Abstract:
One embodiment of the present invention is directed to a bone plate assembly that includes a bone plate, bone screw(s) received in aperture(s) in the bone plate, and screw fixation member(s). The screw fixation member(s) may, alone or in conjunction with the bone plate, fix the bone screw(s) in place when such bone screw(s) are inserted in the aperture(s) in the bone plate. In one example (which example is intended to be illustrative and not restrictive) when the bone screw(s) have been received by the bone plate and inserted into bone and/or tissue, the bone plate assembly can-be used to fuse anatomical structures together (such as adjoining bones) and/or to heal a fracture in bone.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit under 35 U.S.C. 119(e) of U.S. Provisional Application Ser. No. 60/421,819, filed Oct. 28, 2002. 
     
    
     FIELD OF THE INVENTION 
       [0002]    One embodiment of the present invention is directed to a bone plate assembly that includes a bone plate, bone screw(s) received in aperture(s) in the bone plate, and screw fixation member(s). The screw fixation member(s) may, alone or in conjunction with the bone plate, fix the bone screw(s) in place when such bone screw(s) are inserted in the aperture(s) in the bone plate. In one example (which example is intended to be illustrative and not restrictive) when the bone screw(s) have been received by the bone plate and inserted into bone and/or tissue, the bone plate assembly can be used to fuse anatomical structures together (such as adjoining bones) and/or to heal a fracture in bone. 
       BACKGROUND OF THE INVENTION 
       [0003]    Bone plate assemblies are employed in order to fuse bones or to repair fractures in bones. For example, U.S. Pat. No. 6,413,259, incorporated herein by reference, discloses embodiments for bone plates. 
       SUMMARY OF THE INVENTION 
       [0004]    In one embodiment, the present invention is directed to an arrangement for fixing, in a vertebrate, a screw inserted through a plate. In one example (which example is intended to be illustrative and not restrictive) a bone plate assembly according to the present invention may have at least two bone screws, each received in at least two apertures in the bone plate. The bone plate assembly may also have screw fixation members provided for the bone screws. When the bone screws are inserted through the apertures in the bone plate, and installed in bone and/or tissue at a preselected angle, the presence of the screw fixation members may aid in fixing the bone screws in place. Each bone screw may have a head, sized so that the head does not pass through the bone plate, and a shank provided with threads (e.g., which threads may extend substantially to the tip of the bone screw). In yet another embodiment, the bone plate assembly may be provided with washers (e.g., for each screw employed in the assembly) that reside in the apertures in the bone plate. In yet another embodiment, each washer may be provided with an aperture in which the bone screw is received, when the bone screw is inserted into the bone plate. In yet another embodiment, after the bone screw is received in the aperture in the washer, and inserted in bone and/or tissue, the washer may be actuated to fix the angle at which the bone screw has been inserted (e.g., relative to the bone plate). 
         [0005]    In a further embodiment, the washer may be provided with a sidewall, which sidewall defines the aperture though which the bone screw extends. The sidewall may have a thickness that varies with respect to the position along the washer&#39;s perimeter. In one embodiment, the washer may be provided with a first sidewall region on its perimeter that is relatively thicker than a second sidewall region. 
         [0006]    In yet another embodiment, one or more apertures of the bone plate may be provided with a recess that is cut into the sidewall that defines the aperture in the bone plate. The depth to which the recess is cut may vary around the perimeter of the recess. In yet another embodiment, a first region of the recess may have a depth that is greater than a second region of the recess. In yet another embodiment, a washer may reside partially or fully within the recess. 
         [0007]    In yet another embodiment, the washer may reside in the recess, aligned so that the first relatively thicker sidewall region of the washer is positioned within the first relatively deeper region of the recess, and the second relatively thinner sidewall region of the washer is positioned in the second relatively shallower region of the recess. After the bone screw is received in the aperture in the washer, and inserted in bone and/or tissue, the washer may be actuated to fix the angle at which the bone screw has been inserted (e.g., relative to the bone plate). The bone screw may be fixed by rotating the washer, thereby moving the first relatively thicker sidewall region of the washer into the second relatively shallower region of the recess, which effectively causes the first relatively thicker sidewall region to extend laterally, into the aperture in the bone plate, where the washer impinges against the bone screw (e.g., the head of the bone screw), applying a force thereto which wedges the bone screw between the washer and the opposite sidewall of the aperture. This operation thus fixes the bone screw in place, retaining it at a particular angle (e.g., the at which the bone screw is inserted). 
