location spaced radially inward from the surface  212 . The cylindrical surface  216  is centered on the axis  214  of the second fastener opening  210 . 
     An annular shoulder surface  218  (FIGS. 4 and 8) extends radially (relative to the axis  214 ) between the cylindrical surfaces  212  and  216 . The shoulder surface  218  and the larger diameter cylindrical surface  212  define a recess  220  in the outer side surface  262  of the second plate  32 . 
     The axis  214  of the second fastener opening  210  extends transverse to the axis  192  of the first fastener opening  190 . Specifically, the axis  214  of the second fastener opening  210  converges with the axis  192  of the first fastener opening  190  as viewed in a transverse plane at right angles to the vertical axis A, as can be seen from FIG.  4 . In the illustrated embodiment, the axis  214  converges with the axis  192  at angle of about  100  as viewed in this transverse plane. 
     The axis  214  of the second fastener opening  210  also converges with the axis  192  of the first fastener opening  190  as viewed in the sagittal plane, as can be seen in FIG.  2 . In the illustrated embodiment, the axis  214  converges with the axis  192  at an angle of 45° as viewed in the sagittal plane. It is contemplated that this angle of convergence could be in the range of from about 30° to about 60° as viewed in the sagittal plane. 
     The main body portion  160  of the second plate  32  also includes a circular third fastener opening  230  formed at a location adjacent to and intersecting the second rod passage  182  in the second side portion  170  of the second plate. The third fastener opening  230  extends through both the second end surface  178  of the second plate  32  and the outer side surface  162  of the second plate. The distance between the third fastener opening  230  in the second plate  32  and the second fastener opening  210  in the second plate is slightly less than the distance between the third fastener opening  130  in the first plate  30  and the second fastener opening  110  in the first plate. 
     The third fastener opening  230  is partially defined by a larger diameter cylindrical surface  232  (FIG. 8) which extends from the outer side surface  262  of the second plate  32  in a direction into the material of the second side portion  170  of the second plate. The cylindrical surface  232  is centered on an axis  234  (FIG. 4) of the third fastener opening  230 . The cylindrical surface  232  intersects the cylindrical surface  185  which defines the second rod passage  182 . Thus, the third fastener opening  230  overlaps a portion of the second rod passage  182 . 
     The third fastener opening  230  is partially defined by a smaller diameter cylindrical surface  236  (FIG. 8) which extends from the inner side surface  264  of the second plate  32  into the material of the second side portion  170  of the second plate to a location spaced radially inward from the surface  232 . The cylindrical surface  236  is centered on the axis  234  of the third fastener opening  230 . 
     An annular shoulder surface  238  (FIGS. 4 and 8) extends radially (relative to the axis  234 ) between the cylindrical surfaces  232  and  236 . The shoulder surface  238  and the larger diameter cylindrical surface  232  define a recess  240  in the outer side surface  162  of the second plate  32 . 
     The axis  234  of the third fastener opening  230  is coplanar with the axis  214  of the second fastener opening  210 . The axis  234  of the third fastener opening  230  extends transverse to the axis  192  of the first fastener opening  190 . Specifically, the axis  234  of the third fastener opening  230  converges with the axis  192  of the first fastener opening  190  as viewed in a transverse plane at right angles to the vertical axis A, as can be seen from FIG.  4 . In the illustrated embodiment, the axis  234  converges with the axis  192  at an angle of about 10° as viewed in this transverse plane. 
     The axis  234  of the third fastener opening  230  also converges with the axis  192  of the first fastener opening  190  as viewed in the sagittal plane, as can be seen from FIG.  2 . In the illustrated embodiment, the axis  234  converges with the axis  192  at an angle of 45°. It is contemplated that this angle of convergence as viewed in the sagittal plane could be in the range of from about 30° to about  60 °. 
     The second plate  32  includes a lip portion or lip  250  which is formed as one piece with the main body portion  160  of the second plate. The lip  250 , best seen in FIGS. 4 and 7, projects from the second end portion  174  of the main body portion  160  of the second plate  32 . The lip  250  projects in the first direction  94  (FIG. 2) when the second plate  32  is mounted on the second vertebra V 2 . 
