Mechanical properties of human round window, basilar and Reissner's membranes

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.

Preclinical evaluation of a tool for insertion force measurements in cochlear implant surgery

PURPOSE

Trauma that may be inflicted to the inner ear (cochlea) during the insertion of an electrode array (EA) in cochlear implant (CI) surgery can significantly decrease the hearing outcome of patients with residual hearing. Interaction forces between the EA and the cochlea are a promising indicator for the likelihood of intracochlear trauma. However, insertion forces have only been measured in laboratory setups. We recently developed a tool to measure the insertion force during CI surgery. Here, we present the first ex vivo evaluation of our tool with a focus on usability in the standard surgical workflow.

METHODS

Two CI surgeons inserted commercially available EAs into three temporal bone specimens. The insertion force and the orientation of the tool were recorded together with camera footage. The surgeons answered a questionnaire after each insertion to evaluate the surgical workflow with respect to CI surgery.

RESULTS

The EA insertion using our tool was rated successful in all 18 trials. The surgical workflow was evaluated to be equivalent to standard CI surgery. Minor handling challenges can be overcome through surgeon training. The peak insertion forces were 62.4 mN ± 26.7 mN on average. Peak forces significantly correlated to the final electrode insertion depth, supporting the assumption that the measured forces mainly correspond to intracochlear events and not extracochlear friction. Gravity-induced forces of up to 28.8 mN were removed from the signal, illustrating the importance of the compensation of such forces in manual surgery.

CONCLUSION

The results show that the tool is ready for intraoperative use. In vivo insertion force data will improve the interpretability of experimental results in laboratory settings. The implementation of live insertion force feedback to surgeons could further improve residual hearing preservation.

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.

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.

An optically-guided cochlear implant sheath for real-time monitoring of electrode insertion into the human cochlea

In cochlear implant surgery, insertion of perimodiolar electrode arrays into the scala tympani can be complicated by trauma or even accidental translocation of the electrode array within the cochlea. In patients with partial hearing loss, cochlear trauma can not only negatively affect implant performance, but also reduce residual hearing function. These events have been related to suboptimal positioning of the cochlear implant electrode array with respect to critical cochlear walls of the scala tympani (modiolar wall, osseous spiral lamina and basilar membrane). Currently, the position of the electrode array in relation to these walls cannot be assessed during the insertion and the surgeon depends on tactile feedback, which is unreliable and often comes too late. This study presents an image-guided cochlear implant device with an integrated, fiber-optic imaging probe that provides real-time feedback using optical coherence tomography during insertion into the human cochlea. This novel device enables the surgeon to accurately detect and identify the cochlear walls ahead and to adjust the insertion trajectory, avoiding collision and trauma. The functionality of this prototype has been demonstrated in a series of insertion experiments, conducted by experienced cochlear implant surgeons on fresh-frozen human cadaveric cochleae.

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.

Prolonged Insertion Time Reduces Translocation Rate of a Precurved Electrode Array in Cochlear Implantation

HYPOTHESIS

Insertion speed during cochlear implantation determines the risk of cochlear trauma. By slowing down insertion speed tactile feedback is improved. This is highly conducive to control the course of the electrode array along the cochlear contour and prevent translocation from the scala tympani to the scala vestibuli.

BACKGROUND

Limiting insertion trauma is a dedicated goal in cochlear implantation to maintain the most favorable situation for electrical stimulation of the remaining stimulable neural components of the cochlea. Surgical technique is one of the potential influencers on translocation behavior of the electrode array.

METHODS

The intrascalar position of 226 patients, all implanted with a precurved electrode array, aiming a mid-scalar position, was evaluated. One group (n = 113) represented implantation with an insertion time less than 25 seconds (fast insertion) and the other group (n = 113) was implanted in 25 or more seconds (slow insertion). A logistic regression analysis studied the effect of insertion speed on insertion trauma, controlled for surgical approach, cochlear size, and angular insertion depth. Furthermore, the effect of translocation on speech performance was evaluated using a linear mixed model.

RESULTS

The translocation rate within the fast and slow insertion groups were respectively 27 and 10%. A logistic regression analysis showed that the odds of dislocation increases by 2.527 times with a fast insertion, controlled for surgical approach, cochlear size, and angular insertion depth (95% CI = 1.135, 5.625). We failed to find a difference in speech recognition between patients with and without translocated electrode arrays.

CONCLUSION

Slowing down insertion speed till 25 seconds or longer reduces the incidence of translocation.

