Evaluation of insertion quality of a slim perimodiolar electrode array.

OBJECTIVES: The influence of cochlear morphology and electrode array design on scalar position and dislocation rates is of great interest in CI surgery. The aim of this study is to evaluate scalar position and specific points of dislocation in relation to cochlear morphology in patients implanted with a new slim perimodiolar electrode array. MATERIALS AND METHODS: Patients were implanted using the slim modiolar electrode array (= SMA) (= 532/632 electrode array of Cochlear™). Postoperative imaging was performed via cone beam computed tomography (CBCT) and the scans were analyzed regarding cochlear morphology (distances A and B and cochlear height), scalar location of the electrode array, basal insertion depth and apical insertion angle. Furthermore, electrode array design and surgical protocols were evaluated. RESULTS: 81 ears implanted with the SMA were retrospectively included. We evaluated 3 electrode array tip fold over intraoperatively via X-ray imaging and performed revision during the same surgery. The CBCT scans showed 76 initial scala tympani (ST) insertions without dislocation. Two ears showed a dislocated array, one at 77° and the other at 163°. Three arrays were inserted into scala vestibuli (SV) via cochleostomy. These patients showed no signs of obliteration. Cochlear morphology showed no influence on angular insertion depth and scalar position. CONCLUSIONS: The SMA showed a very low rate of scalar dislocations due to its slim electrode array design (2.7%). We could find a learning curve regarding the handling and the risk of dislocation and tip fold over with this electrode array. The rate of intraoperative tip fold over detection via X-ray imaging was 3.7%. Therefore, we highly recommend X-ray imaging and transimpedance matrix measurements within the surgery protocol. Scala vestibuli insertions happened in patients with cochleostomy only. We could identify two specific points of dislocation depending on electrode array design.

Evaluation of hearing preservation in adults with a slim perimodiolar electrode.

PURPOSE: Numerous endeavors have been undertaken to preserve hearing in cochlear implant (CI) patients. Particularly, optimization of electrode array design aims at preservation of residual hearing (RH). This study examines whether a slim perimodiolar (PM) electrode array could bear the capability to preserve hearing. METHODS: A total of 47 patients underwent cochlear implantation receiving the PM electrode. (i) Patients with pure tone audiogram (PTA) thresholds better than 85 dB and/or hearing loss for Freiburg speech test numbers less than 60 dB and more than 50% maximum monosyllabic understanding were assigned to the RH group (n = 17), while all others belonged to the noRH group (n = 30). (ii) Another group implanted with a slim straight, lateral wall (LW) electrode was recruited for comparison. RESULTS: We compared 17 RH-30 noRH patients all receiving the PM electrode. RH in PM recipients decreased faster than in LW recipients. No significant differences were observed between both (RH v/s noRH) groups in NRT thresholds, Freiburg speech test and A§E® phonemes. Analogous satisfaction levels were indicated through the questionnaires in terms of sound quality, hearing in silence, noise and directional hearing in both groups. CONCLUSIONS: The results suggest that hearing preservation is influenced not only by electrode shape but various factors. This study opens an avenue for further investigations to elucidate and enumerate the causes for progressive hearing loss.

Synchrotron radiation X-ray microtomography for the visualization of intra-cochlear anatomy in human temporal bones implanted with a perimodiolar cochlear implant electrode array.

Recently, synchrotron radiation computed microtomography (SRµCT) has emerged as a promising tool for non-destructive, in situ visualization of cochlear implant electrode arrays inserted into a human cochlea. Histological techniques have been the `gold standard' technique for accurate localization of cochlear implant electrodes but are suboptimal for precise three-dimensional measurements. Here, an SRµCT experimental setup is proposed that offers the benefit of a high spatial and contrast resolution (isotropic voxel size = 4.95 µm and propagation-based phase-contrast imaging), while visualizing the soft-tissue structures and electrode array of the cochlear implant simultaneously. In this work, perimodiolar electrode arrays have been tested, which incorporate thick and closely spaced platinum-iridium contacts and wiring. These data can assist cochlear implant and hearing research, can be used to verify electrode segmentation techniques for clinical computed tomography or could be utilized to evaluate cochlear implant electrode array designs.

