Abstract:
Disclosed are devices, systems, methods and surgical techniques for the retention of bone screws used in surgical applications. Various aspects of the invention include features to retain bone screws that are placed in an elongated plate and into a bony member to create a rigid construct and stabilize the member for the purpose of fusion. When the screws are placed through the plate, the retention systems can be engaged to prevent the screws from backing out.

Description:
CROSS-REFERENCE TO OTHER APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Patent Application Ser. No. 61/730,118 entitled “Expanding Blade Screw Retention System,” filed Nov. 27, 2012, the disclosure of which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD 
       [0002]    The present invention relates to devices, instrumentation, systems and methods that facilitate the retention of bone screws and/or other components in constructs used for various surgical applications. More particularly, the invention includes features that selectively retain bone screws or other anchoring devices that have been introduced through a base member and/or elongated plate and into a patient&#39;s bony anatomy. When the screws are advanced through the base member, the retention systems can be engaged, thereby preventing the screws from “backing out” of the member and/or bony anatomy. In various embodiments, the base member can create a rigid construct and stabilize the patient&#39;s anatomy for the purpose of fusion. 
       BACKGROUND OF THE INVENTION 
       [0003]    The invention relates generally to the field of orthopedic surgery and can be used in various applications that use bone screws. The bone screws are placed through many devices and then into the patient&#39;s bone. Because the bony elements are constantly moving there are forces applied to the fusion construct that can cause the screws to loosen. If the screws were to loosen to a degree that they would back out of the construct then they could become dislodged and cause harm to the fusion sight or to the patient. For this reason many have endeavored to use various systems to lock or retain the screw with various amounts of success. Many systems use additional components that need to be attached after the screws are placed which could cause misplacement of the retention device and failure to retain the screw. 
       SUMMARY OF THE INVENTION 
       [0004]    The invention uses an anterior cervical plate as the base substrate for the retention system but the invention can be used in other orthopedic applications as well. As mentioned earlier many systems use an additional construct that is added after the placement of the bone screws. The present invention does not rely on the correct placement of a retention system after the bone screws are placed but the invention&#39;s retention components are placed into position by the manufacturer of the device and are completely assembled prior to the surgery thus reducing the chances of misplacement and reducing the amount of time to perform the surgery. 
         [0005]    In one embodiment, the invention has three components; the base, the dual retention blade and retention screw. As stated earlier the base can be any number of orthopedic fusion devices such as a vertebral body replacement, bone plate or as in the current description an anterior cervical plate, where the plate can be modified to include a recessed surface where the surface will accommodate the size and configuration of the retention blade, and/or may have at least one bone screw threaded hole. In addition, the retention blade may be designed as an elongated plate with a notch and a female threaded hole that receives the retention screw. The notch may allow the dual retention blade to be split into at least two flexible arms. 
         [0006]    In another embodiment, the invention has three components; the base, the single retention blade and retention screw. The base may be specifically designed to include a recessed surface where the surface will accommodate the size and configuration of the retention blade. In addition, the single retention blade may be designed as an elongated plate with a notch and a female threaded hole that receives the retention screw. The notch may allow the single retention blade to be split into at least one flexible arms. 
         [0007]    In another embodiment, the retention screw may be designed with different surfaces and configurations. For example, the retention screw may include a plurality of increasing diameter surfaces, where the surgeon may rotate the retention screw until the increased diameters expand the flexible arms of a dual and/or single retention blade into the base bone screw threaded hole as desired. In another example, the retention screw may have different configurations of surfaces, where the surgeon may rotate the retention screw until it contacts the different configurations of surfaces (i.e., a camming or other action) to expand the flexible arms of a dual and/or single retention blade into the base bone screw threaded hole as desired. Furthermore, when the retention screw is advanced to the final position on the different surfaces or configurations, the retention blade and/or the retention screw can have an audible, tactile and/or visual features to allow the components to snap, or spring into causing an audible click and a tactile feedback on the driver. The surgeon will also be able to clearly see the retention blade covering the screw or screws. 
