Abstract:
A lumbar plate assembly for use between at least two vertebral bodies is disclosed. The assembly includes a lumbar plate having at least one opening for each vertebral body, a screw configured to secure the lumbar plate to a vertebra through the at least one opening, and a rotatable locking mechanism proximate the least one opening configured to rotate from a first configuration to a second configuration, the first configuration allowing the screw to pass into the opening and the second configuration engaging the screw to prevent withdrawal of the screw from the opening.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims priority to U.S. Provisional Patent Application No. 61/135,360 to Butler, filed Jul. 17, 2008, and entitled “A BONE PLATE ASSEMBLY”, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to the field of spinal surgery. In particular, the present invention relates to the field of surgical access to the spine. More particularly, the present invention relates to an apparatus for internal fixation of the spine and a novel locking mechanism for a bone plate assembly. 
     2. Background 
     An increasingly accepted procedure for treating spinal disorders involves using substantially rigid plates to hold vertebrae in desired spatial relationships and orientations relative to each other. The upper cervical spine can be approached anteriorly or posteriorly, although anterior approaches are of more interest in connection with this invention. In either case, holes are drilled and tapped in at least two of the vertebrae, to receive screws or other fasteners used to secure the plate. The holes are accurately positioned with reference to openings formed through the cervical plate. In some cases the screws may be self-tapping. Typically the plate is curved about its longitudinal axis to facilitate contiguous surface engagement of the plates with the vertebrae. With the plate maintained against the vertebrae, the fasteners are secure within the holes. As a result, the plate maintains the attached vertebrae in a desired spacing and orientation with respect to each other. 
     One of the problems associated with this technique is the tendency of screws or other fasteners to gradually work loose after fixation. Slight shock or vibration of the vertebrae, due to walking, climbing stairs or more vigorous activity by the patient following treatment increases this tendency, jeopardizing the integrity of fixation. Moreover, as the fasteners work loose, the outward protrusion of the heads over other components of the fasteners can be a source of discomfort and present the risk of trauma to adjacent and surrounding soft tissue. 
     The curvature of cervical plates typically results in a convergence of fasteners that extend through spaced apart openings in the plate, particularly when each screw is perpendicular to the region of the plate surrounding it. Screws sufficiently short to avoid interfering with one another may not be long enough to assure a secure plate fixation. Further, the physician may encounter difficulties in positioning the plate if one of the vertebrae, due to a particular shape and orientation, cannot readily retain a perpendicularly inserted fastener. 
     There remains a need for greater flexibility in positioning and orienting the bone screws or fasteners, and for a simpler, more reliable means of counteracting the tendency of the bone screws to work loose after cervical plate fixation. 
     Therefore, it is an object of the present invention to provide a bone plate and fixation system in which bone screws or other fasteners are more securely retained and less likely to work loose, without the need for auxiliary screws or other additional fixtures 
     SUMMARY OF THE INVENTION 
     Generally, embodiments of the present invention provide a lumbar plate locking assembly. The assembly includes a lumbar plate having at least one opening, a screw configured to be secured to the lumbar plate through the at least one opening, and a locking mechanism disposed at the least one opening and configured to lock the screw to the lumbar plate to prevent the screw from unintentionally backing out, reversing out, or falling out from the opening. Upon rotation of the locking mechanism in one direction or first configuration, the screw is locked to the lumbar plate and upon rotation of the locking mechanism in another direction or second configuration, the screw is unlocked. 
     In a first aspect, embodiments of the present invention provide a lumbar plate assembly for use between at least two vertebral bodies including a lumbar plate having at least one opening for each vertebral body, a screw configured to secure the lumbar plate to a vertebra through the at least one opening, and a rotatable locking mechanism proximate the least one opening configured to rotate from an first configuration to a second configuration, the first configuration allowing the screw to pass into the opening and the second configuration engaging the screw to prevent withdrawal of the screw from the opening. 
     In many embodiments, the system further includes a locking screw configured to secure the locking mechanism to the plate. 
     In many embodiments, the lumbar plate includes a recessed portion configured to accommodate placement of the locking mechanism. 
     In many embodiments, the locking mechanism includes a center portion and at least protrusion coupled to the center portion, and the at least one protrusion is further configured to engage a partially covered channel within the recessed portion. 
