Evaluation of an electrode prototype for atraumatic cochlear implantation in hearing preservation candidates: preliminary results from a temporal bone study

Pre- and Postoperative Imaging of Cochlear Implantation in Cadaveric Specimens Using Low-Dose Photon-Counting Detector CT

BACKGROUND AND PURPOSE

Anatomically adapted cochlear implantation and efficient postoperative cochlear implant-fitting strategies benefit from reliable and highly detailed imaging techniques. Since image quality in CT is related to the applied radiation dose, this study aimed to evaluate low-dose cochlear imaging with a photon-counting detector by investigating the accuracy of pre- and postoperative cochlear analysis.

MATERIALS AND METHODS

Photon-counting CT images of 10 temporal bone specimens were acquired with 3 different radiation dose levels (regular dose: 27.1 mGy, low dose: 4.81 mGy, and ultra-low dose: 3.43 mGy) before and after cochlear implant electrode carrier insertion. A clinical scan protocol was used with a tube potential of 120 kV in ultra-high-resolution scan mode (detector collimation 120 × 0.2 mm). The accuracy of cochlear duct length measurements for the organ of Corti and electrode contact determination was investigated for all applied settings by 2 independent otosurgeons.

RESULTS

No substantial differences were ascertained between photon-counting CT scans performed with standard dose and dedicated low-dose imaging regarding the accuracy of neither pre- and postoperative cochlear analysis nor postoperative cochlear implant electrode analysis. Radiation dose reduction of 82.3% (low dose) and 87.3% (ultra-low dose) could be realized compared with the clinical standard protocol.

CONCLUSIONS

Ultra-high-resolution cochlear imaging is feasible with very low radiation exposure when using a first-generation photon-counting CT in combination with dedicated low-dose protocols. The accuracy of pre- and postoperative cochlear analysis with the applied dose reduction settings was comparable with a clinical regular-dose protocol.

On the Design, Fabrication, and Characterization of a Novel Thin-Film Electrode Array for Use in Cochlear Implants

Thin-film electrode arrays (TFEAs) have been developed as an alternative to conventional electrode arrays (CEAs) used in cochlear implants. However, TFEAs produced by microfabrication techniques have not yet been used clinically because their structural and mechanical properties are far from those of CEAs. The aim of this study is to design, fabricate, and investigate the mechanical and tribological behavior and evaluate the performance of different TFEA designs. Finite Element Analysis (FEA) is performed to determine the elastic properties of several designs. A custom-build experimental setup is designed to observe the tribological behavior in different speeds and environments where frictional (lateral) and vertical force (normal force) are measured on a flat surface and within artificial cochlea. According to the FEA results, the maximum stiffness of the CEA is 37.93 mN/mm and 0.363 mN/mm and TFEA-4 has a maximum stiffness of 39.08 mN/mm and 0.306 mN/mm in the longitudinal and transverse axes, respectively. It is shown experimentally that adding a dummy wire to the carrier of the EA enhances both its longitudinal and transverse stiffness, thereby postponing the initiation of dynamic sliding due to the elevated buckling limit. It is also revealed that the type of TFEA support structure affects both normal and frictional forces, as well as the coefficient of friction.

Models of Cochlea Used in Cochlear Implant Research: A Review

As the first clinically translated machine-neural interface, cochlear implants (CI) have demonstrated much success in providing hearing to those with severe to profound hearing loss. Despite their clinical effectiveness, key drawbacks such as hearing damage, partly from insertion forces that arise during implantation, and current spread, which limits focussing ability, prevent wider CI eligibility. In this review, we provide an overview of the anatomical and physical properties of the cochlea as a resource to aid the development of accurate models to improve future CI treatments. We highlight the advancements in the development of various physical, animal, tissue engineering, and computational models of the cochlea and the need for such models, challenges in their use, and a perspective on their future directions.

Anatomical Variations of the Human Cochlea Using an Image Analysis Tool

Understanding cochlear anatomy is crucial for developing less traumatic electrode arrays and insertion guidance for cochlear implantation. The human cochlea shows considerable variability in size and morphology. This study analyses 1000+ clinical temporal bone CT images using a web-based image analysis tool. Cochlear size and shape parameters were obtained to determine population statistics and perform regression and correlation analysis. The analysis revealed that cochlear morphology follows Gaussian distribution, while cochlear dimensions A and B are not well-correlated to each other. Additionally, dimension B is more correlated to duct lengths, the wrapping factor and volume than dimension A. The scala tympani size varies considerably among the population, with the size generally decreasing along insertion depth with dimensional jumps through the trajectory. The mean scala tympani radius was 0.32 mm near the 720° insertion angle. Inter-individual variability was four times that of intra-individual variation. On average, the dimensions of both ears are similar. However, statistically significant differences in clinical dimensions were observed between ears of the same patient, suggesting that size and shape are not the same. Harnessing deep learning-based, automated image analysis tools, our results yielded important insights into cochlear morphology and implant development, helping to reduce insertion trauma and preserving residual hearing.