Robotics, automation, active electrode arrays, and new devices for cochlear implantation: A contemporary review

In the last two decades, cochlear implant surgery has evolved into a minimally invasive, hearing preservation surgical technique. The devices used during surgery have benefited from technological advances that have allowed modification and possible improvement of the surgical technique. Robotics has recently gained popularity in otology as an effective tool to overcome the surgeon's limitations such as tremor, drift and accurate force control feedback in laboratory testing. Cochlear implantation benefits from robotic assistance in several steps during the surgical procedure: (i) during the approach to the middle ear by automated mastoidectomy and posterior tympanotomy or through a tunnel from the postauricular skin to the middle ear (i.e. direct cochlear access); (ii) a minimally invasive cochleostomy by a robot-assisted drilling tool; (iii) alignment of the correct insertion axis on the basal cochlear turn; (iv) insertion of the electrode array with a motorized insertion tool. In recent years, the development of bone-attached parallel robots and image-guided surgical robotic systems has allowed the first successful cochlear implantation procedures in patients via a single hole drilled tunnel. Several other robotic systems, new materials, sensing technologies applied to the electrodes, and smart devices have been developed, tested in experimental models and finally some have been used in patients with the aim of reducing trauma in cochleostomy, and permitting slow and more accurate insertion of the electrodes. Despite the promising results in laboratory tests in terms of minimal invasiveness, reduced trauma and better hearing preservation, so far, no clinical benefits on residual hearing preservation or better speech performance have been demonstrated. Before these devices can become the standard approach for cochlear implantation, several points still need to be addressed, primarily cost and duration of the procedure. One can hope that improvement in the cost/benefit ratio will expand the technology to every cochlear implantation procedure. Laboratory research and clinical studies on patients should continue with the aim of making intracochlear implant insertion an atraumatic and reversible gesture for total preservation of the inner ear structure and physiology.

Cochlear Size Assessment Predicts Scala Tympani Volume and Electrode Insertion Force- Implications in Robotic Assisted Cochlear Implant Surgery

Objectives: The primary aim was to measure the volume of the scala tympani (ST) and the length of the straight portion of the cochlear basal turn from micro-computed tomography (μCT) images. The secondary aim was to estimate the electrode insertion force based on cochlear size and insertion speed. Both of these objectives have a direct clinical relevance in robotic assisted cochlear implant (CI) surgery.

Methods: The ST was segmented in thirty μCT datasets to create a three-dimensional (3D) model and calculate the ST volume. The diameter (A-value), the width (B-value), and the straight portion of the cochlear basal turn (S-value) were measured from the oblique coronal plane. Electrode insertion force was measured in ST models of two different sizes, by inserting FLEX24 (24 mm) and FLEX28 (28 mm) electrode arrays at five different speeds (0.1, 0.5, 1, 2, and 4 mm/s).

Results: The mean A-, B-, and S-values measured from the 30 μCT datasets were 9.0 ± 0.5, 6.7 ± 0.4, and 6.9 mm ± 0.5, respectively. The mean ST volume was 34.2 μl ± 7 (range 23–50 μl). The ST volume increased linearly with an increase in A- and B-values (Pearson's coefficient r = 0.55 and 0.56, respectively). The A-value exhibited linear positive correlation with the B-value and S-value (Pearson's coefficient r = 0.64 and r = 0.66, respectively). In the smaller of the two ST models, insertion forces were higher across the range of insertion speeds during both array insertions, when compared to the upscaled model. Before the maximum electrode insertion depths, a trend toward lower insertion force for lower insertion speed and vice-versa was observed.

Conclusion: It is important to determine pre-operative cochlear size as this seems to have an effect upon electrode insertion forces. Higher insertion forces were seen in a smaller sized ST model across two electrode array lengths, as compared to an upscaled larger model. The ST volume, which cannot be visualized on clinical CT, correlates with clinical cochlear parameters. This enabled the creation of an equation capable of predicting ST volume utilizing A- and B-values, thus enabling pre-operative prediction of ST volume.

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.

Hydraulic insertions of cochlear implant electrode arrays into the human cadaver cochlea: preliminary findings

OBJECTIVES

(1) To evaluate the feasibility of a non-invasive, novel, simple insertion tool to perform automated, slow insertions of cochlear implant electrode arrays (EA) into a human cadaver cochlea; (2) to estimate the handling time required by our tool.

METHODS

Basic science study conducted in an experimental OR. Two previously anonymized human cadaver heads, three commercially available EAs, and our novel insertion tool were used for the experiments. Our tool operates as a hydraulic actuator that delivers an EA at continuous velocities slower than manually feasible.

INTERVENTION(S)

the human cadaver heads were prepared with a round-window approach for CI surgery in a standard fashion. Twelve EA insertion trials using our tool involved: non-invasive fixation of the tool to the head; directing the tool to the round window and EA mounting onto the tool; automated EA insertion at approximately 0.1 mm/s driven by hydraulic actuation. Outcome measurement(s): handling time of the tool; post-insertion cone-beam CT scans to provide intracochlear evaluation of the EA insertions.

RESULTS

Our insertion tool successfully inserted an EA into the human cadaver cochlea (n = 12) while being attached to the human cadaver head in a non-invasive fashion. Median time to set up the tool was 8.8 (7.2-9.4) min.

CONCLUSION

The first insertions into the human cochlea using our novel, simple insertion tool were successful without the need for invasive fixation. The tool requires < 10 min to set up, which is clinically acceptable. Future assessment of intracochlear trauma is needed to support its safety profile for clinical translation.

