Abstract:
An implantable orthopedic fastener comprising: (a) a support substrate including a first through hole at least partially defined by an interior wall tapering to decrease a diameter of the first through hole; (b) a nut having an internal wall at least partially defining a second through hole having a diameter less than the diameter of the first through hole, the nut also including a projection radially extending beyond the internal wall to provide the nut with a widthwise dimension greater than the diameter of the first through hole, the nut further including a washer radially extending beyond the internal wall, the washer having a widthwise dimension greater than the diameter of the first through hole, where the projection and the washer cooperate to retain at least a portion of the nut within the first through hole; and (c) a fastening screw comprising a head and a longitudinal shaft extending from the head, the longitudinal shaft including external threads sized to permit through passage of the longitudinal shaft with respect to first and second through holes, the head also including a cap sized to allow entry of the head into the first through hole but prohibiting through passage of the head with respect to the first through hole, the cap further including an opening into a hollow formed into a top of the head, where at least one of the head and the internal wall of the nut includes threads to selectively mount the fastening screw to the nut, the threads operative to allow rotational and vertical motion of the fastening screw with respect to the nut, and where the support substrate, the nut, and the fastening screw cooperate to form a compression joint operatively sandwiching at least a portion of the interior wall between the cap and the washer of the nut to fix an angular orientation of the fastening screw with respect to the support substrate.

Description:
RELATED ART 
     Field of the Invention 
       [0001]    The present disclosure relates to retention devices for surgical procedures and, more specifically, relates to variable angle retention devices to mount bone to a plate material. 
       INTRODUCTION TO THE INVENTION 
       [0002]    It is a first aspect of the present invention to provide an implantable orthopedic fastener comprising: (a) a support substrate including a first through hole at least partially defined by an interior wall tapering to decrease a diameter of the first through hole; (b) a nut having an internal wall at least partially defining a second through hole having a diameter less than the diameter of the first through hole, the nut also including a projection radially extending beyond the internal wall to provide the nut with a widthwise dimension greater than the diameter of the first through hole, the nut further including a washer radially extending beyond the internal wall, the washer having a widthwise dimension greater than the diameter of the first through hole, where the projection and the washer cooperate to retain at least a portion of the nut within the first through hole; and (c) a fastening screw comprising a head and a longitudinal shaft extending from the head, the longitudinal shaft including external threads sized to permit through passage of the longitudinal shaft with respect to first and second through holes, the head also including a cap sized to allow entry of the head into the first through hole but prohibiting through passage of the head with respect to the first through hole, the cap further including an opening into a hollow formed into a top of the head, where at least one of the head and the internal wall of the nut includes threads to selectively mount the fastening screw to the nut, the threads operative to allow rotational and vertical motion of the fastening screw with respect to the nut, and where the support substrate, the nut, and the fastening screw cooperate to form a compression joint operatively sandwiching at least a portion of the interior wall between the cap and the washer of the nut to fix an angular orientation of the fastening screw with respect to the support substrate. 
         [0003]    In a more detailed embodiment of the first aspect, the internal wall of the nut includes internal threads, the head of the fastening screw includes external threads, and the external threads of the head are adapted to interface with the internal threads of the nut. In yet another more detailed embodiment, the projection comprises a collar at least partially circumscribing the internal wall of the nut. In still a further detailed embodiment, the collar is separable from the nut. In a more detailed embodiment, the nut includes a detent at least partially circumscribing the internal wall, the detent having a widthwise dimension less than the diameter of the first through hole, and the collar includes a circumferential shelf to receive the detent of the nut and operatively couple the collar to the nut. In a more detailed embodiment, the head includes external threads, and a vertical spacing between individual threads of the external threads of the head is less than a vertical spacing between individual threads of the external threads of the longitudinal shaft. In another more detailed embodiment, the head includes external threads, and a diameter of the external threads of the head is greater than a diameter of the external threads of the longitudinal shaft. In still another more detailed embodiment, the hollow of the head is at least partially defined by a conical depression, and the hollow is sized to receive a driver to rotate the screw in at least one of a clockwise direction and a counterclockwise direction. 
         [0004]    In yet another more detailed embodiment of the first aspect, the cap exhibits a circular horizontal cross-section, the cap includes an overhang extending radially outward from the screw, and a diameter of the cap is larger than the diameter of the first through hole. In still another more detailed embodiment, a contact surface of the interior wall of the support substrate is at least one of bowl shaped and linearly sloped, a contact surface of the projection is at least one of bowl shaped and linearly sloped, and the contact surface of the projection is adapted to engage the contact surface of the interior wall. In a further detailed embodiment, the support substrate includes a first surface and a second surface, the first through hole extends through the first surface and the second surface, and the second surface includes an opening extending into the support substrate that at least partially defines a cavity that at least partially circumscribes the first through hole. In still a further detailed embodiment, the first through hole is at least partially defined by a circumferential flange, the circumferential flange including the interior wall tapering to decrease the diameter of the first through hole, the support substrate includes an inner wall at least partially defining the cavity of the support substrate, and a terminal end of the circumferential flange is spaced apart from the inner wall of the support substrate to delineate a circumferential cavity at least partially extending around a portion of the circumferential flange. In a more detailed embodiment, the washer of the nut includes a circumferential discontinuity, the support substrate includes a stop, and the stop is received within the circumferential discontinuity of the washer to inhibit rotation of the nut with respect to the support substrate. In a more detailed embodiment, the nut includes a hollow cylinder that defines the second through hole, the hollow cylinder including a first end axially spaced apart from a second end, where the projection is mounted to the hollow cylinder proximate the first end and the washer is mounted to the hollow cylinder proximate the second end so that the projection and washer are axially spaced apart. In another more detailed embodiment, the projection comprises a plurality of projections that are circumferentially spaced apart from one another. 
         [0005]    It is a second aspect of the present invention to provide an implantable orthopedic fastener comprising: (a) a support substrate including a first surface generally opposite a second surface, the first surface including an opening that at least partially defines a tapered flange at least partially defining a first through hole extending through the support substrate, the second surface including an opening leading into a cavity at least partially circumscribing the first through hole and the tapered flange; (b) a nut comprising an interior circumferential wall at least partially defining a second through hole having a diameter less than a diameter of the first through hole, the interior circumferential wall including threads, and the nut including a circumferential recess receiving at least a portion of the tapered flange; and (c) a fastening screw comprising a head and a longitudinal shaft extending from the head, the longitudinal shaft including threads sized to permit through passage of the longitudinal shaft with respect to the first and second through holes, the head sized to allow entry of the head into the first hole, but prohibiting passage of the head beyond the first through hole, the head also including circumferential threads sized to engage the threads of the nut, where the support substrate includes a first anti-rotation feature operative to inhibit rotation of the nut with respect to the support substrate. 
         [0006]    In a more detailed embodiment of the second aspect, the nut includes a projection radially extending beyond the interior circumferential wall to provide the nut with a widthwise dimension greater than the diameter of the first through hole, the nut includes a washer radially extending beyond the interior circumferential wall, the washer having a widthwise dimension greater than the diameter of the first through hole, and the projection and washer cooperate to retain at least a portion of the nut within the first through hole. In yet another more detailed embodiment, the projection comprises a collar at least partially circumscribing the interior circumferential wall of the nut. In a further detailed embodiment, the collar is separable from the nut. In still a further detailed embodiment, the nut includes a detent at least partially circumscribing the interior circumferential wall, the detent having a widthwise dimension less than the diameter of the first through hole, and the collar includes a shelf at least partially circumscribing the interior circumferential wall, the shelf adapted to receive the detent of the nut to operatively couple the collar to the nut. In a more detailed embodiment, the projection comprises a plurality of projections that are circumferentially spaced apart from one another. 
