Abstract:
The invention relates generally to systems and methods for securing adjacent vertebrae in a fixed spacial relationship. In one embodiment, the system includes at least one interbody repair implant, at least one implantable vertebral frame and at least one retention member. In this embodiment, the interbody repair implant is sized to fit in an intervertebral space. The at least one implantable vertebral frame is configured to span between the adjacent vertebrae. The frame is also configured to attach to each of the adjacent vertebra to postoperatively maintain a desired spatial relationship between the vertebrae. The frame has at least one internal aperture there-through for providing visual access to at least a portion of the interbody repair implant, both intra-operatively and post-operatively. Methods of fusing two or more adjacent vertebral bodies in a portion of a spinal column are also disclosed. One such method includes the steps of inserting an interbody repair implant into a intervertebral space, securing an implantable vertebral fixation frame to the adjacent vertebral bodies over the implant, installing a retention member to the frame to cover at least a portion of the aperture, and moving a locking portion of the retention member from an unlocked position to a locked position.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. patent application Ser. No. 12/616,762 entitled “Implantable Vertebral Frame Systems and Related Methods for Spinal Repair”, filed Nov. 11, 2009, which is a continuation-in-part of U.S. patent application Ser. No. 11/855,124 entitled “Implantable Bone Plate System and Related Method for Spinal Repair”, filed Sep. 13, 2007, which claims priority to U.S. Provisional Patent Application Ser. No. 60/954,511 entitled “Implantable Bone Plate System and Related Method for Spinal Repair”, filed Aug. 7, 2007. Each patent application is incorporated herein by reference in its entirety. 
     
    
       [0002]    The present invention relates to a system for performing surgical repair of the spine, such as for but not limited to the delivery of an interbody repair device for the purpose of either fusion or dynamic stabilization. 
       BACKGROUND 
       [0003]    It is current practice in spinal surgery to use bone fixation devices to improve the mechanical stability of the spinal column and to promote the proper healing of injured, damaged or diseased spinal structures. Typically, corrective surgery entails the removal of damaged or diseased tissue, a decompression of one or more neural elements, followed by the insertion of an intervertebral implant for the purposes of a fusion or disc arthroplasty. In cases where spinal fusion is the desired surgical outcome, the final step is often to apply a bone plate in order to immobilize adjacent vertebral bones to expedite osteogenesis across said vertebral segments. 
         [0004]    Most current surgical techniques require that damaged vertebral tissue be placed under rigid axial distraction throughout much of the procedure. This allows for greater ease in the removal of tissue, provides a larger working space for instrument maneuverability, enhances the surgeon&#39;s visibility and assists with the fit of the interbody implant once the distractor apparatus is removed. Conventional distraction of the spine typically employs the use of temporary “distractor pins” placed directly into the bone tissue adjacent to the disc space to be repaired, which are subsequently induced to move axially by the attachment and adjustment of a secondary tool. An alternative method employs the use of a ratcheting spreader device which is inserted directly into the vertebral interspace and is adjusted thereafter to achieve desired distraction. 
         [0005]    In the conventional method, once the implant has been inserted, the distractor device is removed and the vertebrae can be secured by the attachment of a bone plate. Such bone plates, including a plurality of bone screws, are applied near the completion of the procedure to provide vertebral fixation and prohibit undesirable migration of the intervertebral implant. 
         [0006]    Several design constructs have already been proposed in which a device is applied to adjacent vertebrae at the start of a procedure, prior to tissue removal, for the purposes of achieving and maintaining preferred vertebral alignment while serving also to constrain tissue removal throughout the procedure. The disclosed or published art in this method can generally be categorized into two broad categories: removable devices and permanently implantable devices. 
         [0007]    The removable devices differ from the present proposed invention in that the devices used to maintain preferred vertebral alignment are temporary inserts and are subsequently removed after tissue removal so that a repair device may be delivered thereafter. The prior art which discloses permanently implantable devices differs in that the devices function solely to maintain preferred vertebral alignment and are not part of a comprehensive system and related method to precisely control and permanently maintain the preferred spatial relationship of adjacent vertebral members for controlled tissue removal and delivery of a repair device. 
