Automated insertion of preformed cochlear implant electrodes: evaluation of curling behaviour and insertion forces on an artificial cochlear model

A method for accurate and reproducible specimen alignment for insertion tests of cochlear implant electrode arrays

PURPOSE

The trajectory along which the cochlear implant electrode array is inserted influences the insertion forces and the probability for intracochlear trauma. Controlling the trajectory is especially relevant for reproducible conditions in electrode insertion tests. Using ex vivo cochlear specimens, manual alignment of the invisibly embedded cochlea is imprecise and hardly reproducible. The aim of this study was to develop a method for creating a 3D printable pose setting adapter to align a specimen along a desired trajectory toward an insertion axis.

METHODS

Planning points of the desired trajectory into the cochlea were set using CBCT images. A new custom-made algorithm processed these points for automated calculation of a pose setting adapter. Its shape ensures coaxial positioning of the planned trajectory to both the force sensor measuring direction and the insertion axis. The performance of the approach was evaluated by dissecting and aligning 15 porcine cochlear specimens of which four were subsequently used for automated electrode insertions.

RESULTS

The pose setting adapter could easily be integrated into an insertion force test setup. Its calculation and 3D printing was possible in all 15 cases. Compared to planning data, a mean positioning accuracy of 0.21 ± 0.10 mm at the level of the round window and a mean angular accuracy of 0.43° ± 0.21° were measured. After alignment, four specimens were used for electrode insertions, demonstrating the practical applicability of our method.

CONCLUSION

In this work, we present a new method, which enables automated calculation and creation of a ready-to-print pose setting adapter for alignment of cochlear specimens in insertion test setups. The approach is characterized by a high level of accuracy and reproducibility in controlling the insertion trajectory. Therefore, it enables a higher degree of standardization in force measurement when performing ex vivo insertion tests and thereby improves reliability in electrode testing.

Intraoperative Measurement of Insertion Speed in Cochlear Implant Surgery: A Preliminary Experience with Cochlear SmartNav

OBJECTIVES

The objectives were to present the real-time estimated values of cochlear implant (CI) electrode insertion speed (IS) during intraoperative sessions using the Cochlear Nucleus SmartNav System to assess whether this measure affected CI outcomes and to determine whether real-time feedback assists expert surgeons in achieving slow insertion.

METHODS

The IS was measured in 52 consecutive patients (65 implanted ears) using the CI632 electrode. The IS values were analyzed in relation to procedure repetition over time, NRT ratio, and CI audiological outcomes.

RESULTS

The average IS was 0.64 mm/s (SD = 0.24); minimum and maximum values were 0.23 and 1.24 mm/s, respectively. The IS significantly decreased with each array insertion by the operator (p = 0.006), and the mean decreased by 24% between the first and last third of procedures; however, this reduction fell within the error range of SmartNav for IS (+/-0.48 mm/s). No correlation was found between IS and the NRT ratio (p = 0.51), pure-tone audiometry (PTA) at CI activation (p = 0.506), and PTA (p = 0.94) or word recognition score (p = 0.231) at last evaluation.

CONCLUSIONS

The estimated IS reported by SmartNav did not result in a clinically significant reduction in insertion speed or an improvement in CI hearing outcomes. Real-time feedback of IS could potentially be used for training, but its effectiveness requires confirmation through additional studies and more accurate tools. Implementation of IS assessment in clinical practice will enable comparisons between measurement techniques and between manual and robot-assisted insertions. This will help define the optimal IS range to achieve better cochlear implant (CI) outcomes.

