In the field of cochlear implantation, artificial/physical models of the inner ear are often employed to investigate certain phenomena like the forces occurring during implant insertions. Up to now, no such models are available for the analysis of diffusion processes inside the cochlea although drug delivery is playing an increasingly important role in this field. For easy access of the cochlea along its whole profile, e.g., for sequential sampling in an experimental setting, such a model should ideally be longitudinal/uncoiled. Within this study, a set of 15 micro-CT imaging datasets of human cochleae was used to derive an average representation of the scala tympani. The spiral profile of this model was then uncoiled along different trajectories, showing that these trajectories influence both length and volume of the resulting longitudinal model. A volumetric analysis of the average spiral model was conducted to derive volume-to-length interrelations for the different trajectories, which were then used to generate two tubular, longitudinal scala tympani models with volume and length properties matching the original, spiral profile. These models can be downloaded for free and used for reproducible and comparable simulative and experimental investigations of diffusion processes within the inner ear.

Drilling a minimally invasive access to the inner ear is a demanding task in which a computer-assisted surgical system can support the surgeon. Herein, we describe the design of a new micro-stereotactic targeting system dedicated to cochlear implant (CI) surgery and its experimental evaluation in an ex vivo study. Methods: The proposed system consists of a reusable, bone-anchored reference frame, and a patient-specific drilling jig on top of it. Individualization of the jig is simplified to a single counterbored hole drilled out of a blank. For accurate counterboring, the setup includes a manufacturing device for individual positioning of the blank. The system was tested in a preclinical setting using twelve human cadaver donors. Cone beam computed tomograph (CBCT) scans were obtained and a drilling trajectory was planned pointing towards the basal part of the cochlea. The surgical drill was moved forward manually and slowly while the jig constrained the drill along the predetermined path. Results: Drilling could be performed with preservation of facial nerve in all specimens. The mean error caused by the system at the target point in front of the cochlea was 0.30 mm ± 0.11 mm including an inaccuracy of 0.09 mm ± 0.03 mm for counterboring the guiding aperture into the jig. Conclusion: Feasibility of the proposed system to perform a minimally invasive posterior tympanotomy approach was shown successfully in all specimens. Significance: First evaluation of the new system in a comprehensive ex vivo study demonstrating sufficient accuracy and the feasibility of the whole concept.

A minimally-invasive surgical (MIS) approach to cochlear implantation, if safe, practical, simple in surgical handling, and also affordable has the potential to replace the conventional surgical approaches. Our MIS approach uses patient-specific drilling templates (positioning jigs). While the most popular MIS approaches use robots, the robotic aspect is literally put aside, because our high-precision parallel kinematics is only used to individualize a positioning jig. This jig can then be mounted onto a bone-anchored mini-stereotactic frame at the patient's skull and used to create a drill-hole through the temporal bone to the patient's cochlea. We present the first clinical experience where we use sham drill bits of different diameters instead of drilling into the bone in order to demonstrate the feasibility and accuracy.