       Removable Devices 
       [0008]    U.S. Pat. No. 7,153,304 entitled Instrument System for Preparing a Disc Space Between Adjacent Vertebral Bodies to Receive a Repair Device, issued Dec. 26, 2006 to Robie et al., discloses a removable instrument system for preparing a disc space between adjacent vertebral bodies using a series of distractors that restore natural lordosis before a temporary template is attached for vertebral immobilization and to function as a guide for an insertable reamer meant for tissue removal. 
         [0009]    U.S. Pat. No. 7,083,623 to Michelson, entitled Milling Instrumentation and Method for Preparing a Space Between Adjacent Vertebral Bodies, issued Aug. 1, 2006, discloses a removable milling device and method for preparing a space between adjacent vertebral bodies which essentially maintains preferred vertebral alignment while functioning as a saw guide to control bone and soft tissue removal. 
         [0010]    US Pat. App. 2005/0043740 to Haid, entitled Technique and Instrumentation for Preparation of Vertebral Members, published Feb. 24, 2005, discloses a removable instrumentation set and technique for preparation of vertebral members utilizing a docking ring which is temporarily applied to the anterior spine to maintain preferred vertebral alignment and to function as a docking plate for an articulating bone removal device. 
         [0011]    U.S. Pat. No. 7,033,362 to McGahan, entitled Instruments and Techniques for Disc Space Preparation, issued Apr. 25, 2006, discloses a removable instrumentation set and method for disc space preparation whereby an intervertebral device is temporarily inserted for the purpose of constraining tissue removal and guiding the position of an intervertebral repair device. 
         [0012]    US Pat. App. 2003/0236526 to Van Hoeck, entitled Adjustable Surgical Guide and Method of Treating Vertebral Members, published Dec. 25, 2003, discloses a removable surgical guide and method with adjustable functionality for the preparation of adjacent vertebra. 
         [0013]    US Pat. App. No. 2006/0247654 to Berry, entitled Instruments and Techniques for Spinal Disc Space Preparation, published Nov. 2, 2006, discloses a removable milling instrument assembly for vertebral endplate preparation which constrains a cutting path obliquely oriented to the axis of the vertebra. 
       Permanently Implanted Devices 
       [0014]    US Pat. App. 2004/0097925 to Boehm, entitled Cervical Spine Stabilizing System and Method, published May 20, 2004, discloses a permanently implantable spine stabilizing system and method whereby a plate configured to be positively centered along the midline is placed to retain adjacent vertebra in a desired spatial relationship during discectomy and fusion procedures. The disclosed invention uses a series of temporary implants and removable drill templates in an attempt to assure the alignment of the implanted device along the midline of the spinal column. This alignment is typically not considered to be significant in determined the clinical outcome of the procedure and is further considered impractical for the purposes of performing repair procedures on multiple adjacent disk spaces due to the normal scoliotic curvature of the spine. 
         [0015]    US Pat. App. 2005/0149026 to Butler et al., entitled Static and Dynamic Cervical Plate Constructs, published Jul. 7, 2005, describes an implanted cervical bone plate having a graft window located between the bone screw holes for the purposes of providing visualization and access to an intervertebral implant. The device described is applied after the intervertebral space has been repaired and after the implant has been positioned. The specification states specifically that an appropriately “sized dynamic plate is placed over the inserted bone implant”; thereafter the bone plate is located with respect to the implant by viewing the implant through the graft window and secured in place using bone screws. 
         [0016]    Additional bone plate devices are disclosed in U.S. Pat. No. 3,741,205 to Markolf et al, and US Pat. Apps. 2005/0149026 to Butler et al. and 2007/0233107 to Zielinski. 
         [0017]    There remains a need for and advantage to a permanently implantable spinal repair system and related method whereby the implant may be clearly viewed through the vertebral plate both inter-operatively and post-operatively. There is also a need for new systems and methods wherein the intervertebral implant and the bone screws used to secure the plate to the vertebrae can be prevented from backing out from the vertebrae in a quick and effective manner. 
