Abstract:
An implantable cervical plate assembly includes a cervical plate, one or more bone fasteners and a driver tool. The cervical plate comprises an elongated asymmetric body having one or more through-openings extending from the front surface to the back surface of the elongated asymmetric body. The one or more bone fasteners are configured to be inserted through the one or more through-openings, respectively. The bone fasteners comprise a threaded main body and a head that includes one or more flexible structures configured to be flexed and inserted into a groove and then unflex and remain captured within the groove. The driver tool includes an elongated shaft, a handle and a bone fastener-engaging. The bone fastener-engaging component comprises one or more structures that complement and engage at least one of grooves and lobes of the bone fastener opening.

Description:
CROSS REFERENCE TO RELATED CO-PENDING APPLICATIONS 
       [0001]    This application is a divisional application and claims the benefit of co-pending U.S. application Ser. No. 12/894,776 filed Sep. 30, 2010 and entitled “CERVICAL PLATE ASSEMBLY’, the contents of which are expressly incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to a cervical plate assembly, and in particular to a cervical plate assembly including an asymmetric plate and screws for attaching the plate to the bone. 
       BACKGROUND OF THE INVENTION 
       [0003]    Spine fixation assemblies are used to stabilized diseased or surgically removed vertebral elements. Several prior art spine fixation assemblies utilize rods and/or plates as connecting and stabilization elements between the vertebral elements. The rods and/or plates are usually secured to vertebral bones via screws. In situations and/or spinal locations where the vertebral elements are allowed to move after the rod or plate is attached, stresses associated with this motion or stresses due the motion of adjacent vertebral elements often cause the screws to disengage from the rod or plate and finally from the vertebral elements. Accordingly, there is a need for a locking mechanism that would prevent such a disengagement of the screws from the rod or plate and the vertebral elements. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to a system and method for a cervical plate assembly and in particular to a cervical plate assembly that includes an asymmetric bone plate and screws attaching the plate to vertebral elements. The screws include a self-contained locking mechanism that prevents accidental disengagement of the screws due to stresses after they have been attached to the vertebral elements. 
         [0005]    In general, in one aspect, the invention features an implantable cervical plate assembly for stabilization of two adjacent spinal vertebras including a cervical plate and two or more bone fasteners. The cervical plate comprises an elongated asymmetric body having a first straight side surface, a second contoured side surface opposite to the first side surface, front and back surfaces and top and bottom surfaces. The elongated asymmetric body comprises two or more through-openings extending from the front surface to the back surface of the elongated asymmetric body. The two or more bone fasteners are configured to be inserted through the two or more through-openings, respectively, and to be attached to two or more locations in the two adjacent spinal vertebras, respectively, thereby attaching the cervical plate to the spinal vertebras. The through-openings comprise a first diameter at the front surface of the elongated body, a second diameter at the back surface of the elongated body and a third diameter in the area between the front and back surfaces of the elongated body. The first diameter is smaller than the third diameter, thereby forming a lip at the top of the through-openings. The third diameter is larger than the second diameter and the first diameter is larger than the second diameter, thereby forming a groove within the perimeter of the inner wall of the through-openings. The bone fasteners comprise a threaded main body and a head. The threaded main body comprises threads for engaging the spinal vertebras and the head comprises one or more flexible structures configured to be flexed and inserted into the groove and then unflex and remain captured within the groove. 