In-Vitro Study of Speed and Alignment Angle in Cochlear Implant Electrode Array Insertions

OBJECTIVE

The insertion of the electrode array is a critical step in cochlear implantation. Herein we comprehensively investigate the impact of the alignment angle and feed-forward speed on deep insertions in artificial scala tympani models with accurate macro-anatomy and controlled frictional properties.

METHODS

Motorized insertions (n=1033) were performed in six scala tympani models with varying speeds and alignment angles. We evaluated reaction forces and micrographs of the insertion process and developed a mathematical model to estimate the normal force distribution along the electrode arrays.

RESULTS

Insertions parallel to the cochlear base significantly reduce insertion energies and lead to smoother array movement. Non-constant insertion speeds allow to reduce insertion forces for a fixed total insertion time compared to a constant feed rate.

CONCLUSION

In cochlear implantation, smoothness and peak forces can be reduced with alignment angles parallel to the scala tympani centerline and with non-constant feed-forward speed profiles.

SIGNIFICANCE

Our results may help to provide clinical guidelines and improve surgical tools for manual and automated cochlear implantation.

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.

Vestibular Function After Cochlear Implantation in Partial Deafness Treatment

Introduction: Cochlear implantation is a fully accepted method of treating individuals with profound hearing loss. Since the indications for cochlear implantation have broadened and include patients with low-frequency residual hearing, single-sided deafness, or an already implanted ear (meaning bilateral cochlear implantation), the emphasis now needs to be on vestibular protection.

Materials and Methods: The research group was made up of 107 patients operated on in the otorhinolaryngosurgery department: 59 females and 48 males, aged 10.4–80.2 years (M = 44.4; SD = 18.4) with hearing loss lasting from 1.4 to 56 years (M = 22.7; SD = 13.5). The patients underwent cVEMP, oVEMP, a caloric test, and vHIT assessment preoperatively, and, postoperatively, cVEMP and oVEMP at 1–3 months and a caloric test and vHIT at 4–6 months.

Results: After cochlear implantation, there was postoperative loss of cVEMP in 19.2% of the patients, oVEMP in 17.4%, reduction of caloric response in 11.6%, and postoperative destruction of the lateral, anterior, and posterior semicircular canal as measured with vHIT in 7.1, 3.9, and 4% respectively.

Conclusions: Hearing preservation techniques in cochlear implantation are connected with vestibular protection, but the risk of vestibular damage in never totally eliminated. The vestibular preservation is associated with hearing preservation and the relation is statistically significant. Informed consent for cochlear implantation must include information about possible vestibular damage. Since the risk of vestibular damage is appreciable, preoperative otoneurological diagnostics need to be conducted in the following situations: qualification for a second implant, after otosurgery (especially if the opposite ear is to be implanted), having a history of vestibular complaints, and when there are no strict audiological or anatomical indications on which side to operate.

Investigating the Geometry and Mechanical Properties of Human Round Window Membranes Using Micro-Fringe Projection

HYPOTHESIS

The geometry and the mechanical property of the round window membrane (RWM) have a fundamental impact on the function of cochlea.

BACKGROUND

Understanding the mechanical behavior of RWM is important for cochlear surgery and design for the cochlear implant. Although the anatomy of RWM has been widely studied and described in the literature, argument remains regarding the true shape of RWM. The mechanical properties of RWM are also scarcely reported due to the difficulty of the measurement of the small size RWM.

METHODS

In this paper, micro-fringe projection was used to reconstruct the 3-dimensional geometries of 14 RWMs. Mechanical properties of the RWMs were subsequently measured using finite element (FE) model and an inverse method. The three-dimensional surface topographies and the curvatures of the two major directions reconstructed from the micro-fringe projection both demonstrated wide variations among samples.

RESULTS

The diameters of the RWMs vary from 1.65 to 2.2 mm and the curvatures vary from -0.97 to 3.76 mm-1. The nonlinear elasticity parameters in the Ogden model for each sample was measured and the average effective Young's modulus is approximately 1.98 MPa.

CONCLUSION

The geometries and mechanical properties of the human RWM measured in the work could potentially be applied to surgery design and on modeling analysis for the cochlea.

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).

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.

Dynamic intracochlear pressure measurement during cochlear implant electrode insertion

Background: Electrode insertion into the cochlea can cause significant pressure changes inside the cochlea with assumed effects on the cochlea's functionality regarding residual hearing. Model-based intracochlear pressure (ICP) changes were performed statically at the cochlear helix. Aims/objectives: The aim of this study was to observe dynamic pressure measurements during electrode insertion directly at the cochlear implant electrode. Material and methods: The experiments were performed in an uncurled cochlear model that contained a volume value equivalent to a full cochlea. A microfibre pressure sensor was attached at one of two positions on a cochlear implant electrode and inserted under different insertional conditions. Results: We observed the ICP increase depending on the insertional depth. A sensor-position-specific pressure change is insertional-depth dependent. Interval insertion did not lead to a lower peak insertional ICP. Conclusions and significance: In contrast to the static pressure-sensor measurement in the artificial model's helix, a dynamic measurement directly at the electrode shows the pressure profile to increase based on the insertional depth. A mechanical traumatic relevance of the observed pressure values cannot be fully excluded.