       SUMMARY OF THE DISCLOSURE 
       [0018]    The invention relates generally to systems and methods for securing adjacent vertebrae in a fixed spacial relationship. In one embodiment, the system includes at least one interbody repair implant, at least one implantable vertebral frame and at least one retention member. In this embodiment, the interbody repair implant is sized to fit in an intervertebral space. The at least one implantable vertebral frame is configured to span between the adjacent vertebrae. The frame is also configured to attach to each of the adjacent vertebra to postoperatively maintain a desired spatial relationship between the vertebrae. The frame has at least one internal aperture there-through for providing visual access to at least a portion of the interbody repair implant, both intra-operatively and post-operatively. The aperture is sized to have a smaller medio-lateral width than that of the interbody repair implant. The at least one retention member is attachable to the frame to cover at least a portion of the aperture. The retention member has a locking portion movable between an unlocked position and a locked position. In this embodiment, the locking portion prevents the retention member from being separated from the frame when in the locked position. 
         [0019]    In some embodiments similar to the above embodiment, the locking portion includes at least one section that contacts a posterior side of the frame when the locking portion is in the locked position. The locking portion may include two sections that contact the posterior side of the frame on opposite sides of the aperture when the locking portion is in the locked position. 
         [0020]    In some embodiments, the retention member includes at least one screw cover portion. The screw cover portion may cover at least part of a screw securing the frame to one of the adjacent vertebrae so as to prevent the screw from backing out of the vertebra. The retention member may include two, four, or more screw cover portions. 
         [0021]    In some embodiments, the retention member includes a transitory locking portion having at least one resilient arm engageable with the frame for maintaining the retention member on the frame before the locking portion is moved from the unlocked position to the locked position. 
         [0022]    In some embodiments, at least a portion of the retention member is radiolucent. 
         [0023]    In some embodiments, the frame is configured to span between and remain postoperatively attached to at least three or at least four adjacent vertebrae. In these embodiments, the frame has at least two or at least three internal apertures there-through, respectively. Each aperture is configured to provide visual access to at least a portion of an interbody repair implant intra-operatively and post-operatively. In these embodiments, the system may include two or three retention members, respectively. Each retention member is attachable to the frame and is configured to cover at least a portion of one of the apertures. Each retention member has a locking portion movable between an unlocked position and a locked position. The locking portion in these embodiments prevents the retention member from being separated from the frame when in the locked position. 
         [0024]    In some embodiments, the retention member is configured to provide visual, tactile and audible feedback when the locking portion is moved between the unlocked position and the locked position. 
         [0025]    According to aspects of the invention, a method of fusing two or more adjacent vertebral bodies in a portion of a spinal column may be provided. In one such embodiment, the method includes the steps of inserting an interbody repair implant into a intervertebral space and securing an implantable vertebral fixation frame to the adjacent vertebral bodies over the implant. These steps are done such that a desired spatial relationship between the vertebrae is maintained. In this embodiment, the fixation frame has an internal aperture there-through for providing visual access to at least a portion of the interbody repair implant intra-operatively and post-operatively. The aperture is sized to have a smaller medio-lateral width than that of the interbody repair implant. This method further includes the steps of installing a retention member to the frame to cover at least a portion of the aperture, and moving a locking portion of the retention member from an unlocked position to a locked position. This locking of the retention member prevents the retention member from being separated from the frame. 
         [0026]    In some embodiments similar to the above method, the locking portion includes at least one section that contacts a posterior side of the frame when the locking portion is in the locked position. The retention member may further include at least one screw cover portion, wherein the screw cover portion covers at least part of a screw securing the frame to one of the adjacent vertebrae. The screw cover portion prevents the screw from backing out of the vertebra. In some embodiments, there are two, four, or more screw cover portions. 
         [0027]    In some embodiments, the retention member includes a transitory locking portion having at least one resilient arm that engages with the frame and maintains the retention member on the frame between the installing and moving steps. The method may include the step of observing the interbody repair implant with postoperative imaging through the retention member. 
         [0028]    In some embodiments, the securing step involves securing the implantable vertebral fixation frame to at least three adjacent vertebral bodies to maintain a desired spatial relationship between the at least three vertebral bodies. The installing and moving steps may each be performed on more than one retention member. In some inventive methods disclosed herein, the retention member is configured to provide visual, tactile and audible feedback during the moving step. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0029]      FIG. 1  is an anterior plan view showing an exemplary interbody repair device implanted in an intervertebral space and covered by an implantable vertebral frame secured between two adjacent vertebrae according to aspects of the present invention. 
