Robotic Cochlear Implant Surgery: Imaging-Based Evaluation of Feasibility in Clinical Routine

Abstract

Background: Robotic surgery has been proposed in various surgical fields to reduce recovery time, scarring, and to improve patients' outcomes. Such innovations are ever-growing and have now reached the field of cochlear implantation. To implement robotic ear surgery in routine, it is of interest if preoperative planning of a safe trajectory to the middle ear is possible with clinically available image data. Methods: We evaluated the feasibility of robotic cochlear implant surgery in 50 patients (100 ears) scheduled for routine cochlear implant procedures based on clinically available imaging. The primary objective was to assess if available high-resolution computed tomography or cone beam tomography imaging is sufficient for planning a trajectory by an otological software. Secondary objectives were to assess the feasibility of cochlear implant surgery with a drill bit diameter of 1.8 mm, which is the currently used as a standard drill bit. Furthermore, it was evaluated if feasibility of robotic surgery could be increased when using smaller drill bit sizes. Cochlear and trajectory parameters of successfully planned ears were collected. Measurements were carried out by two observers and the interrater reliability was assessed using Cohen's Kappa. Results: Under the prerequisite of the available image data being sufficient for the planning of the procedure, up to two thirds of ears were eligible for robotic cochlear implant surgery with the standard drill bit size of 1.8 mm. The main reason for inability to plan the keyhole access was insufficient image resolution causing anatomical landmarks not being accurately identified. Although currently not applicable in robotic cochlear implantation, narrower drill bit sizes ranging from 1.0 to 1.7 mm in diameter could increase feasibility up to 100%. The interrater agreement between the two observers was good for this data set. Discussion: For robotic cochlear implant surgery, imaging with sufficient resolution is essential for preoperative assessment. A slice thickness of <0.3 mm is necessary for trajectory planning. This can be achieved by using digital volume tomography while radiation exposure can be kept to a minimum. Furthermore, surgeons who use the software tool, should be trained on a regular basis in order to achieve planning consistency.

Keywords: cochlear implantation; keyhole access; minimal invasive surgery; robotic cochlear implantation; robotic surgery.

Figure 1A

Planning procedures with OTOPLAN. Cochlear view for assessing the software-guided cochlear parameters. The observer defines the cochlear view which corresponds to the center of the modiolus, the basal turn of the cochlear, and the round window in the axial, coronal and sagittal view. The diameter, height, width and length of the cochlear are then defined by the observer based on instructions of the software. Consequently, the software automatically calculates the cochlear parameters. The right lower picture displays a 3D model of the planned trajectory. Green dots (selection of round window and lateral wall), blue dots (selection of superior and inferior wall in coronal view), red dots (inferior and superior walls of cochlear in axial view), red shading (cochlear segmentation automatically calculated by the software), green shading (bony overhang automatically calculated by the software), yellow shading (facial nerve), dark blue shading (external ear canal), pink shading (ossicles), orange shading (chorda tympani), light blue shading (drill in position of the automated trajectory).

Figure 1B

Planning procedures with OTOPLAN. The trajectory path to the middle ear/round window is calculated automatically and safety distances to critical anatomic structures are displayed by the software. Red shading (cochlear segmentation automatically calculated by the software), green shading (bony overhang automatically calculated by the software), yellow shading (facial nerve), dark blue shading (external ear canal), pink shading (ossicles), orange shading (chorda tympani), light blue shading (drill in position of the automated trajectory).

Figure 2

Percentage and numbers (in white) of successfully planed ears based on drill bit size (1.8 and < 1.8 mm) and percentage of unsuccessfully planned ears. (A) Ears planned on CT with ≤ 0.3 mm slice thickness. (B) Ears planned based on CT with a slice thickness between 0.3 and ≤ 0.5 mm. (C) Ears planned based on CT with a slice thickness > 0.5 mm; gray bars indicate results of observer 1, black bars indicate results of observer 2; d (slice thickness).