Robotic cochlear implantation is a procedure for minimally invasive inner ear access. Compared to conventional surgery, robotic cochlear implantation involves additional steps that need to be carried out in the operating room. In this article we give a description of the procedure and highlight the important aspects of robotic cochlear implantation.
Robot-assisted systems offer great potential for gentler and more precise cochlear implantation. In this article, we provide a comprehensive overview of the clinical workflow for robotic cochlear implantation using a robotic system specifically developed for a minimally invasive, direct cochlear access. The clinical workflow involves experts from various disciplines and requires training to ensure a smooth and safe procedure. The protocol briefly summarizes the history of robotic cochlear implantation. The clinical sequence is explained in detail, beginning with the assessment of patient eligibility and covering surgical preparation, preoperative planning with the special planning software, drilling of the middle ear access, intraoperative imaging to confirm the trajectory, milling of the inner ear access, insertion of the electrode array, and implant management. The steps that require special attention are discussed. As an example, the postoperative outcome of robotic cochlear implantation in a patient with advanced otosclerosis is presented. Finally, the procedure is discussed in the context of the authors’ experience.
A cochlear implant (CI) is the standard treatment for severe to profound sensorineural hearing loss1. The surgical procedure for cochlear implantation aims to atraumatically insert the cochlear implant electrode array into the cochlea. For the implantation, surgeons must provide access from the surface of the temporal bone to the cochlea. In conventional procedures, this access is created by removing portions of the mastoid bone through a mastoidectomy and posterior tympanotomy2.
Robot-assisted cochlear implantation aims to perform a minimally invasive access through a small tunnel to the inner ear for electrode array insertion. To date, several systems for robot-assisted cochlear implantation are in development or already available on the market. One such system provides robotic-controlled drilling of the mastoid and electrode insertion and has been recently evaluated in patients3. Another device is a patient-specific guiding system for tunnel drilling and electrode insertion4. Two systems that do not provide the inner ear access tunnel but rather the alignment and motorized insertion of electrode arrays have recently received medical device approval in Europe and the United States5,6. The first clinical implementation of a minimally invasive tunnel procedure using a stereotactic guidance frame was performed by Labadie et al.7. The first robotic system and planning software applied in clinical cases was developed through collaboration between the ARTORG Center for Biomedical Engineering at the University of Bern and the Department of Otolaryngology at Bern University Hospital in Switzerland8,9,10,11. The planning software and system were later commercialized by a spin-off company.
Here, the authors present the protocol involved in performing robotic cochlear implantation with a dedicated robotic cochlear implantation system. The aspects of selecting suitable patients, preoperative planning of the access tunnel, and the complete surgical procedure are covered and discussed. The aim of this article is to present an overview of the procedure and share the authors' experience with the system.
This study was performed in compliance with institutional guidelines and was approved by the local institutional review board (ID 2020-02561). The patient gave written informed consent for further use of the images and videos. The video shows the processes involved in performing robotic cochlear implantation with the planning software and the robotic system (please refer to the Table of Materials for further details) according to the procedure described by the manufacturer.
1. Patient candidacy screening
NOTE: Use existing preoperative computed tomography images for this step. Currently, robotic cochlear implantation with the system used in this protocol is only available from a single manufacturer (see Table of Materials) for implant systems. Please refer to the instructions for use manual of the planning software for specific details regarding button clicks, software commands, and user inputs.
2. Fiducial screw insertion
3. Preoperative imaging
4. Preoperative planning
NOTE: Perform preoperative planning in parallel with patient preparation (step 5.) to save time. Please refer to the instructions for use manual of the planning software for mesh generation and for specific details regarding button clicks, software commands, and user inputs.
5. Patient preparation
6. Middle ear access – Phase 1
7. Intraoperative imaging safety check
8. Middle ear access – Phase 2
9. Inner ear access
NOTE: Inner ear access is a semi-automatic procedure that can be stopped by the surgeon at any time for visual inspection.
10. Implant management and electrode insertion
11. Implant telemetry and wound closure
Robotic cochlear implantation is particularly suitable for cases with difficult anatomical conditions. Here, the postoperative results in a patient with far advanced otosclerosis are presented. Figure 1 shows a preoperative CT image. The advanced state of otosclerosis has disintegrated the petrous bone, making the cochlea hardly discernible.
The postoperative outcome is illustrated in Figure 2. The small tunnel access can be seen. In this case, surgical planning was used to preoperatively identify an optimal insertion access to the inner ear. The successful insertion of the electrode array can be seen, with an angular insertion depth of about 270°.
Figure 1: Robotic cochlear implantation in a patient with far-advanced otosclerosis. Axial computed tomography slice of the left temporal bone shows the barely discernible cochlea (red ellipse). Please click here to view a larger version of this figure.
Figure 2: Robotic cochlear implantation in a patient with far-advanced otosclerosis. Postoperative image showing the drilled tunnel and the inserted electrode array. Please click here to view a larger version of this figure.
