Abstract:
A spinal fixation element includes a screw and a washer. The screw comprises an elongated body of a first diameter and the body includes a threaded portion at a distal end and a semispherical head of a second diameter at a proximal end. The second diameter is larger than the first diameter. The washer comprises a semispherical through opening of a third diameter at the top, of a fourth diameter in the middle and of a fifth diameter at the bottom. The third diameter is slightly smaller than the second diameter, the fourth diameter is slightly larger than the second diameter and the fifth diameter is smaller than the second diameter. The washer surrounds the semispherical head, is non-removably attached to the semispherical head and is rotatable and positionable at an angle relative to the elongated body.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application is a continuation in part of U.S. application Ser. No. 11/779,526 filed on Jul. 18, 2007 and entitled SYSTEM AND METHOD FOR FACET FIXATION the contents of which are expressly incorporated herein by reference. 
         [0002]    This application is also a continuation of U.S. application Ser. No. 11/955,621 filed on Dec. 13, 2007 and entitled GUIDANCE SYSTEM, TOOLS, AND DEVICES FOR SPINAL FIXATION the contents of which are expressly incorporated herein by reference. 
         [0003]    This application is also a continuation of U.S. application Ser. No. 12/543,656 filed on Aug. 19, 2009 and entitled SYSTEM AMD METHOD FOR FACET FIXATION the contents of which are expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0004]    The present invention relates to a system and a method for facet fixation, and more particularly to a facet fixation assembly including a polyaxial screw and a washer with protrusions. 
       BACKGROUND OF THE INVENTION 
       [0005]    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 relief 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 spine procedures such as discectomies, laminectomies or corpectomies. Discectomy and fusion or corpectomy and fusion are most commonly performed in the cervical spine but there is increasing application in the thoracic and lumbar spine, as well. 
         [0006]    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. However, achieving and maintaining accurate positioning and guidance of these fixation elements has 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 method and a system for angular guiding and placing of spinal fixation elements. 
       SUMMARY OF THE INVENTION 
       [0007]    In general, in one aspect, the invention features a spinal fixation element including a screw and a washer. The screw comprises an elongated body of a first diameter and the body includes a threaded portion at a distal end and a semispherical head of a second diameter at a proximal end. The second diameter is larger than the first diameter. The washer comprises a semispherical through opening of a third diameter at the top, of a fourth diameter in the middle and of a fifth diameter at the bottom. The third diameter is slightly smaller than the second diameter, the fourth diameter is slightly larger than the second diameter and the fifth diameter is smaller than the second diameter. The washer surrounds the semispherical head, is non-removably attached to the semispherical head and is rotatable and positionable at an angle relative to the semispherical head. 
         [0008]    Implementations of this aspect of the invention may include one or more of the following features. The washer comprises protrusions extending from a bottom surface. The protrusions comprise one of spikes, teeth, serrations, grooves, or ridges. The protrusions are arranged around one or more circles concentric to the semispherical opening. The protrusions are spaced apart by gaps having alternating trigonal and rectangular shapes. The protrusions are arranged around an outer circle and an inner circle and the protrusions of the outer circle comprise teeth with rectangular cross-section and the protrusions of the inner circle comprise teeth with trigonal cross-section. The washer is non-removably attached to the semispherical head by swaging the top of the washer around the semispherical head. The angle varies between +30 degrees and −30 degrees relative to an axis passing through the center of the washer semispherical opening. The elongated body comprises a through opening extending from the proximal end to the distal end. The semispherical head comprises a flat top surface and a through opening being concentric with the through opening of the elongated body. The fixation element is made of stainless steel, titanium, plastic, bioabsorbable material, ceramic material, solid or porous material. 
         [0009]    In general in another aspect the invention features a method for attaching a fixation element to a vertebral location including providing a fixation element. The fixation element comprises a screw and a washer. The screw comprises an elongated body of a first diameter and having a threaded portion at a distal end and a semispherical head of a second diameter at a proximal end. The second diameter is larger than the first diameter. The washer comprises a semispherical through opening of a third diameter at the top, of a fourth diameter in the middle and of a fifth diameter at the bottom. The third diameter is slightly smaller than the second diameter, the fourth diameter is slightly larger than the second diameter and the fifth diameter is slightly smaller than the second diameter. The washer surrounds the semispherical head, is non-removably attached to the semispherical head and is rotatable and positionable at an angle relative to the semispherical head. Next, inserting the screw into a vertebral location along a first direction, setting the washer at an angle relative to the first direction and securing the washer to the vertebral location by penetrating and grabbing an area around the vertebral location with the teeth and then screwing the threaded portion of the screw into the vertebral location. 