     In many embodiments, the at least one protrusion is configured to protrude into the at least one opening and engage the screw upon rotating the locking mechanism to the second configuration. 
     In many embodiments, the screw includes at least one notch disposed on a top portion of the screw and the locking mechanism includes a portion configured to interact with the at least one notch of the screw upon rotating the locking mechanism to the second configuration. 
     In many embodiments, the locking mechanism includes at least one smooth surface configured to create a substantially uninterrupted surface with an interior surface of the at least one opening in the first configuration. 
     In many embodiments, the locking mechanism is configured to have a trapezoidal shape and include at least one locking hook for engaging the screw. 
     In many embodiments, the lumbar plate includes two screw openings configured to accommodate placement of two screws. In many embodiments, the locking mechanism is configured to be positioned between the two openings and further configured to simultaneously secure at least two screws within the two openings upon rotating the locking mechanism to the second configuration. 
     In another aspect, embodiments of the present invention provide a lumbar plate locking assembly including a lumbar plate having at least one opening, a screw configured to be secured to the lumbar plate through the at least one opening, and a locking mechanism disposed at the least one opening and configured engage the screw to prevent the screw from withdrawing from the opening, wherein upon rotation of the locking mechanism in one direction, the screw is locked to the lumbar plate and upon rotation of the locking mechanism in another direction, the screw is unlocked. 
     In many embodiments, the lumbar plate includes a recessed portion configured to accommodate placement of the rotatable locking mechanism. In many embodiments, the locking mechanism is rotatably secured within the recessed portion. In many embodiments, the system further includes a locking screw configured to secure the locking mechanism within the recessed portion. In many embodiments, the recessed portion includes at least one channel configured to connect the recessed portion and the at least one opening, wherein the at least one channel is configured to be partially covered, thereby creating a locking arrangement between the locking mechanism and the lumbar plate. In many embodiments, the at least one channel includes at least one uncovered portion through which the locking mechanism is inserted into the recessed portion. In many embodiments, the locking mechanism includes a center portion and at least protrusion coupled to the center portion, and the at least one protrusion is further configured to fit within the at least one channel. In many embodiments, the at least one protrusion is configured to protrude into the at least one opening upon rotating the locking mechanism. In many embodiments, the at least one protrusion is further configured to engage the screw inserted into the at least one opening. 
     In many embodiments, the screw includes at least one notch disposed on a top portion of the screw and the locking mechanism includes at least one locking tip configured to interact with the at least one notch of the screw. In many embodiments, the locking mechanism includes at least one smooth surface configured to create a substantially uninterrupted surface with an interior surface of the at least one opening upon the locking mechanism being secured with the recessed portion in an unlocked state. 
     In many embodiments, the locking mechanism is configured to have a trapezoidal shape and include at least one locking hook for locking the screw. 
     In many embodiments, the lumbar plate includes four screw openings configured to accommodate placement of four screws. In many embodiments, the locking mechanism is configured to be disposed within a recessed portion between two openings of the four screw openings and further configured to simultaneously secure at least two screws of the four screws. 
     In many embodiments, the lumbar plate is configured to secure screws having a diameter in the range of 5.0 mm to 8.0 mm. 
     In another aspect, embodiments of the present invention provide a method of using a lumbar plate assembly between at least two vertebral bodies, the method including providing a lumbar plate having at least one opening at each vertebral body, inserting a screw through at least one opening, securing the lumbar plate to the vertebra with a screw through the at least one opening at each vertebral body, and rotating at least one locking mechanism proximate the at least one opening from a first configuration to a second configuration, the first configuration allowing the screw to pass into the opening and the second configuration engaging the screw to prevent withdrawal of the screw from the opening. 
     In many embodiments, the screw includes at least one notch disposed on a top portion of the screw and the locking mechanism includes a portion configured to interact with the at least one notch of the screw to prevent screw rotation in at least one direction. 
     In some embodiments, the present invention relates to a method of assembling a lumbar plate assembly. The assembly includes a lumbar plate having at least one opening, a screw configured to be secured to the lumbar plate through the at least one opening, and a locking mechanism disposed at the least one opening and configured to lock the screw to the lumbar plate to prevent the screw from falling out from the opening. The method includes steps of inserting the screw into the at least one opening, and rotating the locking mechanism in one direction to lock the screw. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is described with reference to the accompanying drawings. In the drawings, like reference numbers indicate identical or functionally similar elements. 
