Cochlear Implant Insertion Axis Into the Basal Turn: a Critical Factor in Electrode Array Translocation

Hypothesis: An inappropriate insertion axis leads to intracochlear trauma during cochlear implantation (CI). Background: Few studies assessed the relationship between the insertion axis and the electrode scalar location. Methods: Preimplantation cone-beam CT (CBCT) was performed on 12 human temporal bones. In five temporal bones, an optimal insertion axis was planned, due to the impossibility to attain the ST centerline from the posterior tympanotomy, because of facial canal position. In the seven other temporal bones, an inaccurate insertion axis was intentionally planned (optimal axis+15 degrees). Automated CI array insertion according to the planned axis was performed with a motorized insertion tool driven by a navigated robot-based arm. The cochlea and basilar membrane were segmented from the preimplantation CBCT and the array segmented from the postimplantation CBCT to construct a merged final three-dimensional (3D) model. Microscopical and 3D analysis were performed to determine the intracochlear trauma at the level of each electrode. Results: A good agreement was observed in determining electrode position between microscopic analysis and the 3D model (Cohen's kappa k = 0.67). The angle of approach to the ST centerline was associated with the number of electrodes inserted into the ST (r = −0.65, p = 0.02, [95% CI −0.90 to −0.11] Spearman's rank correlation). Conclusion: A 3D reconstruction model was effective in determining the array position in the cochlea scalae. Our data indicate that the angle of approach to the ST centerline is a critical factor in intracochlear trauma. Additional studies should be conducted to assess the importance of the insertion axis with other array designs. Address correspondence and reprint requests to Renato Torres, M.D., Inserm, Paris 6: Unité “Réhabilitation chirurgicale mini-invasive et robotisée de l’audition”, 16, rue Henri Huchard, 75018 Paris, France; E-mail: renato.torres@inserm.fr This work was supported by Cifre grant (No 269/2015 ANRT/Oticon Medical) and Agir pour l’Audition Foundation (Grant No APA RD-2014-2/R14104DD RAK14030DA). The authors disclose no conflicts of interest. Supplemental digital content is available in the text. Supplemental digital content is available for this article. Direct URL citations appear in the printed text and are provided in the HTML and PDF versions of this article on the journal's Website (http://ift.tt/2i6WMKr). Copyright © 2017 by Otology & Neurotology, Inc. Image copyright © 2010 Wolters Kluwer Health/Anatomical Chart Company

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