Middle ear electromagnetic semi-implantable hearing device: results of the phase II SOUNDTEC direct system clinical trial

The development of active middle ear implants: A historical perspective and clinical outcomes

Objective s

Energy emitting, active middle ear implants (aMEI) have taken more than two decades of research to reach technological sophistication, medical safety, and regulatory approval to become a powerful tool in treating sensorineural, conductive, and mixed hearing loss. The present review covers this era.

Data Source

Literature found from searching Pubmed (MEDLINE); EMBASE, SciSearch, German Medical Science Journals and Meetings, and The Cochrane Library; and published as of February 2017. Study bibliographies were hand-searched to find further materials.

Methods

A systematic literature review was conducted to identify studies evaluating the safety, efficacy, effectiveness, and subjective outcomes of partially implantable aMEIs. Data were extracted on systems with regulatory approval and summarized narratively. Meta-analyses were conducted for aMEIs with more than 25 publications. Study selection, data extraction, and quality appraisal for quantitative data synthesis was carried out by two reviewers.

Results

Four hundred thirty-one studies included in narrative synthesis describe that albeit good audiological outcomes, clinical safety and (dis)investment are major barriers to continued market access. The synthesised risk of adverse events was three fold with the MET than with the VIBRANT SOUNDBRIDGE. With the latter system, audiological outcomes were stable and similar for all indications and age groups.

Conclusion

To date, the majority of the literature covers the clinical application of the VIBRANT SOUNDBRIDGE system as it is applicable to a wide range of otologic and audiological conditions, particularly with the introduction of couplers to extend its clinical reach. The MAXUM and MET still have to find their way into surgical routine.Level of Evidence.

Benefits of active middle ear implants over hearing aids in patients with sloping high tone hearing loss: comparison with hearing aids

In this retrospective chart review we compared the subjective and objective benefits of active middle ear implants (AMEIs) with conventional hearing aids (HAs) in patients with sloping high tone hearing loss. Thirty-four patients with sensorineural hearing loss were treated with AMEIs. Of these, six had sloping high tone hearing loss and had worn an HA for more than 6 months. Objective assessments, a pure-tone audiogram, as well as a word recognition test, and the Korean version of the Hearing in Noise Test (K-HINT), and a subjective assessment, the Abbreviated Profile of Hearing Aid Benefit (APHAB) questionnaire, were performed. Tests were conducted under three circumstances: 1) the unaided state before surgery; 2) the HA-aided state before surgery; and 3) the AMEI-aided state 3 months after surgery. The average high-frequency hearing gain (≥ 2 kHz) was significantly better with AMEIs than with HAs. Although the result had no statistical significance, AMEIs showed a superior word recognition score (WRS) compared to HAs. However, the most comfortable hearing level at which the WRS was tested was significantly decreased with an AMEI compared to an HA. In the K-HINT, patients with an AMEI showed greater recognition than those fitted with an HA under both quiet and noisy conditions. The APAHB scores revealed that patients were more satisfied with an AMEI rather than an HA on all subscales. The use of vibroplasty in patients with sloping high tone loss resulted in positive hearing outcomes when compared to conventional HAs. Based on the data from this study, AMEIs provided better objective and subjective results and could, therefore, be a better alternative for the treatment of sloping hearing loss.

Comparison of an Electromagnetic Middle Ear Implant and Hearing Aid Word Recognition Performance to Word Recognition Performance Obtained Under Earphones

OBJECTIVE

To report the results of patients with the Maxum middle ear implant (MEI) and compare word recognition scores (WRS) and speech perception gap (SP Gap) of Maxum versus optimally fit hearing aids (HA).

STUDY DESIGN

Case series with chart review.

SETTING

Single, private otology clinic.

PATIENTS

Eleven ears, in nine adult patients (two women; average age 62.7 yr).

INTERVENTIONS

Twelve consecutive ears with moderate to severe sensorineural hearing loss (SNHL) underwent implantation of the Maxum system. One patient was not included due to inadequate preoperative testing.

MAIN OUTCOME MEASURES

Primary outcome measures included word recognition score (WRS) and SP Gap (maximum word understanding [PB max] - WRSaided) improvement compared with HAs.

RESULTS

The average Maxum WRS was 64.7% (range, 28-94%), a 41.6% improvement (range, 10-66%) over HAs (p < 0.001). The average Maxum SP Gap was 6.6% (range, -8 to 24%), a 41.6% improvement (range, 10-66%) over HAs (p < 0.001).