Minimizing Intracochlear Pressure: Influence of the Insertion Sheath.

OBJECTIVE: Atraumatic cochlear implantation (CI) and insertion of the electrode in particular are major goals of recent CI surgery. Perimodiolar electrode arrays need a stylet or exosheath for insertion. The sheath can influence the intracochlear pressure changes during insertion of the electrode. The aim of this study was to modify the insertion sheath to optimize intracochlear pressure changes. METHODS: In an artifical cochlear model, 7 different modified insertion sheaths were used. The intracochlear pressure was measured with a micro-optical sensor in the apical part of the model cochlea. RESULTS: Significant lower intracochlear pressure changes were observed when the apical part of the insertion sheath was either shortened or tapered. Modification of the stopper does influence the intracochlear pressure significantly. CONCLUSION: Modification of the insertion sheath leads to lower intracochlear pressure gain. The differences and impact on intracochlear pressure changes found in this study underline the importance of even subtle modifications of the electrode insertion technique.

Comparison of electrophysiological parameters between perimodiolar and lateral wall electrodes in paediatric cochlear implant users.

PURPOSE: (1) To compare the in vivo impedances of electrical contacts of the Nucleus Contour Advance (CA) perimodiolar electrodes and the Nucleus Slim Straight (SS) lateral wall electrodes. (2) To compare the relation between the electrode contact impedances and the behavioural T-/C-levels for both types of electrodes. METHODS: Retrospective case review in two quaternary otologic referral centres was performed. Data on the impedance of the electrode contacts and the T-/C-levels have been collected from 70 consecutive paediatric CI patients. RESULTS: (1) SS electrodes show significantly higher impedance values of the contacts compared to the CA electrodes. This can be explained by differences in the active surface of the electrode contacts and is true for the whole electrode arrays. (2) There are significant negative correlations observed between the impedances of the electrode contacts and the behaviourally measured T-/C-levels. (3) The strength correlation between the electrode impedances and the behavioural T-/C-levels is significantly higher and the T-/C-level variability is lower for the perimodiolar CA electrodes than for the lateral wall SS electrodes. CONCLUSIONS: There exist significant differences in the contact impedance between different cochlear implant electrode arrays. These differences could influence the implant programming parameters and should be considered in any protocols related to automatic implant programming based on objective measures. The predictive value of the electrode impedances for the behavioural T-/C-levels is higher for the perimodiolar CA electrodes than for the lateral wall SS electrodes.

Outcomes for a clinically representative cohort of hearing-impaired adults using the Nucleus® CI532 cochlear implant.

PURPOSE: Hearing performance data was collected from a large heterogeneous group of subjects implanted with the Cochlear™ Nucleus® CI532 with Slim Modiolar Electrode, for the purposes of postmarket clinical follow-up. Data was analysed for factors which may predict postoperative speech recognition scores. METHODS: Data was collected retrospectively from five German clinics for 159 subjects from March 2017 to August 2018. Hearing thresholds and recognition scores for monosyllabic words in quiet and sentences in noise were measured preoperatively and at 3 and 6 months postoperatively. RESULTS: There was a mean gain of 44% points (95% CI 39-49%) at 6 months in monosyllable scores in quiet for implanted ears. Preoperative hearing thresholds in implant ears increased systematically with decreasing age; however, younger subjects had better baseline monosyllable scores with hearing aids compared with older subjects. Baseline performance alone explained 14% of the variation in postoperative scores. Residual hearing was preserved on average to within 22 dB at 250 Hz and 30 dB at 500 Hz of preoperative levels. CONCLUSIONS: In a large and varied cohort of routinely treated hearing-impaired adults, speech recognition with the CI532 for German monosyllabic words in quiet at 6 months was equivalent to performance reported at one year or more in other published studies. Although younger subjects had poorer preoperative pure-tone thresholds, they had better preoperative word recognition scores compared with older subjects, and also had higher post implant scores. Further research is required to identify if this phenomenon is just applicable to German health system assessment and referral practices.

Electrophysiological detection of electrode fold-over in perimodiolar cochlear implant electrode arrays: a multi-center study case series.

