Abstract:
Medical device locking mechanisms and related methods and systems. In some embodiments, the medical device may comprise an outer surface defining one or more fastener openings configured for receiving one or more fasteners. The one or more fasteners may comprise an upper surface configured to be engaged by a component of the locking system to prevent fastener backout. A plurality of petal structures may be configured to be selectively expanded or contracted to engage the head portion and retain the at least one fastener within the fastener opening to prevent the fastener from backing out of the fastener opening. A biasing member may selectively engage the plurality of petal structures to either expand or contract the plurality of petal structures to facilitate locking the fastener(s) in place within the device.

Description:
RELATED APPLICATIONS 
     This application is a divisional of co-pending U.S. patent application Ser. No. 14/277,001, filed on May 15, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 11/875,072, filed on Oct. 19, 2007, which is a continuation-in-part of U.S. patent application Ser. No. 11/804,545, filed on May 18, 2007, which are herein incorporated by reference in their entireties. 
    
    
     FIELD OF THE INVENTION 
     Some embodiments disclosed herein relate generally to locking and/or anti-backout mechanisms for various medical devices and/or implants, and related methods. For example, various features and/or components of embodiments disclosed herein may be incorporated into and/or used in conjunction with various implants, including cervical plates, thoracolumbar fixation plates, anterior lumbar fixation plates, standalone interbody devices, bone fracture fixation plates, pedicle screw couplers, such as pedicle screw tulips, and the like. 
     Some embodiments may comprise one or more novel locking screws and a novel plate that works cooperatively therewith. The locking mechanism, the one or more novel locking screws, and/or a novel plate or other such implants may be used for the fixation/stabilization of the spine, such as the cervical spine. Alternatively, some embodiments may be configured for the fixation/stabilization of the lumbar spine, the sacral spine, and/or the placement of bone grafts, biocompatible inserts, and the like. Still other embodiments may be used for the fixation/stabilization of other anatomical structures and/or non-anatomical structures. 
     BACKGROUND OF THE INVENTION 
     The vertebrae of the human spine are generally arranged in a column, with an intervertebral disc disposed between each. These intervertebral discs transmit forces and perform a “cushioning” function. As a result of the stresses and strains continuously applied to the intervertebral discs, as well as disease, degeneration and/or deformity is relatively common. Typically, diseased, degenerated, and/or deformed intervertebral discs are treated by removal and the insertion of an implant, anatomical (i.e., a bone graft) or mechanical (i.e., a biocompatible insert), in the associated intervertebral space. The adjacent vertebrae are preferably immobilized using a plate, such as a cervical plate, during bone graft or biocompatible insert placement and subsequently until they fuse, for example. 
     Conventional cervical plates typically include a plurality of screw holes and one or more access holes, through which one or more bone grafts or other biocompatible inserts are placed. These cervical plates may span one or multiple levels, with a level defined by the presence of an intervertebral space, and may be secured to the vertebrae of the spine using a plurality of bone screws. Absent some sort of locking mechanism, these bone screws tend to reverse thread, or back out, over time. This reverse threading or backing out is obviously problematic. Various locking mechanisms exist in the art for preventing reverse threading or backing out, and typically involve the use of polymeric bushings, securing caps, securing cover plates, novel thread designs, and the like that prevent the bone screws from disengaging the vertebrae and/or cervical plate subsequent to installation. Many of these locking mechanisms are ineffective, overly complicated, cumbersome to implement, and/or unnecessarily expensive. Thus, what is still needed in the art is a robust, simple, and inexpensive locking mechanism for cervical plates or other medical devices or implants incorporating screws or other fasteners. 
