Patent Publication Number: US-2003236528-A1

Title: Impactor for use with cervical plate

Description:
[0001] This application is related to an application filed concurrently herewith entitled CERVICAL PLATE, by Jeffrey J. Thramann, M.D., attorney docket number 46620 830001 000. 
    
    
     
       FIELD OF THE INVENTION  
       [0002] The present invention relates to apparatuses and methods for treating and correcting spinal abnormalities and, more particularly, to cervical plates useful in procedures relating to the insertion of bone grafts in the spine and fusing vertebrae.  
       BACKGROUND OF THE INVENTION  
       [0003] The vertebrae of the human spine are arranged in a column with one vertebra on top of the next. Between each vertebra exists an intervertebral disc that transmits force between adjacent vertebrae and provides a cushion between the adjacent vertebrae.  
       [0004] Sometimes, back pain is caused by degeneration or other deformity of the intervertebral disc (“diseased disc”). When a diseased disc impinges upon neurological structures or is determined to be a pain generator, surgeons treat the diseased disc by surgically removing the diseased disc and inserting a bone graft in the space vacated by the diseased disc. The adjacent vertebrae are then immobilized relative to one another with a cervical plate and screws Eventually, the vertebrae grow into one solid piece of bone Currently, it can be difficult to insert the bone graft into the vacated space and fuse the adjacent vertebrae. The current process of inserting a bone graft and fusing the adjacent vertebrae will be explained referring to FIGS. 1 and 2 FIG. 1 shows two adjacent vertebrae  102  and  104 . Located between vertebrae  102  and  104  is an intervertebral space  106  partially filled by a bone graft  108 . When the bone graft  108  is first inserted into the intervertebral space  106 , the adjacent vertebrae  102  and  104  are manually kept apart by the surgeon using, for example, a retracting device (not shown). As shown in FIG. 2, once the bone graft  108  is placed, the surgeon releases the adjacent vertebrae  102  and  104  allowing them to squeeze the bone graft  108  and hold the bone graft  108  in place.  
       [0005] To immobilize the vertebrae  102  and  104  with the bone graft  108  in place, the surgeon next applies a cervical plate  202  over the adjacent vertebrae  102  and  104  Cervical plate  202  may have a central viewing window  204  and one or more screw holes  206 , in this example four screw holes  206   a - 206   d  are shown Four bone screws, which are identified by reference numerals  208   a - 208   d , and shown in screw holes  206   a - 206   d  respectively, would be screwed into the vertebrae using the screw holes  206  to anchor the cervical plate to the vertebrae and immobilize the vertebrae with respect to one another.  
       [0006] As can be appreciated, attaching the cervical plate  202  using the bone screws  208  can be a difficult endeavor. Generally, a temporary screw (also not shown) is placed in one of the screw holes, for example  206   a . Bone screw  208   c  would then be partially screwed into the bone at screw hole  206   c . The temporary screw in hole  206   a  would be replaced by bone screw  208   a , which would be tightened. Then the other bone screws  208  would be screwed into the bone in a cross point manner. The ability of the cervical plate to move freely in relation to the vertebrae  102  and  104  and the bone graft  108  until the bone screws anchor the plate causes difficulty in attaching the cervical plate. This is made more difficult because, generally, only a portion of the cervical plate is visible to the surgeon at any given moment (due to space constraints and surgical tools)  
       [0007] While the above example relates to replacement of one intervertebral disc between two adjacent vertebrae, sometimes it is necessary to replace two or more discs spanning three or more vertebrae. The problems associated with replacing one disc become more exacerbated the more discs and vertebrae that are involved  
       [0008] Due to the small margins for error in placing the bone screws into the vertebrae, it would be desirous to develop a cervical plate that was not as free to move prior to attachment with the bone screws, and one that automatically aligned the screw holes over the adjacent vertebral bodies.  
       SUMMARY OF THE INVENTION  
       [0009] The foregoing and other features, utilities and advantages of the invention will be apparent from the following more particular description of a preferred embodiment of the invention as illustrated in the accompanying drawings. Further, the advantages and purpose of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.  