Assessing the Placement of the Cochlear Slim Perimodiolar Electrode Array by Trans Impedance Matrix Analysis: A Temporal Bone Study

New cochlear implant (CI) electrode arrays provide softer insertion dynamics; however, due to their high flexibility, the possibilities of fold-overs or intraoperative displacements must be taken into account. The position of each individual electrode can only be determined by using high-resolution computed tomography or cone-beam CT. The trans-impedance matrix test (TIM) is an electrophysiological method based on electric field imaging that can provide images of electrode position and electrode folding. Objective: In this experimental research, we evaluated the result of TIM as a method of monitoring cochlear insertion for a precurved slim modiolar electrode array in fresh human temporal bones by analyzing the transimpedance matrix patterns and their correlation with electrode position using high-resolution computed tomography. Material and Methods: Sixteen slim modiolar electrode arrays were inserted into eight fresh Human Temporal Bones. Eight electrodes were inserted according to the correct methodology of insertion, and eight were intentionally folded over. After all insertions, a trans-impedance matrix analysis and a Cone Beam CT (CBCT) were performed in each temporal bone. Results: If we correlated the TIM patterns with the radiological electrode position, we observed that better electrode intracochlear positions indicated more “homogeneous” TIM patterns (intracochlear voltage dropped monotonically as the distance between stimulation and recording contact increased, both toward the apex and toward the base). A correlation where fold-over was detected in the TIM results was found in all eight temporal bone radiological findings. Conclusions: Trans-Impedance Matrix patterns were correlated with the radiological CI electrode position. When a tip fold-over appeared, a matrix with a secondary ridge in addition to the primary ridge was observed in all cases. TIM can be an effective method in the control of electrode positioning.

Insertion trauma of a new cochlear implant electrode: evaluated by histology in fresh human temporal bone specimens

BACKGROUND

Combining acoustic and electrical stimulation has been successfully used in patients with low-frequency residual hearing. Electrode insertion trauma, such as electrode translocation could result in loss of residual hearing.

OBJECTIVES

The aim of the study is to evaluate the LCI-20PI electrode array insertion trauma to the intra-cochlear structures in fresh human temporal bone specimens.

MATERIALS AND METHODS

The LCI-20PI electrode arrays were inserted into scalae tympani through round window membrane in 10 cochleae from ten fresh human cadavers. The intracochlear trauma was evaluated histologically by a scale of 0-4: 0 - no observable trauma, 1 - elevation of basilar membrane, 2 - rupture of basilar membrane or spiral ligament, 3-dislocation into scala vestibuli and 4 - fracture of modiolus or osseous spiral lamina. The insertion depth was measured by radiography.

RESULTS

Histological results revealed no observable trauma in seven specimens; basal membrane elevation and rupture in two specimens; the electrode array misled into scala vestibuli in one specimen. The insertion depth varied from 228° to 288°.

CONCLUSIONS AND SIGNIFICANCE

The insertion of the LCI-20PI electrode arrays caused no trauma in the majority of the fresh temporal bone specimens. No translocation of the electrode arrays from the scala tympani to the scala vestibuli was observed.

The Effect of Ultra-slow Velocities on Insertion Forces: A Study Using a Highly Flexible Straight Electrode Array

OBJECTIVE

The present study sought to 1) characterize insertion forces resulting from a flexible straight electrode array (EA) inserted at slow and ultra-slow insertion velocities, and 2) evaluate if ultra-slow velocities decrease insertion forces independent of other variables.

BACKGROUND

Low insertion forces are desirable in cochlear implant (CI) surgery to reduce trauma and preserve hearing. Recently, ultra-slow insertion velocities (lower than manually feasible) have been shown to produce significantly lower insertion forces using other EAs.

METHODS

Five flexible straight EAs were used to record insertion forces into an inelastic artificial scala tympani model. Eleven trial recordings were performed for each EA at five predetermined automated, continuous insertion velocities ranging from 0.03 to 1.6 mm/s.

