We demonstrate a worldwide unique technique for cochlear implantation. The workflow is comprehensive and requires training to ensure a safe procedure. The main advantage of this technique is that it enables to perform an optimally aligned, minimally invasive tunnel access to the inner ear.
To begin, ensure that the distance of the trajectory to the facial nerve is at least 0.4 millimeters, and the distance to the chorda tympani is at least 0.3 millimeters for the trajectory to be drilled safely. Then, mark the retroauricular incision for the cochlear implant. Using a surgical marker, perform the incision, lift the musculocutaneous flap, and use the curette to expose the mastoid cortical bone.
Mark the position of the five fiducial screws. The first four registration screws are positioned approximately 20-30 millimeters retroauricularly, in a trapezoid pattern. The fifth screw is used for patient marker attachment and is placed approximately a thumb distance from the first four screws, as inferior as possible.
Hold the drill perpendicular to the bone surface and use the pre-drill bit and drill hand piece to pre-drill the holes for the screws. Insert the screws into the pre-drilled holes and ensure that the screws are firmly fixed in the bone. Perform computed tomography imaging or cone beam CT imaging under apnea to reduce motion artifacts.
Perform imaging with a minimum resolution of 0.2 by 0.2 by 0.2 millimeters. Verify the image data quality and visibility of all screws in the CT data. Then generate the facial nerve surface mesh by adding points in the fallopian canal centerline tab.
Go to fallopian canal identification and define the fallopian canal by adjusting the points. Next, generate the chorda tympani surface mesh. Plan the drill trajectory and approve the plan with the neuroradiologist.
Prepare the patient by aligning the head within the headrest, such that the neck is supported by the bottom cushion, and the nose is aligned with the center of the top frame of the headrest. Ensure that the patient's head is sufficiently fixed on the headrest. Place the facial nerve monitoring electrodes.
Then, cover the robotic system and navigation platform with sterile drape. Place a line and fix the patient marker on the fifth screw such that it is visible to the tracking camera of the robotic system. Ensure that the patient marker is attached rigidly and that all joints are firmly tightened.
It is critical to avoid any movement of the patient marker after the registration process. Perform patient to plan registration to relate the virtual plan to the actual patient. Use the hand piece with the registration tool and place it onto each fiducial screw four times.
Perform the registration procedure by following the screen on the navigation platform that indicates the screw on which the tool is to be positioned. After all screw positions are digitized, check the fiducial registration error to confirm that the registration accuracy is sufficient to continue. Insert the drill bit into the hand piece and attach the irrigation nozzle.
Confirm the alignment of the drill bit with the virtual trajectory planned in the planning software. Start drilling with the robotic system. The system will drill with a pecking motion, until the first safety checkpoint above the facial recess is reached.
After reaching the first checkpoint, move the robotic arm out of the surgical field. First, perform an intraoperative imaging safety check. Remove the patient marker from the patient.
Perform CT imaging, or cone beam CT imaging, with the neuroradiology team. Load the CT data into the planning software and confirm with the neuroradiologist that the trajectory is safe. For middle ear access, confirm the alignment of the drill bit with the drill tunnel and continue drilling until the first facial nerve stimulation point is reached.
Insert the facial nerve probe to check the integrity of the facial nerve. Then, the robotic system will drill to the next facial nerve stimulation point. In total, five facial nerve stimulation points will be tested.
Start the robotic system to mill the bony overhang. The system will automatically stop after breakthrough to ensure that a sufficient aperture for the electrode array is achieved, while aiming to preserve the round window membrane. Confirm the inner ear access, via either an endoscope or a microscope, through a tympanomeatal flap.
Remove the patient marker and all five fiducial screws. Mark the implant body position using the surgical template and prepare the implant pocket. Fix the cochlear implant body in the pocket and manually insert the electrode array through the insertion guide tube.
Mark the electrode lead using the insertion guide tube as a reference for the intended insertion depth, and mark the array at the lateral end of the guide tube. After the final insertion depth is achieved, remove the insertion guide tube. The preoperative CT image of the patient showed an advanced state of otosclerosis that had disintegrated the petrous bone, making the cochlea hardly discernible.
The postoperative outcome showed the drilled tunnel and the inserted electrode array. In this case, surgical planning used to preoperatively identify optimal insertion access to the inner ear led to the successful insertion of the electrode array, with an angular insertion depth of about 270 degrees. The most important aspect is patient to plan registration for accuracy and safety.
The surgeon must ensure that the screws are firmly in place and that the registration procedure is performed correctly.