PURPOSE: It is important for the surgeon to determine the position of the CI electrode array during and after its placement within the cochlea. Most preferably, this should be within the scala tympani to obtain the best audiological outcome. Thus, misplacement into the scala vestibuli or tip fold-over should be prevented. Since there are different ways to ensure proper positioning of the electrode array within the scala tympani (e.g., intraoperative radiography, electrophysiological recordings), our study was aimed at detecting intraoperative electrophysiologic characteristics to better understand the mechanisms of those electrode tip fold-overs. MATERIAL AND METHODS: In a multi-centric, retrospective case-control series, patients with a postoperatively by radiography detected tip fold-over in perimodiolar electrodes were included. The point of fold-over (i.e., the electrode position) was determined and the intraoperative Auto-NRT recordings were analysed and evaluated. RESULTS: Four patients were found to have an electrode tip fold-over (out of 85 implantees). Significant changes of the Auto-NRT recordings were not detected. All tip fold-overs occurred in the most apical part of the electrodes. DISCUSSION: Cochlear implantation for hearing impaired patients plays a decisive role in modern auditory rehabilitation. Perimodiolar electrode arrays may fold over during the insertion and, hence, could have a negative impact on audiological outcome. Characteristic electrophysiologic changes to possibly predict this were not found in our series.

Comparative study of two different perimodiolar and a straight cochlear implant electrode array: surgical and audiological outcomes.

PURPOSE: To compare the surgical and audiological outcomes with two perimodiolar electrode arrays (Nucleus 512-Contour Advance® y Nucleus 532-Slim Perimodiolar®) and a straight electrode array (Nucleus 422/522). METHODS: Patients were retrospectively selected from our cochlear implant program database. Only patients with a history of bilateral, sensorineural postlingually profound hearing loss who underwent cochlear implant surgery with either a N512, a N532 or a N422 were included. Throughout a year of follow-up, pure tone audiometry (PTA), speech perception, Impedances and T-C Thresholds levels were analyzed. Surgical data were also analyzed. RESULTS: 66 patients were included (19-CI532, 20-CI512 and 27-CI422). The most common type of cochlea access with the N532, N512 and N422 was through an extended round window, a promontorial cochleostomy and a pure round window, respectively. No significant differences were observed after 12 months in Mean PTA and Speech recognition. No significant differences were seen in the levels of hearing preservation at frequencies of 250 and 500. The average values of the impedances were significantly higher in the CI group N532 and N422 than in the N512. The mean values of the T and C levels were significantly lower in the CI groups N532 and N422 compared with the N512. CONCLUSIONS: No significant differences were observed after 12 months in Mean PTA and Speech recognition; however, a faster acquisition of auditory results were observed in the group of patients treated with the CI N532. The type of electrode array influences in the type of cochleostomy.

Review of electrode placement with the Slim Modiolar Electrode: identification and management.

Background - Several cochlear implant recipients experience functionality loss due to electrode array mal-positioning. The application of delicate perimodiolar electrodes has many electrophysiological advantages, however, these profiles may be more susceptible to tip fold-over. Purpose - The prompt realization of such complication following electrode insertion would be auspicious, thus the electrode could be possibly repositioned during the same surgical procedure. Methods - The authors present three tip fold-over cases, experienced throughout their work with Slim Modiolar Electrode implants. Implantations were performed through the round window approach, by a skilled surgeon. Standard intraoperative measurements (electric integrity, neural response telemetry, and electrical stapedial reflex threshold tests) were successfully completed. The electrode position was controlled by conventional radiography on the first postoperative day. Results - Tip fold-over was not tactilely sensated by the surgeon. Our subjects revealed normal intraoperative telemetry measurements, only the postoperative imaging showed the tip fold-over. Due to the emerging adverse perception of constant beeping noise, the device was replaced by a CI512 implant after 6 months in one case. In the two remaining cases, the electrode array was reloaded into a back-up sheath, and reinserted into the scala tympani successfully through an extended round window approach. Discussion - Future additional studies using the spread of excitation or electric field imaging may improve test reliability. As all of these measurements are still carried out following electrode insertion, real-time identification, unfortunately, remains questionable. Conclusion - Tip fold-over could be reliably identified by conventional X-ray imaging. By contrast, intraoperative electrophysiology was not sufficiently sensitive to reveal it.