Here, an overview of the steps involved in robotic cochlear implantation is presented. An important part is the selection of suitable candidates for the procedure. To ensure that the safety margins during surgery can be maintained, careful candidate screening needs to be performed to ensure eligibility for the procedure. The distance between the virtually planned trajectory and the facial nerve should be at least 0.4 mm. In addition, at least 0.3 mm distance to the chorda tympani needs to be available. To provide more flexibility in trajectory planning after preoperative imaging on the day of surgery, even larger limits can be considered for patient selection.
As the robotic system relies on the fiducial landmark screws to transfer the plan to the patient, they are of central importance for a safe procedure. The surgeon should carefully select the positions of the fiducial screws to ensure that enough space is available for trajectory drilling. A linear arrangement of three screws should be avoided. Also, it needs to be ensured that the screw for the patient marker is positioned such that the marker remains visible throughout the procedure. The instructions for use of the robotic system provide detailed guidelines for screw positioning. When placing the screws, it needs to be ensured that the holes are pre-drilled perpendicularly to the surface of the mastoid bone. Tight fixing of the screws ensures that no movement occurs during the procedure.
For preoperative imaging, patients should be scanned in apnea, as the breathing motion of the patient can cause motion artifacts that may not be immediately identifiable in the images but later on during the registration process can cause errors that impede commencing the procedure. It should be ensured that the person performing the preoperative planning has received extensive training to confidently identify and label the anatomical structures. In particular, the course of the facial nerve, the chorda tympani, and the selection of the target at the cochlea (usually the center of the round window membrane) need to be trained. For facial nerve generation, additional safety through over-segmentation of the nerve should be considered. In case no imaging modality is available directly in the operating room or no mobile imaging system can be transported into the operating room, the patient needs to be transferred to the neuroradiological department for imaging. The additional patient transfer time needs to be considered. Preoperative planning can be performed in parallel with patient transfer and preparation to save time.
The team should extensively train head positioning in the headrest to ensure that the patient marker and screws are visible to the system at later stages. Wrong head positing can result in invisibility of the markers or infeasible kinematics of the robotic arm. At all stages during robotic cochlear implantation, it needs to be ensured that all the screws are tightly fixed, the patient marker is rigidly attached, and the handpiece of the robot is fixed.
For intraoperative imaging using mobile imaging devices (e.g., mobile cone beam CT), sufficient clearance of the patient’s head and the headrest with the sterile draping needs to be ensured. Motion artifacts caused by the scanner touching the sterile drape could worsen the image quality of the intraoperative image and impede decision-making on the safety of the drilled trajectory required for commencing of the drilling.
In an optimal case, the round window membrane is preserved after robotic inner ear access, sealing the inner ear from bone dust and blood that might be introduced by the consecutive steps involved in implant management. As the fiducial screws and patient reference marker are required for inner ear access, it is not recommended to prepare the implant bed before inner ear access to ensure sufficient space for screw placement. In case the round window membrane is not intact after inner ear access, the round window could be temporarily covered as a protective measure until the electrode array insertion is performed.
After access to the inner ear is established, the surgeon may use different techniques to visualize the access. Microscopic inspection through a tympanomeatal flap or direct endoscopic inspection are possible. However, for the later electrode array insertion, we recommend performing a tympanomeatal flap to provide direct access to the electrode array, if required13. The electrode array lead can be marked before insertion to indicate full insertions at the surface of the mastoid bone. We also recommend using the insertion guide tube during insertion to avoid contact with blood and bone dust and to constrain the electrode array to the insertion trajectory14.
The presented procedure applies task-autonomous robotics in the field of otological microsurgery. Potential advantages of the procedure include reproducible, minimally invasive access to the cochlea and, ultimately, targeted, and accurate insertion of electrodes, which could expand the pool of CI patients in the future. The current limitations of the system are the associated additional costs for material and trained staff, the longer surgical duration, and the still manually performed electrode insertion. Currently, robotic cochlear implantation requires more time (about 4 h) than conventional cochlear implantation (about 1.5 h). Therefore, the condition of the patient should be also considered for eligibility.
The authors have nothing to disclose.
The authors thank Gianni Pauciello, Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital, Bern University Hospital, for video production and photography. We also thank Dr. Stefan Henle and the team of the Department of Anesthesiology and Pain Medicine, Inselspital, Bern University Hospital and the team at the Department of Diagnostic and Interventional Neuroradiology, Inselspital, Bern University Hospital, Bern, Switzerland.
Cochlear implant | MED-EL, Austria | ||
HEARO Consumable Set | CAScination, Switzerland | REF 50176 | CE-labelled |
HEARO Instrument Set | CAScination, Switzerland | REF 30123 | CE-labelled |
HEARO System Components | CAScination, Switzerland | CE-labelled | |
Mobile cone beam CT scanner | XORAN Xcat | if not availalbe, imaging needs to be performed in the neuroradiological department | |
OTOPLAN | CAScination, Switzerland | REF 20125 | CE-labelled |
Planning laptop | Any computer with enough performance is suitable, software OTOPLAN installed | ||
USB Stick | A surgical plan that was created with OTOPLAN is transferred to the HEARO system via a USB flash drive. |