CONCLUSION

These data demonstrate that the Maxum provides superior WRS than HAs for patients with significant aided SP Gaps. There is a significant, very strong correlation between Maxum WRS and PB max (r = 0.85, p = 0.001). This implies that PB max may reasonably predict WRS outcomes with Maxum before implantation, and the SP Gap can reasonably predict the degree of additional potential benefit with Maxum. In advising patients who may be candidates for both a CI and MEI, PB max and SP Gap measurements will provide useful predictive information to help clinicians counsel patients on their choice of hearing technology.

LEVEL OF EVIDENCE

4.

Evaluation of Maximal Speech Intelligibility With Vibrant Soundbridge in Patients With Sensorineural Hearing Loss

OBJECTIVE

The study investigated improvements in maximal speech intelligibility after Vibrant Soundbridge (VSB) implantation and analyzed the effect of the hearing loss pattern on maximal speech intelligibility represented by a phonetically balanced word score (PBmax). The effect of middle ear implants on PBmax has not been evaluated yet.

STUDY DESIGN

Study.

SETTING

Tertiary academic medical center.

PATIENTS/INTERVENTIONS

Sixty patients who underwent VSB from December 2011 to January 2016 were retrospectively reviewed. All the patients had hearing aids preoperatively.

MAIN OUTCOME MEASURES

Pure-tone and speech audiometry were checked with and without hearing aids and then with the VSB. The patients were divided into two groups: flat and down-sloping type of hearing loss. PBmax score was evaluated at the most comfortable listening level before and after VSB implantation and compared with scores with/without HA.

RESULTS

PBmax for both conventional HA and VSB were significantly higher compared with the unaided condition. The improvement in speech recognition was significantly better using VSB than using HA (p = 0.003). However, there was no significant difference in the improvement provided by VSB and HA in patients with a flat hearing loss. Patients with a down-sloping audiogram showed significantly better improvement with VSB than with HA (p = 0.003). Moreover, patients with greater preoperative high-frequency hearing loss had greater improvement in PBmax after VSB implantation.

CONCLUSION

Speech intelligibility can be significantly improved by VSB implantation, especially in patients with a down-sloping hearing loss. This finding can help select patients who will benefit most from VSB implantation.

Factors associated with benefit of active middle ear implants compared to conventional hearing aids

OBJECTIVE

Identify factors associated with benefit of middle ear implants (MEIs) as compared to conventional hearing aids (HAs).

STUDY DESIGN

Independent review of audiological data from a multicenter prospective U.S. Food and Drug Administration (FDA) clinical trial. Preoperative and postoperative earphone, unaided/aided/implanted pure-tone thresholds, and word recognition scores were evaluated.

RESULTS

Ninety-one subjects were included in this study. Mean word recognition was better with MEIs than with HAs (81.8% ± 12.0% vs. 77.6% ± 14.6%, P = 0.035). Word recognition with MEIs showed a low positive correlation with word recognition measured with earphones (r = 0.25, P = 0.016) and a moderate positive correlation with aided word recognition (r = 0.42, P < 0.001). Earphone word recognition alone was not predictive of MEI benefit over HA benefit (r = 0.09, P = 0.41), unlike differences between scores with earphone and HAs (earphone-aided differences [EAD]) (r = 0.62, P < 0.011). As compared to those with -EADs, subjects with +EADs showed greater improvement in word recognition from unaided to implanted and from HAs to implanted (P < 0.0001). Using the 95% CI for word recognition scores, 16 subjects showed significantly higher scores with the MEI than with HAs. Of those, 14 had +EAD.

CONCLUSION

Word recognition benefit derived from conventional HAs and MEIs from this large, multi-center FDA trial provides further evidence of the importance of aided word recognition in clinical decision making, such as determining candidacy for and success with MEIs.

LEVEL OF EVIDENCE

2b. Laryngoscope, 128:2133-2138, 2018.

A new semi-implantable middle ear implant for sensorineural hearing loss: three-years follow-up in a pilot patient's group

OBJECTIVE

The aim of this article is to report on the long-term follow-up of a new semi-implantable middle ear device utilized for restoration of moderate-to-severe sensorineural hearing loss in a first series of subjects.

METHODS

Three subjects, affected by sensorineural hearing loss, have undergone implantation of Maxum^® middle ear implant, via a transcanal approach. They all underwent an auditory assessment, paying particular attention on the pre- versus post-operative hearing levels under the unaided, best-fitted hearing aided and implant-aided conditions. The audiometric evaluation has been repeated 3 years after implantation and implemented by questionnaires aiming at the evaluation of the quality of life.

