Abstract:
A method and instrument is used for inserting a bone screw through a hole in a bone plate into bone at a maximum angulation of a bone screw central longitudinal axis with respect to a central axis of the hole. The maximum angulation places the head of the bone screw at or below an outwardly facing surface of the bone plate. The instrument has a distal end including a gauge element spaced proximally from an end surface of the distal end when in contact with a counterbore surrounding the plate hole a distance less than a depth of the counterbore. The instrument is tilted with respect to a central axis of the bone plate hole to an angle wherein the gauge element remains at or below the outwardly facing surface of the bone plate adjacent the counterbore. A hole is drilled through a guide bore in the instrument.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The present application is a divisional of U.S. patent application Ser. No. 12/317,703, filed on Dec. 23, 2008, the disclosure of which is incorporated herein by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The invention relates to an angle guide for orienting a bone screw in a bone plate. More particularly, the invention relates to an instrument for insuring the position of the head of a bone screw located within a bone plate hole. 
         [0003]    It is often necessary when utilizing bone plates either for fracture fixation or such as tibial base plates to couple the bone plates to bone via a screw extending through a hole in the plate. When the screw is angled, surgeons have had to eye the correct angle specified by the device manufacturer indicated by the surgical situation. If the bone screw is put in at too great an angle the bone screw head would sit proud of the bone plate which in some situations is undesirable. The surgeon would then either continue to torque the bone screw until the bone screw&#39;s cutting flutes soften the bone in the area and allowed it to sit properly or the bone screw would be backed out and the surgeon would attempt to reinsert the bone screw at a shallower angle. 
         [0004]    The surgeon often had difficulty eyeing the correct angle especially where there was a plurality of bone screws to be inserted, since the correct angle is relatively small i.e. zero to ten degrees. Normally, the surgeon drills a pilot hole in the bone prior to inserting the bone screw and it has been difficult to drill the pilot hole at the correct angle so that the bone screw would seat properly. For example, when using a tibial base plate, it is typical to utilize a polyethylene bearing surface snapped onto the base plate which has been implanted on a prepared tibia. Consequently, if the pilot hole and subsequent bone screw are inserted at an incorrect angle the head of the bone screw could impinge on the distal surface of the polyethylene bearing implant which is undesirable. Such an impingement could lead to metal or polyethylene debris which has been known to cause osteolysis. 
         [0005]    If the surgeon saw that the bone screw did not seat properly or was not at the specified depth, he could continue to torque the bone screw. However, since most bone screws include cutting flutes at the leading ends thereof continued rotation of the cutting flutes causes the bone to degrade and allows more play in the screws positioning. While this may allow the bone screw to seat properly, it reduces the compressive forces holding the plate to the bone by decreasing the holding ability of the screw. 
         [0006]    Alternately, if the surgeon noticed the bone screw did not seat properly or is not at the correct depth, he might reverse the screw and drill a new pilot hole at a slightly different angle. This method may not always be successfully since the drill and screw will have a tendency to follow the original drilled hole. Even if the surgeon is capable of resetting the new desired angle, there is still damage to the bone in the originally drilled area which may cause fracture propagation. Consequently, there has been a long felt need to provide an instrument which can indicate the angle which is not to be exceeded for proper positioning of the bone screw in the bone plate. This instrument will verify that the final implant positioning is accurate and allows the head of the bone screw to be properly located. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    The instrument of the present invention is a drill guide for use in orthopedic surgery. It is intended to specify the maximum angle of a pilot hole drilled in bone when using bone screws for fixation of an orthopedic implant such as a bone plate. The instrument consists of several main features which include a handle which allows a surgeon to maneuver the instrument. A mating feature allows the device to interface with a corresponding implant, such as a bone plate, especially in an area surrounding a hole therein for accommodating a bone screw. This feature may be a part-spherical convex surface for rotating on a similar part-spherical concave surface surrounding the screw hole. A body having an appropriately sized through hole for guiding a drill and includes a circumferential visual reference delineating the amount of angulation a surgeon can put into a pilot hole drilled for receiving the bone screw. 
         [0008]    The visual reference may be a reduction in diameter, a protrusion, an etched line or a laser marked line. Also color and surface finish could be used as visual indicators. Additionally, two or three visual references could be used indicating different angle markings i.e. 5°, 10° or 15°. Thus two or three lines could be used at different levels with the lower line corresponding to the greater angle. The visual reference may be observed by the surgeon and indicates to him that the pilot hole angle he or she is about to drill through the device is compatible with the orthopedic implant, such as a bone plate, and the bone screw securing it. The instrument allows the proper pilot hole angle to be drilled through the device and the implant and allows a bone screw to have the proper angulation and therefore seat properly within the recess hole in the device so that the bone screw head sits correctly in reference to the plate, or in the case of a tibial baseplate below the surface of the plate. 
