Abstract:
The Multi-Thread Iliac Screw represents a novel way to embed fasteners in the ilium by improving fixation of said fasteners in the different parts of the iliac bone tissue. The screw consists of a saddle with a locking screw and fastener with three types of threads to provide a more mechanically stable embedding of the fastener in the iliac bone. The saddle receives a spinal stabilizing rod, which is part of another vertebral mechanical system, and, as such, the saddle provides an anchor point to the stabilizing rod. In another embodiment, the saddle is designed with an integrated rod on its side, which mates to another hollow rod integrated to a cube-shaped connector, thereby replacing the stabilizing rod. The connector provides the interface to the rest of the vertebral mechanical system.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a non-provisional patent submittal corresponding to provisional patent application No. 61/897,199 Multi-Thread Iliac Screw, submitted on Oct. 30, 2013. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows embodiment 1 of the Multi-Thread Iliac Screw design. 
         FIG. 2 a    shows a view of the screw fastener. 
         FIG. 2 b    shows an embodiment of the fastener body. 
         FIG. 2 c    shows another embodiment of the fastener body. 
         FIG. 3  shows the structure of the fastener head. 
         FIG. 4 a    shows a view of the screw fastener head and its hexagonal bore. 
         FIG. 4 b    shows the top view of the fastener head. 
         FIG. 5 a    shows a cross sectional view of the saddle for the screw embodiment 1. 
         FIG. 5 b    shows saddle main surfaces for the screw embodiment 1. 
         FIG. 6  shows the entry of the screw fastener into the saddle for embodiment 1. 
         FIG. 7  shows the screw being driven into bone tissue. 
         FIG. 8  shows a view of the Illiac Screw with the saddle at an angle and with the spine stabilizing rod placed in the saddle U-shaped groove. 
         FIG. 9 a    shows embodiment 2 of the Multi-Thread Iliac Screw design. 
         FIG. 9 b    shows the top view of the cube-shaped connector of embodiment 2 of the Multi-Thread Iliac Screw design. 
         FIG. 9 c    shows another view of embodiment 2 of the Multi-Thread Iliac Screw design. 
         FIG. 10  shows a cross section view of the saddle for embodiment 2. 
         FIG. 11 a    shows a cross section view of the saddle of embodiment 2 with the fastener in the saddle seat and driven into bone while being held in place with the locking fastener. 
         FIG. 11 b    shows a cross section of the locking fastener of embodiment 2. 
         FIG. 12  shows a cross section view of the connector for embodiment 2. 
     
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to spinal fixation devices and more specifically relates to an iliac screw assembly, having two types of saddle elements to couple spinal stabilization systems. 
     Spine disorders comprise conditions that result in misaligned and exaggerated curvatures in certain areas. A healthy spine has smooth curves that support the body and allow natural movement in an individual but certain disorders such as lordosis, kyphosis and scoliosis result in abnormalities that produce unnatural stress in individuals. Lordosis causes significant inward curvature in the lower portion of the back while kyphosis causes abnormal outer curvature in the upper back. In addition, scoliosis causes abnormal sideways curvatures that can be characterized as S or C-shaped. A number of mechanical systems correct these disorders by the use of stabilizing rods that are fixed with connectors and screws anchored to the spine bones. These devices force the spine into a position that produces more natural movement thereby relieving the body of mechanical stress. Mechanisms to affix stabilizing rods, using iliac screws and connectors are described herein. 
     BRIEF SUMMARY OF THE INVENTION 
     The invention described herein refers to an Illiac screw assembly in which the fastener of the assembly is designed with three threads to improve fixation inside the Illiac bone tissue. Two embodiments are described wherein the first one consists of an assembly composed of a saddle and a fastener. In this case, the screw assembly is integrated by clipping the fastener inside the saddle in a spherical seat where the fastener head resides and is free to move through broad angles. The screw assembly is used to fixate spine stabilizing rods to the Iliac bone and said rod connects to another vertebral member on the other side. The saddle is designed with a U-shaped groove to accept the stabilizing rod. 
     The second embodiment consists of the same fastener but in this case the saddle has an integrated rod that extends from its side. This rod is inserted into another hollow rod, which is integrated to a cube connector on the other side, and, by way of this assembly, both rods replace the stabilizing spine rod described in the first embodiment. The cube connector receives the vertebral member, which is part of the spine stabilization system. The saddle rod and the hollow rod slide with respect to each other to attain a desired distance, and, once this is selected, the length is maintained by locking screws that are inserted in the hollow rod. 
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  shows embodiment 1 of the Multi-Thread Iliac Screw, consisting of a fastener  10  and a saddle  80  around which the fastener body rotates. The assembly is integrated by inserting the fastener  10  through the top opening of the saddle  80 , said operation being terminated by placing the fastener  10  in a cavity located in the bottom of the saddle. The fastener  10  is retained by a small protrusion extending from the interior wall of the saddle which deforms to allow entry of the fastener as described below. The saddle is designed with a U-shaped groove, used to place spinal rods which are held in place by a locking screw that threads from the top of the saddle. The spinal rods are part of another assembly used to stabilize the spine for treatment of various spine conditions. The saddle  80  and the fastener  10  provide an anchor point for the stabilizing rod whereby the fastener  10  penetrates the Iliac bone and is held in place free of rotation by the force exerted on it by the rod once the rod is locked by the saddle locking screw. The saddle  80  and the fastener  10  are made of a corrosion-free, strong alloy, such as a titanium alloy, that provides stiffness and durability. 