         [0006]    Implementations of this aspect of the invention may include one or more of the following features. The through-openings comprise an oval-shaped perimeter at the back surface and the oval-shaped perimeter comprises two parallel straight sides and two opposite curved sides. The distance between the two parallel straight sides is smaller than the major diameter of the threads of the bone fasteners and the distance between the curved sides is equal to or larger than the major diameter of the threads of the bone fasteners. The bone fastener head comprises a cylindrical main body and the one or more flexible structures comprise one or more flexible arms extending tangentially from the outer side surface of the cylindrical main body and curving counter-clockwise around the cylindrical main body. The diameter of the bone fastener head including the flexible arms in the unflexed position is larger than the first diameter of the through openings and the flexible arms are configured to flex inward toward the outer side surface of the cylindrical main body when they come in contact with the lip while the bone fastener is rotated clock-wise to be driven into the vertebras and then the flexible arms unflex once they are below the lip. The bone fastener head comprises an opening extending into the threaded main body and the opening comprises an inner surface having six inward protruding lobes and a bottom having six grooves. The assembly may further include a driver tool. The driver tool comprises an elongated shaft, a handle attached to the proximal end of the elongated shaft and a bone fastener-engaging component attached to the distal end of the elongated shaft. The bone fastener-engaging component comprises one or more structures that complement and engage at least one of the grooves and lobes of the bone fastener opening. The structures of the fastener-engaging component comprise four lobes that complement and engage four of the six lobes of the bone fastener opening and two opposite tubular protrusions configured to be positioned and engage two opposite located grooves of the bone fastener opening. The fastener-engaging component comprises a driver and a locking sleeve. The driver comprises an elongated cylindrical body having the structures at its distal end and a slot extending along the driver tool axis. The cylindrical body flexes and snaps into the bone fastener opening and the locking sleeve is configured to move down and lock the driver into the bone fastener opening. The locking sleeve comprises a tubular cylindrical body and a central blade. The tubular cylindrical body is dimensioned to fit and slide over the driver cylindrical elongated body and the central blade is configured to be placed within the driver slot. The structures of the bone fastener-engaging component may be outer threads configured to engage inner threads in the opening of the bone fastener. The flexible arms comprise curved, angled or beveled outer surfaces and the flexible arms outer surfaces cooperate with matching outer surfaces of the lip. The bone fastener head comprises an opening extending into the threaded main body and the opening comprises pentagonal, hexagonal or octagonal geometric shape, or inner threads. The cervical plate may further comprise one or more elongated openings configured to support bone graft material. The bone fasteners may further comprise a tapered portion extending between the threaded main body and the head and in this case the parallel straight sides of the through-openings cut into the diameter of the tapered portion for a tighter secure lock and fit. The through-openings may further include laser-etched ridges extending perpendicular to said groove. The back surface of the cervical plate may have a roughened texture. 
         [0007]    In general in another aspect the invention features an implantable cervical plate assembly for stabilization of two adjacent spinal vertebras including a cervical plate and two or more bone fasteners. The cervical plate comprises an elongated body having first and second side surfaces, front and back surfaces and top and bottom surfaces and the elongated body comprises two or more through-openings extending from the front surface to the back surface of the elongated body. The two or more bone fasteners are configured to be inserted through the two or more through-openings, respectively, and attached to two or more locations in the two adjacent spinal vertebras, respectively, thereby attaching the cervical plate to the spinal vertebras. The bone fasteners comprise a threaded main body and a head and the threaded main body comprises threads for engaging the spinal vertebras. The through-openings comprise a perimeter dimensioned and shaped to match and complement the shape of the bone fastener head. The through-openings further comprise two opposite radially extending slots and two grooves positioned adjacent to the slots within the inner wall of the through openings, respectively. The head comprises two opposite radially protruding tubular extensions dimensioned and configured to be inserted into the two opposite radially extending slots and then rotated and captured within the two adjacent grooves, respectively. 
