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Computer assisted spine surgery follows the basic ideas developed for Computer Assisted Medical Intervention (CAMI). Quantitative analysis of medical images makes it possible to localize with great accuracy anatomical structures. This is fruitfully used to drive guiding systems. This method tends to minimize invasive surgery and increases the quality of surgical interventions. In this article we present our methodology and develop some results leading to clinical experimentations.

Abstract. This paper describes the development and preliminary testing of an image-guided system for the placement of iliosacral screws to stabilize pelvic ring fractures percutaneously, with the aim of decreasing the incidence of surgical complications and increasing the accuracy of screw placement. Pre-operative planning of screw trajectories is performed on a 3D model of the pelvis constructed from CT scans. During surgery, a 6D optical localizer is used to track the positions and orientations of an ultrasound probe, a surgical drill and a reference frame fixed to the posterior iliac crest. Registration of the pre-operative model with curves segmented from the ultrasound scans is performed using a surface-based algorithm. The drill tip and axis are displayed relative to the desired screw trajectories in real time. The accuracy of the system has been verified in four cadaver specimens by comparing actual screw trajectories to the desired trajectories and by measuring the distance from each screw to important anatomical landmarks on post-operative CT scans. All screws were considered to be in correct position.