Electrophysiological effects of electrode pull-back in cochlear implant surgery

Dynamic Behavior and Insertional Forces of a Precurved Electrode Using the Pull-Back Technique in a Fresh Microdissected Cochlea

HYPOTHESIS

This study evaluated the utility of the pull-back technique in improving perimodiolar positioning of a precurved cochlear implant (CI) electrode array (EA) with simultaneous insertion force profile measurement and direct observation of dynamic EA behavior.

BACKGROUND

Precurved EAs with perimodiolar positioning have improved outcomes compared with straight EAs because of lowered charge requirements for stimulation and decreased spread of excitation. The safety and efficacy of the pull-back technique in further improving perimodiolar positioning and its associated force profile have not been adequately demonstrated.

METHODS

The bone overlying the scala vestibuli was removed in 15 fresh cadaveric temporal bones, leaving the scala tympani unviolated. Robotic insertions of EAs were performed with simultaneous force measurement and video recording. Force profiles were obtained during standard insertion, overinsertion, and pull-back. Postinsertion CT scans were obtained during each of the three conditions, enabling automatic segmentation and calculation of angular insertion depth, mean perimodiolar distance ( Mavg ), and cochlear duct length.

RESULTS

Overinsertion did not result in significantly higher peak forces than standard insertion (mean [SD], 0.18 [0.06] and 0.14 [0.08] N; p = 0.18). Six temporal bones (40%) demonstrated visibly improved perimodiolar positioning after the protocol, whereas none worsened. Mavg significantly improved after the pull-back technique compared with standard insertion (mean [SD], 0.34 [0.07] and 0.41 [0.10] mm; p < 0.01).

CONCLUSIONS

The pull-back technique was not associated with significantly higher insertional forces compared with standard insertion. This technique was associated with significant improvement in perimodiolar positioning, both visually and quantitatively, independent of cochlear size.

Effect of Proximity to the Modiolus for the Cochlear CI532 Slim Modiolar Electrode Array on Evoked Compound Action Potentials and Programming Levels

BACKGROUND

The first surgeries with CI532 showed an effect of the proximity of the electrode to the modiolus on the Evoked Compound Action Potentials (ECAPs).

OBJECTIVES

Objectives of the study were to investigate the effect of the "pullback" procedure on intraoperative ECAP responses in three different electrode array positions and additionally to compare behavioral thresholds with the thresholds obtained in a group of patients using the standard insertion. The hypothesis of this study is that pullback will cause lower ECAPs and behavioral thresholds.

PATIENTS

The study included 40 patients, 20 in the pullback insertion group and 20 in the standard insertion group (without pullback).

METHOD

During insertion of the CI532 electrode array, ECAP was performed in three different positions for the pullback group: at initial insertion, at over-insertion, and after pullback. Insertion was monitored by fluoroscopy. In the standard group, ECAP was performed at the initial position, which is also the final position. ECAP thresholds (T-ECAPs) were compared within subjects at the initial and the final position in the pullback group and between groups in the final positions of the pullback and standard groups. Programming levels (C- and T-levels) were compared between the two groups 1 year after switch-on.

RESULTS

Intraoperative measurements pullback shows lower average T-ECAPs after pullback compared to thresholds in initial position. Comparison of intraoperative T-ECAPs at the final positions showed no statistically significant difference between the pullback group and the standard insertion group. Furthermore, 1 year after switch-on there was no statistically significant difference in C- and T-levels between the two groups.

CONCLUSION

The pullback maneuver of the CI532 electrode array after an over-insertion gave significantly lower T-ECAPs compared to the thresholds at the initial position. However, the between-groups analysis of pullback and standard insertion showed neither significantly different T-ECAPs nor different programming levels. Because T-ECAPs and programming levels vary considerably between subjects, large groups are required to detect differences between groups. Additionally, the effect pullback technique to preserving the residual hearing is not known yet.

Factors Influencing Speech Perception in Adults With a Cochlear Implant

Supplemental Digital Content is available in the text.

The primary objective of this study is to identify the biographic, audiologic, and electrode position factors that influence speech perception performance in adult cochlear implant (CI) recipients implanted with a device from a single manufacturer. The secondary objective is to investigate the independent association of the type of electrode (precurved or straight) with speech perception.

Effects of in vivo repositioning of slim modiolar electrodes on electrical thresholds and speech perception

The slim modiolar electrode has been reported to ensure better modiolar proximity than previous conventional perimodiolar electrodes and consistently high scala tympani localization. Nonetheless, variability in modiolar proximity exists even among slim modiolar electrodes, still leaving room for further improvement of modiolar proximity, which may positively affect functional outcomes. Given this, the pull-back maneuver was reported to increase the modiolar proximity of slim modiolar electrodes in a cadaveric study, but in vivo repositioning effects remain to be established. Here we identified that the pull-back maneuver led to better modiolar proximity than conventional insertion while maintaining a similar angular insertion depth. Notably, the reduced electrode-modiolus distance from the pull-back maneuver was associated with significantly lower impedances across electrodes postoperatively as well as reduced intraoperative electrophysiological thresholds than conventional insertion. Among adult cochlear implant recipients, this maneuver resulted in significantly better sentence recognition scores at three months postoperatively when compared to those with a conventional insertion; however, this benefit was not observed at later intervals. Collectively, slim modiolar electrodes with the pull-back maneuver further enhance the modiolar proximity, possibly leading to better open-set sentence recognition, at least in the early postoperative stage.