Robotic assistance during cochlear implantation: the rationale for consistent, controlled speed of electrode array insertion

Cochlear implants (CI) have revolutionized the treatment of patients with severe to profound sensory hearing loss by providing a method of bypassing normal hearing to directly stimulate the auditory nerve. A further advance in the field has been the introduction of "hearing preservation" surgery, whereby the CI electrode array (EA) is carefully inserted to spare damage to the delicate anatomy and function of the cochlea. Preserving residual function of the inner ear allows patients to receive maximal benefit from the CI and to combine CI electric stimulation with acoustic hearing, offering improved postoperative speech, hearing, and quality of life outcomes. However, under the current paradigm of implant surgery, where EAs are inserted by hand, the cochlea cannot be reliably spared from damage. Robotics-assisted EA insertion is an emerging technology that may overcome fundamental human kinetic limitations that prevent consistency in achieving steady and slow EA insertion. This review begins by describing the relationship between EA insertion speed and generation of intracochlear forces and pressures. The various mechanisms by which these intracochlear forces can damage the cochlea and lead to worsened postoperative outcomes are discussed. The constraints of manual insertion technique are compared to robotics-assisted methods, followed by an overview of the current and future state of robotics-assisted EA insertion.

Polymeric fiber sensors for insertion forces and trajectory determination of cochlear implants in hearing preservation

The level of hearing restoration in patients with severe to profound sensorineural hearing loss by means of cochlear implants (CIs) has drastically risen since the introduction of these neuroprosthetics. The proposed CI integrated with polymer optical fiber Bragg gratings (POFBGs) enables real-time evaluation of insertion forces and trajectory determination during implantation irrespective of the speed of insertion, as well as provides high signal quality, low stiffness levels, minimum induced stress even under forces of high magnitudes and exhibits significant reduction of the risk of fiber breakage inside the constricted cochlear geometry. As such, the proposed device opens new avenues towards atraumatic cochlear implantations and provides a direct route for the next generation of CIs with intraoperative insertion force assessment and path planning capacity crucial for surgical navigation. Hence, adaptation of this technology to clinical reality holds promising prospects for the hearing impaired.

Three-dimensional finite element analysis on cochlear implantation electrode insertion

Studying the insertion process of cochlear implant (CI) electrode array (EA) is important to ensure successful, sufficient, and safe implantation. A three-dimensional finite element (FE) model was developed to simulate the insertion process. The cochlear structures were reconstructed from an average statistical shape model (SSM) of human cochlea. The electrode is simplified as a long and tapered beam of homogeneous elastic materials, contacting and interacting with the stiff cochlear structures. A quasi-static insertion simulation was conducted, the insertion force and the contact pressure between the electrode and the cochlear wall, were calculated to evaluate the smoothness of insertion and the risk of potential cochlear trauma. Based on this model, different EA designs were analyzed, including the Young's modulus, the straight or bended shape, the normal or a more tapped section size. The influence of the insertion angle was also discussed. Our simulations indicate that reducing the EA Young's modulus, tapering and pre-bending are effective ways to ensure safe and successful EA implantation. This model is beneficial for optimizing EA designs and is potentially useful for designing patient-specific CI surgery.

A PLLA Coating Does Not Affect the Insertion Pressure or Frictional Behavior of a CI Electrode Array at Higher Insertion Speeds

To prevent endocochlear insertion trauma, the development of drug delivery coatings in the field of CI electrodes has become an increasing focus of research. However, so far, the effect of a polymer coating of PLLA on the mechanical properties, such as the insertion pressure and friction of an electrode array, has not been investigated. In this study, the insertion pressure of a PLLA-coated, 31.5-mm long standard electrode array was examined during placement in a linear cochlear model. Additionally, the friction coefficients between a PLLA-coated electrode array and a tissue simulating the endocochlear lining were acquired. All data were obtained at different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s) and compared with those of an uncoated electrode array. It was shown that both the maximum insertion pressure generated in the linear model and the friction coefficient of the PLLA-coated electrode did not depend on the insertion speed. At higher insertion speeds above 1.0 mm/s, the insertion pressure (1.268 ± 0.032 mmHg) and the friction coefficient (0.40 ± 0.15) of the coated electrode array were similar to those of an uncoated array (1.252 ± 0.034 mmHg and 0.36 ± 0.15). The present study reveals that a PLLA coating on cochlear electrode arrays has a negligible effect on the electrode array insertion pressure and the friction when higher insertion speeds are used compared with an uncoated electrode array. Therefore, PLLA is a suitable material to be used as a coating for CI electrode arrays and can be considered for a potential drug delivery system.

