Abstract:
A minimally invasive tool to facilitate implanting a pedicle screw and housing is provided. The minimaly invasive tool includes a first sleeve having flexible tabs that couple to a housing and a second sleeve slidably engaged in the first sleeve. The second sleeve provides reinforcing such that the first and second sleeve provide counter torque for driving the pedicle screw.

Description:
PRIORITY UNDER 35 USC §119 
       [0001]    The present application claims priority to U.S. Provisional Patent Application Ser. No. 60/865,365, filed Nov. 10, 2006, titled MINIMALLY INVASIVE TOOL TO FACILIATE IMPLANTING A PEDICLE SCREW AND HOUSING, the disclosure of which is expressly incorporated herein by reference. 
       Related Application 
       [0002]    The technology of the present application relates to U.S. patent application Ser. No. 10/915,902, titled Screw and Rod Fixation System, filed Aug. 10, 2004, which is incorporated here by reference. 
     
    
     FIELD OF THE INVENTION 
       [0003]    The present invention relates to spinal fixation devices and more particularly to a pedicle screw and rod fixation assembly useful in stabilizing a spine of a patient. 
       BACKGROUND OF THE INVENTION 
       [0004]    Over the years, several techniques and systems have been developed for correcting spinal injuries and/or degenerative spinal processes. Spinal correction frequently requires stabilizing a portion of the spine to facilitate fusing portions of the spine or other correction methodologies. Medical correction of this type is frequently employed for many spinal conditions, such as, for example, degenerative disc disease, scoliosis, spinal stenosis, or the like. Frequently, these corrections also require the use of implants, such as, bone grafts. Stabilizing the spine allows bone growth between vertebral bodies such that a portion of the spine is fused into a solitary unit. 
         [0005]    Several techniques and systems have been developed for correcting and stabilizing the spine and facilitating fusion at various levels of the spine. In one type of system, a rod is disposed longitudinally along the length of the spine in the region of concern. The rod is arranged according to the anatomy and the correction desired. In this system, the rod is aligned along the spine and engages various vertebrae along its length. The rod engages, or more typically the parallel rods engage, the spine using fixation elements, such as, anchors attached to vertebral bodies by a bone screw. 
         [0006]    Correction frequently require aligning the rod and screw at various angles along the length of the portion of correction. In order to provide this alignment, polyaxial screws/anchors have been developed. Many variations of polyaxial screw and rod fixation systems exist on the market today. Implanting the screws, anchors, and rods as can be appreciated typically requires a relatively large incision and dissection of the skin and muscle of the patient resulting in increased recovery, surgical trauma and the like. 
         [0007]    Accordingly, to reduce for example surgical trauma, there is a need for a screw and rod fixation system that provides a strong, effective, and secure lock of the screw and rod in the desired position and angle that can be implanted using minimally invasive systems. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0008]    The accompanying drawings illustrate various embodiments of the present invention and are a part of the specification. The illustrated embodiments are merely examples and illustrations of the present invention and do not limit the scope of the invention. 
           [0009]      FIG. 1  shows a perspective view of a screw and rod fixation system in accordance with an embodiment of the present invention; 
           [0010]      FIG. 2  shows a perspective view of a housing associated with an embodiment of the present invention shown in  FIG. 1 ; 
           [0011]      FIG. 3  shows a perspective view of a bone screw associated with an embodiment of the present invention shown in  FIG. 1 ; and 
           [0012]      FIG. 4-7  show a tool useful for implanting the screw and rod system. 
       
    
    
     DETAILED DESCRIPTION 
       [0013]    Referring now to  FIG. 1 , and in accordance with certain embodiments of the present invention, a screw and rod fixation system  100  is shown.  FIG. 1  shows a perspective view of system  100 . System  100  includes a bone screw  102 , a housing  104  having an outer surface  106 , a rod  108 , and a compressive member  110 , such as, a setscrew. Housing  104  may contain one or more first mating surfaces  112 . First mating surfaces  112  are designed to mate with a tool (described further below). First mating surfaces  112  may include an alignment ridge  112   a,  which also may be a dimple, detent, protrusion, rib, or the like. Alignment ridge  112   a  conversely may be an alignment channel  112   b  as shown in phantom. Also, setscrew  110  typically has one or more second mating surface  114  to mate with a tool (not specifically shown but generally understood in the art). As shown in FIG. I. first mating surfaces  112  are actually slots on an outer surface  106  of housing  104 . While shown as slots, first mating surfaces  112  may be any number of designs including one or more dimples, hex detents, or other equivalent mechanisms as are known in the art. Second mating surface  114  is shown with a hex shape to accept a hex driver useful in threading the setscrew. Of course, one of ordinary skill in the art would recognize other and equivalent first and second mating surfaces  112 ,  114  are possible. 
