Measurements of electrode position inside the cochlea for different cochlear implant systems

This study demonstrates that the exact location of an electrode inside the cochlea needs to be assessed using two complementary measures, namely the length and angle of insertion, both of which are mandatory if one wants to prevent erroneous outcomes. Knowledge of the contact position may become very useful when tuning a cochlear implant processor in a patient with contralateral residual hearing, or in cases of binaural implants.

Multichannel cochlear implants restore useful hearing to deaf patients. However, several types of intracochlear electrodes are presently available, each featuring a specific technology or design. The aim of this study was to determine precisely the intracochlear position of the contacts for different electrode arrays.

Electrode array insertions were estimated using special radiographs. A total of 26 cochlear implantations were included in the study: 6 Ineraid; 5 Clarion HiFocus I; 11 Clarion HiFocus II; and 4 Med-El Combi40+. In each case, a measurable reference or marker ring placed close to the round window (within 2 mm) could be identified. Insertion lengths and angles were measured and then plotted on a graphl based on 3D reconstructions.

Both Clarion HiFocus I and II electrode arrays were found to be placed close to the inner wall of the cochlea. Ineraid and Med-El Combi40+ electrode arrays were both placed close to the organ of Corti, the Med-El Combi40+ arrays demonstrating the deepest insertions overall. In spite of marked differences in the positions of the contacts, we did not find any correlation with speech perception performance for the different types of implants studied.