Finite element modelling of the surgical procedure for placement of a straight electrode array: Mechanical and clinical consequences

A cochlear implant is an electronic device implanted into the cochlea to directly stimulate the auditory nerve. Such device is used in patients with severe-to-profound hearing loss. The cochlear implant surgery is safe, but involves some risks, such as infections, device malfunction or damage of the facial nerve and it can result on a poor hearing outcome, due to the destruction of any present residual hearing. Future improvements in cochlear implant surgery will necessarily involve the decrease of the intra-cochlear damage. Several implant related variables, such as materials, geometrical design, processor and surgical techniques can be optimized in order for the patients to partially recover their hearing capacities The straight electrode is a type of cochlear implant that many authors indicate as being the less traumatic. From the finite element analysis conducted in this work, the influence of the insertion speed, the friction coefficient between the cochlear wall and the electrode array, and several configurations of the cochlear implant tip were studied. The numerical simulations of the implantation showed the same pattern of the insertion force against insertion depth, thus indicating the different phases of the insertion. Results demonstrated that lower insertion speeds, friction coefficients and tip stiffness, led to a reduction on the contact pressures and insertion force. It is expected that these improved configurations will allow to preserve the residual hearing while reducing surgical complications.

A Capacitive Cochlear Implant Electrode Array Sensing System to Discriminate Fold-Over Pattern

Purpose During insertion of the cochlear implant electrode array, the tip of the array may fold back on itself and can cause serious complications to patients. This article presents a sensing system for cochlear implantation in a cochlear model. The electrode array fold-over behaviors can be detected by analyzing capacitive information from the array tip. Method Depending on the angle of the array tip against the cochlear inner wall when it enters the cochlear model, different insertion patterns of the electrode array could occur, including smooth insertion, buckling, and fold-over. The insertion force simulating the haptic feedback for surgeons and bipolar capacitance signals during the insertion progress were collected and compared. The Pearson correlation coefficient (PCC) was applied to the collected capacitive signals to discriminate the fold-over pattern. Results Forty-six electrode array insertions were conducted and the deviation of the measured insertion force varies between a range of 20% and 30%. The capacitance values from electrode pair (1, 2) were recorded for analyzing. A threshold for the PCC is set to be 0.94 that can successfully discriminate the fold over insertions from the other two types of insertions, with a success rate of 97.83%. Conclusions Capacitive measurement is an effective method for the detection of faulty insertions and the maximization of the outcome of cochlear implantation. The proposed capacitive sensing system can be used in other tissue implants in vessels, spinal cord, or heart.

Robotics for Cochlear Implantation Surgery: Challenges and Opportunities

OBJECTIVES

Recent advancements in robotics have set forth a growing body of evidence for the clinical application of the robotic cochlear implantation (RCI), with many potential benefits. This review aims to summarize these efforts, provide the latest developments in this exciting field, and explore the challenges associated with the clinical implementation of RCI.

DATA SOURCES

MEDLINE, PubMed, and EMBASE databases.

STUDY SELECTION

A search was conducted using the keywords "robotics otolaryngology," "robotic cochlear implant," "minimally-invasive cochlear implantation," "minimally-invasive mastoidectomy," and "percutaneous cochlear implant" with all of their synonyms. Literature selection criteria included articles published in English, and articles from 1970 to present.

RESULTS

The use of robotics in neurotology is a relatively new endeavor that continues to evolve. Robotics is being explored by various groups to facilitate in the various steps of cochlear implant surgery, including drilling a keyhole approach to the middle ear for implants, inner ear access, and electrode insertion into the cochlea. Initial clinical trials have successfully implanted selected subjects using robotics.

CONCLUSIONS

The use of robotics in cochlear implants remains in its very early stages. It is hoped that robotics will improve clinical outcomes. Although successful implants with robots are reported in the literature, there are some challenges that need to be addressed before this approach can become an acceptable option for the conventional cochlear implant surgery, such as safety, time, efficiency, and cost. However, it is hoped that further advancements in robotic technology will help in overcoming these barriers leading to successful implementation for clinical utility.

