Abstract:
The present application describes a spinal cross-connector and related methods for augmenting and stiffening spinal fixation constructs. The cross connector may include multiple rod-stabilization members that simultaneously engage respective rods of a fixation construct. Simultaneous engagement by the rod-stabilization members may be effectuated by a single locking step.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This is a U.S. Patent Application claiming the benefit of priority under 35 USC 119( e ) of commonly owned and U.S. Provisional Patent Application No. 61/221,525 entitled “Systems and Methods for Anterior Fixation of the Spine,” filed Jun. 29, 2009, and U.S. Provisional Patent Application No. 61/233,287 entitled “Spinal Cross Connector,” filed Aug. 12, 2009, the entire contents of which are hereby expressly incorporated by reference into this disclosure as if set forth fully herein. 
    
    
     FIELD OF THE PRESENT INVENTION 
     The disclosed system and associated methods relate to spinal instrumentation for use and implantation during spine surgery. 
     BACKGROUND 
     The spine is formed of a column of vertebrae that extends between the cranium and pelvis. The five sections of the spine are the cervical, thoracic, lumbar, sacral, and coccygeal regions. There are 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal vertebrae. Cervical, thoracic, and lumbar vertebra are separated from one another by intervertebral discs that absorb shock, allow for movement, and maintain appropriate spacing between the vertebrae. The main functions of the spine include providing skeletal support and protecting the spinal cord. Even slight disruptions to either the intervertebral discs or vertebrae can result in serious discomfort due to compression of nervous tissue within or extending from the spinal canal. If a disruption to the spine becomes severe enough, consequences may include pain, loss of sensation, paralysis, etc. . . . Thus, it is of great interest and concern to be able to both prevent and correct ailments of the spine. 
     Surgical intervention, when needed, for treating various spinal ailments often entails fixing two or more vertebrae relative to each other. Spinal fixation constructs often use a combination of rods, plates, pedicle screws and bone hooks for constructing a rigid framework and anchoring it to the affected vertebrae. The optimal configuration required for each patient varies according to the patient&#39;s anatomical characteristics, the specific ailment being treated, and surgeon preference, among other factors. At times, the strength and stability of these custom configurations may be compromised as a result of torsional forces placed on the rods that span two or more vertebrae. 
     Spinal cross connectors are often implanted horizontally between two vertical rods to provide extra stability and decrease the torsional forces acting upon the rods in the customized surgical construct. Implantation of some spinal cross connectors known in the prior art can be time-consuming because locking more than one locking mechanism is required. Needs still exist for modular spinal fixation systems and components that provide maximum strength and stability in an easy-to-use fashion. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a front perspective view of a spinal cross connector assembly engaging two rods, according to one example embodiment; 
         FIG. 2  is a back perspective view the cross connector assembly of  FIG. 1  engaged with a pair of rods; 
         FIG. 3  is a cross section view of the cross connector assembly taken along line  3 - 3  of  FIG. 1 ; 
         FIG. 4  is a cross section view of the cross connector assembly taken along line  4 - 4  of  FIG. 2 ; 
         FIG. 5  is a side view cross section of the cross connector assembly of  FIG. 3 ; 
         FIG. 6  is an exploded view of the cross connector assembly of  FIG. 1 ; and 
         FIG. 7  is a side view cross section of a cross connector assembly, according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Illustrative embodiments of the invention are described below. In the interest of clarity, not all features of an actual implementation are described in this specification. It will of course be appreciated that in the development of any such actual embodiment, numerous implementation-specific decisions must be made to achieve the developers&#39; specific goals, such as a compliance with system-related and business-related constraints, which will vary from one implementation to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking for those of ordinary skill in the art having the benefit of this disclosure. The cross connector assembly disclosed herein boasts a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIGS. 1-6  illustrate a cross connector assembly  10  according to one example embodiment. The cross connector assembly  10  is sized and dimensioned to be attached to two elongate members (e.g. rods  50 ), fixed generally parallel to each other across at least one spinal segment. The cross connector assembly provides additional support to the two elongate members, particularly in resisting torsional stress. The cross connector assembly  10  includes a set screw  11 , an adjustable wedge  12 , a housing  15 , a closure plate  14 , and a set of securing blocks  13 . Preferably, the cross connector assembly  10  is composed of a surgical-grade metal (e.g. titanium, stainless steel, etc. . . . ), but may also be composed of a surgical-grade polymer (e.g. poly-ether-ether-ketone (PEEK)) or any other material suitable for the applications of the present invention. Additionally, the cross connector assembly  10  may be composed of a combination of both metal and polymer materials. 
     The housing  15  includes at least one tool engaging feature  24  situated along the first and second side surfaces  25 ,  26  of the housing  15  for enabling the engagement of a variety of tools. These tools can be used to assist in the placement of the cross connector assembly  10  during a surgical procedure. The housing  15  further includes a cavity  20  which extends generally perpendicular into the housing  15  from the front surface  21 . The cavity  20  includes at least one internal thread  22  for threadably receiving the set screw  11  into the housing  15 . The advancement of the set screw  11  into the housing  15  facilitates securing the elongate members to the housing  15 , as will be described in greater detail below. 