         [0014]    Referring now to  FIG. 2 , housing  104  is described in more detail. Housing  104  may be referred to as a coupling device, seat, or anchor. Housing  104  has a bone facing surface  302 , at least one sidewall  304  having an outer surface  106  and an inner surface  306  (best seen in  FIG. 2 ), first mating surfaces  112 , a pair of opposed slots  308  in sidewall  304 , a top edge  310 , and a through hole  312  extending from top edge  310  to bone facing surface  302 . Top edge  310  may have alignment points  320 , which will be explained in more detail below. Alignment points  320  may be protrusions (as shown by  320   p ) or detents (as shown by  320   d ) as a matter of design choince, but it is believed detents would provided a lower profile. 
         [0015]    The housing  104  is shown with one cylindrically shaped sidewall  304 . It is believed providing housing  104  as a cylindrical shape reduces the profile of the device, but other shapes are possible, such as cubic or the like. If housing  104  had multiple sidewalls  304 , the edges between the multiple sides should be beveled or rounded to inhibit tissue trauma. 
         [0016]    Bone screw  102  will now be described with reference to  FIG. 3 . While a particular bone screw  102  is described for completeness, any conventional bone screw is usable with the technology of the present invention. Bone screw  102  has a threaded portion  502 , a transition portion  504 , and a head portion  506 . Threaded portion  502  can use any conventional thread, but as shown, threaded portion  502  has a shaft  508  and threads  510  machined such that shaft  508  has an increasing diameter from the tip  512  to transition portion  504 . Further, threads  510  become relatively thicker towards transition portion  504 . Designing threaded portion  502  in this fashion increases the frictional engagement of bone screw  102  in bone and generally increases the screw strength. To facilitate fusion between screw  102  and the bone, bone growth channels  509  may be provided in shaft  508 , thread  510 , or a combination thereof. It is believed micro-channels  509  in thread  510  facilitates bone growth and fusion of the screw to bone. 
         [0017]    Transition portion  504  comprises the portion of bone screw  102  between threaded portion  502  and head portion  506 . Transition portion  504  could be integrated into threaded portion  502 . Transition portion  504  may be straight, curved, bowed, flared, or the like to transition threaded portion  502  to head portion  506 . 
         [0018]    Head  506  is shown with a convex outer surface  514  to cooperatively engage a corresponding concave surface in housing  104 , not specifically shown by generally understood in the art. The convex outer surface  514  being designed to cooperatively engage the concave surface in housing  104  allows for polyaxial orientation of bone screw  102  with respect to housing  104 . Head  506  is shown as a conventional flat head screw with a slot  516  to receive a tool, such as a screw driver. Rotation of the tool while engaged with slot  516  drive bone screw  102  into the associated bone. While shown as a flat head having a convex outer surface, other conventional bone screws are possible as are generally known in the art, such as, for example, heads with a more spherical shape, heads with a hex driver mating surface, heads with a fixed orientation with respect to housing  104 , or the like. 
         [0019]    Referring now to  FIGS. 4-8 , a tool  600  is provided to facilitate implanting the above described screws and rods. Tool  600  would typically be inserted through the skin of a patient after sufficient dilation. Tool  600  comprises a series of sleeves that will be explained in turn. Tool  600  includes a first, outer sleeve  602 , sometimes referred to first or outer. First sleeve  602  has an inner surface  602   s  and an outer surface  602   o.  Inner surface  602   s  defines a first sleeve diameter d 1 . First sleeve  602  includes a distal end  604  releasably connectable to housing  104  at first mating surfaces  112 , as will be explained further below. First sleeve  602  has a proximate end  606  residing external to the patient. Extending from distal end  604  towards proximate end  606  are slots  608  separating tabs  610 . Slots  608  include a flared portion  609 . Flared portion  609  increases the flexibility or elasticity of tabs  610 , which is useful in connecting first sleeve  602  to housing  104 . Tabs  610  include first tool mating surface  612  to engage first mating surfaces  112  on housing  104 . Rotating first sleeve  602  causes housing  104  to cause tabs  610  to expand. As first sleeve  602  is rotated, first tool mating surfaces  612 , which are shown as protrusions, slide into first mating surfaces  112 , which are shown as detents or grooves. Flexible tabs  610  collapse towards each other allowing outer sleeve  602  to grip housing  104  when first tool mating surface  612  align with first mating surfaces  112 . First mating surface  612  optionally may be provided with an alignment dimple  614  to mate with alignment ridge  112   a.    