Effect on vestibular function of cochlear implantation by partial deafness treatment-electro acoustic stimulation (PDT-EAS)

Purpose

Although the cochlear implantation procedure does not interfere with vestibular structures directly, both the vestibulum and the cochlea share the same inner ear fluid space, and this fluid may be responsible for transferring possibly damaging forces from one to the other. The purpose of the study is to assess postoperative vestibular function after partial deafness treatment–electro-acoustic stimulation (PDT–EAS) cochlear implantation.

Methods

Fifty-five patients were included in the study (30 females, 25 males, age 11–80, mean 41.8 ± 19.35). cVEMP and oVEMP were performed preoperatively and 1–3 months after cochlear implantation. Caloric and vHIT tests were conducted preoperatively and 4–6 months after cochlear implantation.

Results

Our study shows that, based on a wide range of electrodes, use of PDT–EAS is protective in terms of preserving vestibular function. It gives a rate of saccular damage of 15.79%, utricular damage of 19.04%, and a horizontal semicircular canal response reduction of 15.79%.

Conclusions

PDT–EAS is protective in terms of preserving vestibular function. Nevertheless, it should be emphasized that the risk of vestibular damage cannot be totally eliminated even when hearing preservation techniques are adopted.

Numerical Study and Optimization of a Novel Piezoelectric Transducer for a Round-Window Stimulating Type Middle-Ear Implant

Round window (RW) stimulation is a new application of middle ear implants for treating hearing loss, especially for those with middle ear disease. However, most reports on it are based on the use of the floating mass transducer (FMT), which was not originally designed for round window stimulation. The mismatch of the FMT's diameter and the round window membrane's diameter and the uncontrollable preload of the transducer, leads to a high variability in its clinical outcomes. Accordingly, a new piezoelectric transducer for the round-window-stimulating-type middle ear implant is proposed in this paper. The transducer consists of a piezoelectric stack, a flextensional amplifier, a coupling rod, a salver, a plate, a titanium housing and a supporting spring. Based on a constructed coupling finite element model of the human ear and the transducer, the influences of the transducer design parameters on its performance were analyzed. The optimal structure of the supporting spring, which determines the transducer's resonance frequency, was ascertained. The results demonstrate that our designed transducer generates better output than the FMT, especially at low frequency. Besides this, the power consumption of the transducer was significantly decreased compared with a recently reported RW-stimulating piezoelectric transducer.

In Vivo Measurement of Middle Ear Pressure Changes during Balloon Eustachian Tuboplasty

Background

Balloon Eustachian tuboplasty (BET) is known as a treatment for chronic obstructive Eustachian tube dysfunction (OETD). The precise mechanism of action is not fully understood. Observations in sheep cadavers and human cadavers have shown specific middle ear pressure changes related to BET.

Methods

In this prospective study using a microfibre optical pressure sensor, pressure changes during BET were for the first time monitored transtympanically in five normal human middle ears in vivo.

Results

Middle ear pressure changes during 21 BETs consisted of five stages (insertion, inflation, deflation, withdrawal, and recovery). The highest pressure change occurred in most of the cases during the withdrawal of the balloon catheter. Withdrawal pressure yielded a mean middle ear pressure of 4.76 mmHg (61.89 daPa) with a maximum of 13.88 mmHg (179.55 daPa). Pressure amplitudes capable of causing barotrauma to ear structures were not detected. Internal carotid artery dehiscences were detected as causative of sinusidual pressure changes.

Conclusion

The middle ear pressure changes detected in vivo during BET can be attributed to the balloon inflation. Further human studies with patients affected by OETD are necessary to gain more insight into the mechanism of action of BET to clarify a possible pressure related second mechanism of action of BET.

Redesign of the Hannover Coupler: Optimized Vibration Transfer from Floating Mass Transducer to Round Window

Introduction

In order to reduce the large variations in clinical outcomes of patients with implanted MED-EL Floating Mass Transducer (FMT) at the round window (RW), several approaches were proposed to optimize FMT-RW coupling. Our previous study showed improved FMT-RW coupling by applying static RW loads utilizing the “Hannover Coupler” (HC) FMT-prosthesis but also demonstrated insufficient low frequency performance. Hence, a redesigned HC version (HCv2) was investigated in this study.

Methods

Experiments were performed in ASTM F2504-05 compliant fresh human temporal bones. The HCv2 is a FMT-prosthesis redesigned from a previous prototype to specifically improve low frequency performance. Stapes footplate (SFP) displacements in response to acoustic stimulation of the tympanic membrane and to FMT-RW stimulation at varying static force (0–100 mN) were measured by Laser-Doppler vibrometry.