         FIGS. 1-5  illustrate an exemplary anterior lumbar plate along with its various components, according to some embodiments of the present invention. 
         FIGS. 6-13  illustrate another exemplary anterior lumbar plate along with its various components, according to some embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-5  illustrate an exemplary anterior lumbar plate  100  along with its various components, according to some embodiments of the present invention. In some embodiments, the lumbar plate  100  is an anterior stabilization plate that utilizes two bone screws per vertebral body (not shown in  FIG. 1 ). While two bone screws per body are shown, other embodiments may include one screw or more than two screws per body. The lumbar plate  100  allows bone screw angulation to be convergent along a sagittal plane and divergent along an axial plane for maximum purchase and resistance to screw pullout. The lumbar plate includes a locking mechanism  103 ( a, b ), which is configured to secure bone screws  102 ( a, b, c, d ) and prevent screw back-out. The lumbar plate  100  is further configured to restrict or block the bone screw from backing out of its tightened position. 
     Referring to  FIG. 1 , the lumbar plate  100  includes a housing  120  having an interior opening  130  and screw openings  122 ( a, b, c, d ) disposed about the opening  130 , in the embodiment shown, the screw openings  122  are disposed symmetrically about the opening  130 . In some embodiments, the lumbar plate  100  can include a plurality of interior openings or no interior openings at all. The screw openings  122  are configured to receive respective screws  102 ( a, b, c, d ). In some embodiments, the lumbar plate  100  can accommodate placement of more than four screws (as illustrated in  FIG. 1 ), or less than four screws (not shown). Further, the screws  102  can have various lengths, widths, shapes, or any other characteristics. 
     In some embodiments, the shape of the housing  120  of the lumbar plate  100  can be rectangular, whereby the screw openings  122  are configured to protrude away from the housing  120 , as shown in  FIG. 1 . In some embodiments, the shape of the housing  120  can be square, circular, oval, polygonal, or any other desired shape. Further, the housing  120  has an arcuate shape, wherein, upon insertion of the screws  102 , axis of the screws  102  are configured to converge toward each other (for example, the axis of the screw  102   a  is configured to be convergent with the axis of the screw  102   b ; similarly for screws  102   c  and  102   d ). In some embodiments, the axis of all or some of the screws  102  are configured to converge toward each other, upon being inserted into the screw openings  122 . Such arrangement allows angular placement of the lumbar plate  100  on a vertebral body or any other bone in the body. As can be understood by one skilled in the art, the arcuation of the housing  120  of the lumbar plate  100  can have any angle (including 0 degrees (or 180 degrees), which would correspond to a flat lumbar plate  100 ). In some embodiments, the axis of all or some of the screws  102  are configured to be parallel or converge away each other. In some embodiments, the screw openings  122  can be configured to be contained within the housing  120  and not protrude away from its outer perimeter. 
     The screw openings  122  can be configured to retain screws  102  in various ways. In some embodiments, the screw openings  122  are configured to have a larger diameter near their top surface and a smaller diameter near their bottom surface. The smaller diameter can be selected to prevent screw  102  from falling through the opening  122  upon insertion of the screw  102 . Hence, the smaller diameter can be smaller than the head portion of the screw  102 . In some embodiments, the screw openings  122  can include screw retaining ledges (not shown) that are configured to protrude toward the center of the screw opening  122  and thereby, create a smaller diameter opening disposed in the screw opening  122 . Such smaller diameter opening prevents screw  102  from falling through the opening  122  upon insertion. As can be understood by one skilled in the art, there are other ways of preventing screws  102  from falling through the openings  122 . As can be understood by one skilled in the art, the openings  122  can have any desired shape, e.g., round, square, rectangular, polygonal, etc. 