       [0010] To attain the advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, apparatuses to facilitate the insertion of a bone graft into an intervertebral space and positioning of a cervical plate are provided. In particular, a cervical plate having an attachment mechanism that allows a surgeon to attach the bone graft to the cervical plate is provided The bone graft, when inserted into the intervertebral space, holds the cervical plate in position to facilitate the anchoring of the cervical plate to vertebrae, and by taking advantage of the fixed association of the junction of the graft and the vertebral endplate with the cervical plate, ensures the screw holes of the cervical plate are optimally placed over the adjacent vertebral bodies to further facilitate screw placement for anchoring of the cervical plate to vertebrae  
       [0011] The present invention further provides an impactor. The impactor is releasably coupled to the cervical plate and has a handle and prongs. The prongs assist in separating the vertebrae to facilitate the insertion of the bone graft, which is attached to the cervical plate via an attachment mechanism, into the intervertebral space  
       [0012] The present invention still further provides methods for correcting abnormalities of the spine by inserting bone grafts 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
     [0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present invention, and together with the description, serve to explain the principles thereof Like items in the drawings are referred to using the same numerical reference  
     [0014]FIG. 1 shows adjacent vertebrae with a bone graft;  
     [0015]FIG. 2 shows adjacent vertebrae with a bone graft and cervical plate;  
     [0016]FIG. 3 shows adjacent vertebrae with a bone graft and cervical plate having an attachment mechanism illustrative of the present invention,  
     [0017]FIG. 4 shows a cross-section of the bone graft and cervical plate of FIG. 3;  
     [0018]FIG. 5 shows an alternative attachment mechanism illustrative of the present invention;  
     [0019]FIG. 6 is a flowchart  600  illustrating use of the present invention; FIGS. 7A and 7B show an impactor illustrative of the present invention;  
     [0020]FIG. 8 shows a plan view of the impactor with a cervical plate illustrative of the present invention; and  
     [0021]FIG. 9 is a flowchart illustrative of a use of the impactor consistent with the present invention. 
    
    
     DETAILED DESCRIPTION  
     [0022] Some embodiments of the present invention are described with reference to FIGS.  3  to  9  In particular, FIGS. 3 and 4 show a cervical plate  300  and bone graft  302 . Cervical plate  300  has a viewing window  304 , screw holes  306 , and an attachment mechanism  400  (shown in phantom in FIG. 3). As best seen in FIG. 4, cervical plate  300  has attachment mechanism  400  attaching the bone graft  302  to the cervical plate  300   
     [0023] Attachment mechanism  400  can be any of a number of different attachment mechanisms For example, as shown in FIG. 4, attachment mechanism  400  comprises a pin or stud attached to the cervical plate inserted into a hole or detent in the bone graft  302  Alternatively, attachment mechanism  400  could be a spike inserted into bone graft  302  without bone graft  302  having a corresponding hole or detent to receive the spike, similar to a thumbtack. Alternatively, attachment mechanism  400  could comprise a pin or stud attached to the bone graft  302  inserted into a hole or detent in cervical plate  300 . Also, attachment mechanism  400  could be any style snap lock or friction fitting, such as the cavity formed in FIG. 5 between protrusions  504 , explained in more detail below. Moreover, while two attachment mechanisms  400  are shown, more or less attachment mechanisms could be used. Further, attachment mechanism  400  could be an adhesive layer between the cervical plate  300  and bone graft  302 . Still further, attachment mechanism  400  could be a screw device so that bone graft  302  and cervical plate  300  are attached using a screw mechanism. Finally, the cervical plates  300  could be made integral to the bone graft  302 , although that would be difficult due to the numerous sizes and shapes of bone grafts and plates necessary to perform the surgery.  
     [0024]FIG. 5 shows cervical plate  500  attached to a bone graft  502  by prongs  504  on bone graft  502 . As shown, prongs  504  attached to the bone graft grasp cervical plate  500  forming a frictional engagement. Alternatively, but not shown, cervical plate  500  could have prongs that grasp bone graft  502 .  