     
    
     
       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 schematic posterior view of a patient&#39;s lower back; 
           [0012]      FIG. 2  depicts inserting a first guide wire into the patient&#39;s back of  FIG. 1 ; 
           [0013]      FIG. 3  depicts inserting a bone needle over the first guide wire of  FIG. 2 ; 
           [0014]      FIG. 4  depicts tapping the bone with the bone needle of  FIG. 3 ; 
           [0015]      FIG. 5  depicts removing the bone needle; 
           [0016]      FIG. 6  depicts inserting the first guide member over the first guide wire of  FIG. 5 ; 
           [0017]      FIG. 7  depicts connecting the second guide member to the first guide member of  FIG. 6 ; 
           [0018]      FIG. 8  depicts setting the angle between the first and second guide members and inserting a second guide wire through the second guide member into the patient&#39;s back; 
           [0019]      FIG. 9  depicts removing the second guide member; 
           [0020]      FIG. 10  depicts removing the first guide member; 
           [0021]      FIG. 11  depicts inserting a tissue dilator into over the first guide wire; 
           [0022]      FIG. 12  depicts dilating the tissue around the first guide wire; 
           [0023]      FIG. 13  depicts removing the inner dilator member; 
           [0024]      FIG. 14  depicts inserting a drill into the outer dilator member; 
           [0025]      FIG. 15  depicts drilling into the bone around the first guide wire; 
           [0026]      FIG. 16  depicts the automatic stopping mechanism of the drilling process; 
           [0027]      FIG. 17  depicts removing the drill; 
           [0028]      FIG. 18  depicts inserting a first facet screw into the opening over the first guide wire; 
           [0029]      FIG. 19  is a schematic diagram of the lower vertebra with the installed facet screws; 
           [0030]      FIG. 20  is a schematic diagram of a pivoting guide wire; 
           [0031]      FIG. 21  is a side perspective view of a facet screw assembly; 
           [0032]      FIG. 22  is a detailed view of the bottom surface of the facet screw washer of  FIG. 21 ; 
           [0033]      FIG. 23  is a side view of two different orientations of the facet screw washer of  FIG. 22 ; 
           [0034]      FIG. 24  is a perspective view of another embodiment of the polyaxial facet screw assembly; 
           [0035]      FIG. 25  a cross-sectional side view of the facet screw assembly of  FIG. 24 ; 
           [0036]      FIG. 26  is another cross-sectional side view of the facet screw assembly of  FIG. 24 ; 
           [0037]      FIG. 27  is a perspective view of the facet screw washer of  FIG. 24  before it is swaged and attached to the facet screw; 
           [0038]      FIG. 28A  is a side view of the facet screw washer of  FIG. 24  after it is swaged; 
           [0039]      FIG. 28B  is a bottom view of the facet screw washer of  FIG. 24 ; 
           [0040]      FIG. 29  is a perspective view of a screwdriver assembly; 
           [0041]      FIG. 30A  is a detailed view of the lower portion of the screwdriver assembly of  FIG. 29  with the facet screw assembly retained; and 
           [0042]      FIG. 30B  is a detailed view of the lower portion of the screwdriver assembly of  FIG. 29  with the facet screw assembly released. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    Referring to  FIG. 1-FIG .  19  a new method for facet fixation includes the following steps. First, patient  80  is positioned prone, lying flat on an operating table in preparation for a minimally invasive surgery (MIS) ( 100 ). Next, location  114   a  corresponding to a first facet joint of the L5 lumbar vertebra  84 , is radiographically identified and marked on the patient&#39;s lower back. For MIS procedures, a skin incision  81  is performed and a first guide wire  112  is inserted in the facet joint location  114   a  ( 110 ). The placement of the guide wire  112  is verified by taking a fluoroscopic image of the patient&#39;s back. The fluoroscopic image is further used to identify the location of the facet joints  114   a ,  114   b  of vertebra  84  and the angular relationship between them. Guide wire  112  or Kirschner wire (also called K-wire) is a thin, rigid wire that is used to stabilize bone fragments in orthopedics and other types of medical and veterinary surgery. Kirschner wires were introduced in surgical procedures by Martin Kirschner in 1909. They are sterilized, sharpened, smooth stainless steel pins and have different sizes. These wires can be drilled through the bone to hold bone fragments in place. They are placed percutaneously (through the skin), thus avoiding an operation in some cases. In other cases, the K-wires are used after an operation to hold bone fragments in place. In some cases the K-wires include threads for threading into the bone. In spine surgery K-wires are used as guide wires for the placement of spine fixation components, such as screws and pins. They are inserted either through an open surgical procedure or under fluoroscopic or X-ray observation and are removed after the insertion of the screws. In one example guide wire  112  is a threaded 140 millimeter K-wire, manufacture by SpineFrontier, Inc (Beverly, Mass.). 
