New software applications for interchangeable instrumentation in spinal stereotaxis

Computer image-guided surgery has been widely accepted because it allows the surgeon to track an instrument through unvisualized critical structures of a patient in real-time, thus minimizing the risk of injury. Current spinal and cranial image-guided surgery is, however, limited by the lack of surgical instruments and software applications that would allow rapid interchange of useful instruments to perform the procedures. Most image-guided systems utilize a single standard probe or a few pre-defined instruments that are not necessarily useful for performing the actual surgical procedure. Present image-guided technology for screw placement in spinal surgery utilizes the standard probe only to confirm the entry point location and view the planned trajectory of the screw. The surgeon then resumes the procedure using standard surgical instruments to drill, tap and place screws without the benefit of image guidance. Our clinical laboratory experience with spinal image-guided surgery indicates that there is potential for error between each of these procedural steps of screw placement. Despite accurately locating an entry point, any deviation in the trajectory during drilling of a pilot hole, tapping or screw placement may result in significant errors in screw placement and potential neurovascular injury. We have developed custom software applications and universal hardware adaptation devices for spinal image-guided surgery that allow the use of standard instruments for intraoperative guidance. Utilizing universal dynamic registration hardware and software, standard surgical instruments are adapted for real-time image guided surgery. An array of light emitting diodes can be attached to essentially any rigid instrument with a definable tip and then calibrated to the system for intraoperative use. Laboratory tests using a cadaveric model indicate a difference in accuracy of less than 1.0 mm between the standard probe and a dynamically registered custom instrument and an absolute mean error of less than 2.0 mm for the image-guided system which is clinically insignificant in most cases. This technology is a significant step forward as it allows the surgeon to use a full array of instruments with image guidance and will ultimately make spinal and intracranial surgery safer and more accurate.