Abstract:
A low profile bone screw system includes a retainable washer and a low profile bone screw having a smooth conical head for insertion into the washer. The washer has an axial bore with a conical portion for fully seating the screw head and a smooth outer surface shaped like the head of a conventional compression bone screw head. Washer dispensing units are also provided for assembling screw and washer assembled units.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a divisional of U.S. Ser. No. 12/210,627, filed Sep. 15, 2008, which is hereby incorporated by reference herein in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    This invention relates broadly to surgery. More particularly, this invention relates to orthopedic fasteners. 
         [0004]    2. State of the Art 
         [0005]    According to recent trends, there is a need to reduce the profile of bone plates and screws for internal fixation of fractured bones. This is especially important for plates used to repair fractures of the elbow, which has relatively little protection by overlying soft tissues and is highly vulnerable, for example, to accidental bumping as the fracture heals. Development of very thin, anatomically conforming bone plates has created new challenges related to plate-to-bone attachment. More specifically, improved designs for fastener systems are needed so that minimal implanted hardware protrudes undesirably above the top surface of the plate and irritates and/or inflames the overlying tissues. 
         [0006]    In general, there is also a need to reduce the inventory of bone screws required for internal fixation procedures due to the high cost of providing and maintaining a sterilizable surgical kit containing a large quantity of different screw sizes and types for the varied patient anatomies and fracture types. 
         [0007]    There have been developed bone screws and retainable (or captive) washers that attach to the screw head. However, the focus on such prior systems apparently was not to provide a low profile screw and washer assembly for use on bone plates that are thinner than previous, conventional bone plates. Nor was emphasis placed on providing a bone screw that may be used for multiple functions, thereby reducing the required inventory of screws required for a surgical procedure. 
       SUMMARY OF THE INVENTION 
       [0008]    A low profile bone screw system includes a retainable washer and a low profile bone screw having a head for insertion into the washer. The washer has an axial bore for receiving the screw head. In accord with one preferred aspect of the invention, the maximum diameter of the washer is located above the vertical center of the washer. The lower surface of the washer is smoothly curving from the lowest portion to the portion of maximum diameter, and preferably provided with a radius of curvature. These features allow the washer to seat low in a plate hole to minimize protrusion of the washer and screw head above the plate. 
         [0009]    In accord with another aspect of the invention, various means are provided for engaging the washer relative to the screw head to lock the two components together. According to several embodiments, the washer is adapted to engage a non-threaded conical screw head. For such screws, the means for engaging the washer relative to the screw includes at least one interference element extending radially inward from the axial bore on the washer. The at least one interference element may be resiliently or plastically deformable. When a user inserts the screw into the washer and the screw head is fully seated in the washer, either one or both of the interference element and the head of the screw deforms, such that the screw and washer are sufficiently joined together to be handled as a unit during the surgical procedure. According to another embodiment, the washer is adapted to engage a threaded screw head. In such embodiment, the engagement means is a threaded axial bore. The washer preferably includes a recess at its upper end in order to receive the screw head in a low profile manner. 
         [0010]    According to another aspect of the invention, dispensers are provided including one or more stores of washers in the dispensers. The dispensers are preferably operably associated with a sterilizable surgical tray also containing a plurality of low profile orthopedic screws, additional orthopedic implants and/or orthopedic instruments. 
         [0011]    Additional advantages of the invention will become apparent to those skilled in the art upon reference to the detailed description taken in conjunction with the provided figures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a perspective view of an assembly of a bone screw and washer according to a first embodiment of the invention. 
           [0013]      FIG. 2  is a perspective view of a washer according to the first embodiment of the invention. 
           [0014]      FIG. 3  is a section view of the washer of  FIG. 2 . 
           [0015]      FIG. 4  is a section view similar to  FIG. 2  showing the assembly of the bone screw to the washer. 