         [0008]    In yet another embodiment, the present invention may allow for the bone screw(s) to toggle (i.e., move within a confined range) after being installed through the bone plate and being held by the washer. This can be arranged, for example, by actuating the washer to an intermediate position, which allows the screw to toggle. 
         [0009]    In yet a further embodiment of the present invention, a bone plate assembly may be provided in which the bone plate assembly may include a bone plate, bone screw(s) received in aperture(s) in the bone plate, and washer(s). The washer(s) may, alone or in conjunction with the bone plate, fix the bone screw(s) in place when the bone screw(s) are inserted in the aperture(s) in the bone plate. Here the washer of the bone plate assembly may be adapted to reside over the bone screw and be joined therewith in a locking arrangement. In yet another embodiment, the head of the bone screw may be provided with a number of tangs, spaced apart from each other, mounted on the upper surface of the head. The tangs may be mounted upon wedges, which wedges extend up from the head of the screw. The wedges may be not as wide as the tangs, and may be narrowed by an undercut. 
         [0010]    In a further embodiment, the washer may be provided with a washer body through which a central opening is provided. A number of lobes may be provided on the periphery of the central opening. In one example (which example is intended to be illustrative and not restrictive) three lobes are provided (it should be understood that other arrangements are, of course, possible). In yet another embodiment, the washer may also be provided with splays which are provided on the exterior of the washer. The splays may be separated from the remainder of the washer body by tracks, which tracks extend into the washer body. 
         [0011]    In yet another embodiment, the washer and the wedges and/or tangs may be designed to engage with each other in a locking arrangement. Relative to each other, the wedges may be slightly wider than the width of at least a portion of the track. 
         [0012]    In yet another embodiment, when the bone plate assembly is implanted in a person, the bone plate may be positioned on the bone, tissue and bone, or tissue to be joined by the bone plate. The bone screw may be inserted through the aperture in the bone plate and installed in bone and/or tissue by known techniques. The bone screw may be installed at a preselected angle, relative to the bone plate. To fix the screw at the angle at which it is installed, the washer may be placed over the head of the bone screw, and positioned so that the wedges are poised to enter the track portions. In yet another embodiment of the invention, a tool may be provided, the tool having a head adapted to fit within the central washer opening, which tool then engages with the central washer opening, to rotate the washer. The wedges may thereby enter the track portions. Since the wedges maybe wider than at least a portion of the tracks, the splays may be forced outward when the wedges enter the intermediate track portion(s). In this arrangement, the splays may be forced into an abutting arrangement with the sidewalls of the aperture in which the bone screw and washer reside. The abutting arrangement between the splays and the sidewalls of the aperture may fix the bone screw at a particular angle (e.g., the angle at which the bone screw was installed). 
         [0013]    In yet another embodiment, a bone plate assembly may be generally provided with a bone plate, at least two bone screws received in apertures in the bone plate, and moveable doors that fix the bone screws in place when the bone screws are inserted in the apertures in the bone plate. The bone screw employed in this embodiment may have a head sized so that the head does not pass through the bone plate. The bone screw may further have a shank provided with threads (e.g., which threads may that extend to the tip of the bone screw). In another embodiment, the bone plate assembly may be provided with a cut out portion on its upper surface, to which the doors are slidably mounted. The cut out portion may be positioned adjacent the bone screw apertures, at a portion of the edge thereof. 
         [0014]    In yet another embodiment, the sliding doors may be dimensioned to substantially not cover the apertures in the bone plate in a first position (in which first position the bone screws may be installed), yet slide and at least partially cover the apertures once the screws have been inserted (to thereby fix the bone screws in place). In yet another embodiment, the doors may be positioned in the cut out portion on the upper surface of the bone plate, and may be retained therein by a lip provided at the upper sidewall of the cut out portion. In yet another embodiment, the cut out portion may be sized slightly greater than the sliding doors. Thus, when a bone screw is positioned in the aperture of the bone plate, the sliding door can be slid in the direction of the hole, in order to cover the bone screw (and to fix the bone screw in place). 