     The lip  250  has a planar configuration as viewed in the first direction  94 , for example, as seen in FIG.  2 . The lip  250 , as viewed in a direction parallel to the plane of the outer side surface  162  of the second plate  32 , has an arcuate configuration generally following the arcuate configuration of the inner side surface  164  of the main body portion  160  of the second plate  32 . The lip  250  extends continuously between the first and second side portions  168  and  170  of the second plate  32 . Alternatively, the lip  250  may be discontinuous at one or more locations along the width of the second plate  32 . 
     The lip  250  has an outer end surface  252  (FIG. 2) which is formed as an extension of the second end surface  178  of the main body portion  160  of the second plate  32 . An opposite inner end surface  254  (FIGS. 2 and 8) of the lip  250  extends parallel to the outer side surface  252 . The lip  250  also has an inner side surface  256  which extends between the inner and outer end surfaces  252  and  254  of the lip  250 . The second and third fastener openings  210  and  230  extend partially through the lip  250 . The second fastener opening  210 , as well as the third fastener opening  230 , extend through the corner between, or intersection of, the lip  250  and the main body portion  160  of the second plate  32 . 
     The fasteners  38 ,  40 ,  42 ,  44 ,  46 , and  48 , which connect the first plate  30  with the first vertebra V 1  and the second plate  32  with the second vertebra V 2 , are identical to each other. Because the fasteners  38 - 48  are identical, only the fastener  40  is described herein in detail. 
     The fastener  40  (FIG. 3) includes a sleeve  300  and an expander  310 . The sleeve  300  has a hollow, elongate shank portion  302  centered on a longitudinal central axis  304  of the fastener  40 . The shank portion  302  defines a cylindrical central opening  308  in the sleeve  300 . A coarse external helical thread convolution  306  is formed on the outer peripheral surface of the shank portion  302  of the sleeve  300 . 
     The shank portion  302  of the sleeve  300  is radially and axially slotted so that the shank portion is expandable radially. A series of projections (not shown) are formed on the inner surface of the sleeve  300  for engagement by the expander  310  to expand the shank portion  302  of the sleeve in a manner described below. 
     A head end portion  314  of the sleeve  300  has a cylindrical outer side surface  316 . An annular lip or rim  318  extends around the head end portion  314  of the sleeve  300  and projects radially outward from the outer side surface  316 . The head end portion  314  of the sleeve  300  has a conical inner side surface  320  and a conical inner side surface  322 . The conical inner side surface  322  merges with an internal thread convolution  324  formed on the sleeve  300 . 
     The head end portion  314  of the sleeve  300  is radially and axially slotted to define four segments  326  of the head end portion. The four segments  326  are movable radially relative to each other and to the axis  304  of the fastener  40  so that the head end portion  314  of the sleeve  300  is expandable radially. 
     The expander  310  has a head end portion  340  and a shank portion  342 . An inner end  344  of the shank portion  342  of the expander  310  is slightly larger in diameter than the cylindrical central opening  308  in the sleeve  300 . 
     The head end portion  340  of the expander  310  has an X-shaped driver slot  346  for receiving a driving tool for rotating the expander relative to the sleeve  300 . The head end portion  340  has a conical outer side surface  348  and a conical outer side surface  350 . The conical outer side surface  350  on the head end portion  340  of the expander  310  has a different angle of taper than does the conical inner side surface  322  on the head end portion  314  of the sleeve  300 . 
     The conical outer side surface  350  on the head end portion  340  of the expander  310  merges with an external thread convolution  352  formed on the expander  310 . The external thread convolution  352  on the expander  310  screws into the internal thread convolution  324  on the sleeve  300 . 
     To install the apparatus  10  on the spinal column C, the rods  12  and  14  are first assembled with the plates  30  and  32 . Specifically, the first rod  12  is inserted through the first rod passage  80  in the first plate  30  and through the first rod passage  180  in the second plate  32 . One of the tapered pilot surfaces  83  and  84  on the first plate  30 , and one of the tapered pilot surfaces  183  and  184  on the second plate  32 , guide insertion of the first rod  12 . The second rod  14  is inserted through the second rod passage  82  in the first plate  30  and through the second rod passage  182  in the second plate  32 . One of the tapered pilot surfaces  86  and  87  on the first plate  30 , and one of the tapered pilot surfaces  186  and  187  on the second plate  32 , guide insertion of the second rod  14 . 