         [0008]    In another embodiment, the base, bone screws, retention blade and/or the retention screw may be pre-assembled by the manufacturer prior to the insertion of cervical spinal fixation system to the targeted bone segment. This allows the surgeon to attach the cervical spinal fixation system to in-situ to the targeted bone segment and secure the bone screws in a single operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will be more fully understood with reference to the detailed description and the accompanying drawings. 
           [0010]      FIG. 1  is an isometric view of one embodiment of a cervical spinal fixation system; 
           [0011]      FIG. 2  is an isometric exploded view of the cervical spinal fixation system in  FIG. 1 ; 
           [0012]      FIG. 3  is a top view of one embodiment of an anterior cervical plate; 
           [0013]      FIG. 4  is a side view of the anterior cervical plate of  FIG. 3 ; 
           [0014]      FIG. 5  is a sectioned view along lines  5 - 5  of the anterior cervical plate in  FIG. 3 ; 
           [0015]      FIG. 6  is a bottom view of the anterior cervical plate of  FIG. 3 ; 
           [0016]      FIG. 7  is an enlarged view of area  7  of the anterior cervical plate in  FIG. 3 ; 
           [0017]      FIG. 8  is an enlarged partial sectioned along lines  8 - 8  of the anterior cervical plate in  FIG. 4 ; 
           [0018]      FIG. 9  is a top view of one embodiment of a dual-bladed retention blade; 
           [0019]      FIG. 10  is an end view of the dual-bladed retention blade of  FIG. 9 ; 
           [0020]      FIG. 11  is a top view of one embodiment of a retention screw; 
           [0021]      FIG. 12  is a side view of the retention screw of  FIG. 11 ; 
           [0022]      FIG. 13  is an enlarged view of area  13  the retention screw in  FIG. 12 ; 
           [0023]      FIG. 14  is a top view of one embodiment of a bone screw; 
           [0024]      FIG. 15  is a side view of the bone screw of  FIG. 14 ; 
           [0025]      FIG. 16  is a top view of one embodiment of the retention subassembly demonstrating the neutral position of the retention blade; 
           [0026]      FIG. 17  is a side view of the retention subassembly of  FIG. 16  demonstrating the neutral position of the retention blade; 
           [0027]      FIG. 18  is an enlarged view of area  18  of the retention subassembly in  FIG. 17 ; 
           [0028]      FIG. 19  is a top view of the retention subassembly demonstrating the retention position of the retention blade; 
           [0029]      FIG. 20  is a side view of the retention subassembly demonstrating the retention position of the retention blade; 
           [0030]      FIG. 21  is an enlarged view of area  21  of the retention subassembly in  FIG. 20 ; 
           [0031]      FIG. 22  is a top view of one embodiment of a cervical spinal fixation system highlighting the retention features in the neutral position; 
           [0032]      FIG. 23  is a partial sectioned end view along lines  23 - 23  of the cervical spinal fixation system in  FIG. 22 ; 
           [0033]      FIG. 24  is an enlarged view of area  24  of the retention subassembly in  FIG. 23 ; 
           [0034]      FIG. 25  is an enlarged view of area  25  of the retention subassembly in  FIG. 23 ; 
           [0035]      FIG. 26  is a top view of one embodiment of a cervical spinal fixation system highlighting the retention features in the retention position; 
           [0036]      FIG. 27  is a partial sectioned end view of the cervical spinal fixation system along lines  26 - 26  in  FIG. 25 ; 
           [0037]      FIG. 28  is an enlarged view of area  28  of the retention subassembly in  FIG. 27 ; 
           [0038]      FIG. 29  is a top view of an alternate embodiment of a cervical spinal fixation system containing a single retention blade embodiment in the retention position; 
           [0039]      FIG. 30  is an isometric view of the cervical spinal fixation system containing a single retention blade of  FIG. 29  in the retention position; 
           [0040]      FIG. 31  is a top view of an alternate embodiment of a cervical spinal fixation system containing a single retention blade in the neutral position; 
           [0041]      FIG. 32  is an exploded isometric view of the cervical spinal fixation system containing a single retention blade of  FIG. 31  in the neutral position; and 
           [0042]      FIG. 33  is a top view of the single-bladed retention blade. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0043]    For the purpose of demonstrating how the invention functions it is shown as part of an anterior cervical plate. As stated earlier, those familiar with the art should clearly understand that various embodiments of an expanding blade screw retention system can be incorporated into many different types of devices, including those involving bone screws or other anchoring mechanisms, and therefore is not limited to the use of an anterior cervical plate only. 
