Abstract:
An apparatus for connecting a pair of bone screws of a vertebral level includes a first end member, a second end member, and a transverse member. The first end member includes a track for removably attaching to a head of a first one of the bone screws. The second end member includes a track for removably attaching to a head of a second one of the bone screws. The transverse member connects the first and second end members.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 61/446,361, filed on Feb. 24, 2010, and is incorporated herein by reference in its entirety. This application is related to co-pending U.S. Application No.______ , docket number: 0137US2 entitled “APPARATUS FOR LINKING IMPLANTS AND REDUCING DEFORMITIES”. 
     
    
     FIELD 
       [0002]    The present disclosure generally relates to the field of spinal orthopedics, and more particularly to an apparatus for linking spinal implants and reducing spinal deformities 
       BACKGROUND 
       [0003]    The spine is a flexible column formed of a plurality of bones called vertebrae. The vertebrae are hollow and piled one upon the other, forming a strong hollow column for support of the cranium and trunk. The hollow core of the spine houses and protects the nerves of the spinal cord. The different vertebrae are connected to one another by means of articular processes and intervertebral, fibrocartilaginous bodies. Various spinal disorders may cause the spine to become misaligned, curved, and/or twisted or result in fractured and/or compressed vertebrae. It is often necessary to surgically correct these spinal disorders. 
         [0004]    The spine includes seven cervical (neck) vertebrae, twelve thoracic (chest) vertebrae, five lumbar (lower back) vertebrae, and the fused vertebrae in the sacrum and coccyx that help to form the hip region. While the shapes of individual vertebrae differ among these regions, each is essentially a short hollow shaft containing the bundle of nerves known as the spinal cord. Individual nerves, such as those carrying messages to the arms or legs, enter and exit the spinal cord through gaps between vertebrae. 
         [0005]    The spinal disks act as shock absorbers, cushioning the spine, and preventing individual bones from contacting each other. Disks also help to hold the vertebrae together. The weight of the upper body is transferred through the spine to the hips and the legs. The spine is held upright through the work of the back muscles, which are attached to the vertebrae. While the normal spine has no side-to-side curve, it does have a series of front-to-back curves, giving it a gentle “S” shape. If the proper shaping and/or curvature are not present due to scoliosis, neuromuscular disease, cerebral palsy, or other disorder, it may be necessary to straighten or adjust the spine into a proper curvature. 
         [0006]    Generally the correct curvature is obtained by manipulating the vertebrae into their proper position and securing that position with a rigid system of screws and rods. The screws may be inserted into the pedicles of the vertebrae to act as bone anchors, and the rods may be inserted into heads of the screws. Two rods may run substantially parallel to the spine and secure the spine in the desired shape and curvature. Thus the rods, which are shaped to mimic the correct spinal curvature, force the spine into proper alignment. Bone grafts are then placed between the vertebrae and aid in fusion of the individual vertebrae together to form a correctly aligned spine. 
         [0007]    In addition, transverse or cross-link connectors may be attached to couple one spinal rod to the other spinal rod in order to reduce torsional forces on the spinal rods and provide a more rigid construct. The connectors may include clamps or other attachment features that typically require some clearance between the spinal rod and the vertebrae and/or the heads of the screws. Various spinal features, such as the spinous process and the superior articular process, may extend between the spinal rods. These spinal features may interfere with and limit options for placement of the connectors. Thus, it may be desirable to provide a more flexible system for linking spinal rods that is less impacted by clearances and/or interference. 
       SUMMARY 
       [0008]    An apparatus for connecting a pair of bone screws of a vertebral level includes a first end member, a second end member, and a transverse member. The first end member includes a track for removably attaching to a head of a first one of the bone screws. The second end member includes a track for removably attaching to a head of a second one of the bone screws. The transverse member connects the first and second end members. 
         [0009]    In other features, each of the tracks engages with a channel on corresponding ones of the heads. The transverse member includes an arcuate profile. Each track includes a locking feature to engage that engages with an attachment feature of each head. The locking feature includes a projection and the attachment feature includes a recess. The end members include apertures that align with threaded apertures of the heads, wherein a set screw couples the end members to the heads. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a partial perspective view of an exemplary cross-link apparatus for linking implants, such as bone anchors, in vertebrae of a spinal column according to the principles of the present disclosure. 
           [0011]      FIG. 2  is a perspective view of a head of an exemplary bone anchor according to the principles of the present disclosure. 
           [0012]      FIG. 3  is a partial perspective view of the cross-link, bone anchor, and a spinal rod according to the principles of the present disclosure. 
           [0013]      FIG. 4  is a partial perspective view of an end of the cross-link according to the principles of the present disclosure. 
           [0014]      FIG. 5  is another partial perspective view of the end of the cross-link according to the principles of the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The systems and methods for linking implants and reducing deformities of the present disclosure include various features to enable linking of implants, such as bone anchors, pedicle screws, and the like, transversely using cross-links The cross-links attach to the heads of the screws and eliminate the need for clearance between the spinal rods and the vertebrae. The cross-links bypass spinal features that may otherwise interfere with passage of the connector across the vertebrae. The cross-links include other features to enable linking of multiple cross-links longitudinally along the spinal column using a coupling feature and longitudinal members. The longitudinal members attach to the coupling features to link each cross-link to provide a more rigid construct. Furthermore, the cross-links include other features to enable attachment of instruments to assist with derotation of the spine using an attachment feature. The instruments may apply forces to the cross-link at the attachment feature during derotation. Because the bone anchors are linked by the cross-link and longitudinal members, stresses due to the forces may be distributed across two or more bone anchors, thus reducing the likelihood of damage to the screws, heads, and/or vertebrae. 
