Cochlear implants provide an effective treatment option for those with severe hearing loss, including those with preserved low frequency hearing. However, certain issues can reduce implant efficacy including intracochlear tissue response and delayed loss of residual acoustic hearing. We describe a mouse model of cochlear implantation with chronic electric stimulation that can be used to study cochlear implant biology and related pathologies. Twelve normal hearing adult CBA/J mice underwent unilateral cochlear implantation and were evenly divided into one group receiving electric stimulation and one not. Serial impedance and neural response telemetry (NRT) measurements were made to assess implant functionality. Functionality was defined as having at least one electrode with an impedance ≤ 35 kOhms. Mouse cochleae were harvested for histology and 3D x-ray microscopy 21 days post-operatively, or, in case the implant was still functional, at a later time point when the implant failed. A separate experiment measured the hearing preservation rate in 7 adult CBA/J mice undergoing unilateral cochlear implantation with serial auditory brainstem response (ABR) and distortion product otoacoustic emissions (DPOAE). Implants maintained functionality for a mean of 35 days in the non-stimulated group and 19.8 days in the stimulated group. Reliable NRT and behavioral responses to electric stimulation were recorded. A robust intracochlear peri-implant tissue response with neo-ossification was seen in all cochleae. Six of seven mice maintained intact low frequency hearing up to 6 weeks following cochlear implantation. We demonstrate the feasibility of cochlear implantation and behaviorally significant electric stimulation in the mouse, with the potential for hearing preservation. This model may be combined with established mouse models of hearing loss and the large genetic and molecular research toolkit unique to the mouse for mechanistic and therapeutic investigations of cochlear implant biology.

Objective(s): Robotic‐assisted electrode array (EA) insertion is a promising technique that may enhance hearing preservation in cochlear implant (CI) surgery. The purpose of our study is to understand the extent to which robotic‐assisted EA insertion improves hearing preservation. Methods: Twenty‐four adult patients underwent CI surgery with manual EA insertion and 27 adult patients underwent CI surgery with robotic‐assisted EA insertion using the iotaSOFT system. The EAs used included the Flex 20/24/26. The primary outcome variable was low frequency pure‐tone average (LFPTA), defined as mean audiometric threshold at 125, 250, and 500 Hz. This was measured preoperatively, at initial activation (within 4 weeks of surgery), and subsequently at 2 weeks, 3 months, 6 months, and 1 year. Functional acoustic hearing was defined as LFPTA < 80 dB HL. Results: Seventeen out of 24 patients (71%) in the manual insertion group and 23 out of 27 patients (85%) in the robotic‐assisted EA insertion group had preserved functional acoustic hearing (< 80 dB HL) up till 1 year (Fisher's exact test (two‐tailed) is not statistically significant, p = 0.31). The number needed to treat with robotic‐assisted EA insertion to prevent one additional negative outcome of loss of functional acoustic hearing would be 7 (1/0.14). Conclusion: Robotic‐assisted EA insertion is associated with improved hearing preservation over 1 year compared with manual insertion. Hearing preservation leads to improved outcomes and therefore every effort should be made to preserve the delicate structure and function of the cochlea during EA insertion. Robotic‐assisted EA insertion advances that objective. Level of Evidence: III (cohort study).

This study evaluates intracochlear electrocochleography (ECochG) for real-time monitoring during cochlear implantation. One aim tested whether adjusting the recording electrode site would help differentiate between atraumatic and traumatic ECochG amplitude decrements. A second aim assessed whether associations between ECochG amplitude decrements and post-operative hearing loss were weaker when considering hearing sensitivity at the ECochG stimulus frequency compared to a broader frequency range. Eleven adult cochlear implant recipients who were candidates for electro-acoustic stimulation participated. Single-frequency (500-Hz) ECochG was performed during cochlear implantation; the amplitude of the first harmonic of the difference waveform was considered. Post-operative hearing preservation at 500 Hz ranged from 0 to 94%. The expected relationship between ECochG amplitude decrements and hearing preservation was observed, though the trend was not statistically significant, and predictions were grossly inaccurate for two participants. Associations did not improve when considering alternative recording sites or hearing sensitivity two octaves above the ECochG stimulus frequency. Intracochlear location of a moving recording electrode is a known confound to real-time interpretation of ECochG amplitude fluctuations, which was illustrated by the strength of the correlation with ECochG amplitude decrements. Multiple factors contribute to ECochG amplitude patterns and to hearing preservation; these results highlight the confounding influence of intracochlear recording electrode location on the ECochG.

Objective(s): Robotic‐assisted electrode array (EA) insertion is a promising technique that may enhance preservation of residual acoustic hearing after cochlear implant (CI) surgery. The purpose of this study is to evaluate the impact of robotic‐assisted EA insertion on rates of delayed‐onset hearing loss (DOHL). Methods: Sixty (Advanced Bionics [AB]: 30, MED‐EL: 30) adult patients underwent CI surgery with manual EA insertion and 29 (AB: 13, MED‐EL: 16) with robotic‐assisted insertion using the iotaSOFT system. The primary outcome variable was longitudinal change in low frequency pure‐tone average (LFPTA). DOHL was defined as a decrease in LFPTA of > 10 dB compared to previous best postoperative LFPTA. Results: Twenty‐two (37%) out of the 60 subjects in the manual cohort and two (7%) out of the 29 subjects in the robotic‐assisted cohort had DOHL over the entire length of available follow‐up ( p = 0.002, Fisher's exact test, two‐tailed). When evaluating DOHL results for subjects who had LFPTA data at 12 months (±4 weeks) post initial activation, 11 (29%) out of the 38 (AB: 15, MED‐EL: 23) subjects in the manual cohort and zero (0%) out of the 18 (AB: 8, MED‐EL: 10) subjects in the robotic‐assisted cohort had DOHL ( p = 0.011, Fisher's exact test, two‐tailed). The number needed to treat was 4. Conclusion: Robotic‐assisted EA insertion is associated with a clinically meaningful reduction in rates of DOHL. Preservation of residual acoustic hearing is a critical goal in CI surgery, and robotic‐assisted EA insertion contributes towards achieving this goal. Level of Evidence: 3.