         [0044]      FIG. 1  shows the invention in an anterior cervical plate assembly  100 . This is an isometric view and represents how the invention is fully deployed in what is hereafter referred to as the “retention” position. 
         [0045]      FIG. 2  shows an exploded view of the invention with the following components: the base substrate or “base” (hereafter referenced as an anterior cervical plate  200 ), a dual-bladed retention blade  300 , various retention screws  400  and bone screws  500 . In this embodiment of the invention there are three sets of the expanding blade retention system. Each set utilizes one retention blade nest  207  in the base, one dual-bladed retention blade  300 , one retention screw  400  and two bone screws  500 . It should be understood that two bone screws and a double retention blade are not required for the invention to work. It should be understood that an embodiment using a single bone screw  500  and single bladed retention blade  320 , as shown in  FIGS. 29-30 , will perform the required screw retention. 
         [0046]      FIG. 3  is a top view of an anterior cervical plate  200  containing the invention in three separate areas of the plate. The outside contour  201  of the plate is a typical design of a bone plate and has no significant bearing on the invention itself (and similar considerations should be understood for the openings  202  between the screw holes). These surfaces are for visual representations of a typical anterior cervical plate. It should be understood that such shapes and features of the plate need not be present for the invention to function as desired. Also shown in  FIG. 3  are three blade nests  207 , three female threaded holes  213  to receive the retention screws  400 , six bone screw holes  203  and a top surface  210 . This view also contains sectional view  5 - 5  and enlarged view  7  of the anterior cervical plate  200  which are shown in  FIGS. 5 and 7  respectively. 
         [0047]      FIG. 4  is a side view of the anterior cervical plate  200  and contains partial section  8 - 8  shown in  FIG. 8 . 
         [0048]      FIG. 5  is an enlarged sectional view along line  5 - 5  of  FIG. 3 . The following is a detailed description of one of the six bone screw  500  holes  203 . Each hole  203  consists of a conical taper  204 , which desirably allows the bone screw  500  to be inserted in and/or positioned at various angles; a spherical diameter  205 , which mates with spherical diameter  502  of the bone screw  500  (see  FIG. 15 ) (thereby facilitating the bone screw placement and plate engagement at various angles), and a reduced diameter  206  which desirably prevents the bone screw  500  from passing through the anterior cervical plate  200 . Additionally pictured in this view are the underside surface  209  of the anterior cervical plate  200  which desirably rests against the bone, and the two planar surfaces, retention blade nest  207  and upper retention blade surface  208  that capture the dual-bladed retention blade  300  in the anterior cervical plate  200 . 
         [0049]      FIG. 6  is the bottom view of the anterior cervical plate  200  and shows the bottom surface  209 . This bottom surface  209  is placed against the bony surface during surgery. 
         [0050]      FIG. 7  is an enlarged top view of area  7  of  FIG. 3 . This view highlights the top surface  210  (see  FIG. 3 ) of the anterior cervical plate  200  and the contours between the top surface  210  and upper blade retention blade surfaces  208  of one of the three retention blade nests  207 . In each retention blade nest  207  there is a female threaded hole  213  that receives the retention screw  400 . Also shown in the view is the notch  214  which receives the retention blade tang  307  of the dual-bladed retention blade  300  which desirably secures the central position of the dual retention blade  300 . Also shown are two concentric radii  215  which allow for the passage of the retention screw  400  into the retention blade nest  207  and the surface  217  which desirably contains the radial end  312  (see  FIG. 9 ) of the dual retention blade  300 . 