     The assembly of the rods  12  and  14  and the plates  30  and  32  is then positioned over the exposed anterior surface of the spinal column C. The first plate  30  (FIG. 2) is positioned adjacent to the first vertebra V 1  so that the first end surface  154  on the lip  150  of the first plate engages a lower surface  360  on the first vertebra V 1 . The lower surface  360  on the first vertebra V 1  faces toward the second vertebra V 2 . The second plate  32  is positioned adjacent to the second vertebra V 2  so that the first end surface  254  on the lip  250  of the second plate engages an upper surface  362  on the second vertebra V 2 . The upper surface  362  on the second vertebra V 2  faces toward the first vertebra V 1 . 
     With the first plate  30  on the first vertebra V 1 , and the second plate  32  on the second vertebra V 2 , a suitable drill guide and drill (not shown) are used to drill fastener openings in the first vertebra V 1  and in the second vertebra V 2 . 
     The fasteners  38 ,  40  and  42  are inserted to connect the first plate  30  with the first vertebra. The insertion and securing of the fastener  40 , although not necessarily performed first, will be described as exemplary. 
     The sleeve  300  of the fastener  40  is inserted through the second fastener opening  110  in the first plate  30 . The sleeve  300  of the fastener  40  is threaded into the drilled opening in the vertebra V 1  in a known manner (not shown) to fix the sleeve in position in the vertebra V 1 . The unexpanded head portion  314  of the sleeve  300  is disposed in the recess  120  in the first plate  30 . 
     The expander  310  of the fastener  40  is then inserted into the sleeve  300 . The externally threaded portion  352  of the expander  310  is screwed into the internal threads  324  on the sleeve  300 . When the expander  310  is fully screwed into the sleeve  300 , the inner end portion  344  of the expander  310  causes the shank portion  302  of the sleeve to expand radially outward, helping to lock the sleeve in place in the vertebra V 1 . When the expander  310  is fully screwed into the sleeve  300 , the head portion  340  of the expander  310  engages the head portion  314  of the sleeve  300 . The head portion  340  of the expander  310  wedges the locking segments  326  on the sleeve  300  radially outward into engagement with the first plate  30  to rigidly lock the fastener  40  in position relative to the first plate. The head of the fastener  40  is adjacent to the lip  150 . 
     The remaining fasteners  38  and  42  for the first plate  30  are similarly secured to the vertebra V 1  and are rigidly locked to the first plate. The heads of the fasteners  38  and  42  are adjacent to the lip  150 . As a result, the first plate  30  is securely connected with the first vertebra V 1 . 
     The fasteners  44 ,  46  and  48  are similarly used to connect the second vertebra V 2  and the second plate  32 . The heads of the fasteners  44 ,  46 , and  48  are adjacent to the lip  250 . As a result, the fasteners  44 ,  46  and  48  are rigidly locked to the plate  32  and the plate  32  is securely connected with the second vertebra V 2 . 
     As can be seen in FIG. 2, the fastener  40  (as well as the fastener  42 , not shown in FIG. 2) extends at an angle (upward as viewed in FIG. 2) to the lip  150 . Accordingly, when the fasteners  40  and  42  are tightened into the first vertebra V 1 , the fasteners tend to draw the lip  150  of the first plate  30  tightly against the surface  360  of the vertebra, that is, in an upward direction as viewed in FIG.  2 . At the same time, the fasteners  40  and  42 , as well as the fastener  38 , tend to draw the main body portion  60  of the first plate  30  tightly against the anterior surface of the first vertebra V 1 , that is, in a direction to the left as viewed in FIG.  2 . Accordingly, it can be seen that tightening the fasteners  38 ,  40  and  42  tends to draw the first plate  30  in two directions against the first vertebra V 1 . 
     The first fastener  38  has a longitudinal central axis which is coincident with the axis  92  of the first fastener opening  90  when the first fastener  38  is disposed in the first fastener opening  90  in the first plate  30 . When the second fastener  40  is disposed in the second fastener opening  110  in the first plate  30 , the longitudinal central axis  304  of the second fastener  40  is coincident with the axis  114  of the second fastener opening  110 . 
