Abstract:
A bone plate includes a first through hole extending through the plate along a first longitudinal axis from a proximal surface of the plate to a bone-facing distal surface thereof which, when the plate is placed on a target portion of bone in a desired orientation, faces the bone. An outer wall of the first through hole includes three wall sections provided with projections for receiving a screw head of a bone screw. The three wall sections are straight or convex.

Description:
PRIORITY CLAIM 
       [0001]    The present application claims priority to U.S. Provisional Application Ser. No. 61/350,691 filed on Jun. 2, 2010 and entitled “Bone Plate,” the entire disclosure of which is incorporated herein by reference. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention generally relates to a bone plate which can be fixed to a bone by means of bone screws. More particularly, the present invention relates to a bone plate having a through hole with an internal thread to threadably receive a locking bone screw. 
       BACKGROUND OF THE INVENTION 
       [0003]    Bone plates with through holes comprising a cylindrical or conical interior thread to receive a locking head bone screw are commonly used in the field of osteosynthesis. Due to the threaded connection between the head of the bone screw and the through hole in the bone plate the bone screw is firmly anchored in the through hole in the bone plate. However, one problem that can arise is that if the bone screw is not exactly coaxially inserted with respect to the through hole axis the thread of the through hole can be damaged. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention relates to a bone plate being able to receive at least a central bone screw in such a way that the thread in the through hole in the bone plate is not damaged when a bone screw is inserted. 
         [0005]    According to the present invention, described is a bone plate with a proximal surface, a bone-oriented distal surface and a through hole the wall of which has three or more straight or convex sections provided with projections such as thread or thread-like structures for receiving a screw head of a bone screw. 
         [0006]    One of the advantages of the bone plate according to the present invention include a compact entry for setting at choice bone screws under a variable angle is provided in such a way that the thread in the through hole in the bone plate is not damaged when a bone screw is not coaxially inserted with respect to the longitudinal axis of the through hole. Furthermore, due to the configuration of a through hole with three or more straight or convex sections, a bone screw inserted through the through hole may be angled relative to a longitudinal axis of the through hole with a reduction of damage to the threads of the through hole. 
         [0007]    In an exemplary embodiment of the bone plate, the through hole has a cross-sectional area orthogonal to the longitudinal axis with a center of the cross-sectional area being centered on the longitudinal axis and wherein each of the three or more straight or convex sections is limited by two radii intersecting each other in the center and enclosing an angle Ω which is smaller than or equal to 360°/n (where n is the number of straight or convex sections), as will be described in greater detail below. 
         [0008]    In a further exemplary embodiment of the bone plate, the through hole has a cross-sectional area orthogonal to the longitudinal axis which is generally polygonal, preferably with rounded corners. 
         [0009]    In a further embodiment of the bone plate, the through hole tapers in a direction towards a distal surface of the bone plate. 
         [0010]    In again a further embodiment of the bone plate, the three or more straight or convex sections are radially symmetric. 
         [0011]    In another embodiment of the bone plate, a thread or thread-like structure extends over the whole length of the three or more straight or convex sections. 
         [0012]    In another embodiment of the bone plate, the thread or thread-like structure has a constant depth of thread within the straight or convex sections. 
         [0013]    In yet another embodiment of the bone plate the depth of thread of the thread or thread-like structure decreases towards each end of each of the straight or convex sections. 
         [0014]    In still another embodiment of the bone plate the depth of thread of the thread or thread-like structure decreases outside each end of each of the straight or convex sections. 
         [0015]    In again another embodiment of the bone plate, the thread or thread-like structure extends over the whole periphery of the through hole. 
         [0016]    In a further embodiment of the bone plate according to the present invention, the bone plate comprises two or more peripheral holes connected to and open to a through hole. The peripheral holes include a thread for receiving peripheral bone screws therein. The two or more peripheral holes are arranged peripherally around the through hole in such a way that they overlap with the through hole to form a composite hole structure able to receive two or more peripheral bone screws therein while a central bone screw is received in the through hole. 