         [0044]    Next, a bone needle  122  is inserted over the guide wire  112  ( 120 ) and tapped into the facet joint  114   a  ( 130 ). I one example, bone needle  122  is a Jamshide bone needle, manufactured by Baxter-Allegiance. The bone needle is then removed ( 140 ), and first arm  152  of an X-guide tool  400  is inserted over the guide wire  112  ( 150 ). Second arm  154  of the X-guide tool  400  is connected to the first arm  152  at pivot point  156  ( 160 ) and the angle  60  between the two arms  152 ,  154  is set so that a second guide wire  116  inserted through the second arm will meet the location of the second facet joint  114   b  of vertebra  84 . Angle  60  was determined from the fluoroscopic image of the patient&#39;s back, as was mentioned above. Second guide wire is then inserted through the second arm  154  of the X-guide tool  400  into the location of the second facet joint  114   b  ( 170 ). Second guide wire  116  includes two elongated members  116   a ,  116   b  pivotally connected at point  117 , as shown in  FIG. 20 . In one example, guide wire  116  is a threaded  50  centimeter pivoting K-wire, manufacture by SpineFrontier, Inc (Beverly, Mass.) and the X-guide tool  400  is a two arm angular positioning guide manufactured also by SpineFrontier, Inc (Beverly, Mass.). Next, the two guide arms  154 ,  152  are removed ( 180 ), ( 190 ), and the upper arm  116   a  of the pivoting guide wire  116  is pivoted out of the plane of the first guide wire  112 , as shown in  FIG. 11  ( 200 ). A tissue dilator  350  is then inserted over the first guide wire  112  ( 200 ). Tissue dilator  350  include an outer dilator cannula  352  and an inner dilator  354  configured to slide within the outer dilator cannula  352 , as shown in  FIG. 24 . In one example, tissue dilator  350  is a dilator manufactured by SpineFrontier, Inc (Beverly, Mass.). The inner dilator  354  is advanced within the outer dilator cannula and the tissue around the first guide wire  112  is dilated ( 210 ). Next the inner dilator  354  is removed and the outer dilator cannula  352  is advanced into the patient&#39;s tissue ( 220 ), as shown in  FIG. 13 . Next a hand drill  360  is inserted into the outer dilator cannula ( 230 ). Referring to  FIG. 25 , hand drill  360  has a handle  364  and an adjustable stop  362 . The distance  363  between the drill stop  362  and handle  364  is adjusted to correspond to the length of the facet screw that need to be inserted into the facet joint  114   a . Accordingly, in step  240  length  363  is adjusted to match the length  301  of the facet screw  21 , shown in  FIG. 21  and then the handle is advanced down until it hits the stop  362  ( 250 ). In one example, hand drill  360  is a drill manufactured by SpineFrontier, Inc (Beverly, Mass.). Next, the hand drill  360  is removed ( 260 ) and a screwdriver  370  with a removable attached screw  300  is inserted in the location  114   a  via the outer dilator cannula  354  ( 270 ). The screw  300  is attached to location  114   a  and the screwdriver  370  and the outer dilator cannula  354  are removed. Referring to  FIG. 26 , in one example screwdriver  370  has a removable screw attaching mechanism  376  and is manufactured by SpineFrontier, Inc (Beverly, Mass.). 
         [0045]    Next, the upper arm  116   a  of the second guide wire  116  is straighten and the process of dilation, drilling and screw driving is repeated for the second facet joint location  114   b  resulting in two facet joint screws  300   a ,  300   b  being attached to locations  114 ,  114   b , respectively ( 280 ). Similarly, additional facet screws are driven in other facet joint locations of adjacent vertebras  82  and  86 . 
