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

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.