Robotic milling of the electrode lead channel during cochlear implantation

Hermann, Jan; Müller, Fabian; O'Toole Bom Braga, Gabriela; Weber, Stefan (6 October 2021). Robotic milling of the electrode lead channel during cochlear implantation (Submitted). In: BMT 2021. Hannover. 07.10.2021.

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Introduction
Robotic cochlear implantation has been developed to overcome the limits of human perception and dexterity due to the submillimeter size of the targeted anatomy. During this procedure, the robot precisely drills a small-diameter access hole to the cochlea. Since there is no cavity like the mastoidectomy in the conventional surgery, and the robotic system is already installed, we propose to robotically mill the electrode lead channel on the temporal bone surface. The goal is to further standardise the procedure, ensure protection of the electrode from trauma, and pre-vent fatigue fractures caused by micro-movements. We propose a workflow consisting of preoperative planning on cone-beam computed tomography and its robotic execution. The planning provides a low-curvature channel of sufficient depth below the temporal bone surface, with a channel shape designed to immobilize the electrode with a slight press-fit.
Methods
This workflow was planned for three ex-vivo human cephalic specimens, considering a safety margin of 1.0 mm from the channel to surrounding anatomical and artificial structures. The planning was then executed using a commercially available robotic system. To evaluate safety and efficacy, the lateral and depth displacement of the resulting channel, as well as the channel depth and width were measured in a micro-computed tomography scan.
Results
Three out of the three cases have been successfully completed, and the electrode leads could be gently embedded within the resulting channels. The mean lateral and depth displacements were -0.05 ± 0.06 mm standard deviation (SD), and -0.06 ± 0.14 mm (SD), respectively. The resulting channel never left the planned safety margin. The mean channel width was measured to be 1.19 ± 0.06 mm (SD), where the planned channel width and tool diameter was 1.2 mm. The mean channel depth was measured to be 2.41 ± 0.13 mm (SD), where the planned channel depth was 2.3 mm.
Conclusion
This study proposes the robotic creation of a channel for cochlear implant electrode leads, which has been shown to be safe and effective in an ex-vivo model. The proposed procedure step could further standardize cochlear implantation and provide for a decreased risk of device failure due to trauma or fatigue, thus potentially leading to in-creased implant longevity.

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