         [0017]    In a further embodiment of the bone plate each of the peripheral holes comprises a spherical recess penetrating partially into the bone plate from a proximal surface thereof. The advantage of this configuration is that a conventional cortex screw with an unthreaded spherical head may be introduced into such a peripheral hole at an angle relative to the longitudinal axis selected by the user. 
         [0018]    In a further embodiment of the bone plate according to the invention, each of the peripheral holes and the through hole includes a thread for locking the screw received therein at a fixed angle. 
         [0019]    In another embodiment of the bone plate, the peripheral holes include threading for receiving peripheral bone screws at user selected variable angles relative to the longitudinal axes of these peripheral holes while the through hole is configured to receive a central bone screw at a fixed angle. 
         [0020]    In a further embodiment of the bone plate, the threads of the holes extend over at least half of a circumference of each of the holes. 
         [0021]    In still a further embodiment of the bone plate, a number, N, of holes are arranged at the corners of a central through hole being generally polygonal with N corners. The polygon defined by the hole axes of the N holes, when viewed in a cross-section orthogonal to the longitudinal axis of the through hole, can be a triangle, square, pentagon or hexagon. 
         [0022]    In another embodiment of the bone plate the fixed angle of insertion of bone screws through the peripheral holes is in the range of ±0° to ±20°, preferably of ±8° to ±15° with respect to the longitudinal axis. 
         [0023]    In yet another embodiment of the bone plate the pitch of the threads is in the range of 0.30 to 2.00 mm, preferably in the range of 0.5 to 1.0 mm. 
         [0024]    In again another embodiment of the bone plate the threads are multiple threads. This allows the advantage that the pitch matches the bone thread pitch. 
         [0025]    In still another embodiment of the bone plate the centers of two adjacent holes are at a distance of 4 to 15 mm from each other. 
         [0026]    In a further embodiment of the bone plate the diameter of the holes is in the range of 3 to 10 mm. 
         [0027]    In again a further embodiment of the bone plate, an inscribed circle to the wall of the central through hole has a diameter of 2 to 10 mm, preferably of 3 to 7 mm. 
         [0028]    In another embodiment according to the present invention, the bone plate comprises at least one peripheral bone screw wherein the plate is made of stainless steel and the at last one peripheral bone screw is made of a CoCr alloy or vice versa. Thus, the advantage can be achieved that since the threads are less damaged by the plate according to the invention there is also less corrosion between plate and screws. 
         [0029]    In again another embodiment of the bone plate a hole axis of the at least one hole is not parallel to the longitudinal axis of the though hole and preferably angled relative thereto at an angle of ±5° to ±20°. 
         [0030]    In again another embodiment the bone plate comprises more than one through hole. 
         [0031]    In again another embodiment of the bone plate, the wall of the through hole has n=3 straight or convex sections. 
         [0032]    In a further embodiment a bone plate is provided with a proximal surface, a bone-oriented distal surface and a through hole with a longitudinal axis connecting the proximal and distal surfaces, wherein the wall of the through hole has n≧3 non-concave sections provided with a thread or thread-like structures for receiving a screw head of a bone screw. 
         [0033]    According to a further object of the invention a kit for bone fixation is provided comprising a bone plate according to the invention, a central bone screw and N peripheral bone screws. 
         [0034]    In a special embodiment of the kit, the central bone screw comprises a screw head with an external thread matching the thread or thread-like structure in the through hole of the bone plate and the N peripheral bone screws comprise a screw head each with an external thread matching the thread in the N≧2 holes. 
         [0035]    In another embodiment of the kit, the screw head of the central bone screw is conically or spherically shaped and the screw heads of the peripheral bone screws are conically or spherically shaped. 
         [0036]    In again another embodiment the kit comprises more than one central bone screws with differently shaped screw heads and a number of 2×N peripheral bone screws with differently shaped screw heads. This configuration allows the advantage that the surgeon can select between:
       a central bone screw with a conically shaped threaded screw head that is placed at fixed angle relative to the bone plate;   a central bone screw with a spherically shaped threaded screw head that can be placed at a variable angle relative to the bone plate;   N peripheral bone screws with a conically shaped threaded screw head that are placed at a fixed angle relative to the bone plate; or   N peripheral bone screws with a spherically shaped threaded screw head that are placed at a variable angle relative to the bone plate.       