         [0008]    In general in another aspect the invention features a bone fastener driver tool including an elongated shaft, a handle attached to the proximal end of the elongated shaft and a bone fastener-engaging component attached to the distal end of the elongated shaft. The bone fastener-engaging component comprises one or more structures that complement and engage at least one of grooves and protruding lobes within an opening of a bone fastener. The bone fastener-engaging component further comprises a driver and a locking sleeve. The driver comprises an elongated cylindrical body having the structures at its distal end and a slot extending along the driver tool axis. The cylindrical body flexes and snaps into the bone fastener opening and the locking sleeve is configured to move down and lock the driver into the bone fastener opening. The structures of the fastener-engaging component comprise four lobes that complement and engage four lobes in the bone fastener opening and two opposite tubular protrusions configured to be positioned and engage two opposite located grooves in the bone fastener opening. The locking sleeve comprises a tubular cylindrical body and a central blade and the tubular cylindrical body is dimensioned to fit and slide over the driver cylindrical elongated body and the central blade is configured to be placed within the driver slot. The structures of the fastener-engaging component may be outer threads configured to engage inner threads in the bone fastener opening. 
         [0009]    In general in another aspect the invention features a method for stabilizing two adjacent spinal vertebras, including providing a cervical plate and then inserting two or more bone fasteners through two or more through-openings of the cervical plate, respectively, and attaching them to two or more locations in the two adjacent spinal vertebras, respectively, thereby attaching the cervical plate to the spinal vertebras. The cervical plate comprises an elongated asymmetric body having a first straight side surface, a second contoured side surface opposite to the first side surface, front and back surfaces and top and bottom surfaces. The elongated asymmetric body comprises two or more through-openings extending from the front surface to the back surface of the elongated asymmetric body. The through-openings comprise a first diameter at the front surface of the elongated body, a second diameter at the back surface of the elongated body and a third diameter in the area between the front and back surfaces of the elongated body. The first diameter is smaller than the third diameter, thereby forming a lip at the top of the through-openings. The third diameter is larger than the second diameter and the first diameter is larger than the second diameter, thereby forming a groove within the perimeter of the inner wall of the through-openings. The bone fasteners comprise a threaded main body and a head. The threaded main body comprises threads for engaging the spinal vertebras and the head comprises one or more flexible structures configured to be flexed and inserted into the groove and then unflex and remain captured within the groove. 
     
    
     
       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 cervical plate assembly; 
           [0012]      FIG. 2A  is a perspective view of the cervical plate of  FIG. 1 ; 
           [0013]      FIG. 2B  is a side view of the cervical plate of  FIG. 2A ; 
           [0014]      FIG. 3  is a top view of the cervical plate of  FIG. 2A ; 
           [0015]      FIG. 4A  is a side view of end  111   b  of the cervical plate of  FIG. 2B ; 
           [0016]      FIG. 4B  is a cross-sectional view of the cervical plate along line  113 ; 
           [0017]      FIG. 5  is a perspective view of the screw of  FIG. 1 ; 
           [0018]      FIG. 6A  is a top view of the screw of  FIG. 5 ; 
           [0019]      FIG. 6B  is a side view of the screw of  FIG. 5 ; 
           [0020]      FIG. 7  is a cross-sectional view of the cervical plate assembly; 
           [0021]      FIG. 8A  is a detailed side view of area A in  FIG. 7   
           [0022]      FIG. 8B  is a detailed top view of area A in  FIG. 7 ; 
           [0023]      FIG. 9  is top perspective view of the cervical plate assembly of  FIG. 7 ; 
           [0024]      FIG. 10  is a cross-sectional view depicting an angular placement of a the screw within an opening of the cervical place; 
           [0025]      FIG. 11  depicts a two-component driver tool; 
           [0026]      FIG. 11A  depicts a driver tool end in the unlocked position; 
           [0027]      FIG. 11B  depicts the driver tool end of  FIG. 11A  in the locked position; 
           [0028]      FIG. 11C  is a cross-sectional view of  FIG. 11A ; 
           [0029]      FIG. 11D  is a cross-sectional view of  FIG. 11B ; 
           [0030]      FIG. 11E  is a detailed view of the lower end of the driver tool in the locked position; 
           [0031]      FIG. 11F  is an exploded view of  FIG. 11C ; 
           [0032]      FIG. 11G  is a detailed bottom view of the driver  210 ; 
           [0033]      FIG. 11H  is a detailed bottom view of the driver  210  with the lowered blade  226 ; 
           [0034]      FIG. 12  is an exploded view of  FIG. 11A ; 
           [0035]      FIG. 13  depicts detailed views of the driver lower end and the locking sleeve end; 
           [0036]      FIG. 14A  depicts a driver tool end for removing a bone screw; 
           [0037]      FIG. 14B  is an exploded view of the driver tool end of  FIG. 14A ; 
           [0038]      FIG. 15A  is another embodiment of a bone screw with a self-contained locking mechanism; 
           [0039]      FIG. 15B  is a partial view of the cervical plate with an opening that cooperates with the bone screw of  FIG. 15A ; 
           [0040]      FIG. 16  is another embodiment of the cervical plate; 
           [0041]      FIG. 17  is another embodiment of the cervical plate; and 
           [0042]      FIG. 18  is another embodiment of the cervical plate. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0043]    The present invention relates to a system and method for a cervical plate assembly that includes an asymmetric bone plate and screws attaching the plate to vertebral elements. The screws include a self-contained locking mechanism that prevents accidental disengagement of the screws due to stresses after they have been attached to the vertebral elements. 
