Abstract:
The present invention relates to medical devices and methods generally aimed at spinal surgery. In particular, the disclosed system and associated methods relate to performing spinal fixation.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
     The present application is a nonprovisional patent application claiming benefit under 35 U.S.C. §119(e) from U.S. Provisional Application Ser. No. 60/534,650, filed on Jan. 6, 2004, the entire contents of which are hereby expressly incorporated by reference into this disclosure as if set forth fully herein. 
    
    
     BACKGROUND OF THE INVENTION 
     I. Field of the Invention 
     The present invention relates to medical devices and methods generally aimed at spinal surgery. In particular, the disclosed system and associated methods relate to performing spinal fixation. 
     II. Discussion of the Prior Art 
     Fixation systems are often surgically implanted into a patient to aid in the stabilization of a damaged spine or to aid in the correction of other spinal geometric deformities. Spinal fixation systems are often constructed as a framework stabilizing a particular section of the spine. Existing systems often use a combination of rods, plates, pedicle screws and bone hooks for fixing the framework to the affected vertebrae. The configuration required for each patient varies due to the patient&#39;s specific anatomical characteristics and ailments. As a result, there is a need for a modular spinal fixation system that allows for a large degree of custom configurations. 
     The present invention is directed at addressing this need and eliminating, or at least reducing, the effects of the shortcomings of the prior art systems as described above. 
     SUMMARY OF THE INVENTION 
     The present invention discloses a system and methods for performing spinal fixation. The system includes at least one pair of elongate members, a plurality of pedicle screws and at least one transverse connector. 
     The elongate members are installed along the length of the spine of the patient. The elongate members are coupled to vertebrae by a set of pedicle screws. In addition, to increase the rigidity of the fixation system, at least one transverse connector may be used to interconnect the elongate members. 
     The elongate members may include rods with sufficient length to span the affected area. The rods are constructed with an outer surface that is compatible with the head of a pedicle screw, bone hook or transverse connector. The elongate member may be of a length sufficient to span the entire length of the affected spinal section. Alternatively, the elongate members may be constructed from a plurality of the members coupled together. 
     Pedicle screws are included to couple the elongate rod members to the bony structures in the spine. Pedicle screws may have heads that are rigid with respect to the screw shank or heads that may be angularly adjusted with respect to the screw shank. As used herein, a poly-axial pedicle screw shall be understood to encompass the latter configuration. 
     The transverse connectors are designed to extend between and couple a pair of elongate members. The transverse connectors are adjustable in length along the longitudinal axis and both ends are able to rotate along the longitudinal axis. Furthermore, the angle of each end with respect to the longitudinal axis is adjustable. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
         FIG. 1  is a perspective view of a spinal fixation system of the present invention incorporating (by way of example only) a single axis pedicle screw, a poly-axial pedicle screw, a spherical-ended rod member, and a transverse connector, each forming a unique and patentable aspect of the present invention; 
         FIG. 2  is a perspective and exploded view of the spinal fixation system shown in  FIG. 1  (sans transverse connector) illustrating the method of implanting the pedicle screws and rod member according to the present invention; 
         FIG. 3  is a perspective view of the spinal fixation system of the present (sans transverse connector) after implantation as shown in  FIG. 2 ; 
         FIG. 4  is a perspective view of the transverse connector of the present invention being introduced onto the rod members of the spinal fixation system of the present invention; 
         FIGS. 5-6  are side views of the rod member according to the present invention; 
         FIGS. 7-9  are perspective, side and top views, respectively, of a fixed angle pedicle screw assembly of the present invention, having a shaft diameter of 5.5 mm and a length of 45 mm; 
         FIGS. 10-12  are perspective, side and top views, respectively, of a fixed angle pedicle screw assembly of the present invention, having a shaft diameter of 6.5 mm and a length of 45 mm; 
         FIGS. 13-15  are perspective, side and top views, respectively, of a fixed angle pedicle screw assembly of the present invention, having a shaft diameter of 7.5 mm and a length of 45 mm; 
         FIG. 16  is a perspective exploded view of a poly-axial pedicle screw assembly according to one embodiment of the present invention; 
         FIGS. 17-19  are perspective, side and top views, respectively, of a screw member forming part of the poly-axial pedicle screw system of the present invention; 
         FIGS. 20-22  are perspective, side and top views, respectively, of a pivot ring forming part of the poly-axial pedicle screw system of the present invention; 
         FIGS. 23-26  are perspective, first side, second side, and top views, respectively, of a load ring forming part of the poly-axial pedicle screw system of the present invention; and 
         FIGS. 27-29  are perspective, side and top views, respectively, of a transverse connector according to the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     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 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 system and method for performing spinal fixation disclosed herein boast a variety of inventive features and components that warrant patent protection, both individually and in combination. 
