Objectives
Current approaches for improved hearing preservation following cochlear implant (CI) surgery focus on the reduction of intraoperative insertion forces to prevent trauma. Studies have shown an influence of the trajectory along which the electrode array (EA) is advanced. However, only idealized, tangential trajectories have been considered so far. As these can usually be blocked by critical anatomical structures in vivo, the aim of this work was to investigate the influence of trajectory variations around realistic trajectory choices.
Methods
A realistic trajectory through the facial recess was determined by a CI surgeon for five digitally segmented temporal bone specimens. An EA was inserted into corresponding 3D printed artificial cochlea models (ACMs) using a test bench with an adjustable insertion trajectory and an EA guide to avoid extracochlear buckling. The trajectory was biaxially varied around the realistic trajectory by ± 10° in steps of 5° without considering collisions with the facial recess. Insertion forces were measured below the ACMs and post-processed to compute the maximum force as well as the insertion work.
Results
In the most extreme case for each model, a variation of the trajectory could reduce the insertion work by 46.7% on average with a maximum value of 59.0%. Occasionally, even small angular variations had a large influence. The largest gradient for each model was a reduction of the insertion work per degree of orientation adjustment of 7.4%/° on average with a maximum of 8.8%/°. Similar values were observed for the maximum force. 
Conclusion
The trajectory along which the EA is advanced into the inner ear has a considerable influence on the insertion forces. The results of this work highlight the potential of trajectory optimization for CI surgery. As the ACMs used in the experiments have different sizes, their influence will need to be considered. To ensure the results are not only valid for our ACM, ex vivo verifications will be a next step. Moreover, future experiments will additionally consider anatomical boundaries to investigate only feasible trajectories.

Adjustment of realistic trajectories can reduce the insertion force in cochlear implant surgery

It is with great pleasure and enthusiasm, that on behalf of the Cochlear Implant centers of the Radboud UMC in Nijmegen and Erasmus MC Sophia Children’s Hospital in Rotterdam to invite you to attend the 16th European Symposium on Pediatric Cochlear Implantation to Rotterdam, the Netherlands in 2023.

Yours sincerely, on behalf of the CI Centers at Radboud UMC and Erasmus MC,