           [0030]      FIG. 2  is a lateral view showing the repair device and vertebral frame of  FIG. 1 . 
           [0031]      FIG. 3  is a perspective view showing the top of the repair device of  FIG. 1  with an exemplary retention member installed. 
           [0032]      FIG. 4  is a perspective view of the bottom side of the repair device and retention member of  FIG. 3 . 
           [0033]      FIG. 5  is an exploded perspective view showing the repair device and retention member of  FIGS. 3 and 4 . 
           [0034]      FIG. 6  is an enlarged perspective view showing an end portion of the exemplary retention member. 
           [0035]      FIG. 7  is a top plan view showing the exemplary retention member with its locking arm removed for clarity. 
           [0036]      FIG. 8  is a bottom view showing the exemplary retention member with its locking arm removed for clarity. 
           [0037]      FIG. 9  is a side view showing the exemplary retention member with its locking arm removed for clarity. 
           [0038]      FIG. 10  is an exploded end view showing the exemplary retention member with its locking arm disassembled. 
           [0039]      FIG. 11A  is an exemplary bone screw for use in securing the vertebral frame to adjacent vertebrae. 
           [0040]      FIG. 11B  is a perspective view showing the bone screw of  FIG. 11A  installed in a vertebral frame. 
           [0041]      FIG. 12  is an anterior view depicting a retention member (semi-transparent for clarity) attached to a vertebral frame and in an unlocked position. 
           [0042]      FIG. 13  is an anterior view depicting a retention member (semi-transparent for clarity) attached to a vertebral frame and in a locked position. 
           [0043]      FIG. 14  is a perspective view showing an exemplary vertebral frame configured for spanning three adjacent vertebral bodies. 
           [0044]      FIG. 15  is a perspective view showing an exemplary vertebral frame configured for spanning four adjacent vertebral bodies. 
           [0045]      FIG. 16  is a bottom view showing the exemplary vertebral frames of  FIGS. 3 ,  14  and  15 . 
           [0046]      FIG. 17  is a perspective view showing the vertebral frame of  FIG. 15  attached to four adjacent vertebral bodies. 
           [0047]      FIG. 18  is an anterior view showing the vertebral frame of  FIG. 15  attached to four adjacent vertebral bodies. 
           [0048]      FIG. 19  is a lateral cross-sectional view showing the vertebral frame of  FIG. 15  attached to four adjacent vertebral bodies. 
           [0049]      FIG. 20  is a cranio-caudal cross-sectional view showing the vertebral frame of  FIG. 15  attached to a vertebral body. 
           [0050]      FIG. 21  is an enlarged lateral cross-sectional view showing a portion of the vertebral frame of  FIG. 15 . 
       
    
    
     DETAILED DESCRIPTION 
       [0051]      FIGS. 1 and 2  show portions of an exemplary system constructed according to aspects of the present invention for securing adjacent vertebrae. Such systems are particularly useful for plating anterior surfaces of vertebral bodies of the cervical portion of the human spine, such as for treating compressions of the spine. Additional background and details of tools and surgical procedures associated with these systems can be found in U.S. patent application Ser. No. 12/616,762 entitled “Implantable Vertebral Frame Systems and Related Methods for Spinal Repair”, filed Nov. 11, 2009. 
         [0052]    The exemplary single-level system includes an interbody repair device  100  implanted in an intervertebral space between adjacent vertebral bodies  102  and  104 . In some embodiments, the opposing endplates of adjacent vertebral bodies  102  and  104  are at least partially removed to prepare the intervertebral space to receive repair device  100 . Device  100  may be configured to facilitate the fusion of vertebral bodies  102  and  104 . 
         [0053]    The exemplary system of  FIGS. 1 and 2  also includes an implantable vertebral frame  106  configured to span between vertebral bodies  102  and  104 . Two bone screws  108  may be used to rigidly secure frame  106  to each of the vertebral bodies  102  and  104 . In this embodiment, frame  106  is secured to the anterior faces of vertebral bodies  102  and  104  along the medial centerline of the spine. The combination of repair device  100  and vertebral frame  106  may be used to permanently secure vertebral bodies  102  and  104  in a desired position relative to each other, such as for fusing the vertebral bodies together. 
