Warning navigation system using real-time safe region monitoring for otologic surgery

Purpose We developed a surgical navigation system that warns the surgeon with auditory and visual feedback to protect the facial nerve with real-time monitoring of the safe region during drilling. Methods Warning navigation modules were developed and integrated into a free open source software platform. To obtain high registration accuracy, we used a high-precision laser-sintered template of the patient's bone surface to register the computed tomography (CT) images. We calculated the closest distance between the drill tip and the surface of the facial nerve during drilling. When the drill tip entered the safe regions, the navigation system provided an auditory and visual signal which differed in each safe region. To evaluate the effectiveness of the system, we performed phantom experiments for maintaining a given safe margin from the facial nerve when drilling bone models, with and without the navigation system. The error of the safe margin was measured on postoperative CT images. In real surgery, we evaluated the feasibility of the system in comparison with conventional facial nerve monitoring. Results The navigation accuracy was submillimeter for the target registration error. In the phantom study, the task with navigation (0.7 ± 0.25 mm) was more successful with smaller error, than the task without navigation (1.37 ± 0.39 mm, P<0.05). The clinical feasibility of the system was confirmed in three real surgeries. Conclusions This system could assist surgeons in preserving the facial nerve and potentially contribute to enhanced patient safety in the surgery.