         [0007]    It is a third aspect of the present invention to provide an implantable orthopedic fastener comprising: (a) a support substrate including an internal circumferential wall at least partially defining a first through hole, the support substrate including a locking ring channel; (b) a threaded washer at least partially defining a second through hole and sized to be received within the first through hole of the support substrate, but the size of the threaded washer prohibits egress of the threaded washer completely through the first through hole; (c) a locking ring at least partially defining a third through hole and adapted to be received within the locking ring channel of the support substrate; and (d) a fastening screw comprising a head and a longitudinal shaft, the longitudinal shaft including threads sized to permit through passage of the longitudinal shaft with respect to first, second, and third through holes, the head sized to allow entry of the head into the first hole and the second hole, and allowing passage of the head through the third hole, but the size of the head prohibits egress of the head completely through the first through hole, where at least one of the threaded washer and the support substrate includes an anti-rotation feature operative to inhibit rotation of the threaded washer with respect to the support substrate, where the threaded washer includes threads adapted to interface with circumferential threads of the head of the fastening screw to couple the threaded washer to the fastening screw, and where the locking ring prohibits removal of the threaded washer from the first through hole. 
         [0008]    In a more detailed embodiment of the third aspect, the threaded washer includes a projection, the internal circumferential wall includes an indentation adapted to receive the projection of the threaded washer, and the projection and the indentation comprise the anti-rotation feature operative to inhibit rotation of the threaded washer with respect to the support substrate. In yet another more detailed embodiment, the anti-rotation feature comprises a follower and track engagement between the threaded washer and the support substrate in which the follower and the track are sized so that the follower engages the track and restrains the threaded washer from spinning within the first through hole. In a further detailed embodiment, the threaded washer includes at least one follower that engages the track formed within the support substrate. In still a further detailed embodiment, the support substrate includes at least one follower that engages the track formed within the threaded washer. In a more detailed embodiment, the invention further includes a washer at least partially defining a fourth through hole and sized to be received within the first through hole of the support substrate, but the size of the washer prohibits egress of the washer completely through the first through hole, where the longitudinal shaft of the fastening screw is sized to permit through passage of the longitudinal shaft with respect to fourth through hole, but the size of the head of the fastening screw prohibits passage of the head with respect to the fourth through hole. In a more detailed embodiment, the internal circumferential wall includes a circumferential taper that prohibits passage of the washer with respect to the first through hole. In another more detailed embodiment, an internal wall of the washer that partially defines the fourth through opening is tapered, and a transition between the head and the longitudinal shaft of the fastening screw is tapered to decrease a diameter of the fastening screw. In yet another more detailed embodiment, the locking ring, fastening screw, washer, threaded washer, and support substrate create a compression joint that forces the washer against the support substrate when the threaded washer is forced against the locking ring as the head of the fastening screw is rotated within the second through hole. 
         [0009]    It is a fourth aspect of the present invention to provide an implantable orthopedic fastener comprising: (a) a support substrate including an internal circumferential wall at least partially defining a first through hole, the internal circumferential wall including a first anti-rotation feature and a second anti-rotation feature different from the first anti-rotation feature; (b) a threaded washer comprising a wall at least partially defining a second through hole, the wall including an internal surface having threads and an external surface including a third anti-rotation feature, the threaded washer sized to be received within the first through hole of the support substrate; (c) a locking ring including a semi-circular wall at least partially defining a third through hole, the locking ring including a fourth anti-rotation feature; and (d) a fastening screw comprising a head and a longitudinal shaft extending from the head, the longitudinal shaft including threads sized to permit through passage of the longitudinal shaft with respect to first, second, and third through holes, the head sized to allow entry of the head into the first through hole and the second through hole, and allowing passage of the head through the third through hole, but prohibiting passage of the head with respect to the first through hole, the head also including circumferential threads sized to engage the threads of the threaded washer, where the combination of the first anti-rotation feature and the third anti-rotation feature inhibit rotation of the threaded washer with respect to the internal circumferential wall of the support substrate, but permit axial motion of the threaded washer with respect to the internal circumferential wall of the support substrate, and where the combination of the second anti-rotation feature and the fourth anti-rotation feature inhibit rotation and axial motion of the locking ring with respect to the internal circumferential wall of the support substrate. 
         [0010]    In a more detailed embodiment of the fourth aspect, the threaded washer includes a protrusion comprising the third anti-rotation feature, the internal circumferential wall includes an indentation adapted to receive the protrusion of the threaded washer, and the indentation comprises the first anti-rotation feature. In yet another more detailed embodiment, the first anti-rotation feature and the third anti-rotation feature comprises a follower and track engagement between the threaded washer and the support substrate in which the follower and the track are sized so that the follower engages the track and restrains the threaded washer from rotation within the first through hole. In a further detailed embodiment, the threaded washer includes the follower that engages the track formed within the support substrate. In still a further detailed embodiment, the support substrate includes the follower that engages the track formed within the threaded washer. In a more detailed embodiment, a washer at least partially defining a fourth through hole and sized to be received within the first through hole of the support substrate, but prohibiting egress of the washer completely through the first through hole, where the longitudinal shaft of the fastening screw is sized to permit through passage of the longitudinal shaft with respect to fourth through hole, but the head of the fastening screw is sized prohibit passage of the head with respect to the fourth through hole. In a more detailed embodiment, the internal circumferential wall includes a circumferential taper that prohibits passage of the washer completely through the first through hole. In another more detailed embodiment, the locking ring, fastening screw, washer, threaded washer, and support substrate create a compression joint that forces the washer against the support substrate when the threaded washer is forced against the locking ring as the head of the fastening screw is rotated within the second through hole. 
         [0011]    It is a fifth aspect of the present invention to provide a method of mounting a base plate to a biologic material, the method comprising: (a) inserting and retaining a threaded nut within a first through hole of a base plate, the first hole at least partially defined by an interior circumferential wall, the base plate including a first anti-rotation feature, and the threaded nut comprising: (1) a cylindrical inner wall at least partially defining a second through hole, and (2) an engaging wall extending radially and proximate an end of the threaded nut and at least partially circumscribing and extending toward an opposing end of the threaded nut, where the threaded nut is axially repositionable and selectively rotatable within the first through hole of the base plate, and where the threaded nut includes a second anti-rotation feature adapted to selectively engage the first anti-rotation feature of the base plate to inhibit rotation of the threaded nut with respect to the base plate; (b) inserting a screw through the first and second through holes so that at least a portion of a threaded shaft extends beyond the interior circumferential wall of the base plate, where at least a portion of the screw is maintained within the first and second through holes, and where the screw has angular freedom other than being coaxial with the first hole; (c) rotating the screw with respect to the base plate and the threaded nut to operatively engage a head of the screw with the threaded nut, where continued rotation of the screw after engagement between the head and the threaded nut is operative to axially reposition the threaded nut along a length of the screw; (d) inserting the screw into a biologic substrate; and (e) locking an angular orientation of the screw with respect to the base plate by axially repositioning the threaded nut via rotation of the screw so the engaging wall of the threaded nut and the head of the screw sandwich a flange of the base plate to form a compression joint, where the flange at least partially defines the first hole. 
         [0012]    It is a sixth aspect of the present invention to provide a method of mounting a base plate to a biologic material, the method comprising: (a) mounting a threaded nut to a base plate so the threaded nut is axially and angularly repositionable with respect to the base plate, but the threaded nut remains mounted to the base plate, the base plate including a first through hole at least partially occupied by the threaded nut, the threaded nut including a second through hole; (b) inserting at least a portion of a threaded shaft of a screw through the first and second through holes so that some of the threaded shaft extends beyond the base plate, wherein at least a segment of the screw is maintained within the first and second through holes, and wherein the threaded shaft has axial and angular freedom with respect to the first and second through holes; (c) initially rotating the screw with respect to the base plate and the threaded nut so that the screw becomes coupled to the threaded nut, where, upon initial rotation, the threaded shaft continues to have angular freedom with respect to the first through hole; and (d) continuing rotating the screw with respect to the threaded nut to axially reposition the threaded nut along a portion of the screw and concurrently insert the screw into a biologic substrate, whereby rotation of the screw ultimately causes the screw and threaded nut to sandwich a portion of the base plate therebetween such that the threaded nut, screw, and the portion of the base plate form a compression joint that discontinues the angular freedom of the threaded shaft with respect to the first through hole. 
