Objectives: To study the relation between variables related to cochlear implant electrode position and speech perception performance scores in a large patient population. Design: The study sample consisted of 203 patients implanted with a CII or HiRes90K implant with a HiFocus 1 or 1J electrode of Advanced Bionics. Phoneme and word score averages for the 1- and 2-year follow-up were calculated for 41 prelingually deaf and 162 postlingually deaf patients. Analyses to reveal correlations between these performance outcomes and 6 position-related variables (angle of most basal electrode contact, surgical insertion angle, surgical insertion, wrapping factor, angular insertion depth, linear insertion depth) were executed. The scalar location, as an indication for the presence of intracochlear trauma, and modiolus proximity beyond the basal turn were not evaluated in this study. In addition, different patient-specific variables (age at implantation, age at onset of hearing loss, duration of deafness, preoperative phoneme and word scores) were tested for correlation with performance. Results: The performance scores of prelingual patients were correlated with age at onset of hearing loss, duration of deafness and preoperative scores. For the postlingual patients, performance showed correlations with all 5 patient-specific variables. None of the 6 position-related variables influenced speech perception in cochlear implant patients. Conclusions: Although several patient-specific variables showed correlations with speech perception outcomes, not one of the studied angular and linear position-related variables turned out to have a demonstrable influence on performance.

This study demonstrates a large variety in cochlear morphology, which significantly impacts electrode position in terms of modiolus proximity and insertion depth. The effect size is, however, relatively small compared with surgical insertion distance. PCA is shown to be an accurate reduction method for describing cochlear shape.

Objective: It was the aim of this study to investigate the occurrence of electrode migration of a cochlear implant in patients with and without complaints. Methods: We performed a retrospective case review in a tertiary referral center. The electrode position was evaluated in 35 cochlear implantees, 16 with a CII HiFocus1 (non-positioner) and 19 with a HiRes90K HiFocus1J, using multiplanar reconstructions of the postoperative CT scans. Of 5 patients, a second scan was obtained to evaluate complaints of performance drop, vertigo, tinnitus, headache or nonauditory stimulation. Displacements of the electrode contacts were calculated and displacements of >1 mm were considered a migration. The possible correlation with implant type, insertion depth or presence of complaints was analyzed. Results: Migrations were detected in 10 patients (29%). There was a significant effect of the implant type in favour of the HiFocus1, but no relation with the original insertion depth of the device. In the 5 patients scanned because of complaints, two migrations were detected. Conclusions: In our patient population, electrode migration was not uncommon and turned out to occur in patients with and without complaints.

Objectives: In this study, the effects of the intracochlear position of cochlear implants on the clinical fitting levels were analyzed. Design: A total of 130 adult subjects who used a CII/HiRes 90K cochlear implant with a HiFocus 1/1J electrode were included in the study. The insertion angle and the distance to the modiolus of each electrode contact were determined using high-resolution CT scanning. The threshold levels (T-levels) and maximum comfort levels (M-levels) at 1 year of follow-up were determined. The degree of speech perception of the subjects was evaluated during routine clinical follow-up. Results: The depths of insertion of all the electrode contacts were determined. The distance to the modiolus was significantly smaller at the basal and apical cochlear parts compared with that at the middle of the cochlea (p < 0.05). The T-levels increased toward the basal end of the cochlea (3.4 dB). Additionally, the M-levels, which were fitted in our clinic using a standard profile, also increased toward the basal end, although with a lower amplitude (1.3 dB). Accordingly, the dynamic range decreased toward the basal end (2.1 dB). No correlation was found between the distance to the modiolus and the T-level or the M-level. Furthermore, the correlation between the insertion depth and stimulation levels was not affected by the duration of deafness, age at implantation or the time since implantation. Additionally, the T-levels showed a significant correlation with the speech perception scores (p < 0.05). Conclusions: The stimulation levels of the cochlear implants were affected by the intracochlear position of the electrode contacts, which were determined using postoperative CT scanning. Interestingly, these levels depended on the insertion depth, whereas the distance to the modiolus did not affect the stimulation levels. The T-levels increased toward the basal end of the cochlea. The level profiles were independent of the overall stimulation levels and were not affected by the biographical data of the patients, such as the duration of deafness, age at implantation or time since implantation. Further research is required to elucidate how fitting using level profiles with an increase toward the basal end of the cochlea benefits speech perception. Future investigations may elucidate an explanation for the effects of the intracochlear electrode position on the stimulation levels and might facilitate future improvements in electrode design.

After cochlear reimplantation with the same device, electrode-array position can be accurately replicated and speech perception can be regained or even improved within weeks.