RESULTS

The post-operative hearing threshold and discrimination in quiet appear to be similar or better than those provided by conventional hearing aids, with a concomitant improvement of the subjects' quality of life. The application of the present device showed to be easy and reproducible, with no severe adverse effects recorded at the 3-years follow-up. Mild issues due to the external component were also observed, such as difficulty of keeping it continuously in place due to excess canal sweating in one subject, and a temporary loss of stability due to occurring irregularities of the external coating in another subject.

CONCLUSIONS

Long-term, preliminary data reveal that the Maxum^® device may provide equal or better functional gain and word recognition scores in quiet in patients with moderate-to-severe sensorineural hearing loss, in comparison to optimally fitted hearing aids, with a satisfactory improvement of their quality of life.

Implantable hearing devices

Combined hearing loss is an essential indication for implantable hearing systems. Depending on the bone conduction threshold, various options are available. Patients with mild sensorineural deafness usually benefit from transcutaneous bone conduction implants (BCI), while percutaneous BCI systems are recommended also for moderate hearing loss. For combined hearing losses with moderate and high-grade cochlear hearing loss, active middle ear implants are recommended. For patients with incompatibilities or middle ear surgery, implants are a valuable and proven addition to the therapeutic options.

Cost-Utility of Partially Implantable Active Middle Ear Implants for Sensorineural Hearing Loss: A Decision Analysis

BACKGROUND

Partially implantable active middle ear implants (aMEIs) offer a solution for individuals who have mild to severe sensorineural hearing loss and an outer ear medical condition that precludes the use of hearing aids. When otherwise left untreated, individuals report a lower quality of life, which may further decrease with increasing disability. In the lack of cost-effectiveness studies and long-term data, there is a need for decision modeling.

OBJECTIVE

To explore individual-level variance in resource utilization patterns following aMEI implantation.

METHODS

A Markov model was developed and analyzed as microsimulation to estimate the incremental cost utility ratio (ICUR) of partially implantable aMEIs compared with no (surgical) intervention in individuals with sensorineural hearing loss and an outer ear medical condition in Australia. Cost data were derived mostly from the Medicare Benefit Schedule and effectiveness data from published literature. A third-party payer perspective was adopted, and a 5% discount rate was applied over a 10-year time horizon.

RESULTS

Compared with baseline strategy, aMEIs yielded an incremental cost of Australian dollars (AUD) 13,339.18, incremental quality-adjusted life-year (QALY) of 1.35, and an ICUR of AUD 9,913.72/QALY. Of the respective number of simulated patients who visited each health state, 75.73% never had a minor adverse event, 99.82% did not experience device failure, and 97.75% did not cease to use their aMEIs. Probabilistic sensitivity analyses showed the ICUR to differ by only 0.95%.

CONCLUSIONS

In the Australian setting, partially implantable aMEIs offer a safe and cost-effective solution compared with no intervention and are also well accepted by users.

Evaluating speech perception of the MAXUM middle ear implant versus speech perception under inserts

OBJECTIVES/HYPOTHESIS

To evaluate the speech perception of the Ototronix MAXUM middle ear implant relative to the cochlear potential for speech perception of patients.

STUDY DESIGN

Clinical study chart review.

METHODS

We performed an evaluation of data from a prospective clinical study of 10 MAXUM patients. Primary outcome measures included comparison of word recognition (WR) scores with MAXUM (WR_MAXUM ) versus word recognition under inserts (WR_inserts ), and the functional gain improvement for pure-tone average (PTA) (0.5, 1, and 2 kHz) and high-frequency pure-tone average (2, 3, and 4 kHz).

RESULTS

Ten ears in 10 adult patients (six female; average age 68.7 years) were included. The average speech perception gap (difference between WR_inserts and WR_MAXUM ) with MAXUM was -9.2% (range, -26% to 4%). A negative number indicates that WR_MAXUM was higher than the WR_inserts . The average PTA with MAXUM was 23.1 dB (range, 18.7-30 dB), a 38.0-dB gain over the preoperative unaided condition (range, 20-53.3 dB). The average high-frequency pure-tone average with MAXUM was 34.4 dB (range, 26-43.3 dB), a 42.8-dB gain over the preoperative unaided condition (range, 32.3-58.7 dB).