     The fastener  10  is shown in  FIG. 2 a    and is composed of a head  61 , a tip  14  and a body  16  comprised of three threads. The fastener head  61  and the body  16  are symmetrical with respect to longitudinal axis AA′. As shown in  FIG. 3 , the head  61  is designed with an underside  63  of radius r 1  with respect to the center  62  and an upper side  64  composed of a spherical section of radius r 2  sitting on a flat surface wherein the spherical section is centered around the A-A′ axis and protrudes from the flat surface at a predetermined distance. The upper side  64  is located at a predetermined distance with respect to the bottom of the underside  63 . The fastener body  16  is coupled with the head  61  through a curved interface  65 . In addition as shown in  FIG. 4 a   , the head  61  provides a hexagonal bore  67  along the longitudinal axis A-A′ of the fastener  10  to allow the insertion of a screwdriver with a hexagonal tip in order to insert the fastener  10  into bone tissue. The hexagonal bore  67  is defined by radius r 3  as shown in  FIG. 4 b   . Optionally, the fastener  10  can be canulated along the A-A′ axis through a bore whose opening  68  is located at the head  61  as shown in  FIG. 4   b.    
     As shown in  FIG. 2 a   , the body of the fastener is comprised of three external threads. The proximal thread  11  has a pitch P 1 ; the middle thread  13  has a pitch P 2 ; and the distal thread  12  has a pitch P 3 . In general, the proximal, middle and distal threads have lengths d 1 , d 2 , and d 3 , respectively. 
       FIG. 2 b    depicts an embodiment of the fastener  10  design. The body of the fastener  10  is defined by a shaft  200 , which is composed of a non-tapered section  202  of length L 1 , a first tapered section  204  of length L 2 , a second tapered section  206  of length L 3  and a tip  208 . The second tapered section  206  is designed with a tapering greater than that of first tapered section  204 . The fastener  10  threads are disposed along these body sections. The body of the fastener  10  may be canulated along axis BB′. 
       FIG. 2 c    depicts another embodiment of the fastener  10  design. The body of the fastener  10  is defined by a shaft  220 , which is composed of a first tapered section  222  of length S 1 , a second tapered section  224  of length S 2  and a tip  226 . The second tapered section  224  is designed with a tapering greater than that of the first tapered section  222 . The fastener  10  treads are disposed along these fastener sections. The body of the fastener may be canulated along axis CC′. 
     The saddle  80  of embodiment 1 is shown in  FIG. 5 a   . The saddle  80  is defined by an outer surface  89 , which terminates in a cylindrical shape at the top  87  and a curved surface at the bottom  82  which also contains a circular opening  90 . The saddle  80  is symmetrical with respect to the plane P that passes through the central axis DD′ perpendicularly to the cross section of the  FIG. 5 a   . The saddle  80  has a bore  86  with an inner thread  84  that extends downward until the thread  84  terminates at a predetermined distance from the top of the saddle  87 . The saddle  80  is designed with a U-shaped groove  85 , defined by a U-shaped virtual surface that intersects the saddle  80 , that extends downward until it terminates at a predetermined distance from the top  87 , allowing the placement of a spine stabilizing rod. Slots  92  and  93  cut parallel to the plane P on the outer surface  89  of the saddle  80  and are used to manipulate the saddle  80  with a surgical tool. The bottom section of the saddle  80  provides an inner chamber  81  with a spherical surface with a radius comparable to that of the fastener head  61  underside  63  and said chamber  81  encases the head  61  of the fastener  10 . The main defining surfaces of the saddle are shown in  FIG. 5 b   . The fastener  10 , in one method as shown in  FIG. 6 , is inserted at the top  87 , tip  14  first, and it is moved downward until its head  61  clips through the protrusion  88  by deformation inside the saddle inner chamber  81 . The underside  63  diameter of the fastener head  61  is less than the diameter of the inner thread  84  except at the protrusion  88 , which retains the screw head  61  into position and prevents any upward movement of the fastener head  61 . The fastener threaded body  16  comes out of the circular opening  90  at the bottom of saddle and as such the fastener  10  rotates freely through broad angles with respect to the longitudinal axis D-D′ of the saddle  80 . The bottom of the chamber  81  transitions downward to the circular opening  90  through a short extension  83  that opens at an angle until the bottom  82  is reached. 
     Once the saddle  80  and the fastener  10  have been assembled together, the fastener  10  is screwed into bone by a screwdriver  90  with a hexagonal tip  94  as shown in  FIG. 7 . This tip  94  is inserted in the hexagonal bore  67  at the top of the fastener head  61 . The gap left between the saddle  80  lower surface  82  and the bone allows the saddle to rotate freely with respect the bone and the inserted fastener  10  so that the stabilizing rod can be engaged through several positions. The saddle may be moved by a surgical tool that grasps the saddle outer surface grooves  92  and  93  on both sides. 
