Conclusion: Our study results confirm that it is possible to preserve preoperative hearing levels in the majority of subjects when using the Nucleus 24 Contour Advance provided that there is adherence to the major principles of 'soft surgery'. Our study group demonstrated that 71-86% of subjects showed preservation of preoperative hearing thresholds at 6 months to varying degree.
Objectives: The aim of the study was to assess the degree of residual hearing preserved postoperatively in a group of standard cochlear implant (CI) candidates following implantation via soft surgery with a Nucleus 24 Contour Advance CI. Surgical technique variations from the soft surgery guidelines provided were assessed and their potential impact upon the conservation of residual hearing was examined.
Subjects and methods: A prospective multicentre study involving a within-subject repeated measures design with each subject acting as their own control was performed. Pure-tone audiometric thresholds were assessed and compared in both implanted and contralateral ears for each subject preoperatively as baseline measures and at 6 months postoperatively. Surgeons were asked to complete a questionnaire to capture various aspects of the surgical technique used for each subject. Variations in the surgical technique performed were examined for potential correlation with conservation of residual hearing. Twenty-eight adult subjects, with a severe to profound hearing impairment, were enrolled in the study across eight implant clinics in four countries.
Results: In all, 36% of subjects demonstrated preservation of thresholds to within 10 dB of preoperative thresholds across the frequency range (0.25, 0.5, 1.0, 2.0 and 4.0 KHz) and for the low frequency range (0.25-1.0 KHz). Approximately two-thirds of subjects demonstrated preservation of preoperative thresholds to within 20 dB. Preservation of low frequency thresholds post-implant was shown to correlate moderately with cochleostomy site, being more likely for subjects with a site anterior-inferior to the round window but also possible with inferior locations; weakly with cochleostomy size, being more likely when smaller than 1.2 mm; and also with the use of Healon as a sealant and lubricant. Preservation of hearing thresholds across up to 4000 Hz was shown to correlate weakly with the use of suction following opening of the endostium and with bone dust contamination, both having a negative effect upon preservation, while no correlation was observed with the preservation of thresholds for low frequencies alone.