Abstract:
A method of forming a bone plate comprising fabricating a bone plate to include a first through hole, where at least one of a width and a length of the hole changes along a depth of the hole; plunge milling an interior surface of the bone plate demarcating the first through hole to remove at least a portion of the bone plate to increase at least one of the width and the length of the through hole; and, threading at least a portion of the first through hole.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a divisional of U.S. patent application Ser. No. 13/019,639, filed Feb. 2, 2011, and entitled “Bone Plate Having Combination Locking and Compression Screw Holes,” the disclosure of which is expressly incorporated in its entirety herein by this reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present disclosure is directed to bone plates and, more specifically, to bone plates having fastener holes that may be utilized as locking holes or as compression holes, depending upon the initial placement of the fastener with respect to the fastener hole. 
       BRIEF DISCUSSION OF RELATED ART 
       [0003]    Bone plates used in conjunction with screws to fix bone fractures often contain locking screw holes and compression slots. Locking screw holes provide additional plate-to-screw fixation to lock bone fragments in place and aid in healing of bone fractures. Compression slots, on the other hand, are used to compress the ends of bone fragments together to aid in primary healing. 
         [0004]    Typically, a bone plate includes at least one locking screw hole and at least one compression slot. The location of the holes and slots dictate the locations on the bone plate where the surgeon can apply locking or compression forces. 
       INTRODUCTION TO THE INVENTION 
       [0005]    The present invention is directed to bone plates having fastener holes that may be utilized as locking holes or as compression holes, depending upon the initial placement of the fastener with respect to the fastener hole. By providing a single hole that can act as a compression hole or a locking hole, the bone plate provides a surgeon with greater flexibility as to the placement of locking fasteners and compression fasteners in a smaller footprint than in a traditional plate having dedicated space for each type of hole. 
         [0006]    It is a first aspect of the present invention to provide a bone plate including a hybrid through screw hole, where the hybrid through screw hole includes a top opening and a bottom opening, the top opening being generally circular and including a widthwise dimension and a lengthwise dimension normal to the widthwise dimension, where an interior wall of the bone plate extends between the top opening and the bottom opening, where at least a portion of the interior wall proximate the top opening is threaded, and where at least one of the widthwise dimension and the lengthwise dimension is decreased between the top opening to the bottom opening, while the other of the widthwise dimension and the lengthwise dimension does not substantially decrease between the top opening and the bottom opening. 
         [0007]    In a more detailed embodiment of the first aspect, the interior wall includes a first portion having a first circumferential curvature and a second portion having a second circumferential curvature, wherein the first circumferential curvature is larger than the second circumferential curvature. In yet another more detailed embodiment, the second portion does not include threads. In a further detailed embodiment, the first portion is at least one of arcuate and tapered in the vertical direction and, the second portion includes a vertical wall. In still a further detailed embodiment, the interior wall includes a first portion having a first circumferential curvature, a second portion having a second circumferential curvature, and a third portion having a third circumferential curvature, wherein the first circumferential curvature is larger than the second circumferential curvature and the third circumferential curvature. In a more detailed embodiment, the second portion is opposite the third portion. In a more detailed embodiment, the second circumferential curvature is generally the same as the third circumferential curvature. In another more detailed embodiment, the first portion includes threads, the second portion does not include threads and, the third portion does not include threads. In yet another more detailed embodiment, the first portion is at least one of arcuate and tapered in the vertical direction, the second portion includes a vertical wall and, the third portion includes a vertical wall. 
         [0008]    It is a second aspect of the present invention to provide a bone plate comprising a combination compression and locking through hole, where the combination hole includes a first portion having a circular, horizontal cross-section and a second portion having an oblong, horizontal cross-section, where the circular, horizontal cross-section and the oblong, horizontal cross-section lie along differing planes perpendicular to a central axis extending through the combination compression and locking through hole. 
