Abstract:
An apparatus for connecting between an upper cervical vertebrae and a cervical fixation network that includes a screw for rotationally entering and gripping the upper cervical vertebrae. A bridge is configured to route between the cervical fixation network and the screw. A connector holding the screw and bridge together includes a portion of the screw and the bridge that is configured differently for a complementary, low profile engagement of the bridge and screw in which varying configurations of the connector and bridge, either alone, or in combination, are envisioned.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
       [0001]    This application claims the benefit of U.S. Provisional Application Ser. No. 60/906,272 filed on Mar. 12, 2007, which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to cervical support devices, and, more particularly, to a system for providing low profile cervical support to the vertebrae. 
       BACKGROUND OF THE INVENTION 
       [0003]    With the advent of modern surgical techniques, methods and systems using rigid cervical support devices have been developed to manage instability of the upper cervical spine in a human body. Such methods and systems have been implemented successfully in patients with cervical disorders requiring stabilization resulting in improved spinal support for the neck and head as well as improvements in relief from pain resulting from such instability. 
         [0004]    One drawback to systems providing sub-axial cervical spine fixation is stabilization support for certain upper vertebrae, referred to as the C1 and C2 vertebrae. Until recently, common techniques for the placement of screws in the C2 for fixation to a fixation network such as a lateral mass screw and rod fixation system resulted in significant risks to the vertebral artery. These risks were reduced by the discovery of techniques for the unique placement of screws in the C2 for connecting the C2 to the rigid cervical rods. A description of C2 fixation problems and a technique of the type suitable for solving such problems is disclosed in “Posterior C2 Fixation Using Bilateral, Crossing C2 Laminar Screws” by Neil M. Wright, MD in the Journal of Spinal Disorders &amp; Techniques, Vol. 17, No. 2 (April 2004), which is incorporated herein by reference. 
         [0005]    While fit for their intended purpose, one problem created by such C2 fixation techniques is that the location and angle of the screw entry and alignment is not well suited for screw insertion and attachment to a rigid cervical rod using existing rigid cervical fixation hardware during surgery. 
         [0006]    Thus, the need exists for a system and method to connect the C2 vertebrae to a fixation schema using the improved techniques that reduce risk to the vertebral artery that have been identified above. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention relates to an apparatus for connecting between an upper cervical vertebrae and a cervical fixation network that includes a screw having a portion with a tapered shaft with a helical rim for rotationally entering and gripping the upper cervical vertebrae. A bridge is configured to route between the cervical fixation network and the screw. A connector holding the screw and bridge together includes a portion of the screw and the bridge that is configured differently for a complementary, low-profile engagement of the bridge and screw. 
         [0008]    The invention further includes a device for connecting to an upper cervical vertebrae including a screw having a portion with a tapered shaft threaded for rotationally entering and gripping the upper cervical vertebrae. The screw includes a connector portion for directly contacting a strip routed to a cervical fixation network to provide a low profile connection. 
         [0009]    In another aspect of the invention, a device is included for connecting between a post anchored in an upper cervical vertebrae and a cervical fixation network. The device includes a bridge having at least one end configured for complementary connection to a post. The bridge includes at least one portion that adjusts relative to the post for routing of the bridge between the post and the cervical fixation network. 