     An exemplary screw  102  is illustrated in  FIG. 2 . Referring to  FIG. 2 , the screw  102  includes a top portion  202 , a middle portion  210 , and a tip portion  208 . To place the screw into a bone, a user (or any medical professional) would place the tip portion  208  proximate to the bone, and upon application of an instrument to the top portion  202  exert an appropriate amount of force to drive (by rotating) the screw  102  into the bone. In some embodiments, the screw  102  is configured to be inserted into a pre-tapped hole in the bone. The middle portion  210  includes threading  206  that is configured to allow such driving in a circular motion. The top portion  202  further includes instrument retaining opening  204  that accommodates placement of tools and instruments for driving the screw into the bone. In some embodiments, the opening  204  can have a hexagonal arrangement that allows placement of specialized tooling that matches such arrangement. The top portion  202  of the screw  102  can have a smooth outside surface or, in the alternative, can have locking grooves, as shown in  FIGS. 8 and 9  and discussed below. 
     The housing  120  of the lumbar plate  100  further includes locking mechanisms  103 ( a, b ). The locking mechanisms  103  are configured to be placed between screw openings  122  into their respective locking mechanism openings  125 ( a, b ). The locking mechanism openings  125  are configured to connect screw openings  122 . In some embodiments, the opening  125   a  is configured to connect screw openings  122   a  and  122   b , and the opening  125   b  is configured to connect screw openings  122   c  and  122   d . Referring to  FIGS. 3 and 4 , the locking mechanism  103  is illustrated ( FIG. 3 ) being placed into the opening  125   b . Referring to  FIG. 4 , the opening  125   b  is configured to include a center portion  415  connected to channels  411 ( c, d ) on each side of the center portion  415 . The channels  411  further connect with respective openings  122 ( c, d ). The center portion  415  has a circular form that allows the locking mechanism  103   b  to rotate, once the mechanism  103   b  is placed into the center portion  415 . The channels  411  are configured to be partially covered by respective extensions  404 ( c, d ). The extensions  404  are configured to protrude from the body  120  of the lumbar plate  100 . The extensions  404  further prevent the locking mechanism  103  from falling out, once it is secured inside the body  120 . 
     Referring to  FIG. 3 , the locking mechanism  103  is illustrated in further detail. The mechanism includes a body portion  307  coupled to two protrusions  303 ,  305  on the body. In the embodiment shown, the protrusions are bars  303  and  305  on each side of the body  307 . In some embodiments, the body portion  307  includes a slot  309  that allows detachable coupling of an instrument for rotation of the locking mechanism  103 . In some embodiments, the body portion  307  includes rounded edge that allows the mechanism  103  to rotate inside the opening  125  (not shown in  FIG. 3 ). Further, in some embodiments, the bars  303  and  305  can be configured to have a round cross-section that allows rotation of the bars inside the partially covered channels  411 . As can be understood by one skilled in the art, the body  307  and the protrusion or bars  303 ,  305  can have any other desired shape. In some embodiments, the channels  411  and extensions  404  may have a locking feature to engage the protrusion or bars  303 ,  305  that locks the locking mechanism  103  in place when protrusion or bars  303 ,  305  lock the screw  102 . This may include ramps or detents within channels  411  that engage protrusion or bars  303 ,  305 . In other words, in this embodiment there may be two locking features, the first locking feature being when the protrusion or bars  303 ,  305  lock the screw  102  in the plate and the second locking feature being when the protrusion or bars  303 ,  305  are locked in the channels  411 , so the locking mechanism does not rotated backwards to allow release of the screw. 
     In one embodiment shown in  FIG. 4 , the locking mechanism  103  is placed into the opening  125  by aligning the bars  303 ,  305  with the channels  411  and dropping the mechanism  103  into the opening  125 . The mechanism  103  is secured to the body  120  of the lumbar plate  100  after at least one screw  102  is placed into the screw openings  122  (as shown in  FIG. 5 ). Once the screw  102  is inserted through the screw openings  122 , the locking mechanism  103  is inserted into the opening  125  (with bars  303  and  305  being placed through the channels  411 ). To secure the screws  102 , the locking mechanism  103  is rotated with the bars  303 ,  305  being rotated toward the partially closed portion of the channels  411 . Hence, the bars  303 ,  305  lock the screws  102  to the screw openings  122 , thereby preventing screws  102  from falling out. To unlock the screws  102 , the locking mechanism  103  is rotated in an opposite direction and removed from the opening  125 , thereby releasing the screws  102  and allowing them to be removed. As stated above, the rotation of the locking mechanism  103  can be accomplished using any number of tools (including hands). A locked lumbar plate  100  arrangement is illustrated in  FIG. 5 . In other embodiments, the locking mechanism  103  may be held in place within the opening  125  with a locking screw, such as screw  605  or  1100 , discussed below. Once in place, the locking mechanism  103  may be rotated from a first position in which the bars  303 ,  305  are positioned to allow screws  102  be inserted through the screw openings  122  to a second position in which the bars  303 ,  305  engage and lock the screws  102  (shown in  FIGS. 1 and 5 ). 