         [0013]    It is a seventh aspect of the present invention to provide a method of mounting a base plate to a biologic material, the method comprising: (a) inserting a threaded washer within a first through hole of a base plate, the first hole at least partially defined by an interior circumferential wall, and the threaded washer defining a second through hole; (b) inserting a locking ring within the first hole of the base plate, the locking ring being seated within a groove formed within the interior circumferential wall, and the locking ring at least partially defining a third through hole; (c) inserting at least a portion of a threaded shaft of a screw through the first, second, and third through holes so that some of the threaded shaft extends beyond the interior circumferential wall of the base plate, where at least a portion of the screw is maintained within the first through hole, and wherein the screw has angular freedom other than being coaxial with the first and second through holes; (d) initially rotating the screw with respect to the base plate and threaded nut so that the screw becomes coupled to the threaded nut, where, upon initial rotation, the threaded shaft has angular freedom with respect to the first through hole; and (e) continuing rotation of the screw with respect to the threaded nut to axially reposition the threaded nut along a portion of the screw and concurrently insert the screw into a biologic substrate, whereby rotation of the screw ultimately causes the threaded nut to be forced against the locking ring, thereby discontinuing the angular freedom of the threaded shaft with respect to the first through hole. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is an elevated, perspective, cross-sectional view of a first exemplary embodiment of the instant disclosure. 
           [0015]      FIG. 2  is a top view of an exemplary plate in accordance with the instant disclosure. 
           [0016]      FIG. 3  is a bottom view of the exemplary plate of  FIG. 2 . 
           [0017]      FIG. 4  is a cross-sectional view of the exemplary plate of  FIG. 3  taken along lines  3 - 3 . 
           [0018]      FIG. 5  is a bottom of an exemplary threaded nut in accordance with the instant disclosure. 
           [0019]      FIG. 6  is a top view of the exemplary threaded nut of  FIG. 5 . 
           [0020]      FIG. 7  is a profile view of the exemplary threaded nut of  FIG. 5 . 
           [0021]      FIG. 8  is a cross-sectional view of the exemplary threaded nut of  FIG. 6  taken along line  6 - 6 . 
           [0022]      FIG. 9  is a top view of an exemplary retention ring in accordance with the instant disclosure. 
           [0023]      FIG. 10  is a profile view of the exemplary retention ring of  FIG. 9 . 
           [0024]      FIG. 11  is a cross-sectional view of the exemplary retention ring of  FIG. 10  taken along line  10 - 10 . 
           [0025]      FIG. 12  is a top view of an exemplary screw in accordance with the instant disclosure. 
           [0026]      FIG. 13  is a profile view of the exemplary screw of  FIG. 12 . 
           [0027]      FIG. 14  is a cross-sectional view of the exemplary screw of  FIG. 13  taken along line  13 - 13 . 
           [0028]      FIG. 15  is an exploded view of the first exemplary embodiment of  FIG. 1 . 
           [0029]      FIG. 16  is a cross-sectional view of the first exemplary embodiment of  FIG. 1 , without the retention ring and screw. 
           [0030]      FIG. 17  is an elevated, perspective, cross-sectional view of a second exemplary embodiment of the instant disclosure. 
           [0031]      FIG. 18  is a bottom view of a second exemplary threaded nut in accordance with the instant disclosure. 
           [0032]      FIG. 19  is a top view of the exemplary threaded nut of  FIG. 18 . 
           [0033]      FIG. 20  is a profile view of the exemplary threaded nut of  FIG. 18 . 
           [0034]      FIG. 21  is a cross-sectional view of an exemplary threaded nut of  FIG. 19  taken along lines  19 - 19 . 
           [0035]      FIG. 22  is a cross-sectional view of the second exemplary embodiment of  FIG. 17 , with the washer nut relaxed and without the screw. 
           [0036]      FIG. 23  is a cross-sectional view of the second exemplary embodiment of  FIG. 17 , with the washer nut (not relaxed) and screw sandwiching the flange. 
           [0037]      FIG. 24  is a cross-sectional view of a third exemplary embodiment of the instant disclosure. 
           [0038]      FIG. 25  is a bottom view of a third exemplary threaded nut in accordance with the instant disclosure. 
           [0039]      FIG. 26  is a profile view of the exemplary threaded nut of  FIG. 25 . 
           [0040]      FIG. 27  is a top, perspective view of the exemplary threaded nut of  FIG. 25 . 
           [0041]      FIG. 28  is across-sectional view of the third exemplary embodiment of  FIG. 24 , with the washer nut relaxed and without the screw. 
           [0042]      FIG. 29  is a cross-sectional view of the third exemplary embodiment of  FIG. 24 , with the washer nut (not relaxed) and screw sandwiching the flange. 
           [0043]      FIG. 30  is an exploded view of a fourth exemplary embodiment of the instant disclosure. 
           [0044]      FIG. 31  is an isolated, elevated perspective, cross-sectional profile view of the exemplary embodiment of  FIG. 30 . 
           [0045]      FIG. 32  is an isolated, cross-sectional profile view of the exemplary embodiment of  FIG. 30 . 
           [0046]      FIG. 33  it a profile view of an exemplary base plate of the embodiment of  FIG. 30 . 
           [0047]      FIG. 34  is a frontal view of an exemplary base plate of the embodiment of  FIG. 30 . 
           [0048]      FIG. 35  is a top view of an exemplary base plate of the embodiment of  FIG. 30 . 
           [0049]      FIG. 36  is an isolated, elevated perspective view of the exemplary base plate of the embodiment of  FIG. 30 . 
           [0050]      FIG. 37  is an isolated, cross-sectional frontal view of an exemplary base plate of the embodiment of  FIG. 30 . 
           [0051]      FIG. 38  is a bottom view of an exemplary washer of the embodiment of  FIG. 30 . 
           [0052]      FIG. 39  is a profile view of the exemplary washer of  FIG. 38 . 
           [0053]      FIG. 40  is a top, perspective view of the exemplary washer of  FIG. 38 . 
           [0054]      FIG. 41  is a profile view of an exemplary threaded washer of the exemplary base plate of the embodiment of  FIG. 30 . 
           [0055]      FIG. 42  is a top view of the exemplary threaded washer of  FIG. 41 . 
           [0056]      FIG. 43  is a bottom, perspective view of the exemplary threaded washer of  FIG. 41 . 
           [0057]      FIG. 44  is a top view of an exemplary retainer ring of the embodiment of  FIG. 30 . 
           [0058]      FIG. 45  is a profile view of the exemplary retainer ring of  FIG. 44 . 
           [0059]      FIG. 46  is an elevated perspective view of the exemplary retainer ring of  FIG. 44 . 
           [0060]      FIG. 47  is a bottom, perspective view of the exemplary retainer ring of  FIG. 44 . 
           [0061]      FIG. 48  is a profile view of an exemplary screw of the embodiment of  FIG. 30 . 
           [0062]      FIG. 49  is an elevated perspective view of the exemplary screw of  FIG. 48 . 
       
    
    
     DETAILED DESCRIPTION 
       [0063]    The exemplary embodiments of the present disclosure are described and illustrated below to encompass retention devices for surgical procedures and methods of fabricating the retention devices and using the retention devices in a surgical procedure. Of course, it will be apparent to those of ordinary skill in the art that the preferred embodiments discussed below are exemplary in nature and may be reconfigured without departing from the scope and spirit of the present invention. However, for clarity and precision, the exemplary embodiments as discussed below may include optional steps, methods, and features that one of ordinary skill should recognize as not being a requisite to fall within the scope of the present invention. 
         [0064]    Referencing  FIG. 1 , a first exemplary variable angle locking screw assembly  10  comprises a base plate  12 , a screw  14 , a washer nut  16 , and a retention ring  18 . These components cooperate to retain the screw  14  at one of a multitude of predetermined angles with respect to the base plate  12  when the screw is mounted to a biologic substrate  20 , such as human bone, and the screw  14  is tightened with respect to the other components of the variable angle locking screw assembly  10 . 
         [0065]    Referring specifically to  FIGS. 1-4 , the base plate  12  includes at least one through opening  30  adapted to allow throughput of the shaft of the screw  14 , while inhibiting throughput of the head of the screw. In this exemplary embodiment, the through opening  30  is partially defined by an annular flange  32  that extends vertically downward from a top surface  34  of the base plate  12 . An upper surface  36  of the flange  32  is arcuate and operates to create a bowl-shaped depression within the top surface  34  that funnels the screw into the through opening  30 . As a result, a narrowest portion of the through opening  30  is defined by a leading edge  38  of the flange  32 . This leading edge  38  transitions into a back-cut face  40  having a trailing edge  42  that is positioned radially outside of and axially below the leading edge  38 . In other words, the diameter of the through opening  30  at the leading edge  38  is less than the diameter of the through opening  30  at the trailing edge  42 . As will be discussed in more detail below, the back-cut face  40  provides for a range of angles that the screw may be oriented other than perpendicular (i.e., coaxial) with respect to the through opening  30 . 