         [0046]    Referring to  FIG. 21 ,  FIG. 22  and  FIG. 23 , facet screw assembly  300  includes a polyaxial screw  302  and a washer  308 . Screw  302  has an elongated body  302   a  having a semispherical head  306  with a flat top  306   a  at one end and a threaded portion  304  at the opposite end. Washer  308  is non-removably fitted around head  306 . Washer  308  has a semispherical through opening  308   a  supporting the semispherical head  306  and is configured to pivot around the head  306  at an angle  313 , as shown in  FIG. 23 . Washer  308  also has teeth  312  in its bottom surface for grabbing and holding into the bone, tissue, biologic or synthetic material, as shown in  FIG. 22 . In other embodiments, the bottom surface of washer  308  include ridges, serrations, grooves, or spikes. In one example, facet screw  300  has a length  301  of about 40 millimeters, a non-threaded portion length  303  of 20 millimeters, screw body width  311  of 4.5 millimeters, washer width  309  of about 9 millimeters, washer height of 2 millimeters and a washer pivoting angle  313  of 7.5 degrees. Facet screw  300  is manufactured by SpineFrontier, Inc (Beverly, Mass.) and may be made of metal such as stainless steel or titanium, plastic, bioabsorbable material, ceramic material, or other solid or porous materials. 
         [0047]    Referring to  FIG. 24 , in another embodiment the facet screw assembly  160  includes a polyaxial screw  170  and a washer  180 . Screw  170  has a cannulated elongated body  174  having a through opening  175  extending from its proximal end  174   a  to its distal end  174   b . The elongated body  174  has a semispherical head  172  at the proximal end  174   a  and a threaded portion  173  at the distal end  174   b . The semispherical head  172  is swaged locked within the opening  182  of the washer  180 , as shown in  FIG. 25 . In one example, screw  170  has a length of 35 mm, a diameter of 3.5 mm at the unthreaded body portion and a diameter of 4.5 mm at the threaded body portion. Screw head  172  is polyaxially rotatable within the opening  182  of the washer  180 , as shown in  FIG. 26 , until it is secured into the bone with the screwdriver. The head  172  has a hexagonal through opening  176  for receiving a hexagonal screwdriver tip. 
         [0048]    Referring to  FIG. 27 ,  FIG. 28A , and  FIG. 28B  washer  180  has a cylindrical body  184  with a top  190   a  and a bottom  190   b . Two concentric rows (inner  186   a , outer  186   b ) of teeth  186  extend from the bottom  190   b  of the washer body  184 . Cylindrical body  184  has a semispherical through opening  182  for holding the semispherical screw head  172 . The opening  182  at the top  190   a  is initially straight, as shown in  FIG. 27 , and is flared inwards (i.e., swaged) after the screw head  172  is placed into the opening  182  to lock the head  172  into the opening  182  and prevent it from moving up, as shown in  FIG. 28A  and  FIG. 24 . The diameter  191  of the opening  182  at the top  190   a  is initially slightly larger than the diameter of the semispherical head and becomes slightly smaller  181  after the swaging. The opening  182  at the bottom  190   b  has a diameter  183  smaller than the diameter of the semispherical head  172  and larger than the diameter of the unthreaded portion of the elongated screw body  174 , thus preventing the head  172  from passing through the opening. Inner row  186   a  has teeth  186  with trigonal cross-section  194  and outer row  186   b  has teeth with rectangular cross-section  192 . The gaps  198 ,  196  between the teeth  186  in each row have alternating rectangular and trigonal shapes, respectively. This teeth geometry and arrangement allow the washer to penetrate and grab into the bone or tissue and to prevent it from rotating once it is engaged into the bone or tissue. The washer pierces the bone/tissue in order to achieve a more secure padding for compression and distributes the compression force onto a flatter wider surface. The piercing of the bone by the washer also promotes bone growth. 
         [0049]    Referring to  FIG. 29 , a screwdriver assembly  370  is used to deliver and screw the facet screw assembly  160  into the bone through the cannula  202 . The screwdriver assembly  370  includes a screw retention sleeve  374  and a handle  371  attached to the proximal end of the retention sleeve  374 . Handle  371  includes a detachable T-shaped component  372  that can be used to provide additional torque for driving the screw assembly  160  into the bone. The screw assembly  160  is attached to the distal end  376  of the retention sleeve  374  and can be released or retained by moving the screw release/capture component  375  up or down. Detailed views of the retained and released facet screw assembly are shown in  FIG. 30A , and  FIG. 30B , respectively. 
         [0050]    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.