Frictional Behavior of Cochlear Electrode Array Is Dictated by Insertion Speed and Impacts Insertion Force

Background: During cochlear implantation, the electrode array has significant friction with the sensitive endocochlear lining and causes mutual mechanical trauma while the array is being inserted. Both, the impact of insertion speed on electrode friction and the relationship of electrode insertion force and friction have not been adequately investigated to date. Methods: In this study, friction coefficients between a CI electrode array (31.5 mm) and a tissue simulating the endocochlear lining have been acquired, depending on different insertion speeds (0.1, 0.5, 1.0, 1.5, and 2.0 mm/s). Additionally, the electrode insertion forces during the placing into a scala tympani model were recorded and correlated with the friction coefficient. Results: It was shown that the friction coefficient reached the lowest value at an insertion speed of 0.1 mm/s (0.24 ± 0.13), a maximum occurred at 1.5 mm/s (0.59 ± 0.12), and dropped again at 2 mm/s (0.45 ± 0.11). Similar patterns were observed for the insertion forces. Consequently, a high correlation coefficient (0.9) was obtained between the insertion forces and friction coefficients. Conclusion: The present study reveals a non-linear increase in electrode array friction, when insertion speed raises and reports a high correlation between friction coefficient and electrode insertion force. This dependence is a relevant future parameter to evaluate and reduce cochlear implant insertion trauma. Significance statement: Here, we demonstrated a dependence between cochlear electrode insertion speed and its friction behavior and a high correlation to insertion force. Our study provides valuable information for the evaluation and prevention of cochlear implant insertion trauma and supports the optimization of cochlear electrode arrays regarding friction characteristics.

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).

Scalar Translocation Comparison Between Lateral Wall and Perimodiolar Cochlear Implant Arrays - A Meta-Analysis

Objectives/Hypothesis

Two types of electrode arrays for cochlear implants (CIs) are distinguished: lateral wall and perimodiolar. Scalar translocation of the array can lead to intracochlear trauma by penetrating from the scala tympani into the scala vestibuli or scala media, potentially negatively affecting hearing performance of CI users. This systematic review compares the lateral wall and perimodiolar arrays with respect to scalar translocation.

Study Design

Systematic review.

Methods

PubMed, Embase, and Cochrane databases were reviewed for studies published within the last 11 years. No other limitations were set. All studies with original data that evaluated the occurrence of scalar translocation or tip fold‐over (TF) with postoperative computed tomography (CT) following primary cochlear implantation in bilateral sensorineuronal hearing loss patients were considered to be eligible. Data were extracted independently by two reviewers.

Results

We included 33 studies, of which none were randomized controlled trials. Meta‐analysis of five cohort studies comparing scalar translocation between lateral wall and perimodiolar arrays showed that lateral wall arrays have significantly lower translocation rates (7% vs. 43%; pooled odds ratio = 0.12). Translocation was negatively associated with speech perception scores (weighted mean 41% vs. 55%). Tip fold‐over of the array was more frequent with perimodiolar arrays (X² = 6.8, P < .01).

Conclusions

Scalar translocation and tip fold‐overs occurred more frequently with perimodiolar arrays than with lateral wall arrays. In addition, translocation of the array negatively affects hearing with the cochlear implant. Therefore, if one aims to minimize clinically relevant intracochlear trauma, lateral wall arrays would be the preferred option for cochlear implantation. Laryngoscope, 131:1358–1368, 2021

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.

Integrated Force Sensor in a Cochlear Implant for Hearing Preservation Surgery

Cochlear Implant is used for patients with severe hearing loss. It is a neural-prosthesis that stimulates the nerve endings within the cochlea, which is the organ of hearing. The surgical technique involves inserting the electrode array of the implant into a very small "snail-like" spiral structure. During this insertion process, the surgeon's finger tip is not able to perceive the resistance from the contact of the implant and the cochlea's internal structure, below the internal rupture threshold. This can potentially damage vital structures and result in the worsening of residual hearing and poor speech perception. Currently, there is no clinically and commercially available intra-operative force feedback system. A custom made sensor is therefore proposed, integrated within the implant to enable real-time force readings. The device will provide surgeons with the vital force feedback information related to the implants' position within the cochlea. This paper concentrates on demonstrating that the proposed sensor is capable of measuring the contact force below the rupture threshold of the cochlea's internal structure.

