gms | German Medical Science

Speech perception was significantly better in a group of 25 patients implanted with the CII HiFocus1 with a partially inserted positioner compared to 20 patients without. The objectives of this study were to document the intracochlear position of individual contacts of those two groups and the effect of these positions on spread of current and excitation. Finally, it was studied to what extent the newly designed HiFocus4L could realize the most desirable position.

The position of all contacts was determined with post-operative MSCT-scans. The accuracy of this semi-automatic quantitative analysis was tested in a phantom study. Data obtained with EFI-recordings were correlated with these measurements. Furthermore, the position of the single-piece HiFocus4L was studied with MSCT-scans in human temporal bones.

The phantom study demonstrated an accuracy of the position measurements of approximately 0.1mm. In line with expectations, the distance of the contacts to the modiolus was significantly smaller with the positioner at the base of the cochlea (p<0.01), whereas apically no difference could be demonstrated. Moreover, due to the outer wall course the HiFocus1 without positioner showed smaller insertion depths (basalmost to apicalmost contact: 35˚-401˚ vs. 6˚-439˚). EFI-recordings showed significantly higher longitudinal current spread in this group, in line with the elevated T-levels found basally without positioner. The contact positions with the HiFocus4L turned out to be comparable with the positioner group.

MSCT-scans are applicable to measure the position of individual electrode contacts. The new Hifocus4L electrode meets its design criteria and is worth clinical evaluation.