Abstract:
Disclosed is a spinal transconnector device for coupling longitudinal spinal rods on either side of the mid-sagittal plane. The device includes two interconnected rod engagement elements, a first rod engagement elements having a vaulted surface adapted to secure to a first longitudinal spinal rod via an interference fit comprising compression of the first longitudinal spinal rod against the generally vaulted surface; and an interference pin that advances into a bore of the first rod engagement element forming an interference fit between the interference pin and the rod engagement element. The interference fit can be associated with elastic deformation of the first rod engagement element occurring as a consequence of the interference pin being advanced through the bore in the engagement element and contacting a surface of the first longitudinal spinal rod.

Description:
REFERENCE TO PRIORITY DOCUMENT 
     This application claims the benefit of priority of co-pending U.S. provisional patent application Ser. No. 61/013,595, entitled “Spinal Transverse Connector,” filed Dec. 13, 2007. Priority of the aforementioned filing date is hereby claimed and the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND 
     The use of spinal rods is conventional for correction of spinal trauma or conditions, such as curvature of the spine. Generally, an orthopedic stabilization system may include a pair of spinal rods that are coupled to a bone or bones. The rods are generally contoured and longitudinally disposed adjacent to vertebral bodies of a spine. 
     In some cases, a pair of spinal rods are fastened in parallel on either side of the spinous process. The assembly can be significantly strengthened by using at least one additional stiffening member known as a transverse connector or cross link to horizontally connect the pair of spine rods. A number of different transverse connectors are known. Generally, the transverse connectors should provide strength and control torsion. Stresses can act to return a stabilized bone system to a deformed position. For example, stresses on a spine and on a spinal stabilization system often operate to return a corrected spine to a deformed position. Transverse connectors can inhibit rod movement of the spinal stabilization system during a post-operative period so that the spine remains in a corrected position. 
     Rods of an orthopedic stabilization system can be aligned along a longitudinal axis of the spine generally parallel to each other on each side of the midline of the spine. Due to a wide variety of factors, two rods are rarely three dimensionally geometrically aligned. That is, two rods very rarely are located a uniform distance from each other along their entire length. Generally, the two rods have some convergence or divergence in the medial-lateral direction. The two rods may also not have the same orientation with respect to the coronal plane. The rods might also not have a coplanar geometry from a lateral view. 
     To address the variations of geometrical alignment, surgeons sometimes will bend the rods to accommodate a transverse connector or bend the transverse connector to accommodate the rods. In addition, transverse connectors have been developed that have some adjustability to adapt for variations from geometrical alignment. Two piece transverse connectors allow for the stabilization of rods that are oriented in different horizontal and vertical planes. Further, the connection between multi-shaft transverse connectors must resist shear to avoid separation and provide stability to the rods. 
     Because of the forces acting along the transverse connector and the movement of the spinal rods, the connection between the transverse connector and the rod must be secure to avoid movement of the transverse connector along the spinal rod. Some rod fastening systems of transverse connectors use threaded fasteners to attach the transverse connector to adjacent rods. The threaded fastener can be a set screw or a nut. Not tightening a threaded fastener enough may allow movement of the transverse connector. Overtightening a threaded fastener could result in damage to the system and failure of the transverse connector. 
     Installation of a spinal fixation device is a lengthy and complicated surgical procedure. Simplification of the assembly of the device will tend to reduce the complications associated with the procedure. 
     SUMMARY 
     There is a growing need for improved devices that link tissue structures in an animal body. In particular, there is a need for a simple spine fixation assembly having a minimum of components and a minimum of steps for installation. Further, there is a need for an easily adjustable transverse connector that can accommodate a variety of geometrical orientations. There is also a need for a transverse connector that resists movement along the spinal rod and a connector that avoids contact with the dura and spinal column during installation. 
     Disclosed in the present application is an apparatus that includes a central universal joint element that maintains the transverse connector in an A-frame architecture to protect the dura of the spinal column. The axis of the joint element of the device is roughly parallel with the general axis of the connecting rod elements. 