Results

SFP displacements were highly dependent on the applied RW load and had a global maximum at 15 mN when averaged at speech relevant frequencies (0.5–4 kHz). SFP responses at frequencies ≤ 1 kHz were up to 25 dB higher than responses achieved with the previous HC version.

Conclusion

Optimizing the HC prosthesis design resulted in improved SFP responses to RW stimulation especially at lower frequencies (≤1 kHz).

The Hannover Coupler: Controlled Static Prestress in Round Window Stimulation With the Floating Mass Transducer

INTRODUCTION

Stimulation of the cochlear round window (RW) with the floating mass transducer (FMT) still suffers from large variation in clinical outcomes. Beside the geometric mismatch between RW and FMT diameter that is a known limiting factor in achieving optimal coupling between actuator and RW membrane, the applied static force between FMT and RW is usually undefined. In this study, the feasibility and efficacy of a specially designed FMT coupler permitting application of static preloads to the RW membrane to optimize FMT-RW coupling was investigated.

METHODS

Experiments were performed in fresh human cadaveric temporal bones. The "Hannover Coupler" FMT-prosthesis has a spherical tip (d=0.5 mm) at the front end and a spring at the prosthesis back that enables the application of static preloads and mobility of the FMT at the same time. Stapes footplate (SFP) displacements in response to acoustic stimulation of the tympanic membrane and to RW stimulation by the FMT were measured by a Laser-Doppler vibrometer.

RESULTS

Average SFP displacement responses of ASTM standard F2504-05 compliant temporal bones to RW stimulation by the "Hannover Coupler" were dependent on the applied force (∼0-100 mN) and increased by up to 25 dB at frequencies ≥ 1 kHz. When averaged at speech relevant frequencies (0.5, 1, 2, 4 kHz) SFP displacements showed a global maximum at RW preloads of ∼4 mN.

CONCLUSION

The coupling between FMT and RW membrane was improved by the application of static RW preloads as indicated by increased SFP amplitudes to RW stimulation.

Measurement of middle ear pressure changes during balloon eustachian tuboplasty: a pilot study

CONCLUSION

The middle ear pressure changes detected during BET can be directly attributed to the balloon inflation and may represent a second, immediate, mechanism of action of BET. BET seems to be safe with respect to the risk of a barotrauma. Further human studies are now necessary to confirm the results and gain more insight into the mechanism of action of BET.

OBJECTIVE

Since the introduction of Balloon Eustachian Tuboplasty (BET) as a treatment of chronic Eustachian tube dysfunction, the precise mechanism of action is unknown. Long-term effects of BET may be related to observed microfractures of the Eustachian tube cartilage. However, clinical observations indicate a second, immediate mode of action. Therefore, this study investigated and characterized middle ear pressure changes occurring directly during BET procedure.

METHODS

Using a micro-optical pressure sensor, pressure changes during BET were monitored transtympanically in a cadaveric animal study using heathland sheep.

RESULTS

Middle ear pressure amplitudes during BET are dependent on the speed of balloon inflation as well as the maximum inflation pressure. A 10-bar inflation pressure yielded a mean middle ear pressure of 5.34 mmHg (71.0 daPA). Negative pressure amplitudes occurring on withdrawal of the balloon catheter are influenced by the speed of withdrawal. No pressure amplitudes capable of causing barotrauma to membranous ear structures could be detected.

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.

Damage to inner ear structure during cochlear implantation: Correlation between insertion force and radio-histological findings in temporal bone specimens

Cochlear implant insertion should be as least traumatic as possible in order to reduce trauma to the cochlear sensory structures. The force applied to the cochlea during array insertion should be controlled to limit insertion-related damage. The relationship between insertion force and histological traumatism remains to be demonstrated. Twelve freshly frozen cadaveric temporal bones were implanted with a long straight electrodes array through an anterior extended round window insertion using a motorized insertion tool with real-time measurement of the insertion force. Anatomical parameters, measured on a pre-implantation cone beam CT scan, position of the array and force metrics were correlated with post-implantation scanning electron microscopy images and histological damage assessment. An atraumatic insertion occurred in six cochleae, a translocation in five cochleae and a basilar membrane rupture in one cochlea. The translocation always occurred in the 150- to 180-degree region. In the case of traumatic insertion, different force profiles were observed with a more irregular curve arising from the presence of an early peak force (30 ± 18.2 mN). This corresponded approximately to the first point of contact of the array with the lateral wall of the cochlea. Atraumatic and traumatic insertions had significantly different force values at the same depth of insertion (p < 0.001, two-way ANOVA), and significantly different regression lines (y = 1.34x + 0.7 for atraumatic and y = 3.37x + 0.84 for traumatic insertion, p < 0.001, ANCOVA). In the present study, the insertion force was correlated with the intracochlear trauma. The 150- to 180-degree region represented the area at risk for scalar translocation for this straight electrodes array. Insertion force curves with different sets of values were identified for traumatic and atraumatic insertions; these values should be considered during motorized insertion of an implant so as to be able to modify the insertion parameters (e.g axis of insertion) and facilitate preservation of endocochlear structures.