     SUMMARY 
     In various exemplary embodiments, the present invention provides such a robust, simple, and inexpensive locking and/or anti-backout mechanism for a screw and/or other fastener of a plate or other medical implant or device. Various embodiments may be elegant in design and effective in performance. Some embodiments may utilize a plate with holes one or more of which may comprise a locking lip structure and/or receiving well, and locking screws that may incorporate a head portion having petal structures that are outwardly biased prior to insertion via an internally-disposed c-ring or another similar biasing member. Advantageously, in some embodiments, the lead-in torque of each of the locking screws is less than the lead-out torque of each of the locking screws. Thus, reverse threading or backing out is prevented. 
     In a specific example of an embodiment of a fastener locking system for a medical device, such as, for example, a cervical plate, a thoracolumbar fixation plate, an anterior lumbar fixation plate, an intervertebral device, a bone fracture fixation plate, or a pedicle screw coupler, the system may comprise an outer surface defining at least one fastener opening in the outer surface configured for receiving a fastener. The at least one fastener opening may comprise a lip structure positioned adjacent to the outer surface. 
     The system may further comprise at least one fastener, such as a locking screw, configured to be received in the at least one fastener opening. The at least one fastener may comprise a head portion comprising a plurality of petal structures configured to expand and contract to expand and contract a size of the head portion. 
     The system may further comprise a biasing member, such as a c-ring, configured to be positioned within the plurality of petal structures to expand a size of the head portion. The at least one fastener may be configured to contract to extend past the lip structure and then be expanded by the biasing member within the head portion such that the petal structures engage the lip structure to inhibit the at least one fastener from being removed from the at least one fastener opening. 
     In some embodiments, an upper portion of the lip structure may be angled inward towards a central axis of the at least one fastener opening such that the plurality of petal structures contracts as the head portion is inserted into the at least one fastener opening. 
     In another specific example of an embodiment of a fastener locking system for a medical device, the system may comprise a medical device comprising an outer surface defining at least one fastener opening in the outer surface configured for receiving a fastener. The at least one fastener opening may be defined at least in part by a plurality of petal structures configured to expand and contract. 
     The system may comprise a biasing member configured to be positioned around the plurality of petal structures to provide an inward bias to the plurality of petal structures and contract a size of the at least one fastener opening. 
     The system may further comprise at least one fastener configured to be received in the at least one fastener opening. The at least one fastener may comprise a head portion configured to be retained in the at least one fastener opening by the plurality of petal structures and the biasing member. 
     In some embodiments, the head portion may comprise an upper surface, and the plurality of petal structures may be configured to engage the upper surface after the biasing member has been positioned around the plurality of petal structures with the at least one fastener in the at least one fastener opening. 
     In some embodiments, the biasing member may be configured to be positioned concentrically around the plurality of petal structures. 
     In still another specific example of a fastener locking system for a medical device, the system may comprise a medical device comprising an outer surface defining one or more fastener openings configured for receiving a fastener. The system may comprise at least one fastener configured to be received in the at least one fastener opening. The at least one fastener may comprise a head portion comprising an upper surface. 
     The system may further comprise a plurality of petal structures configured to be selectively expanded or contracted to engage the head portion and retain the at least one fastener within the at least one fastener opening to inhibit the fastener from backing out of the at least one fastener opening. A biasing member may be configured to selectively engage the plurality of petal structures to either expand or contract the plurality of petal structures between an open configuration in which the at least one fastener is able to be removed from the at least one fastener opening and a closed configuration in which the at least one fastener is at least inhibited from being removed from the at least one fastener opening. The plurality of petal structures may be configured to engage the upper surface of the at least one fastener in the closed configuration. 
     In some embodiments, the plurality of petal structures may be part (in some embodiments an integral part) of the head portion. In some such embodiments, the biasing member may be configured to be positioned within the plurality of petal structures to expand a size of the head portion. 
     In some embodiments, the plurality of petal structures may together define a central driver bore configured to be engaged by a keyed tool. In some such embodiments, the central driver bore may comprise a polygonal shape. 
     In some embodiments, at least a subset of the plurality of petal structures may comprise an inner groove configured to receive the biasing member therein. In some such embodiments, each of the plurality of petal structures may comprise an inner groove configured to receive the biasing member therein. 
