Abstract:
A spinal screw assembly includes a bone-anchoring member, a washer, and a seat. The bone-anchoring member includes a main shaft, a washer head, and a spherical head. The spherical head extends upward from the top end of the main shaft and the washer head extends laterally from a location of the main shaft between the main shaft&#39;s top end and bottom end. The washer is polyaxially rotatable and positionable around the washer head and is configured to be placed at a first angle relative to the main shaft. The seat is polyaxially rotatable and positionable around the spherical head independent from the washer and is configured to be placed at a second angle relative to the main shaft, wherein the second angle is independent from the first angle.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application claims the benefit of U.S. provisional application Ser. No. 61/301,346 filed Feb. 4, 2010 and entitled “SPINAL SCREW ASSEMBLY’, the contents of which are expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a system and a method for facet fixation and spinal stabilization, and more particularly to a spinal screw assembly including a polyaxial screw, and a washer with protrusions to be used with spinal stabilization rods. 
       BACKGROUND OF THE INVENTION 
       [0003]    The human spine consists of individual vertebras that are connected to each other. Under normal circumstances, the structures that make up the spine function to protect the neural structures and to allow us to stand erect, bear axial loads, and be flexible for bending and rotation. However, disorders of the spine occur when one or more of these spine structures are abnormal. In these pathologic circumstances, surgery may be tried to restore the spine to normal, achieve stability, protect the neural structures, or to relieve the patient of discomfort. The goal of spine surgery for a multitude of spinal disorders, especially those causing compression of the neural structures, is often decompression of the neural elements and/or fusion of adjacent vertebral segments. Fusion works well because it stops pain due to movement at the facet joints or intervertebral discs, holds the spine in place after correcting deformity, and prevents instability and or deformity of the spine after surgical procedures such as discectomies, laminectomies, or corpectomies. Discectomy and fusion or corpectomy and fusion are most commonly performed on the cervical spine but there is also increasing application on the thoracic and lumbar spine. 
         [0004]    Several spinal fixation systems exist for stabilizing the spine so that bony fusion is achieved. The majority of these fixation systems utilize fixation elements such as rods, wires, or plates that attach to screws threaded into the vertebral bodies, facets, or the pedicles. Because the outer surface of the vertebral body is typically non-planar and the structure of the vertebras is relatively complex, it is important that the fixation elements (e.g., rods, plates, wires, staples and/or screws) are properly aligned when they are inserted into the vertebras. Improper alignment may result in improper or unstable placement of the fixation element and/or disengagement of the fixation element. Achieving and maintaining accurate positioning and guidance of these fixation elements, however have proven to be quite difficult in practice. Such positioning difficulties are further complicated by the fact that the alignment angle for a fixation device through one vertebral body or pair of vertebral bodies will be unique to that individual due to individual differences in the spinal curvature and anatomies. Accordingly, there is a need for a spinal fixation assembly that provides flexibility and polyaxial positioning of the fixation elements, preferably independent from each other. 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention relates to a spinal screw assembly, and in particular to a spinal screw assembly used in connection with spinal stabilization rods. 
         [0006]    In general, in one aspect, the invention features a spinal screw assembly including a bone-anchoring member, a washer, and a seat. The bone-anchoring member includes a main shaft, a washer head and a spherical head. The spherical head extends upward from the top end of the main shaft and the washer head extends laterally from a location of the main shaft between the main shaft&#39;s top end and bottom end. The washer is polyaxially rotatable and polyaxially positionable around the washer head and is configured to be placed at a first angle relative to the main shaft. The seat is polyaxially rotatable and polyaxially positionable around the spherical head independent from the washer and is configured to be placed at a second angle relative to the main shaft. The second angle is independent from the first angle. 