         [0009]    In a more detailed embodiment of the second aspect, the bone plate further includes a plurality of combination compression and locking through holes, where each of the plurality of combination compression and locking through holes includes a first portion including a circular, horizontal cross-section and a second portion including an oblong, horizontal cross-section. In yet another more detailed embodiment, the combination compression and locking through hole is at least partially threaded. In a further detailed embodiment, the first portion is threaded and the second portion is unthreaded. In still a further detailed embodiment, the first portion includes a diameter D, the second portion includes a maximum length L and, the diameter D is approximately equal to the length L. 
         [0010]    It is a third aspect of the present invention to provide a bone plate comprising a through screw hole demarcated by an interior surface of the bone plate that extends between a top opening and a bottom opening, the top opening having a continuous arcuate shape and allowing throughput of a first imaginary cylinder having a circular cross-section with a diameter D 1 , the interior surface having a first segment that is at least partially threaded and tapers to a stopping distance SD to inhibit throughput of the first imaginary cylinder at a location between the top opening and the bottom opening, the interior surface having a second segment adjacent to the first segment, the first segment and the second segment allowing throughput of a second imaginary cylinder having a circular cross-section with a diameter D 2 , where the diameter D 1  is greater than the diameter D 2 , where the stopping distance SD is greater than D 2 , and wherein a maximum horizontal distance across the second segment is greater than 1.3 times D 2 . 
         [0011]    In a more detailed embodiment of the third aspect, the interior surface of the first segment includes a first circumferential curvature and the second segment includes a second circumferential curvature, wherein the first circumferential curvature is larger than the second circumferential curvature. In yet another more detailed embodiment, the second segment does not include threads. In a further detailed embodiment, the first segment is at least one of arcuate and tapered in the vertical direction and, the second segment includes a vertical wall. In still a further detailed embodiment, the interior surface includes a first segment having a first circumferential curvature, the second segment includes a second portion having a second circumferential curvature and a third portion having a third circumferential curvature, wherein the first circumferential curvature is larger than the second circumferential curvature and the third circumferential curvature. In a more detailed embodiment, the second portion lies generally opposite the third portion. In a more detailed embodiment, the second circumferential curvature is generally the same as the third circumferential curvature. In another more detailed embodiment, the first portion includes threads, the second portion does not include threads and, the third portion does not include threads. In yet another more detailed embodiment, the first portion is at least one of arcuate and tapered in the vertical direction, the second portion includes a vertical wall and, the third portion includes a vertical wall. 
         [0012]    It is a fourth aspect of the present invention to provide a method of forming a bone plate comprising: (a) fabricating a bone plate to include a first through hole, where at least one of a width and a length of the hole changes along a depth of the hole; (b) plunge milling an interior surface of the bone plate demarcating the first through hole to remove at least a portion of the bone plate to increase at least one of the width and the length of the through hole; and (c) threading at least a portion of the first through hole. 
         [0013]    In a more detailed embodiment of the fourth aspect, threading at least a portion of the first through hole occurs before the plunge milling act. In yet another more detailed embodiment, threading at least a portion of the first through hole occurs after the plunge milling act. In a further detailed embodiment, the length and width of the through hole at a top surface of the bone plate are identical. In still a further detailed embodiment, the length and width of the through hole at a bottom surface of the bone plate are identical after the fabricating act and, the length and width of the through hole at the bottom surface of the bone plate are not identical after the plunge milling act. In a more detailed embodiment, the plunge milling act includes using an end mill to remove material in a cylindrical swath, a first axis extends through a center of the through hole, a second axis extends through a circular center of the cylindrical swath and, the first axis is parallel with the second axis. In a more detailed embodiment, the plunge milling act includes using an end mill to remove material in a cylindrical swath, the plunge milling act includes applying the cylindrical swath to opposing ends of the through hole to create a first cylindrical swath and a second cylindrical swath, the first cylindrical swath includes a first axis extending through a circular center thereof, the second cylindrical swath includes a second axis extending through a circular center thereof, the first axis is parallel with the second axis and, the first axis is offset from the second axis. 