     In some embodiments, the plurality of petal structures may at least partially define the at least one fastener opening, and the biasing member may be configured to be positioned around the plurality of petal structures to provide an inward bias to the plurality of petal structures. 
     In some embodiments, the at least one fastener opening may comprise a lip structure positioned adjacent to the outer surface. As mentioned elsewhere herein, in some such embodiments, the petal structures may be configured to retain the fastener within the fastener opening beneath the lip structure such that the lip structure contacts an upper surface of a head portion of the fastener. 
     The features, structures, steps, or characteristics disclosed herein in connection with one embodiment may be combined in any suitable manner in one or more alternative embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments are illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like system components and/or method steps, as appropriate, and in which: 
         FIG. 1  is an exploded perspective view of one exemplary embodiment of the cervical plate locking mechanism of the present invention (being installed using a keyed screwdriver or the like), the cervical plate locking mechanism including both novel plate and novel locking screw designs; 
         FIG. 2  is an exploded perspective view of one exemplary embodiment of the novel locking screw design of  FIG. 1 , the locking screw including a head portion that incorporates a plurality of petal structures that are outwardly biased by an internally-disposed c-ring or the like; 
         FIG. 3  is a perspective view of the novel locking screw design of  FIGS. 1 and 2 , the locking screw being in its “as inserted” state, with the c-ring being installed and the head portion being compressed; 
         FIG. 4  is a partial cross-sectional view of the cervical plate locking mechanism of  FIG. 1 , the novel locking screw of  FIGS. 1-3  in the process of being inserted into the novel plate of  FIG. 1 ; 
         FIG. 5  is a partial cross-sectional view of the cervical plate locking mechanism and locking screw of  FIGS. 1-4  being fully inserted into the novel plate of  FIGS. 1 and 4 ; 
         FIG. 6  is a partial cross-sectional view of the cervical plate locking mechanism and locking screw of  FIGS. 1-5  after the locking screw has been fully inserted into the locking plate and allowed to expand therein; 
         FIG. 7  is a partial cross-sectional view of the cervical plate locking mechanism of  FIGS. 1, 4, and 5 , the novel locking screws of  FIGS. 1-5  being inserted into the novel plate of  FIGS. 1, 4, and 5  at various exemplary angles; 
         FIG. 8  is a perspective view of another exemplary embodiment of the cervical plate locking mechanism of the present invention, the cervical plate locking mechanism again including both novel locking plate and novel screw (not illustrated) designs; 
         FIG. 9  is a partial perspective view of the cervical plate locking mechanism of  FIG. 7 , the novel locking plate incorporating one or more screw-receiving holes each including a plurality of petal structures configured to engage and retain the novel screws (not illustrated); 
         FIG. 10  is an exploded perspective view of the cervical plate locking mechanism of  FIGS. 7 and 8 , a novel screw being inserted into a screw-receiving hole of the novel locking plate; 
         FIG. 11  is a perspective view of the cervical plate locking mechanism of  FIGS. 7-9 , novel screws fully inserted into all of the screw-receiving holes of the novel locking plate; 
         FIG. 12  is a partial perspective view of the cervical plate locking mechanism of  FIGS. 7-10 , novel screws fully inserted into all of the screw-receiving holes of the novel locking plate; and 
         FIG. 13  is a partial cross-sectional view of the cervical plate locking mechanism of  FIGS. 7-11 , a novel screws fully inserted into a screw-receiving holes of the novel locking plate. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     As described above, in various exemplary embodiments, the present invention provides a robust, simple, and inexpensive locking and/or anti-backout mechanism. Some embodiments may be elegant in design and effective in performance, and may utilize a plate with holes that each incorporate a locking lip structure and/or receiving well. Associated locking screws may each incorporate a head portion having petal structures that are outwardly biased prior to insertion via an internally-disposed c-ring or the like. Advantageously, in some embodiments, the lead-in torque of each of the locking screws is less than the lead-out torque of each of the locking screws. Thus, reverse threading or backing out may be prevented. 