Intracochlear Pressure Transients During Cochlear Implant Electrode Insertion: Effect of Micro-mechanical Control on Limiting Pressure Trauma

HYPOTHESIS

Use of micro-mechanical control during cochlear implant (CI) electrode insertion will result in reduced number and magnitude of pressure transients when compared with standard insertion by hand.

INTRODUCTION

With increasing focus on hearing preservation during CI surgery, atraumatic electrode insertion is of the utmost importance. It has been established that large intracochlear pressure spikes can be generated during the insertion of implant electrodes. Here, we examine the effect of using a micro-mechanical insertion control tool on pressure trauma exposures during implantation.

METHODS

Human cadaveric heads were surgically prepared with an extended facial recess. Electrodes from three manufacturers were placed both by using a micro-mechanical control tool and by hand. Insertions were performed at three different rates: 0.2 mm/s, 1.2 mm/s, and 2 mm/s (n = 20 each). Fiber-optic sensors measured pressures in scala vestibuli and tympani.

RESULTS

Electrode insertion produced pressure transients up to 174 dB SPL. ANOVA revealed that pressures were significantly lower when using the micro-mechanical control device compared with insertion by hand (p << 0.001). No difference was noted across electrode type or speed. Chi-square analysis showed a significantly lower proportion of insertions contained pressure spikes when the control system was used (p << 0.001).

CONCLUSION

Results confirm previous data that suggest CI electrode insertion can cause pressure transients with intensities similar to those elicited by high-level sounds. Results suggest that the use of a micro-mechanical insertion control system may mitigate trauma from pressure events, both by reducing the amplitude and the number of pressure spikes resulting from CI electrode insertion.

Patient-specific estimation of detailed cochlear shape from clinical CT images

PURPOSE

A personalized estimation of the cochlear shape can be used to create computational anatomical models to aid cochlear implant (CI) surgery and CI audio processor programming ultimately resulting in improved hearing restoration. The purpose of this work is to develop and test a method for estimation of the detailed patient-specific cochlear shape from CT images.

METHODS

From a collection of temporal bone [Formula: see text]CT images, we build a cochlear statistical deformation model (SDM), which is a description of how a human cochlea deforms to represent the observed anatomical variability. The model is used for regularization of a non-rigid image registration procedure between a patient CT scan and a [Formula: see text]CT image, allowing us to estimate the detailed patient-specific cochlear shape.

RESULTS

We test the accuracy and precision of the predicted cochlear shape using both [Formula: see text]CT and CT images. The evaluation is based on classic generic metrics, where we achieve competitive accuracy with the state-of-the-art methods for the task. Additionally, we expand the evaluation with a few anatomically specific scores.

CONCLUSIONS

The paper presents the process of building and using the SDM of the cochlea. Compared to current best practice, we demonstrate competitive performance and some useful properties of our method.

Individual Optimization of the Insertion of a Preformed Cochlear Implant Electrode Array

Purpose. The aim of this study was to show that individual adjustment of the curling behaviour of a preformed cochlear implant (CI) electrode array to the patient-specific shape of the cochlea can improve the insertion process in terms of reduced risk of insertion trauma. Methods. Geometry and curling behaviour of preformed, commercially available electrode arrays were modelled. Additionally, the anatomy of each small, medium-sized, and large human cochlea was modelled to consider anatomical variations. Finally, using a custom-made simulation tool, three different insertion strategies (conventional Advanced Off-Stylet (AOS) insertion technique, an automated implementation of the AOS technique, and a manually optimized insertion process) were simulated and compared with respect to the risk of insertion-related trauma. The risk of trauma was evaluated using a newly developed “trauma risk” rating scale. Results. Using this simulation-based approach, it was shown that an individually optimized insertion procedure is advantageous compared with the AOS insertion technique. Conclusion. This finding leads to the conclusion that, in general, consideration of the specific curling behaviour of a CI electrode array is beneficial in terms of less traumatic insertion. Therefore, these results highlight an entirely novel aspect of clinical application of preformed perimodiolar electrode arrays in general.

