Axial alignment of a drill guide

摘要

The drill guide 16 for drill 28 is to be aligned with a transverse hole 26 in a femoral nail 21 located within a bone 12 so that when drilling holes in the bone the drill will pass cleanly through the hole 26. A coil 36 mounted within the nail 21 generates an alternating magnetic field along the axis of the hole 26. Two sensor discs 46 & 47 are axially spaced along the guide 16 and each carries four angularly spaced sensing coils 51-54 and 61-64 to determine when the centre of the disc 46 or 47 is in alignment with the axial magnetic field. Display units 81 and 82 show by means of LEDs 86-89 and 94-97 when there is any deviation from the required alignment, allowing the guide tube 41 to be correctly aligned for drilling.