         [0014]    It is a fifth aspect of the present invention to provide a method of forming a bone plate comprising fabricating a bone plate to include a combination compression and locking hole, where the combination compression and locking hole includes a first portion having a circular cross-section and a second portion having an oblong cross-section, where the circular cross-section and the oblong cross-section lie along differing planes perpendicular to a central axis extending through the combination compression and locking hole. 
         [0015]    In yet another more detailed embodiment of the fifth aspect, the fabricating step includes machining a bone plate from a solid block of material. In still another more detailed embodiment, a first portion of the hole tapers to reduce a cross-sectional area of the hole. In a further detailed embodiment, the fabricating step includes forming threads within an interior surface of the bone plate demarcating the hole. In still a further detailed embodiment, the fabricating step includes removing some of the bone plate to increase at least one of a width and a length of the hole after the hole has been formed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is an elevated perspective view of an exemplary bone plate incorporating at least one combination locking and compression screw hole. 
           [0017]      FIG. 2  is an overhead view of the exemplary combination locking and compression screw hole shown in  FIG. 1 . 
           [0018]      FIG. 3  is a cross-sectional view taken along line C in  FIG. 2 . 
           [0019]      FIG. 4  is a cross-sectional view taken along line B in  FIG. 2 . 
           [0020]      FIG. 5  is an overhead view of a locking screw hole while a portion is bored out using an end mill. 
           [0021]      FIG. 6  is an overhead view of the locking screw hole of  FIG. 5 , with an opposing portion being bored out using an end mill to form the combination locking and compression screw hole. 
           [0022]      FIG. 7  is an elevated perspective view of an exemplary locking screw. 
           [0023]      FIG. 8  is a vertical cross-section of the exemplary locking screw of  FIG. 7  taken at the middle. 
           [0024]      FIG. 9  is an elevated perspective view of an exemplary compression screw. 
           [0025]      FIG. 10  is a vertical cross-section of the exemplary compression screw of  FIG. 9  taken at the middle. 
           [0026]      FIG. 11  is a vertical cross-section of the exemplary bone plate of  FIG. 1  in position with respect to a bone, where a compression screw is partially inserted into the combination locking and compression screw hole. 
           [0027]      FIG. 12  is a vertical cross-section of the exemplary bone plate of  FIG. 1  in position with respect to a bone, where a compression screw is fully inserted into the combination locking and compression screw hole in order to shift the position of the plate and compress the bone. 
           [0028]      FIG. 13  is a vertical cross-section of the exemplary bone plate of  FIG. 1  in position with respect to a bone, where a locking screw is partially inserted into the combination locking and compression screw hole. 
           [0029]      FIG. 14  is a vertical cross-section of the exemplary bone plate of  FIG. 1  in position with respect to a bone, where a locking screw is fully inserted into the combination locking and compression screw hole in order to lock the angular position of the screw with respect to the plate and bone. 
       
    
    
     DETAILED DESCRIPTION 
       [0030]    The exemplary embodiments of the present disclosure are described and illustrated below to encompass bone plates and, more specifically, to bone plates having fastener holes that may be utilized as locking holes or as compression holes, depending upon the initial placement of the fastener with respect to the fastener hole. 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. 
         [0031]    Referencing  FIG. 1 , an exemplary bone plate  100  comprises a clavicle bone plate. This clavicle bone plate  100  includes an elongated, longitudinal dimension that includes a series of fastener holes  102 ,  103 ,  102 A distributed in a spaced-apart fashion along the longitudinal length. Each fastener hole  102 ,  103 ,  102 A extends between the top surface  104  and bottom surface  106 . In this exemplary embodiment, the top surface  104  is generally convex from superior to inferior, while the bottom surface  106  is generally concave from superior to inferior. This shape is operative to form a channel defined by the bottom surface  106  that is adapted to receive a biologic substrate, such as bone. And each fastener hole  102 ,  103 ,  102 A is generally centered between a superior side  108  and an inferior side  110 . 