         [0009]    An instrument is provided for determining the position of a bone screw head with respect to a bone plate outer surface having a concave surface surrounding a screw hole in the plate. The instrument has a shaft having a leading end with a convex surface including a gauge element spaced from the end of the concave surface of the shaft. The gauge element is spaced a distance from the end surface of the shaft equal to or less than a distance from an outwardly facing surface of the bone plate, opposite a bone contacting surface, to the countersunk screw head seating surface surrounding the hole. Preferably the leading end of the shaft has a convex part-spherical portion for engaging a concave part-spherical countersunk surface on the bone plate. The gauge element is a mark extending around an outer circumference of the leading end of the shaft. The gauge element preferably is a circular line or indentation located intermediate the part-spherical portion and a cylindrical portion of the leading shaft end. The shaft leading end has a central bore therethrough for guiding a drill. The bore preferably has a central axis extending perpendicular to a plane containing the circumferential mark. 
         [0010]    A method is taught for inserting a bone screw through a hole in a bone plate and into bone at a maximum angulation of a bone screw central longitudinal axis with respect to a central axis of the hole. The method includes placing a bone plate having at least one screw hole surrounded by a concave counterbore on an outwardly facing surface of the bone plate on a bone surface. Thereafter inserting the instrument having a distal end including the gauge element into the counterbore. The gauge element is spaced proximally from an end surface of the distal end. In one embodiment, the spacing is less than or equal to a distance from the counterbore surface to the outwardly facing surface of the bone plate. Alternatively, the gauge element can be greater than or equal to a distance from the counterbore surface to the outwardly facing surface of the bone plate. The instrument is tilted with respect to a central axis of the bone plate hole to an angle wherein the gauge element remains at or below the outwardly facing surface in the first scenario and at or above the bone plate in the second scenario. Then the hole is drilled in the bone through a guide bore in the instrument. The instrument is removed from the bone plate and the bone screw is inserted into the bone plate screw hole. The gauge element may be a circular ring mounted on the instrument on a circular line around the instrument. The tilting of the instrument is up to a maximum angle that maintains the circular ring or line at or below the outwardly facing surface of the bone plate surrounding the counterbore. Design intent guides the location of the gauge element from the distal end of the instrument which determines the corresponding maximum angle intended by the designer. An angled handle attached to the distal end of the instrument is used to tilt the distal end of the instrument. The distal end of the instrument is preferably part-spherical in shape matching the shape of the counterbore. The bore in the distal end extends perpendicular to a plane containing the gauge element. 
         [0011]    As used herein when referring to bones or other parts of the body, the term “proximal” means close to the heart and the term “distal” means more distant from the heart. The term “inferior” means toward the feet and the term “superior” means toward the head. The term “anterior” means toward the front part or the face and the term “posterior” means toward the back of the body. The term “medial” means toward the midline of the body and the term “lateral” means away from the midline of the body. When referring to the instrument, distal means further from the user. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    A more accurate appreciation of the subject matter of the present invention and the various advantages thereof can be realized by reference to the following detailed descriptions which makes reference to the accompanying drawings in which similar reference numerals relate to similar elements throughout several views: 
           [0013]      FIG. 1  is an isometric view of the instrument of the present invention from the side; 
           [0014]      FIG. 2  is an isometric view of the instrument of the present invention from above with respect to  FIG. 1 : 
           [0015]      FIG. 3  is a side elevation view of the leading end of the instrument of  FIG. 1 ; 
           [0016]      FIG. 4  is a top view of the tip of  FIG. 3 ; 
           [0017]      FIG. 5  is a bottom view of the instrument of  FIG. 3 ; 
           [0018]      FIG. 6  is a cross-sectional view of the instrument of the present invention along lines  6 - 6  of  FIG. 4 ; 
           [0019]      FIG. 7  is a cross-sectional view of the handle of the present invention separate from the bone plate engaging drill guide of  FIG. 6 ; 
           [0020]      FIG. 8  shows the instrument of the present invention engaged in a tibial base plate mounted on a tibia; 
           [0021]      FIG. 9  shows the instrument of the present invention angled at a desired angle prior to inserting a drill for drilling a pilot hole; 
           [0022]      FIG. 10  is a cross-sectional view of an alternate embodiment of the present invention; 
           [0023]      FIG. 11  is a cross-sectional view of yet another embodiment of the present invention; 
           [0024]      FIG. 12  is a cross-sectional view of a further embodiment of the present invention; 
           [0025]      FIG. 13  is a cross-sectional view of an additional embodiment of the present invention; and 
           [0026]      FIG. 14  is a cross-sectional view of yet another embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0027]    Referring to  FIG. 1 , there is shown an isometric view of the instrument of the present invention generally denoted as  10 . Instrument  10  includes a handle portion  12  and a leading or distal end  14  which includes a drill guide element  16  as can be seen in  FIGS. 2 ,  4  and  5 . Drill guide element  16  includes a guide bore  18 . Guide bore  18  is adapted to receive a drill bit  20  such as shown in  FIG. 9 . 
