Background Cochlear implant (CI) candidacy increasingly includes patients with residual hearing, making atraumatic electrode insertion essential. Motorized insertion tools (MITs) aim to standardize electrode insertion and reduce mechanical stress, but their effects compared with manual insertion remain insufficiently understood. We hypothesized that MIT-assisted insertion results in lower postoperative impedance values and improved hearing preservation.Methods In this matched cohort study, 56 patients were analyzed. Patients were matched based on demographic and clinical characteristics including age, preoperative low-frequency pure-tone average (LF-PTA), cochlear duct length, and angular insertion depth. Clinical impedance measurements were obtained intraoperatively and at 1, 3, and 6 months postoperatively. Associations between insertion technique, impedance values, and hearing outcomes were analyzed using a linear mixed-effects model.Results Impedance values showed a characteristic postoperative course with an early peak followed by stabilization over time. MIT-assisted insertion was associated with consistently lower postoperative impedance values in the basal cochlear region than manual insertion (p≤0.004). Lower impedance values were associated with better residual hearing. Insertion technique was not significantly associated with hearing preservation. In patients with substantial preoperative residual hearing, thresholds remained more stable in the MIT cohort at 6 months.Conclusion MIT-assisted insertion was associated with lower postoperative impedance values in the basal cochlear region, suggesting a reduced insertion-related intracochlear tissue response. These findings indicate that insertion technique primarily affects the basal cochlea, where mechanical stresses during electrode advancement are greatest. Spatially resolved impedance measurements may provide a clinically accessible biomarker to characterize intracochlear responses to different insertion techniques.
Bircher et al. (Tue,) studied this question.