Mechatronical Assistance in the Surgery of Petrous Bone: First Experiences with a Navigation-Controlled Drill

Introduction: High-resolution CT of temporal bone can be used as a basis for three-dimensional representation of at-risk structures (facial nerve, semicircular canal) and preoperative planning. The drill can be registered by 3-D-camera systems. By using the principle of navigated control, the force of the drill can be regulated on the basis of the preoperative planned working space and safety margins. The goal of this study is the investigation of the feasibility and the minimum accuracy of the overall system.

Methods and Material: 1.0 mm slice CT scanning of the temporal bone was used to reconstruct in 3-D. The main risk structure was the Facial Nerve. The semicircular canals were defined as safety regions. The regulation of the drill was realized following the intraoperative registration of the 3-D-camera system. The experiment evaluated the accuracy of the registration and deviation between planned and resulting resection cavity in 5 preparations.

Results: Segmentation of the examined risk structures succeeds both manually and using the semiautomatic mode with a satisfying clinical result. The average expenditure of time is 14 minutes per case. The average registration accuracy of the instrument was 1.3 mm. Maximal deviation between planned and resulting cavity was 1.9 mm.

Conclusion: The principle of navigated control permits control of a drill in surgery of the temporal bone and other parts of the bony skull base. Insufficient accuracy must be compensated with a high safety margin. This problem should be solved with technical modifications in future development. An outstanding advantage of the represented principle is that it supports the surgeon intraoperatively without substantial changes in the surgical workflow.