         [0028]    Referring to  FIG. 3 , the drill guide element  16  has a leading end  22  which, in the preferred embodiment is cylindrical and includes a part-spherical convex contact surface  24  for engaging a part-spherical concave surface  28  surrounding a plate bore as shown in  FIGS. 8 and 9 . In the preferred embodiment, the element  16  includes a marking ring or line  30  which can be etched or laser marked or even being a groove of a reduced diameter in a predetermined axial location along the axial direction of element  16 . The spacing of marking  30  with regard to end  26  of element  16  is determined by the design of recess  28  surrounding the hole in, for example, a tibial base plate and the size of the head of the bone screw. The location of marking  30  is such as to ensure that the head of the screw, after insertion at a desired angle, is below, above, or at the surface of the plate per the design intent. 
         [0029]    In the preferred embodiment, as shown in  FIGS. 6 and 7 , the handle  12  is preferably made as a separate element which can be either permanently or releasably coupled to drill guide element  16 . For example, drill guide element  16  could have a threaded portion  32  which could engage a threaded portion  34  in a bore  38  of handle  12 . Thus, element  16  could be screwed into the handle prior to use. Obviously, a plurality of elements  16  having different size surfaces  24  could be provided as a kit to engage with a multiplicity of bone plate hole designs of various thicknesses and counterbores. 
         [0030]    Again referring to  FIG. 6 , a stop surface  39  on element  16  sets the distance from a bottom surface  40  of handle  12  can be set to a desired length. Preferably the outer surface of locking element  16  is cylindrical and has a diameter equal to or less than the diameter of the opening or counterbore in the bone plate or other device adjacent its outwardly facing surface. 
         [0031]    Referring to  FIGS. 8 and 9 , there is shown a tibial base plate  40  which includes a pair of bores  42  which, in the preferred embodiment, each are surrounded by a part spherical surface  28  matching the part spherical surface  24  on drill guide element  16 . 
         [0032]    As can be seen in  FIGS. 8 and 9 , pilot holes may be drilled with drill  20  which, in the preferred embodiment, may be a ⅛ inch drill so that pilot holes may be drilled through the tibial base plate screw holes. The pilot holes can be angulated up to ten degrees if a surgeon desires cortical fixation of the screws. The maximum allowable angulation of the screw is indicated by the drill guide. The bottom marking  30  of the drill guide  16  should not be visible when drilling a pilot hole. This ensures that the angulation is no more than ten degrees. If the marking is visible while drilling the pilot hole, as shown in  FIG. 9 , the screw head (not shown) may sit proud of the base plate outer surface  44 . As described above, this could interfere with the polyethylene bearing element that would be received within the tibial base plate  40 . 
         [0033]    Alternately, as will be described below, a protrusion, such as a ring, may protrude outwardly from the distal instrument tip to provide a tactile reference for the surgeon to know that the device is at or past its maximum angle. For example, an embodiment having a hard stop may be provided for limiting the maximum angle but allowing freedom to position the device until that angle is reached. These features can be put on a spherical or non-spherical drill guide that is meant to enter a spherical or non-spherical hole. A spherical drill guide can be matched with a non-spherical hole or visa-versa if desired. 
         [0034]    Referring to  FIG. 10  there is shown a drill guide  204  within a hole in a bone plate  212  having a tactile feature in the form of a protruding ring  200  around the outer surface of the drill guide. The ring  200  is located distally on a shaft  202  of drill guide  204 . Thus, when an axis  206  of the drill guide  204  is coaxial with an axis  208  of a hole  209  having a countersunk bore  210  in plate  212  ring  200  sits below a top surface  214  of bone plate  212  opposite a bone contacting surface  216  thereof. As protruding ring  200  engages the wall of the counter sunk bore  210  it causes a drag as the drill guide element  204  is moved via movement of a handle  218 . This drag is felt by the surgeon and is a tactile indication of the acceptability of the drill guide position. Once the protruding ring  200  engages the wall of the counter sunk bore  210  the surgeon will feel this and know that the drill guide shaft  204  is at its maximum angle. The maximum diameter of protruding ring  200  is sized in conjunction with the countersunk bore  210  dimensions to produce such an effect. 