         [0066]    The trailing edge  42  transitions into an arcuately shaped underneath surface  44  of the flange  32  that intersects a horizontal surface  46  of a cavity  48  formed within a bottom surface  50  of the base plate  12 . The cavity  48  is generally circular in horizontal cross-section (see  FIGS. 3 and 4 ) and is defined by a circumferential vertical wall  52  extending into the interior of the plate material. This circumferential vertical wall  52  co-axially outlies the through opening  30  formed within the top surface  34  of the base plate  12 . Consequently, the circumferential vertical wall  52 , the horizontal surface  46 , and the underneath surface  44  of the flange  32  cooperate to define a recess  54  adapted to receive a portion of the washer nut  16 . Within the recess  54  are at least two radially extending stops  56  bridging between the circumferential vertical wall  52  and the flange  32  that are equidistantly spaced from one another and adapted to interact with features on the washer nut  16  to selectively inhibit rotation of the washer nut with respect to the base plate  12  as will be discussed below. 
         [0067]    Referencing FIGS.  1  and  5 - 8 , the washer nut  16  includes a hollow cylinder  60  having internal threads  62  formed into or extending from an interior surface  64  of the cylinder. As will be discussed in more detail below, these threads  62  are adapted to interface with threads formed into or extending from the screw  14 . The cylinder  60  also includes an upper end  66 , opposite a lower end  68 , having a discontinuous lip  70  that extends radially from an exterior surface  72  of the cylinder  60 . In this exemplary embodiment, the lip  70  includes two sections, with each section being equidistantly spaced and extending approximately 160 degrees around the cylinder  60 , thereby leaving two gaps  74  between the lip sections. The lip  70  includes a sloped surface  76  sloping downward from the cylinder  60  and a lower horizontal surface  78  that converge at a point  80 , with the point being the farthest radially from the center of the cylinder  60 . The lower horizontal surface  78  of the lip  70  intersects the generally smooth, exterior surface  72  of the cylinder  60  proximate the upper end  66 . 
         [0068]    The lower end  68  of the cylinder  60  includes a discontinuous dome-shaped washer  82  arcuately extending radially outward from the cylinder  60  and vertically toward the upper end  66 . The dome-shaped washer  82  includes opposed concave and convex surfaces  84 ,  86 , where the concave surface generally faces the lip  70 . In this exemplary embodiment, the dome-shaped washer  82  includes two circumferential sections, with each section being equidistantly spaced and extending approximately 160 degrees around the cylinder  60 , thereby leaving two circumferential spaces  88  between the washer sections. Both gaps  74  between the lip  70  sections and the spaces  88  between the washer  82  sections are radially aligned, where the spaces are adapted to selectively receive the radially extending stops  56  of the plate material to inhibit rotation of the washer nut  16  with respect to the base plate  12 , presuming the retention ring  18  is in place. 
         [0069]    Referring to FIGS.  1  and  9 - 11 , the retention ring  18  comprises a discontinuous circular ring adapted to reside within the bowl-shaped depression  36  within the top surface of the base plate  12  (created by the flange  32 ) and to engage the lip  70  of the washer nut  16  in order to retain at least a portion of the washer nut within the through opening  30 . The discontinuity of the retention ring  18  allows the ring to be deformed slightly. A top surface  90  of the retention ring in the present embodiment is generally planar and meets an outer sloped surface  92  at a circumferential point  94 , and sloped downwardly and radially inward from the point  94 . As will be discussed in more detail below, the angular orientation of the sloped surface  92  may match that of the upper surface  36  of the flange  32  or may differ from the angular orientation of the upper surface of the flange. The circumferential point  94  defines the outer diameter of the retention ring  18 , in contrast to the inner diameter of the retention ring that is defined by an interior wall  96 . The angular orientation of the interior wall  96  is adapted to approximate the angular orientation of the smooth exterior surface  72  of the cylinder  60 . This interior wall  96  and the top surface  90  are interposed by a circumferentially extending step  98  formed into the top surface retention ring  18  and extending radially from the interior wall  96 . The step  98  comprises a horizontal surface  100  and a vertical surface  102 . As discussed above, the inner diameter of the step  98  is defined by the boundary of the interior wall  96 , where the inner diameter is slightly larger than the outer diameter of the cylinder  60 . As will be discussed in more detail below, the horizontal surface  100  of the retention ring  18  is adapted to engage the horizontal lip surface  78  of the washer nut  16  in order to retain at least a portion of the washer nut within the through opening  30  as the screw  14  is inserted and tightened. 
         [0070]    Referencing FIGS.  1  and  12 - 14 , the screw  14  comprises a head  110  and a shaft  112  extending from the head. The head  110  comprises a dome  114  that transitions into a vertical circumferential surface  116 . This vertical circumferential surface  116  transitions into an underneath planar surface  118  on the bottom of the head  110 . Opposite the bottom of the head  110  is an opening  120  formed at the apex of the dome  114 . The opening  120  extends through the head  110  and into a head end  122  of the shaft  112 . In exemplary form, the opening  120  is defined by a series of six alternating semicircular walls  124  and six straight walls  126  that form a hexagonal pattern. At the base of the walls  124 ,  126  is a conical wall  128  that defines a conical part of the opening  120  terminating in the head end  122  of the shaft  112 . An exterior surface  130  of the head end  122  of the shaft  112  includes threads  132  that are adapted to engage the threads  62  of the washer nut  16 . These threads  132  extend along a predetermined longitudinal section of the shaft  112  and transition into a second set of threads  134  adapted to engage the biologic substrate  20 . The second set of threads  134  extends along the shaft until reaching a conical projection  136  at an opposite end  138  of the screw  14 . 
         [0071]    Referencing  FIGS. 1-16 , the first exemplary variable angle locking screw assembly  10  may be utilized to secure the biologic substrate  20 , such as human bone, in a constant position for proper healing. An exemplary procedure for securing the substrate  20  to the base plate  12  may include drilling a hole into the substrate  20 , where the hole has a diameter less than the diameter of the second set of threads  134  on the opposite end  138  of the screw  14 . Prior to drilling the hole into the substrate  20 , the washer nut  16  has already been mounted within the cavity  48  of the base plate  12  using the retention ring  18 . 
         [0072]    By way of example, the washer nut  16  is oriented so that the upper end  66  of the cylinder  60  is inserted initially into the cavity  48  of the base plate  12 , followed by the washer  82  end of the washer nut. At generally the same time, the spaces  88  between the washer  82  sections are aligned to receive the radially extending stops  56  located within the cavity  48 . The cylinder  60  is moved further into the cavity  48  so that the leading edge  38  of the flange  32  circumscribes the exterior surface  72  of the cylinder  60  and the lip  70  extends upward beyond the leading edge. Likewise, the spaces  88  between the washer  82  sections receive the radially extending stops  56 . To ensure the cylinder  60  is sufficiently inserted upward into the through opening  30 , the concave surface  84  of the washer  82  may contact the underneath surface  44  of the flange  32 . In this orientation, the retention ring  18  may be inserted within the through opening  30  in the top surface  34  of the base plate  12  and expanded to increase the internal diameter sufficient to allow the interior surface of the ring to pass beyond the point  80  of the washer nut  16  lip  70 . The sloped surface  76  of the lip  70  acts to cam the ring  18  radially outward as the ring and washer nut  16  are forced axially towards one another. After passing beyond the point  80 , the retention ring  18  may be allowed to return to its default orientation. This default orientation of the ring  18  exhibits an internal diameter that is less than the outside diameter of the lip  70  as measured across the point  80 . After the ring  18  has returned to its default orientation, the upper horizontal surface  100  of the retention ring step  98  is below the lower horizontal lip surface  78  of the washer nut  16 . Thereafter, the force retaining the concave surface  84  of the washer  82  against the underneath surface  44  of the flange  32  may be released. Releasing this temporary retention force causes the cylinder  60  to move downward, toward the bottom surface  50  of the base plate  12  so that the lower horizontal lip surface  78  of the washer nut  16  contacts and rides upon the upper horizontal surface  100  of the retention ring  18  step  98 , thereby retaining a portion of the cylinder  60  within the through opening  30 . At the same time, releasing this temporary retention force causes the concave surface  84  of the washer  82  to no longer contact the underneath surface  44  of the flange  32 . But, the spaces  88  between the washer  82  sections continue to receive the radially extending stops  56 . In this exemplary embodiment, the outside diameter of the retention ring  18  is greater than the diameter of the through opening  30  at the leading edge  38  of the flange  32  so that the sloped surface  92  of the ring contacts the upper surface  36  of the flange, which operates to retain a portion of the cylinder  60  within the through opening  30 . 