       FIG. 1  is a perspective view of a spinal fixation system  10  of the present invention. The spinal fixation system  10  is suitable for effecting fixation between adjacent vertebral levels within the spine. The spinal fixation system  10  of the present invention as shown in this embodiment includes a pair single axis or “fixed” pedicle screw assemblies  12 , a pair of poly-axial pedicle screw assemblies  14 , a pair of cannulated rod members  16 , and a transverse connector  18  spanning between the pair of cannulated rod members  16 . Each of the single axis pedicle screw assembly  12 , poly-axial pedicle screw assembly  14 , cannulated rod member  16 , and transverse connector  18  form a unique and patentable aspect of the present invention. 
     The spinal fixation system  10  is shown and described herein as a “single level” fixation system, meaning the single axis pedicle screw assemblies  12  will be fixed to a first vertebral body, the poly-axial pedicle screw assemblies  14  will be fixed to a second vertebral body (adjacent to the first vertebral body), the rod members  16  will be disposed on either side of (and generally parallel to) the midline of the spine, and the transverse connector  18  will span between the rod members  16  generally perpendicularly to the mid-line of the spine. Although shown and described herein as a “single level” construct, it will be appreciated that the spinal fixation system  10  of the present invention may be used in multi-level procedures without departing from the scope of the present invention. 
     Moreover, before addressing the specifics of each the single axis pedicle screw assembly  12 , poly-axial pedicle screw assembly  14 , cannulated rod member  16 , and transverse connector  18 , it is to be appreciated that the combination shown in  FIG. 1  is set forth by way of example only. That is, the spinal fixation system  10  of the present invention may comprise any number of variations of that shown without departing from the scope of the invention. For example, the spinal fixation system  10  may comprise four (4) of the single axis pedicle screw assemblies  12 , four (4) of the poly-axial pedicle screw assemblies  14 , and/or any combination of single and poly-axial pedicle screw assemblies  12 ,  14 , in conjunction with the rod members  16  to effect spinal fixation. 
     Each single axis pedicle screw assembly  12  of the present invention includes a screw member  20  having a shaft  22  and a housing  24 , as well as a locking screw  26 . The shaft  22  and housing  24  are integrally formed as a unitary article such that the shaft  22  and housing  24  are in fixed relation, hence the term “single axis” to describe this type of pedicle screw assembly  12  according to the present invention. The shaft  22  includes a thread  28  suitable for introduction into and purchase within bone. Each housing  24  includes first and second branches  30 ,  32 , which collectively form a generally “U” shaped area dimensioned to receive at least one of a ball portion  34  and/or a rod portion  36  (forming either end of the rod member  16  according to a further aspect of the present invention) and thereafter the locking screw  26 . In a preferred aspect, each component of the fixed angle pedicle screw assembly  12  is cannulated (i.e. it is equipped with a longitudinal lumen extends through the locking screw  26  and screw member  20 ) such that a K-wire may be used to guide the fixed angle pedicle screw assembly  12  into the patient. 
