Hypothesis: The aim of the study is to investigate the insertion depth angles for different types of electrode arrays and its variability depending on the individual cochlear size.
Background: Preoperative estimation of the insertion depth angles for different electrode arrays can help surgeons choose the optimal electrode length, especially for low-frequency residual hearing preservation.
Methods: Four different electrode arrays varying in lengths (20, 24, 28, and 31 mm) were inserted in 10 temporal bones to quantify the insertion depth angle of each inserted electrode. High-resolution 3D radiographs provided by Flat Panel Computed Volume Tomography (FPCT) were used to determine electrode array insertion depth angle and diameter of the cochlea's basal turn.
Results: The high-resolution FPCT images from all electrode arrays inserted into the temporal bones allowed reliable measurements of insertion depth angles. In particular, statistically significant different insertion depth angles between the various array types were identified. The insertion of the 20-, 24-, 28-, and 31-mm arrays yielded a mean insertion depth angle of 341 degrees (SD, 22 degrees), 477 degrees (SD, 36 degrees), 587 degrees (SD, 42 degrees), and 673 degrees (SD, 38 degrees), respectively. Furthermore, a statistically significant negative correlation between insertion depth angle and diameter of the cochlea's basal turn was found for the 20- and 31-mm arrays.
Conclusion: The results suggest an individually adapted length of electrode arrays, which should be taken into account for an improved decision paradigm for patients scheduled for cochlear implantation. This is of particular importance for patients with low-frequency residual hearing.