         [0044]    Referring to  FIG. 1 , cervical plate assembly  100  includes a cervical plate  110  and screws  120 . Cervical plate  110  is a two-level bone plate configured to stabilize three adjacent vertebras (not shown). Referring to  FIG. 2A ,  FIG. 2B ,  FIG. 3 ,  FIG. 4A  and  FIG. 4B , plate  110  includes an elongated asymmetric body  118  that has six through-openings  114   a - 114   f  extending from the top surface  112   a  to the bottom surface  112   b  of body  118 . Body  118  has one side  109   b  that is straight and an opposite side  109   a  that is contoured around the openings  114   a - 114   c.  The width  118   a  of plate  110  in the area inbetween openings  114   a,    114   b  and inbetween  114   b,    114   c  is smaller than the width  118   b  in the areas across openings  114   a,    114   f  at the end  111   a  of the plate, across openings  114   c,    114   d  at the end  111   b  of the plate and across openings  114   b,    114   e  at the center  116  of the plate. In one example, body  118  has a length  118   c  of 43 millimeters, a width  118   a  of 13 millimeters and a width  118   b  of 17 millimeters. There are also two additional through-openings  119   a,    119   b  arranged along the straight side  109   b  of the plate between two adjacent main openings  114   f,    114   e  and  114   e,    114   d,  respectively. The reduced width  118   a  of the plate due to the contoured side  109   a  and the presence of openings  119   a,    119   b  along the straight side  109   b  help improve the line of sight. Openings  119   a,    119   b  are also used for inserting bone graft material. Cervical plate  110  is also curved along its width and is thicker along the center  108  relative to the sides  109   a,    109   b.  In one example, the plate thickness at the center is 2.55 millimeters, the width at the sides is 2.3 millimeters and the curvature R along its width 27 millimeters. The increased thickness along the center  108  provides stability and additional strength. The overall plate thickness is kept at a minimum level in order to maintain a low profile and the overall contour of the plate is configured to provide improved anatomical interface. Cervical plate ends  111   a,    111   b  are chamfered to minimize damage of the adjacent soft tissue. Through-openings  114   a - 114   f  receive the screws  120 , which are used to attach the plate  110  to the vertebras. Openings  114   a - 114   f  have an essentially circular perimeter at the top surface  112   a  of the plate. The diameter  131   a  of each opening  114   a - 114   f  near the top surface  112   a  is larger than the diameter  131   b  near the bottom surface  112   b,  as shown in  FIG. 4B . Both top and bottom diameters  131   a,    131   b  are smaller than the diameter  131   c  at the center of the opening. In one example, diameter  131   a  is 6 millimeters, diameter  131   b  is 4.20 millimeters and diameter  131   c  is 6.4 millimeters. A lip  132  is formed around each opening  114   a - 114   f  near the top surface  112   a.  Lip  132  is designed to interface with flexible arms  121   a - 121   c  extending from the screw head  122  and thereby to lock the screw  120  onto the plate  110 , as will be explained below. Openings  114   a - 114   f  have a chamfered bottom portion  117 , as shown in  FIG. 4B . Chamfered bottom portion  117  allows the screws  120  to assume variable trajectory and angled orientation when engaged in the vertebral bone, as shown in  FIG. 10 . In some embodiments, polyaxial screws  120  are used and the chamfered bottom  117  allows them to be positioned at a desired angular orientation  146  prior to being locked. The bottom portion  117  of the openings  114   a - 114   f  is oval-shaped and has two parallel straight sides  117   a,    117   b  and two opposite curved sides  117   c,    117   d.  