Is the Position of the Basal-Most Electrode Depending on Electrode Array Design and Influencing Postoperative Speech Perception? A Retrospective Analysis of 495 Ears.

OBJECTIVE:The objective of this study is to examine the influence of electrode array design on the position of the basal-most electrode in cochlear implant (CI) surgery and therefore the stimulability of the basal cochlea. Specifically, we evaluated the angular insertion depth of the basal-most electrode in perimodiolar and straight electrode arrays in relation to postoperative speech perception. MATERIALS AND METHODS:We conducted a retrospective analysis of 495 patients between 2013 and 2018 using the Cochlear™ Contour Advance® (CA), Cochlear™ Slim Straight® (SSA), or Cochlear™ Slim Modiolar® (SMA) electrode arrays, as well as the MED-EL Flex24 (F24), MED-EL Flex28 (F28), and MED-EL FlexSoft (F31.5) electrode arrays. Cochlear size and the position of the basal-most electrode were measured using rotational tomography or cone beam computed tomography, and the results were compared with postoperative speech perception in monosyllables and numbers. RESULTS:The straight electrode arrays, specifically the F31.5 (31.5 mm length) and the F28 (28 mm length), exhibited a significantly greater angular insertion depth of the basal-most electrode. No significant correlation was found between cochlear morphology measurements and the position of the basal-most electrode artifact. Cochleostomy-inserted electrode arrays showed a significantly higher insertion depth of the basal-most electrode. Nevertheless, the position of the basal-most electrode did not have a significant impact on postoperative speech perception. CONCLUSION:Straight electrode arrays with longer lengths achieved deeper angular insertion depths of the basal-most electrode. Cochlear morphology does not have a substantial influence on the position of basal-most electrode. The study confirms that the basal area of the cochlea, responsible for high-frequency range during acoustic stimulation, is not the primary region for speech understanding via electrical stimulation with CI.