         [0007]    Implementations of this aspect of the invention may include one or more of the following features. The seat comprises a tulip-shaped body having a semispherical inner bottom portion and a cylindrical side portion extending upward from the bottom portion. The bottom portion is configured to hold the spherical head and has a diameter equal or larger than the diameter of the spherical head. The bottom portion further has a through-opening dimensioned to receive and allow the main shaft to pass through and to prevent the spherical head from passing therethrough, while allowing the tulip shaped seat to polyaxially rotate and be polyaxially positioned around the spherical head. The spinal screw assembly further includes a stabilization rod placed perpendicular to the main shaft. The cylindrical side portion of the seat has a horizontal channel dimensioned to receive the stabilization rod. The spinal screw assembly further includes a rod seat and the rod seat has a diameter equal or smaller than the diameter of the cylindrical side portion and is configured to be placed within the cylindrical side portion. The rod seat has a channel configured to hold the stabilization rod. The spinal screw assembly further includes a cap and the cap has a ring-shaped body having outer threads in the outer surface of the ring-shaped body and inner threads in the inner surface of the ring-shaped body. The cap is configured to be placed on top of the stabilization rod and the outer threads are dimensioned to engage inner threads formed in the upper inner portion of the cylindrical side portion of the seat. The spinal screw assembly further includes a rod-locking element comprising outer threads configured to engage the inner threads of the cap and thereby to lock the stabilization rod within the seat. The washer head has a flat top and a semispherical bottom. The washer has a cylindrical top portion and an outward extending bottom portion and protrusions extending downward from the bottom portion. The washer has a semispherical through-opening extending from the top portion to the bottom portion and being dimensioned to receive the washer head and to prevent the washer head from passing therethrough while allowing the washer to polyaxially rotate and be polyaxially positioned around the washer head. The main shaft further has bone engaging outer threads located near its bottom end. The spherical head has a hexagonal top opening and the hexagonal top opening extends into a cylindrical opening of the main shaft and the cylindrical opening extends from the main shaft&#39;s top end to its bottom end. The main shaft has an adjustable length. The main shaft has an upper portion and a lower portion and the upper portion includes the spherical head extending from its top end and the lower portion includes the washer head. The upper portion has an adjustable length and thereby the spherical head is positionable at an adjustable distance from the washer head. The upper portion of the main shaft further includes a threaded bottom end and the washer head has a threaded inner opening dimensioned to receive and engage the threaded bottom end of the upper portion. Threading the threaded bottom end of the upper portion in or out of the threaded inner opening of the washer head adjusts the length of the main shaft. The seat has a cylindrical body having outer threads on its outer surface and having a semispherical inner bottom portion. The bottom portion is configured to hold the spherical head and comprises a diameter equal or larger than the diameter of the spherical head. The spinal screw assembly further includes a stabilization rod placed in line with the main shaft and having a spherical end and the spherical end is configured to be placed within the cylindrical body and on top of the spherical head. The spinal screw assembly further includes an outer cylindrical cap having inner threads and the inner threads are dimensioned to engage the outer threads of the seat&#39;s cylindrical body. The spinal screw assembly further includes a rod seat dimensioned to be placed within the seat&#39;s cylindrical body. The rod seat includes a cylindrical ring having a spherical inner wall dimensioned to receive the spherical head. The stabilization rod includes first and second rod components pivotally connected to each other. 
         [0008]    In general, in another aspect, the invention features a method for polyaxially positioning a washer and a seat relative to a main shaft of a spinal screw assembly independent from each other. The method includes providing a bone-anchoring member having a main shaft, a washer head and a spherical head. The spherical head extends upward from the top end of the main shaft and the washer head extends laterally from a location of the main shaft between the main shaft&#39;s top end and bottom end. Next, the method includes providing a washer polyaxially rotatable and polyaxially positionable around the washer head and placing the washer at a first angle relative to the main shaft. Next, the method includes providing a seat polyaxially rotatable and polyaxially positionable around the spherical head independent from the washer and placing the seat at a second angle relative to the main shaft. The second angle is independent from the first angle. 
