Electrode Translocations in Perimodiolar Cochlear Implant Electrodes: Audiological and Electrophysiological Outcome

Despite using the soft-surgery technique, cochlear implantation may increase the damage of the intracochlear structures due to a scalar translocation of the electrode. The aim of this work was to investigate the incidence as well as the audiological and electrophysiological outcome for electrode translocations and complete scala tympani insertions of perimodiolar electrodes within a large group of patients.

The investigations were performed retrospectively on 255 adult subjects with a Nucleus Contour Advance or Slim Modiolar electrode (Cochlear Ltd.). The scalar position was assessed by postoperative rotational tomography. Intraoperative and one year after CI activation measured ECAP thresholds were examined as well as the postoperative speech recognition in quiet using the Freiburg monosyllable word test.

The incidence of a translocation was significantly lower with the Slim Modiolar than with the Contour Advance electrode (5.1% versus 32.3%; p<0.05). With a scala tympani placement the median speech recognition score was 75% (range: 20- 100%) with the Contour Advance and 72.5% (range: 27.5-95%) with the Slim Modiolar electrode. In cases with an electrode translocation, speech recognition scores show a median of 75% (range: 45-100%) and 73.8% (range: 40-80%), respectively. No significant differences in speech recognition were found between translocations and scala tympani insertions with both electrodes. Compared to scala tympani insertions, electrode translocations yielded higher ECAP thresholds at apical and medial electrode contacts (p<0.05).

The incidence of an electrode translocation is determined for both perimodiolar electrode types analyzed in this work. ECAP measurements provide additional information for detecting translocations compared to radiological imaging. However, the postoperative speech recognition in quiet was not affected by the scalar position in the electrodes examined here.