Cochlear Implantation with the CI512 and CI532 Precurved Electrode Arrays: One-Year Speech Recognition and Intraoperative Thresholds of Electrically Evoked Compound Action Potentials.

INTRODUCTION: Precurved cochlear implant (CI) electrode arrays were developed in an attempt to improve the auditory outcome of cochlear implantation, which varies greatly. The recent CI532 (Cochlear Corp., Sydney, Australia) may offer further advantages as its electrode array is thinner than previous precurved CI electrode arrays. The aims here were to investigate 1-year postoperative speech recognition, intraoperative electrically evoked compound action potentials (ECAPs), and their possible relation in patients implanted with a CI532 or its predecessor CI512. METHODS: A retrospective analysis of data from 63 patients subjected to cochlear implantation at the Karolinska University Hospital, Sweden, was performed. Speech recognition of the implanted ear was evaluated using phonemically balanced monosyllabic Swedish words at 65 dB SPL. ECAPs were evaluated using the intraoperative ECAP threshold across ≥8 electrodes generated by the automated neural response telemetry of the CI. RESULTS: The median aided speech recognition score (SRS) 1 year after implantation was 52% (quartile 1 = 40%, quartile 3 = 60%, n = 63) and did not differ statistically significantly between patients with CI512 (n = 38) and CI532 (n = 25). The mean ECAP threshold was 188 CL (current level; SD = 15 CL, n = 54) intraoperatively and did not differ statistically significantly between patients with CI512 (n = 32) and CI532 (n = 22), but the threshold for each electrode varied more between patients with a CI512 (p < 0.0001). A higher mean ECAP threshold was associated with a worse SRS (Spearman's ρ = -0.46, p = 0.0004, n = 54). The association remained among those with a CI512 (Spearman's ρ = -0.62, p = 0.0001, n = 32) when stratified by CI electrode array. CONCLUSION: No statistically significant difference in speech recognition 1 year after cochlear implantation or in mean threshold of ECAP intraoperatively was found between patients with a CI512 and the more recent, slim CI532, but the ECAP thresholds varied more between those with a CI512. A statistically significant association between SRS and mean ECAP threshold was found, but stratified analysis suggests that the association may be true only for patients with a CI512.

Comparison of Place-versus-Pitch Mismatch between a Perimodiolar and Lateral Wall Cochlear Implant Electrode Array in Patients with Single-Sided Deafness and a Cochlear Implant.

BACKGROUND: In electric-acoustic pitch matching experiments in patients with single-sided deafness and a cochlear implant, the observed "mismatch" between perceived pitch and predicted pitch, based on the amended Greenwood frequency map, ranges from -1 to -2 octaves. It is unknown if and how this mismatch differs for perimodiolar versus lateral wall electrode arrays. OBJECTIVES: We aimed to investigate if the type of electrode array design is of influence on the electric-acoustic pitch match. METHOD: Fourteen patients (n = 8 with CI422 + lateral wall electrode array, n = 6 with CI512 + perimodiolar electrode array; Cochlear Ltd.) compared the pitch of acoustic stimuli to the pitch of electric stimuli at two test sessions (average interval 4.3 months). We plotted these "pitch matches" per electrode contact against insertion angle, calculated from high-resolution computed tomography scans. The difference between these pitch matches and two references (the spiral ganglion map and the default frequency allocation by Cochlear Ltd.) was defined as "mismatch." RESULTS: We found average mismatches of -2.2 octaves for the CI422 group and -1.3 octaves for the CI512 group. For any given electrode contact, the mismatch was smaller for the CI512 electrode array than for the CI422 electrode array. For all electrode contacts together, there was a significant difference between the mismatches of the two groups (p < 0.05). Results remained stable over time, with no significant difference between the two test sessions considering all electrode contacts. Neither group showed a significant correlation between the mismatch and phoneme recognition scores. CONCLUSION: The pitch mismatch was smaller for the perimodiolar electrode array than for the lateral wall electrode array.

Cochleostomy and facial recess packing alter cochlear implant electrode location in a human cochlea model.