     Each poly-axial pedicle screw assembly  14  of the present invention includes a screw member  40 , a housing  44 , and a locking screw  46 . The screw member  40  includes a shaft  42 . The screw member  40  and housing  44  are separate articles such that the angle of the housing  44  relative to the screw member  40  may be varied in any number of fashions prior to locking them together, hence the term “poly axial” to describe this type of pedicle screw assembly  14  according to the present invention. The shaft  42  includes a thread  48  suitable for introduction into and purchase within bone. Each housing  44  includes first and second branches  50 ,  52 , which collectively form a generally “U” shaped area dimensioned to receive at least one of the ball portion  34  and/or rod portion  36  (forming either end of the rod member  16  according to a further aspect of the present invention) and thereafter the locking screw  46 . In a preferred aspect, each component of the poly-axial pedicle screw assembly  14  is cannulated (i.e. it is equipped with a longitudinal lumen extends through the locking screw  46  and screw member  40 ) such that a K-wire may be used to guide the poly-axial pedicle screw assembly  14  into the patient. 
     The transverse connector  18  of the present invention includes a pair of rod clamping assemblies  60  capable of fixedly engaging regions on the respective rod members  16 , as well as a linkage assembly  62  extending between the rod clamping assemblies  60 . Each rod clamping assembly  60  includes a top clamp member  64 , a bottom clamp member  66  (not shown), a clamp screw  68 , and a poly-axial pivot ring  70  (not shown). The linkage assembly  62  includes a slotted link member  72 , a grooved link member  74 , and a link screw  76 . The operation and details of the rod clamping and linkage assemblies  60 ,  62  will be described in greater detail below. 
       FIG. 2  illustrates a method of using the spinal fixation system  10  according to one embodiment of the present invention. As noted above, the fixed and poly-axial pedicle screw assemblies  12 ,  14  are preferably cannulated (i.e. a longitudinal lumen extends through the locking screws  26 ,  46  and screw members  20 ,  40 , respectively). As such, each the pedicle screw assemblies  12 ,  14  of the present invention may be advanced over a K-wire  80  and thereby guided into the patient. More specifically, the K-wires  80  may be used (with or without image guidance, such as X-ray and/or fluoroscopy systems) to target the location and trajectory to introduce the shafts  22 ,  42  of the screw members  20 ,  40 , respectively, into the pedicle of interest. Once the desired location and trajectory are identified, the screw members  20 ,  40  may be advanced over a respective K-wire  80  until the distal end of the shafts  22 ,  42  contact the pedicle, after which point the screw members  20 ,  40  may be rotated about the K-wire  80  (e.g., by rotating the housings  24 ,  44  via any suitable instrumentation) until the shafts  22 ,  42  are introduced a desired depth into the pedicle and/or vertebral body. This may be preceded by any number of suitable preparatory steps, such as drilling and/or tapping a pilot hole to better accommodate the shafts  22 ,  42  and/or threads  28 ,  48  prior to the introduction of screw members  20 ,  40 . 
     Once the screw members  20 ,  40  have been introduced as described above, rod members  16  may thereafter be advanced into the patient for engagement with the pedicle screw assemblies  12 ,  14  of the present invention. To facilitate this, the rod member  16  may be provided with one or more cannulations (e.g. cannulation  82  in the ball portion  34  and/or cannulation  84  in the rod region  36 ) such that one or more ends of the rod member  16  may be guided over a K-wire  80  and into a respective housing  24 ,  44 . Although described herein with the ball portion  34  engaging within the housing  24  of the fixed angle pedicle screw assemblies  12  and the rod portion  36  engaging within the housing  44  of the poly-axial pedicle screw assembly  14 , it will be appreciated that this may be reversed in one or both sides without departing from the scope of the present invention. Any number of suitable instruments may be employed to facilitate the above-identified step, including but not limited to a pushing or holding device for guiding the rod member  16  into the patient. 
     After the rod member  16  is introduced as described above, the locking screws  26 ,  46  may thereafter be introduced and engaged with the housings  24 ,  44 . It may be desirable to adjust the position of the rod member  16  relative to the pedicle screw assemblies  12 ,  14  according to a still further aspect of the present invention. More specifically, as will be discussed in greater detail below, the spherical nature of the ball region  34  of the rod member  16  will (prior to locking) allow it to rotate within the housing  24 . As such, the ball region  34  will be loosely disposed within the housing  24  such that the remainder of the rod member  16  may be angled therefrom in any number of desired manners (e.g. up, down, side-to-side and/or any variation thereof) depending upon the situation and need. This may advantageously facilitate positioning the rod region  36  into the housing  44  after the ball region  34  has already been positioned within housing  24 . Moreover, this may reduce if not eliminate the need to bend the rod member  16  as with traditional rod members of prior art pedicle screw systems. 