The evaluation of a slim perimodiolar electrode: surgical technique in relation to intracochlear position and cochlear implant outcomes

Purpose

In cochlear implantation (CI), the two factors that are determined by the surgeon with a potential significant impact on the position of the electrode within the cochlea and the potential outcome, are the surgical technique and electrode type. The objective of this prospective study was to evaluate the position of the slim, perimodiolar electrode (SPE), and to study the influence of the SPE position on CI outcome.

Methods

Twenty-three consecutively implanted, adult SPE candidates were included in this prospective cohort study conducted between December 2016 and April 2019. Mean age at surgery was 59.5 years. Mean preoperative residual hearing was 92.2 dB. Intra-operative fluoroscopy and high-resolution computed tomography scans were performed to evaluate electrode position after insertion using a cochleostomy (CS) approach. Follow-up was 12 months after implantation; residual hearing (6–8 weeks) and speech perception (6–8 weeks and 12 months) were evaluated in relation to the intracochlear SPE position.

Results

In most patients in whom the SPE was positioned in the scala tympani residual hearing was preserved [mean absolute increase in PTA of 4.4 dB and 77.2% relative hearing preservation (RHP%)]. Translocation into the scala vestibuli occurred in 36% of the insertions, resulting in a mean absolute increase in PTA of 17.9 dB, and a RHP% of 19.2%. Participants with a translocation had poorer speech perception scores at 12-month follow-up.

Conclusion

Given the incidence of CS-associated translocations with the SPE and the negative effect on outcome, it is advised to insert the SPE using the (extended) round window approach.

Intracochlear Pressure Changes After Cochlea Implant Electrode Pullback-Reduction of Intracochlear Trauma

Objective

Different aspects should be considered to achieve an atraumatic insertion of cochlear implant electrode arrays as an important surgical goal. Intracochlear pressure changes are known to influence the preservation of residual hearing. By using the intraoperative “pullback technique,” an electrode position closer to the modiolus can be achieved than without the pullback. The aim of the present study was therefore to investigate to what extent the pullback technique can influence intracochlear pressure changes.

Methods

Insertions of cochlear implant electrodes were performed in an artificial cochlear model with two different perimodiolar arrays. Intracochlear pressure changes were recorded with a micro‐optical pressure sensor positioned in the apical part of the cochlear. After complete insertion of the electrode array, a so‐called pullback of the electrode was performed.

Results

Statistically significant pressure differences were measured if the electrode array was wet (ie, moisturized) during the pullback. Relative pressure changes in electrodes with smaller total volume are lower than pressure changes in larger electrodes.

Conclusion

The preservation of residual hearing and, thus, the resulting postoperative audiological outcome has a major impact on the quality of life of the patients and has become of utmost importance. Intracochlear pressure changes during the pullback manoeuver are small in absolute terms, but can even be still reduced statistically significantly by a moistening the electrode before insertion. Using the pullback technique in cases with residual hearing does not affect the probability of preservation of residual hearing but could lead to a better audiological outcome.

Level of Evidence

NA

Electric compound action potentials (ECAPs) and impedances in an open and closed operative site during cochlear implantation

INTRODUCTION

In patients undergoing cochlear implantation, intraoperative measures of impedance and electrically evoked compound action potentials (ECAPs) are used to confirm device integrity and electrode array position. However, these electrophysiological parameters have been shown to decrease over time, with a small decrement observable as early as 24 h post implantation and becoming more apparent after 6 months. Whether the intraoperatively measured impedances and ECAPs recorded immediately after electrode insertion versus later in the operation or in an open versus closed operative site vary has not been documented. Such variation in measurement procedure may affect the ultimate operative outcome.

PATIENTS AND METHODS

Between February and October 2016, 38 patients received a cochlear implant (Cochlear^®), with half receiving a CI 522 device and the other half receiving a CI 512 device. These patients were distributed into three groups. In the first (group A; n = 21), the impedance and threshold neural response telemetry (tNRT) measures were taken before (M1) and after cutaneous suture (M2), whereas in the second group (group B; n = 11) they were taken twice in the open operative site, once at the time of electrode insertion (M1) and then again 10 min later (M2). The last group (group C; n = 6) was measured only once after a 10 min waiting time before closing the operative site.

RESULTS

tNRTs of both group A and B were significantly higher at M1 than measured at M2. The magnitude of change in tNRT did vary significantly by group (P = .027) with group A having a bigger decrease than group B. For impedances there was evidence for a significant difference in M2 between the three groups (P = .012), with group C having significantly higher values compared to group A and B.