         [0073]    After the retention ring  18  and washer nut  16  are mounted to one another, thereby mounting the washer nut  16  to the base plate  12 , a surgeon may then insert a drill bit (not shown) into the through hole  30  and into an opening defined by the hollow cylinder  60  in order for the drill bit to contact the biologic substrate  20 , such as human bone. At this time, the surgeon controls the drill bit to create a hole within the substrate  20  that will ultimately receive the screw  14  in order to mount the base plate  12  to the substrate  20 . After the drill bit has completed boring the hole within the substrate  20 , the drill bit is withdrawn from the substrate  20 , from the through hole  30 , and from the hollow cylinder  60 . 
         [0074]    After removing the drill bit, the screw  14  may be inserted into the through hole  30  and into the hollow cylinder  60  at a desired angular orientation (up to approximately 15 degrees or greater from axial alignment with the through hole  30 ), with the opposite end  138  of the shaft  112  being inserted first. Specifically, the opposite end  138  of the shaft  138  and the second set of threads  134  are sized to pass into the hollow cylinder  60  without engaging the threads  62  on the interior surface  64  of the cylinder. As the shaft  112  of the screw  14  continues to be inserted and travel through the through hole  30  and into and beyond the hollow cylinder  60 , ultimately the head end  122  of the shaft reaches the hollow cylinder  60  at approximately the same time as the conical projection  136  at the opposite end  138  of the screw  14  reaches the previously drilled hole in the substrate  20 . 
         [0075]    After the screw  14  has been angularly oriented and aligned with the previously drilled hole into the biologic substrate  20 , the screw  14  may be tightened and in so doing, retain the angular position of the screw. This may be accomplished by rotating the screw  14  in a clockwise direction so that the threads  132  at the head end  122  engage the threads  62  on the interior of the cylinder  60  to couple the screw  14  to the washer nut  16 . At the same time, clockwise rotation of the screw  14  is operative to engage the second set of threads  134  with the biologic substrate  20 . As the screw  14  is rotated in a clockwise direction (between 1-3 turns, for example), the stops  56  of the base plate  12  continue to be received within the spaces  88  of the washer  82  to inhibit rotation of the washer nut  16  with respect to the base plate  12 . In other words, rotation of the screw  14  does not result in rotation of the washer nut  16  because the stops  56  retard rotational motion of the washer nut. However, rotation of the screw  14  is operative to vertically reposition the washer nut  16  so that the concave surface  84  of the washer  82  is forced against the underneath convex surface  44  of the flange  32 . Eventually, after a predetermined amount of clockwise rotation of the screw  14 , the head  110  of the screw  14 , the base plate  12 , and the washer nut  16  cooperate to create a compression joint that locks the screw in the appropriate angular orientation. This is accomplished by the sandwiching action of the washer  82  and the head  110  to capture the flange  32  therebetween as the washer and head are drawn toward one another by the rotation of the screw  14 . Conversely, loosening of the compression joint is accomplished by simply rotating the screw  14  in a counterclockwise direction, thereby discontinuing the compression joint. 
         [0076]    Referencing  FIG. 17 , a second exemplary variable angle locking screw assembly  200  comprises the same base plate  12  and screw  14  from the first exemplary embodiment, but uses a different washer nut  202  and does not include a retention ring  18 . As with the first exemplary embodiment  10 , the components of this second exemplary embodiment  200  cooperate to retain the screw  14  at one of a multitude of predetermined angles with respect to the base plate  12  when the screw is mounted to a biologic substrate  20 , such as human bone, and when the screw  14  tightened with respect to the other components of the variable angle locking screw assembly  10 . 
         [0077]    Referring to  FIGS. 18-21 , the washer nut  202  includes a hollow cylinder  204  having internal threads  206  formed into or extending from an interior surface  208  of the cylinder. As will be discussed in more detail below, these threads  206  are adapted to interface with threads formed into or extending from the screw  14 . The cylinder  204  also includes an upper end  210 , opposite a lower end  212 , having a discontinuous collar  214  that extends radially out from an exterior surface  216  of the cylinder. In this exemplary embodiment, the collar  214  includes two circumferential sections, with each section being equidistantly spaced and extending approximately 160 degrees around the cylinder  204 , thereby leaving two gaps  218  between the collar sections. The collar  214  includes an upper sloped surface  220  and a second lower sloped surface  222  that converge at a point  224 , with the point being that portion of the collar  214  that is the farthest radially from the center of the cylinder  204 . The lower sloped surface  222  intersects the generally smooth, arcuate exterior surface  216  of the cylinder  204 . 
         [0078]    The lower end  212  of the hollow cylinder  204  includes a discontinuous dome-shaped washer  226  arcuately extending radially outward and upward from the cylinder  204  and vertically toward the upper end  210 . The washer  226  includes opposed concave and convex surfaces  228 ,  230 , where the concave surface  228  generally faces the collar  214 . In this exemplary embodiment, the washer  226  includes two circumferential sections, with each section being equidistantly spaced and extending approximately 160 degrees around the cylinder  204 , thereby leaving two spaces  232  between the washer sections. Both gaps  218  between the collar  214  sections and the spaces  232  between the washer  226  sections are radially aligned, where the spaces  232  are adapted to selectively receive the stops  56  (see  FIGS. 3 and 4 ) to inhibit rotation of the washer nut  202  with respect to the base plate  12 . 
         [0079]    Referencing  FIGS. 17 ,  22 , and  23 , the second exemplary variable angle locking screw assembly  200  may also be utilized to secure the biologic substrate  20 , such as human bone, in a constant position for proper healing. As with the first exemplary locking screw assembly  10 , the second locking screw assembly  200  installation procedure may include drilling a hole into the substrate  20  at a desired angular orientation, where the hole has a diameter less than the diameter of the second set of threads  134  on the opposite end  138  of the strew  14 . 
         [0080]    In this exemplary embodiment, the washer nut  202  is already mounted to the base plate  12 . When the washer nut  202  is mounted to the base plate  12 , the default position (presuming the top surface  34  of the base plate  12  is oriented upward) of the washer nut includes the lower sloped surface  222  of the collar  214  contacting the upper surface  36  of the flange  32  (see  FIG. 22 ). Because the outside diameter of the collar  214 , measured at the point  224 , is greater than the diameter of the through opening  30  measured at the leading edge  38 , the collar cannot pass through the through opening. Likewise, because the diameter of the washer  226 , measured at its outermost tip, is larger than the diameter of the through opening  30  measured at the leading edge  38 , the washer cannot pass through the through opening. In addition, a portion of the hollow cylinder  204  occupies the through opening  30  proximate the leading edge  38  of the flange  32 . 
         [0081]    After the washer nut  202  is mounted to the base plate  12 , a surgeon may then insert a drill bit (not shown) into the through hole  30  and into an opening defined by the hollow cylinder  204  to contact the biologic substrate  20 , such as human bone. At this time, the surgeon controls the drill bit to create a hole within the substrate  20  that will ultimately receive the screw  14  in order to mount the base plate  12  to the substrate  20 . After the drill bit has completed boring the hole within the substrate  20 , the drill bit is withdrawn from the substrate  20 , from the through hole  30 , and from the hollow cylinder  204 . 