         [0010]    In yet another aspect of the invention, a connector for use in a cervical fixation device includes a base configured to receive at least two rods in a locking engagement. The base includes at least one channel having an aperture to receive at least one rod at any location along a shaft of the rod and a set screw fastened into the base to hold the at least two rods against the base. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Other aspects, advantages and novel features of the invention will become more apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings wherein: 
           [0012]      FIG. 1  is a diagram incorporating functional block for certain structures of a screw with a connector and bridge according to the present invention; 
           [0013]      FIG. 2A  is a top plan view of a screw according to the present invention; 
           [0014]      FIG. 2B  is a side view of the screw in  FIG. 2A  according to the present invention; 
           [0015]      FIG. 2C  is an exploded perspective side view of a screw with a connector according to the present invention; 
           [0016]      FIG. 3A  is a top plan view of a screw according to the present invention; 
           [0017]      FIG. 3B  is a side view of the screw in  FIG. 3A  according to the present invention; 
           [0018]      FIG. 4A  is a top plan view of a screw according to the present invention; 
           [0019]      FIG. 4B  is a side view of the screw in  FIG. 4A  according to the present invention; 
           [0020]      FIG. 5  is a side view of a bridge according to the present invention; 
           [0021]      FIG. 6  is a side view of a bridge according to the present invention; 
           [0022]      FIG. 7  is a side view of a bridge according to the present invention; 
           [0023]      FIG. 8  is a side view of the screw with connector of  FIG. 2C  and bridge of  FIG. 6  connected between a C2 vertebrae and a fixation network according to the present invention; 
           [0024]      FIG. 9A  is a front view of an alternate screw and bridge configuration according to the present invention; 
           [0025]      FIG. 9B  is a side view of the screw and bridge of  FIG. 9A  with a different rotational displacement relative to  FIG. 9A  according to the present invention; 
           [0026]      FIG. 10A  is a side view of a connector according to the present invention; and 
           [0027]      FIG. 10B  is a front view of the connector of  FIG. 10A  according to the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    With reference to the drawings for purposes of illustration, an improved system  20  is provided for fixation of the C2 to a rigid cervical fixation network  22  such as, but not limited to, a screw and rod system, using a screw or post  24 . Advantageously, a low profile bridge  26  is provided between the rigid cervical fixation network  22  and the screw  24 . Furthermore, a connector  28  is included that facilitates connection of the screw  24  to the bridge  26 . Presently the screw  24 , connector  28  and the bridge  26  may be made from any material or material combination, without limitation, suitable for insertion into a living body. For example, but not by means of limitation, the materials may include stainless steel, a cobalt/chrome alloy, titanium or any alloy combination thereof. Presently, titanium alloy materials are preferred in the medical community and therefore, for that reason, would be preferred in this invention. However, changes in materials preferred by the medical community may be substituted so long as those substitutions conform to the preferred features of the invention described below, including, but not limited to, strength of the screw to withstand rotational torque into a bone mass and strength of the combination of the screw with connector and the bridge to provide the desired amount of cervical fixation. 
         [0029]    C2 screw and Connector 
         [0030]    With reference to  FIGS. 2A-C , the screw  24  is a threaded fastener that includes a shaft  30 , cylindrical and tapering to a point  32  at one end with a helical ridge  34  or thread formed on it. The helical ridge is of the self-tapping type for rotational insertion into the C2 vertebrae. The shaft diameter narrows to form a shaft connector portion  36 , cylindrical and non-tapering with a helical ridge or thread  38  formed on it. A ledge or ridge  40  is formed at the point along the shaft where the wider tapered shaft transitions to the non-tapered head shaft portion  36 . The helical ridge  38  of the shaft connector portion  36  is of a non-self tapping type for insertion into an aperture  42  of a nut  44  ( FIG. 2C ) preformed with a complementary cylindrical wall having a helix. The free end of the shaft connector portion ( FIG. 2A ) is shaped to allow locking engagement  46  with a fastening tool such as a screwdriver or wrench. As presently illustrated in  FIG. 2A , a hexagonal socket  46  for receiving a hex wrench is shown which permits rotation of the shaft causing the tapered portion of the shaft to be received in the C2 vertebrae. At the region of the ridge  40 , the ridge preferably has radial width of 0.5 mm where the shaft of the shaft connector portion  36  has a radial diameter of 1 to 2 mm and the shaft of the tapered portion  30  at the ridge has a diameter of 3 to 4 mm. The length of the screw may vary according to the size of the C2 vertebrae in which the screw is to be inserted. 
         [0031]    The shaft connector portion  36  has a length sufficient to receive a wide slotted aperture  48  from a screw connector portion  50  of a strip  52  comprising a portion of the bridge about the narrow diameter of the shaft connector portion  36  that rests upon the ledge  40  of the shaft. The wide slotted aperture  48  extends along the length of the metal strip  52  for a length sufficient to allow positional adjustments between the metal strip  52  and the screw  24 . The nut  44  may include a locking device. Locking devices of the type suitable for this purpose may include, but are not limited to, nylon lock nuts, a serrated-face nut, a nut with a lock washer, such as a star washer, locking adhesives, a castellated nut with a pin, a split beam lock nut or any combination thereof. The nut  44  may be capped and may include an outer surface for tightening such as, but not limited to, a polygonal circumference for tightening by a wrench or a serrated face for gripping and tightening by hand or pliers. 
