Toward the next generation of simulator for intraoperative navigation of scoliotic spine surgeries

Surgical navigation systems are useful for planning pedicle screw positioning and guiding drilling trajectories. However, it is not yet possible to intraoperatively predict the correction of the scoliotic spine resulting from specific screw and rod configuration and instrumentation maneuvers. In this context, the objective of this study is to develop a novel intraoperative simulator for navigated scoliotic spine surgeries. An instrumentation strategy (pedicle screw insertion, rod attachment and rotation, set screw tightening) was computationally simulated on a synthetic model of a scoliotic spine using the preoperative radiographs in the standing position and various parameters recreating the preoperative conditions. The intraoperative decubitus position was then simulated. The resulting geometry was identified using a navigation system and transferred to the simulator, which enabled the updating of the preoperative planning, computing of clinical indices (Cobb angles, etc.) and simulation of instrumentation maneuvers. The Cobb angle decreased from 34° to 24° between the simulated pre- and intraoperative spine (before the instrumentation). Difference in pedicle screw positioning between the preoperative planning and the intraoperative situation was less than 0.5 mm. The intraoperative simulation of the rod attachment and rotation maneuvers resulted in a 12° Cobb angle. In conclusion, this preliminary study is a first step toward developing an integrated simulator for preoperative planning and intraoperative navigation of scoliotic spine surgeries. Once completed, the new intraoperative simulator will enable the surgeon to obtain real-time biomechanical feedback during the navigated surgery of a scoliotic spine, and may contribute to improve the resulting correction and instrumentation parameters (instrumented levels, surgical maneuvers, generated forces, etc.).