         [0015]    In yet another embodiment, a bone screw may be provided with a number of splays positioned around the periphery of the head of the bone screw. The splays may be mounted upon wedges that extend up from the head of the screw. In one embodiment, there is a space between at least a portion of the splay and the head of the bone screw. When the screw is installed in an aperture in the bone plate at a preselected angle, a tool may be employed to force the splays outward, into a locking and abutting arrangement with the sidewalls of the bone plate aperture. In yet another embodiment, a cam may be positioned in the interior space defined by the splays. When the cam is rotated, the cam may force the splays outward, into a locking and abutting arrangement with the sidewalls of the bone plate aperture. The presence of the cam may further provide a counterforce, which counterforce may maintain the splays in the locking and abutting arrangement. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view of an embodiment of the present invention; 
           [0017]      FIG. 2  is a top plan view of the embodiment of  FIG. 1 ; 
           [0018]      FIG. 3A  is a cross sectional view of the embodiment of  FIG. 1 ; 
           [0019]      FIG. 3B  is a cross sectional view showing in greater detail the circled portion of  FIG. 3A ; 
           [0020]      FIG. 4A  is a cross sectional view of the bone plate of the embodiment of  FIG. 1  (shown across the long side); 
           [0021]      FIG. 4B  is a cross sectional view showing in greater detail the circled portion of  FIG. 4A ; 
           [0022]      FIG. 5  is a side elevational view of a screw employed in the embodiment of  FIG. 1 ; 
           [0023]      FIG. 6  is a cross sectional view of the bone plate of the embodiment of  FIG. 1  (shown across the short side); 
           [0024]      FIG. 7A  is a top plan view of a washer used in an embodiment of the present invention; 
           [0025]      FIG. 7B  is a perspective view of the washer of  FIG. 7A ; 
           [0026]      FIG. 8A  is a cross-sectional view of a tool used in conjunction with the embodiment of  FIG. 1 ; 
           [0027]      FIG. 8B  is a perspective view of a portion of the tool of  FIG. 8A ; 
           [0028]      FIG. 9  is a cross sectional view of the washer of  FIG. 7A ; 
           [0029]      FIG. 10  is a partially sectioned perspective view of a portion of the embodiment of  FIG. 1 ; 
           [0030]      FIG. 11  is a partially sectioned view showing an the undercut or recess in connection with the embodiment of  FIG. 1 ; 
           [0031]      FIG. 12A  depicts the washer of  FIG. 7A  in the open or unactuated position; 
           [0032]      FIG. 12B  depicts the washer of  FIG. 7A  in the closed or actuated position; 
           [0033]      FIG. 13  is a partially sectioned perspective view of another embodiment of the present invention; 
           [0034]      FIG. 14  is a perspective view of a washer and screw of the embodiment of  FIG. 13 ; 
           [0035]      FIG. 15  is a perspective view of the washer of the embodiment of  FIG. 13 ; 
           [0036]      FIG. 16  is a top plan view showing in greater detail an aspect of the washer of the embodiment of  FIG. 13 ; 
           [0037]      FIG. 17  is a top plan view of the screw of the embodiment of  FIG. 13 ; 
           [0038]      FIG. 18  is a side elevational view of the screw of the embodiment of  FIG. 13 ; 
           [0039]      FIG. 19  is a perspective view of the screw of the embodiment of  FIG. 13 ; 
           [0040]      FIG. 20  is a cross sectional view of the washer and screw of the embodiment of  FIG. 13 ; 
           [0041]      FIG. 21  is a perspective view of the embodiment of  FIG. 13 , where the washer has been opened; 
           [0042]      FIG. 22A  is a top plan view of another embodiment of the present invention; 
           [0043]      FIG. 22B  is a perspective view of the embodiment of  FIG. 22A ; 
           [0044]      FIG. 22C  is cross sectional view of the embodiment of  FIG. 22A ; 
           [0045]      FIG. 23  is a perspective view of another embodiment of the present invention; 
           [0046]      FIG. 24  is top plan view of the embodiment of  FIG. 23 ; 
           [0047]      FIG. 25  is a cross sectional view of the embodiment of  FIG. 23 ; 
           [0048]      FIG. 26  is a side elevational view of the embodiment of  FIG. 23 ; 
           [0049]      FIG. 27  is a perspective view of the embodiment of  FIG. 23 ; 
           [0050]      FIG. 28  depicts another embodiment of the present invention; 
           [0051]      FIG. 29  depicts, in a perspective view, another embodiment in which a double lobed washer is employed; 
           [0052]      FIG. 30  depicts, in a perspective view, another embodiment in which a tri-lobed washer is employed; and 
           [0053]      FIG. 31  depicts, in a perspective view, a split-ring washer according to another embodiment of the present invention. 