           [0016]      FIG. 5  is a perspective view of an assembly of a bone screw and washer according to a second embodiment of the invention. 
           [0017]      FIG. 6  is a perspective view of a washer according to the second embodiment of the invention. 
           [0018]      FIG. 7  is a top view of the washer of  FIG. 6 . 
           [0019]      FIG. 8  is a section view of the washer of  FIG. 6 . 
           [0020]      FIG. 9  is a section view similar to  FIG. 8  showing the assembly of the bone screw to the washer. 
           [0021]      FIG. 10  is a perspective view of a partial assembly of a bone screw and washer according to a third embodiment of the invention. 
           [0022]      FIG. 11  is a perspective view of a washer according to the third embodiment of the invention. 
           [0023]      FIG. 12  is a section view of the washer of  FIG. 11 . 
           [0024]      FIG. 13  is an end perspective view of the bone screw and washer assembly according to the third embodiment of the invention. 
           [0025]      FIG. 14  is a broken perspective view of surgical kit including a first embodiment of a washer dispenser according to the invention. 
           [0026]      FIG. 15  is a schematic view of the washer dispenser according to the invention. 
           [0027]      FIG. 16  is broken perspective view of a second embodiment of a washer dispenser according to the invention. 
           [0028]      FIG. 17  is a broken top view of the second embodiment of a washer dispenser according to the invention. 
           [0029]      FIG. 18  is a side elevation of the second embodiment of a washer dispenser according to the invention. 
           [0030]      FIG. 19  is a broken bottom view of the second embodiment of a washer dispenser according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0031]    Referring to  FIGS. 1 through 4 , an embodiment of a low profile bone screw system  10  is shown. The system  10  includes a low profile bone screw  12  having a conical head  14  (seen best in  FIG. 4 ) with a driver engaging slot  15 , and shaft  16  with bone engaging threads  18 . Such a low profile conical head screw  12  may be inserted into a threaded, locking hole in an orthopedic plate (without threaded engagement therein) or assembled with a washer  20  retained on the head  14  of the screw for use in a dynamic compression slot of an orthopedic plate. 
         [0032]    The washer  20  has a top  22 , a bottom  24 , and a maximum vertical dimension V between the top  22  and bottom  24  that defines a vertical center C at a midpoint of the maximum vertical dimension. A smoothly curving lower surface  26  extends from the bottom  24  to the circumference  28  of the washer at the maximum diameter D of the washer, which occurs above the vertical center C. More preferably, the maximum diameter D is located approximately two-thirds up from the bottom  24  of the washer  20 . These features allow the washer to seat low in a plate hole to minimize protrusion of the washer  20  and screw head  14  above a plate so as to reduce tissue irritation/inflammation and minimize patient discomfort. 
         [0033]    An axial bore  30  extends through the washer  20  and has an upper conical portion  32  and a lower cylindrical portion  34 . The upper conical portion  32  is defined by a bore surface  36  inclined by 22°±3° relative to the bore axis A. The bore  30  includes means for engaging the head  14  of the screw  12  to the washer  20  such that the screw  12  and washer  20  are assembled to each other to be handled together as a unit during a surgical procedure. According to a first embodiment, a circumferential ridge  38  is provided within the axial bore  30 . Retaining tabs  40  are circumferentially displaced along the ridge  38  and directed radially inwardly into the bore  30 . The tabs  40  have a first portion  42  angled at 25°±3° relative to the bore axis A, and a free end  44  parallel to the bore axis A. The free ends  44  are substantially co-planar with the top  22  of the washer  20  ( FIG. 4 ). Preferably six tabs  40  are provided, with each tab extending 5°±3° about the circumference of the ridge  38  ( FIG. 2 ). A channel  46  is defined between the tabs and the bore ( FIGS. 2 and 3 ). 