         [0032]    In this exemplary embodiment, the fastener holes  102 ,  103 ,  102 A generally take on three forms. A first form hole  102  includes a generally circular through opening that extends between the top and bottom surfaces  104 ,  106 . This first form hole  102  has a horizontal circular cross-section that changes in diameter in order to provide a taper in the hole, with the taper being located proximate the bottom surface. It should be noted, however, that wherever a horizontal cross-section of this first hole  102  is taken, the cross-section will be circular. In order to form this hole, a milling machine (not shown) uses an end mill to remove material from the bone plate in order to form the interior wall that defines the through hole. As part of this first form hole  102 , the milling machine removes material from the hole to create a taper from top to bottom so that the area of the horizontal, circular cross-sections at some point between the top and bottom decreases. After the milling machine has formed the hole, the wall of the hole is relatively smooth. Thereafter, a threading procedure is carried out to form threads on the interior of the hole  102 . These threads, however, do not generally change the circular cross-section of the hole. But the second form hole  103  does not include a horizontal circular cross-section. 
         [0033]    In contrast to the first hole  102 , the second form hole  103  includes an elongated shape having a non-circular cross-section. By way of example, the second form hole  103  includes a longitudinal dimension that is greater than a widthwise dimension (superior to inferior). At the top of the second form hole  103 , proximate the top surface  104 , the longitudinal dimension accommodates multiple longitudinal positions for a screw (such as a locking screw  180  or a compression screw  210 ). But the widthwise dimension is generally uniform and allows for positioning of the screw in only a single widthwise position. In other words, the second form hole  103  allows for positioning the screw in a number of longitudinal positions, but the position of the screw in the superior-to-inferior (i.e., widthwise) direction is generally not amendable to multiple positions. Similarly, the first form hole  102  does not allow for multiple positions of the screw in the inferior-to-superior direction. But, conversely to the second form hole  103 , the first form hole  102  fails to allow multiple positions of the screw in the longitudinal direction. 
         [0034]    The two screw form holes  102 ,  103  also differ in that the first form hole  102  is threaded, while the second form hole  103  is not threaded. In order to retain the screw within the second form hole  103 , a circumferential flange  140  (recessed in between the top and bottom surfaces  104 ,  106 ) extends into the hole and is operative to decrease the through hole diameter enough so that throughput of the screw head is retarded. Because of the longitudinal position variance provided by the second form hole  103 , compression screws  210  are more commonly inserted into this hole, as opposed to locking screws  180 . As would be expected, the threaded nature of the first form hole  102  results in locking screws  180  being inserted into these holes more commonly than compression screws  210 . 
         [0035]    A third form hole  102 A comprises a hybrid hole that may be utilized as a locking screw hole or as a compression screw hole. In exemplary form, the hybrid fastener hole  102 A includes a circular cross-section at the top surface  104  and an oblong cross-section at the bottom surface  106 . More specifically, the oblong cross-section of the hole  102 A at the bottom surface  106  includes a first, larger dimension  112  running longitudinally along the longitudinal dimension of the hole  102 A, and a second, smaller dimension  114  running inferiorly between the superior and inferior sides  108 ,  110 . It should be noted that the larger dimension  112  is approximately the same as the diameter of the hole  102 A at the top surface  104 . In this exemplary embodiment, the larger dimension  112  is 0.205 inches, while the smaller dimension is 0.145 inches. Those skilled in the art will understand that differing dimensions (greater or lesser) are well within the scope of the invention. 
         [0036]    Located between the top and bottom surfaces  104 ,  106  for the first and third form holes  102 ,  102 A are helical threads  120  that extend from portions of an interior wall  122  to delineate the vertical cross-section of each hole  102 A. The interior wall  122  takes on a general shape that resembles a bowl or a frustum, where portions of the interior wall  122  departing from the bowl or frustum shape may not include the helical threads  120 . 
         [0037]    An exterior of the bone plate  100  includes a number of indentations  130  that are formed into the superior and inferior sides  108 ,  110 . Each indentation  130  is located opposite another indentation so that a pair of indentations generally interposes consecutive fastener holes  102 ,  102 A. In this exemplary embodiment, each indentation  130  operates to decrease the widthwise dimension (superior  108  to inferior  110 ) of the bone plate  100 , while at the same time cooperating with arcuate depressions  132  to decrease the thickness (top surface  104  to bottom surface  106 ) of the bone plate. Specifically, the arcuate depressions  132  extend along the top surface  104  and terminate just shy of the superior-inferior midline extending longitudinally along the length of the bone plate  100 . 