PURPOSE: Determine the effect of cochleostomy and facial recess packing on cochlear implant electrode distance from the modiolus. MATERIALS AND METHODS: Two otolaryngology residents (PGY5 and PGY6) and one attending ear surgeon performed electrode insertions on a human cochlea model using perimodiolar (Cochlear® Slim Modiolar 532™, CI532) and lateral wall electrodes (Cochlear® Slim Straight 522™, CI522) via a cochleostomy. Packing material was simulated using cotton and placed in the cochleostomy and facial recess under the following conditions: 1) inferior to the electrode, 2) superior, 3) both inferior and superior, and 4) no packing. Distance of the electrode from the modiolus at the proximal, middle, and distal basal turn of the cochlea were measured by photomicrograph analysis. RESULTS: Packing superior to the CI532 resulted in a significant decrease in distance from the modiolus at the middle and distal basal turn compared to the inferior condition, with the largest effect in the middle basal turn (0.25 mm vs. 1.92 mm, respectively, p < 0.001). For the CI522, packing superior similarly resulted in decreased distance to the modiolus when compared to the inferior packing condition at the middle and distal basal turn regions, with the largest effect in the middle basal turn (1.25 mm vs. 1.75 mm, respectively, p = 0.002). CONCLUSIONS: Packing of the cochleostomy site and facial recess has a significant effect on electrode distance from the modiolus in the middle and distal basal turn using a model of a human cochlea. Effects were more pronounced when using the perimodiolar (CI532) electrode.

Cochlear implantation with the nucleus slim modiolar electrode (CI532): a preliminary experience.

To combine the benefits of perimodiolar stimulation with minimal insertion trauma, a thin, pre-curved electrode (CI532) was recently developed by Cochlear Ltd. (Sidney). This array is held straight prior to insertion by an external polymer reloadable sheath that is removed after full electrode insertion. Sixty-seven patients suffering from severe-to-profound sensorineural hearing loss (mean age 42.2 years; mean duration of the hearing loss 19.6 years; mean PTA thresholds at 250-2000 Hz 92.4 dB HL) were implanted with the CI532. Mean duration of surgery was 58.7 min. In 61 patients, a round window (RW) approach was used. In the remaining six cases, a cochleostomy was done because of RW ossification. Impedances and NRT for each electrode are reported. NRT ratio average value was 0.86 ± 0.12 predicting correct scala tympani electrode placement. Post-operative PTA threshold in the implanted ear was 102.9 dB HL. Finally, speech recognition level in quiet at 65 dB HL was 44.6%, after a short follow-up (mean 5.2 months). Our preliminary experience with the new CI532 shows good surgical, electrophysiological, and audiological outcomes. In particular, our results are promising regarding the possibility to achieve minimal insertion trauma and good residual hearing preservation with the use of a deep inserted close modiolar electrode.

Insertion trauma of a cochlear implant electrode array with Nitinol inlay.

The integration of a shape memory actuator is a potential mechanism to achieve a consistent perimodiolar position after electrode insertion during cochlear implant surgery. After warming up, and therefore activation of the shape memory effect, the electrode array will change from a straight configuration into a spiral shaped one leading to a final position close to the modiolus. The aim of this study was to investigate whether the integration of an additional thin wire (referred to as an "inlay") made of Nitinol, a well-established shape memory alloy, in a conventional hearing preservation electrode array will affect the insertion behaviour in terms of increased risk of insertion trauma. Six conventional Hybrid-L electrode arrays (Cochlear Ltd., Sydney, Australia) were modified to incorporate a wire inlay made of Nitinol. The diameter of the wires was 100 µm with a tapered tip region. Electrodes were inserted into human temporal bone specimens using a standard surgical approach. After insertion and embedding in epoxy resin, histological sections were prepared to evaluate insertion trauma. Insertion was straightforward and no difficulties were observed. The addition of a shape memory wire, thin but also strong enough to curl the electrode array, does not result in histologically detectable insertion trauma. Atraumatic insertion seems possible.

Exploration of different electrode types inserted in a 3D model of a patient with incomplete partition type III inner ear malformation.