Characterization of intracochlear rupture forces in fresh human cadaveric cochleae

HYPOTHESIS

To develop a method to measure the forces required for a probe to translocate from the scala tympani (ST) to the scala vestibuli (SV) in fresh human cochleae.

BACKGROUND

Translocation of cochlear implant electrodes from the ST to the SV may lead to suboptimal audiologic outcomes. Prior work investigating the rupture forces of human intracochlear membranes comes from a single study conducted on isolated ex vivo cadaveric specimens.

METHODS

Fresh (postmortem <120 h), nonfixed, never-frozen human temporal bones underwent preparation consisting of surgical isolation of the cochleae and exposure of the osseous spiral lamina, basilar membrane, and Reissner's membrane complex by removing bone covering the ST and the SV. Each isolated cochlea was mounted to a force sensor using an adjustable mounting platform. A 300-μm-diameter ball-tipped probe was attached to a piezoelectric linear motor and advanced at 1 mm/s from the ST to the SV while recording force from the load cell concurrent with video.

RESULTS

Ten specimens were successfully exposed and analyzed. The range of rupture forces was 42 to 122 mN, with a mean of 88 mN. Nine of the 10 specimens failed via simple puncture, whereas one failed by being avulsed from its medial attachment.

CONCLUSION

Using a novel technique, we report the forces required to translocate a model of an electrode from the ST to the SV. Correlation to human perceptual ability is necessary to determine if a surgeon can detect such translocation during cochlear implant surgery.

Sound transfer of active middle ear implants

Implantable hearing aids are gaining importance for the treatment of sensorineural hearing loss and also for mixed hearing loss. The various hearing aid systems, combined with different middle ear situations, give rise to a wide range of different reconstructions. This article attempts to summarize the current knowledge concerning the mechanical interaction between active middle ear implants (AMEIs) and the normal or reconstructed middle ear. Some basic characteristics of the different AMEIs are provided in conjunction with the middle ear mechanics. The interaction of AMEIs and middle ear and the influence of various boundary conditions are discussed in more detail.

Intracochlear fluid pressure changes related to the insertional speed of a CI electrode

Introduction. To preserve residual hearing the atraumaticity of the cochlea electrode insertion has become a focus of cochlear implant research. In addition to other factors, the speed of insertion is thought to be a contributing factor in the concept of atraumatic implantation. The aim of our study was to observe intracochlear fluid pressure changes due to different insertional speeds of an implant electrode in a cochlear model. Materials and Methods. The experiments were performed using an artificial cochlear model. A linear actuator was mounted on an Advanced Bionics IJ insertional tool. The intracochlear fluid pressure was recorded through a pressure sensor which was placed in the helicotrema area. Defined insertions were randomly performed with speeds of 0.1 mm/sec, 0.25 mm/sec, 0.5 mm/sec, 1 mm/sec, and 2 mm/sec. Results. A direct correlation between speed and pressure was observed. Mean maximum values of intracochlear fluid pressure varied between 0.41 mm Hg and 1.27 mm Hg. Conclusion. We provide the first results of fluid pressure changes due to insertional speeds of CI electrodes in a cochlear model. A relationship between the insertional speed and intracochlear fluid pressure was observed. Further experiments are needed to apply these results to the in vivo situation.

The round window: is it the "cochleostomy" of choice? Experience in 130 consecutive cochlear implants

OBJECTIVE

To demonstrate that the round window insertion (RWI) for cochlear implantation with multichannel electrodes is a reliable, safe, and effective technique.

STUDY DESIGN

Retrospective case review.

SETTING

Academic tertiary referral center.

PATIENTS

One hundred thirty consecutive cochlear implants (72 female and 58 male subjects) performed from August 2009 to August 2011. Devices included 83 Cochlear, 40 Med El, and 7 Advanced Bionics (AB) cochlear implants.

INTERVENTION

Subsequent to a full audiometric assessment, patients underwent a mastoidectomy with facial recess approach whereby the primary surgical objective was to perform a RWI. When the surgeon was unable to access the round window safely, a cochleostomy was performed anterior and inferior to the round window. Postoperative performance was measured with Hearing in Noise Test, the Consonant-Nucleus-Consonant test, and/or the Arizona Biomedical Sentences test.

MAIN OUTCOME MEASURES

Surgical feasibility of reliably performing a RWI, reason for cochleostomy, postoperative complications, and audiometric performance.

RESULTS

In 111 (85.4%) of 130 procedures, a RWI was performed; in 19 (14.6%), a cochleostomy was readily performed by the same approach. Reasons for creating a cochleostomy included facial nerve and jugular bulb location. There were no major postoperative complications in either group and 13 total minor complications. There was no statistically significant difference in postoperative complications or in audiometric performance between the 2 groups.

CONCLUSION

The RWI may offer several advantages over a cochleostomy, and it seems to be a reliable, safe, and effective technique for cochlear implantation with today's cochlear implant electrodes. Further studies would be necessary to verify these findings for broad application to the cochlear implant patient population.