     Additionally, the housing  15  includes two arched recesses  23  that are each shaped and dimensioned to allow the secure reception of an elongate member (e.g. rod  50 ). Although the arched recesses  23  are arched in this example, it will be appreciated that the size and shape of the recess may be adapted to complement non-cylindrical rods as well. Permanently securing the elongate members within the arched recesses  23  involves the radial translation of the securing blocks  13  within the housing  15 , such that they are forced out towards the elongate members. The radial translation of the securing blocks  13  is caused by advancement of the set screw  11 , as will be discussed in more detail below. 
     A closure plate  14  may be secured at the base  18  of the housing  15  and may be provided with a radial profile along its interior and exterior surfaces  52 ,  51  so that when the cross connector assembly  10  is viewed from the top or bottom (as best illustrated in  FIG. 5  and  FIG. 7 ) the exterior surface  51  of the closure plate  14  is generally concave. The concave feature of the cross connector assembly  10  allows the closure plate  14  to avoid unnecessary dural impingement once the cross connector assembly  10  is implanted, particularly when the cross connector assembly  10  is assembled to a posterior spinal fixation assembly. It is also contemplated that the cross connector assembly may not have a closure plate  14 . In such an embodiment, the securing blocks  13  may be contained and guided by pins or other suitable retaining mechanisms. 
     The internal surface  52  of the closure plate  14  includes at least two bumpers  53  which extend at least partially along the internal surface  52  of the closure plate  14  and interact with the positioning cavities  61  of the securing blocks  13  (as best illustrated in  FIGS. 3 and 6 ). The bumpers  53  at least partially function to assist in the positioning of the securing blocks  13 . Radial translation of the securing blocks  13  is at least partially guided by the radial indented slots  27  (as best shown in  FIG. 6 ) within the housing  15 . 
     Securing blocks  13  frictionally engage the elongate members at their engagement surfaces  62 . The engagement surface  62  of the securing block  13  and/or the surfaces within the arched recesses  23  may have surface features, or surface roughening, to enhance the frictional engagement between the cross connector assembly  10  and elongate members for secure positioning. The cross connector assembly  10  is preferably provided in multiple sizes for versatility. The housing  15  may be dimensioned, for example, so that the distance between the center of the first arched recess  23  and the center of the second arched recess  23  is approximately within the range of about 11-80 mm. 
     The securing blocks  13  include a tapered surface  67  which allows the spherical wedge  42  of the adjustable wedge  12  to apply force onto the securing block  13  and force the securing block  13  to translate towards the arched recess  23 . Wings  68  extend out from both sides of the securing blocks  13  and mate with indented slots  27  within the housing  15 . The indented slots  27  provide a pathway for the wings  68  to travel through the housing  15  and assist in maintaining proper alignment of the securing blocks  13 . The indented slots  27  are radially disposed so that the wings  68  (which may also have a radial side profile) guide the translation of the securing blocks  13  radially through the housing  15 . 
     The set screw  11  of the cross connector assembly  10  includes a generally recessed tool engagement feature  30  centrally located at a first end which functions to engage a variety of tooling that assist in advancing the set screw  11  into the housing  15 . Centrally located at a second end of the set screw  11  is a spherical recess  35 . The spherical recess  35  provides a socket for the spherical joint end  41  of the adjustable wedge  12 , such that the adjustable wedge  12  and set screw  11  interact similar to a ball and socket joint. At least one exterior thread  43  radially extends from the outer surface of the set screw  11  for threaded advancement into the housing  15 . Upon advancement of the set screw  11  along its central axis into the housing  15 , the spherical recess  35  pushes against the spherical joint end  41  of the adjustable wedge  12 . As the adjustable wedge  12  is forced in the direction of the securing blocks  13 , the adjustable wedge  12  swivels within the spherical recess  35  to align and compress the spherical wedge  42  evenly between the pair of securing blocks  13 . 
     The adjustable wedge  12  includes a spherical joint end  41  which, as described above, mates and interacts with the spherical recess  35  of the set screw  11 . During assembly of the cross connector assembly  10 , the spherical joint end  41  is mated with the spherical recess  35  of the set screw  11 . The circumferential distal end of the set screw  11  may be then slightly bent inward so that the spherical joint end  41  of the adjustable wedge  12  is unable to completely disengage from the set screw  11  while still allowing the adjustable wedge  12  to freely rotate and articulate. At the opposite end of the adjustable wedge  12  is the spherical wedge  42  which rests in contact with the tapered surfaces  67 . The ability of the spherical wedge  42  to align itself evenly between the tapered surfaces  67  (by way of the spherical joint end  41  swiveling in the spherical recess  35 ) allows the spherical wedge  42  to distribute force evenly between the pair of securing blocks  13 . Radial translation of the securing blocks  13  thus occurs evenly, even in the presence of geometric variations (e.g. machining, tolerances, etc.) that could otherwise result in the uneven application of force to the securing blocks  13 , and ultimately to the elongate members. The adjustable wedge  12  thus ensures even force is applied to each of the securing blocks  13 , resulting in equal compression on the elongate members and secure engagement therein. 