 
         [0041]    In a further embodiment the kit comprises a bone plate, a central bone screw with a screw head that is conically or spherically shaped and comprises an external thread and N conventional cortex screws as peripheral bone screws. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0042]    Several exemplary embodiments of the invention will be described in the following by way of example and with reference to the accompanying drawings in which: 
           [0043]      FIG. 1  illustrates a perspective view of an exemplary embodiment of the bone plate according to the present invention; 
           [0044]      FIG. 2  illustrates the bone plate according to  FIG. 1  with an inserted central bone screw; 
           [0045]      FIG. 3  illustrates a lateral view of the bone plate according to  FIG. 2 ; 
           [0046]      FIG. 4  illustrates a cross section through the bone plate according to  FIG. 2 ; 
           [0047]      FIG. 5  illustrates perspective view onto the top of the bone plate according to  FIG. 1  with inserted peripheral screws; 
           [0048]      FIG. 6  illustrates perspective view onto the bottom of the bone plate according to  FIG. 1  with inserted peripheral screws; 
           [0049]      FIG. 7  illustrates a cross section through the bone plate according to  FIG. 5 ; 
           [0050]      FIG. 8  illustrates a lateral view of the bone plate according to  FIG. 5 ; 
           [0051]      FIG. 9  illustrates a perspective view of another exemplary embodiment of the bone plate according to the present invention; 
           [0052]      FIG. 10  illustrates a cross section through the bone plate according to the embodiment of  FIG. 9 ; 
           [0053]      FIG. 11  illustrates a lateral view of the bone plate according to the embodiment of  FIG. 9 ; 
           [0054]      FIG. 12  illustrates a top view onto a further embodiment of the bone plate according to the invention; 
           [0055]      FIG. 13  illustrates a magnified perspective view of detail A in  FIG. 12 ; 
           [0056]      FIG. 14  illustrates a schematic top view of detail A in  FIG. 12 ; 
           [0057]      FIG. 15  illustrates a schematic top view onto a further exemplary embodiment of the through hole in the bone plate according to the present invention; 
           [0058]      FIG. 16  illustrates a schematic top view onto another exemplary embodiment of the through hole in the bone plate according to the present invention; 
           [0059]      FIG. 17  illustrates a schematic top view onto again another embodiment of the through hole in the bone plate according to the present invention; and 
           [0060]      FIG. 18  illustrates a cross-section along line A-A in  FIG. 17 . 
       
    
    
     DETAILED DESCRIPTION 
       [0061]    The present invention is directed to a system for the fixation of fractured or otherwise damaged bones via one or both of a variable angle insertion and a fixed angle insertion of a bone screw through a bone plate hole. Specifically, a bone plate according to the present invention is provided with a central through hole configured to receive a first bone screw therethrough at any user selected angle relative to a longitudinal axis of the through hole within a permitted range of angulation. A plurality of second bone screws may also be inserted through outlying portions of the bone plate hole, each defining a separate plate hole axis. The outlying portions of the bone plate hole are formed as substantially circular peripheral holes configured to overlap and be open to the through hole to form a composite hole having any of a plurality of shapes depending on the placement and number of the peripheral holes relative to the through hole, as will be discussed in greater detail with respect to particular embodiments. The peripheral holes may be configured with holes axes selected so that the second bone screws may only be inserted therethrough at predetermined angles relative to a surface of the bone plate. It is noted that although the peripheral holes and through holes are depicted with predetermined angles in the system of the present invention, these bone plate holes may extend through the bone plate at any angle without deviating from the spirit and scope of the present invention and may be selected to conform to the requirement of a particular procedure. 