The effect of static force on round window stimulation with the direct acoustic cochlea stimulator

The Direct Acoustic Cochlea Stimulator Partial Implant (DACS PI, Phonak Acoustic Implants SA, Switzerland) is intended to stimulate the cochlea by a conventional stapedotomy piston that is crimped onto the DACS PI artificial incus. An alternative approach to the round window (RW) is successfully done with other devices, having the advantage of being also independent of the existence of middle ear structure (e.g. ossicles). Here the possibility of stimulating the RW with the DACS actuator is investigated including the impact of static force on sound transmission to the cochlea. The maximum equivalent sound pressure output with RW stimulation was determined experimentally in fresh human temporal bones. Experiments were performed in analogy to the ASTM standard (F2504.24930-1) method for the output determination of implantable middle ear hearing devices (IMEHDs) in human cadaveric temporal bones (TBs). ASTM compliant temporal bones were stimulated with a prosthesis having a spherical tip (∅0.5 mm) attached to the actuator. The stimulation was performed perpendicular to the round window membrane (RWM) at varying position relative to the RW and the resulting static force on the RW membrane was determined. At each position the displacement output of the DACS PI actuator and the stapes footplate (SFP) vibration in response to actuator stimulation was measured with a Laser Doppler Velocimeter (LDV). By comparison of the achieved output at the stapes footplate in response to sound and transducer stimulation the equivalent sound pressure level at the tympanic membrane at 1Vrms input voltage was calculated assuming that the SFP displacement in both conditions is a measure of perceived loudness, as it is done in the ASTM standard. Ten TB preparations within the acceptance range of the ASTM standard were used for analysis. The actuator driven stapes footplate displacement amplitude as well as the resulting equivalent sound pressure level was highly dependent on the static force applied to the RW. The sound transfer efficiency from the RW to the stapes footplate increased monotonically with increasing static load. At a moderate static force load (approx. 3.9 mN) the obtained average sound equivalent sound pressure level was 102-120 eq. dB SPL @ nominally 1Vrms input for frequencies ≤4 kHz. At higher frequencies (6-10 kHz) the achieved output dropped to ∼90 dB SPL. This output was obtained at loading conditions compatible with the actuator safe operating range, although it was possible to increase the output further by increasing the static force load. Our results demonstrate for a first time that static force applied to the RW is crucial for sound transmission efficiency. Further we could show that RW stimulation with the DACS PI actuator is possible having a maximum output that is sufficient to treat moderate and pronounced sensorineural hearing losses (SNHL). This article is part of a Special Issue entitled "MEMRO 2012".

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.

Magnetic Guidance of Cochlear Implants: Proof-of-Concept and Initial Feasibility Study

Cochlear implants have become a standard treatment for many with severe to profound sensorineural hearing loss. However, delicate cochlear structures can be damaged during surgical insertion, which can lead to loss of residual hearing and decreased implant effectiveness. We propose a magnetic guidance concept in which a magnetically tipped cochlear implant is guided as it is inserted into the cochlea. In a scaled in vitro experimental study, we record insertion forces for nonguided and magnetically guided insertion experiments and compare the results. Results indicate that magnetic guidance reduced insertion forces by approximately 50%. Using first principles, we discuss the effects of scaling down our in vitro experiments, and account for realistic clinical dimensions. We conclude that scale–down effects are negligible, but to produce the same field strength as in our experiments and provide sufficient clearance between the patient and the manipulator, the magnet dimensions should be increased by approximately four times.

Cochlear implant electrode insertion: in defence of cochleostomy and factors against the round window membrane approach

INTRODUCTION

The round window membrane (RWM) is an increasingly popular route for electrode insertion in cochlear implantation especially for hearing preservation. Limitations to this route include anatomical, physiological, and surgical aspects. The established soft-tissue cochleostomy route for electrode insertion is thought to place the basilar membrane and spiral ligament at risk. However, the mammalian model response to soft-tissue cochleostomy has not yet been quantified.

METHODS

Firstly, an on-line literature search was conducted to gather evidence of the anatomical and physiological functions of the RWM and adjacent structures. Secondly, experimental guinea pigs underwent left soft-surgery cochlestomy. Four weeks post-operatively they were euthanased and the cochlea's harvested for histology. Surgical damage to the cochlea and auditory neurons was assessed.

RESULTS

The literature review with regard to the RWM anatomy revealed evidence for difficulty in approach/visualization, possible absence, and impedance of electrode insertion by the hook region. It also has a number of higher functions including immune defence and absorption/secretion of molecules. Experimental cochlea's 4 weeks post-soft-tissue cochleostomy showed only mild and localized inflammatory response adjacent to the scala tympani cochleostomy site. There was no spiral neuronal ganglion loss.

CONCLUSIONS

The RWM route may be compromised or absent. Electrode insertion via the RWM could interfere with its higher functions. Mammalian soft-tissue cochleostomy has been shown to elicit a limited tissue response and does not reduce the number of cochlear spiral ganglion neurones. It should therefore remain within the hearing implant surgeon's armamentarium.