CONCLUSIONS

These data demonstrate that a significant, very strong correlation was observed between WR_inserts and WR_MAXUM scores (r = 0.86, P = .001), and a patient's WR_inserts score may be used to reasonably predict the word recognition outcomes with MAXUM.

LEVEL OF EVIDENCE

4. Laryngoscope, 128:456-460, 2018.

The ototronix MAXUM middle ear implant for severe high-frequency sensorineural hearing loss: Preliminary results

OBJECTIVES/HYPOTHESIS

To report the preliminary results of the Ototronix MAXUM middle ear implant for treatment of severe high-frequency sensorineural hearing loss.

STUDY DESIGN

Case series with chart review.

METHODS

Six consecutive ears with severe high-frequency sensorineural hearing loss (≥75 dB HL at 2, 3, and 4 kHz) and poor aided word recognition performance (≤60% single words) underwent implantation of the MAXUM system at a single, private otologic referral center. Primary outcome measures included frequency-specific functional gain and word recognition score improvement compared to optimally fitted hearing aids.

RESULTS

Six ears, in four adult patients (two female; median age 67.5 years) were included. The median unaided preoperative high-frequency pure-tone average (HFPTA) (2, 3, and 4 kHz) was 80.0 dB (range, 75.0-85.0 dB), and the median best-aided word recognition score was 48.0% (range, 24%-60%). The median HFPTA functional gain with the MAXUM system was 47.2 dB, a 25.0 dB improvement (range, 16.7-33.3 dB) (P = .03) over optimally fit hearing aids, and the median word recognition score with MAXUM was 81.5%, a 42.0% improvement (range, 20%-48%) (P = .03) with the MAXUM middle ear implant over optimally fitted hearing aids.

CONCLUSIONS

These preliminary data demonstrate that the MAXUM middle ear implant provides superior functional gain and word recognition scores in quiet for patients with severe high-frequency sensorineural hearing loss compared to optimally fitted hearing aids. Future studies with greater patient numbers and patient reported outcome measures are needed to confirm these promising but preliminary results.

LEVEL OF EVIDENCE

4 Laryngoscope, 126:2124-2127, 2016.

Middle ear implants for rehabilitation of sensorineural hearing loss: a systematic review of FDA approved devices

OBJECTIVE

To systematically review the safety and efficacy of the 3 Food and Drug Administration-approved middle ear implant (MEI) systems currently in use for the rehabilitation of sensorineural hearing loss.

DATA SOURCES

MEDLINE and Cochrane Library databases were systematically searched by 2 independent reviewers.

STUDY SELECTION

An initial search yielded 3,020 articles that were screened based on title and abstract. A full manuscript review of the remaining 80 articles was performed, of which 17 unique studies satisfied inclusion criteria and were evaluated.

DATA EXTRACTION

Variables including functional gain, speech recognition score improvement, audiometric threshold shift following surgery, adverse events, and patient reported outcome measures were recorded. Study quality was appraised according to author conflict of interest, prospective or retrospective study design, inclusion criteria, number of patients, proper use of study controls, outcome measures reported, length of follow-up, and level of evidence.

DATA SYNTHESIS

Heterogeneous outcome reporting precluded meta-analysis; instead a structured review was performed using best available data.

CONCLUSION

The majority of studies evaluating the safety and efficacy of MEIs are retrospective in nature with limited follow-up. To date, no prospective randomized controlled trial exists comparing contemporary air conduction hearing aid performance and MEI outcomes. Based on available data for patients with sensorineural hearing loss, functional gain and word recognition improvement seems similar between conventional hearing aids and MEIs, whereas patient-perceived outcome measures suggest that MEIs provide enhanced sound quality and eliminate occlusion effect.

A micro-drive hearing aid: a novel non-invasive hearing prosthesis actuator

The direct hearing device (DHD) is a new auditory prosthesis that combines conventional hearing aid and middle ear implant technologies into a single device. The DHD is located deep in the ear canal and recreates sounds with mechanical movements of the tympanic membrane. A critical component of the DHD is the microactuator, which must be capable of moving the tympanic membrane at frequencies and magnitudes appropriate for normal hearing, with little distortion. The DHD actuator reported here utilized a voice coil actuator design and was 3.7 mm in diameter. The device has a smoothly varying frequency response and produces a precisely controllable force. The total harmonic distortion between 425 Hz and 10 kHz is below 0.5 % and acoustic noise generation is minimal. The device was tested as a tympanic membrane driver on cadaveric temporal bones where the device was coupled to the umbo of the tympanic membrane. The DHD successfully recreated ossicular chain movements across the frequencies of human hearing while demonstrating controllable magnitude. Moreover, the micro-actuator was validated in a short-term human clinical performance study where sound matching and complex audio waveforms were evaluated by a healthy subject.