       FIG. 1  is an exploded perspective view of one exemplary embodiment of a cervical plate locking mechanism  10  of the present invention (being installed using a keyed tool, such as a keyed screwdriver  18  or the like), the cervical plate locking mechanism  10  including both novel plate and novel locking screw designs, as are described in greater detail herein below. Specifically, the cervical plate locking mechanism  10  comprises a plate  12  that is configured to be securely fixed to adjacent vertebrae of the cervical spine or the like via one or more locking screws  14  and one or more c-rings  16 . The keyed screwdriver  18  may be used to drive the one or more locking screws  14  through the plate  12  and into the adjacent vertebrae. 
     The plate  12  may comprise one or more screw-receiving holes  13  and, optionally, one or more access holes  15  for the placement of one or more bone grafts, biocompatible inserts, or the like. Preferably, the plate  12  is manufactured from a biocompatible material and is sized such that it achieves its intended purpose. Material, shape, and size selection may be selected according to the knowledge of those of ordinary skill in the art. Each of the one or more locking screws  14  may comprise a threaded portion  17  and a head portion  19 . The threaded portion  17  of each of the one or more locking screws  14  may be configured to pass through the one or more screw-receiving holes  13  of the plate  12  and securely fix the plate  12  to the adjacent vertebrae. Thread selection is well known to those of ordinary skill in the art. 
     The head portion  19  of each of the one or more locking screws  14  may be configured to securely engage each of the one or more locking screws  14  with the plate  12 . As described in greater detail herein below, the head portion  19  of each of the one or more locking screws  14  may be outwardly biased by the c-ring  16 , or by another similar biasing member or other mechanism or feature. Such mechanism or feature may be inserted and/or compressed into the head portion  19  of a given locking screw  14 . In some embodiments, the head portion  19  may expand automatically upon insertion of the c-ring  16 . 
     The c-ring  16 , or another comparable mechanism, and the head portion  19  of the given locking screw  14  may be again compressed and subsequently allowed to expand as they are inserted into a given screw-receiving hole  13  of the plate  12 . More specifically, in some embodiments, the head portion  19  of a given locking screw  14  may be allowed to expand in the receiving well of the given screw-receiving hole  13 . This insertion may be accomplished using, for example, a matching flat, triangle, square, star, hexagon, octagon, or other keyed screwdriver  18 , as appropriate. Preferably, the shape of the outside of the head portion  19  of each of the locking screws  14  substantially corresponds to the shape of the inside of the associated receiving well, although this is not a requirement. 
       FIG. 2  is an exploded perspective view of one exemplary embodiment of the novel locking screw design of  FIG. 1 , the locking screw  14  including a head portion  19  that incorporates a plurality of petal structures  20  that are outwardly biased by the internally-disposed c-ring  16  or the like. Locking screw  14  and/or its accompanying locking features may be incorporated into and/or used in conjunction with various implants, such as cervical plates, thoracolumbar fixation plates, anterior lumbar fixation plates, standalone interbody devices, bone fracture fixation plates, pedicle screw couplers, such as pedicle screw tulips, and the like. 
     As described above, c-ring  16 , or other comparable mechanism, may be selectively inserted and/or compressed into the head portion  19  of a given locking screw  14 , and then allowed to expand. The c-ring  16 , or other comparable mechanism, and the head portion  19  of the given locking screw  14  may then be compressed again and subsequently allowed to expand as they are inserted into a given screw-receiving hole  13  ( FIG. 1 ) of plate  12  ( FIG. 1 ), or of another screw-receiving hole of another plate or other implant or medical device. 
     More specifically, the head portion  19  of the given locking screw  14  may be allowed to expand in a receiving well of the given screw-receiving hole  13 . This insertion may be accomplished using a matching flat, triangle, square, star, hexagon, octagon, or other keyed screwdriver  18  (as shown in  FIG. 1 ), as appropriate. 