The distance between the two parallel straight sides  117   a,    117   b  (width of the opening)  131   b  is smaller than the major diameter  91  of the threaded portion  124  of the screw  120  and equal or larger than the minor diameter  92  of the threaded portion  124 . The distance  131   d  between the curved sides  117   c  and  117   d  of the opening (diameter) is larger or equal to the major diameter  91  of the threaded portion  124  of the screw. The oval-shaped structure of the bottom portion  117  of openings  114   a - 114   f  cooperates with the screw threads  124   a  to allow the screw  120  to move downward or upwards through the opening when the screw  120  is rotated and prevents backing out or moving forward of the screw  120  when the screw is pushed up or down, respectively. Since the width  131   b  of the opening at the bottom portion  117  is smaller than the major diameter  91  of the threaded portion  124  of the screw  120  and the diameter  131   d  is larger or about the same size as the major diameter  91  of the threaded portion  124 , the screw threads  124   a  move through the opening as they are rotated clock-wise only when they are in line with the diameter  131   d.  Once the screw threads  124   a  pass below the bottom portion  117  of the opening, they cannot be accidentally pushed straight up because they will hit the straight parallel sides  117   a,    117   b  of the oval-shaped opening, whose spacing  131   d  is smaller than the major diameter  91  of the screw. This “threading” of the screw  120  through the oval-shaped opening (i.e.” captive geometry“) of the bottom portion  117  of the plate  110  locks the screw  120  to the plate  110  and prevents accidental backing out of the screw  120 . Furthermore, screw  120  includes a tapered portion (angled sides  125   a,    125   b ) and at this tapered portion the straight parallel sides  117   a,    117   b  cut into the diameter of the tapered portion for a tighter secure lock and fit. 
         [0045]    Referring to  FIG. 5  to  FIG. 10 , bone screw  120  has a threaded main body  124  and a head  122 . Main body  124  includes threads  124   a  for engaging the vertebral bone. Head  122  has a flat top  123 , a cylindrical center  126  and a tapered portion  125  with angled bottom sides  125   a,    125   b,  as shown in  FIG. 7 . Top  123  includes an opening  128  extending into the main body  124 . Opening  128  has six lobes  127   a - 127   f,  and at the bottom between two adjacent lobes six grooves  99   a - 99   f  are formed, as shown in  FIG. 11F . As will be explained later, the geometry of opening  128  interfaces with the geometry of a screw engaging component  284  to lock a driver tool  200  into the opening  128 , as shown in  FIG. 11B . Three flexible arms  121   a - 121   c  extend tangentially from the outer side of the cylindrical center  126  and curve around the center  126 . The effective diameter  136  of the screw head  122  including the arms  121   a - 121   c  in the unflexed position is larger than the top diameter  131   a  of openings  114   a - 114   f,  shown in  FIG. 9 . Arms  121   a - 121   c  flex inward toward the central axis  140  when they come in contact with lip  132  of the openings  114   a - 114   f  while the screw  120  is being rotated clock-wise to be driven into the vertebral body. The effective diameter of the screw head  122  including the arms  121   a - 121   c  in the inward flexed position is smaller than the top diameter  131  a of openings  114   a - 114   f,  and this allows the screw head  122  including the arms  121   a - 121   c  to move below the lip  132 . Once the arms  121   a - 121   c  are below the lip  132  they expand back up to their unflexed position within the space  133  formed in the opening  114   a  between the lip  132  and the chamfered sides at the bottom portion  117  of the opening. 