     It may be preferred to distract the screw members  20 ,  40  prior to fully locking the locking screws  26 ,  46  within the housings  24 ,  44 . In this fashion, the surgeon can ensure that the proper disk height is attained prior to locking the rod members  16  to the pedicle screw assemblies  12 ,  14 . This screw distraction may be accomplished using any number of suitable instruments. The locking screws  26 ,  46  may be secured or locked within the respective housing  24 ,  44  via any number of suitable mechanisms, including but not limited to the manner shown, namely threading the exterior of the locking screws  26 ,  46  and providing grooves along the interior of the housings  24 ,  44 . 
     The spinal fixation system  10  of the present invention is suitable for both open and/or percutaneous procedures. In an open procedure, any or all of the components of the pedicle screw systems  12 ,  14  and rod member  16  may be introduced without the assistance of a K-wire (and, for that matter, such components may be non-cannulated). During a percutaneous procedure, however, both the pedicle screw assemblies  12 ,  14  and rod member  16  may be introduced percutaneously through the use of K-wire guidance. According to one embodiment, this may be accomplished by percutaneously (i.e. using a K-wire for guidance) introducing a first fixed pedicle screw assembly  12  into a first vertebral body, introducing a first poly-axial pedicle screw assembly  14  in an adjacent vertebral body, creating an incision extending between and down to the first fixed and poly-axial pedicle screw assemblies  12 ,  14 , introducing the rod member  16  into the housings  24 ,  44 , respectively, (optionally distracting), and introducing the locking screws  26 ,  46  to lock the rod member  16  relative to the pedicle screw assemblies  12 ,  14 . In this fashion, the ball portion  34  of the rod member  16  will be locked in the housing  24  and the rod portion  36  will be locked in the housing  44 . The K-wires  80  may then be withdrawn. Any number of suitable instruments may be employed to facilitate the above-identified steps, including but not limited to a screwdriver for screwing the locking screws  26 ,  46  into the housings  24 ,  44 . 
     In either event (open or percutaneous introduction), the spinal fixation system  10  of the present invention, once implanted, will appear as shown in  FIG. 3 . As shown in  FIG. 4 , the transverse connector  18  of the present invention may thereafter be employed to establish a rigid coupling between the adjacent rod members  16 . 
     The rod member  16  will now be described in detail with reference to  FIGS. 5-6 . As set forth above, the rod member  16  of the present invention includes the ball portion  34  at one end and the rod portion  36  at the other end. According to the present invention, the ball portion  34  and/or the rod portion  36  may be cannulated for purposes of accommodating a K-wire for guiding the rod member  16  into the patient, such as represented by cannulations  82 ,  84 . The cannulation  82  is preferably provided as a generally cylindrical lumen extending through the general center of the ball portion  34  such that it the center of the ball portion  34  may be guided directly into the spherical receiving area within the housing  24  (or housing  44  if the rod member  16  is reversed). The cannulation  84 , on the other hand, has a generally elongated shape to accommodate variations in the distance between the housing  24  and housing  44 , which may exist due to surgeon placement or other factors. According to the present invention, the ball portion  34  is equipped with a plurality of circumferential ridges  86  disposed generally perpendicularly to the longitudinal axis of the rod member  16 . As will be described below, these circumferential ridges  86  cooperate with circumferential ridges provided within the housings  24 ,  44  such that, when the ball portion  34  is locked therein, the two areas of circumferential ridges engage and meld together to prevent any rotation or movement therebetween. The rod member  16  of the present invention may be of any length suitable or desirable to connect two or more vertebrae, and may be generally provided in a range of 25-300 mm. 