         [0032]    With reference to  FIGS. 3A-B , where like structures to  FIGS. 2A-C  incorporate the reference numerals above, a screw  24  having a tapered shaft portion  30  and a non-tapered shaft portion  36  includes a wider region  56  that tapers quickly from the ridge  40  to the tapered shaft diameter providing a conical outline similar to the bell of a bugle. The wider region  56  allows for the ridge width range to vary from 0.5 to 1 mm and for the range of the shaft connector portion  36  diameter to include a range of 1 to 4 mm. It should be noted that the wider region may be non-tapered and cylindrical without departing from the present invention. 
         [0033]    With reference to  FIGS. 4A-B , where like structures to  FIGS. 2A-C  incorporate the reference numerals above, a screw  24  having a tapered shaft portion  30  and a non-tapered shaft portion  36  includes a wider region  58  that extends between the two shaft portions providing a non-tapered outline having a polygonal shaped circumference that accommodates a rotational torque tool such as a wrench. For purposes of illustration only, a hexagonal shape is shown. The wider region  58  allows for the ridge width range to vary from 0.5 to 1 mm and for the range of the shaft connector portion  36  diameter to include a range of 1 to 4 mm. It should be noted that in this embodiment, the locking engagement  46  at the head of screw may be optional. 
         [0034]    Regardless of the embodiment preferred for a particular use, each of the screws described provides a threaded fastener for secure fixation to a bone mass. The connector features a low profile solution for fixation of the screw to a rigid cervical fixation network. Furthermore the connector configuration permits adjustment of the positional relationship between the bridge and the screw. 
         [0035]    Bridge 
         [0036]    With reference to  FIG. 5 , a bridge includes a plate or strip  52  in which the length of the bridge  26  is adapted for a general range of distances for connection between a C2 screw  24  and a rigid cervical fixation network  22 . The bridge width and thickness are proportionally configured in respective sizes according to criteria such as the modulus of elasticity of the material used, the forces received on the material when installed to provide fixed support under such forces in a fixation network, a degree of flexibility when a threshold of force is exceeded through manual pressure applied by a user during insertion to conform the plate to a compatible mating with each of the screw and the fixation network. The plate or strip  52  includes a fixation network connector  60  at one end in the form of a C-shaped sleeve  62  with a semi-cylindrical interior wall  64  with an opening for receiving a rod  66  from a fixation network. The opening of the sleeve faces out away from the opposite end of bridge. The C-shaped sleeve includes a rigid connection to the rod. The rigid connection may be accomplished by any rigid connection means suitable for a permanent rigid connection, which by way of example and not by limitation, can be by crimping or bending by force of the sleeve  62  onto the rod  66  or secured by a set screw  68  inserted through a bore hole  70  in the C-shaped sleeve  62  for rigid fixation of the rod between the screw and the C-shaped wall. A the opposite end of the bridge the strip includes the screw connector portion  74  having a wide slotted aperture  76  sized and shaped such that it is elongated along the length for spatial displacement of the bridge  26  relative to the screw  24  and dimensioned such that opposing sides the strip about the aperture may rest upon the ridge  40  ( FIG. 4C ) which snuggly receives the shaft connector portion  36  of the screw  24  there between. As presently illustrated, the bridge includes a generally 90-degree twist  78  ( FIG. 5 ) in the strip  52  to demonstrate in this written description that the region between the ends may be twisted and bent to route the bridge  26  from the screw having an angle of insertion at a point in the C2 vertebrae to a fixation network having a different angle and for providing a low profile path there between the contours of the bone masses along the route. The single 90-degree angle illustrated in the application is merely to facilitate understanding and illustration of the ends of the bridge while demonstrating the ability of the structure to be bent. 
         [0037]    With reference to  FIG. 6 , where like structures to  FIG. 5  incorporate the reference numerals above, the plate or strip  52  includes a fixation network connector  60  at one end in the form of a C-shaped sleeve  80  with a semi-cylindrical interior wall  82  with an opening for receiving a rod  66  from a fixation network. The opening of the sleeve faces inward toward the opposite end of bridge. The C-shaped sleeve  80  includes a rigid connection to the rod. The rigid connection may be accomplished by any rigid connection means suitable for a permanent rigid connection, which by way of example and not by limitation, can be by crimping or bending by force of the sleeve  80  onto the rod  66  or secured by a set screw  68  inserted through a bore hole  70  in the C-shaped sleeve  80  for rigid fixation of the rod  66  between the screw  68  and the C-shaped wall  82 . 