Tubular manipulators: a new concept for intracochlear positioning of an auditory prosthesis

The aim of this study was to investigate the applicability of tubular manipulators as an actuator mechanism for intracochlear positioning of the electrode array (EA) of a cochlear implant (CI). This is motivated by the vision of an atraumatic insertion of the EA into the inner ear (cochlea) without any damage to the intracochlear structures in combination with a well-defined final position. To realize this, an actuator mechanism is required which allows consideration of the patient-specific anatomy. We propose a tubular manipulator for this task. It consists of three concentric tubes: A straight outer tube serves as a guiding sleeve to enter the inner ear (cochlea) and two additional telescoping, superelastic, helically precurved tubes. By selecting helical tube parameters of both tubes prior insertion, a patient-specific curling behaviour of the tubular manipulator can be achieved. For preliminary investigation, segmentation and skeletonization of 5 human scala tympani were performed to determine their centrelines. These centrelines were considered as individual ideal insertion paths. An optimization algorithm was developed to identify suitable tube set parameters (curvature, diameter, length, torsion, stiffness) as well as configuration parameters (translation and rotation of the 2 inner tubes). Different error values describing the deviation of the shape of the tubes with respect to the insertion path were used to quantify the optimization results. In all cases tube set parameters for a final position within the cochlea were found, while keeping the maximum error below 1mm. These preliminary results are promising in terms of the potential applicability of tubular manipulators for positioning auditory prosthesis inside the scala tympani of the inner ear.

Cochlear Dummy Electrodes for Insertion Training and Research Purposes: Fabrication, Mechanical Characterization, and Experimental Validation

To develop skills sufficient for hearing preservation cochlear implant surgery, surgeons need to perform several electrode insertion trials in ex vivo temporal bones, thereby consuming relatively expensive electrode carriers. The objectives of this study were to evaluate the insertion characteristics of cochlear electrodes in a plastic scala tympani model and to fabricate radio opaque polymer filament dummy electrodes of equivalent mechanical properties. In addition, this study should aid the design and development of new cochlear electrodes. Automated insertion force measurement is a new technique to reproducibly analyze and evaluate the insertion dynamics and mechanical characteristics of an electrode. Mechanical properties of MED-EL's FLEX²⁸, FLEX²⁴, and FLEX²⁰ electrodes were assessed with the help of an automated insertion tool. Statistical analysis of the overall mechanical behavior of the electrodes and factors influencing the insertion force are discussed. Radio opaque dummy electrodes of comparable characteristics were fabricated based on insertion force measurements. The platinum-iridium wires were replaced by polymer filament to provide sufficient stiffness to the electrodes and to eradicate the metallic artifacts in X-ray and computed tomography (CT) images. These low-cost dummy electrodes are cheap alternatives for surgical training and for in vitro, ex vivo, and in vivo research purposes.

Three-dimensional histological specimen preparation for accurate imaging and spatial reconstruction of the middle and inner ear

PURPOSE

This paper presents a highly accurate cross-sectional preparation technique. The research aim was to develop an adequate imaging modality for both soft and bony tissue structures featuring high contrast and high resolution. Therefore, the advancement of an already existing micro-grinding procedure was pursued. The central objectives were to preserve spatial relations and to ensure the accurate three-dimensional reconstruction of histological sections.

METHODS

Twelve human temporal bone specimens including middle and inner ear structures were utilized. They were embedded in epoxy resin, then dissected by serial grinding and finally digitalized. The actual abrasion of each grinding slice was measured using a tactile length gauge with an accuracy of one micrometre. The cross-sectional images were aligned with the aid of artificial markers and by applying a feature-based, custom-made auto-registration algorithm. To determine the accuracy of the overall reconstruction procedure, a well-known reference object was used for comparison. To ensure the compatibility of the histological data with conventional clinical image data, the image stacks were finally converted into the DICOM standard.