     Various aspects of the fixed angle pedicle screw assembly  12  of the present invention will now be described in detail with reference to  FIGS. 7-9 . According to one embodiment of the present invention, the interior of the first and second branches  30 ,  32  are provided with grooves  90  to threadedly engage with threads provided on the exterior of the locking screw  26 . The grooves  90  and threads on the locking screw  26  may be configured such that the first and second branches  30 ,  32  are pulled together to prevent splaying during introduction of the locking screw  26  or due to use, such as by establishing a helical point-contact between the grooves  90  and threads on the locking screw  26 . In a still further aspect of the present invention, the bottom of the housing  24  is provided with a plurality of circumferential grooves  92  and  94  dimensioned to engage with the circumferential grooves  86  on the ball portion  34  of the rod member  16 . As mentioned above, this bolsters the purchase between the ball portion  34  and housing  26  such that the two are more effectively locked in position relative to one another after the locking screw  26  has been tightened.  FIG. 8  best illustrates the “U” shaped opening in the housing  24 , which may accommodate either the ball portion  34  and/or rod portion  36  of a rod member  16 . 
     According to a still further aspect of the present invention, the thread  28  is designed to have a uniform pitch regardless of the diameter of the shaft  22 . For example, as shown in  FIGS. 10-12 , the thread  28  has the same pitch for the 6.5 mm diameter shaft  22  as in the 5.5 mm diameter shaft  22  shown in  FIGS. 7-9 . In similar fashion, as shown in  FIGS. 13-15 , the thread  28  has the same pitch for the 7.5 mm diameter shaft  22  as in the 5.5 mm diameter shaft  22  shown in  FIGS. 7-9  and the 6.5 mm diameter shaft  22  shown in  FIGS. 10-12 . This is advantageous, among other reasons, because it provides the ability to use the same cutting tools for all sizes of the thread form. The fixed angle pedicle screw assembly of the present invention may be of any length and width suitable or desirable to purchase the vertebrae, and may be generally provided with a width range of 5.5-7.5 mm and a length range of 30-50 mm. 
     Various aspects of the poly-axial pedicle screw assembly  14  of the present invention will now be described in detail. As best shown in  FIG. 16 , the screw member  40  and a housing  44  are separate articles. With combined reference to  FIGS. 16-19 , the screw member  40  includes a hemi-spherical head region  100 , which according to a preferred embodiment is equipped with a plurality of circumferential grooves  102 . As best shown in  FIG. 19 , the screw member  40  is cannulated to receive a K-wire for guidance and includes a hex-type receiving area in the head region  100  to receive a screwdriver instrument. To facilitate the cooperation and engagement between the screw member  40  and the housing  44 , the poly-axial pedicle screw assembly  14  is provided with a pivot ring  104  and a load ring  106 . With combined reference to  FIGS. 16  and  20 - 22 , the pivot ring  104  is dimensioned to rest within a region within the bottom of the housing  44  and allow the head region  100  to pivot within the housing  44  prior to being locked in position. With combined reference to FIGS.  16  and  23 - 26 , the load ring  106  will rest on top of the head portion  100  of the screw member  40  and forms the receiving area for the ball portion  34  and/or rod portion  36  of the rod member  16  of the present invention. To facilitate this, the load ring  106  is equipped with a plurality of circumferential grooves  108  and  110  to engage and lock with the circumferential grooves  86  provided on at least the ball portion  34 . The poly-axial pedicle screw assembly of the present invention may be of any length and width suitable or desirable to purchase the vertebrae, and may be generally provided with a width range of 5.5-7.5 mm and a length range of 30-55 mm. 
     With reference to  FIGS. 27-29 , the transverse connector  18  of the present invention includes a pair of rod clamping assemblies  60  capable of fixedly engaging regions on the respective rod members  16 , as well as a linkage assembly  62  extending between the rod clamping assemblies  60 . Each rod clamping assembly  60  includes a top clamp member  64 , a bottom clamp member  66  (not shown), a clamp screw  68 , and a poly-axial pivot ring  70  (not shown). The linkage assembly  62  includes a slotted link member  72 , a grooved link member  74 , and a link screw  76 . The transverse of the present invention may be of any length suitable or desirable to stabilize a pair of rods, and may be generally provided with a length range of 45-100 mm. 
     While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the description herein of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.