         [0038]    To fabricate the exemplary bone plate  100 , a solid block of metal (e.g., stainless steel, titanium, etc.) is milled to form the general shape of the bone plate. This includes milling the bone plate  100  to have the requisite length, width, and thickness, in addition to providing a top surface  104  that is convex and a bottom surface  106  that is concave along the longitudinal length. In addition, the milling is operative to form the indentations  130  and remove material from the bone plate  100  in order to form the depressions  132 . After the general shape of the bone plate is finished, the fastener holes of the first and second form  102 ,  103  are formed through the bone plate  100 . 
         [0039]    Referring to  FIGS. 5 and 6 , in order to form the hybrid holes  102 A, an additional step is taken to modify one or more of the first form holes  102 . Specifically, a milling machine is utilized to carry out a plunge down operation on the first form hole  102  that removes a portion of the internal threads and interior wall in the longitudinal direction to create an oblong opening at the bottom of the hole. As discussed previously, the first form hole  102  has a diameter of 0.205 inches (and a circumferential curvature that matches this 0.205 inch diameter) at the top surface  104  and a diameter of 0.145 inches at the bottom surface  106  prior to the plunge down operation. After the plunge down operation is complete, the diameter of 0.205 inches at the top surface  104  remains unchanged, while the longitudinal dimension of the hole at the bottom surface  106  is changed to create an oblong shape. Specifically, the plunge down operation creates an oblong hole at the bottom surface  106  having a longitudinal dimension of 0.205 inches, while maintaining the widthwise dimension of 0.145 inches. 
         [0040]    The plunge down operation involves using an end mill  150  having an outside diameter of 0.138 inches, where the end mill is oriented in parallel to the through axial center of the hole and is longitudinally offset 0.03 inches from this axial center, but is centered in the superior-to-inferior direction. In a first plunge down operation (see  FIG. 5 ), the end mill  150  is longitudinally offset 0.03 inches in the proximal direction and removes a portion of the interior surface to create a wall having a circumferential curvature of a circle having a diameter of 0.138 inches. In a second plunge down operation, the end mill  150  is longitudinally offset 0.03 inches in the distal direction (see  FIG. 6 ) and removes another portion of the interior surface to create another wall having a circumferential curvature of a circle having a diameter of 0.138 inches. The result of the plunge down operation is a hole  102 A having hybrid characteristics to accept either a locking or compression screw  180 ,  210  without sacrificing the functionality of a locking screw or the functionality of a compression screw. 
         [0041]    Referring to  FIGS. 7 and 8 , an exemplary locking screw  180  includes a head  182  and a shaft  184  extending from the head. The head  182  comprises a dome  186  that transitions into an arcuate circumferential surface  188  that includes helical threads  190  adapted to engage the threads  120  of the bone plate holes  102 ,  102 A. The circumferential surface  188  transitions into an underneath planar surface  192  at the bottom of the head  182  to take on a frustum profile. Opposite the bottom of the head  182  is an opening  194  formed at the apex of the dome  186 . The opening  194  extends through the head  182  and into a head end  196  of the shaft  184 . In exemplary form, the opening  194  is defined by a series of six alternating semicircular walls  198  and six straight walls  200  that form a hexagonal pattern. At the base of the walls  198 ,  200  is a conical wall  202  that defines a conical part of the opening  194  terminating in the head end  196  of the shaft  184 . An exterior surface  204  of the shaft  184  includes helical threads  206  that are adapted to engage a biologic substrate (not shown), such as bone. The threads  206  extend along the shaft until reaching a pointed projection  208  at a far end of the screw  180 . 