RESULTS

The image fusion of data from temporal bone specimens' and from non-destructive flat-panel-based volume computed tomography confirmed the spatial accuracy achieved by the procedure, as did the evaluation using the reference object.

CONCLUSION

This systematic and easy-to-follow preparation technique enables the three-dimensional (3D) histological reconstruction of complex soft and bony tissue structures. It facilitates the creation of detailed and spatially correct 3D anatomical models. Such models are of great benefit for image-based segmentation and planning in the field of computer-assisted surgery as well as in finite element analysis. In the context of human inner ear surgery, three-dimensional histology will improve the experimental evaluation and determination of intra-cochlear trauma after the insertion of an electrode array of a cochlear implant system.

A manually operated, advance off-stylet insertion tool for minimally invasive cochlear implantation surgery

The current technique for cochlear implantation (CI) surgery requires a mastoidectomy to gain access to the cochlea for electrode array insertion. It has been shown that microstereotactic frames can enable an image-guided, minimally invasive approach to CI surgery called percutaneous cochlear implantation (PCI) that uses a single drill hole for electrode array insertion, avoiding a more invasive mastoidectomy. Current clinical methods for electrode array insertion are not compatible with PCI surgery because they require a mastoidectomy to access the cochlea; thus, we have developed a manually operated electrode array insertion tool that can be deployed through a PCI drill hole. The tool can be adjusted using a preoperative CT scan for accurate execution of the advance off-stylet (AOS) insertion technique and requires less skill to operate than is currently required to implant electrode arrays. We performed three cadaver insertion experiments using the AOS technique and determined that all insertions were successful using CT and microdissection.

In vitro modifications of the scala tympani environment and the cochlear implant array surface

OBJECTIVES/HYPOTHESIS

To investigate the influence of alterations of the scala tympani environment and modifications of the surface of cochlear implant electrode arrays on insertion forces in vitro.

STUDY DESIGN

Research experimental study.

METHODS

Fibroblasts producing neurotrophic factors were cultivated on the surface of Nucleus 24 Contour Advance electrodes. Forces were recorded by an Instron 5542 Force Measurement System as three modified arrays were inserted into an artificial scala tympani model filled with phosphate-buffered saline (PBS). The recorded forces were compared to control groups including three unmodified electrodes inserted into a model filled with PBS (unmodified environment) or Healon (current practice). Fluorescence microscopy was used before and after the insertions to identify any remaining fibroblasts. Additionally, three Contour Advance electrodes were inserted into an artificial model, filled with alginate/barium chloride solution at different concentrations, while insertion forces were recorded.

RESULTS

Modification of the scala tympani environment with 50% to 75% alginate gel resulted in a significant decrease in the insertion forces. The fibroblast-coated arrays also led to decreased forces comparable to those recorded with Healon. Fluorescence microscopy revealed fully cell-covered arrays before and partially covered arrays after the insertion; the fibroblasts on the arrays' modiolar surface remained intact.

CONCLUSIONS

Modifications of the scala tympani's environment with 50% to 75% alginate/barium chloride and of the cochlear implant electrode surface with neurotrophic factor-producing fibroblasts drastically reduce the insertion forces. As both modifications may serve future intracochlear therapies, it is expected that these might additionally reduce possible insertion trauma.