         [0020]    A second or inner sleeve  620  is provided to slidingly engage outer sleeve  602 . Second sleeve  620  has a second outer surface  620   o  defining an second diameter d 2  which is less than d 1  and allows second sleeve to fit inside first sleeve in a sliding relation. Second sleeve  620  comprises distal end  622  and proximate end  624 . Distal end  622  includes alignment portions  626  (which may be protrusions  626   p  (as shown) to mate with alignment detents  320   d  or which may be alignment detents  626   d  to mate with alignment protrusions  320   p ). Alignment portion  626  mate with corresponding alignment points  320  along top edge  310  of housing  104 . 
         [0021]    Second sleeve  620  includes at least one, but as shown two, alignment channels  628 . Alignment channel  628  arc shown opposite each other but could be otherwise configured. First sleeve  602  has at least one, but as shown two, corresponding alignment tabs  630  attached to an inner surface  602   s.  Alignment channel(s)  628  and alignment tab(s)  630  are matched such that when second sleeve  620  is slidably received in first sleeve  602 , alignment tab(s)  630  move along and engage alignment slot(s)  628  to facilitate mating alignment portion  626  with alignment point  320 . Second sleeve  620 , optionally, may include one or more alignment tracks  625 . Alignment tracks  625  fittingly engage with alignment ridge  627  (shown in  FIG. 5 ) to facilitate alignment points  320  aligning with alignment portions  626  and alignment channels  628  aligning with alignment tabs  630 . 
         [0022]    Once slid into place second sleeve is rotationally locked to housing  104  by alignment portions  626  and alignment points  320  and rotationally locked to the first sleeve by alignment channels  628  and alignment tabs  630 . Thus, second. sleeve  620  acts as a strengthening member to inhibit torque from causing first sleeve  602  to twist off of housing  104  while driving, for example, bone screw into bone. To facilitate the connection, pin alignment tabs  630  may have a flared surface  637 . Moreover, alignment channels  628  may be tapered to pinch or grasp tabs  630 . 
         [0023]    Once second sleeve  620  is slidably inserted into first sleeve  602 , a connector  650  couples the proximate ends of the sleeves  602  and  620  together. In this exemplary embodiment, connector  650  causes first sleeve  602  and second sleeve  620  to clamp and lock to housing  104 . For example, connector  650  may have a shaft  652  with outer surface  654  having threads  656 . Inner surface  602   s  of first sleeve  602  at the proximate end would have corresponding threads  658 . Shaft  652  would have a pushing surface  660  that abuts a proximate edge  662  of second sleeve  620 . Threading connector  650  onto corresponding threads  658  pulls first sleeve  602  in direction A and pushes second sleeve in a direction B, opposite direction A by causing pushing surface  660  to push down on proximate edge  662 . The relative forces between first sleeve  602  and second sleeve  620  clamps first sleeve  602  and second  620  to housing  104 . In this exemplary embodiment, first tool mating surface  612  to applies a force against first mating surfaces  112  in direction A and the distail edge of second sleeve  620  applies a force against top edge  310  of housing  104  providing a clamping force. Connector  650  may have a tool mating surface  660  to allow a tool to thread the connector  650  to and from first sleeve  602 . 
         [0024]    Once connected, a bone screw drive can be inserted through second sleeve  620  to thread bone screw  102  into the bone. First and second sleeve  602  and  620  provide counter torque to allow driving the screw. 
         [0025]    While the invention has been particularly shown and described with reference to an embodiment thereof, it will be understood by those skilled in the art that various other changes in the form and details may be made without departing from the spirit and scope of the invention.