         [0054]    As shown, frame  106  may be provided with an aperture  110  there-through. Aperture  110  may be used to view aspects of repair device  100 , such as its position, during surgery. After surgery, the aperture may be useful in viewing the development of bony ingrowth from the vertebral bodies  102  and  104  into repair device  100 , as will be described further below. In some embodiments, the cranio-caudal dimension of aperture  110  is large enough to view a portion of each vertebral body where it contacts repair device  100 , as shown. In some embodiments, aperture  110  is sized to have a smaller medio-lateral width than that of the repair device  100 . Such an arrangement can allow frame  106  to assist in keeping repair device  100  from migrating in an anterior direction out of the intervertebral space. 
         [0055]      FIGS. 3 and 4  show a retention member  112  attached to vertebral frame  106  and locked in place. In this embodiment, much of the anterior-posterior thickness of retention member  112  is received within a complementary-shaped recess  114  (shown in  FIG. 1 ) in the anterior face of frame  106 . This arrangement provides a generally smooth outer contour when retention member  112  is coupled to frame  106 . Retention member  112  may cover aperture  110  as shown. In some embodiments, retention member  112  may serve to help retain repair device  100  in place. In some embodiments, retention member  112  serves to lock screws  108  in place as shown, as will be described in more detail below. 
         [0056]    As seen in  FIG. 4 , retention member  112  may include a movable locking arm  116  on its posterior side for locking retention member  112  to frame  106 . In this embodiment, locking arm  116  is operated by inserting a tool (not shown) in a keyed recess  118  on the anterior side of retention member  112  (shown in  FIG. 3 ) and rotating locking arm  116  from an unlocked cranio-caudal orientation to a locked medio-lateral orientation, shown in  FIG. 4 . Retention member  112  may also include a transitory locking feature such as one or more resilient arms  120  engageable with frame  106 . The transitory locking feature maintains retention member  112  on frame  106  before the locking arm  116  is moved from its unlocked position to its locked position. The construction and operation of these locking features are described in more detail below. 
         [0057]    Referring to  FIG. 5 , vertebral frame  106  and retention member  112  are shown separated from each other and from the bottom (posterior) side. Retention member  112  is shown with locking arm  116  in the unlocked position. In this embodiment, retention member  112  is provided with a pair of resilient arms  120  downwardly depending from near each longitudinal end of the retention member. Each arm  120  is L-shaped and has a flange  122  projecting outwardly from its distal end, as best seen in  FIG. 6 . Inwardly facing, complementary-shaped recesses  124  may be formed in opposite longitudinal ends of aperture  110  of frame  106  for receiving the projecting flanges  122 . Retention member  112  may be assembled to frame  106  from above by pressing it down over aperture  110 . Beveled leading edges on flanges  122  cause resilient arm  120  to flex inwardly as they come into contact with the opposite sides of aperture  110 . Once retention member  112  is fully received within aperture  110  and recess  114  (shown in  FIG. 1 ), resilient arms  120  snap back to urge flanges  122  into recesses  124 , thereby holding retention member  112  in place before locking arm  116  is actuated. With locking arm  116  in the unlocked position, retention member  112  can be removed from frame  106 , such as by inserting a probe or other instrument into one or both of the pockets  125  formed in the anterior aspect of resilient arms  120  (best seen in  FIG. 7 ), and applying a force to disengage resilient arms  120  from frame  106 . This can be done interoperatively or during a subsequent revision procedure. A tool may also be inserted into pockets  125  and/or slots  126  surrounding the resilient arms  120  to grasp retention member  112  for removal and/or insertion. 
         [0058]    As can be seen in  FIGS. 5 and 6 , in this embodiment retention member has a lower portion  128  that fits within aperture  110  of frame  106 , and a larger flange portion  130  that resides above aperture  110  when coupled to frame  106 . Retention member  112  may be provided with one, two, three, four, or more screw cover portions. In this exemplary embodiment, retention member  112  is provided with four screw cover portions  132 , one located at each corner of the retention member. As best seen in  FIGS. 5 and 6 , each screw cover portion  132  is curved and has a notch for receiving a portion of the head of a screw  108 . This arrangement prevents the screws  108  from backing out of the vertebrae once they are installed and retention member  112  is locked in place.  FIG. 3  shows the inter-engagement between screw cover portions  132  and screws  108 . 