Design of a Tool Integrating Force Sensing With Automated Insertion in Cochlear Implantation

The quality of hearing restored to a deaf patient by a cochlear implant in hearing preservation cochlear implant surgery (and possibly also in routine cochlear implant surgery) is believed to depend on preserving delicate cochlear membranes while accurately inserting an electrode array deep into the spiral cochlea. Membrane rupture forces, and possibly, other indicators of suboptimal placement, are below the threshold detectable by human hands, motivating a force sensing insertion tool. Furthermore, recent studies have shown significant variability in manual insertion forces and velocities that may explain some instances of imperfect placement. Toward addressing this, an automated insertion tool was recently developed by Hussong et al. By following the same insertion tool concept, in this paper, we present mechanical enhancements that improve the surgeon's interface with the device and make it smaller and lighter. We also present electomechanical design of new components enabling integrated force sensing. The tool is designed to be sufficiently compact and light that it can be mounted to a microstereotactic frame for accurate image-guided preinsertion positioning. The new integrated force sensing system is capable of resolving forces as small as 0.005 N, and we provide experimental illustration of using forces to detect errors in electrode insertion.

Force of cochlear implant electrode insertion performed by a robotic insertion tool: comparison of traditional versus Advance Off-Stylet techniques

OBJECTIVE

Robotic cochlear implant electrode array insertion offers substantial potential advantages, namely repeatability and minimization of insertion forces, leading to decreased intracochlear trauma. Using such a robotic insertion tool, we sought to analyze force profiles during deployment of stylet-containing electrode arrays using either traditional insertion, in which the stylet is withdrawn after complete insertion of the electrode, or Advance Off-Stylet (AOS) insertion, in which the stylet is withdrawn simultaneous with electrode array insertion.

STUDY DESIGN

Prospective.

SETTING

Tertiary referral center.

INTERVENTIONS

A robotic cochlear implant insertion tool coupled with a force-sensing carriage was used to perform electrode array insertions into an anatomically correct, three-dimensional scala tympani model during either straight insertion (n = 4) or AOS insertion (n = 4).

MAIN OUTCOME MEASURES

Both insertion techniques begin with a 7-mm straight insertion during which forces were similar averaging approximately 0.006 N. For insertion from 7 to 17 mm, traditional insertion forces averaged 0.046 ± 0.027 N, with a peak of 0.093 N, and AOS insertion forces averaged 0.008 ± 0.006 N, with a peak of 0.034 N. Beyond 9.74 mm, the difference between traditional and AOS insertion forces was highly significant.

CONCLUSION

With the use of a robotic insertion tool, which minimizes operator variability and maximizes repeatability, we have shown that cochlear implant electrode insertion via AOS is associated with lower average and maximum insertion forces compared with traditional insertion. These findings support the use of AOS over traditional, straight insertion.

Determination of the curling behavior of a preformed cochlear implant electrode array

PURPOSE

Accurate insertion of a cochlear implant electrode array into the cochlea's helical shape is a crucial step for residual hearing preservation. In image-guided surgery, especially using an automated insertion tool, the overall accuracy of the operative procedure can be improved by adapting the electrode array's intracochlear movement to the individual cochlear shape.

METHODS

The curling characteristic of a commercially available state-of-the-art preformed electrode array (Cochlear Ltd. Contour Advance(TM) Electrode Array) was determined using an image-processing algorithm to detect its shape in series of images. An automatic image-processing procedure was developed using Matlab and the Image Processing Toolbox (MathWorks, Natick, Massachusetts, USA) to determine the complete curvature of the electrode array by identifying the 22 platinum contacts of the electrode. A logarithmic spiral was used for a comprehensive mathematical description of the shape of the electrode array. A fitting algorithm for nonlinear least-squares problems was used to provide a complete mathematical description of the electrode array. The system was tested for curling behavior as a function of stylet extraction using nine Contour Advance Research Electrodes (RE) and additionally for nine Contour Advance Practice Electrodes (PE).

RESULTS

All arrays show a typical pattern of curling with adequate predictability after the first 2 or 3 millimeters of stylet extraction. Although non-negligible variations in the overall curling behavior were detected, the electrode arrays show a characteristic movement due to the stylet extraction and only vary minimally after this initial phase.

CONCLUSION

These results indicate that the risk of intracochlear trauma can be reduced if the specific curling behavior of the electrode carrier is incorporated into the insertion algorithm. Furthermore, the determination of the curling behavior is an essential step in computer-aided cochlear implant electrode development. Experimental data are required for accurate evaluation of the simulation model.