Robot-assisted distal locking of long bone intramedullary nails: Localization, registration, and in vitro experiments

We are developing an image-guided robot-based system to assist orthopaedic surgeons in performing distal locking of long bone intramedullary nails. The system consists of a bone-mounted miniature robot fitted with a drill guide that provides rigid mechanical guidance for hand-held drilling of the distal screws' pilot holes. The robot is automatically positioned so that the drill guide and nail distal locking axes coincide using a single fronto-parallel fluoroscopic X-ray. This paper describes new methods for accurate and robust drill guide and nail hole localization and registration and reports the results of our in-vitro system accuracy experiments. Tests of 17 runs show a mean angular error of 1.3° (std = 0.4°) between the computed drill guide axes and the actual locking holes axes, and a mean 3.0mm error (std = 1.1mm) in the entry and exit drill point, which is adequate for successfully locking the nail.