Drill guide with angle verification

Abstract

A method and instrument is used for inserting a bone screw into 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 maximum angulation is that which 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. The space is less 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 of the bone plate adjacent the counterbore. A hole is drilled in the bone through a guide bore in the instrument.

1 . An instrument for determining the position of a bone screw head with respect to a bone plate outer surface, the surface surrounding a screw hole in the plate, the instrument comprising:
 a shaft having a guide bore at a leading end, the leading end including a gauge element spaced from an end surface of the shaft, the gauge element 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 a countersunk screw head seating surface surrounding the screw hole.   
     
     
         2 . The instrument as set forth in  claim 1  wherein the leading end of the shaft has a part-spherical portion for engaging a part-spherical countersunk surface on the bone plate. 
     
     
         3 . The instrument as set forth in  claim 2  wherein the gauge element is a mark extending around an outer circumference of the leading end of the shaft. 
     
     
         4 . The instrument as set forth in  claim 3  wherein the gauge element is a circular ring located intermediate the part-spherical portion and a cylindrical portion of the leading shaft end 
     
     
         5 . The instrument as set forth in  claim 3  wherein the shaft leading end has a central bore therethrough for guiding a drill. 
     
     
         6 . The instrument as set forth in  claim 5  wherein the bore has a central axis extending perpendicular to a plane containing the circumferential mark. 
     
     
         7 . A method 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, comprising:
 placing a bone plate having at least one screw hole surrounded by a counterbore on an outwardly facing surface of the bone plate on a bone surface;   inserting an instrument having a distal end including a gauge element, the gauge element spaced proximally from an end surface of the distal end into the counterbore surrounding the plate hole, the spacing less than or equal to a distance from the counterbore surface to the outwardly facing surface of the bone plate;   tilting the inserted instrument 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;   drilling a hole in the bone through a guide bore in the instrument;   removing the instrument from the bone plate; and   inserting a bone screw into the bone plate screw hole.   
     
     
         8 . The method as set forth in  claim 7  wherein the gauge element is a circular ring mounted on the instrument. 
     
     
         9 . The method as set forth in  claim 8  further comprising tilting the instrument to a maximum angle that maintains the circular ring at or below the outwardly facing surface of the bone plate surrounding the counterbore. 
     
     
         10 . The method as set forth in  claim 9  wherein the maximum angle of instrument tilt is 10°. 
     
     
         11 . The method as set forth in  claim 8  wherein the instrument is tilted by manipulating a handle attached to the distal end of the instrument. 
     
     
         12 . The method as set forth in  claim 7  wherein the distal end of the instrument is part-spherical in shape. 
     
     
         13 . The method as set forth in  claim 12  wherein the gauge element is a ring extending around the circumference of the distal end of the instrument. 
     
     
         14 . The method as set forth in  claim 13  wherein the bore in the distal end extends perpendicular to a plane containing the gauge element. 
     
     
         15 . The instrument as set forth in  claim 13  wherein the ring has a diameter greater than a diameter of the distal end of the instrument. 
     
     
         16 . The method as set forth in  claim 13  further comprising contacting the counterbore in the plate with the ring to provide a tactile indication of the angle of the guide bore with respect to the central axis of the bone plate hole. 
     
     
         17 . The instrument as set forth in  claim 1  wherein the gauge element includes a protrusion for contacting the plate and providing a tactile indication of the angle of the guide bore with respect to a central axis of the screw hole.