         [0051]      FIG. 8  is an enlarged sectional view along line  8 - 8  of  FIG. 4 . This view is sectioned to show further detail of the retention nest  207 . The retention nest  207  has surfaces  218  and,  219  that are desirably offset from surfaces  216  and  217  respectively and surface  220  in order to create a cavity that will retain the dual-bladed retention blade  300  in both the retention and neutral configurations. Surfaces  218 ,  219  and  220  also create the upper retention blade surface  208  (see  FIG. 5 ). Surfaces  214  and  215  need not necessarily have offset surfaces because they are used to receive the retention screw  400  and retention blade tang  307 . Symmetric surfaces  220  are formed to capture the radii  309  of dual-bladed retention blade  300 . Symmetric surfaces  218  are formed to capture surfaces  304  of the dual-bladed retention blade  300  when the dual-bladed retention blade  300  is in the retention configuration. Radial surface  207  is formed to capture radial surfaces  312  of the dual-bladed retention blade  300  when the dual-bladed retention blade  300  is either in the retention or neutral configurations. 
         [0052]      FIG. 9  is the detailed top view of the dual-bladed retention blade  300 . This embodiment of the invention details a dual blade configuration because this embodiment is designed to retain two bone screws  500  simultaneously. It is understood that a single blade embodiment  320 , as shown in  FIGS. 28 ,  29 ,  30  and  31  may operate in the same or a similar manner as the dual blade retention blade  300 . It is also understood that any configuration of the retention blade can be manufactured from various types of materials such as, but not limited to, titanium, super-elastic memory metal, polymers or carbon based materials. It is further understood that the manufacturing process used to manufacture the retention blade can be, but not limited to, conventional machining with tool bits, laser cut, water jet or photo etch. The dual blade configuration of the dual-bladed retention blade  300  can include symmetrical surfaces  301 ,  303 ,  304 ,  305 ,  306 ,  308 ,  309  and  310 , although non-symmetrical surfaces are contemplated by the present invention as well (see  FIG. 33 , for example). In this embodiment the surfaces  301  and  304  are collinear and are separated by radius  303 . Radius  303  is a clearance for the bone screw  500  when the dual-bladed retention blade  300  is in the neutral configuration. It should be known to those familiar in the art that the retention blade might not need a radius  303  or other indented area in applications where clearance for a component may not be an issue. Where no radius  303  is required, surfaces  301  and  304  may be one continuous surface. It should be also clearly known that the surface defined by surfaces  301 ,  303  and  304  can have unlimited variation in their features and surfaces as long as the retention of a screw is the intended result. Surfaces  304  and  306  plus surfaces  308  and  309  desirably form flexible arms  314  which flex and/or deform when the dual-bladed retention blade  300  transitions from the neutral to retention configurations and vise-versa. It is understood that the invention need not be limited to four or other number of surfaces to properly operate within the scope of the invention. As described earlier, tab  307  is used to center the dual-bladed retention blade  300  in the retention nest  207  when the dual-bladed retention blade  300  is in either the neutral or retention configurations. There are two surfaces  310  that form a channel or gap  302 . It is understood that the invention is not limited to these two parallel surfaces to operate within the scope of the invention as long as there is a separation between the sides. The dual-bladed retention blade  300  is shown in the neutral position or relaxed position. This neutral position is the shape that this embodiment of the dual-bladed retention blade  300  is manufactured to but those familiar in the art can recognize that the retention blades can be manufactured in the retention position and the retention screw could be designed and manipulated in various ways and/or configurations to move the retention blade to the neutral position, if desired. 
         [0053]      FIG. 10  is an end view of the dual-bladed retention blade  300  showing top surface  314  and bottom surface  313 . It is understood that though the dual-bladed retention blade  300  is shown as two parallel surfaces the invention can have numerous other surfaces or features as mentioned in the description of  FIG. 9  and still be within the scope of the invention. 
         [0054]      FIG. 11  is the top view of the retention screw  400 . In this embodiment, the head diameter  410  is desirably larger than the opening formed by surfaces  305 ,  306  and  308  of the dual-bladed retention blade  300 . The retention screw  400  can be moved, manipulated, driven, twisted and/or rotated by the hex driving feature  411  that is recessed into the head top surface  412 . It is understood that the driving feature of the invention is not limited to a hex but may be any driving feature that is commonly known to drive screws. 