         [0059]      FIG. 7  shows the top or anterior side of the exemplary retention member  112 . The locking arm and keyed recess assembly is omitted from this view for clarity. As shown, a central hole  134  and counterbore  136  may be provided in the center of retention member  112  for receiving the locking arm and keyed recess assembly, as will be later described. Counterbore  136  allows the assembly to be recessed within retention member  112 . 
         [0060]      FIG. 8  shows the bottom or posterior side of the exemplary retention member  112 . The locking arm and keyed recess assembly is again omitted from this view for clarity. 
         [0061]      FIG. 9  shows a side or lateral view of the exemplary retention member  112 . The locking arm and keyed recess assembly is again omitted from this view for clarity. 
         [0062]      FIG. 10  shows an end or cranio-caudal view of the exemplary retention member  112 . The locking arm and keyed recess assembly is shown with components in an exploded fashion for clarity. Locking arm  116  may be formed on or otherwise rigidly coupled to a cylindrical boss  138 . In this embodiment, boss  138  has a keyed recess  118  (shown in  FIG. 3 ) formed through its top surface. Boss  138  is configured to be rotatably received through the bottom side of central hole  134  within retention member  112 . Cap ring  140  may be threaded, press-fit, welded, swaged or otherwise attached around the top of boss  138 . This arrangement sandwiches the bottom of counterbore  136  between locking arm 116  and cap ring  140 , thereby captivating the locking arm assembly on retention member  112  and allowing locking arm  116  to rotate relative thereto. Locking arm  116  is configured to slide along bottom surface  142 , which is shown in  FIGS. 8 and 9 . As can be appreciated by viewing the configuration of the four portions  128  that depend from bottom surface  142  shown in  FIG. 8 , the locking arm may be oriented along the longitudinal (cranio-caudal axis) of retention member  112  in an unlocked position, or it may be rotated 90 degrees counter-clockwise (when viewed from below as in  FIG. 8 ) to a locked position. As shown in  FIG. 10 , locking arm  116  has a length that is longer than the width of the lower portion  128  of retention member  112 . As such, the tips of locking arm  116  will extend beyond the bottom surface  142  of retention member  112  when in the locked position, and into recesses  144  formed in the bottom of frame  106 , as shown in  FIG. 4 . In this locked position, retention member  112  is securely coupled to frame  106  and bone screws  108  (shown in  FIG. 3 ) are prevented from backing out. 
         [0063]      FIGS. 12 and 13  show retention member  112  coupled to vertebral frame  106  from an anterior view to further illustrate the locking of retention member  112  to frame  106 . In both figures, the retention member  112  is shown as being semi-transparent for clarity.  FIG. 12  shows locking arm  116  in an unlocked position, while  FIG. 13  shows it turned 90 degrees in a clockwise direction to a locked position. According to aspects of the invention, at least one hole  146  may be provided through retention member  112  to align with locking arm  116  when it is either in the unlocked position (as shown in  FIG. 12 ), or when it is in the locked position (not shown). Locking arm  116  may have a brightly colored dot on its surface to line up with hole  146 , or locking arm  116  may be made from or coated with a brightly colored material. With this arrangement, a surgeon can clearly see whether locking arm  116  is in the unlocked position (or locked position). A detent feature (not shown) can be provided between locking arm  116  and retention member  112  to provide tactile feedback to a surgeon when locking arm  116  enters a locked position. The detent feature or a similar feature can also be configured to provide audible feedback to a surgeon. Thus, in some embodiments of the invention, a surgeon is provided with visual, tactile and audible feedback when locking arm  116  is moved between the unlocked position and the locked position. In other embodiments, only two, one, or none of these feedback features is provided. 