         [0046]    Once the entire screw head  122  is in place within space  133 , the lip  132  prevents the screw head from accidentally moving up (i.e., backing out) from space  133  due to stresses applied during spinal motion. In cases where the mounted screw is rotated counter-clockwise, arms  121   a - 121   c  hit the lip  132  and sidewall  133   a  and flex outward away from the central axis  140 , thereby increasing the effective diameter of the screw head so that it is even larger than the top diameter  131   a.  This outward flexing of the arms  121   a - 121   c  prevents the screw head  122  from accidentally moving up and out of space  133 . The surgeon may pull out the screw with a driver tool, as will be described below. 
         [0047]    In operation, plate  110  is attached to the vertebras with the screws  120 . During the driving in of the screws into the selected vertebral locations, the screw threads  124   a  cooperate with the “captive geometry” at the bottom portion of the plate  117  and the flexible arms  121   a - 121   c  are flexed inward and move in space  133  where they expand back up to their unflexed state. The combination of these two mechanisms, i.e., “threading” the screw  120  though the bottom portion  117  of the plate  110  and positioning and locking of the flexible arms  121   a - 121   c  in space  133 , lock the screw  120  onto the plate  110  and prevent accidental disengagement due to stresses generated during motion. 
         [0048]    Referring to  FIG. 15A , in another embodiment bone screw  240  includes a threaded main body  246  and a spherical head  242  having two horizontally extending protrusions  244   a,    244   b.  Protrusions  244   a,    244   b  extend outward radially from the spherical head  242 . Referring to  FIG. 15B , opening  252  in the cervical plate  110  includes two diametrically opposite slots  254   a,    254   b  dimensioned and shaped to receive the protrusions  244   a,    244   b,  respectively. Placing protrusions  244   a,    244   b  in the slots  254   a,    254   b,  respectively, and rotating the spherical head in the direction  245  locks the screw  240  in the cervical plate opening  252  and prevents accidental removal of the screw. 
         [0049]    Referring to  FIG. 11  to  FIG. 13 , a two-component tool  200  is used to drive screw  120  through the openings  114   a - 114   f  of the cervical plate  100  into the bone. Tool  200  includes an elongate shaft  280  having a handle  282  at its proximal end and a screw engaging component  284  at its distal end. Screw engaging component  284  includes a driver  210  and a locking sleeve  220 . Driver  210  has an elongated cylindrical body  212  with a cylindrical top  214  and a driver end  216 . The driver end  216  includes four lobes  217   a - 217   d  that match and interface with four of the six lobes  127   a,    127   c,    127   d,    127   f  of opening  128  in the screw top  123 , respectively. Driver end  216  also includes two tubular protrusions  218   a,    218   b  positioned between lobes  217   a,    217   d  and  217   d,    217   c,  respectively. Protrusions  218   a,    218   b  fit within opposite located grooves  99   a  and  99   d  formed between adjacent lobes in opening  128 . The interfacing of the driver end geometry with the screw head opening  128  geometry engages the driver  210  to the screw head  122 . In this engaged position, the driver is used to rotate screw  120  clockwise or counter-clockwise. An elongated slot  215  extends along the length of the cylindrical body  212  through its center and allows the body  212  to flex and snap into opening  128  of the screw head. Once the driver end  216  is snapped into opening  128 , the locking sleeve  220  is moved down to lock the driver  210  into the opening  128  of the screw head. Locking sleeve  220  has a cylindrical body  222  with a diameter larger than the diameter of the cylindrical body  212  of the driver. Cylindrical body  222  has a central opening  224  extending the entire length of body  222  and a central blade  226  extending from about the middle of body  222  toward and past the lower end  222   a  of body  222 . Driver  210  is inserted into the central opening  224  of the locking sleeve  220  and slot  215  is aligned with and placed over blade  226 , as shown in  FIG. 11A  and  FIG. 11C . After placing the driver end  216  into the screw opening  128 , the locking sleeve  220  is moved down in the direction  219  so that the blade  226  is positioned in the slot area of the driver end  216 , shown in  FIG. 11B  and  FIG. 11D . The two parallel sides  226   a,    226   b  of blade  226  protrude through the sides of slot  215 , as shown in  FIG. 11E . The protruding blade sides  226   a,    226   b  interface with two opposite lobes  127   b,    127   e  in opening  128 , respectively. The placing of the blade  226  within the slot  215  in the screw head opening  128  prevents the lower end of body  212  from flexing and thereby locks the driver  210  within the screw head opening  128 . The locked driver  210  is then used to rotate clockwise or counter-clockwise screw  120  into or out of the desired bone location, respectively, and to drive or pull the screw  120  in or out of place. 