Preservation of auditory brainstem response thresholds after cochleostomy and titanium microactuator implantation in the lateral wall of cat scala tympani

HYPOTHESIS

The safety of implanting a titanium microactuator into the lateral wall of cat scala tympani was assessed by comparing preoperative and postoperative auditory brainstem response (ABR) thresholds for 1 to 3 months.

BACKGROUND

The safety of directly stimulating cochlear perilymph with an implantable hearing system requires maintaining preoperative hearing levels. This cat study is an essential step in the development of the next generation of fully implantable hearing devices for humans.

METHODS

Following GLP surgical standards, a 1-mm cochleostomy was drilled into the lateral wall of the scala tympani, and a nonfunctioning titanium anchor/microactuator assembly was inserted in 8 cats. The scala media was damaged in the 1 cat. ABR thresholds with click and 4- and 8-kHz stimuli were measured preoperatively and compared with postoperative thresholds at 1, 2, and 3 months. Nonimplanted ear thresholds were also measured to establish statistical significance for threshold shifts (>28.4 dB). Two audiologists independently interpreted thresholds.

RESULTS

Postoperatively, 7 cats implanted in the scala tympani demonstrated no significant ABR threshold shift for click stimulus; one shifted ABR thresholds to 4- and 8-kHz stimuli. The eighth cat, with surgical damage to the scala media, maintained stable click threshold but had a significant shift to 4- and 8-kHz stimuli.

CONCLUSION

This cat study provides no evidence of worsening hearing thresholds after fenestration of the scala tympani and insertion of a titanium anchor/microactuator, provided there is no surgical trauma to the scala media and the implanted device is securely anchored in the cochleostomy. These 2 issues have been resolved in the development of a fully implantable hearing system for humans. The long-term hearing stability (combined with histologic studies) reaffirm that the microactuator is well tolerated by the cat cochlea.

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.

Implantable hearing devices: the Ototronix MAXUM system

For many hearing-impaired individuals, the benefits of conventional amplification may be limited by acoustic feedback, occlusion effect, and/or ear discomfort. The MAXUM system and other implantable hearing devices have been developed as an option for patients who derive inadequate assistance from traditional HAs, but who are not yet candidates for cochlear implants. The MAXUM system is based on the SOUNDTEC Direct System technology, which has been shown to provide improved functional gain as well as reduced feedback and occlusion effect compared to hearing aids. This and other implantable hearing devices may have increasing importance as future aural rehabilitation options.

Implantable and semi-implantable hearing AIDS: a review of history, indications, and surgery

Introduction The complaints associated with the use of conventional amplifying hearing aids prompted research at several centers worldwide that ultimately led to the development of implantable devices for aural rehabilitation. Objectives To review the history, indications, and surgical aspects of the implantable middle ear hearing devices. Data Synthesis Implantable hearing aids, such as the Vibrant Soundbridge system (Med-El Corporation, Innsbruck, Austria), the Maxum system (Ototronix LLC, Houston, Texas, United States), the fourth-generation of Carina prosthesis (Otologics LLC, Boulder, Colorado, United States), and the Esteem device (Envoy Medical Corporation - Minnesota, United States), have their own peculiarities on candidacy and surgical procedure. Conclusion Implantable hearing aids, which are currently in the early stages of development, will unquestionably be the major drivers of advancement in otologic practice in the 21st century, improving the quality of life of an increasingly aged population, which will consequently require increased levels of hearing support.

The role of active middle-ear implants in the rehabilitation of hearing loss

The surgical implantation of auditory devices to improve or restore the sensation of hearing in affected individuals is a rapidly growing area of modern ear, nose and throat, and audiological practice. Following the enormous success of cochlear implantation and set to take an increasing role in the rehabilitation of deafness is the active middle-ear implant. They should be viewed as an alternative to conventional hearing aids for individuals who are either unable to wear hearing aids or reject them for a variety of reasons. This article discusses the different types of middle-ear implant that are currently in use and examines the significant challenges that remain to be overcome to further advance this field.

Systematic review of middle ear implants: do they improve hearing as much as conventional hearing AIDS?

OBJECTIVE

A systematic review to determine whether middle ear implants (MEIs) improve hearing as much as hearing aids.