         [0035]    Referring to  FIG. 11  there is shown an alternate embodiment in which a drill guide  300  has a drill guide element  301  located in a counterbore  304  of a bone plate  302 . Counterbore  304  surrounds a hole  303  in bone plate  302  for receiving a distal end  306  of drill guide  300 . A ring-like protrusion  308  is provided. Protrusion  308  is located on a shaft  310  of drill guide element  301  in a proximal distal location so that when the drill guide is rotated via handle a  312  a bottom surface  314  of ring  308  contacts upper surface  316  of plate  302 . In this design, protrusion  308  exhibits a tactile indication of the maximum angle to the surgeon as well as a hard stop surface. The preferred hard stop style drill guide formed by protrusion  308  is an increased radius or collar around the drill guide. As the drill guide is rotated in the counterbore  304  the protruding ring provides an indication of the maximum angulation the drill guide may take before the screw head protrudes above surface  316 . When the drill guide is rotated by the surgeon to the point where the protrusion  308  contacts upper surface  316  of plate  302  the surgeon will be prevented from any further increase in the angle of the drill guide. In the preferred embodiment a circular protrusion is provided to ensure that the drill guide can be angulated in any direction with respect to the central axis of the hole  303  in plate  302 . 
         [0036]    Referring to  FIG. 12 , there is shown a cross-sectional view of a drill guide  400  located in a hole  401  in plate  402 . In this embodiment plate  402  has a counterbore  404  which has a conical surface  406 . Drill guide  400  includes a drill guide element  407  having leading or distal end  408  on a shaft  410 . Preferably end  408  is conically tapered, however, the leading end  408  can also be part-spherical or, for that matter, any shape which will allow the drill guide to pivot within the counterbore  404  of plate  402 . A groove  412  may be provided to give a visual indication of the maximum angle that a handle  414  may be oriented to allow drilling of the pilot hole. A protrusion as discussed above may also be used. 
         [0037]    Referring to  FIG. 13  there is shown an embodiment similar to the embodiment of  FIGS. 1-9  wherein a drill guide  500  is provided which includes a drill guide element  501  which has a part-spherical tip  502  for receipt in a counterbore  504  of a bone plate  506 . Rather than a groove as shown in  FIG. 6  a shaft  508  of drill guide element  501  includes a marking line or engraved line  507  indicating the maximum angle at which the drill guide  500  can be rotated via handle  510 . When the surgeon sees the proximal edge  512  of the marking aligned with an upper surface  514  of bone plate  506  the surgeon will know that the maximum angulation has been reached. Note one or more additional parallel lines  507  could be added with each line indicating a different angle, for example 5, 10 or 15 degrees. 
         [0038]    Referring to  FIG. 14  there is shown a drill guide  600  which is similar to the aforementioned drill guides but having a part-spherical distal end  602  for engaging a conical counterbore  604  in a plate  606 . This embodiment illustrates the possibility that the geometry of the distal end, for example 602 of drill guide  600  can be different than the shape of a counterbore such as  604 . As long as the distal end of the drill guide can rotate in the counterbore to the point where one of the above-mentioned indicators lines up with the top surface  608  of a bone plate such as  606  then such a combination can be utilized. Obviously other markers may be used which can either be seen or felt by the surgeon to indicate the alignment of the marker with the top surface of the bone plate when in a position of a maximum angulation of the drill guide to place the screw head at or below the surface of the plate. Specifically a two color system could be used with the leading or distal end of the gauge having a highly visible color at or above the line so that the surgeon would need to see all the color above the top plate surface to insure the maximum angle had not been exceeded. Also different surface textures could be utilized instead of different colors. 
         [0039]    Also, should it be acceptable for the screw head to sit above the outwardly facing surface of the bone plate then the gauge element may be located at a distance from the bottom end, of the shaft which contacts the counterbore surface which is greater than the distance from the outer plate surface to the bottom of the counterbore. 
         [0040]    Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. Specifically the drill guide can be used with any plate being attached to a subsurface, such as a metal plate to wood, to insert the head of the screw is at or below the top surface of the plate when the screw is inserted at an angle. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.