         [0050]    Referring to  FIG. 14   a , and  FIG. 14B , the driver tool  200  includes an inner cylindrical shaft  232  having a screw  236  at its distal end, instead of an inner central blade  226 . Screw  236  is used for removing a bone screw from a vertebral location. In this case, opening  128  in the bone screw head top  123  includes inner threads. Inner cylindrical shaft  232  rotates clockwise independently of the outer sleeve  238  and attaches screw  236  to the threaded hole  128 , thereby locking the driver tool  200  to the screw  120 . Rotating the driver tool  200  counter-clockwise removes the screw  120  from its place. 
         [0051]    Other embodiments may include the following. The cervical plate  110  may be one-level bone plate configured to stabilize two adjacent vertebras and may have four through-openings  114 , shown in  FIG. 16 . In yet other embodiments, plate  110  may be a three or four level plate stabilizing four or five adjacent vertebras, respectively. The plate  110  may have various lengths in order to provide better interface with the vertebral anatomy. The plate length and/or width may be adjustable. As shown in  FIG. 16 , cervical plate  110  includes pinholes  151   a,    151   b  for temporary support pins  152  used to hold the plate in place, while it is being fastened down. The bone plate  110  may be made of metal, plastic, ceramic, bone, polymers, composites, absorbable material, biodegradable material, or combinations thereof. In other embodiments the back surface of cervical plate  110  is roughened, as shown in  FIG. 18 . The roughened surface structure  260  is used for providing a secure grip into the vertebral surfaces. The screw head  122  may be integral or non-integral with the screw main body  124 . Opening  128  may have other geometrical shapes including, pentagonal, hexagonal, and octagonal, among others. The flexible arms  121   a - 121   c  may be integral or non-integral with the screw head. In yet other embodiments, the flexible arms may extend from the main body  124  of the screw and may be integral or non-integral with the main body  124 . The number of flexible arms  121   a - 121   c  may be more or less than three. Each arm  121   a - 121   c  may be composed of multiple parts. Flexible arms  121   a - 121   c  may comprise curved, angled or beveled outer surfaces  129   a - 129   d  which cooperate with the corresponding outer surfaces of lip  132  during the driving of the screw  120  into the vertebral location. The flexing of the flexible arms during insertion and the following unflexing of the flexible arms once they are in place, serve as a visual indicator to the user that the screw is fully inserted and engaged into the plate and vertebra. In other embodiments through-openings  114   a - 114   b  include laser-etched ridges  255  arranged perpendicular to the groove  133  around the inner wall perimeter of the openings, as shown in  FIG. 17 . Ridges  255  interface and engage with complementing structures in the outer surface of the cylindrical center  126  of the bone screw head  122  and further prevent the bone screw  120  from rotational and axial movement. 
         [0052]    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.