         [0009]    The details of one or more embodiments of the invention are set forth in the accompanying drawings and description below. Other features, objects and advantages of the invention will be apparent from the following description of the preferred embodiments, the drawings, and the claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Referring to the figures, wherein like numerals represent like parts throughout the several views: 
           [0011]      FIG. 1  is a perspective view of a first embodiment of the spine fixation device; 
           [0012]      FIG. 2A  is a side view of the spine fixation device of  FIG. 1  with the tulip-shaped seat and stabilization rod at an angle relative to the bone-anchoring member; 
           [0013]      FIG. 2B  is a cross-sectional view of the spine fixation device of  FIG. 2A ; 
           [0014]      FIG. 3  is an exploded view of the spine fixation device of  FIG. 1 ; 
           [0015]      FIG. 4  is a perspective view of a second embodiment of the spine fixation device having a tulip-shaped seat arranged at an adjustable height relative to the bone-anchoring member; 
           [0016]      FIG. 5A  is a side view of the spine fixation device of  FIG. 4  with the tulip-shaped seat arranged at a tall height relative to the bone-anchoring member; 
           [0017]      FIG. 5B  is a side view of the spine fixation device of  FIG. 4  with the tulip-shaped seat arranged at a short height relative to the bone-anchoring member; 
           [0018]      FIG. 6A  is a side view of the spine fixation device of  FIG. 4  with the tulip-shaped seat and the stabilization rod at an angle relative to the bone-anchoring member; 
           [0019]      FIG. 6B  is a cross-sectional view of the spine fixation device of  FIG. 6A ; 
           [0020]      FIG. 7  is an exploded view of the spine fixation device of  FIG. 4 ; 
           [0021]      FIG. 8  is a perspective view of a third embodiment of the spine fixation device; 
           [0022]      FIG. 9A  is a side view of the spine fixation device of  FIG. 8  with the tulip-shaped seat and the stabilization rod at an angle relative to the bone-anchoring member; 
           [0023]      FIG. 9B  is a cross-sectional view of the spine fixation device of  FIG. 9A ; 
           [0024]      FIG. 10  is an exploded view of the spine fixation device of  FIG. 8 ; 
           [0025]      FIG. 11  is a perspective view of a fourth embodiment of the spine fixation device; 
           [0026]      FIG. 12  is an exploded view of the spine fixation device of  FIG. 11 ; and 
           [0027]      FIG. 13  is a cross-sectional side view of the spine fixation device of  FIG. 11   
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0028]    The present invention relates to spinal screw assemblies used in connection with spinal stabilization rods. 
         [0029]    Referring to  FIG. 1  to  FIG. 3 , a spinal screw assembly  100  includes a bone-anchoring member  110 , a washer  140 , a tulip-shaped seat  150 , a stabilization rod  170 , a rod seat  160 , a cap  180  and a locking element  190 . 
         [0030]    The bone-anchoring member  110  is usually a screw having outer threads. Referring to  FIG. 3 , the bone-anchoring member  110  includes a main shaft  111 , a washer head  120  and an upper post portion  130 . The main shaft  111  includes outer threads  112  at the distal end and the washer head  120  at the proximal end. Washer head  120  has a flat top  121   a  and a semispherical lower portion  121 . Upper post portion  130  includes an upper shaft  131  extending from the flat top  121   a  of the washer head  120  and terminating to a spherical head  132 . Spherical head  132  has a hexagonal top opening  123 , which extends into a cylindrical through-opening  122 . Cylindrical through-opening  122  extends from about the center of the spherical head  132  through the upper shaft  131 , through the main shaft  110  to the distal end of the bone-anchoring member  110 . Washer  140  includes a cylindrical top portion  144  and a flat bottom surface  141  having protrusions  142  extending from it. Protrusions  142  are dimensioned to bite and grip onto the facet surface. A semispherical through-opening  143  extends from the top portion  144  to the bottom surface  141  with the spherically shaped portion arranged toward the bottom surface  141 . Opening  143  is shaped and dimensioned to receive the washer head  120 , as shown in  FIG. 2   b , and allows the washer head  120  to rotate within the washer  140  and to be oriented together with the bone-anchoring member  110  at an angle relative to