       FIG. 7  illustrates another embodiment of the present cross connector assembly  10  wherein the radial curvature of at least the closure plate  14 , indented slots  27 , and top and bottom surfaces  65 ,  66  of the securing blocks  13  can be observed. As mentioned above, the radial curvature of the closure plate  14  assists in avoiding dural impingement once the cross connector assembly  10  is implanted, particularly when the cross connector assembly  10  is assembled to a posterior spinal fixation assembly. Additionally, this embodiment illustrates the possibility for the set screw  11  and adjustable wedge  12  to be positioned offset from the center of the housing  15 , without deviating from the scope of the invention. Accordingly, the securing blocks  13  assembled within the housing  15  may be dimensioned differently depending upon the desired set screw  11  positioning. 
       FIGS. 1 ,  2 , and  5  illustrate an example embodiment of a cross connector assembly  10  assembled to a pair of elongate structures (e.g. rods  50 ) which make up at least a part of a spinal fixation assembly (not shown). Preferably, the cross connector assembly  10  is inserted laterally into a patient&#39;s spine and assembled to elongate members that make up at least a portion of a lateral spinal fixation assembly. For example, once a pair of rods  50  are surgically implanted and positioned such that they are generally parallel to each other along at least a portion of a lateral aspect of the spine, the cross connector assembly  10  can then be assembled to the pair of rods  50 . It is envisioned that the cross connector assembly  10  may also be sized and dimensioned to be inserted posteriorly into a patient&#39;s spine and assembled to elongate members that make up at least a portion of a posterior spinal fixation assembly. For example, once a pair of rods  50  are surgically implanted and positioned such that they are generally parallel to each other along at least a portion of a posterior aspect of the spine, the cross connector assembly  10  can then be assembled to the pair of rods  50 . 
     To assemble the cross connector  10  to a pair of rods, a first arched recess  23  of the cross connector  10  is aligned and placed over a section of a first rod  50 . Then a second arched recess  23  of the cross connector is aligned and placed over a section of the second rod  50 . 
     The cross connector assembly  10  may be provided with machined slots  29  located at the distal end of each of the arched recesses  23  which form tabs  28 . The tabs  28  may be slightly bent inward (not shown) toward the arched recess  23 . The bent tab  28  deflects outward as the elongate member passes. Once an elongate member clears the tab  28 , the bent tab  28  returns to its original formation which produces a tactile indication to the user that the elongate member is positioned completely within the arched recess  23 . Additionally, the tab  28  assists in retaining the elongate member  50  within the arched recess  23  until the user is able to permanently secure the elongate members  50  with the set screw  11 . 
     The cross connector assembly  10  may be provided with the set screw  11  pre-engaged in an un-secured position into the housing  15 . When the cross connector assembly  10  is in the desired position along the rods  50 , tooling can be used to engage the tooling feature  30  at the exposed end of the set screw  11  and advance the set screw  11  in the direction of the securing blocks  13  within the housing  15 . As the set screw  11  is advanced towards the securing blocks  13 , the spherical recess  35  applies a force onto the spherical joint  41  of the adjustable wedge  12 . The applied force delivered by the set screw  11  onto the adjustable wedge  12  is a linear force directed along the centerline of the set screw  11 . As described above, the spherical joint  41  of the adjustable wedge  12  swivels within the spherical recess  35  to situate itself and equal force is transferred to the rods  40  and the rods  50  become securely engaged in the cross connector assembly  10 . Once the cross connector assembly  10  is securely engaged to the rods  50 , the engagement tool used to advance the set screw  11  can be disengaged from the tooling feature  30  and the cross connector assembly  10  can be left to remain permanently implanted. In the event the cross-connector needs to be removed, the set screw may be retracted back to the unlocked position, releasing the force on the securing blocks  13  such that the cross connector assembly  10  may then be pulled off of the elongate members. 
     While not specifically described above, it will be understood that various other steps may be performed in using and implanting the devices disclosed herein, including but not limited to creating an incision in a patient&#39;s skin, distracting and retracting tissue to establish an operative corridor to the surgical target site, advancing the implant through the operative corridor to the surgical target site, removing instrumentation from the operative corridor following insertion of the implant, and closing the surgical wound. Furthermore, procedures described, for example only, may be applied to any region of the spine without departing from the scope of the present invention and dimensioning of the implant may be adjusted to accommodate any region. 
     While this invention has been described in terms of a best mode for achieving this invention&#39;s objectives, it will be appreciated by those skilled in the art that variations may be accomplished in view of these teachings without deviating from the spirit or scope of the invention.