         [0034]    As the screw head  14  is forced through the washer  20  during assembly, the head  14  deflects the tabs  40  radially outward to provide sufficient access for the head to be received with the conical portion  32  of the bore  30 , and the tabs  40  then snap back over the head  14  to lock the head relative to the washer  20 . The head  14  and conical portion  32  have a common inclination permitting a stable assembly. The angled first portion  42  of each tab  40  is configured to seat against a convex top surface of the head  14  of the screw. In addition, by having the free end  44  of the tab  40  terminate even with the top  22 , the contour profile at the top of the assembly has an increased smoothness to reduce any potential irritation. 
         [0035]    Turning now to  FIGS. 5 through 9 , according to another embodiment, a washer  120  preferably having the same outer shape as washer  20  described above is provided with different means for engaging the same screw  12 . In general, the means includes a structure provided within an upper portion of the bore that either (i) plastically deforms upon contact with the washer, or (ii) causes plastic deformation of the washer, or (iii) causes a combination thereof, as the screw head  14  is forced within the axial bore  130  of the washer  120  upon assembly of the washer relative to the screw head. More particularly, the axial bore  130  of the washer  120  includes a central conical portion  132 , a lower cylindrical portion  134 , and an upper cylindrical portion  135 . The upper cylindrical portion  135  is provided with a plurality of evenly spaced interference elements  140  (proximate the top of the washer) that radially extend into the upper cylindrical portion  135  to define a diameter smaller than the diameter of the screw head  14  that seats in the corresponding portion of the bore. 
         [0036]    The screw  12  and washer  120  may be formed from stainless steel, titanium, titanium alloy, cobalt chrome, or a polymer. In addition, the screw  12  and washer  120  may be formed from the same material to allow a cold formed weld assembly. The screw  12  and washer  120  may alternatively be formed from dissimilar materials of different hardnesses, depending on the desired deformation of interference elements  140  and the screw head  14 . The washer  120  may be constructed of a softer material than the screw head  14  to facilitate deformation of the interference elements  140  by the screw head  14 , or the washer  120  (or at least the interference elements  140  thereof) may be formed of a harder material than the screw head  14  to facilitate deformation of the screw head by the interference elements  140 . 
         [0037]    When a user forces the screw  12  into the washer  120  and the screw head  14  fully seats in the washer, either one or both of the interference elements  140  and the head  14  of the screw  12  deforms. The resulting assembly, as seen in  FIGS. 5 and 9 , is sufficiently joined together to be handled as a unit during the surgical procedure. 
         [0038]    Referring now to  FIGS. 10 through 13 , according to yet another embodiment, the system  210  includes a screw  212  with a cylindrical head  214  having a machine thread  216  thereabout and a threaded shaft  218 . The screw  212  is normally used for fixed angle coupling relative to a plate with a mating threaded hole. The system also includes a washer  220 , which preferably has substantially the same external shape as the previously described washers. The washer  220  defines an axial cylindrical bore  230  having an internal helical thread  232 . The screw head  214  stably threads into engagement with the thread  232  in the washer bore  230 . The washer  220  preferably includes a recess  234  at its upper end in order to receive and recess the screw head  214  in a low profile manner. When the screw  214  and washer  220  are assembled, the screw  214  is converted from a fixed angle locking screw to a lagging screw ( FIG. 13 ). 