     Preferably, the shape of the outside of the head portion  19  of each of the locking screws  14  at least substantially corresponds to the shape of the inside of the associated receiving well, although this is not a requirement. Accordingly, the head portion  19  of each of the locking screws  14  may comprise a plurality of concentrically-arranged petal structures  20  that are disposed around a central driver bore  21 , which may have a shape corresponding to that of the keyed screwdriver  18 . In one exemplary embodiment, the plurality of petal structures  20  may be formed by cutting concentrically-arranged slots into the head portion  19  of the locking screw  14 . Thus, the plurality of petal structures  20  may, in some embodiments and implementations, be integrally formed with the head portion  19  of the locking screw  14 . Alternatively, the plurality of petal structures  20  may be formed separately and then joined to the head portion  19  of the locking screw  14 . 
     The material characteristics and/or configuration of the plurality of petal structures  20  may, in some embodiments, impart the plurality of petal structures  20  with an inherent outward bias, which bias in some embodiments may be independent of the c-ring  16  or other comparable mechanism, although this is not required. 
     In some embodiments, the plurality of petal structures  20  may define an inner groove  22  extending around an inner perimeter of head portion  19 , such as around an exterior perimeter of central driver bore  21 , as shown in  FIG. 2 . Inner groove  22  may be configured to receive and retain the c-ring  16  or other comparable mechanism within the head portion  19  of the locking screw  14 .  FIG. 2  illustrates the head portion  19  of the locking screw  14  in an “unlocked” configuration, with the plurality of petal structures  20  being “open,” either due to the eventual insertion of the c-ring  16  or other comparable mechanism, or inherently.  FIG. 3  illustrates the head portion  19  of the locking screw  14  in a “locked” configuration, with the plurality of petal structures  20  being “closed,” either inherently or due to the eventual insertion of the head portion  19  of the locking screw  14  into a receiving well. Thus, in some embodiments, the plurality of petal structures  20  may be configured to be flexibly biased towards a locked/closed configuration such that the petals  20  can be flexed open to an unlocked/open configuration to receive c-ring  16  and then automatically revert to a locked/closed configuration with c-ring  16  therein. In some embodiments, the presence of c-ring  16  within head portion  19  may partially flex petals  20  towards an unlocked/open configuration (but not fully) so as to enlarge the diameter of head portion  19  and retain head portion  19  within a locking hole of a device, such as cervical plate  12 . 
     It can also be seen in  FIGS. 2 and 3  that petal structures  20  each partially defines an upper surface of head portion  19  of locking screw  14 . In the depicted embodiment, this upper surface is flat. In this manner, the upper surface of head portion  19  may be engaged with a lip structure of a locking hole of a device, such as cervical plate  12 , as discussed in greater detail below.  FIGS. 2 and 3  further depict that petal structures  20  together define central driver bore  21  (as shown in  FIG. 3 ) comprising a polygonal opening, and can be expanded by flexing petal structures  20  (as shown in  FIG. 2 ) such that petal structures  20  no longer define the same bore opening. In this manner, a keyed tool, such as keyed screwdriver  18 , may be used to expand central driver bore  21  by inserting the keyed tool and rotating it. This may allow for the c-ring  16  to be inserted into inner groove  22 .  FIG. 3  also illustrates that, in a closed configuration, petal structures  20  at least substantially enclose c-ring  16  within head portion  19  to prevent inadvertent removal of c-ring  16  after a locking screw  14  has been fully engaged within a corresponding receiving hole  13 . 
