The Influence of New Bone Formation After Cochlear Implant Surgery on Electrode Impedances, Intracochlear Voltage Distribution and Loss of Residual Hearing

Surgical insertion of cochlear implant electrodes may induce delayed changes within the cochlea due to insertion trauma and tissue response. These responses can be inflammation, fibrosis and new bone formation (NBF), possibly affecting the stimulation of the nerve. Human temporal bone studies showed contrasting effects of NBF on electrode stimulation patterns and audiometric outcomes. In this study high-resolution CT-scan was used to relate electrode position and electrode trajectory on the occurrence of NBF and, secondly, to investigate the influence of NBF on electrode impedances, the intracochlear voltage distribution and on residual hearing.

Participants were 126 postlingually deafened adult users of the Cochlear device with Contour Advanced or with Slim Straight electrode implanted at one single CI centre. CT-scans were made at least one year post-implantation. Electrode position variables investigated were: electrode scalar trajectory including scalar translocation, electrode insertion angle and wrapping factor (electrode proximity to the modiolus). NBF around the electrode was reviewed and scored per electrode contact by two radiologist. Impedance and voltage distribution measurements were made using experimental Cochlear Electrode Voltage Telemetry (EVT) software. Preoperative and postoperative residual hearing was measured using pure-tone audiometry.

The preliminary results showed NBF in 60,3% of the patients, and 91,4% of the NBF was located around the nine most basal contacts. Further analysis of the new bone formation after cochlear implantation will be presented, and correlated with electrode impedances, the voltage distribution and residual hearing.