       
    
    
       [0054]    Among those benefits and improvements that have been disclosed, other objects and advantages of this invention will become apparent from the following description taken in conjunction with the accompanying figures. The figures constitute a part of this specification and include illustrative embodiments of the present invention and illustrate various objects and features thereof. 
       DETAILED DESCRIPTION OF THE INVENTION 
       [0055]    Detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely illustrative of the invention that may be embodied in various forms. In addition, each of the examples given in connection with the various embodiments of the invention are intended to be illustrative, and not restrictive. Further, the figures are not necessarily to scale, some features may be exaggerated to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. 
         [0056]    Referring now generally to  FIGS. 1-3 , it is seen that a bone plate assembly  10  is provided with bone plate  12 , bone screw(s)  14  received in aperture(s)  16  in the bone plate  12 , and washer(s)  18  that, alone or in conjunction with the bone plate  12 , fix the bone screw(s)  14  in place (e.g., when the bone screw(s)  14  are inserted in the aperture(s)  16  in the bone plate). Each bone screw  14  has a head  20  sized so that it does not pass through the bone plate  12 . Further, each bone screw  14  has a shank  22  provided with threads  24  (e.g., which threads  24  may extend to tip  26 ). The head  20  of bone screw  14  is further provided with an opening  15  that is dimensioned to mate with the head of a tool, so that the bone screw  14  can be installed in tissue and/or bone. In one embodiment, the head  20  of the bone screw  14  may be provided with grooves  21  (see, e.g.,  FIGS. 3B and 5 ). Bone plate assembly  10  is also provided with washer(s)  18 . Each washer  18  has an opening  19  though which a bone screw is received (see, e.g.,  FIG. 3B ). 
         [0057]    Referring now generally to  FIG. 3B , it is seen that each washer  18  is provided with a sidewall  28  (which sidewall  28  defines the aperture  19  though which the bone screw extends) and that the sidewall  28  has a varying thickness with respect to position along the washer&#39;s perimeter (see also, for example,  FIG. 7A ). In one embodiment, the washer  18  is provided with a first sidewall region  28   a  that is relatively thicker than a second sidewall region  28   b  (i.e., in this embodiment dimension “a” is greater than dimension “b” (see  FIG. 3B )). 
         [0058]    Referring now to  FIGS. 7A ,  7 B,  8 A,  8 B,  9  and  31 , it is seen that in these examples (which examples are intended to be illustrative and not restrictive) the washer may be provided with a series of splines  31  that are spaced at intervals around the inside perimeter of the washer (the washer of  FIG. 31  is similar to the washers of  FIGS. 7A ,  7 B,  8 A,  8 B and  9 , with the exception that the washer of  FIG. 31  is a split-ring washer). As depicted in the Figures, the splines may be solid members (which may extend from the perimeter of the washer towards the aperture  19  of the washer), and may be spaced apart by openings  32 . The arrangement of the splines  31  and openings  32  may be complementary to a spline  41  and opening  42  arrangement provided on the head  44  of a tool  40  (see, e.g.,  FIGS. 8A and 8B ). In operation, when the splines of the washer are engaged with the spaces of the tool, and vice versa, the application of a rotational force to the tool is translated to the washer, thereby turning the washer. The tool may, for example, be operated manually by handle  43 , or by drill, in which case drill bit receiving channel  45  may be provided. 
         [0059]    Referring once again to  FIG. 7A , it is seen that in one example (which example is intended to be illustrative and not restrictive) the washer  18  may be provided with a detent  50  positioned on the outside of the sidewall  28 . In this example, the sidewall of the bone plate may be provided with an indentation  52 , which is sized to receive the detent provided on the washer  18  (see, e.g.,  FIG. 10 ). When the bone plate and washer are assembled, the washer can be aligned so that the detent  50  resides in the indentation  52 . This arrangement may inhibit unwanted rotation of the washer (e.g., until the time to actuate it, as described below). 
         [0060]    As seen in  FIG. 6 , bone plate  12  may be constructed with an arcuate shape. Of course, plates with other shapes and/or dimensions are possible. 