       FIG. 4  is a partial cross-sectional view of the cervical plate locking mechanism  10  of  FIG. 1 , the novel locking screw  14  of  FIGS. 1-3  in the process of being inserted into the novel plate  12  of  FIG. 1 . It should be noted that the head portion  19  of the locking screw  14 , and specifically the lower, outer portion of each of the plurality of petal structures  20 , optionally incorporates a recessed or otherwise weakened area  24 , or flexure, in order to facilitate the flexibility and/or outward biasing of the plurality of petal structures  20  by the c-ring  16  or other comparable mechanism, after it is inserted into the inner groove  22  that is manufactured into the middle, inner portion of each of the plurality of petal structures  20 . 
     One or more of the one or more screw-receiving holes  13  of the plate  12  or other such device may comprise an annular lip structure  26  through which the head portions  19  of the locking screws  14  may be inserted (with a compression/expansion action). This annular lip structure  26  may serve to retain the head portion  19  of the given locking screw  14  once it is fully inserted and expanded, thereby preventing the reverse threading or backing out of the locking screw  14 . 
     Optionally, the inner annular surface  28  of each of the screw-receiving holes  13  of the plate  12  may be curved in a generally concave manner, as shown in  FIGS. 4-6 , but shaped such that the lead-in torque of a given locking screw  14  is less than the lead-out torque or the locking screw  14 , i.e., the inner annular surface angles adjacent to the outer surface  29  of the plate  12  (at the “top” and “bottom” of the lip structure  26 ) vary as experienced by an inserted locking screw  14  versus a removed locking screw  14 , with the “top” angle being greater (more vertical or steep) and the “bottom” angle being smaller (more horizontal or shallow), for example. 
     As also shown in  FIGS. 4-6 , the portion of the lip structure  26  immediately adjacent to the upper surface of petal structures  20  is preferably angled slightly inward towards a center axis of central driver bore  21  to facilitate desirable feel and function of head portion  19  of the locking screw  14  fitting into screw-receiving hole  13  and preventing backout of locking screw  14  thereafter. 
       FIG. 5  is a partial cross-sectional view of the cervical plate locking mechanism  10  of  FIGS. 1 and 4 , the novel locking screw  14  of  FIGS. 1-4  being fully inserted into the novel plate  12  of  FIGS. 1 and 4 . Again, it should be noted that the head portion  19  of the locking screw  14 , and specifically the lower, outer portion of each of the plurality of petal structures  20 , optionally incorporates a recessed or otherwise weakened area  24 , or flexure, in order to facilitate the flexibility and/or outward biasing of the plurality of petal structures  20  by the c-ring  16  or other comparable mechanism, after it is inserted into the inner groove  22  that is manufactured into the middle, inner portion of each of the plurality of petal structures  20 . Each of the one or more screw-receiving holes  13  of the plate  12  may comprise an annular lip structure  26  through which the head portions  19  of the locking screws  14  are inserted (with a compression-expansion action). 
     This annular lip structure  26  serves to retain the head portion  19  of the given locking screw  14  once it is fully inserted and expanded, as illustrated, thereby preventing the reverse threading or backing out of the locking screw  14 . As described above, optionally, the inner annular surface  28  of each of the screw-receiving holes  13  of the plate  12  is curved in a generally concave manner, but shaped such that the lead-in torque of a given locking screw  14  is less than the lead-out torque or the locking screw  14 , i.e. the inner annular surface angles adjacent to the outer surface  29  of the plate  12  (at the “top” and “bottom” of the lip structure  26 ) vary as experienced by an inserted locking screw  14  versus a removed locking screw  14 , with the “top” angle being greater (more vertical or steep) and the “bottom” angle being smaller (more horizontal or shallow), for example. 
       FIG. 6  depicts head portion  19  of locking screw  14  after it has been allowed to expand within receiving hole  13  by the expansion of c-ring  16 . As depicted in this figure, once this expansion takes place, an upper surface of head portion  19  of locking screw  14  contacts a lower surface of lip structure  26  to retain locking screw  14  in place and prevent, or at least reduce the possibility of, backup. 