         [0064]    Referring to  FIG. 11A , a proprietary bone screw  108  may be used to secure vertebral frame  106  to the vertebrae it spans. Bone screw  108  includes a head  145  and a threaded shank  147 . Threaded shank  147  may be configured to be self drilling and/or self tapping. Bone screw  108  may be provided with head relief portion  149  to cooperate with screw cover portions  132  of retention member  112 , as previously described. Bone screw  108  may also include a shoulder portion  148 . In some embodiments, shoulder portion  148  has a spherical contour as shown. This contour cooperates with a mating contour on the anterior side of screw holes  154  in frame  106 . This arrangement allows screw  108  to be mounted into a vertebral body at a variable angle relative to frame  106 , as depicted in  FIG. 11B . In some embodiments, this variability is defined by a 14 degree included angle. In other embodiments, fixed angle screws are used, or a combination of fixed angle and variable angle screws may be used. 
         [0065]    Referring to  FIGS. 14-16 , additional embodiments of the inventive vertebral frame and retainer member are shown. While the previously described frame  106  is configured to span two adjacent vertebral bodies (i.e. a single-level system), vertebral frame  150  shown in  FIG. 14  is configured to span three adjacent vertebral bodies (i.e. a two-level system), and vertebral frame  152  shown in  FIG. 15  is configured to span four adjacent vertebral bodies (i.e. a three-level system). The posterior side of all three vertebral frames  106 ,  150  and  152  and retention members  112  is shown in  FIG. 16 . 
         [0066]    The construction and operation of multi-level vertebral frames  150  and  152  is similar to those of single-level frame  106 . A repair implant similar to device  100  shown in  FIGS. 1 and 2  may be implanted between each of the adjacent vertebrae connected by these multi-level frames. As with frame  106 , a pair of holes  154  is provided through the frame in these exemplary multi-level embodiments to receive a pair of screws  108  for attaching the frame to each vertebral body. In the exemplary embodiments shown, multiple retention members  112  are used on each frame  150  and  152  to retain screws  108 . Each retention member  112  secures four screws  108 , with the middle screws each being retained by two retention members  112 . Each retention member  112  may be symmetrical and identical, thereby allowing it to be put in any position on the frame and in either orientation. This arrangement reduces the part count in surgical kits containing one or more types of vertebral frames and simplifies the surgical procedures for implanting them. In other embodiments (not shown), a single retention member may be used. As previously described, each retention member may have a transitory locking portion having at least one resilient arm engageable with the frame for maintaining the retention member on the frame before a locking portion is moved from an unlocked position to a locked position. 
         [0067]      FIGS. 17 and 18  show vertebral frame  152  implanted across four adjacent vertebral bodies  102 ,  104 ,  154  and  156 . 
         [0068]      FIG. 19  shows a medio-lateral looking cross-section of the vertebral frame  152  and adjacent vertebral bodies of  FIGS. 17 and 18 , taken along a cranio-caudal line running through the central axis of four screws  108  on one side of frame  152 . 
         [0069]      FIG. 20  shows a cranio-caudal looking cross-section of a portion of vertebral frame  152  and a vertebral body of  FIGS. 17 and 18 , taken along a medio-lateral line running through the central axis of two adjacent screws  108  in a single vertebral body. 
         [0070]    Aspects of the present invention can also be utilized to construct vertebral frames spanning more than four vertebral bodies. 
         [0071]    According to aspects of the invention, the vertebral frames  106 ,  150  and  152  are configured to be low-profile for minimal interference with surrounding anatomy. In some embodiments, the vertebral frames are 2.1 mm at their thickest points. 1.2 mm leading and latereal edges may be provided as shown for easy insertion and in-situ adjustment. In some embodiments, the vertebral frames are 18 mm at their greatest width, and 13 mm at their narrowest width. The aperture(s) of each frame may be configured to be about 8 mm wide and about 12 mm long. The vertebral frames may have a pre-lordosed design as shown. Frames may be configured to allow translation up to about 1.5 mm per level. In some embodiments, the vertebral frames are made of titanium. 