     [0025] As one of ordinary skill in the art would recognize on reading this disclosure, the number of ways the bone grafts could be attached to the cervical plate is numerous. To the extent alternative attachment means are not expressly identify above, this description should not be limited to the embodiments identified and described above. Rather, the specific embodiments identified are for illustrative purposes  
     [0026]FIG. 6 is a flowchart  600  illustrating a method of using the present invention In particular, the surgeon fits a bone graft sizer into the intervertebral space to size the bone graft, step  602 . Then, the appropriate sized intervertebral graft is secured and the surgeon sizes a cervical plate based on the size of the graft and the length of the overall construct, step  604  Once the cervical plate and bone graft are sized, the surgeon attaches the bone graft and the cervical plate, step  606  Next, the bone graft and plate device is placed in the intervertebral space such that the adjacent vertebral endplates hold the bone graft and plate in place, step  608 . The cervical plate is then anchored to the adjacent vertebral bodies, step  610 . Because the surgeon attached the cervical plate to the bone graft, and the adjacent vertebrae hold the bone graft in place, the cervical plate remains fixed in place while the surgeon anchors the plate to the vertebrae  
     [0027] As one of ordinary skill in the art would recognize on reading the above disclosure, the same general device and procedure can be used when inserting multiple bone grafts For example, if fusing four vertebrae, a surgeon would need to place three bone grafts Conventionally, three bone grafts are sized and placed in the intervertebral space and a cervical plate is sized for the construct. Using the present invention, one intervertebral space at the top, bottom, or middle is left devoid of a bone graft. The intervertebral space is sized with a bone graft sizer. The appropriate sized graft would then be secured. A cervical plate measured to fit the three level construct would then be secured and the sized bone graft would be attached to the cervical plate. The one bone graft with the cervical plate attached is fitted into the patient The one bone graft attached to the cervical plate provides stability to the cervical plate and proper orientation of the screw holes to the adjacent vertebral body to facilitate attachment of the cervical plate to the vertebrae.  
     [0028] Alternatively, two or more bone grafts could be sized using sizers and attached to the cervical plate prior to insertion of the grafts in the intervertebral space While this alternative method is possible, it is believed to be more difficult due to surgical space constraints.  
     [0029] As mentioned above, conventionally inserting the bone graft and cervical plate includes using a retracting device to hold the adjacent discs apart, inserting the bone grafts, removing the retracting device, allowing the adjacent discs to squeeze the bone grafts, then placing and anchoring the cervical plate. A difficulty arises using the present invention because the conventional retracting devices need to be removed prior to placing and anchoring the combined bone graft and cervical plate On removing the retracting devices, the adjacent discs move together making it difficult to insert the bone graft between the adjacent discs.  
     [0030]FIG. 7A shows an impactor  700  capable of opening the space between the discs to ease the insertion of the bone graft attached to the cervical plate Impactor  700  has a handle  702  and a cervical plate holder  704 . A distracter  701  and a collar  703  fits over handle  702  such that cervical plate holder  704  extends just below collar  703 . Extending from collar  703  are prongs  706  forming cavity  708  Impactor  700  could have various numbers of prongs, but it is believed two prongs work well Cervical plate holder  704  is designed to hold the cervical plate such that the prongs  706  extend downward beyond the cervical plate and bone graft attachment The cervical plate holder  704  could be attached to the cervical plate by, for example, a pin and detent, a spike, an adhesive, a friction coupling, a snap lock, etc. Prongs  706  could be spaced to form cavity  708  such that placing the cervical plate in the cavity  708  would form a friction fitting releasably coupling the cervical plate to the impactor  700 . However, because the bone graft is often wider than the cervical plate, and depending on whether the prongs function as a scissor like assembly or a wedge like assembly, it is likely the cavity formed by the prongs would not be a sufficient attachment mechanism.  