         [0062]      FIGS. 1 to 8  illustrate a first exemplary embodiment of the invention comprising a bone plate  1  including one through hole  9  and three partially cylindrical peripheral holes  2  arranged peripherally around the through hole  9  in such a way that they overlap with the through hole  9  and are open thereto, as will be described in greater detail below. It is noted that although the through hole  9  is depicted with a triangular cross-sectional shape, any other cross-sectional shape may be employed without deviating from the spirit and scope of the present invention. The bone plate  1  comprises a proximal surface  7  and a bone-oriented distal surface  8 . The through hole  9  has a longitudinal axis  6  connecting the proximal and distal surfaces  7 ,  8 , the longitudinal axis  6  extending orthogonally to the proximal surface  7 . The through hole  9  is at least partially bordered by a wall  10  including three convex sections  15  provided with projections such as a thread  5  or thread-like structures for receiving a central bone screw  30  under a variable angle. As will be described in greater detail later, each of the three convex sections  15  of  FIG. 1  is curved with a predetermined radius of curvature. In an alternate embodiment (not shown), any number and combination of the convex sections  15  may be formed with a first radius of curvature while the remainder of the convex sections  15  may be formed with a second radius of curvature. 
         [0063]    Each of the peripheral holes  2  each has a hole axis  11  extending between the proximal and distal surfaces  7 ,  8  and are provided with a thread  4  for receiving peripheral bone screws  20 , as shown in  FIGS. 6-8 . The peripheral holes  2  are arranged peripherally around the through hole  9  at equal angles relative to each other. In the embodiment shown where three peripheral holes  2  are employed, the axes  11  of the peripheral holes  2 , when viewed in a cross-section orthogonal to the longitudinal axis  6  of the through hole  9 , define an equilateral triangle. Furthermore, the three peripheral holes  2  overlap the through hole  9  in such a way that the peripheral holes  2  and through hole  9  form a composite hole structure suitable to receive  3  peripheral bone screws  20 , as shown in  FIGS. 5 to 8  and/or one central bone screw  30 , as shown in  FIGS. 2 to 4 . As shown in  FIG. 5 , the peripheral holes  2  each also comprise a thread  4 , which, in one embodiment of the present invention, may be a multiple thread. 
         [0064]    When viewed in a cross-section orthogonal to the longitudinal axis  6  of the through hole  9 , each of the convex sections  15  is centrally positioned along a respective corner of an equilateral triangle. Each convex section  15  is convexly curved in a direction from the proximal surface  7  to the distal surface  9  so that an apex of each of the convex sections  15  is located radially outside the through hole  9 . A bone screw  30  can be inserted into the through hole  9  under a surgeon selected angle so that a screw axis  33  of the bone screw  30  is offset by an angle a relative to the longitudinal axis  6  of the through hole  9 . The through hole  9  of the present invention may be con figured so that the bone screw  30  insertable therethrough is smaller, larger or the same size as the bone screws  20  insertable through the peripheral holes  2 . 
         [0065]    The composite hole structure therefore includes three radially symmetrically arranged convex sections  15  centrally located on the sides of an equilateral triangle and three peripheral holes  2  in the corners of the equilateral triangle. The axes  11  of the peripheral holes  2  are arranged at a distance from the longitudinal axis  6  which is dimensioned in such a way that the peripheral holes  2  overlap the through hole  9  and extend over an angle of more than 180° between their transitions to the through hole  9 . The wall  10  of the through hole  9  comprises n=3 wall portions with each wall portion being limited by a transition to the periphery of a first peripheral hole  2  at one of its ends and by a transition to the periphery of a second peripheral hole  2  at its other end. In the present embodiment each convex section  15  does not extend over the whole length of the wall portion limited by the transitions. The thread  5  or thread-like structure extends over the whole length of the three convex sections  15  with a constant depth of thread. The depth of thread of the thread  5  or thread-like structure decreases between each end of the convex section  15  and each of the two transitions to one of the peripheral holes  2 . 
