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Hypothesis: Application of different lubricants during the cochlear implant electrode insertion can affect the insertion forces., Background: Parameters related to cochlear trauma, such as insertion forces, gained more and more importance, especially in regard to preservation of residual hearing. The impact of lubricants on the insertion forces has not been systematically examined yet., Methods: Nucleus 24 Contour Advance electrodes were inserted into an artificial model of the human scala tympani filled with glycerin, sodium hyaluronate (Healon), and water or soap solution of 10% Bathox and 90% distilled water. A specially designed insertion protocol was applied so as any remains of the lubricants in the scala tympani model or on the electrodes' surface could be completely removed. Force measurements were performed by a force measurement system equipped with a 10 N load cell. Average (AF) and maximum (MF) insertion forces were recorded for every lubricant., Results: The highest values were documented with water (AF = 0.139 N, MF = 0.367 N) and the lowest with the soap solution (AF = 0.065 N, MF = 0.148 N). Application of Healon and glycerin resulted in low, comparable values between each other., Conclusion: The application of lubricants affects significantly the electrode insertion forces. As soap solution is not usable, for the time being, in human cochlear implantation, low insertion forces combined with the antiadhesive features of Healon make it a proper lubricant for intracochlear application. Because of the low recorded forces, soap solution represents an ideal experimental model for in vitro electrode-mechanics studies.

Hypothesis: Objective of the present experimental research study was to examine the hypothesis that cochlear implant insertion speed can significantly affect the insertion forces., Background: Cochlear implant electrode insertion forces can influence the insertion trauma and the preservation of residual hearing. The effect of the electrode insertion speed on the insertion forces still remains unknown., Methods: Force measurements were performed while inserting human electrodes in an artificial scala tympani model at different speeds. For these measurements, an Instron 5542 Force Measurement System with a 10 N load cell and Nucleus 24 Contour Advance electrodes were used. Additionally, the insertion speed was measured through videos of 116 human implantations; these videos were recorded in our theaters and involved different surgeons and electrode types., Results: Progressive increase in insertion speed from 10 to 200 mm/min resulted in significant, proportional increase in the average insertion forces from 0.09 to 0.185 N and in the maximum forces from 0.18 to 0.42 N, respectively. The average insertion speed used in the theaters during human cochlear implantations was 96.5 mm/min (range, 42-165.2 mm/min) and depended on the electrode type and the surgeon., Conclusion: High insertion speeds cause significant increase of the forces. Cochlear implant surgeons should use low and stable speeds during the insertion. Insertion speed close to the average value used in the theaters should be applied on experimental models, to approximate human implantation conditions.

Objective: The objective of this study was to investigate the long-term effect of intraoperative application of steroid suspension and coating of the electrode contacts with a thin film of iridium oxide on the intracochlear impedance development after cochlear implantation and on the impedance difference before and after stimulation., Design: Time-dependent development of intracochlear impedances was investigated in 4 different groups of adult patients up to 4 years after implantation. Additionally, during rehabilitation period just after first fitting, impedances before and after stimulation were measured as to investigate the influence of electrical stimulation on the impedances. Results from standard Nucleus 24 Contour (control), standard Nucleus 24 Contour with intraoperative application of steroids, iridium-coated Nucleus 24 Contour, and iridium-coated Nucleus 24 Contour with intraoperative application of steroids were compared., Results: Steroid application reduced impedances significantly throughout the observation period of up to 4 years after implantation. Iridium oxide coating had no effect. Differences between the groups were mainly found on the basal and middle parts of the cochlea, but not close to the tip of the array, also indicating that postoperative fibrous tissue growth is stronger in the basal region of the cochlea. Group mean values of the stimulation effect were not influenced by the different treatments. Nevertheless, only in both steroid-treated groups a correlation between the impedance before stimulation and the stimulation effect was found., Conclusion: Although the differences between control and steroid-treated groups decrease with time, single intraoperative intracochlear steroid deposition was proven to lower postoperative impedances during first 3 to 4 years after implantation probably because of reduction of fibrous tissue growth.