     [0031] Impactor  700  could function as either a scissor like assembly or a wedge like assembly. FIG. 7B shows impactor  700  assuming a scissor like assembly. As shown handle  702  extends internal to distracter  701  Distracter  701  is formed by two distracter handles  701   a  and  701   b  attached to a pivot  710  on collar  703  Each prong  706  also is formed by two blades  706   a  and  706   b  attached to the pivot  710 . Separating distracters  701   a  and  701   b  would cause blades  706   a  and  706   b  to move apart also. Thus, in operation, blades  706   a  and  706   b  would be inserted between two adjacent vertebrae. Distracter handles  701   a  and  701   b  would be moved apart causing the blades to move apart and open the intervertebral space. To ease insertion of the blades between adjacent vertebrae, the blades should be as thin as possible, but thick enough to withstand the force necessary to separate the vertebrae without fracture Further, is would be possible to jog the blades  706   a  and  706   b  off the centerline so that the blades would be at a slight angle. For example, if blades  706   a  and  706   b  were angled to the left (top) to right (bottom) and a jog (not shown) connected the blades  706   a  and  706   b  to the pivot  710 . In this case, the angle of the blades would make it easier for the surgeon to insert the blades between the vertebrae In this case, it would be preferable if the jog and blades formed an acute angle  
     [0032] Impactor  700  is shown with handle  702  and distracter handles  701   a  and  701   b . This is because in operation, the distracter is placed with the graft residing above the intervertebral space. The blades  706   a  and  706   b  and distracter handles  701   a  and  701   b  are inserted between adjacent vertebrae. The distrater handles  701   a  and  701   b  are separated causing blades  706   a  and  706   b  to separate and open the intervertebral space. With the space open, handle  702  having the cervical plate and bone graft attached to cervical plate holder  704  is lowered relative to the distracter and blades until the bone graft and plate are placed. The distracter handles are closed causing the vertebrae to close and squeeze the bone graft. While other design possibilities are within the spirit and scope of the present invention, it is believed relative movement between the handle and distracter handles/blades is the easiest to implement in surgery.  
     [0033] As an alternative to the blade method above, the prongs  706  could be wedge shaped. In this case, the distracter  701 , collar  703  and pivot  710  could be removed from the mechanism The prongs  706  would then start at a point at the end and angle outward and upward towards the handle  702  The wedge would separate the adjacent discs allowing placement of the bone graft in the intervertebral space. In this case, while the wedge and bone graft could move together, it may be beneficial to include a distracter and collar so the wedge could open the space prior to insertion of the bone graft.  
     [0034] Once the bone graft is placed using either style, the impactor  700  would be completely removed from the patient Thus, the cervical plate would be releasably coupled to the cervical plate holder of the impactor prior to insertion. FIG. 8 shows a top side elevation view of the impactor  700  holding a cervical plate  802 . Cervical plate  802  is shown without a viewing window or a bone graft, but one could be used if desired. Further, FIG. 8 shows impactor  700  without the jog and using blades instead of a wedge.  
     [0035]FIG. 9 is a flowchart  900  illustrating using the impactor  700  with the cervical plate  802  For convenience, flowchart  900  is described for insertion of a single bone graft. One of skill in the art will recognize on reading the disclosure, however, that the device and procedure would be usable with insertion of multiple bone grafts. Initially, the surgeon sizes a bone graft with the bone graft sizers, step  902 . For a single level fusion, once the bone graft is sized, the size of the cervical plate is automatically determined because the relationship between the end of the bone graft and the overhang on the cervical plate needed to ensure the screw holes of the cervical plate are optimally placed over the adjacent vertebral bodies is fixed, step  904 . Once the cervical plate and bone graft are sized, the surgeon attaches the bone graft and the cervical plate, step  906 . Next, the impactor is releasably attached to the cervical plate, step  908 . The impactor with the cervical plate and bone graft is used to separate the adjacent vertebrae, step  910 . With the impactor holding the adjacent vertebrae apart, the bone graft is inserted in the intervertebral space such that the screw holes of the cervical plate are placed to facilitate anchoring to the adjacent vertebrae, step  912 . The impactor is removed allowing the adjacent vertebrae to hold the bone graft and cervical plate in place, step  914 . Finally, the cervical plate is anchored to the vertebrae, step  916   
     [0036] While the invention has been particularly shown and described with reference to some embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.