Evaluation of tip fold over in 1,575 cochlear implant electrode arrays

Abstract

Objective Cochlear implant (CI) surgery aims to achieve atraumatic electrode array insertion to preserve residual hearing and optimize outcomes. Tip fold-over, a mechanical complication during insertion, can compromise stimulation effectiveness and may require reinsertion or revision surgery. This study investigates the incidence, influencing factors, and diagnostic approaches for tip fold-over across a large patient cohort implanted with various CI electrode array designs. Methods We conducted a retrospective analysis of adult patients who underwent CI surgery between 2013 and 2024 at the Department of Otorhinolaryngology–Head and Neck Surgery, Medical Center–University of Freiburg. Included electrode arrays were from Cochlear™ (Slim Straight [SSA], Slim Modiolar [SMA], Contour Advance [CA]), MED-EL (FlexSoft, Flex28, Flex26, Flex24), and Advanced Bionics (SlimJ, Mid Scala [MS]). Detailed reviews of surgical reports, intraoperative electrophysiological data, and postoperative imaging—evaluated independently by at least two reviewers—were performed. Diagnostic imaging modalities included cone beam computed and digital volume tomography (DVT). Results Among 1,575 implanted ears, 13 cases of tip fold-over were detected, yielding an overall incidence of 0.83%. Notably, 10 of these occurred with precurved, perimodiolar arrays (SMA and CA, Cochlear™; MS, Advanced Bionics), while only 3 were found in straight lateral wall designs (SSA, Cochlear™). No tip fold-over events were observed with any MED-EL electrode arrays or with the SlimJ electrode array from Advanced Bionics. Intraoperative Transimpedance matrix (TIM) analysis and intraoperative X-ray reliably detected tip fold-over in cases with normal anatomy. Conclusion Electrode array design significantly influences tip fold-over risk. A potentially higher incidence has been observed with perimodiolar electrode arrays compared with flexible straight arrays. The importance of intraoperative diagnostics is underscored in this study. TIM analysis and intraoperative X-ray imaging proved effective in detecting tip fold-over events in real-time, allowing for immediate corrective action and avoiding revision surgeries. This large-scale retrospective study confirms that tip fold-over remains a rare but significant complication in CI surgery, with a higher prevalence in precurved perimodiolar electrode arrays. This study emphasizes the need for ongoing vigilance across all CI systems.