       FIGS. 6-13  illustrate another exemplary embodiment of an anterior lumbar plate  600 , according to some embodiments of the present invention.  FIG. 7  is a partial cross-sectional view of the assembled bone plate  600  along with screws  602 ( a, b, c, d ).  FIGS. 8-9  illustrate an exemplary bone screw  602  having a notched head ( FIG. 9 ).  FIG. 10  illustrates an exemplary curved locking tooth  604  shown in  FIG. 6 , according to some embodiments of the present invention.  FIG. 11  illustrates an exemplary securing screw  1100  for securing the curved locking tooth  604 , according to some embodiments of the present invention.  FIGS. 12-13  illustrate another exemplary embodiment of the locking tooth  1200  for locking the screws  602 . In some embodiments, the bone screws  602  can be have a diameter between 5.0 mm and 8.0 mm, preferable between 6.0 mm and 7.0 mm, and a length between 20 mm and 60 mm. 
     In some embodiments, the lumbar plate  600  is configured to allow unrestricted clockwise rotation of the bone screw  602  while restricting its counterclockwise rotation. The lumbar plate  600  includes an anti-counterclockwise rotation mechanism that is configured to allow the bone screw  602  to properly align with the stabilization plate  600  and be fully seated. 
     Referring to  FIG. 8 , bone screws are machined with “hook” shape notches in a circular pattern around the top face of the head (as shown in  FIG. 9 ). A rectangular shaped recess  1227  is cut out of the bone plate  1220  horizontally between the two bone screw holes (as shown in  FIG. 12 ). A threaded small diameter hole is drilled in the recess, centered horizontally and vertically between the bone screw holes. Once the bone screw is tightened, a trapezoidal shaped tooth (as shown in  FIG. 13 ) is placed in the corresponding recess and secured to the plate with a small hex screw (as shown in  FIG. 11 ). The curvature of the tooth lock into the “hook” notch in the bone screws and prevent the bone screw from rotating counter-clockwise or backing out. After further analysis, it was observed that the trapezoidal shape tooth only locked into screws on the left side of the plate (as shown in  FIG. 12 ). This embodiment may be used in a one screw configured plate (not shown). 
     Referring to  FIG. 6 , bone screws are machined with “hook” shape notches in a circular pattern around the top face of the head (as shown in  FIGS. 8 and 9 ). An “S” shaped recess  625  is cut out of the bone plate horizontally between the two bone screw holes  622 . A threaded small diameter hole is drilled in the recess, centered horizontally and vertically between the bone screw holes. An “S” shaped tooth  604  (as shown in  FIG. 10 ) is placed in the corresponding recess  625  and held in place with a small hex screw  1100  (as shown in  FIG. 11 ). As the bone screw is tightened (clockwise rotation), the convex side of the “S” shaped tooth contacts the bone screw moving it into the recess of the plate. The “S” shaped tooth does not restrict tightening the bone screw. Once the bone screws are tightened, the concave side of the “S” shaped tooth locks into the “hook” shape notches in the head of the bone screw preventing the bone screw from rotating counter-clockwise or backing out. The “S” shaped tooth is locked into place via a small hex screw. In other embodiments, the “S” shaped tooth may be bias against the screw, with a spring or other means, and have a ratchet type engagement with the screw during tightening. 
     Referring to  FIG. 6 , the lumbar plate  600  includes a housing  620  having an interior opening  630  and screw openings  622 ( a, b, c, d ) configured to be disposed symmetrically about the opening  630 . In some embodiments, the lumbar plate  600  can include a plurality of interior openings or no interior openings at all. The screw openings  622  are configured to receive respective screws  602 ( a, b, c, d ). In some embodiments, the lumbar plate  600  can accommodate placement of more than four screws (as illustrated in  FIG. 6 ) or less than four screws, and may have differing number of screws at each body. Further, the screws  602  can have various lengths, widths, shapes, or any other characteristics. 