DATA SOURCES

Databases included MEDLINE, EMBASE, DARE, and Cochrane searched with no language restrictions from 1950 or the start date of each database.

STUDY SELECTION

Initial search found 644 articles, of which 17 met the inclusion criteria of MEI in adults with a sensorineural hearing loss, where hearing outcomes and patient-reported outcome measures (PROMs) compared MEI with conventional hearing aids (CHAs).

DATA EXTRACTION

Study quality assessment included whether ethical approval was gained, the study was prospective, eligibility criteria specified, a power calculation made and appropriate controls, outcome measures, and analysis performed. Middle ear implant outcome analysis included residual hearing, complications, and comparison to CHA in terms of functional gain, speech perception in quiet and in noise, and validated PROM questionnaires.

DATA SYNTHESIS

Because of heterogeneity of outcome measures, comparisons were made by structured review.

CONCLUSION

The quality of studies was moderate to poor with short follow-up. The evidence supports the use of MEI because, overall, they do not decrease residual hearing, result in a functional gain in hearing comparable to CHA, and may improve perception of speech in noise and sound quality. We recommend the publication of long-term results comparing MEI with CHA, reporting a minimum of functional gain, speech perception in quiet and in noise, complications, and a validated PROM to guide the engineering of the new generation of MEI in the future.

Comparisons of electromagnetic and piezoelectric floating-mass transducers in human cadaveric temporal bones

Electromagnetic floating-mass transducers for implantable middle-ear hearing devices (IMEHDs) afford the advantages of a simple surgical implantation procedure and easy attachment to the ossicles. However, their shortcomings include susceptibility to interference from environmental electromagnetic fields, relatively high current consumption, and a limited ability to output high-frequency vibrations. To address these limitations, a piezoelectric floating-mass transducer (PFMT) has recently been developed. This paper presents the results of a comparative study of these two types of vibration transducer developed for IMEHDs. The differential electromagnetic floating-mass transducer (DFMT) and the PFMT were implanted in two different sets of three cadaveric human temporal bones. The resulting stapes displacements were measured and compared on the basis of the ASTM standard for describing the output characteristics of IMEHDs. The experimental results show that the PFMT can produce significantly higher equivalent sound pressure levels above 3 kHz, due to the flat response of the PFMT, than can the DFMT. Thus, it is expected that the PFMT can be utilized to compensate for high-frequency sensorineural hearing loss.

A micropower miniature piezoelectric actuator for implantable middle ear hearing device

This paper describes the design and development of a small actuator using a miniature piezoelectric stack and a flextensional mechanical amplification structure for an implantable middle ear hearing device (IMEHD). A finite-element method was used in the actuator design. Actuator vibration displacement was measured using a laser vibrometer. Preliminary evaluation of the actuator for an IMEHD was conducted using a temporal bone model. Initial results from one temporal bone study indicated that the actuator was small enough to be implanted within the middle ear cavity, and sufficient stapes displacement can be generated for patients with mild to moderate hearing losses, especially at higher frequency range, by the actuator suspended onto the stapes. There was an insignificant mass-loading effect on normal sound transmission (<3 dB) when the actuator was attached to the stapes and switched off. Improved vibration performance is predicted by more firm attachment. The actuator power consumption and its generated equivalent sound pressure level are also discussed. In conclusion, the actuator has advantages of small size, lightweight, and micropower consumption for potential use as IMHEDs.

Middle ear implantable hearing devices: an overview

Hearing loss affects approximately 30 million people in the United States. It has been estimated that only approximately 20% of people with hearing loss significant enough to warrant amplification actually seek assistance for amplification. A significant interest in middle ear implants has emerged over the years to facilitate patients who are noncompliant with conventional hearing aides, do not receive significant benefit from conventional aides, or are not candidates for cochlear implants. From the initial studies in the 1930s, the technology has greatly evolved over the years with a wide array of devices and mechanisms employed in the development of implantable middle ear hearing devices. Currently, these devices are generally available in two broad categories: partially or totally implantable using either piezoelectric or electromagnetic systems. The authors present an up-to-date overview of the major implantable middle ear devices. Although the current devices are largely in their infancy, indications for middle ear implants are ever evolving as promising studies show good results. The totally implantable devices provide the user freedom from the social and practical difficulties of using conventional amplification.