Hypothesis: Chronic implantation and electric stimulation with a human prototype auditory midbrain implant (AMI) array within the inferior colliculus achieves minimal neuronal damage and does not cause any severe complications., Background: An AMI array has been developed for patients with neural deafness and, based on animal studies, has shown to possess potential as an auditory prosthesis in humans. To investigate the safety of the AMI for clinical use, we characterized the histomorphologic effects of chronic implantation and stimulation within its target structure, the inferior colliculus., Methods: Eight cats were chronically implanted for 3 months, and histologic sections were analyzed to assess long-term tissue effects. Four of the 8 cats were additionally stimulated for 60 days (4 h/d) starting 4 weeks after implantation to assess if clinically relevant stimuli further affected the tissue response., Results: In general, both neurons and neuropil surrounding the implant track were apparently unaffected, whereas a fibrillary sheath (approximately 50 microm thick) developed around the array. There was a significant decrease in neuron density 50 to 100 microm away from the track with a significantly elevated number of glial cells out to approximately 250 to 350 microm. Chronic stimulation seemed to improve the tissue response and neuronal survival around the implant, although further studies are needed to confirm this finding., Conclusion: The histomorphologic effects and extent of neuronal damage observed for our AMI array are similar to those of other neural implants currently and safely used in humans. The minimal tissue damage surrounding the implanted array is encouraging with regard to the safety of the array for human use.

Objective: The objective of this study was to investigate the effect of intraoperative application of steroid suspension and coating of the electrode contacts with a thin film of iridium oxide on the short-term, time-dependent development of the intracochlear impedance in adults implanted with the Nucleus 24 Contour electrode., Study Design: The time-dependent development of intracochlear impedances was investigated in four different groups of adult patients at daily and later weekly intervals until the first fitting. The four groups were as follows: 1) standard Nucleus 24 Contour (control, n = 7); 2) standard Nucleus 24 Contour with intraoperative application of steroids (Group S, n = 6); 3) iridium-coated Nucleus 24 Contour control (Group I, n = 8); and 4) iridium-coated Nucleus 24 Contour with intraoperative application of steroids (Group I + S, n = 5). All patients had postlinguistic onset of severe to profound sensorineural hearing loss and no or little benefit of conventional hearing aids. Absence of ossification or any other cochlear anomaly and also absence of signs of retrocochlear or central origin to the hearing impairment bilaterally had to be confirmed preoperatively., Results: Steroid application reduced impedances significantly (Groups S and I + S), whereas iridium coating lowered variance of the impedance among patients but did not reduce the impedance significantly. The steroid-induced reduction is more pronounced at basal electrode contacts. Furthermore, there is some indication that the tissue growth could be faster in patients having the iridium-coated Contour electrode., Conclusion: Provided that the reduction of electrode impedances with application of steroids is persisting, intracochlear application of steroids can be considered on a regular basis. Iridium coating of the electrode contacts seems not to be justified to be included as standard procedure.

Objective: The concept and design of new cochlear implant electrodes is a challenging process. To evaluate new electrode designs, we present a study that uses a microgrinding procedure to evaluate damage to the microstructures of the cochlea resulting from the insertion procedure. In this study, we compared different insertion techniques with the Contour electrode with Softip for placement inside the cochlea and any resulting damage., Methods: Twenty-five fresh frozen human temporal bones were used to compare electrode insertion characteristics with three insertion techniques (i.e., conventional insertion, Advance Off-Stylet performed manually, and Advance Off-Stylet performed with insertion tool) and two prototype variants of the Contour electrode with Softip (referred as Softip I and Softip II in this article). Five temporal bones were used for each arm of the study: Softip I electrode and conventional insertion; Softip I electrode and manual Advance Off-Stylet insertion; Softip I electrode and Advance Off-Stylet insertion with an early experimental insertion tool; Softip II prototype electrode and manual Advance Off-Stylet insertion; and Softip II prototype and Advance Off-Stylet insertion with a prototype insertion tool. The temporal bones were dehydrated and embedded in epoxy and used for the microgrinding procedure. Resulting images were documented and compared with conventional radiographic images., Results: Our results showed that, especially when using the conventional insertion technique with Softip I electrode arrays, basilar membrane perforations were observable. Using the prototype insertion tool, good placement of the electrode array but also two basilar membrane perforations (one with each type of electrode) were observed. In contrast, the Advance Off-Stylet insertion technique did not show basilar membrane perforation with Softip I and II electrodes and resulted in reliable perimodiolar placement of the arrays., Conclusion: Using microgrinding of temporal bones, the Advance Off-Stylet insertion technique was proven to enable more atraumatic insertions of Contour electrodes with Softip and to provide very reliable perimodiolar placements.