     In one embodiment, disclosed is a spinal transconnector device for coupling longitudinal spinal rods on either side of the mid-sagittal plane. The device includes two interconnected rod engagement elements, a first rod engagement element having a vaulted surface adapted to secure to a first longitudinal spinal rod via an interference fit comprising compression of the first longitudinal spinal rod against the generally vaulted surface. The device also includes an interference pin that advances into a bore of the first rod engagement element forming an interference fit between the interference pin and the rod engagement element. The interference fit is associated with elastic deformation of the first rod engagement element occurring as a consequence of the interference pin being advanced through the bore in the engagement element and contacting a surface of the first longitudinal spinal rod. 
     In another embodiment, disclosed is a spinal transconnector device for coupling longitudinal spinal rods on either side of the mid-sagittal plane that includes a first rod engagement element having a convex spherical element and a second rod engagement element. The second rod engagement element has a passage for receiving the convex spherical element, at least a portion of the passage having a first concave spherical surface geometry that can mate with at least a portion of the convex spherical element and an interference element having a second concave spherical surface geometry. The convex spherical element articulates within the passage and is sandwiched between the first concave spherical surface of the passage and the second concave spherical surface of the interference element. 
     In another embodiment, disclosed is a spinal transconnector device for coupling longitudinal spinal rods on either side of the mid-sagittal plane that includes two interconnected rod engagement elements each adapted to secure to a respective longitudinal spinal rod, the rod engagement elements interconnected in a manner that permits relative articulation therebetween. The relative articulation of the two rod engagement elements results from the separation or approximation of contacting elements of a deployment tool that engage surfaces on either of the rod engagement elements. Each contacting element has a mating surface with a generally spherical geometry. 
     In another embodiment, disclosed is a spinal transconnector device for coupling longitudinal spinal rods on either side of the mid-sagiftal plane that includes two interconnected rod engagement elements that are coupled by mating surfaces with segments of generally spherical surfaces, the rod engagement elements connected in a male-female relationship through an aperture, wherein the diameter of either of the mating spherical surfaces exceeds the diameter of the aperture. 
     In another embodiment, disclosed is a spinal transverse connector device for coupling spinal rods including first and second longitudinal elements, a connector element, and first and second interference elements. The first longitudinal element includes a threaded bore and a passage having a portion that intersects a portion of the threaded bore. The second longitudinal element includes a bore. The connector element connects the first and second longitudinal elements and includes a convex spherical region and a stem region. The convex spherical region extends into the passage of the first longitudinal element and the stem region extends into the bore of the second longitudinal element. The convex spherical region has a diameter that exceeds a diameter of an opening into the passage. The opening into the passage is surrounded by internal walls having partially spherical concave surface geometry. The first interference element includes a first surface that has a generally concave conical geometry and a second surface that has a generally concave spherical geometry. The second interference element includes a first region that has a convex truncated conical surface geometry and a second region that has a threaded surface geometry. Advancement of the second interference element into the threaded bore presses the first region of the second interference element against the first surface of the first interference element displacing the first interference element towards the convex spherical region of the connector element thereby pressing the convex spherical region against the internal walls surrounding the passage opening therein forming three generally spherical mating surfaces whose approximation to each other inhibits relative movement between the first and second longitudinal elements. 
     Other features and advantages will be apparent from the following description of various embodiments, which illustrate, by way of example, the principles of the disclosed devices and methods. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a perspective view of one embodiment of a transverse connector assembly. 
         FIG. 2  shows an exploded view of the transverse connector assembly embodiment of  FIG. 1 . 
         FIG. 3A  shows a side, cross-section view of the transverse connector assembly embodiment of  FIG. 1 . 
         FIG. 3B  shows a detail view at circle B of the transverse connector assembly embodiment of  FIG. 3A . 
         FIGS. 4A-4B  show a side view schematic of placement of the transverse connector of  FIG. 1  onto rods. 
         FIG. 5  shows a perspective view of an embodiment of a sleeve. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  shows an exemplary transverse connector  100  for interconnecting a pair of longitudinal members or rods (not shown in the figure) that can be connected to vertebrae of a spinal column. It is contemplated that the transverse connector  100  can interconnect any suitable longitudinal member, such as plates or rods of other shapes, such as hexagonal rods. The rods can be located anywhere along the spinal column. In one embodiment the longitudinal spinal rods are on either side of the mid-sagittal plane of the spine. Each of the rods can be elongate and have sufficient length to span at least two vertebrae. A plurality of fixation elements can connect the rods to the vertebrae. The fixation elements can be of any known or desired configuration. In an embodiment, the fixation elements are pedicle screw assemblies that include a receiver member that removably mates with a screw member in a poly-axial or mono-axial configuration. 