         [0055]      FIG. 12  is a side view of the retention screw  400  and shows the three areas of the screw  401 ,  413  and  414 . Area  401  is the threaded section that screws into the female threaded holes  213  of the anterior cervical plate  200 . Area  413  is the area where the opening formed by surfaces  305 ,  306  and  308  of the dual-bladed retention blade  300  rests when the dual-bladed retention blade  300  is in the neutral configuration. Area  414  is the area where the opening formed by surfaces  305 ,  306  and  308  of the dual-bladed retention blade  300  rests when the dual-bladed retention blade  300  is in the retention configuration. 
         [0056]      FIG. 13  is an enlarged view of area  13  of the retention screw  400  on  FIG. 12 . Area  413 , shown in  FIG. 12 , contains diameter  403  and is enclosed by lower neutral conical surface  402  and upper neutral conical surface  404 . When the opening formed by surfaces  305 ,  306  and  308  of the dual-bladed retention blade  300  is encompassing diameter  403  the retention blade is in its unrestrained, or neutral position. The conical surfaces  402  and  404  desirably prevent the dual-bladed retention blade  300  from migrating out of area  413 . See detailed descriptions for  FIGS. 16 ,  17  and  18  for further explanation of the neutral relationships between the dual-bladed retention blade  300  and retention screw  400 . When the retention screw  400  is advanced by turning or rotating the retention screw  400  with a driver placed in the driving feature  411 , the screw can advance into the plate, with the retention blade travelling up the conical surface  404  and onto diameter  406 . During this transition from diameter  403  to diameter  406  the channel  302  of the dual-bladed retention blade  300  is spreading open. As the retention screw  400  continues to be driven and/or rotated by the driver in the driving feature  411 , the screw can continue advancing into the plate, with the retention blade lower surface  313  dropping down the lower conical retention surface  407  and settling into area  414  and remain in the retention configuration. This transition from diameter  406  to diameter  408  can cause an audible click (in various embodiments) and/or a tactile movement indication can be felt as the retention blade lower surfaces drops onto the diameter  408 . Area  414 , shown in  FIG. 12 , contains diameter  408  and is desirably enclosed by lower retention conical surface  407  and shoulder  409 . When the opening formed by surfaces  305 ,  306  and  308  of the dual-bladed retention blade  300  is encompassing diameter  408  the retention blade is a “restrained” or retention position. The conical surfaces  407  and shoulder  409  can desirably prevent the dual-bladed retention blade  300  from migrating out of area  414 , if desired. See detailed descriptions for  FIGS. 19 ,  20  and  21  for further explanation of the retention relationships between the dual-bladed retention blade  300  and retention screw  400 . 
         [0057]      FIG. 14  is the top view of one exemplary embodiment of a bone screw  500 . Head diameter  505  is desirably larger than the reduced diameter  206  (or “necked” portion) of the anterior cervical plate  200 , which desirably prevents the screw from advancing through the anterior cervical plate  200 . The bone screw  500  can be driven by the hexalobe or star driving feature  504  that is recessed into the head top surface  503 . It is understood that the driving feature of the invention is not limited to a hexalobe but may be any driving feature that is commonly known to drive screws. 
         [0058]      FIG. 15  is the side view of the bone screw  500  and is one of substantially generic design. Only the significant features of the bone screw that directly interact with the invention will be detailed here. The thread diameter  501  can be smaller than the reduced diameter  206  of the anterior cervical plate  200  (if desired) to allow unimpeded passage of the bone screw  500  through the anterior cervical plate  200 . Spherical diameter  502  mates with the spherical diameter  205  of the anterior cervical plate  200 , thereby allowing for angular placement of the bone screw  500 . In various embodiments, the top surface  503  will desirably contact the dual-bladed retention blade  300  when it is in the retention configuration, thereby retaining the bone screw  500  and prevent it from backing out of the anterior cervical plate  200 . See detailed descriptions for  FIGS. 25 ,  26  and  27  for further explanation of the retaining feature and the relationships between the dual-bladed retention blade  300  and bone screw  500 . 
         [0059]      FIG. 16  is the top view of a partial assembly of the dual-bladed retention blade  300  and retention screw  400 , in the neutral configuration, in order to demonstrate the working relationship between the two components. 
