Abstract: A system that enables axis-to-axis targeting of an instrument placed within a drill bushing includes a computer, a probe, and a pair of sensor planes mounted to a drill bushing so the planes are perpendicular to one another. The probe has two drive coils that may be mounted near its distal end. The two coils are placed close to one another and are oriented so that when they are selectively coupled to an alternating current source they generate magnetic fields that are orthogonal to one another. The computer receives electrical signals from the sensors in the sensor planes and computes target position, bushing alignment, and bushing orientation values. These values may be presented on a display associated with the computer or used to illuminate directional arrows associated with the drill bushing.

Abstract: The instrumentation is used by orthopaedic surgeons for accurate and rapid placement of distal locking screws in intramedullary nails. A probe inserted into the intramedullary nail positions two electromagnetic drive coils with their magnetic axes parallel to and at a fixed offset from the axis of a transverse hole to be drilled. The drive coils generate alternating magnetic fields over intermittent and non-overlapping time intervals in a manner that provides independent sources of positional information. A hand-held guide, containing a drill bushing and four receiving coils with the same offset as the drive coils, when moved about in the vicinity of the probe, produces a corresponding movement of graphical images on a display screen. The graphical images provide intuitive information as to how the guide must be moved to accurately align the drill bushing with the axis of the transverse hole.