Hearing preservation outcomes after cochlear implantation depending on the length of electrodes in patients with partial deafness.

Objectives: To evaluate the impact of electrode length on hearing preservation (HP) in a selected group of adults with Partial Deafness Treatment-electric complementation (PDTEC) receiving one of two kinds of flexible electrodes: the longer 24 mm electrode array or shorter 20 mm electrode array. Material: Twenty-three PDT-EC patients (with preoperative air-conduction thresholds ≤30 dB up to 500 Hz) were divided into two groups: Flex20 electrode (Med-EL GmbH, Innsbruck, Austria) (12 patients) and Flex24 electrode (Med- EL GmbH, Innsbruck, Austria) (11 patients). The mean of age of patients with Flex20 at the time of surgery was M=49.6 years (standard deviation, SD=15.5) and M=52.8 (SD=15.2) for patients with Flex24. Methods: Hearing threshold measurements were conducted on all patients five times: preoperatively, 1 month after the operation (at activation), 6 months after the operation, 12 months after the operation, and 24 months after the operation. HP was established using the HEARRING group formula. The Pruszewicz monosyllabic word test was conducted in free-field at the preoperative period under unaided and aided configurations (with hearing aids) under the best conditions. All participants were subjected to minimally invasive cochlear implantation using the round window approach. Results: Analysis of HP for every individual indicates that more than half the patients with Flex20 and Flex24 had complete HP at 6 months follow-up. None of the patients from either group had complete loss of hearing. At activation, average air-conduction thresholds for low frequencies (125--500 Hz) were slightly better for the short electrode (M=29.03) than for the long (M=39.10) but the difference was not statistically significant (p=0.067). The effect of electrode (Flex20 versus Flex24) was not significant in terms of pure tone audiometry and speech recognition at long-term follow-up. Conclusions: In early postoperative observations, complete HP was possible in the majority of patients from both groups, although slightly better HP outcomes were achieved by the Flex20. In the long-term, however, the electrode length (20 or 24 mm) does not affect the degree of HP or speech understanding, at least in the hands of an experienced otosurgeon. Considering that HP is also possible using a deeply inserted long electrode array, and that most patients have progressive hearing loss, the use of a longer, flexible electrode seems to be a better choice. [ABSTRACT FROM AUTHOR]