         [0060]      FIG. 17  is the side view of a partial assembly of the dual-bladed retention blade  300  and retention screw  400 , in the neutral configuration, in order to demonstrate the working relationship between the two components. In this embodiment, the dual-bladed retention blade  300  is nestled in the area  413  (see  FIG. 12 ) of the retention screw  400  between conical surfaces  402  and  404 . 
         [0061]      FIG. 18  is an enlarged sectional view of the dual-bladed retention blade and retention screw defined by the line  18 - 18  from  FIG. 17 . The diameter  403  of the retention screw  400  is shown between the surfaces  306  of the dual-bladed retention blade  300 . The dual-bladed retention blade  300  is shown in the neutral position. 
         [0062]      FIG. 19  is the top view of a partial assembly of the dual-bladed retention blade  300  and retention screw  400 , in the retention configuration, in order to demonstrate the working relationship between the two components. 
         [0063]      FIG. 20  is the side view of a partial assembly of the dual-bladed retention blade  300  and retention screw  400 , in the retention configuration, in order to demonstrate the working relationship between the two components. The retention blade  300  is contacting the enlarged diameter  408  (see  FIG. 12 ) of the retention screw  400  between the shoulder  407  and conical surface  409 . 
         [0064]      FIG. 21  is an enlarged sectional view defined by the line  21 - 21  from  FIG. 20 . The diameter  408  of the retention screw  400  is shown between the surfaces  306  of the dual-bladed retention blade  300 . The dual-bladed retention blade  300  is shown in the retention position. Because diameter  408  is larger than the smaller diameter  403  portion of the retention screw  400 , the retention blade is forced open to angle α. 
         [0065]      FIG. 22  is the top view of the anterior cervical plate assembly  100  in the neutral position and contains sectional view line  23 - 23  and view area  24 . 
         [0066]      FIG. 23  is a cross-sectional view of the anterior cervical plate assembly  100  defined by the line  23 - 23  from  FIG. 22 , which sections the anterior cervical plate  200 , dual-bladed retention blade  300  and retention screw  400 . 
         [0067]      FIG. 24  is an enlarged partial view of area  24  of the of the anterior cervical plate assembly  100  from  FIG. 22 . The dual-bladed retention blade  300  is shown in the neutral configuration where the radius  303  is positioned so the head diameter  505  of the bone screw  500  can travel past the dual-bladed retention blade  300  without hindrance. Also shown is the tang  307  of the dual-bladed retention blade  300  placed into the notch  214  of the anterior cervical plate  200 . Though not completely shown the end surface  312  (see  FIG. 9 ) of the dual-bladed retention blade  300  is captured inside the area defined by radius  218 , surface  207 , surface  208  and radius  219  of the anterior cervical plate (see  FIG. 25 ). 
         [0068]      FIG. 25  is an enlarged view of area  25  of the anterior cervical plate assembly  100  from  FIG. 23 , which sections the anterior cervical plate  200 , dual-bladed retention blade  300  and retention screw  400  in the neutral position. The top surface  412  of the retention screw  400  is shown above the top surface  210  of the anterior cervical plate. The surfaces  310  and  311  of the dual-bladed retention blade  300  are shown between the conical surfaces  402  and  404  and in area  413  of the retention screw  400 . The surfaces  310  and  311  of the dual-bladed retention blade  300  are shown captured between surfaces  208  and  207  of the anterior cervical plate  200  at radii  219  and  220 . One feature of the invention is that these areas at the radii  219  and  220  retain the dual-bladed retention blade  300  which in turn retains the retention screw because it is constrained by the conical surfaces  402  and  404  and the mating threads  213  and  415 . This feature allows the dual-bladed retention blade  300  and retention screw  400  to be preassembled before the surgery, thereby reducing surgery time. 
         [0069]      FIG. 26  is the top view of the anterior cervical plate assembly  100  in the retention position and contains sectional view line  27 - 27 . Though not completely shown the end surface  312  (see  FIG. 9 ) of the dual-bladed retention blade  300  is inside the area defined by radius  218 , surface  207 , surface  208  and radius  219  of the anterior cervical plate and under the surfaces (see  FIG. 9 ). 