         [0042]    Referencing  FIGS. 9 and 10 , an exemplary compression screw  210  includes a head  212  and a shaft  214  extending from the head. The head  212  includes a dome  215  that transitions into a rounded or tapered circumferential surface  216  that operates to decrease the cross-section of the head from proximal to distal, where the distal aspect transitions into the shaft. Extending through the dome  215  is an opening  218  that extends through the head  212  and into a head end  220  of the shaft  214 . In exemplary form, the opening  218  is defined by a series of six alternating semicircular walls  220  and six straight walls  222  that form a hexagonal pattern. At the base of the walls  220 ,  222  is a conical wall  224  that defines a conical part of the opening  218  terminating in the head end  220  of the shaft  214 . An exterior surface  226  of the shaft  214  includes helical threads  228  that are adapted to engage a biologic substrate (not shown), such as bone. The threads  228  extend along the shaft  214  until reaching a tapered projection  230  at a far end of the screw  210 . 
         [0043]    Referring to  FIGS. 11 and 12 , the hybrid holes  102 A of the exemplary bone plate  100  may be utilized to receive a compression screw  210  in order to exert a compressive force on the bone  240 . In exemplary form, a bone or bone fragments  240  is mounted to the bone plate  100  using a combination of compression and locking screws  210 ,  180 . Presuming a surgeon finds it desirable to provide compression using the hybrid hole  102 A, a pilot hole may be drilled to receive a compression screw  210 . By way of example, the pilot hole is offset distally with respect the axial center of the hole  102 A, which allows for the compression screw  210  to be axially offset from the center of the hole (see  FIG. 11 ). When the compression screw  210  is initially inserted, the smaller diameter threaded shaft  214  is aligned with the pilot hole and extends through the hybrid hole  102 A with the shaft contacting, but not actively engaging the threads on the side of the hole  102 A. A pair of reference lines  242 ,  244  denotes the position of the bone  240  with respect to the bone plate  100  prior to compression. As the screw  210  is inserted farther into the bone  240 , the circumferential surface  216  of the head  212  initially comes in contact with the top of the hole  102 A. 
         [0044]    When the circumferential surface  216  of the head  212  comes in contact with the top of the hole  102 A, further insertion of the head is operative to push the head against the distal wall of the hole. This causes the position of the bone plate  100  to shift distally with respect to the bone  240 , thereby creating a compressive force on the bone in the distal direction. As can be seen in  FIG. 12 , the reference lines  242 ,  244  are no longer aligned, as the reference mark  242  for the plate  100  has shifted distally with respect to the reference mark for the bone  240 . 
         [0045]    Referring to  FIGS. 13 and 14 , the hybrid holes  102 A of the exemplary bone plate  100  may be utilized to receive a locking screw  180 , such as a variable angle locking screw, in order fix the position of the bone plate  100  with respect to the bone  240  where screw angles other than perpendicular may be desired. In exemplary form, a bone or bone fragments  240  is mounted to the bone plate  100  using a combination of compression and locking screws  210 ,  180 . Presuming a surgeon finds it desirable to mount the plate  100  to the bone  240  using a locking screw at an angle other than perpendicular (perpendicular could also be used as well), a pilot hole may be initially drilled. By way of example, the pilot hole is angled based upon the orientation of the bone or bone fragments  240 . After the hole is drilled, a locking screw  180  is inserted through the hole  102 A so that the smaller diameter threaded shaft  184  is aligned with the pilot hole. Thereafter, the locking screw  180  is rotated to fasten the screw to the bone  240 , while at the same time pulling the head  182  into contact with the bounds of the hole  102 A. Specifically, the threads  190  of the screw head  182  engage the threads  120  on the interior of the hole  102 A in order to lock the angular position of the screw head (and screw) with respect to the bone plate  100 . 
         [0046]    It should be noted that the dimensions set forth for the exemplary embodiments are just that, exemplary. Deviations from these dimensions may be made without departing from the scope and spirit of the instant disclosure. For example, the holes  102  may have an upper diameter larger or smaller than 0.205 inches. Likewise, the holes may not necessarily have a circular cross-section at any point. Moreover, the holes may generally take on any dimensions that provides for dual functionality and use as both a compression hole and a locking hole. 
         [0047]    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.