Vestibular electrode position stability over time

OBJECTIVES: In vestibular implants (VI), the electrode position is thought to be important for optimal neural activation. The objective of this study was to evaluate the stability of the vestibular electrode position over time. METHODS: Seven patients implanted with a VI were followed for one year. When possible, the fenestrations of the semicircular canals were kept very small (approximately 0.8 mm) to stabilize the electrode lead. Additionally, the electrodes were fixed at their fenestration sites using bone cement. A temporal bone CT scan was performed intraoperatively, and one week and one year postoperatively. In one patient reliable analysis of the intraoperative CT scan was not possible due to a technical error. A displacement of the vestibular electrodes of more than 0.5 mm was considered significant. RESULTS: Fourteen out of 18 electrodes did not show a significant displacement between the intraoperative scan and the first postoperative scan. In the remaining four electrodes, a displacement of ≥ 0.5 mm occurred (mean 0.54 mm, range 0.50-0.58 mm). These four electrodes were found in the two first implanted patients. In both cases, the intraoperative CT scan had a slice thickness of 0.5 mm and showed severe scattering. This might imply that the measured displacement was (partially) related to a higher measurement error. None of the vestibular electrodes migrated outside of the ampulla. No displacement was observed in any of the vestibular electrodes between the first postoperative scan and the one-year follow-up scan. CONCLUSION: The current surgical technique seems to securely stabilize the vestibular VI electrodes over time.