Position Control of Flexible Electrodes With Regard to Intracochlear Structure Preservation and Hearing Outcomes: A Retrospective Study With Implementation of the Electrode Contact View.

Abstract

Objective: To investigate complications related to electrode design, such as incomplete insertion, electrode tip fold-over (ETFO), and scalar deviation, and to evaluate hearing outcomes with a flexible 28-mm cochlear implant electrode.

Study design: Retrospective.

Setting: Tertiary referral center.

Patients: Postoperative computed tomographic (CT) data analysis of 36 patients with regular cochlear anatomy was performed who received a flexible 28-mm-long electrode.

Interventions: All patients received secondary reconstructions of flat-panel volume CT (fpVCTSECO; slice thickness: 99 μm), along with audiological testing. Radiologic analyses were performed using the otosurgical software OTOPLAN®, which included the following: (I) measurement of the cochlear parameters (A value and cochlear duct length [CDL]), (II) evaluation of insertion status and ETFO including angular insertion depth (AID), cochlear coverage, and apical electrode contact frequency; and (III) determination of the scala electrode position with the newly developed "electrode contact view," analyzing individual electrode contact positioning within the cochlear duct. The audiological outcome with CI was tested with a monosyllabic word test at 65 dB SPL in quiet and correlated with several parameters.

Main outcome measures: Complete insertion, ETFO, scalar deviation, postoperative hearing results.

Results: Full electrode insertion was achieved in all patients with no observed cases of ETFO. The "electrode contact view" identified no cases of scalar deviation (34 electrodes inserted in the scala tympani and two electrodes deliberately inserted into the scala vestibuli via cochleostomy). The cochlear canal's cranial-caudal height averaged 2.3 mm at electrode contact 12 and 1.1 mm at electrode contact 1. Cochlear parameters averaged 9.3 mm for the A value and 36.9 mm for the CDL value. The AID of the most apical canal ranged from 459 to 705 degrees, with an average cochlear coverage of 81.2%. There was a significant negative correlation between cochlear size (A value and CDL) and AID. Audiological testing showed a 50% average improvement in monosyllables word scores with CI.

Conclusion: This case series suggests that a 28-mm flexible electrode can achieve reliable full insertion with minimal risk of scalar deviation. Despite its high flexibility, ETFO was not observed. However, cochlea size influences AID, which may impact hearing results.