Physiological assessment of active middle ear implant coupling to the round window in Chinchilla lanigera

OBJECTIVE

To study the effects of various active middle ear implant loading parameters on round window stimulation in an animal model.

STUDY DESIGN

Physiological measurements of the cochlear microphonic and stapes velocity were made from active middle ear implant-generated sinusoidal stimuli with controlled changes in loading parameters.

SETTING

Prospective study at an academic research institution.

SUBJECTS AND METHODS

Cochlear microphonic and stapes velocities (H(EV)) were measured in 6 study subjects (Chinchilla lanigera) in response to active middle ear implant (Otologics MET, Boulder, Colorado) round window stimulation with assessment of effects of varying parameters of loading pressure, interposed connective tissue, and angle of stimulation with respect to the round window membrane.

RESULTS

The measured performance variabilities in repeated applications of the active middle ear implant to the round window were 2.5 dB and 5.0 dB for H(EV) and cochlear microphonic thresholds, respectively. Loading pressure applied to the round window (51-574 dynes) and angle of approach (±30° with respect to coronal plane) did not have a significant effect on cochlear microphonic thresholds or H(EV). Significant improvements in cochlear microphonic thresholds and H(EV) were observed for interposed connective tissue regardless of tissue type.

CONCLUSION

Variability in performance due to repeated couplings of the active middle ear implant to the round window is small and reproducible. Interposition of connective tissue significantly improves vibration energy transfer to the cochlea. Neither changes in loading pressure nor angle of stimulation of the round window affected active middle ear implant performance.

Force measurement of insertion of cochlear implant electrode arrays in vitro: comparison of surgeon to automated insertion tool

CONCLUSIONS

We have demonstrated that an automated insertion tool (i.e. a robot) can be used to duplicate a complex surgical motion in inserting cochlear implant (CI) electrode arrays via the 'advance-off-stylet' (AOS) technique. As compared with human operators, the forces generated by the robot were slightly larger but the robot was more reliable (i.e. less force maxima).

OBJECTIVES

We present force data collected during CI electrode insertion by human operators and by an automated insertion tool.

MATERIALS AND METHODS

Using a three-dimensional, anatomically correct, translucent model of the scala tympani chamber of the cochlea, CI electrodes were inserted either by one of three surgeons (26 insertions) or by the robotic insertion tool (8 insertions). Force was recorded using a load beam cell calibrated for expected forces of <0.1 Newtons (N). The insertions were also videotaped to allow correlation of force with depth of penetration into the cochlea and speed of insertion.

RESULTS

Average insertion force used by the surgeons was 0.004+/-0.001 N and for the insertion tool it was 0.005+/-0.014 N (p<0.00001, Student's t test). While the average insertion force of the automated tool was larger than that of the surgeons, the surgeons did have intermittent peaks during the AOS component of the insertion (between 120 degrees and 200 degrees ).

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.

Direct measurement flow resistance of cochlear aqueduct in guinea pigs

OBJECTIVE

The cochlear aqueduct connects the scala tympani to the subarachnoid space and is the main pressure equalization canal for the inner ear. Increases in inner ear volume and pressure are thought to cause clinical symptoms such as vertigo, tinnitus and fluctuating hearing loss. In this study the flow resistance of the cochlear aqueduct was determined and its relation with inner ear pressure was studied.

MATERIAL AND METHODS

Inner ear pressure was measured in the scala tympani through the round window using a micropipette. Through a second micropipette, artificial perilymph was infused into, or withdrawn from, the scala tympani at various constant rates. From the infusion rate and the change in perilymphatic pressure during infusion the flow resistance of the cochlear aqueduct was calculated.

RESULTS

The flow resistance was found not to be constant but to depend on the position of the round window membrane and possibly on the magnitude and direction of fluid flow through the aqueduct. Measured flow resistance values were in the range 11-45 Pa s/nl. For very small flow values the flow resistance averaged over 6 animals was 21 Pa s/nl.

CONCLUSIONS

The flow resistance of the cochlear aqueduct is not a constant value. The cochlear aqueduct is a canal with dynamic properties and may play a role in the complicated process of inner ear pressure regulation.

Measurement of guinea pig basilar membrane using computer-aided three-dimensional reconstruction system

Cochleas are known to have the ability to analyze a frequency widely, and this ability seems to be owed mostly to the basilar membrane (BM) configuration. However, the relationship between the cochlear frequency-position map and the BM configuration is not clear. Therefore, in this paper, the internal structures of a guinea pig cochlea, especially the BM configuration, were reconstructed and measured using a computer-aided three-dimensional (3-D) reconstruction system. Then, an attempt was made to examine the influence of the BM configuration on the cochlear frequency-position map. The measurement results indicate that the width of the BM increased and its thickness decreased with an increase in the distance from the basal turn towards the apical turn. Theoretical consideration reveals that the wide frequency-position of the cochlea is achieved by not only the BM configuration change along the length of the cochlea but also the change of the Young's modulus of the BM along the length of the cochlea.