         [0061]    In another example (which example is intended to be illustrative and not restrictive) bone plate  12  may be provided with one or more recesses  30 , positioned within the bone plate  12  (see  FIGS. 4A ,  4 B,  5  and  6 ). Each recess  30  may extend around the perimeter of each aperture  16  in the bone plate  12 . Each recess  30  may be cut into the sidewall of the apertures in the bone plate  12 . The lateral depth to which each recess  30  is cut may vary depending on the location on the perimeter of the recess  30 . In one example (which example is intended to be illustrative and not restrictive), a first region  30   a  of the recess  30  may have a lateral depth that is greater than the lateral depth of a second region  30   b  of the recess  30  (i.e., in this embodiment dimension “a” is greater than dimension “b” (see  FIG. 4B )). In another example (which example is intended to be illustrative and not restrictive), the lower portion of aperture  16  may be provided with a tapered sidewall  16   a  against which the bottom portion of the screw head  20  may rest (see  FIG. 4B ). The washer  18  may reside within the recess, aligned so that the first relatively thicker sidewall region  28   a  of the washer  18  is positioned within the first relatively deeper region  30   a  of the recess, and the second relatively thinner sidewall region  28   b  of the washer  18  is positioned in the second relatively shallower region  30   b  of the recess. In one embodiment, when the bone screw  14  is inserted into the aperture  16  of the bone plate  12 , the washer  18  is substantially coplanar with the head  20  of the bone screw  14 . 
         [0062]    Referring now to  FIG. 11 , certain characteristics of the recess  30  as seen from the bottom of the bone plate  12  are shown. As shown here, the lateral depth of the second recess region  30   b  may be minimal (and may not be present at all) and a lateral depth may be provided essentially only in the first recess region  30   a.    
         [0063]    Referring now generally to  FIGS. 12A and 12B , it is seen that when the bone plate assembly is implanted in a person, the bone plate is positioned over the bone, bones, and/or tissue to be joined by the bone plate  12 . The bone screw(s) are inserted through the aperture(s) in the washer(s) (which washer(s) may reside in the recess(s) provided in the aperture(s) of the bone plate) and the bone screw(s) are installed in bone and/or tissue by known techniques. Each bone screw may be installed at a preselected angle, relative to the bone plate. In the position in which a washer is unlocked, the bone screw may pass through the opening in the washer (e.g., so that the bone screw may be installed at a preselected angle) (see  FIG. 12A ). To fix the bone screw (e.g., at the angle at which the bone screw is installed), the washer may be actuated by rotating the washer (e.g., with the tool, as described above). When the washer is rotated, the first relatively thicker sidewall region of the washer may move into the second relatively shallower region of the recess. Such movement may effectively cause the first relatively thicker sidewall region to extend laterally into the aperture in the bone plate (where the relatively thicker sidewall region impinges against the head of the bone screw, thereby applying a force thereto which wedges the bone screw between the washer and the opposite sidewall of the aperture) (see  FIG. 12B ). Such wedging of the bone screw may fix the bone screw at an angle (e.g., the angle at which the bone screw was inserted).  FIGS. 10 and 12B  depict the condition where the bone screw is wedged after actuating the washer. 
         [0064]    In yet another embodiment of the present invention, depicted in  FIGS. 13-21 , another bone plate assembly is depicted. Shown here is a bone plate, bone screw, and a washer. With this arrangement, a bone plate that does not have a recess can be employed with this screw and washer pairing. 
         [0065]    More particularly,  FIG. 13  depicts a bone plate assembly  100 , generally provided with bone plate  102 , bone screw(s)  104  received in aperture(s)  106  in the bone plate  102 , and washer(s)  108  that, alone or in conjunction with the bone plate  102 , fix the bone screw(s)  104  in place (i.e., when the bone screw(s)  104  are inserted in the aperture(s)  106  in the bone plate  102 ). Each bone screw  104  has a head  110  sized so that it does not pass through the bone plate  102 . Further, each bone screw  104  has a shank  112  provided with threads  114  (e.g., which threads  114  extend to tip  116 ). In one embodiment, the head  110  of each bone screw  104  may be provided with grooves  118  (see, e.g.,  FIGS. 4 and 5C ). Bone plate assembly  100  is provided with washer(s)  108 , each of which (as described below) is adapted to reside over a bone screw  104  and be joined therewith in a locking arrangement. 
