Robotic Milling of Electrode Lead Channels During Cochlear Implantation in an ex-vivo Model.

Jan Hermann,Fabian Mueller,Stefan Weber,Gabriela O'Toole Bom Braga,Daniel Schneider

doi:10.3389/fsurg.2021.742147

Abstract

Objective: Robotic cochlear implantation is an emerging surgical technique for patients with sensorineural hearing loss. Access to the middle and inner ear is provided through a small-diameter hole created by a robotic drilling process without a mastoidectomy. Using the same image-guided robotic system, we propose an electrode lead management technique using robotic milling that replaces the standard process of stowing excess electrode lead in the mastoidectomy cavity. Before accessing the middle ear, an electrode channel is milled robotically based on intraoperative planning. The goal is to further standardize cochlear implantation, minimize the risk of iatrogenic intracochlear damage, and to create optimal conditions for a long implant life through protection from external trauma and immobilization in a slight press fit to prevent mechanical fatigue and electrode migrations.Methods: The proposed workflow was executed on 12 ex-vivo temporal bones and evaluated for safety and efficacy. For safety, the difference between planned and resulting channels were measured postoperatively in micro-computed tomography, and the length outside the planned safety margin of 1.0 mm was determined. For efficacy, the channel width and depth were measured to assess the press fit immobilization and the protection from external trauma, respectively.Results: All 12 cases were completed with successful electrode fixations after cochlear insertions. The milled channels stayed within the planned safety margins and the probability of their violation was lower than one in 10,000 patients. Maximal deviations in lateral and depth directions of 0.35 and 0.29 mm were measured, respectively. The channels could be milled with a width that immobilized the electrode leads. The average channel depth was 2.20 mm, while the planned channel depth was 2.30 mm. The shallowest channel depth was 1.82 mm, still deep enough to contain the full 1.30 mm diameter of the electrode used for the experiments.Conclusion: This study proposes a robotic electrode lead management and fixation technique and verified its safety and efficacy in an ex-vivo study. The method of image-guided robotic bone removal presented here with average errors of 0.2 mm and maximal errors below 0.5 mm could be used for a variety of other otologic surgical procedures.

Highlights

Cochlear implantation is a neuro-otologic technique used to restore hearing to profoundly deaf patients with sensorineural hearing loss
The proposed technique for the electrode lead management during robotic cochlear implantation foresees the creation of a channel without self-crossings on the surface of the temporal bone, starting in the middle ear access tunnel, and leading to a ramped bone recess for the electrode lead exit of the receiverstimulator (Figure 1A)
In three out of the 12 cases, full insertion could not be achieved by 2–3 mm

Summary

Introduction

Cochlear implantation is a neuro-otologic technique used to restore hearing to profoundly deaf patients with sensorineural hearing loss. A microphone and audio processor are worn around the auricle, and a transmission coil is magnetically connected to the implanted receiver-stimulator This receiverstimulator is placed in the temporal region underneath the skin in a subperiosteal pocket, while an attached electrode array is inserted into one of the ducts of the cochlea, into the scala tympani. Prior to insertion, the exact electrode lead length needed and the potential electrode surplus cannot be ascertained by the surgeon, since the electrode lead is not yet inside the cochlea This can be resolved with an accurate surgical planning on the medical images taken for the robotic procedure. Patient registration was performed by recording three points on the bone surface with a tracked tool, while the patient was fixated rigidly Their optimal milling parameters were 30,000 revolutions per minute (RPM) spindle speed, a feed forward rate of 5 mm/s for calvarium, and 1 mm/s for mastoid bone. In a later work with the same robot and the same application, Stolka et al presented an intraoperative method to generate bone surface meshes for planning through tracked ultrasound measurements with a reconstruction precision of about 0.7 mm, and a final implant bed precision of about 1 mm [54]

Methods

Results

Discussion

Conclusion