A totally implantable hearing system--design and function characterization in 3D computational model and temporal bones

Implantable middle ear hearing devices are emerging as an effective technology for patients with mild to moderately severe sensorineural hearing loss. Several devices with electromagnetic or piezoelectric transducers have been investigated or developed in the US and Europe since 1990. This paper reports a totally implantable hearing system (TIHS) currently under investigation in Oklahoma. The TIHS consists of implant transducer (magnet), implantable coil and microphone, DSP-audio signal processor, rechargeable battery, and remote control unit. The design of TIHS is based on a 3D finite element model of the human ear and the analysis of electromagnetic coupling of the transducer. Function of the TIHS is characterized over the auditory frequency range in three aspects: (1) mass loading effect on residual hearing with a passive implant, (2) efficiency of electromagnetic coupling between the implanted coil and magnet, and (3) functional gain of whole unit in response to acoustic input across the human skin. This paper focuses on mass loading effect and the efficiency of electromagnetic coupling of TIHS determined from the FE model of the human ear and the cadaver ears or temporal bones. Some preliminary data of whole unit function are also presented in the paper.

Implantable hearing aids

The aim of this article is to give readers a general overview of the concepts involved in the latest generation of implantable hearing aids. A section on ear biomechanics has also been included to familiarize readers with the basic concepts involved. These devices have been developed over the last 20 years, driven by problems with conventional hearing aids and by advances in the understanding of middle-ear mechanics. The use of technology borrowed from cochlear implants has enabled the first generation of fully implantable aids to be trialled. The author examines the theoretical advantages and disadvantages of implantable hearing aids over conventional aids and then reviews the technology and clinical results of a range of devices that have been trialled.

Integration des aktiven Mittelohrimplantates in die plastische Ohrmuschelrekonstruktion

BACKGROUND

Patients with high-grade microtia and atresia require a sophisticated and specific treatment. Apart from the plastic reconstruction of the auricle, in some cases hearing rehabilitation is medically indicated or is desired by the patients. The long-term results of simultaneous middle ear reconstruction with tympanoplasty are often inadequate owing to a persisting air-bone gap, and new techniques in hearing rehabilitation are needed for these patients.

METHODS

We present three cases of unilateral atresia to illustrate a combined approach integrating hearing rehabilitation using the active middle ear implant Vibrant Soundbridge (VSB) into plastic auricular reconstruction. The VSB was attached to the stapes suprastructure via the titanium clip in two of these cases and in the third case a subfacial approach was used to attach it directly to the membrane of the round window.

RESULTS

The air-bone gap was reduced to 17 dB, 14 dB and 0.25 dB HL. In free-field speech recognition tests at 65 dB SPL the patients achieved 100%, 90% and 100% recognition with the activated implant. No postoperative complications such as facial nerve paresis, vertigo or inner ear damage were found.

CONCLUSIONS

The integration of active middle ear implants in auricular reconstruction opens up a new approach in complete hearing rehabilitation. The additional implantation of the VSB does not have any negative effect on the healing process or the cosmetic outcome of the auricular reconstruction.

Anatomical study of the human middle ear for the design of implantable hearing aids

OBJECTIVE

To generate anatomical data on the human middle ear and adjacent structures to serve as a base for the development and optimization of new implantable hearing aid transducers. Implantable middle ear hearing aid transducers, i.e. the equivalent to the loudspeaker in conventional hearing aids, should ideally fit into the majority of adult middle ears and should utilize the limited space optimally to achieve sufficiently high maximal output levels. For several designs, more anatomical data are needed.

METHODS

Twenty temporal bones of 10 formalin-fixed adult human heads were scanned by a computed tomography system (CT) using a slide thickness of 0.63 mm. Twelve landmarks were defined and 24 different distances were calculated for each temporal bone.

RESULTS

A statistical description of 24 distances in the adult human middle ear which may limit or influence the design of middle ear transducers is presented. Significant inter-individual differences but no significant differences for gender, side, age or degree of pneumatization of the mastoid were found. Distances, which were not analyzed for the first time in this study, were found to be in good agreement with the results of earlier studies.

CONCLUSION

A data set describing the adult human middle ear anatomy quantitatively from the point of view of designers of new implantable hearing aid transducers has been generated. In principle, the method employed in this study using standard CT scans could also be used preoperatively to rule out exclusion criteria.

Magnetic Resonance Imaging Compatibility and Safety of the SOUNDTEC Direct System

OBJECTIVE/HYPOTHESIS

The purpose of this study was to evaluate magnetic resonance imaging (MRI) compatibility and safety of an electromagnetic implanted hearing device (the SOUNDTEC Direct System; SOUNDTEC, Inc., Oklahoma City, OK) implant during a 0.3-Tesla open MRI imaging examination of the head and neck and to develop an MRI protocol that maximizes patient safety while minimizing the need for implant removal. The current literature regarding MRI compatibility of implantable hearing devices was reviewed.