         [0016]    Embodiments of the invention will now be described with reference to the Figures, wherein like numerals reflect like elements throughout. The terminology used in the description presented herein is not intended to be interpreted in any limited or restrictive way, simply because it is being utilized in conjunction with detailed description of certain specific embodiments of the invention. Furthermore, embodiments of the invention may include several novel features, no single one of which is solely responsible for its desirable attributes or which is essential to practicing the invention described herein. The words proximal and distal are applied herein to denote specific ends of components of the instrument described herein. A proximal end refers to the end of an instrument nearer to an operator of the instrument when the instrument is being used. A distal end refers to the end of a component further from the operator and extending towards the surgical area of a patient and/or the implant. 
         [0017]    Referring now to  FIG. 1-5 , a system  100  for linking implants and reducing deformities of the spine includes bone anchors  102 , cross-links  104 , and spinal rods  106 . A surgeon may drill and tap holes in the vertebrae to receive screws  108  of the bone anchors  102 . In other examples, the screws  108  may be self-tapping. Heads  110  may be coupled to the screws  108  prior to or after securing the screws  108 . The heads  110  may be configured to receive the spinal rods  106  as shown in  FIG. 3 . The cross-links  104  may attach to the heads  110  to link pairs of the bone anchors  102  transversely across the spinal column. Once the spinal rods  106  have been inserted into the heads  110 , a setscrew or other locking mechanism may be used to secure the rods  106 . An exemplary bone anchor assembly may be found in U.S. Pub. No. 2010/0036443, entitled “Systems and Methods for Spinal Fixation”, incorporated herein by reference. The cross-link  104  includes a transverse member  112  and end members  114  that attach to the heads  110  of the bone anchors  102 . The transverse member  112  may include curvature or an arcuate profile to enable clearance of any features of the vertebrae such as the spinous process or articular processes. In  FIG. 1 , the spinous processes of the vertebrae have been removed only to provide clear view of the cross-links  104  of the system  100 . 
         [0018]    Referring now to  FIG. 2 , the head  110  of the bone anchor  102  may include various features that enable insertion of the spinal rod  106  and attachment of the cross-link  104 . The head  110  includes a passageway  140  that is sized and configured to accommodate placement and securing of a rod. For example, the passageway  140  may include a curved distal portion  142  and two side portions  144  extending proximally therefrom to form a U-shaped portion of the head  110 . The curved portion  142  may include a radius of curvature that corresponds to the diameter of the spinal rod  106 . The two side portions  144  may include threads (not shown) configured to receive setscrews (not shown) that lock the spinal rods  106  within the heads  110 . To secure the rod  106  inside the screw head  110 , the rod  106  is placed into the passageway  140  and then the set screw is placed on top of the rod  106  and secured using threads disposed on the interior walls of the passageway  140 . 
         [0019]    The passageway  140  can be configured to include recessed edges or channels  146  that are configured to accommodate placement of the end member  114  of the cross-link  104 . Each side portion  144  includes additional features for attachment of the cross-link  104 . For example, the side portion  144  may include the channels  146  extending from the proximal end of the head  110  towards the curved portion  142  of the passageway  140 . A proximal end of the channel  146  may be tapered towards a top surface  148  of the head  110 . The taper may ease insertion of the cross-link  104  as described in detail below. The distal end of the channel  146  may include an attachment feature  150 , such as a pocket, dimple, or recess that provides a snap-fit attachment of the cross-link  104 . Other features may include a recessed portion  152  for attachment of various other instruments such as rod reducers and adjustment instruments for seating the spinal rod  106  within the head  110 . 
         [0020]    Referring now to  FIGS. 3-5 , the cross-link  104  includes features that may provide sliding engagement with the channels  146  on the head  110  and secure attachment to the attachment feature  150 . In  FIG. 8 , the transverse member  112  terminates in the end member  114 . The end member  114  includes a cavity  156  configured to engage with one of the side portions  144  of the head  110 . For example, the cavity  156  may include a contoured portion  158  that corresponds with curvature of the side portion  144  of the head  110 . Side walls  160  of the end member  114  wrap around the channels  146  on the head  110  and further include protrusions or tracks  162  that slidably engage within the channels  146 . A locking feature  164  of the track  162 , such as a projection or bump stop, may be configured to couple with the attachment feature  150  on the head  110 . The locking feature  164  may provide permanent and/or temporary attachment of the cross-link  104  to the heads  110 . In other examples, the transverse member  112  may include an aperture  166  that aligns with a threaded aperture  154  in the head  110 . The aperture  166  may communicate with the posterior surface  120 , passing through the end member  114 , and communicate with the interior contoured portion  158 . A set screw (not shown) inserted through the aperture  166  may secure the transverse member  112  to the head  110  via the threaded aperture  154 . In addition, tabs (not shown) similar to the tabs of the screw extenders in the U.S. Pub. No. 2010/0036443, may removably couple with the recessed portion  152  of the head  110 . 
         [0021]    Furthermore, because the cross-links  104  are attached to the side portions  144  of the heads  110 , the spinal rods  106  may be inserted after the surgeon has positioned the vertebrae for the correct curvature. When the spinal rods  106  are inserted prior to the derotation process, the forces on the bone anchors  102  may cause elements of the system  100  and the vertebrae to pivot about the spinal rods. Thus, without the spinal rods  106 , the system  100  and vertebrae may be positioned more freely than when the spinal rods  106  are attached. 
         [0022]    Example embodiments of the methods and systems of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.