         [0082]    After removing the drill bit, the screw  14  may be inserted into the through hole  30  and into the hollow cylinder  204  at a desired angular orientation (up to approximately 15 degrees or greater from axial alignment with the through hole  30 ), with the opposite end  138  of the shaft  112  being inserted first. Specifically, the opposite end  138  of the shaft  112  and the second set of threads  134  are sized to pass into the hollow cylinder  204  without engaging the threads  206  on the interior surface  208  of the cylinder. As the shaft  112  of the screw  14  continues to be inserted and travel through the through hole  30  and into and beyond the hollow cylinder  204 , ultimately the head end  122  of the shaft reaches the hollow cylinder  204  at approximately the same time as the conical projection  136  at the opposite end  138  of the screw  14  reaches the previously drilled hole in the substrate  20 . 
         [0083]    After the screw  14  has been angularly oriented and aligned with the previously drilled hole within the biologic substrate  20 , the screw  14  may be tightened and in so doing, retain the angular position of the screw. This may be accomplished rotating the screw  14  in a clockwise direction so that the threads  132  at the head end  122  engage the threads  206  on the interior surface  208  of the cylinder  204  to couple the screw  14  to the washer nut  202 . At the same time, clockwise rotation of the screw  14  is operative to engage the second set of threads  134  with the biologic substrate  20 . As the screw  14  is rotated in a clockwise direction (between 1-3 turns, for example), the stops  56  of the base plate  12  (see  FIGS. 3 and 4 ) continue to be received within the spaces  232  of the washer  226  to inhibit rotation of the washer nut  202  with respect to the base plate  12 . In other words, rotation of the screw  14  does not result in rotation of the washer nut  202  because the stops  56  retard rotational motion of the washer nut. However, rotation of the screw  14  is operative to vertically reposition the washer nut  202  so that the concave surface  228  of the washer  226  is forced against the underneath convex surface  44  of the flange  32 . Eventually, after a predetermined amount of clockwise rotation of the screw  14 , the head  110  of the screw  14 , the base plate  12 , and the washer nut  202  cooperate to create a compression joint that locks the screw in the appropriate angular orientation (see  FIG. 23 ). This is accomplished by the sandwiching action of the washer  226  and the head  110  to capture the flange  32  therebetween as the washer and head are drawn toward one another by the rotation of the screw  14 . Conversely, loosening of the compression joint is accomplished by simply rotating the screw  14  in a counterclockwise direction, thereby discontinuing the compression joint (see  FIG. 17 ). 
         [0084]    Referencing  FIG. 24 , a third exemplary variable angle locking screw assembly  300  comprises the same base plate  12  and screw  14  from the first exemplary embodiment, but uses a different washer nut  302  and does not include a retention ring  18 . As with the first exemplary embodiment  10 , the components of this third exemplary embodiment  300  cooperate to retain the screw  14  at one of a multitude of predetermined angles with respect to the base plate  12  when the screw is mounted to a biologic substrate  20 , such as human bone, and, when the screw  14  is tightened with respect to the other components of the variable angle locking screw assembly  300 . 
         [0085]    Referring to  FIGS. 25-27 , the washer nut  302  includes a hollow cylinder  304  having internal threads  306  formed into or extending from an interior surface  308  of the cylinder. As will be discussed in more detail below, these threads  306  are adapted to interface with threads formed into or extending from the screw  14 . The cylinder  304  also includes an upper end  310 , opposite a lower end  312 , having a plurality of trapezoidal projections  314  that extend radially out and vertically up from the upper end  310 . In this exemplary embodiment, there are three trapezoidal projections  314  being equidistantly spaced and circumferentially distributed about the circumference of the upper end  310 , thereby leaving three gaps  318  between the trapezoidal projections. The outer end  320  of each trapezoidal projection  314  cooperates to define an annular perimeter having a diameter that is greater than the diameter of the through hole  30  measured at the leading edge  38  of the flange  32 . 
         [0086]    The lower end  312  of the hollow cylinder  304  includes a discontinuous dome-shaped washer  326  arcuately extending radially outward from the cylinder  304  and vertically up toward the upper end  310 . The washer  326  includes opposed concave and convex surfaces  328 ,  330 , where the concave surface  328  generally faces the trapezoidal projections  314 . In this exemplary embodiment, the washer  326  includes two circumferential sections, with each section being equidistantly spaced and extending approximately 160 degrees around the cylinder  304 , thereby leaving two spaces  332  between the washer sections. The spaces  332  between the washer  326  sections are adapted to selectively receive the stops  56  (see  FIGS. 3 and 4 ) of the base plate  12  to inhibit rotation of the washer nut  302  with respect to the base plate  12 . 
         [0087]    Referencing  FIGS. 24 ,  28 , and  29 , the third exemplary variable angle locking screw assembly  300  may also be utilized to secure the biologic substrate  20 , such as human bone, in a constant position for proper healing. As with the first exemplary locking screw assembly  10 , the third locking screw assembly  300  installation procedure may include drilling a hole into the substrate  20  at the desired angular orientation, where the hole has a diameter less than the diameter of the second set of threads  134  on the opposite end  138  of the screw  14 . 
         [0088]    By way of example, the washer nut  302  is oriented so that the upper end  310  of the cylinder  304  is inserted initially into the cavity  48 , followed by the washer  326  end of the washer nut  302 . The cylinder  304  is moved further into the cavity  48  so that the trapezoidal projections  314  are immediately below leading edge  38  of the flange  32 . In other words, the perimeter defined by the leading edge  38  is generally coaxial with the perimeter defined by the far ends  320  of the trapezoidal projections  314 . The trapezoidal projections  314  are deformed radially inward to reduce the diameter of the perimeter defined by the far ends  320  of the trapezoidal projections  314  until the diameter is small enough pass by the leading edge  38  of the flange  32 , thereby allowing insertion of the near end  310  of the cylinder  304  further into the through opening  30 . After the deformed trapezoidal projections  314  clear the through opening  30  at the leading edge  38  of the flange  32 , the trapezoidal projection are allowed to return to a default position. This default position includes radially deforming the trapezoidal projections  314  outward to increase the diameter of the perimeter defined by the far ends  320  of the trapezoidal projections  314  until the diameter is large enough to inhibit removal of the near end  310  of the cylinder  304  beyond the through opening  30 . This procedure effectively mounts the washer nut  302  to the base plate  12 . 
         [0089]    After the washer nut  302  is mounted to the base plate  12 , a surgeon may then insert a drill bit (not shown) into the through hole  30  and into the through hole defined by the hollow cylinder  304  to contact the biologic substrate  20 , such as human bone. At this time, the surgeon controls the drill bit to create a hole within the substrate  20  that will ultimately receive the screw  14  in order to mount the base plate  12  to the substrate  20 . After the drill bit has completed boring the hole within the substrate  20 , the drill bit is withdrawn from the substrate  20 , from the through hole  30 , and from the hollow cylinder  304 . 
         [0090]    After removing the drill bit, the screw  14  may be inserted into the through hole  30  and into the hollow cylinder  304  at a desired angular orientation (up to approximately 15 degrees or greater from axial alignment with the through hole  30 ), with the opposite end  138  of the shaft  112  being inserted first. Specifically, the opposite end  138  of the shaft  112  and the second set of threads  134  are sized to pass into the hollow cylinder  304  without engaging the threads  306  on the interior surface  308  of the cylinder. As the shaft  112  of the screw  14  continues to be inserted and travel through the through hole  30  and into and beyond the hollow cylinder  304 , ultimately the head end  122  of the shaft reaches the hollow cylinder  304  at approximately the same time as the screw  14  (specifically the conical projection  136  at the opposite end  138  of the screw  14 ) reaches the hole in the substrate  20 . 