RESULTS

An ultra-slow insertion velocity of 0.03 mm/s resulted in a median insertion force of 0.010 N at 20 mm of insertion depth, and 0.026 N at 24.3 mm-the final insertion depth. These forces represent only 24 to 29% of those measured using 1.6 mm/s. After controlling for insertion depth of the EA into the artificial scala tympani model and trial insertion number, decreasing the insertion velocity from 0.4 to 0.03 mm/s resulted in a 50% decrease in the insertion forces.

CONCLUSION

Using the tested EA ultra-slow velocities can decrease insertion forces, independent of variables like insertion depth. Our results suggest ultra-slow velocities can reduce insertion forces at least 60%, compared with humanly feasible continuous velocities (≥0.9 mm/s).

A simple tool to automate the insertion process in cochlear implant surgery

Purpose

Automated insertion of electrode arrays (EA) in cochlear implant surgery is presumed to be less traumatic than manual insertions, but no tool is widely available in the operating room. We sought (1) to design and create a simple tool able to automate the EA insertion process; and (2) to perform preliminary evaluations of the designed prototype.

Methods

A first prototype of a tool with maximum simplicity was designed and fabricated to take advantage of hydraulic actuation. The prototype facilitates automated forward motion using a syringe connected to an infusion pump. Initial prototype evaluation included: (1) testing of forward motion at different velocities (2) EA insertion trials into an artificial cochlear model with force recordings, and (3) evaluation of device handling, fixation and positioning using cadaver head specimens and a surgical retractor. Alignment of the tool was explored with CT imaging.

Results

In this initial phase, the prototype demonstrated easy assembly and ability to respond to hydraulic actuation driven by an infusion pump at different velocities. EA insertions at an ultra-slow velocity of 0.03 mm/s revealed smooth force profiles with mean maximum force of 0.060 N ± 0.007 N. Device positioning with an appropriate insertion axis into the cochlea was deemed feasible and easy to achieve.

Conclusions

Initial testing of our hydraulic insertion tool did not reveal any serious complications that contradict the initially defined design specifications. Further meticulous testing is needed to determine the safety of the device, its reliability and clinical applicability.

First Experience With a New Thin Lateral Wall Electrode in Human Temporal Bones

INTRODUCTION

A modern cochlear implant electrode array design must combine: improved surgical ease of use, structure preservation, particularly important for pediatric application, stable position within the cochlea over time, and a meaningful balance between hearing preservation against addressing sufficient cochlear tissue to support electrical-only hearing. The aim of this study was to investigate a new lateral wall electrode array design from Advanced Bionics on human temporal bones (TBs).

METHODS

Ten fresh-frozen TBs were implanted with the SlimJ electrode array via the round window. The electrode array is 23 mm long, with a cross-section varying from 0.25 × 0.55 mm at the most apical contact to 0.6 × 0.8 mm at the proximal marker contact. To assess location of the electrode array, the TBs were postoperatively scanned using cone beam computed tomography, and histology was performed to assess intracochlear trauma (Grades 0-4).

RESULTS

All electrode arrays were considered easy to insert. The average insertion depth was 432 degrees measured from the round window with a range from 411 to 450 degrees azimuth. Nine out of 10 electrode arrays were inserted fully (<0.5 mm out of the cochlea), one electrode array was left 1.5 mm out of the cochlea. No translocations were observed in all 10 cochleae, slight touching of the basilar membrane at the distal portion of the array was observed in 50% of the cases.

CONCLUSION

The results from the new thin lateral wall electrode array from Advanced Bionics provided consistent scala tympani locations. No translocations were observed and almost all electrode arrays were fully inserted. These results are promising and the new electrode array will be further studied in clinical practice investigating hearing preservation capabilities and speech performance.

Comparison of a Mid Scala and a Perimodiolar Electrode in Adults: Performance, Impedances, and Psychophysics

OBJECTIVES

The HiFocus Mid-Scala electrode array (HFms) is designed to sit within the scala tympani without touching either the lateral wall or the modiolus. The aim of this study was to compare the HFms to the Helix perimodiolar electrode array.

METHOD

Two groups of recipients with Helix (n = 22 ears) and HFms (n = 29 ears) electrode arrays were retrospectively identified and matched by age at implantation and duration of severe to profound deafness. Most comfortable listening levels (M), impedances, Freiburger Monosyllables in quiet, and Oldenburg sentences in adaptive noise were compared at 3, 6, and 12 months postimplant.

