Impact of insertion depth on auditory performance with lateral wall nucleus CI622 electrodes in postlingually deafened adults

This study examines the relationship between the insertion depth of lateral wall CI622 electrodes and auditory performance in postlingually deafened adult cochlear implant (CI) patients. A total of 70 CI patients with 73 implants were evaluated, analyzing preoperative and postoperative imaging (CBCT) to assess cochlear length, electrode insertion depth, cochlear coverage, and insertion angle. Postoperative performance was measured using the Freiburger Monosyllabic Speech Test in quiet at 65 dB SPL, the HSM Sentence Test at 10 dB SNR, and the adaptive Oldenburg Sentence Test in S0N0 condition. The study aimed to determine if the positioning parameters of the electrode array correlated with postoperative performance. The average cochlear length of the cohort was 34 mm±2 mm (mean±standard deviation; range 29.6 to 38.7 mm). The average electrode insertion depth was 21.1±1.4 mm (range: 18.8 to 23.8) with an insertion angle of 384°±19° (range: 360° to 430°), achieving cochlear coverage of 62±4% (range 54% to 74%). One year post-insertion, patients achieved an average speech understanding of 65±21% in the Freiburger Monosyllabic Test, 25±24% in the HSM Sentence Test, and a Speech Reception Threshold (SRT) of 3.3±5 dB SNR in the adaptive Oldenburg Sentence Test. The study found a weak correlation between deeper electrode insertion and improved speech comprehension, although this correlation was not statistically significant. Further investigation with matching of the individual patients with respect to relevant prognostic factors in order to achieve comparability of the insertion parameters in the respect of their performance and further enlargement of the cohort size is planned.