     As shown in  FIG. 8 , once the fastener  10  is put in place inside the saddle  80 , and the assembly is screwed into bone tissue, a stabilizing rod  100  is placed in the saddle U-shaped groove  85 . Then, a locking screw  91  is threaded along the saddle  80  inner thread  84  until the stabilizing rod  100  is forced next to the fastener head  61 . The locking screw  91  is designed with a hexagonal bore  96  to allow reception of a screwdriver with a hexagonal tip. By way of the rod downward force, the fastener  10  is held rigidly into place to prevent any movement with respect to the saddle or the bone tissue. 
     Embodiment 2 of the Multi-Thread Iliac Screw  140  is shown in  FIG. 9 a   ,  FIG. 9 b    and  FIG. 9 c   . In this design, the body of the fastener  10  is free to rotate in all directions around the saddle  50  but once it is driven into bone tissue a locking screw  170 , shown in  FIG. 9 c   , holds the fastener  10  into place free of rotation. A rod  51  of radius r 6  is affixed to the side of the saddle  50 . This rod  51  slides into a hollow rod  52 , of outer radius r 7  and inner radius comparable to radius r 6 , affixed to connector  53 , which is cube-shaped. The hollow rod  52  incorporates two locking screws  54  and  55  on top to tighten rod  51  inside of rod  52 . In this way, the distance between connector  53  and the saddle  50  can be varied. Rods  51  and  52  replace the stabilizing spine rod  100  described in embodiment 1. Connector  53  contains two perforations. The side perforation  152  with radius r 4 , shown in  FIG. 9 a    and  FIG. 9 c   , traverses the body of the connector  53  to allow the insertion of a vertebral rod (not shown). The top perforation  150  with radius r 5 , shown in  FIG. 9 b    and  FIG. 9 c    is threaded so that a locking screw  160 , shown in  FIG. 9 c   , can tighten the vertebral rod into position. 
     The saddle  50  of embodiment 2 is shown in  FIG. 10 . As shown in  FIG. 10 , the saddle  50  is designed with an outer surface  125 , which terminates in a cylindrical shape at the top  127  and a curved surface at the bottom  122 , which also contains a circular opening  128 . The saddle  50  is symmetrical with respect to the central axis E-E′, excluding the extending rod  51 . The saddle  50  has a bore  124  with an inner thread  130  that extends downward until it terminates at a predetermined distance from the top  127 . The bottom section of the saddle  50  provides an inner chamber  121  with a spherical surface with a radius comparable to that of the underside  63  of the fastener  10  and said chamber encases the head  61  of the fastener  10 . Said fastener  10 , in one method as in embodiment 1, is inserted at the top  127 , tip  14  first, and is moved downward until its head  61  clips by deformation through the protrusion  126  inside the saddle inner chamber  121 . The diameter of the fastener  10  underside  63  is less than the diameter of the inner thread  130  except at the protrusion  126 , which retains the fastener head  61  into position and prevents any upward movement of the fastener head  61 . The fastener threaded body  16  comes out of the circular opening  128  at the bottom of the saddle and as such the fastener  10  rotates freely through broad angles with respect to the longitudinal axis E-E′ of the saddle  50 . The bottom of the chamber  121  transitions downward to the circular opening  128  through a short extension  131  that opens at an angle until the bottom  122  is reached 
     A screwdriver with a hexagonal tip drives the fastener  10  into bone. The screwdriver enters the saddle  50  through the bore  124  at the top. The fastener  10  has a hexagonal bore  67  in the head for reception of the screwdriver tip. 
     As shown in  FIG. 11 a   , once the fastener  10  is put in place inside the saddle  50 , and the assembly is screwed into bone tissue, a locking screw  170  is threaded along the saddle inner thread  130  until the it forces the fastener  10  into place.  FIG. 11 a    shows the assembly at a right angle with respect to the bone surface, but the locking screw  170  can hold the screw into position if the saddle  50  is tilted. As shown in  FIG. 11 b   , the locking screw  170  is designed with a hexagonal bore  142  to allow reception of a screwdriver with a hexagonal tip. In addition, the locking screw  170  is designed with a curved surface  144  at the bottom, which provides a contact surface with the fastener  10 . By way of the locking screw  170  downward force, the fastener  10  is held rigidly in place to prevent any movement with respect to the saddle  50  or the bone tissue. 
     A cross section of connector  53  is shown in  FIG. 12 . The connector  53  is a cube with a top  155  and a bore  150  with an inner thread  154  that extends to the middle of the cube  53  and has radius r 5 . A bore  152  with radius r 4  and perpendicular to bore  150  extends from side  156  to side  157  of the cube. A vertebral rod  158  enters the bore  152  and is affixed by screw  159 , which is threaded through the bore  150 . The screw  159  has a hexagonal key  160  for reception of a screwdriver with a hexagonal tip.