         [0038]    With reference to  FIG. 7 , where like structures to  FIG. 5  incorporate the reference numerals above, the plate or strip  52  includes a fixation network connector  60  at one end in which the strip transitions from a generally rectilinear cross-sectional shape to a generally cylindrical shape to form a rod  86  having a diameter sized to conventional rod diameters of a fixation network. The rod shape then may be connected to the fixation network using a fixation network connector for adding a rod to a fixation network. 
         [0039]    It will further be appreciated that other configurations for the fixation network connector may be used without departing from the features of the present invention. Furthermore, the bridge may span between to screws in which the opposite ends of the bridge may include screw connector portions  74  at each end. 
         [0040]    When in use, an example ( FIG. 8 ) of a screw  24 , a connector and bridge  26  is shown for attachment between a C2 vertebrae  100  and rod  102  of a fixation network  22  having two rods traversing the C2 vertebrae  100  and running the along the length of the spine for possible connection of the C2 vertebrae  100  to other vertebrae (not shown) as medically desired for the patient&#39;s medical needs. The embodiment of the screw  24  as shown in  FIG. 2C  and the embodiment of the bridge  26  as shown in  FIG. 6  are used for illustration purposes only, but where like reference numerals of like structures are used herein. Each of the screws  24  is entered into the lamina  104  portion of the C2 vertebrae  100  from opposing angled sides using conventional insertion techniques. As shown in this configuration there is no rotational configuration of the bridge  26  required. The fixation network connector  60  in this exemplary embodiment is made by both crimping and using the setscrew  68  to hold each bridge  26  rigidly with respective rods  102 . It is understood by one of ordinary skill in the art of fixation network insertion that any combination of the above described screws and bridges may be used to accomplish this connection. It is further understood by those skilled in the art of inserting fixation networks in a living body that the cervical structures encountered in a living body may vary and that screws and bridges of varying embodiments and dimensions within the ranges and lengths described may be provided and used as needed medically to make the connection. 
         [0041]    With reference to  FIGS. 9A-B , an alternative embodiment of a screw  120  and bridge  122  in the form of a rod in which the connector  124  is hingedly attached together by a hinge pin  125  to allow for the angle  126  of a thread tapered shaft portion  128  of the screw  120  to be adjusted relative to the angle of the bridge  122 . This configuration reduces the profile of the connector  124  at the screw  120  and allows for the bridge  122  to be angled appropriately after insertion of the screw  120  for routing to a fixation network, in which the rod shape of the bridge  122  is sized to conform with existing rod configurations for connection of the rod to a fixation network using connectors. As shown for purposes of illustration, the bridge  122  may be connected to another rod  130  using a connector  132  for two rods using a setscrew  134 . However, it will be appreciated by those skilled in the art that any of the connector configurations described above may be used herein without departing this invention. It will further be appreciated that this embodiment allows for the rotationally hinged connection between the screw and the bridge to operate as a manual insertion tool to facilitate rotational entry of the screw in the C2 vertebrae and at recommended location and insertion angle by bending of the hinge sufficiently to use the leverage of the bridge to achieve the desired rotational movement. 
         [0042]    With reference to  FIGS. 10A-B , a connector  200  formed to connect two rods traversing at generally 90 degrees includes generally base  202  having a seat  204  forming a channel with a C-shaped opening  206  for receiving a first rod  208  there through. The seat  204  is presently preferred to be, but not limited to, concave in cross-section. An aperture  210  allows for a second rod  212  to slide through the connector at an angle offset from the first rod. As presently illustrated the aperture  210  is generally perpendicular to the seat  204 ; however, the angular displacement of the aperture  210  relative to the seat  204  may vary and a plurality of connectors allowing for rods to intersect at various angles may be used. The first and second rods are held fast by the connector using a setscrew  214  inserted through a borehole  216  which the compresses the two rods  212  and  208  together between the setscrew  214  and the seat  204 . It will further be appreciated that the shape of the rods may be varied to increase the fastening between them by for example including a flat surface about at least a portion of the circumference such that when the two flat surfaces overlie each other the surface area in contact increases the amount of force required to move the rods relative to each other and the connector. 
         [0043]    Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.