     As described above, the axis  92  of the first fastener opening  90  and the axis  114  of the second fastener opening  110  converge at an acute angle as viewed in the sagittal plane (FIG.  2 ). Therefore, the longitudinal axis of the first fastener  38  and the longitudinal axis  304  of the second fastener  40  converge at an acute angle as viewed in the sagittal plane (FIG. 2) when the first and second fasteners  38  and  40  connect the first plate  30  with the first vertebra V 1 . In the illustrated embodiment, the axis of the first fastener  38  and the axis  304  of the second fastener  40  converge at an angle of about 45° as viewed in the sagittal plane. It is contemplated that this angle of convergence in the sagittal plane could be in the range of from about 30° to about 60°. 
     When the third fastener  42  is disposed in the third fastener opening  130  in the first plate  30 , the longitudinal central axis of the third fastener  42  is coincident with the axis  134  of the third fastener opening  130 . As described above, the axis  92  of the first fastener opening  90  and the axis  134  of the third fastener opening  110  converge at an acute angle as viewed in the sagittal plane (FIG.  2 ). Therefore, the longitudinal axis of the first fastener  38  and the longitudinal axis of the third fastener  42  converge at an acute angle as viewed in the sagittal plane (FIG. 2) when the first and third fasteners  38  and  42  connect the first plate  30  with the first vertebra V 1 . In the illustrated embodiment, the axis of the first fastener  38  and the axis of the third fastener  42  converge at an angle of about 45° as viewed in the sagittal plane. It is contemplated that this angle of convergence in the sagittal plane could be in the range of from about 30° to about 60°. 
     The second plate  32  is, in a similar manner, secured in position relative to the second vertebra V 2 . Tightening the fasteners  44 ,  46  and  48  tends to draw the second plate  32  in two directions against the second vertebra V 2 . 
     When the first fastener  44 , the second fastener  46 , and the third fastener  48  connect the second plate  32  with the second vertebra V 2 , the axis of the first fastener  44  and the axis of the second fastener  46  converge at an acute angle as viewed in the sagittal plane (FIG.  2 ). Also, the axis of the first fastener  44  and the axis of the third fastener  48  converge at an acute angle as viewed in the sagittal plane (FIG.  2 ). In the illustrated embodiment, these axes converge at an angle of about 45° as viewed in the sagittal plane. It is contemplated that this angle of convergence in the sagittal plane could be in the range of from about 30° to about 60°. 
     The fact that there are three screws which secure each one of the plates  30  and  32  to the spinal column C also helps to maintain proper placement of the plates. These features help the apparatus  10  maintain the vertebrae V 1  and V 2  in place when the cervical spine is subjected to various degrees of motion of the human head. 
     When the second plate  32  is being connected with the second vertebra V 2 , the outer fasteners  46  and  48  secure the second plate and the second vertebra. The fasteners  46  and  48  also serve to interlock the second plate  32  with the rods  12  and  14 . This is because the locking segments  326  on the sleeves  300  of the fasteners  46  and  48  (FIG. 4) move radially outward into engagement with the rods  12  and  14 , respectively, when each fastener&#39;s expander is fully screwed into the fastener&#39;s sleeve. The engagement between the fasteners  46  and  48  and the rods  12  and  14  blocks movement of the fasteners  46  and  48  relative to the rods. The radial movement of the locking segments  326  of the fasteners also causes the rods to be clamped against the cylindrical surfaces  181  and  185  which define the rod passages  180  and  182 , respectively in the second plate  32 . As a result, the expanded fasteners  46  and  48  block movement of the second plate relative to the rods  12  and  14 . 
     The first plate  30 , in contrast, is movable relative to the rods  12  and  14 , because the second and third fastener openings  110  and  130  are spaced apart from the rod passages  80  and  82 . Therefore, the first plate  30  is movable relative to the second plate  32 . 