     In some embodiments, the shape of the housing  620  of the lumbar plate  600  can be rectangular, whereby the screw openings  622  are configured to protrude away from the housing  620 , as shown in  FIG. 6 . In some embodiments, the shape of the housing  620  can be square, circular, oval, polygonal, or any other desired shape. Further, the housing  620  has an arcuate shape, wherein, upon insertion of the screws  602 , axis of the screws  602  are configured to converge toward each other (for example, the axis of the screw  602   a  is configured to be convergent with the axis of the screw  602   b ; similarly for screws  602   c  and  602   d ). In some embodiments, the axis of all or some of the screws  602  are configured to converge toward each other, upon being inserted into the screw openings  622 . Such arrangement allows angular placement of the lumbar plate  600  on a vertebral body or any other bone in the body. As can be understood by one skilled in the art, the arcuation of the housing  620  of the lumbar plate  600  can have any angle (including 0 degrees (or 180 degrees), which would correspond to a flat lumbar plate  600 ). In some embodiments, the axis of all or some of the screws are configured to be parallel or converge away each other. In some embodiments, the screw openings  622  can be configured to be contained within the housing  620  and not protrude away from its outer perimeter. 
     The screw openings  622  can be configured to retain screws  602  in various ways. In some embodiments, the screw openings  622  are configured to have a larger diameter near their top surface and a smaller diameter near their bottom surface. The smaller diameter can be selected to prevent screw  602  from falling through the opening  622  upon insertion of the screw  602 . Hence, the smaller diameter can be smaller than the head portion of the screw  602 . In some embodiments, the screw openings  622  can include screw retaining ledges (not shown) that are configured to protrude toward the center of the screw opening  622  and thereby, create a smaller diameter opening disposed in the screw opening  622 . Such smaller diameter opening prevents screw  602  from falling through the opening  622  upon insertion. As can be understood by one skilled in the art, there are other ways of preventing screws  602  from falling through the openings  622 . As can be understood by one skilled in the art, the openings  622  can have any desired shape, e.g., round, square, rectangular, polygonal, etc. 
     An exemplary screw  602  is illustrated in  FIGS. 8-9 . Referring to  FIG. 8 , the screw  602  includes a top portion  802 , a middle portion  810 , and a tip portion  808 . To place the screw into a bone, a user (or any medical professional) would place the tip portion  808  proximate to the bone, and upon application of an instrument to the top portion  802  exert an appropriate amount of force to drive (by rotating) the screw  602  into the bone. The middle portion  810  includes threading  806  that is configured to allow such driving in a circular motion. The top portion  802  further includes instrument retaining opening  804  that accommodates placement of tools and instruments for driving the screw into the bone. In some embodiments, the opening  804  can have a hexagonal arrangement that allows placement of specialized tooling that matches such arrangement. The top portion  802  of the screw  602  can have a smooth outside surface or, in the alternative, can have locking grooves or notches  821 . The notches  821  are configured to interlock the screw  602  with the locking tooth  604  (shown in  FIGS. 6 and 10 ) or the locking tooth  1200  (shown in  FIGS. 12 and 13 ). The notches  821  are configured to be slanted, thus, creating a stopper for the locking tooth  604  or  1200 , thereby, preventing rotation of the screw  602 . 
     Referring again to  FIG. 6 , the housing  620  of the lumbar plate  600  further includes locking teeth  604 ( a, b ). The locking teeth  604  are configured to be placed between screw openings  622  into their respective locking mechanism openings  625 ( a, b ). The locking mechanism openings  625  are configured to connect screw openings  622 . In some embodiments, the opening  625   a  is configured to connect screw openings  622   a  and  622   b , and the opening  625   b  is configured to connect screw openings  622   c  and  622   d . Referring to  FIGS. 6-7  and  10 - 11 , the locking tooth  604  is illustrated ( FIG. 7 ) being placed into the opening  625   b.    