         [0091]    After the screw  14  has been angularly oriented and aligned with the previously drilled hole into the biologic substrate  20 , the screw  14  may be tightened and in so doing, retain the angular position of the screw. This may be accomplished by rotating the screw  14  in a clockwise direction so that the threads  132  at the head end  122  of the shaft  112  engage the threads  306  on the interior of the cylinder  304  to couple the screw  14  to the washer nut  302 . At the same time, clockwise rotation of the screw  14  is operative to engage the second set of threads  134  with the biologic substrate  20 . As the screw  14  is rotated in a clockwise direction (between 1-3 turns, for example), the stops  56  (see  FIGS. 3 and 4 ) of the base plate  12  continue to be received within the two spaces  332  of the washer  326  to inhibit rotation of the washer nut  302  with respect to the base plate  12 . In other words, rotation of the screw  14  does not result in rotation of the washer nut  302  because the stops  56  retard rotational motion of the washer nut. However, rotation of the screw  14  is operative to vertically reposition the washer nut  302  so that the concave surface  328  of the washer  326  is forced against the underneath convex surface  44  of the flange  32 . Eventually, after a predetermined amount of clockwise rotation of the screw  14 , the head  110  of the screw  14 , the base plate  12 , and the washer nut  302  cooperate to create a compression joint that locks the screw in the appropriate angular orientation (see  FIG. 29 ). This is accomplished by the sandwiching action of the washer  326  and the head  110  to capture the flange  32  therebetween as the washer and head are drawn toward one another by the rotation of the screw  14 . Conversely, loosening of the compression joint is accomplished by simply rotating the screw  14  in a counterclockwise direction, thereby discontinuing the compression joint (see  FIG. 24 ). 
         [0092]    Referencing  FIGS. 30-32 , a fourth exemplary variable angle locking screw assembly  400  comprises a base plate  402 , a positioning washer  404 , a threaded pressing washer  406 , a locking ring  408 , and a screw  410 . These components cooperate to retain the screw  410  at one of a multitude of predetermined angles with respect to the base plate  402  when the screw is mounted to a biologic substrate  412 , such as human bone, as well as when the screw  410  is tightened with respect to the other components of the variable angle locking screw assembly  400 . 
         [0093]    Referring specifically to  FIGS. 32-37 , the exemplary base plate  402  includes an upper tray  414  integrally mounted to a threaded stem  416 . The upper tray  414  includes a plurality of through holes  418 ,  420 , at least two of which  418  are each adapted to receive a fixed orientation fastener (not shown), while another pair  420  are each adapted to receive a washer  404 , a threaded washer  406 , a locking ring  408 , and a variable angle screw  410 . 
         [0094]    Referring specifically to  FIGS. 36 and 37 , each of the through holes  420  receiving components of the variable angle locking screw assembly  400  are defined by a circumferential wall  422 . The circumferential wall  422  actually comprises a series of vertical wall segments that are stacked upon one another and contoured to specifically accommodate the components of the variable angle locking screw assembly  400  in a predetermined order. A first vertical wall segment  424  is located at the bottom of the through hole  420  and comprises a hollow cylindrical tube with a beveled cut. The portion of the first vertical wall segment  424  that is completely circumferentially bounded has a circular cross-section with a substantially constant diameter along its vertical length. A lip  426  differentiates the first wall segment  424  from a second wall segment  428 . 
         [0095]    The second wall segment  428  also comprises a hollow cylindrical tube that is generally bowl-shaped. Specifically, starting at the lip  426 , the second segment  428  exhibits a circular cross-section that is defined by an arcuate wall  430  tapering outward and upward as the vertical distance from the lip increases. A series of cut-outs or notches  432  are formed into the top portion of the arcuate wall  430  and circumferentially distributed therealong. As will be discussed in more detail below, these cutouts  432  receive circumferential projections of the threaded washer  406  to inhibit the washer  406  from rotating. The arcuate wall  430  essentially provides a bowl-shaped contour that transitions into a second arcuate wall  434  at the very top of the second wall segment  428 , opposite the lip  426 . As with the first arcuate wall  430 , the cutouts  432  are also formed into the second arcuate wall  434 . But the top of the second arcuate wall  434  signals a significant change in the contour of the circumferential wall  422  to a third vertical wall segment  436 . 
         [0096]    A horizontal ledge  438  signals the transition from the second vertical wall segment  428  to the third vertical wall segment  436 . The ledge  438  is adjacent to the second arcuate wall  434  and is generally circular, but at its ends abuts a vertical, planar wall  440  extending tangentially with respect to the arcuate wall  434 . This planar wall  440  also intersects a vertical, circumferential wall  442  that extends vertically from the ledge  438  to a top beveled edge  444  of the through hole  420 . A semicircular depression  446  is formed within the circumferential wall  442  in order to receive a portion of the locking ring  408  (see  FIGS. 30 and 31 ) to mount the locking ring to the base plate  402 . 
         [0097]    Referencing  FIGS. 38-40 , the positioning washer  404  comprises a generally circular body having a continuous outer wall  450  and a substantially flat, circular top surface  452  that transitions at the outermost perimeter to an arcuate or dome-shaped circumferential surface  454 . The circumferential surface  454  tapers inward to decrease the outer diameter of the washer  404  as the distance from the top surface  452  increases. The bottom of the circumferential surface  454  rounds over to seamlessly transition into a substantially flat, circular bottom surface  456 . Similar to the top surface  452 , the bottom surface  456  partially defines a circular opening  458  that extends through the washer  404 . The circular opening  458  is defined by an internal surface  460  that extends between the top and bottom surfaces  452 ,  456  and is inset with respect to the circumferential surface  454 . The internal surface  460  comprises a first wall section  462 , adjacent the bottom surface  456 , having a substantially constant diameter. A bead  464  interposes the first wall section  462  and a second wall section  466 . This second wall section  466  extends upward and includes an arcuate surface operative to gradually increase the diameter of the opening  458  to a maximum diameter adjacent the top surface  452 . When assembled, the washer  404  is inserted into the base plate  402  first, followed by the threaded washer  406 . 
         [0098]    Referencing  FIGS. 41-43 , the threaded pressing washer  406  comprises a ring-shaped body having a continuous wall  470  with a substantially flat, bottom surface  472 . The bottom surface  472  transitions into a generally dome-shaped outer circumferential surface  474  and an inner circumferential surface  476 . The continuous wall  470  embodies a wall thickness that increases from a maximum at the bottom surface  472 , to a minimum at the top surface  478 . In vertical cross-section, from top to bottom, the continuous wall  470  embodies a generally triangular shape with the base of the triangle comprising the bottom surface  472  and the apex of the triangle comprising the top surface  478 . In between the top and bottom surfaces  472 ,  478 , the outer circumferential surface  474  embodies a vertically arcuate shape and is substantially circular in horizontal cross-section, but for a series of projections  480  extending radially from the outer circumferential surface. In this exemplary embodiment, each projection  480  comprises a generally rectangular projection and three projections  480  are equidistantly spaced about the circumference of the threaded washer  406 . Opposite the projections  480 , on the inner circumferential surface  476 , are threads  482  extending into a circular opening  484  within the interior of the threaded washer  406 . These threads  482  are adapted to engage the threaded head of the screw  410  as will be discussed below. 
         [0099]    Referencing  FIGS. 44-47 , the locking ring  408  comprises a semi-circular body having opposed open ends  490 ,  492 . Each end  490 ,  492  is a mirror image of the other end and includes a vertical, planar side surface  494 . The planar side surface  494  is perpendicular to a planar top surface  496  embodying a semi-circular shape. The circumferential width of the top surface  496  is substantially constant, but for three notches  498  formed axially through the top surface along an inner circumferential surface  500 . By way of summary, the notches  498  mirror, but are slightly oversized with respect to, the projections  480  of the threaded washer  406 . A circumferential edge  502  of the top surface  496  is rounded over to define a semi-circular rim  504  that transitions into a recessed circumferential vertical surface  506 . This vertical surface  506  is perpendicular to a bottom surface  508  that circumferentially extends between the ends  490 ,  492 . In this exemplary embodiment, the top surface  496  is oriented in parallel to the bottom surface  508  so that the arcuate interior surface  500  interposes the surfaces  496 ,  508 . The arcuate interior surface  500  is curved so that the diameter of an opening  512 , which extends vertically through the locking ring  408 , decreases from the bottom surface  508  to just beneath the top surface  496 . However, where the notches  498  are located within the top surface  496 , these notches vertically extend into the interior surface  500  so that the notches do not exhibit the arcuate shape of the remainder of the interior surface. 