         [0066]    As illustrated in  FIGS. 2 to 4  the through hole  9  tapers radially inward toward the distal surface  8  of the bone plate  1 . A central bone screw  30  with a screw axis  33  and a screw head  31  is inserted in the through hole  9 . The screw head  31  is spherically shaped and comprises an external thread  32  so that the central bone screw  30  can be inserted into the through hole at a user-selected angle α between the screw axis  33  and the longitudinal axis  6  of the through hole  9 . 
         [0067]    Instead of a central bone screw  30  comprising a spherically shaped screw head  31  with an external thread  32  a central bone screw comprising a conically shaped screw head with an external thread could be inserted into the through hole  9 . In the latter case the central bone screw would be inserted into the through hole  9  at a fixed angle (e.g., with the screw axis and the longitudinal axis  6  of the through hole  9  coinciding). 
         [0068]    As shown in  FIGS. 7 and 8 , the peripheral holes  2  are configured so that each of the hole axes  11  is angled at approximately 20° relative to the longitudinal axis  6  of the through hole  9 . In another embodiment of the present invention, the peripheral holes  2  may be angled at any other angle relative to the longitudinal axis  6  and may optionally also each extend along different angles, as those skilled in the art will understand. 
         [0069]    As illustrated in  FIG. 7  each of the peripheral holes  2  tapers radially inward towards the distal surface  8  of the bone plate  1 . A peripheral bone screw  20  with a screw axis  23  and a screw head  21  is inserted into each of the peripheral holes  2 . The screw head  21  is conically shaped and comprises an external thread  22  so each peripheral bone screw  20  can be inserted into one of the peripheral holes  2  at a fixed angle with the screw axis  23  and the hole axis  11  of the peripheral hole  2  coinciding. 
         [0070]    Instead of peripheral bone screws  20  comprising conically shaped screw heads  21  with an external thread  22 , peripheral bone screws comprising spherically shaped screw heads with an external thread may be inserted into the peripheral holes  2 . In the latter case the peripheral bone screws may be inserted at a user selected variable angle between the screw axis  23  and the hole axis  11  of the peripheral hole  2 . 
         [0071]    In  FIGS. 9 to 11  another embodiment is illustrated which differs from the embodiment of  FIGS. 1 to 8  only in that the generally polygonal through hole  9  comprises rounded corners instead of the N=3 peripheral holes  2  arranged in the corners. Similarly to the embodiment of  FIGS. 1 to 8 , the wall  10  of the through hole  9  comprises n=3 convex sections  15  which in a cross-section orthogonal to the longitudinal axis  6  are centrally located on the sides of an equilateral triangle. Each of the convex sections  15  is convexly curved in a cross-section orthogonal to the longitudinal axis  6  of the through hole  9  with the apex of each convex section  15  located on a middle line orthogonal to one side of the equilateral triangle. Due to the convex sections  15 , a bone screw  30  may be inserted into the through hole  9  under a surgeon selected angle relative to the axis  6 . 
         [0072]    The through hole  9  includes three radially symmetrically arranged convex sections  15  centrally located on the sides of an equilateral triangle and three concavely rounded sections in the corners of the equilateral triangle. The wall  10  of the through hole  9  therefore comprises n=3 wall portions whereof each wall portion extends along one side of an equilateral triangle and is limited by a transition to a first concavely rounded section at one of its ends and by a transition to a second concavely rounded section at its other end. In the present embodiment each convex section  15  extends over the whole length of the wall portion limited by the transitions. The thread  5  or thread-like structure extends over the whole periphery of the through hole  9 . The depth of thread of the thread  5  or thread-like structure can decrease in the concavely rounded sections. 
         [0073]    As illustrated in  FIG. 10  the through hole  9  tapers towards the distal surface  8  of the bone plate  1 . A central bone screw  30  with a screw axis  33  and a screw head  31  is inserted in the through hole  9 . The screw head  31  is spherically shaped and comprises an external thread  32  so that the central bone screw  30  can be inserted into the through hole at a user-selected variable angle α between the screw axis  33  and the longitudinal axis  6  of the through hole  9 . 