     Accordingly, the first vertebra V 1  is movable vertically downward relative to the second vertebra V 2 . This relative movement allows for the maintaining of a load on bone graft placed between the vertebrae V 1  and V 2 . If the first plate  30  were not movable vertically downward relative to the second plate  32 , then the distance between the vertebrae V 1  and V 2  would be fixed. If bone graft were placed between the vertebrae V 1  and V 2  and the bone graft resorbed sufficiently, the bone graft could possibly shrink out of engagement with one or both of the vertebrae V 1  and V 2 . Allowing relative movement of the plates  30  and  32  can help to maintain a desired load on bone graft placed between the vertebrae V 1  and V 2  and maintains the vertebrae in contact with the bone graft to facilitate bone growth. The lips  150  and  250  on the plates  30  and  32  are, preferably, configured so that the lips do not contact bone graft placed between the vertebrae. 
     The caps  50  and  54  on the rods  12  and  14 , respectively, limit movement of the first vertebra V 1  in a direction away from the second vertebra V 2 . This helps to maintain a load on the bone graft and maintain the vertebrae V 1  and V 2  in contact with the bone graft. 
     It may not be necessary or desirable, in some circumstances, to use a dynamic (movable) plate such as the plate  30 . In such circumstances, two locking plates identical to the plate  32  can be used in the same apparatus  10 . Such a system is illustrated in FIG.  9 . The upper plate  32  (FIG. 9) is fixed in position relative to the vertebra V 1  and to the rods  12  and  14 . The lower plate  32  (FIG. 9) is fixed in position relative to the vertebra V 2  and to the rods  12  and  14 . Accordingly, the apparatus  10  (FIG. 9) blocks relative movement between the vertebrae V 1  and V 2 . 
     FIGS. 10 and 11 illustrate a plate  30   a  which is constructed in accordance with a second embodiment of the present invention. The plate  30   a  can be substituted, in the apparatus  10 , for the plate  30 . The plate  30   a  is generally similar to the plate  30  (FIGS.  5  and  6 ), and similar reference numerals are used to designate similar parts, with the suffix “a” added in FIGS. 10 and 11 for clarity. 
     In the plate  30   a , a pair of set screws  370  are provided for engaging the rods  12  and  14  to block movement of the plate, and thereby its associated bone portion, relative to the rods. Specifically, the outer side surface  62   a  of the plate  30   a  is recessed at  372  adjacent to the second rod passage  82   a . A seat  374  extends inwardly from the recess  372  to a threaded opening  376 . An inner end portion  378  of the opening  376  intersects with the second rod passage  82   a . On the opposite side portion  68   a  of the plate  30   a , a second threaded opening  380  intersects the first rod passage  80   a.    
     After the plate  30   a  is assembled with the rods  12  and  14  and positioned adjacent to the spinal column C, fasteners such as the fasteners  38 - 42  are inserted through fastener openings  90   a ,  110   a , and  130   a  in the plate  30   a , to secure the plate to its associated bone portion. The head end portions of the fasteners for the plate  30   a  do not engage the rods  12  and  14 , and do not clamp the rods against the plate  30   a.    
     A set screw  370  is threaded into the opening  376 . An inner end portion  382  of the set screw  370  engages the cylindrical outer surface of the second rod  14 . The engagement of the set screw  370  with the second rod  14  clamps the rod against the second side portion  70   a  of the plate  30   a . Another set screw  370  is threaded into the opening  380  to engage the first rod  12  and clamp the first rod against the first side portion  68   a  of the plate  30   a.    
     As a result, the set screws  370 , the rods  12  and  14 , and the plate  30   a  are interlocked. The plate  30   a  is movable relative to (along the length of) the rods  12  and  14 . Because the plate  30   a  is fixed to its associated bone portion, then the bone portion also is movable relative to the rods  12  and  14 . 
     In the plate  30   a , a portion of the lip  150   a  is removed at the location of the fastener openings  110   a  and  130   a , to provide better visibility. This provides two lip segments  151  and  153  at the side portions  68   a  and  70   a , respectively, of the plate  30   a . The lip segments  151  and  153  are spaced apart on opposite sides of the longitudinal axis, or centerline, of the plate  30   a . A portion of the lip  150   a  also is removed at the lateral center of the plate  30   a , and a notch  384  is provided in the plate  30   a , again to increase visibility. 
     From the above description of the invention, those skilled in the art will perceive improvements, changes and modifications in the invention. Such improvements, changes and modifications within the skill of the art are intended to be covered by the appended claims.