         [0039]    Referring now to  FIGS. 14 and 15 , according to another aspect of the invention, a first kit  300  is provided for dispensing and facilitating assembly of any of the washers  20  ( 120 ,  220 ) described herein with screws in accord with the invention. The kit includes a dispenser  302  having a store of washers  20  on a tray  303  or other carrier. More particularly, the tray  303  has two longitudinally offset rows  304   a,    304   b  of recesses  306  with central holes  308  therein in communication with a lower cavity  314  ( FIG. 15 ). The washers are received in the recesses  306  with the axial bores  30  of the washers centered over the central holes  308 . A lid  310  is coupled relative to the tray  303  to retain the washers therein. The lid  310  preferably indexes in a slidable manner relative to the store to controllably expose the axial bore of one washer  20  at a time. The lid  310  is shaped to define two cutouts  312   a,    312   b  which alternately align relative to the axial bores  30  of the washers  20  in the alternate rows  304   a,    304   b  as the lid  310  is indexed from one predetermined location to the next. As the lid  310  is indexed to expose an axial bore of a washer, the area surrounding the respective cutouts, e.g., cutout  312   a,  allows the lid  310  to provide contact against the periphery of a washer  30  to stabilize the washer while its axial bore  20  is exposed. Such stabilization allows axial and/or rotational forces to be applied by a screw  12  ( FIG. 15 ) to the washer  30  during assembly of the screw to the washer. The screw shaft is received in the cavity  314  during assembly. Once the screw  12  is assembled to the washer  20 , the lid  310  is indexed another step to release the assembled screw and washer from the dispenser  302  and expose the axial bore of a next washer  30 a. 
         [0040]    The dispenser  302  may accept replaceable cartridges of washers. The dispenser  302  is preferably operably associated with a sterilizable surgical tray  316  also containing a plurality of low profile orthopedic screws  12 , additional orthopedic implants such as plates for placement on the diaphysis or metaphysis of long bones, and/or orthopedic instruments for implanting such implants including, e.g., rotational drivers  318  for the screws, plate benders  320  for shaping orthopedic plates, and drill bits  322  for drilling holes into bone to accept orthopedic fasteners such as screw  12 . 
         [0041]    Turning now to  FIGS. 16 through 19 , a second dispenser  402  for a kit is provided for dispensing and facilitating assembly of any of the washers  20  ( 120 ,  220 ) described herein with screws in accord with the invention. The dispenser  402  has a store of washers  20  on a carrier  403 . The carrier  403  defines at least one, and preferably a plurality of, elongate keyhole slots  404  defining lateral grooves  406  in which the peripheries of the washers  20  are received and supported. Screws  12  can be inserted through the supported washers  20  and forced into engagement therein, as described above. An enlarged generally circular opening  408  through which the washers  20  can be individually loaded into the slot  404  and removed therefrom is provided at an end of each slot  404 . The lower portion of the carrier has a recess  410  adjacent each enlarged opening  408 . A sheet  411  has an end fixed relative to the lower surface of the carrier  403 . The sheet  411  defines leaf springs  412  that extend from the fixed end along both sides of each of the slots  404 . The leaf springs  412  each have a retainer  414  that enters a respective recess  410 . The retainers  414  inhibit release of washers  20  through the enlarged openings  408  unless sufficient manual force is applied to a washer  20  to resiliently deform a respective leaf spring  412  to permit passage of a washer  20  from the slot  404  into the adjacent enlarged opening  408 , particularly once the washer  20  is assembled with the screw  12  so that the screw and washer are engaged together so as to be handled as a unit. The carrier  403  may be coupled to or incorporated into a surgical kit, and may be in the form of a cartridge that is removable and replaceable within a surgical kit. 
         [0042]    The versatility of using a single bone screw in either a locking screw hole or with a retainable washer in an elongated hole of a bone plate reduces the quantity of screws that must be available during the surgical procedure. This potentially reduces the overall cost of the surgical kit because it is much less expensive to make retainable washers than to make bone screws. 
         [0043]    There have been described and illustrated herein several embodiments of a washers for screws, screw and washer assemblies, and kits for dispensing washers during a surgical procedure. While particular embodiments of the invention have been described, it is not intended that the invention be limited thereto, as it is intended that the invention be as broad in scope as the art will allow and that the specification be read likewise. Thus, while materials have been disclosed with respect to particularly embodiments, it will be appreciated that such materials can be used with respect to all embodiment of the invention. It will therefore be appreciated by those skilled in the art that yet other modifications could be made to the provided invention without deviating from its spirit and scope as claimed.