         [0066]    As shown in FIGS.  13  and  17 - 19 , for example, in this embodiment the head  110  of bone screw  104  is provided with a number of tangs  120 , spaced apart from each other, mounted on the upper surface of the head  110 . The tangs  120  include wedges  122 , which wedges  122  are not as wide as the upper portions of the tangs  120  (the wedges  122  are 5 narrowed by an undercut). The head  110  is provided with an opening  107  in which a tool can be received to apply a rotational force, which rotational force permits the installation of the screw in tissue and/or bone. 
         [0067]    Each washer  108  is sized and dimensioned to fit within one of the aperture(s)  106  in the bone plate  102 . Each washer  108  is provided with a washer body  124  through  10  which a central opening  125  is provided. A number of lobes  126  are provided on the periphery of the central opening  125 . As depicted in the embodiment of  FIG. 14 , for example, three lobes are provided, though it should be understood that other arrangements are possible. Each washer  108  is also provided with splays  127 , which are provided on the exterior of the washer  108 . The splays  127  are separated from the remainder of the washer body  124  by tracks  128 , which tracks  128  extend into the washer body  124 . The tracks  128  are provided with an entrance portion  130 , an intermediate track portion  132 , and a terminus  134 . The entrance portion  130  and the terminus  134  are wider than the intermediate track portion  132 . The width of the intermediate track portion  132  is narrowed by the presence of nubs  136  that extend into the track (e.g., from the washer body  124  and/or the splays  128 ). 
         [0068]    The washer  108  and the wedges  122 /tangs  120  are designed to engage with each other in a locking arrangement. Relative to each other, the wedges  122  are slightly wider than the width of at least the intermediate track portion  132 . 
         [0069]    In operation, when the bone plate assembly is implanted in a person, the bone plate is positioned over the bone, bones, and/or tissue to be joined by/to the bone plate. The bone screw(s) are inserted through the aperture(s) in the bone plate and installed in bone and/or tissue by known techniques. Each bone screw may be installed at a preselected angle, relative to the bone plate. To fix the bone screw at a preselected angle (e.g., the angle at which the bone screw is installed), the washer is placed over the head of the bone screw, positioned so that the wedges  122  are poised to enter the track portions  128 . A tool, provided with a head adapted to fit within the central washer opening  125  and lobes  126  is inserted into the washer, which is then rotated. The wedges  122  thereby enter the track portions  128 . Since wedges  122  are wider than at least the intermediate track portions  132 , the splays  127  are forced outward when the wedges enter the intermediate track portions  132  (see, e.g.,  FIG. 21 ). The splays are forced into an abutting arrangement with the sidewalls of the aperture in which the bone screw  106  and washer reside  108 . The abutting arrangement between the splays  127  and the sidewalls of the bone plate  102  fixes the bone screw  104  (e.g., at the angle at which the bone screw  104  was installed). 
         [0070]    In another example (which example is intended to be illustrative and not restrictive) the splays  127  may enter an undercut  140  in the aperture(s)  106  (see, e.g.,  FIG. 13 ). 
         [0071]    In another embodiment  FIG. 29  depicts, in a perspective view, a double lobed washer. The double lobed washer may be shaped differently than the recess and/or aperture in the bone plate which received the washer. When the washer is rotated, it is deformed, compressing it against the bone screw, fixing the angle of the bone screw (e.g., the angle at which the bone screw is inserted). The embodiment of  FIG. 30  is similar.  FIG. 30  depicts, in a perspective view, a tri-lobed washer. Again, the tri-lobed washer may be shaped differently than the recess and/or aperture in the bone plate. When the washer is rotated, it is deformed, compressing it against the bone screw and fixing the angle of the bone screw (e.g., the angle at which the bone screw is inserted). The embodiments of  FIGS. 29 and 30  may thus operate without a recess. 
