Patient-specific interactive software module for virtual preoperative planning and visualization of pedicle screw entry point and trajectories in spine surgery

Background: Lumbar pedicle screw insertion involves a steep learning curve for novice spine surgeons and requires image guidance or navigation. Small volume centers may be handicapped by the lack of cost-effective user-friendly tools for preoperative planning, guidance, and decision making. Objective: We describe a patient-specific interactive software module, pedicle screw simulator (PSS), for virtual preoperative planning to determine the entry point and visualize the trajectories of pedicle screws. Materials and Methods: The PSS was coded in Python for use in an open source image processing software, 3D Slicer. Preoperative computed tomography (CT) data of each subject was loaded into this module. The entry-target (ET) mode calculates the ideal angle from the entry point through the widest section of the pedicle to the desired target in the vertebral body. The entry-angle (EA) mode projects the screw trajectory from the desired entry point at a desired angle. The performance of this software was tested using CT data from four subjects. Results: PSS provided a quantitative and qualitative feedback preoperatively to the surgeon about the entry point and trajectories of pedicle screws. It also enabled the surgeons to visualize and predict the pedicle breach with various trajectories. Conclusion: This interactive software module aids in understanding and correcting the orientation of each vertebra in three-dimensions, to identify the ideal entry points, angles of insertion and trajectories for pedicle screw insertion to suit the local anatomy.