STUDY DESIGN

Linear and torsional forces, heating, and implant magnetization were evaluated in vitro. Implanted fresh-frozen human temporal bones were used to evaluate image distortion. A prospective study of 11 volunteers previously implanted with the SOUNDTEC Direct System was conducted to evaluate MRI compatibility and safety. A MEDLINE search of the literature between 1980 and July 2005 was reviewed to summarize MRI compatibility testing of implantable hearing devices.

METHODS

Torsional and linear forces experienced by eight implant magnets were measured using calibrated neurologic Von Frey Hairs and compared with finite element analysis predictions as well as forces required to separate the incudostapedial joints of 12 fresh-frozen human temporal bones. Implant heating was determined by measuring the temperature change of eight implant vials compared with saline controls immediately after a head MRI scan. Implant magnetization was evaluated after repeated exposure to a 0.3-Tesla magnetic field. An 11-patient prospective study was performed to evaluate MRI compatibility in a 0.3-Tesla open MRI environment using adult volunteers previously implanted with the SOUNDTEC Direct System. A modified MRI protocol was developed to maximize patient safety. Each individual underwent an audiometric and otologic examination immediately before and after MRI.

RESULTS

Peak linear force at the MRI entry measured 0.5 g +/- 0.2 standard deviation (SD). Maximum torque occurred at isocenter and measured 11.4 g-cm +/- 1.2 SD. The mean torque required to separate the incudostapedial joint was 33.8 g-cm +/- 20.4 SD. The average increase in temperature of the eight implant vials was 0.45 degrees C +/- 0.11 SD, whereas the increase in temperature of the three saline controls measured 0.47 degrees C +/- 0.11 SD. The average change in magnetic flux density of the 14 implant magnets tested was 22.0 gauss. Maximum image distortion occurred during the gradient echo sequence and measured 8.6 cm in diameter with a volume of 5,096 mm. Eleven patients completed a total of 12 head, one shoulder, and three lumbar 0.3-Tesla open MRI scans without patient- or device-related complications other than degradation of the MR image. There was no report of discomfort, tinnitus, dizziness, change in hearing, or change in device performance. All post-MRI changes in pure-tone thresholds, speech discrimination, soundfield thresholds, and aided soundfield thresholds were within the range of test-retest variability.

CONCLUSION

When considering MRI of implantable ferromagnetic hearing devices, issues related to mechanical forces, implant heating, current induction, implant demagnetization, image degradation, and acoustic trauma must be considered. The SOUNDTEC Direct System is both MRI-compatible and safe in a 0.3-Tesla open MRI environment when a modified protocol is used. Degradation of the head MRI image may impair visualization of the ipsilateral temporal bone and adjacent structures within a 2.5- to 4.3-cm radius of the implant and is minimized by using a fast spin echo sequence.

Experience with the SOUNDTEC implantable hearing aid

OBJECTIVE

To assess the efficacy, morbidity, and patient satisfaction of the SOUNDTEC semi-implantable hearing aid.

STUDY DESIGN

Retrospective case review.

SETTING

Two tertiary referral centers (the Silverstein Institute and the Atkins Institute).

PATIENTS

Sixty-four (four bilateral placements) patients with bilateral moderately severe sensorineural hearing loss: 47 patients had previously worn hearing aids.

INTERVENTIONS

After separating the incudostapedial joint, a magnet encased in a titanium canister with a ring was introduced onto the stapes neck. Gelfoam or adipose tissue was used to stabilize the magnet. After 3 months, the external processor was fitted.

MAIN OUTCOME MEASURES

At 1 month, audiometric testing was performed and functional gain was assessed. Patient acceptance and implant performance were measured by a visual analogue questionnaire.

RESULTS

The device produced an average functional gain of 26 dB. Fifty-five percent of patients complained of magnet movement; this was eliminated in 80% of Silverstein Institute patients when the external processor was worn and fat was used to stabilize the magnet.

CONCLUSION

The SOUNDTEC direct device is well tolerated in the majority of patients, with a significant increase in functional gain. Magnet instability and noise were the most frequent complaints and improved with processor placement and anchoring the magnet with fat. This electromagnetic semi-implantable hearing aid confers greater functional gain over conventional hearing aids and reduces occlusion effect and feedback.