BACKGROUND: Incomplete partition type III (IP III) represents a rare malformation of the inner ear, posing challenges during cochlear implantation due to inevitable cerebrospinal fluid (CSF) leaks and the potential misplacement of electrodes within the internal auditory canal (IAC). Despite the absence of a consensus on electrode selection, literature suggests both straight and perimodiolar electrodes as viable options for proper insertion. Limited implantation series contribute to the ambiguity in electrode choice. In this study, we evaluated the insertion performance of three electrode types in a 3D model simulating an IP III patient's inner ear. METHODS: A 3D model replicating the inner ear of a patient with IP III undergoing surgery was created, incorporating a canal wall up mastoidectomy and an enlarged round window approach. Insertions were carried out using a straight electrode, a perimodiolar electrode, and a slim perimodiolar electrode, inserted through a sheath in the basal turn of the cochlea. Electrode positions were assessed after each insertion, with each type being tested 20 times. RESULTS: Successful insertion rates were 95 % for the slim perimodiolar electrode, 85 % for the perimodiolar electrode, and 75 % for the slim straight electrode. Notably, the slim perimodiolar electrode required an adapted insertion technique due to the altered cochlear position in IP III cases. Statistical analysis revealed the slim perimodiolar electrode's superiority over the slim straight electrode in achieving successful insertions. CONCLUSIONS: The 3D model of the IP III inner ear proved to be an effective tool for electrode testing and insertion training prior to surgery. Following multiple insertions in the 3D model, the slim perimodiolar electrode demonstrated the highest success rate, emphasizing its potential as the preferred choice for cochlear implantation in IP III cases.

Influence of the Electrode Array Design on Incidence of Vertigo Symptoms and Vestibular Function After Cochlear Implantation.

PURPOSE: To evaluate if a specific type of cochlear implant (CI) electrode array (EA) reveals higher rates/prevalence of vestibular symptoms and to characterize their respective relationship to intracochlear position and objective vestibular function. METHODS: This retrospective study included 71 cochlear implantations in patients older than 18 years. The electrode position within the cochlea, electrode insertion angle, and cochlear coverage were determined from postoperative multiplanar reconstructed cone-beam computed tomography scans. All device manufacturers were represented. Data related to preoperative and postoperative PTA as well as vestibular symptoms in the preoperative and postoperative stages were collected from the patient's records. RESULTS: Twelve of the 71 (16.9%) CI patients experienced vertigo symptoms in the early postoperative period. In 5 (7.0%) patients, the vertigo complaints lasted until the time of the first activation (5-6 weeks postoperative). Postoperative onset of vestibular symptoms was more often seen in patients receiving lateral wall (LW)/straight EAs (19%) compared to perimodiolar/precurved EAs (7%), but this was only a trend and no statistical significance was observed. Moreover, preoperative pathologic caloric responses (CRs) better predicted the postoperative onset of vestibular symptoms. CONCLUSION: The preoperative consideration of a complicated CI-induced vertigo is important in the counseling particularly of elderly patients. We identified some risk factors for post-CI vertigo that should be considered in the patient's counseling: preoperative pathologic CRs, the extent of surgical trauma, and possibly the use of an LW EA, regardless of the length.

Relationship between electrode position and temporal modulation sensitivity in cochlear implant users: Are close electrodes always better?

Temporal modulation sensitivity has been studied extensively for cochlear implant (CI) users due to its strong correlation to speech recognition outcomes. Previous studies reported that temporal modulation detection thresholds (MDTs) vary across the tonotopic axis and attributed this variation to patchy neural survival. However, correlates of neural health identified in animal models depend on electrode position in humans. Nonetheless, the relationship between MDT and electrode location has not been explored. We tested 13 ears for the effect of distance on modulation sensitivity, specifically targeting the question of whether electrodes closer to the modiolus are universally beneficial. Participants in this study were postlingually deafened and users of Cochlear Nucleus CIs. The distance of each electrode from the medial wall (MW) of the cochlea and mid-modiolar axis (MMA) was measured from scans obtained using computerized tomography (CT) imaging. The distance measures were correlated with slopes of spatial tuning curves measured on selected electrodes to investigate if electrode position accounts, at least in part, for the width of neural excitation. In accordance with previous findings, electrode position explained 24% of the variance in slopes of the spatial tuning curves. All functioning electrodes were also measured for MDTs. Five ears showed a positive correlation between MDTs and at least one distance measure across the array; 6 ears showed negative correlations and the remaining two ears showed no relationship. The ears showing positive MDT-distance correlations, thus benefiting from electrodes being close to the neural elements, were those who performed better on the two speech recognition measures, i.e., speech reception thresholds (SRTs) and recognition of the AzBio sentences. These results could suggest that ears able to take advantage of the proximal placement of electrodes are likely to have better speech recognition outcomes. Previous histological studies of humans demonstrated that speech recognition is correlated with spiral ganglion cell counts. Alternatively, ears with good speech recognition outcomes may have good overall neural health, which is a precondition for close electrodes to produce spatially confined neural excitation patterns that facilitate modulation sensitivity. These findings suggest that the methods to reduce channel interaction, e.g., perimodiolar electrode array or current focusing, may only be beneficial for a subgroup of CI users. Additionally, it suggests that estimating neural survival preoperatively is important for choosing the most appropriate electrode array type (perimodiolar vs. lateral wall) for optimal implant function.