     At least one transverse connector  100  can interconnect rods across the vertebral midline. The transverse connector  100  blocks relative movement of the rods so that the vertebrae connected to the rods are maintained in their desired relative positions and do not pivot relative to an anterior/posterior axis or a longitudinal central axis of the spinal column, or vertebral midline. The transverse connector  100  increases the torsional strength of the rod construct to provide stability when the spinal column twists, such as when the shoulders are turned or angled relative to the legs in a standing position. The transverse connector  100  can be located anywhere along the rods and any number of transverse connectors  100  can be used. 
     With reference to  FIGS. 1 and 2 , the transverse connector  100  includes longitudinal rod engagement elements or connecting arms. A first connecting arm  105  and a second connecting arm  110  extend toward each other between each longitudinal member or spinal rod. The first and second connecting arms  105 ,  110  can connect by a variety of mechanisms or configurations. The first and second connecting arms  105 ,  110  can be generally elongate and positioned a distance apart from one another. The first and second connecting arms  105 ,  110  can be adjusted transversely. The first and second connecting arms  105 ,  110  can also be angularly and rotationally adjusted relative to one another to allow the connecting arms  105 ,  110  to be positioned as desired. The transverse, angular and rotational adjustability of the transverse arms  105 ,  110  with respect to one another allows them to mate to parallel, non-parallel, diverging, and converging spinal rods that are implanted within a patient&#39;s spinal system. 
     One embodiment of a transverse connector assembly  100  includes a first connecting arm  105  and a second connecting arm  110 . The connecting arms  105 ,  110  mechanically link or connect to each other transversely (i.e., across the midline of the vertebral column) in a male-female relationship to be described in more detail below. For example, the connection can be by way of an intermediate element  115  that forms a central joint  120  with connecting arm  105 . The joint  120  permits relative articulation of the arms  105 ,  110  and allows for transverse as well as angular and rotational adjustability of the transverse connector  100 , also to be described in more detail below. The joint  120  is adapted to be selectively locked in order to fix the desired angle of connection between the connecting arms  105 ,  110  along a spinal column of a patient. 
     The connecting arms  105 ,  110  are elongated structures that contact rods near their lateral ends at rod engagement portion  125 . The rod engagement portion  125  has a generally vaulted geometry that mates with the external surface of the connecting rods. The rod engagement portion  125  can have a splined or knurled mating surface  130 . The knurled mating surface  130  reduces rotational instability associated with the engaging surfaces of the hinged transverse connector  100  and the connecting rods. Similarly, the connecting rods can have a splined or knurled surface that further enhances contact between the mating surfaces to reduce rotational instability. 
     A person skilled in the art will appreciate that while the transverse connector  100  is described herein as being adapted to engage a spinal fixation element, such as a spinal fixation rod, that a transverse connector disclosed herein can be configured to engage a variety of spinal fixation devices, such as anchors, cables, fixation plates, etc. For simplicity, the fixation element engaged by the transverse connector will be described herein as a longitudinal rod. Moreover, the transverse connector  100  can include only one connector member for engaging a spinal fixation device, and the opposed terminal end of the transverse connector  100  can be adapted for other uses. For example, the opposed terminal end of the transverse connector  100  can be configured to be fixedly attached to a vertebra. The transverse connector  100  disclosed herein can also include any combination of features described and/or illustrated herein, and the transverse connector  100  is not limited to the illustrated embodiment. 