the washer  140 . The tulip-shaped seat  150  includes a cylindrical base  154  and two side portions  152 ,  153  extending from the base  154  and forming a U-shaped slot  151  between them, as shown in  FIG. 3 . The U-shaped slot  151  is shaped and dimensioned to receive the stabilization rod  170 . The tulip-shaped seat  150  has a cylindrical through-opening  156  terminating into a semi-spherical bottom  156   a . Opening  156  is dimensioned to receive the spherical head  132  in the semi-spherical bottom  156   a  without letting it go through (as shown in  FIG. 2   b ). The spherical head  132  is allowed to rotate in the semi-spherical bottom  156   a  and to be oriented at an angle relative to the tulip-shaped seat  150 . The tulip-shaped seat  150  has grooves and cuts  155  along the sides  152  and  153 . These grooves and cuts  155  may be threaded cuts, straight grooves, or barbed cuts. The rod seat  160  includes a cylinder  161  having a U-shaped side slot  163  and a spherical cut out  162  at the bottom side, as shown in  FIG. 2   b . The spherical cut out  162  is dimensioned to fit concentrically on top of the spherical head  132 . The rod seat  160  is designed and dimensioned to fit inside the tulip-shaped seat  150  and the U-shaped slot  163  is shaped and dimensioned to receive the stabilization rod  170 . The cap  180  is comprised of a cylinder with outer threads  181 , dimensioned to engage the cuts  155  along the sides  152 ,  153  of the tulip-shaped seat. Cap  180  also includes a center through hole  182  extending from top to bottom and inner threads  183  running along the inner walls of the through hole  182 . The locking element  190  is comprised of a cylinder that is shaped and dimensioned to fit within the center through hole  182  and includes threads  191  on its outer wall. Threads  191  are designed and dimensioned to engage the inner threads  183  of the cap  180  and thereby to compress down and lock in position the stabilization rod  170 , rod seat  160 , tulip-shaped seat  150 , and the bone-anchoring member  110 . 
         [0031]    In operation, the bone-anchoring member  110  is pre-attached to the washer  140 , the tulip-shaped seat  150  and rod seat  160 . As was mentioned above, the washer head  120  is allowed to rotate within the washer opening  143  so that the bone-anchoring member  110  is placed at an angle relative to the washer  140 . Similarly, the spherical head  132  is allowed to rotate in the semi-spherical bottom  156   a  of the tulip shaped seat  150  so that the bone-anchoring member  110  is also placed at an angle relative to the tulip-shaped seat  150 . The bone-anchoring member  110  is driven through the facet joint along a transpedicular axis, thereby binding the facet joints together and stabilizing them in place. The washer  140  is rotated around the washer head  120  to be arranged at a desired orientation relative to the facet surfaces and then the protrusions  142  bite and grip into the facet surfaces and thereby secure the washer  140  to the facet surfaces. The tulip-shaped seat  150  is then rotated around the spherical head  132  to be arranged at a desired orientation and then it is articulated to receive the stabilization rod  170  for stabilizing another vertebra. Once the stabilization rod  170  is in place and has the desired orientation, the cap  180  is placed in the tulip-shaped seat  150  and its outer threads  181  engage the grooves  155  of the seat  150  to loosely hold the rod  170  in place. Once the assembly is in the desired position and orientation, the locking element  190  is screwed into the central through-opening  182  of the cap  180  to lock down the stabilization rod  170 , the rod seat  160 , the tulip-shaped seat  150 , and the bone-anchoring member  110  and thereby to achieve spinal stabilization. 
         [0032]    Referring to  FIG. 4-FIG .  7 , in a second embodiment  101 , the upper post portion  130  of the bone-anchoring member  110  is a separate component from the bone-anchoring member  110 . In this embodiment, the upper post portion  130  also includes a threaded shaft  133  as shown in  FIG. 7 . The washer head  120  of the bone-anchoring member  110  includes a hexagonal opening  123  on the flat top  121   a . Opening  123  is shaped and dimensioned to receive a hexagonal screwdriver for driving the bone-anchoring member  110  into place. Opening  123  extends into cylindrical opening  122  which now includes inner threads  124  designed and dimensioned to receive and engage the threaded shaft  133  of the upper post portion  130 , as shown in  FIG. 6   a.    
