Introduction:
The insertion of a cochlear implant electrode may impede propagation of a travelling wave in the implanted cochlea. The primary objective of this study was to evaluate whether the impeded cochlea biomechanics affected the patient’s hearing preservation.

Material and methods:
There were 17 adults who were implanted with Flex 20 (n = 1); Flex 24 (n = 8); Flex 28 (n = 1); FlexSoft (n = 5); Medium (n = 1), and Standard (n = 1) electrode arrays with Pulsar, Concerto, or Sonata cochlear implants (Med-El). Implantation was via the round window. Acoustically evoked intracochlear potentials were recorded from cochlear implant electrodes. Tone pips at 500 Hz generated by a Nicolet EDX system (Natus Medical Inc.) were presented via inserts. Postoperative CT scans of the implanted cochlea were made and analysed. The unaided pre-implantation and post-implantation hearing thresholds were compared in all subjects.

Results:
In 9 subjects the highest amplitude response to the tone pip matched the 500 Hz excitation area in the postoperative CT scan. The low-frequency difference was found between the pre-implantation and the post-implantation unaided thresholds in this group was 12.4 dB. Impeded basilar membrane biomechanics was observed in 8 other patients. In these 8 patients, the highest amplitude at 500 Hz was shifted either apically (1 case) or basally (7 cases) with respect to the 500 Hz excitation area suggested by the postoperative CT scan. The threshold difference in this group was 8.4 dB. However, the threshold differences in both groups were not statistically significant.

Conclusions:
These preliminary data suggest that impeded biomechanics of the basilar membrane does not appear to affect hearing preservation.