     Thus, some embodiments may be configured to have a first, fully open configuration in which the petal structures  20  are fully open to receive c-ring  16 , a second, partially open configuration in which c-ring  16  flexes petal structures  20  partially open, and a third, fully-closed configuration in which c-ring  16  is absent and petal structures  20  are able to fully compress together. 
       FIG. 7  is a partial cross-sectional view of the cervical plate locking mechanism  10  of  FIGS. 1, 4, 5, and 6  the novel locking screws  14  of  FIGS. 1-5  being inserted into the novel plate  12  of  FIGS. 1, 4, 5, and 6  at various exemplary angles relative to both the plate  12  and the underlying vertebrae. In this embodiment, each of the receiving wells may be asymmetrical in shape such that the head portion  19  of each of the locking screws  14  snugly and securely engages the receiving well, although this is not necessarily illustrated. In other words, each of the receiving wells may be appropriately angled in the plate  12  in order to receive each of the angled locking screws  14 . 
     Referring to  FIGS. 8-13 , in another exemplary embodiment of a locking mechanism  100  of the present invention, the locking mechanism  100  again comprises both novel locking plate and novel screw designs, as are described in greater detail herein below. Locking mechanism  100  also comprises a cervical plate locking mechanism although, as mentioned above, this locking mechanism may be applied to a wide variety of other devices and implants, such as thoracolumbar fixation plates, anterior lumbar fixation plates, standalone interbody devices, bone fracture fixation plates, pedicle screw couplers, such as pedicle screw tulips, and the like. 
     More specifically, the cervical plate locking mechanism  100  comprises a locking plate  102  that is configured to be securely fixed to adjacent vertebrae of the cervical spine or the like via one or more screws  104  and one or more c-rings  106 . The keyed screwdriver (not illustrated) is used to drive the one or more screws  104  through the locking plate  102  and into the adjacent vertebrae. The locking plate  102  comprises one or more screw-receiving holes  103  and, optionally, one or more access holes  105  for the placement of one or more bone grafts, biocompatible inserts, or the like. 
     In some embodiments, the locking plate  102  may be manufactured from a biocompatible material and may be sized such that it achieves its intended purpose. Material, shape, and size selection may be selected by those of ordinary skill in the art. Each of the one or more screws  104  may comprise a threaded portion  107  and a head portion  109 . The threaded portion  107  of each of the one or more screws  104  may be configured to pass through the one or more screw-receiving holes  103  of the locking plate  102  and securely fix the locking plate  102  to the adjacent vertebrae. Thread selection may be as desired to those of ordinary skill in the art. 
     The head portion  109  of each of the one or more screws  104  is configured to securely engage each of the one or more screws  104  with the locking plate  102 . As described in greater detail herein below, a plurality of petal structures  120  disposed about each of the screw-receiving holes  103  may be inwardly biased by the c-ring  106 . Petal structures  120  may be incorporated into plate  102 , or into another implant or device comprising screw-receiving holes. A c-ring  106 , or another comparable mechanism may be expanded and subsequently allowed to contract around the petal structures  120  as the head portion  109  of a screw  104  is disposed in the receiving well of the given screw-receiving hole  103 . This insertion may be accomplished using a matching flat, triangle, square, star, hexagon, octagon, or other keyed screwdriver, as appropriate. Preferably, the shape of the outside of the head portion  109  of each of the screws  104  substantially corresponds to the shape of the inside of the associated receiving well, although this is not a requirement. Thus, in this exemplary embodiment, the plurality of petal structures  120  and the c-ring  106  have been shifted from the one or more screws  104  to the locking plate  102 , accomplishing the same purposes. 
     It can be best seen in  FIG. 13  that, once screw  104  is positioned in the receiving well/hole  103  and c-ring  106  has been positioned about the plurality of petal structures  120 , at least a portion of the locking mechanism (namely, a portion of the petal structures  120 ) extends above a top surface of screw  104  to secure screw  104  within hole  103  and prevent, or at least inhibit, backout of screw  104 . 
     Although the present invention has been illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following claims.