     Referring to  FIGS. 10-11 , the locking tooth  604  is illustrated in further detail. The tooth  604  includes a body portion  1007  having two curved ends  1003  and  1005  on each side of the body  1007 . In some embodiments, the body portion  1007  includes an opening  1009  that allows removable insertion of a hex-locking screw  1100  (shown in  FIG. 11 ) (same as screw  605  shown in  FIG. 6 ). The hex-locking screw  1100  is configured to secure the tooth  604  to the plate  600  inside the openings  625  and allow rotation of the tooth  604 . Referring to  FIG. 11 , the hex locking screw  1100  includes a shaft portion  1102  having partial threads portion  1104  that secure the screw  1100  to the body portion  620  of the lumbar plate  600  and an unthreaded portion  1105  having a length that is approximately equal to the width of the tooth  604 . The screw  1100  also includes a top portion  1106  that allows a user (or any other medical professional) to secure the screw to the plate  600  using an instrument (or a hand). Referring back to  FIG. 10 , the tooth  604  is configured to have smooth curving surfaces throughout, so that when the tooth  604  is placed into the opening  625 , its smooth surfaces are configured to create an uninterrupted surface with the interior surface of the openings  622 . As shown in  FIG. 6 , the tooth  604  is configured to create a smooth surface with two interior surfaces of screw openings  622 , and thus, accommodate locking of two screws  602 . In other words, the locking mechanism or tooth  604  is configured to rotate from a first configuration in which the tooth  604  creates an uninterrupted surface with the interior surface of the openings  622  allowing the screw to pass, to a second configuration in which the tooth  604  engages and locks the screw  602  in place. 
     Referring back to  FIG. 6 , the locking tooth  604  is placed into the opening  625  by aligning the curved tips  1003 ,  1005  with corresponding curved portions of the opening  625  and dropping the tooth  604  into the opening  625  (first configuration). The tooth  604  can be secured to the body  620  of the lumbar plate  600  after at least one screw  602  is placed into the screw openings  622  (as shown in  FIG. 6 ). To secure the screws  602 , the locking tooth  604  is rotated with the tips  1003 ,  1005  of the tooth  604  being rotated until the snap into the notches  821  disposed on the screws  602  (second configuration). Hence, the tips  1003 ,  1005  lock the screws  602  to the screw openings  622 , thereby preventing screws  602  from falling out. In some embodiments, the screws  602  can be placed after the tooth  604  is secured to the body  620 . In such case, the tooth  604  is secured using hex-locking screw  605  inside the opening  625  of the body  620 , then the tooth  604  is rotated into an unlocked position (whereby the tips  1003  and  1005  form a smooth surface with the interior surfaces of corresponding screw openings  622 ) and screws  602  are inserted. To lock the screws, the tooth  604  is rotated until the tips  1003 ,  1005  are snapped into one of the notches  821  of the screws  602 . To unlock the screws  602 , the locking tooth  604  is rotated in an opposite direction, thereby releasing the screws  602  and allowing them to be removed. As stated above, the rotation of the locking tooth  604  can be accomplished using any number of tools (including hands). A locked lumbar plate  600  arrangement is illustrated in  FIG. 6 . 
       FIGS. 12-13  illustrate another exemplary embodiment of the present invention&#39;s locking tooth  1200 . The locking tooth  1200  is configured to have a trapezoidal shape with locking tips  1303 ,  1305 , where the tips are configured to interact with the notches  821  of the screws  602 . The locking tips  1303 ,  1305  are configured to be disposed at the bottom of the trapezoid. The tooth  1200  further includes an opening  1209  that is configured to secure the tooth  1200  inside the opening  1227  of the body  1220  of the plate  1201 . The tooth  1200  can be secured to the body  1220  using the hex-locking screw  1100  shown in  FIG. 11 . To lock the screws  602 , the tooth  1200  can be lifted from the opening  1227  and rotated (in some embodiments, the tooth  1200  can remain secured to the body  1220  using the hex-locking screw, i.e., the tooth  1200  is not being removed). Then, the screws  602  are inserted and then the tooth  1200  is rotated in an opposite direction and re-inserted into the opening  1227 , thereby locking the screws  602 . 
     Example embodiments of the methods and components of the present invention have been described herein. As noted elsewhere, these example embodiments have been described for illustrative purposes only, and are not limiting. Other embodiments are possible and are covered by the invention. Such embodiments will be apparent to persons skilled in the relevant art(s) based on the teachings contained herein. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.