         [0070]      FIG. 27  is a sectional view of the anterior cervical plate assembly  100  defined by the line  27 - 27  from  FIG. 26  and sections the anterior cervical plate  200 , dual-bladed retention blade  300  and retention screw  400 . 
         [0071]      FIG. 28  is an enlarged view of area  28  of the anterior cervical plate assembly  100  from  FIG. 27  and sections the anterior cervical plate  200 , dual-bladed retention blade  300  and retention screw  400  in the retention position. The top surface  412  of the retention screw  400  is now shown just above the top surface  210  of the anterior cervical plate, although the top surface  412  of the retention screw  400  could similarly be at (i.e., flush with) or below the top surface  210  of the cervical plate  200  (see  FIGS. 1 and 30 , for example) without hindering the intended function of the retention screw  400 . The surfaces  310  and  311  of the dual-bladed retention blade  300  are shown between the conical surface  407  and shoulder  409  and in area  414  of the retention screw  400 . The surfaces  310  and  311  of the dual-bladed retention blade  300  are shown captured between surfaces  208  and  207  of the anterior cervical plate  200  at radii  219  and  220  and also under surfaces  216 . Another feature of the invention is that these areas at the radii  219  and  220  retain the dual-bladed retention blade  300  which in turn retains the retention screw  400  because it is constrained by the conical surface  407 , planar surface  409  and the mating threads  213  and  415 . This feature holds the assembly in the retention position and does not absolutely require the retention screw  400  to be torqued tightly to prevent the retention screw from backing out since it is retained in position by the dual-bladed retention blade  300 . 
         [0072]      FIG. 32  is an exploded isometric view of another embodiment of an anterior cervical plate  220  containing a single-bladed embodiment  120  of the invention in the neutral position. For the single-bladed configuration the retention screw  400  and bone screw  500  features can remain the same, if desired, however the anterior cervical plate  220  shown now has a smaller nest than the retention blade nest  207  of the embodiment  100  because the retention feature has only a one-sided retention blade  320  while the prior embodiment of the invention depicted a dual-bladed symmetric design  300 . 
         [0073]      FIG. 33  is a top view of another alternative embodiment of a retention blade, specifically a single-bladed retention blade. Instead of the symmetric bladed design of the dual-bladed retention blade  300 , the single blade retention blade  320  includes a shorter leg portion  321  that serves a similar functional purpose as the longer leg of the dual-bladed retention blade  300 , but including a smaller profile. 
         [0074]    Those who are skilled in the art understand that the profile of the single blade retention blade  320  can vary in the same manner as the dual bladed retention blade  300 , as previously described, as long as the retention of a screw is the intended result. 
         [0075]    All references, including any publications, patent applications, and patents, cited herein are hereby incorporated by reference to the same extent as if each reference were individually and specifically indicated to be incorporated by reference and were set forth in its entirety herein. 
         [0076]    The various headings and titles used herein are for the convenience of the reader, and should not be construed to limit or constrain any of the features or disclosures thereunder to a specific embodiment or embodiments. It should be understood that various exemplary embodiments could incorporate numerous combinations of the various advantages and/or features described, all manner of combinations of which are contemplated and expressly incorporated hereunder. 
         [0077]    The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g., i.e., “such as”) provided herein, is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention unless otherwise claimed. No language in the specification should be construed as indicating any non-claimed element as essential to the practice of the invention. 
         [0078]    Preferred embodiments of this invention are described herein, including the best mode known to the inventor for carrying out the invention. Variations of those preferred embodiments may become apparent to those of ordinary skill in the art upon reading the foregoing description. The inventor expects skilled artisans to employ such variations as appropriate, and the inventor intends for the invention to be practiced otherwise than as specifically described herein. Accordingly, this invention includes all modifications and equivalents of the subject matter recited in the claims appended hereto as permitted by applicable law. Moreover, any combination of the above-described elements in all possible variations thereof is encompassed by the invention unless otherwise indicated herein or otherwise clearly contradicted by context.