Defining the ideal trajectory into the inner ear in image-guided cochlear implant surgery.

The aim of robot-assisted cochlear implant surgery (RACIS) is to access the inner ear with minimal trauma. High-resolution imaging, empowered with a highly accurate navigation system can enable the planning of a direct keyhole drilling trajectory toward the inner ear. The time has come to (re)define the ideal trajectory into the inner ear with robot-assisted tools that can drill with the highest accuracy. The trajectories of past RACIS procedures were analysed to gain insight into how to calculate the most ideal trajectory and to determine which trajectory parameters influence the course of the procedure. Data-analysis was performed on three groups of previously performed RACIS-procedures. Group 1 included the RACIS-procedures with a round window (RW) approach. Group 2 included the RACIS-procedures with difficulty entering the inner ear. Group 3 included the converted cases to conventional CI surgery due to inadequate intra-operative safety margins. The RW diameter was significantly smaller and its orientation significantly less favourable in group 2 compared to group 1. A smaller surface size and an unfavourable orientation of the RW in relation to the drilling trajectory are thus associated with a more difficult electrode array insertion in RACIS. Both must be taken into account when planning a drilling trajectory into the inner ear.