         [0033]    This embodiment allows for adjustable height positioning of the tulip-shaped seat and thereby of the stabilization rod. The upper post portion  130  is driven in or out to achieve a desired height or distance between the polyaxial washer head  120  and the spherical head  132 , as shown in  FIGS. 5   a  and  5   b.    
         [0034]    Referring to  FIG. 8-FIG .  10 , in a third embodiment  102 , the seat  150  is designed and dimensioned to receive a stabilization rod  170  from the top along the axial direction  179 . The seat  150  is comprised of a cylinder  157  having outer threads  156  formed on its outer surface  157   a . The stabilization rod  170  includes an elongated shaft  172  terminating in a spherical head  171  at one end. In this embodiment, the rod seat  160  comprises a spherical inner wall  164  designed and dimensioned to receive the spherical head  171  of the stabilization rod  170 . This embodiment also includes an outer cap  185 , which includes a cylinder with a top surface  189 , and a side wall  188  protruding downward from the top surface  189 . The side wall  189  includes multitude of flat sides  186  arranged concentrically and equidistantly around the cylinder. Cap  185  also includes a through-opening  187  along the center axis and a curved cut  187   a  along the top of the through-opening  187  designed and dimensioned to capture the spherical head  171  of the stabilization rod  170 . Side walls  188  include inner threads  188   a  designed and dimensioned to capture and engage the outer threads  156  of the seat  150 . 
         [0035]    In operation, the spherical head  171  of the stabilization rod  170  is inserted onto the rod seat  160  inside the seat  150 . The stabilization rod  170  is then arranged at the desired position and angular orientation, as shown in  FIG. 9   a  and then the outer cap  185  is driven and tightened onto the seat  150 , thereby locking the stabilization rod  170  at the desired angle, the rod seat  160 , the seat  150 , and bone-anchoring member  110 . 
         [0036]    In a fourth embodiment, the stabilization rod  170  is also inserted along the axial direction  179  and has the ability to pivot. Referring to  FIG. 11-FIG .  13 , in a fourth embodiment  103 , the stabilization rod  170  includes an elongated shaft  172  and an end  172   a  having a slot cut  173  extending from a mid-plane to the outer side edge. End  172   a  also includes a through-opening  174  extending perpendicular to the rod axis  179  from the same side as the slot cut  173 . Opening  174  includes inner threads  175  on the inner walls of the opening. In this embodiment the upper post portion comprises a pivot shaft  200 . The pivot shaft  200  includes a threaded shaft  201  and a pivot post  202 . Threaded shaft  201  is designed and dimensioned to be inserted into the cylindrical through-opening  122  of the bone-anchoring member  110  and to engage the inner threads  124  of the cylindrical through-opening  122 . Pivot post  202  has a larger diameter than the threaded shaft  201  and has an end  202   b  attached to the threaded shaft  201  and an opposite end  202   a . Pivot post  202  also includes a slot cut  203  formed on end  202   a  and extending from the top of the pivot post  202  partially downward and from the mid-plane outward to the side ends. End  202   a  also includes a through-opening  204  extending perpendicular to the pivot post shaft axis  200   a  from the slot cut  203 . This embodiment also includes a pivot screw  210  designed and dimensioned to pass through the pivot post through-opening  204  and to be threaded into the through-opening  174  on the stabilization rod  170 . Pivot screw  210  includes threads  211  dimensioned to capture and engage the inner threads  175  of opening  174 . 
         [0037]    In operation, the stabilization rod  170  is loosely attached to the pivot shaft  200  via the pivot screw  210 . Once the bone-anchoring member  210  is in place, the threaded shaft  201  of the pivot shaft  200  is threaded into the cylindrical through-opening  122  of the bone-anchoring member  110 . The stabilization rod  170  is then pivoted into the desired location and rotated at a desired angle and then the pivot screw  210  is tightened to secure the stabilization rod  170  in place. 
         [0038]    Other embodiments are within the scope of the following claims. The screw assembly is made of metal, plastic, ceramic, bone, polymers, composites, absorbable material, biodegradable material, or combinations thereof. 
         [0039]    Several embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.