     With reference to  FIGS. 1 and 2 , the connecting rods are held tight against the knurled mating surface  130  by a rod interference pin  135 . The rod interference pins  135  (see  FIG. 2 ) can be inserted through bores  140  extending through each of the connecting arms  105 ,  110  near the rod engagement portion  125 . The interference pins  135  can be advanced into the bores  140  without a threaded interface. When the interference pins  135  are deployed through the bores  140  they are driven toward the connecting rod displacing it medially or toward the midline of the connector  100 . The result is fixation of the rod against the mating surface  130  within the rod engagement portion  125  by an interference fit. The vaulted region of the rod engagement portion  125  can be associated with some elastic deformation such that a tighter interference fit is achieved. The interference pin  135  can be of any number of shapes to effect an interference fit with the rod engagement portion  125  of the connecting arms  105 ,  110 . For example, the interference pin  135  can have a tapered or generally conical shape. In one embodiment, the interference pin  135  has an “hour-glass” profile such that the convex outer wall of the rod rests within the concavity or “waist” of the interference pin  135  when in the secured or locked position. The interference pins  135  can also be sheathed with a sleeve  505  or the like in order to accommodate longitudinal rods of varying diameters (see  FIG. 5 ). The interference pins  135  can also have shapes that provide for insertion through and removal from the bore  140  such as with a tool adapted for such procedures. 
     As mentioned above, the connecting arms  105 ,  110  connect to each other transversely across the midline of the vertebral column by way of a an intermediate element  115  that connects to and forms a medial joint  120  with connecting arm  105  permitting relative articulation. This articulating mechanical linkage between the arms  105 ,  110  involves at least two mating surfaces each having segments of contacting spherical geometries capable of relative movement. The joint  120  can be a universal joint such as a ball and socket joint. A universal joint  120  allows for maximum angular and rotational as well as transverse adjustability of the connector  100 . Such adjustability is particularly important in the connection of diverging and converging longitudinal rods. The joint can also be a hinge joint or other type of connection. 
       FIG. 2  shows the intermediate element  115  has an angularly and rotationally adjustable feature at one end, such as a ball or other spheroid member  205 , and a stem region or elongate shaft  210  at the other end. The spheroid member  205  connects the intermediate element  115  to connecting arm  105 . The elongate shaft  210  affixes the intermediate element  115  to connecting arm  110 . The elongate shaft  210  is slidably inserted into an internal shaft or pocket  215  at the medial end of connecting arm  110  and is permanently affixed within the pocket  215  by way of locking pins  220  or other locking means. The locking pins  220  extend through bore  225  near the medial region of connecting arm  110 . 
     The elongate shaft  210  can be of varying lengths. The different lengths provide for transverse adjustability of the transverse connector  100 . The spheroid member  205  also provides some degree of transverse adjustability. For example, the spheroid member  205  can be positioned in such a way as to impart an A-frame architecture to the connector  100  and change the distance that the connector  100  can span. A further advantage of the A-frame architecture is that it allows for the connector  100  to avoid contact with the dura and/or the spinal column while in use. In addition, the connector  100  can have incorporated a protective stop that inhibits the A-frame architecture from collapsing past a pre-determined angle such that the connector  100  does not impinge on the dura. If the pre-determined maximum angle results in a transverse span of the connector  100  that is too short to clamp onto the elongate rods, the user can select a connector  100  having a different length shaft  210 . The spheroid member  205  also provides angular and rotational adjustability to the connection between the intermediate element  115  and the connecting arm  105 , to be described in more detail below. 
     The spheroid member  205  lies within bore  230  of connecting arm  105 .  FIGS. 3A and 3B  illustrate how bore  230  extends from the upper surface of connecting arm  105  to the medial end of connecting arm  105  at an angle with respect to the longitudinal axis of the connecting arm  105 . The internal surface of bore  230  near its medial opening has a shape that is at least partially spherical. The spherical portion of the bore&#39;s internal surface also forms a lip  232  near the medial opening such that the diameter of the medial opening of the bore  230  is smaller than the spheroid member  205 . This prevents the spheroid member  205  from being pulled through the medial opening of the bore  230 . 
     The spheroid member  205  and bore  230  along with a wedge member  260  form the joint  120  between the connecting arms  105 ,  110 . The wedge  260  lies within bore  230  such that one end of the wedge  260  contacts the spheroid member  205 . The end of the wedge  260  that contacts the spheroid member  205  forms a mating surface or socket  265  in which the spheroid member  205  can freely move. The socket  265  of the wedge  260  has a shape that mirrors the exterior surface of the spheroid member  205 . 