RESULTS

Median scores for monosyllables in quiet for the HFms group were significantly better than the Helix group at each test interval (p < 0.05). Speech perception in quiet also significantly improved from 3 to 12 months for both groups (p < 0.001). There was no significant difference between the groups for speech in noise. Impedances were significantly lower for the HFms group at 12 months (p < 0.05) except at the basal end and M levels were generally higher.

CONCLUSIONS

The HFms group had better median performance for monosyllables in quiet than the Helix group at each test interval, although performance in noise was similar. For speech in noise, the HFms group appear to reach optimum performance quicker than the Helix group. Impedances were lower in the HFms group across the array, other than at the most basal end, and support our hypothesis that the HFms assumes a more lateral position within the cochlea than the Helix electrode, although our article did not include imaging data.

An In-Vitro Insertion-Force Study of Magnetically Guided Lateral-Wall Cochlear-Implant Electrode Arrays

Hypothesis:

Insertion forces can be reduced by magnetically guiding the tip of lateral-wall cochlear-implant electrode arrays during insertion via both cochleostomy and the round window.

Background:

Steerable electrode arrays have the potential to minimize intracochlear trauma by reducing the severity of contact between the electrode-array tip and the cochlear wall. However, steerable electrode arrays typically have increased stiffness associated with the steering mechanism. In addition, steerable electrode arrays are typically designed to curve in the direction of the basal turn, which is not ideal for round-window insertions, as the cochlear hook's curvature is in the opposite direction. Lateral-wall electrode arrays can be modified to include magnets at their tips, augmenting their superior flexibility with a steering mechanism. By applying magnetic torque to the tip, an electrode array can be navigated through the cochlear hook and the basal turn.

Methods:

Automated insertions of candidate electrode arrays are conducted into a scala-tympani phantom with either a cochleostomy or round-window opening. The phantom is mounted on a multi-degree-of-freedom force sensor. An external magnet applies the necessary magnetic bending torque to the magnetic tip of a modified clinical electrode array, coordinated with the insertion, with the goal of directing the tip down the lumen. Steering of the electrode array is verified through a camera.

Results:

Statistical t-test results indicate that magnetic guidance does reduce insertion forces by as much as 50% with certain electrode-array models. Direct tip contact with the medial wall through the cochlear hook and the lateral wall of the basal turn is completely eliminated. The magnetic field required to accomplish these insertions varied from 77 to 225 mT based on the volume of the magnet at the tip of the electrode array. Alteration of the tip to accommodate a tiny magnet is minimal and does not change the insertion characteristic of the electrode array unless the tip shape is altered.

Conclusion:

Magnetic guidance can eliminate direct tip contact with the medial walls through the cochlear hook and the lateral walls of the basal turn. Insertion-force reduction will vary based on the electrode-array model, but is statistically significant for all models tested. Successful steering of lateral-wall electrode arrays is accomplished while maintaining its superior flexibility.

De Miguel A, Falcon-González JC. Mechanisms of electrode fold-over in cochlear implant surgery when using a flexible and slim perimodiolar electrode array

OBJECTIVES

This study evaluates the design of a thin perimodiolar cochlear implant electrode array (CI532) and assesses insertion-related rotation and fold-over.

METHODS

The study consisted on a cochlear model and temporal bone insertion studies. Twenty insertions were studied, under four different surgical insertion conditions in vitro, the intracochlear disposition of the electrode array and presence of tip fold over were recorded. Also, eight fresh human temporal bones were studied after insertion in two conditions: correct alignment of the electrode array during the insertion and misaligned. These surgical situations were investigated within this study using a video recording of the dynamics of insertion techniques and X-ray, including fluoroscopy, Cone Beam CT, and digital imaging analysis.

RESULTS

For electrodes inserted with a correct surgical technique, the placement was perfect, within the scala tympani. The wrapping factor was 0.53, and the perimodiolar distance was below 0.3 mm, with a mean insertion depth of 405°.

CONCLUSIONS

A perimodiolar position can be achieved with the new CI532 electrode array. The new electrode also seems to be reliable for atraumatic intracochlear placement in scala tympani (ST).