         [0074]    In  FIGS. 12 to 14  another embodiment of the bone plate  1  is illustrated which comprises two through holes  9 . Similarly to the embodiment of  FIGS. 9 to 11 , the through hole  9  has cross-sectional area orthogonal to the longitudinal axis  6  with a center  14  located on the longitudinal axis  6  with each of the n=3 convex sections  15  being limited by two radii intersecting each other in the center  14  and enclosing an angle Ω which is smaller than 120°. The wall  10  of each of the two through holes  9  comprises n=3 wall portions with each wall portion extending along one side of an equilateral triangle and limited by a transition to a first concavely rounded section at one of its ends and by a transition to a second concavely rounded section at its other end. Similarly to the embodiment of  FIGS. 9 to 11 , each convex section  15  extends over the whole length of the wall portion limited by the transitions. The through holes  9  differ from the through hole  9  of the embodiment of  FIGS. 9 to 11  only in that the thread  5  or thread-like structure does not extend over the whole periphery of the through hole  9 . The depth of thread of the thread  5  or thread-like structure decreases on each end of the convex section  15  at the transition between the convex section  15  and the concavely rounded section in such a way that a portion of the concavely rounded sections is unthreaded. 
         [0075]    As illustrated in  FIG. 13  the through hole  9  tapers radially inward toward the distal surface  8  of the bone plate  1 . Similarly to the embodiment of  FIGS. 9 to 11 , a central bone screw  30  with a screw axis  33  and a screw head  31  can be inserted in the through hole  9 . By using a central bone screw  30  the screw head  31  of which is spherically shaped with an external thread  32 , the central bone screw  30  may be inserted into the through hole  9  at a user-selected, variable angle α of the screw axis  33  to the longitudinal axis  6  of the through hole  9 . 
         [0076]      FIG. 15  illustrates a further embodiment of the through hole  9  which differs from the embodiment of  FIGS. 12 to 14  only in that it comprises n=4 convex sections  15 . Each of the n=4 convex sections  15  is limited by two radii intersecting each other in the center  14  and enclosing an angle Ω which smaller than 90° . The wall  10  of each of the two through holes  9  comprises n=4 wall portions with each wall portion extending along one side of a square and limited by a transition to a first concavely rounded section at one of its ends and by a transition to a second concavely rounded section at its other end. Similarly to the embodiment of  FIGS. 9 to 11 , each convex section  15  extends over the whole length of the wall portion limited by the transitions. The thread  5  or thread-like structure does not extend over the whole periphery of the through hole  9 . The depth of thread of the thread  5  or thread-like structure decreases on each end of the convex section  15  at the transition between the convex section  15  and the concavely rounded section in such a way that a portion of the concavely rounded sections is unthreaded. 
         [0077]      FIG. 16  illustrates again a further embodiment of the through hole  9  which differs from the embodiment of  FIG. 15  only in that the wall  10  of the through hole  9  comprises n=4 straight sections  15  and that the depth of thread of the thread  5  or thread-like structure decreases from a middle line orthogonal to one side of the square towards the transition between the straight section  15  and each of the concavely rounded sections in such a way that the concavely rounded sections are unthreaded. 
         [0078]      FIGS. 17 and 18  illustrate again a further embodiment of the through hole  9  which differs from the embodiment of  FIG. 14  only in that the N=3 peripheral holes  2  are configured to receive conventional cortex screws. Each peripheral hole  2  comprises a spherical recess  25  penetrating partially into the bone plate  1  from the proximal surface  7  and axially adjacent to a conically enlarging lower section  26  extending between the spherical recess  25  and the distal surface  8  of the bone plate  1 . Due to the spherical recess  25 , a conventional cortex screw with a spherical head may be inserted into each of the peripheral holes  2  at a user-selected angle with respect to the axis  11  of the peripheral hole  2 . The n=3 straight or convex sections  15  of the wall  10  of the through hole  9  are configured similarly to the embodiment of  FIG. 14 . 
         [0079]    Although the invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, composition of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. 
         [0080]    It will be appreciated by those skilled in the art that various modifications and alterations of the invention can be made without departing from the broad scope of the appended claims. Some of these have been discussed above and others will be apparent to those skilled in the art.