         [0100]    Referencing  FIGS. 48 and 49 , the screw  410  comprises a head  520  and a shaft  522  extending from the head. The lead  520  includes a cavity  524  centrally located and spaced from an outer circumferential surface  526 . The cavity  524  is partially defined by a series of vertical surfaces  528  oriented in a hexagonal pattern that perpendicularly intersect a horizontal floor  530 . The horizontal floor  530  includes a central conical depression  532 , which is also part of the cavity  524 . Threads  534  extend from the outer circumferential surface  526  of the head  520  and are adapted to engage the threads  482  of the threaded washer  406 . Just below the threads  534 , the head  520  includes an exterior surface  535  that tapers inward to join the shaft  522 . Just below the tapering portion, the shaft  522  includes helical threads  536  that extend almost the entire length of the shaft to a conical tip  538 . In this exemplary embodiment, the helical threads  536  include at least one discontinuity  540  proximate the conical tip  538  to facilitate aligning the screw  410  with a hole within the biologic substrate  412 . 
         [0101]    Referencing  FIGS. 30-49 , the fourth exemplary variable angle locking screw assembly  400  may be utilized to secure the biologic substrate  412 , such as human bone, in a constant position for proper healing. An exemplary procedure for securing the substrate  412  to the base plate  402  may include drilling a hole into the substrate  412  at a desired angular orientation, where the hole has a diameter less than the diameter of the helical threads  536  on the shaft  522  of the screw  410 . Prior to mounting the screw  410  to the substrate  412 , the remaining components of the variable angle locking screw assembly  400  are mounted to the base plate  402 . 
         [0102]    By way of example, the base plate  402  is oriented so that the upper tray  414  is accessible, specifically at least one of the through holes  420 . With the upper tray  414  oriented to face upward and exposing the entire length of the circumferential wall  422 , the positioning washer  404  is first inserted into the through hole  420 . More specifically, the rounded bottom surface  456  of the washer  404  is inserted into the through hole  420  first, followed by the top surface  452  of the washer. This orientation ensures that the rounded circumferential surface  454  of the washer  404 , which transitions into the bottom surface  456 , is adjacent and seated within the arcuate wall  430  of the second wall segment  428 . When the washer  404  is seated adjacent to the arcuate wall  430 , the top surface  452  is slightly recessed below the second arcuate wall  434 . After the washer  404  is installed within the circumferential wall  422 , the threaded pressing washer  406  is next installed. 
         [0103]    The threaded washer  406  is inserted within the circumferential wall  422  so that the bottom surface  472  enters the circumferential wall first, followed by the top surface  478 . Vertical lowering of the threaded washer  406  within the circumferential wall  422  continues until the bottom surface  472  sits upon the top surface  452  of the washer  404 . But before the bottom surface  472  can sit upon the top surface  452  of the washer  404 , the projections  480  on the outer circumferential surface  474  of the threaded washer  406  are aligned with the cut-outs  432  formed within arcuate wall  430  of the second segment  428 . After the projections  480  are aligned with the cut-outs  432 , the threaded washer  406  may be lowered within the circumferential wall  422  so that the bottom surface  472  sits upon the top surface  452  of the washer  404 . Because the projections  480  are seated within the cut-outs  432 , rotation of the threaded washer  406  with respect to the base plate  402  is inhibited. As soon as the bottom surface  472  of the threaded washer  406  sits upon the top surface  452  of the washer  404 , the locking ring  408  may be inserted within the circumferential wall  422 . 
         [0104]    Insertion of the locking ring  408  within the circumferential wall  422  begins with inserting the bottom surface  508  first, followed by the top surface  496 . Because the locking ring  408  is not circular, only a single rotational orientation is possible to install the locking ring within the circumferential wall  422  the base plate  402 . Just before the locking ring  408  is inserted within the circumferential wall  422 , the vertical side surface  494  is oriented in parallel to the vertical wall  440  of the circumferential wall. This orientation also inherently aligns the notches  498  with the cut-outs  432  of the circumferential wall  422 . After the locking ring  408  has been aligned, it may be lowered so that the bottom surface  508  is proximate the ledge  438 . But before the bottom surface  508  can reach the ledge  438 , the locking ring  408  is circumferentially compressed to reduce the outside diameter of the locking ring, which can be accomplished because of the space between the open ends  490 ,  492 . Reduction in the outside diameter of the locking ring  408  allows the semi-circular rim  504  to pass vertically beyond the top beveled edge  444  of the through hole  420 . After passing the top beveled edge  444 , the semi-circular rim  504  of the locking ring  408  rides upon the circumferential wall  422  just above the semicircular depression  446 . But when the semi-circular rim  504  of the locking ring  408  reaches the semicircular depression  446 , the inherent spring in the locking ring forces the semi-circular rim outward and into the semicircular depression, thereby mounting the locking ring securely to the base plate  402 . After the locking ring  408  is seated within the semicircular depression  446 , it is not possible to remove the washer  404  and/or the threaded washer  406  from the through hole  420 . 
         [0105]    After the washer  404 , the threaded washer  406 , and the locking ring  408  are inserted within the circumferential wall  422 , a surgeon may then insert a drill bit (not shown) into the through hole  420  to contact the biologic substrate  412 , such as human bone. At this time, the surgeon controls the drill bit to create a hole within the substrate  412  that will ultimately receive the screw  410  in order to mount the base plate  402  to the substrate  412 . After the drill bit has completed boring the hole within the substrate  412 , the drill bit is withdrawn from the substrate  412  and the through hole  420 . 
         [0106]    After removing the drill bit, the screw  410  may be inserted through the openings  458 ,  484 ,  512  with the conical tip  538  first, followed by the remainder of the shaft  522  or at least as much of the shaft as is necessary so the tip  538  reaches the hole within the biologic substrate  412 . Because the diameter of the helical threads  536  is less than the diameter of the openings  458 ,  484 ,  512  extending through the washer  404 , the threaded washer  406 , and the locking ring  408 , the shaft  522  passes right through the openings. In addition, the construction of the variable angle locking screw assembly  400  allows the screw to be oriented at angles other than axially aligned with circumferential wall  422  of the base plate  402  to reach the hole within the biologic substrate  412 . 
         [0107]    Generally, the threads  534  on the outer circumferential surface  526  of the screw head  520  initially engage the threads  482  on the inner circumferential surface  476  of the threaded washer  406  at approximately the same time as the tip  538  reaches the hole within the biologic substrate  412 . At this point, the screw  410  is rotated by inserting a driver (not shown) into the cavity  524  and rotating the driver. Rotation of the screw  410  in the clockwise direction is operative to pull the shaft  522  into the biologic substrate  412  and to draw the threaded washer  406  upward vertically along the shaft  522  and also vertically within the through hole  420 . This upward vertical motion of the threaded washer  406 , while creating a gap (compare  FIGS. 31 and 32 ) between the bottom surface  472  of the threaded pressing washer  406  and the top surface  452  of the washer  404 , also operates to draw the outer circumferential surface  474  of the threaded washer  406  closer to the arcuate interior surface  500  of the locking ring  408 . Eventually, clockwise rotation of the screw  410  (generally around 1-3 rotations of the screw, for example) causes the outer circumferential surface  474  of the threaded washer  406  to contact the arcuate interior surface  500  of the locking ring  408 , thus creating a compression joint between the second wall section  466  of the washer  404  and the exterior tapered surface  535  of the screw  410 , thereby inhibiting further rotation of the screw  410  with respect to the washer  404 . At the same time, the compression joint is also formed between the threaded washer  406  and the locking ring  408 . In order to discontinue the compression joints, the screw  410  is rotated in the counterclockwise direction, thereby allowing reversing the foregoing process. 
         [0108]    The aforementioned components may, in exemplary from, be manufactured from titanium or stainless steel. However, it should be understood that any suitable material may be utilized to fabricate the aforementioned components including, without limitation, plastics, ceramics, metals, and alloys of the foregoing. 
         [0109]    Following from the above description and invention summaries, it should be apparent to those of ordinary skill in the art that, while the methods and apparatuses herein described constitute exemplary embodiments of the present invention, the invention contained herein is not limited to this precise embodiment and that changes may be made to such embodiments without departing from the scope of the invention as defined by the claims. Additionally, it is to be understood that the invention is defined by the claims and it is not intended that any limitations or elements describing the exemplary embodiments set forth herein are to be incorporated into the interpretation of any claim element unless such limitation or element is explicitly stated. Likewise, it is to be understood that it is not necessary to meet any or all of the identified advantages or objects of the invention disclosed herein in order to fall within the scope of any claims, since the invention is defined by the claims and since inherent and/or unforeseen advantages of the present invention may exist even though they may not have been explicitly discussed herein.