An Evaluation of the Surgical Trauma to Intracochlear Structures After Insertion of Cochlear Implant Electrode Arrays: A Comparison by Round Window and Antero-Inferior Cochleostomy Techniques

To evaluate the extent of intracochlear damage by histologic assessment of cadaveric temporal bones after insertion of cochlear implants by: round window approach and cochleostomy approach. Cochlear implantation was performed by transmastoid facial recess approach in 10 human cadaveric temporal bones. In 5 temporal bones, electrode insertion was acheieved by round window approach and in the remaining 5 bones, by cochleostomy approach. The bones were fixed, decalcified, sectioned and studied histologically. Grading of insertion trauma was assessed. In the round window insertion group, 2 bones had to be excluded from the study: one was damaged during handling with electrode extrusion and another bone did not show any demonstrable identifiable cochlear structure. Out of the 3 temporal bones, a total of 35 sections were examined: 24 demonstrated normal cochlea, 4 had basilar membrane bulging and 7 had fracture of bony spiral lamina. In the cochleostomy group, histology of 2 bones had to be discarded due to lack of any identifiable inner ear structures. Out of the 3 bones studied, 18 sections were examined: only 3 were normal, 4 sections had some bulge in spiral lamina and 11 had fracture of bony spiral lamina. The fracture of spiral lamina and bulge of basement membrane proportion is relatively higher if we perform cochleostomy as compared to round window approach. Therefore, round window insertion is relatively less traumatic as compared to cochleostomy. However, our sample size was very small and a study with a larger sample is required to further validate these findings.

Insertion forces and intracochlear trauma in temporal bone specimens implanted with a straight atraumatic electrode array

The aim of the study was to evaluate insertion forces during manual insertion of a straight atraumatic electrode in human temporal bones, and post-implantation histologic evaluation of the samples to determine whether violation of intracochlear structures is related to insertion forces. In order to minimize intracochlear trauma and preserve residual hearing during cochlear implantation, knowledge of the insertion forces is necessary. Ten fresh frozen human temporal bones were prepared with canal wall down mastoidectomy. All samples were mounted on a one-axis force sensor. Insertion of a 16-mm straight atraumatic electrode was performed from different angles to induce "traumatic" insertion. Histologic evaluation was performed in order to evaluate intracochlear trauma. In 4 of 10 samples, dislocation of the electrode into scala vestibuli was observed. The mean insertion force for all 10 procedures was 0.003 ± 0.005 N. Insertion forces measured around the site of dislocation to scala vestibuli in 3 of 4 samples were significantly higher than insertion forces at the same location of the cochleae measured in samples without trauma (p < 0.04). Mean force during the whole insertion process of the straight atraumatic electrode is lower than reported by other studies using longer electrodes. Based on our study, insertion forces leading to basilar membrane trauma may be lower than the previously reported direct rupture forces.

Effects of intraoperatively applied glucocorticoid hydrogels on residual hearing and foreign body reaction in a guinea pig model of cochlear implantation

CONCLUSION

The intraoperative application of glucocorticoid-loaded hydrogels seems to cause a reduction in neutrophil infiltration. No beneficial effect on hearing thresholds was detected.

OBJECTIVES

To evaluate the application of dexamethasone- and triamcinolone acetonide-loaded hydrogels for effects on hearing preservation and foreign body reaction in a guinea pig model for cochlear implantation (CI).

METHODS

A total of 48 guinea pigs (n = 12 per group) were implanted with a single channel electrode and intraoperatively treated with 50 μl of a 20% w/v poloxamer 407 hydrogel loaded with 6% dexamethasone or 30% triamcinolone acetonide, a control hydrogel, or physiological saline. Click- and tone burst-evoked compound action potential thresholds were determined preoperatively and directly postoperatively as well as on days 3, 7, 14, 21, and 28. At the end of the experiment, temporal bones were prepared for histological evaluation by a grinding/polishing technique with the electrode in situ. Three ears per treatment group were serially sectioned and evaluated for histological alterations.

RESULTS

The intratympanic application of glucocorticoid-loaded hydrogels did not improve the preservation of residual hearing in this cochlear implant model. The foreign body reaction to the electrode appeared reduced in the glucocorticoid-treated animals. No correlation was found between the histologically described trauma to the inner ear and the resulting hearing threshold shifts.