CONCLUSION

Intraoperative tNRT measures change significantly over time, including within the first 10 min of implantation. One underlying etiology of this phenomenon for tNRTs seems to be the condition of the surgical site whereas changes of impedances can be best explained by the 'electrochemical cleaning' theory associated with the first stimulation of the electrode. However, for both impedances and tNRTs there also is an important impact of time as well as of acute perioperative changes in electrical conductivity.

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.

Advances to electrode pullback in cochlear implant surgery

Objective. To observe the intracochlear behavior of a cochlear implant electrode insertion technique (called “pullback”) in temporal bones. Study Design. Experimental. Settings. Tertiary referral center. Method. The change of the intracochlear electrode position was investigated under various conditions of an electrode pullback (N = 54) in 9 radiologically, size-estimated temporal bones (TBs). Those TBs were prepared by removal of the cochlear scalar roof to apply digital video capture procedures to monitor the pullback procedures. The digitally captured pictures were analyzed with specific software. Results. An optimal pullback of the electrode varied between 1.37 mm and 2.67 mm. While a limited pullback is without risk, an extended pullback bears the risk of removing the electrode tip out of its initial position or out of the cochlea. A correlation between cochlear size and the amount of pullback was not found. Conclusion. An initial insertion to the first or the second marker on the electrode followed by a limited pullback of about 1.37 mm to 1.5 mm can be recommended to achieve an optimized perimodiolar position. A pullback of up to two marker positions bears the risk of removing the electrode tip out of its initial position.

Assessing the placement of a cochlear electrode array by multidimensional scaling

Correct placement of the electrode is crucial for cochlear implantation (CI) surgery. It determines the access to the auditory nerve and subsequent hearing performance. Here, we propose an objective measures tool that can partially verify the electrode position. The intracochlear spread of the electrical fields is measured and analyzed by means of multidimensional scaling resulting in an intuitive visual representation. The user can then detect major issues, such as electrode foldover or ossification. Other implantation issues, such as electrode migration into the scala vestibuli, may not significantly alter the electrical conduction pattern and remain undetected. Still, as the measurement is quick and readily available, it may be a valuable intraoperative verification tool.

The effect of pulling out cochlear implant electrodes on inner ear microstructures: a temporal bone study

The exchange of an cochlear implant or the re-positioning of an electrode have become more frequently required than a decade ago. The consequences of such procedures at a microstructural level within the cochlea are not known. It was the aim of the present study to further investigate the effects of an CI electrode pull-out. Therefore 10 freshly harvested temporal bones (TB) were histologically evaluated after a cochlear implant electrode pull-out of a perimodiolar electrode. In additional 9 TB the intrascalar movements of the CI electrode while being pulled-out were digitally analysed by video- capturing. Histologically, a disruption of the modiolar wall or the spiral osseous lamina were not observed. In one TB, a basilar membrane lifting up was found, but it could not be undoubtedly attributed to the pull-out of the electrode. When analyzing the temporal sequence of the electrode movement during the pull-out, the electrode turned in one case so that the tip elevates the basilar membrane. The pull- out of perimodiolarly placed CI electrodes does not damage the modiolar wall at a microstructural level and should be guided (e.g., forceps) to prevent a 90 o turning of the electrode tip into the direction of the basilar membrane.

Audiological outcome of the pull-back technique in cochlear implantees

OBJECTIVES/HYPOTHESIS

The distance of the cochlear implant electrode contacts to the modiolus can be reduced by a surgical technique called "pull-back." This procedure changes the location of the fully inserted electrode array by moving the electrode out of the cochlea until the first silicon ring is visible in the cochleostomy. This leads to a more focused stimulation, which in turn could possibly improve hearing performance. The objective of the present study was to investigate the influence of the pull-back technique on frequency difference limens (FDL) and speech perception.

STUDY DESIGN

Double-blind trial.

METHODS

Twelve pull-back and 12 matched controls (matched by age, gender, duration of deafness, and duration of implant use) were used. Twenty-four patients were implanted with the Nucleus-24 Contour Advance array. In 12 patients the pull-back technique was used and in 12 matched controls a standard insertion technique was applied. Twelve months after the initial stimulation speech perception, spread of neuronal excitation (SOE) at electrodes 5, 10, and 15; and FDLs at 1, 2, and 4 kHz were measured.

RESULTS

There was no significant difference of speech perception performance between the two groups. However, the mean FDL for the 4 kHz reference tone was significantly lower in the pull-back group compared to the controls. The SOE was significantly reduced at basal, middle, and apical electrodes in the electrode pull-back group.

CONCLUSIONS

The pull-back technique seems to have its greatest effect on perimodiolar position in the basal regions of the cochlea. Therefore, it is most likely to observe improved FDL in the 4 kHz region. Current speech recognition tests do not reflect the lower FDL.