Interactive Repositioning of Bone Fracture Segments

This paper presents an application for semiautomatic repositioning of bone fractures that allows the merging of several fragments. This application has been developed with regard to orthopaedic surgeons who want to simulate the position and orientation of bone fragments preoperatively. The interactive algorithm includes volumetric collision detection for intuitive navigation and coarse manual positioning. Additionally, an optimization process for the mathematically exact repositioning of the bone fragments is implemented. In order to accelerate the volumetric collision detection, octree structures are used that are efficiently implemented as an hierarchy of oriented bounding boxes (OBB). The collision test uses the separating axis theorem for a fast traversal of the octree. To improve the manual part of the repositioning process, the principal axes of each fragment are precalculated initially. Subsequently, the fragments are pre-justified by the user. Finally, an optimization process is performed based on Powell’s algorithm for multidimensional minimization. The optimal position of the bone fragments is determined by the use of a voxel-based metric, that exploits the same bounding box hierarchy.