         [0072]    In another embodiment, shown in  FIGS. 22A ,  22 B and  22 C, there is shown a bone plate assembly  150 , generally provided with bone plate  152 , bone screw(s)  154  (which bone screw(s)  154  are received in aperture(s)  156  in the bone plate  152 ), and  25  moveable doors  158  (which moveable doors  158  may slide and may fix the bone screw(s)  154  in place when the bone screw(s)  154  are inserted in the aperture(s)  156  in the bone plate  152 ). Each bone screw  154  has a head sized so that the head does not pass through the bone plate  152 . Further, each bone screw  154  has a shank provided with threads that extend to a tip. In one example (which example is intended to be illustrative and not restrictive), the head of the bone screw may be provided with grooves. Bone plate assembly  150  is provided with cut out portion(s)  164 , on an upper surface of the bone plate assembly  150 , to which the moving doors  158  are slidably mounted. The cut out portion(s)  164  are positioned adjacent the aperture(s)  156 , at a segment of the edge thereof. 
         [0073]    In one example (which example is intended to be illustrative and not restrictive), each moveable door  158  is provided with two substantially flat sides  166 , 167 , cutouts of partial circles  168 , full cut out circle  169 , and arcuate side  172 . It should be apparent that other dimensional arrangements are possible. The moveable doors  158  are positioned in the cut out portion(s)  164  on the upper surfaced of the bone plate  152 , and are retained therein by lip  174  provided at the upper sidewall of the cut out portion  164 . Dovetail undercuts may also be present along other upper sidewalls to maintain the doors in place. The cut out portion(s)  164  are sized slightly greater than the moveable doors. Thus, when each bone screw is positioned in an aperture  156  of the bone plate  152 , the moveable door  158  can be slid in the direction of the aperture  156 , in order to cover the bone screw  154  (and thus fix the bone screw  154  in place). 
         [0074]    Referring now to  FIG. 22C , in one example (which example is intended to be illustrative and not restrictive) a channel  180  is fully or partially bored into the bone plate  152  at a location between the cut out portions(s)  164 . Still referring to  FIG. 22C , in another example (which example is intended to be illustrative and not restrictive) the moveable doors  158  are provided with stops  182  that depend from the doors, into the channel  180 . When the door is moved into the locked position, as shown in the left hand side of  FIG. 22C , the stop engages channel sidewall  184 , inhibiting further movement of the door. Detents  186  and indentations  188  may also be used if desired. 
         [0075]    Another embodiment of the present invention is depicted in  FIGS. 23-27 . In this embodiment a bone screw  200  is provided with a head  202  sized so that it does not pass through a bone plate (not shown) and shank  204  provided with threads (not shown) that extend to tip  208 . In one example (which example is intended to be illustrative and not restrictive), the head  202  of the bone screw  200  may be provided with grooves (not shown). 
         [0076]    As seen in these Figures, the head  202  of bone screw  200  is provided with a number of splays  212 , spaced apart from each other, and extending around the periphery of the head of the bone screw  200 . The splays  212  are mounted on the upper surface of the head  202 , and in one example (which example is intended to be illustrative and not restrictive), may have an arcuate shape. Each splay  212  extends around a portion of the periphery of the head of the bone screw  200 . Each splay  212  is mounted upon a wedge  214 , (wherein the wedges  214  extend up from the head of the screw). The wedges  214  join the splay  212  at the base of the splay  212 , elevating the splay  212  off of the head of the bone screw  200 . Spaces  215  are present between the portions of the splay  212 , which extend over the periphery of the head of the bone screw  200 , and the head of the bone screw  200  itself. 
         [0077]    In this embodiment, after the bone screw  200  has been inserted into an aperture in a bone plate, and installed at a preselected angle, the angle can be fixed by forcing the splays outward (i.e., into a locking and abutting arrangement with the sidewalls of the aperture in the bone plate). In operation, a tool is inserted into the interior space  216  and rotated (to force the splays outward, into an abutting and locking arrangement with the sidewalls of the apertures). 
         [0078]    In another embodiment, shown in  FIG. 28 , a cam  218  may be utilized. In one example (which example is intended to be illustrative and not restrictive), the cam may be rotatably mounted to the head  202  of the bone screw  200 . In operation, the splays are forced outward, by rotating the cam  218  (which cam  218  moves against the interior walls of the splays). Here, the cam  218  provides a counterforce against the force applied by the sidewalls of the apertures (which counterforce facilitates the maintaining of the splays  212  in a locking and abutting arrangement with the sidewalls of the aperture in the bone plate). 
         [0079]    In another embodiment one or more of the washers may be a split-ring washer. While a number of embodiments of the present invention have been described, it is understood that these embodiments are illustrative only, and not restrictive, and that many modifications may become apparent to those of ordinary skill in the art.