         [0072]    Surgical kits may be provided that include various sizes of vertebral frames. In some embodiments, the kits include single-level plates ranging from about 22 mm to about 34 mm long, In some embodiments, the kits include two-level plates ranging from about 36 mm to about 55 mm long. In some embodiments, the kits include three-level plates ranging from about 50 mm to about 77 mm long. In some embodiments, the kits include more than one type of vertebral frame. The kits may also include a range of self-drilling and self-tapping screws, fixed-angle screws, variable-angle screws, and recovery screws. In some embodiments, screws having a 4.0 mm nominal diameter are provided, and recovery screws having a 4.5 mm nominal diameter are also provided. 
         [0073]    In some embodiments, retention member  112  is made of PEEK or another radiolucent material. This allows bone growth into an implant beneath retention member  112  to be viewed with various imaging techniques. Locking arm  116  may be made of titanium or another radio-opaque material so its locked status can be confirmed by imaging. 
         [0074]    One exemplary method of installing a vertebral frame according to aspects of the invention is as follows. An incision is made and the anterior surfaces of the cervical vertebral bodies to be plated are exposed, as is well known in the art. The vertebral bodies may be distracted at this point to provide a desired spacial arrangement, to provide room to prepare the intervertebral space(s), and/or to insert the repair implant(s)  100 . The intervertebral space(s) may be prepared, such as by removing at least portions of the disk annulus fibrosus, disk nucleus, and/or vertebral body endplates. The repair implant(s) may then be inserted between the adjacent vertebral bodies. Vertebral frame  106 ,  150  or  152  is then placed over the adjacent vertebral bodies covering the repair implant(s). The vertebral frame is typically placed on the anterior surfaces of the vertebral bodies along the medial centerline of the spine, and centered cranio-caudally over each repair implant  100 . The aperture(s)  110  in the frame allow the surgeon to view the positioning of the implant(s)  100  during the procedure. 
         [0075]    Once the vertebral frame  106 ,  150  or  152  is in the desired position on the vertebral bodies, it may be secured in place with bone screw  108 . In the exemplary embodiments disclosed herein, two screws  108  are used for each vertebral body involved in the procedure. The screws may be self drilling and/or self tapping. Alternatively, holes may be pre-drilled in the bone before inserting the screws. The vertebral frame may be used as a drilling template, or a separate drilling template may be temporarily placed over the vertebral bodies for drilling prior to placement of the vertebral frame. In some embodiments, a separate drill guide may be attached to the drilling template or vertebral frame to aid in drilling and/or tapping. 
         [0076]    Bone screws  108  are tightened, thereby securing vertebral frame  106 ,  150  or  152  to the vertebral bodies. The vertebral frame cooperates with repair implant(s)  100  to hold the vertebral bodies in the desired position postoperatively. Retention member(s)  112  may now be installed in the vertebral frame. As previously described, each retention member  112  may be placed over and partially into an aperture  110 , and snapped into place by transitory locking features such as resilient arms  120  shown in  FIG. 5 . With a single 90 degree twist of each keyed recess  118  (shown in  FIG. 3 ), the retention member  112  is locked into place by locking arm  116  (shown in  FIG. 4 ), thereby fully securing implant  100  and four bone screws  108 . As previously described, visual, tactile and audible feedback may be provided to the surgeon when the locking portion is moved between the unlocked position and the locked position. Each retention member  112  may be removed, if desired, by turning its keyed recess  118  in the opposite direction and prying the retention member  112  away from the frame against the force of the resilient arms  120 . Once all retention members  112  are in place and locked, the plating procedure may be completed by closing the incision, as is well known in the art. 
         [0077]    In some procedures it is desired that boney ingrowth from the vertebral bodies and/or bone growth material placed in repair implant(s)  100  allows the adjacent vertebral bodies to fuse together. Post-operative imaging can be used to monitor the progress of this healing process by viewing the implant-to-vertebral body interfaces through the aperture(s)  110  of the vertebral frame  106 ,  150  or  152 . This is enabled by the large viewing aperture(s)  110  provided by aspects of the present invention along with retention member(s)  112  being made from a radio-translucent material. 
         [0078]    While inventive vertebral frame systems and associated methods have been described in some detail by way of illustration, such illustration is for purposes of clarity of understanding only. It will be readily apparent to those of ordinary skill and in the art in light of the teachings herein that certain changes and modifications may be made thereto without departing from the spirit and scope of the appended claims. 
         [0079]    All publications and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.