     The rotational and angular position of the joint  120 , such as after deployment of the connector  100  onto rods (to be described below), and thus the position of the connecting arms  105 ,  110  with respect to one another is fixed by an interference element such as a set screw  235  threaded through a bore  240  in connector arm  105 . The set screw  235  displaces at least one mating surface and inhibits relative movement by displacing spherical surfaces against the other. As best shown in  FIGS. 3A and 3B , bore  240  extends perpendicularly through connecting arm  105  and is accessible from the upper surface of the connecting arm  105 . The internal surface of bore  240  has a tapered portion  242  and a threaded portion  250 . The tapered portion  242  of bore  240  intersects bore  230  near the upper surface of the connecting arm  105  such that the openings of bores  230  and  240  unite into a single elongated opening at the upper surface of the connecting arm  105  (best shown in  FIG. 2 ). 
     As described above, bore  230  receives wedge member  260 . Bore  240  receives the set screw  235 . One end of the wedge  260  has a mating surface  265  that contacts the spheroid member  205 . The opposite end of the wedge  260  has a mating surface  270  that contacts the set screw  235 . In particular, the mating surface  270  engages the tapered head  255  of the set screw  235  upon tightening of the set screw  235  into bore  240 . 
     The set screw  235  has external threads  245  and the surface of the bore  240  has internal threads  250 . Thus, rotation of the set screw  235 , such as with a hex wrench, results in the set screw threads  245  engaging the bore internal threads  250  and tightening of the set screw  240  in a downward direction. As best shown in  FIG. 3B , tightening of the set screw  235  in the downward direction (arrow A), results in the engagement of the tapered head  255  with mating surface  270  of the wedge member  260  (set screw/wedge interface  305 ). The tapered head  255  is such that the diameter increases as the set screw is further advanced in a downward direction (arrow A). This engagement results in the wedge  260  moving toward the spheroid member  205  (arrow B) and engagement of the mating surface  265  onto the spheroid member  205  (spheroid member/wedge interface  310 ). The wedge member  260  presses the spheroid member  205  against the lip  232  of the bore  230  (spheroid member/lip interface  315 ). In turn, the intermediate member  115  and the angular position of the connecting arms  105 ,  110  with respect to one another is fixed in place. It should be appreciated that all these mating surfaces can be textured to improve contact. 
       FIGS. 4A-4B  show a side view schematic of placement of the transverse connector  100  onto rods R. Deployment of the connector  100  onto rods R can be performed, for example, by a tool such as a hinged deployment tool having contacting elements T. An operator can place the tool contacting elements T into recesses or pockets  275  open to the upper surface of each connecting arm  105 ,  110 . The tool contacting element T can have a shape that is generally spherical to help engage the internal pocket  275  surfaces, which can be in non-parallel planes. Relative articulation of the two connecting arms result from separation or approximation of the tool contacting elements T For example, separating the tool contacting elements T causes the joint  120  to straighten or the A-frame to collapse and move in a generally downward direction (Arrow A). Simultaneously, the connecting arms  105 ,  110  move in a generally lateral or outward direction (Arrows B). The rods R are forced into the rod engagement portions  125  of each of the connecting arms  105 ,  110 . Further, angle θ ( FIG. 4A ) of the A-frame architecture of the connector  100  increases, for example, to angle θ 1  ( FIG. 4B ) as the A-frame further collapses. Upon placement of the connector  100  onto the rods R, the set screw  235  can be tightened as described above to fix the position of the connector  100 . Similarly, interference pins  135  can be deployed such that they form an interference fit with the rods R and the vaulted region of the rod engagement portions  125 . 
     As described above, the connector  100  can have incorporated a protective stop that inhibits the angle of the A-frame architecture from exceeding a pre-determined angle such that the connector  100  does not impinge on the dura. If the pre-determined maximum angle results in a transverse span of the connector  100  that is too short to clamp onto the elongate rods, the user can select a connector  100  having a different length shaft  210 . 
     While this specification contains many specifics, these should not be construed as limitations on the scope of an invention that is claimed or of what may be claimed, but rather as descriptions of features specific to particular embodiments. Certain features that are described in this specification in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment can also be implemented in multiple embodiments separately or in any suitable sub-combination. Moreover, although features may be described above as acting in certain combinations and even initially claimed as such, one or more features from a claimed combination can in some cases be excised from the combination, and the claimed combination may be directed to a sub-combination or a variation of a sub-combination. Similarly, while operations are depicted in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. 
     Only a few examples and implementations are disclosed. Variations, modifications and enhancements to the described examples and implementations and other implementations may be made based on what is disclosed.