Variations in microanatomy of the human cochlea

The human cochlea shows considerable interindividual variability in size and morphology. In order to develop atraumatic cochlear implant (CI) electrodes, high-precision details of the variability of human anatomy are required. Sixteen human temporal bones were cut around the cochlea in blocks of approximately 3.5 × 3.5 cm. The bones were scanned by using a Skyscan 1173 micro-computed tomography (μCT) device. Mimics software (Materialise, Leuven, Belgium) was used to segment out the scala tympani (ST) from the μCT images. A three-dimensional surface model of the segmented area was generated for each cochlea. Cross-sectional images were taken and analyzed by custom-designed software in MATLAB. Comparison of different STs showed large variability in cross-sectional diameter (CSD), vertical trajectory, and height of the ST. Relative standard deviations of the CSD were between 9 and 15%. Heights measured at the center of the ST exceeded those in the modiolar and lateral regions of the scala. At the lateral region, the height decreased significantly at the beginning of the second turn. In the vertical trajectory, critical anatomic features were observed, such as dips, vertical jumps, and peaks. Rosenthal's canal (RC) extended to between 560 and 650°. We found a correlation between the length of the RC and that of the ST. The ST was segmented and the internal dimensions measured by using μCT. We observed large dimensional variability between different STs. These differences could have considerable implications for approaches to the design of CI arrays, especially in terms of their ability to preserve residual hearing during insertion of the electrode array. J. Comp. Neurol. 522:3245–3261, 2014. © 2014 Wiley Periodicals, Inc.

Round window membrane insertion with perimodiolar cochlear implant electrodes

OBJECTIVE

The round window membrane (RWM) approach is designed to provide an atraumatic approach to scala tympani implantation with the goal of enhanced preservation of hearing and vestibular receptor function. Perimodiolar electrode designs offer advantages in electrophysiologic testing. However, perimodiolar arrays have only been investigated in insertion trials using temporal bone material. The aim of the present study was to evaluate perimodiolar electrode placement in a clinical trial.

MATERIALS AND METHODS

The prospective nonrandomized study included 27 patients (October 2010 to February 2011). Due to the RWM approach, cochlear implantation electrode insertion was performed using a perimodiolar electrode array fitted with a stylet that enables movement through the first cochlear turn by withdrawing the stylet. We judged the feasibility of RWM approaches with perimodiolar electrodes and the electrode placement using flat panel detector radiography. Hearing preservation, vestibular receptor function (vestibular evoked myogenic potentials, subjective haptic vertical, and caloric irrigation), and subjective vertigo were evaluated in all RWM approaches.

RESULTS

For anatomic reasons, RWM insertions were possible in 21 cases (78%). The basilar membrane disruption rate was 19% in RWM insertions using perimodiolar electrodes. In those patients with the electrode position within the scala tympani, vestibular receptor functions and subjective vertigo remained unchanged. The residual hearing preservation was unsatisfactory. The mean pure-tone average loss was 21 dB.

CONCLUSION

We believe that if performed regularly, the RWM insertion technique has almost no negative effects on vestibular receptor function and produces no vertigo. However, cochlear hair cells may be more sensitive to electrode insertion traumas than vestibular receptor cells. The use of perimodiolar electrodes may require more atraumatic electrodes to achieve hearing preservation.

Friction force measurement during cochlear implant insertion: application to a force-controlled insertion tool design

HYPOTHESIS

The aim of the study was to evaluate force profiles during array insertion in human cochlea specimens and to evaluate a mechatronic inserter using a 1-axis force sensor.

BACKGROUND

Today, the surgical challenge in cochlear implantation is the preservation of the anatomic structures and the residual hearing. In routine practice, the electrode array is inserted manually with a limited sensitive feedback.

MATERIALS AND METHODS

Hifocus 1J electrode arrays were studied. The bench test comprised a mechatronic inserter combined to a 1-axis force sensor between the inserter and the base of the array and a 6-axis force sensor beneath the cochlea model. Influence of insertion tube material, speed (0.15, 0.5, and 1.5 mm/s) and lubricant on frictions forces were studied (no-load). Different models were subsequently evaluated: epoxy scala tympani model and temporal bones.

RESULTS

Frictions forces were lower in the plastic tube compared with those in the metal tube (0.09 ± 0.028 versus 0.14 ± 0.034 at 0.5 mm/s, p < 0.001) and with the use of hyaluronic acid gel. Speed did not influence frictions forces in our study. Insertion force profiles provided by the 1- and 6-axis force sensors were similar when friction forces inside the insertion tool (no-load measurements) were subtracted from the 1-axis sensor data in the epoxy and temporal bone models (mean error, 0.01 ± 0.001 N).

CONCLUSION

Using a sensor included in the inserter, we were able to measure array insertion forces. This tool can be potentially used to provide real-time information to the surgeon during the procedure.