Electrode array positioning after cochlear reimplantation from single manufacturer.

OBJECTIVE: To investigate whether revision surgery with the same device results in a change in three key indicators of electrode positioning: scalar location, mean modiolar distance (M¯), and angular insertion depth (AID). METHODS: Retrospective analysis of a cochlear implant database at a university-based tertiary medical center. Intra-operative CT scans were obtained after initial and revision implantation. Electrode array (EA) position was calculated using auto-segmentation techniques. Initial and revision scalar location, M¯, and AID were compared. RESULTS: Mean change in M¯ for all ears was -0.07 mm (SD 0.24 mm; P = 0.16). The mean change in AID for all ears was -5° (SD 67°; P = 0.72). Three initial implantations with pre-curved EAs resulted in a translocation from Scala Tympani (ST) to Scala Vestibuli (SV). Two remained translocated after revision, while one was corrected when revised with a straight EA. An additional five translocations occurred after revision. CONCLUSIONS: In this study examining revision cochlear implantation from a single manufacturer, we demonstrated no significant change in key indicators of EA positioning, even when revising with a different style of electrode. However, the revision EA is not necessarily confined by the initial trajectory and there may be an increased risk of translocation.

Modeling and simulation of cochlear perimodiolar electrode based on composite spring-mass model.

This paper proposes, a method for the physical modeling of the perimodiolar electrode, particularly for the process of recovering its preset shape with the guide wire drawn out, based on the composite spring-mass model by employing the virtual-volumetric spring inspired from the traditional spring-mass model. Simulation experiments of modeling and virtual insertion of perimodiolar electrode were carried out. The results indicated that the mean and standard deviation of the difference between the local deformation angles of the simulated and measured sets of mass points, (1, 2, 3), (2, 3, 4), …, (13, 14, 15), were 6.34° and 5.98°, respectively. Additionally, the physical model of the perimodiolar electrode can reflect the overall morphological changes of the real perimodiolar electrode.

Cochlear implant explantation: An in vitro model to evaluate electrode explant force and trauma.

OBJECTIVES: Removal of a cochlear implant and its intracochlear electrode array is sometimes necessary, potentially causing cochlear explant trauma. Explantation typically occurs years post-implantation by which time reactive tissue has formed around the electrode. We aimed to create an in-vitro electrode explant model to examine explant forces and intracochlear trauma across multiple electrode types and insertion depths. STUDY DESIGN: An in-vitro model using gel to represent tissue surrounding the electrode was developed. Pre-curved electrodes and straight electrodes at different insertion depths (20mm, 25mm, 28mm) were explanted from the model. During explantation, explant force was measured, and high-definition videos were recorded to capture electrode exit path and gel disruption. RESULTS: Explant force patterns varied based on electrode position in the scala tympani. Explant forces did not correlate with gel disruption, which represented explant trauma. The least gel disruption occurred with pre-curved electrodes and the under-inserted straight electrode. The greatest disruption occurred with the overly inserted straight electrode. CONCLUSION: An in-vitro model using gel to mimic tissue surrounding the electrode may provide insights into potential electrode explant trauma. Explant force did not correlate with explant trauma in our model. Pre-curved electrodes and shallower insertion depth of a straight electrode resulted in the least amount of explant trauma.