Influence of the Coupling on the Hearing Outcome After Implantation of an Active Middle Ear Implant: Comparison of the Transmission Behavior in Temporal Bone Experiments With Clinical Data.

OBJECTIVES: The active middle ear implant, Vibrant Soundbridge (VSB), can be implanted with a variety of couplers. Hearing outcome after implantation has been investigated in both temporal bone (TB) experiments and patient studies, but the relationship between experimental and clinical data is still weak in the literature. Therefore, experimental data from TB experiments should be compared with patient data in a retrospective study, in which the floating mass transducer is used with couplers of the third generation. Actuator coupling structures included the long (LP coupler) and short (SP coupler) incus process, the stapes head (Clip coupler), and the round window membrane (RW soft coupler). METHODS: In the TB experiments, the sound transmission after vibroplasty on the above-mentioned actuator coupling structures was determined in 32 specimens by means of laser Doppler vibrometry on the stapes footplate. Data of 69 patients were analyzed. The main target audiometric parameters were the postoperative aided word recognition score (WRS) in the free field at 65 dB SPL (WRS 65 dB in %), the preoperative and postoperative pure-tone average (PTA4, including the frequencies 0.5, 1, 2, and 4 kHz) of the bone conduction hearing threshold (PTA4BC), the aided postoperative air conduction hearing threshold in the free field (PTA4FF) and the direct threshold (Vibrogram) at least 6 months postoperatively. The coupling efficiency of the actuator (Vibrogram-PTA4BC) as well as the effective hearing gain (PTA4FF-PTA4BC) was compared between the couplers. RESULTS: The analysis in the main speech range (0.5-4 kHz) indicated that in the TB experiments, the LP coupler tends to have the best coupling quality at low frequencies (500-1000 Hz). This was up to 15 dB above the worst actuator (RW soft coupler). However, the results missed the significance level ( p > 0.05). In the high frequencies (2000-4000 Hz), the Clip coupler showed the best coupling quality. This was 15 dB above the worst actuator (SP coupler). However, the results missed the significance level ( p > 0.05), too. The postoperative WRS at 65 dB SPL and the postoperative PTA4FF were independent of the actuator coupling structure. The PTA4BC was stable at 6 months postoperatively. For the PTA4 of the coupling efficiency, there were no significant differences between the actuator coupling structures (LP 8.9 dB ± 12.9; SP 9.5 ± 6.5 dB; Clip 5.2 ± 10.5 dB; RW 12.7 ± 11.0 dB). However, the tendential inferiority of the RW soft coupler with regard to transmission in the low-frequency range and the tendential superiority of the Clip coupler in the high-frequency range that have already been displayed experimentally could be confirmed in the clinical results. However, the clinical results missed the significance level, too ( p > 0.05). CONCLUSIONS: In vivo, there are no significant differences in the postoperative outcome stratified according to coupling the target structure. The differences known from the experimental setting were repressed by individual biasing factors. However, to ensure sufficient postoperative speech intelligibility, the frequency-specific transmission behavior of the couplers should be taken into account when setting the indication for VSB implantation.

Examination of a mechanical amplifier in the incudostapedial joint gap: FEM simulation and physical model.

Implantable assembly components that are biocompatible and highly miniaturized are an important objective for hearing aid development. We introduce a mechanical transducer, which could be suitable as part of a prospective fully-implantable hearing aid. The transducer comprises a sensor and an actuator unit in one housing, located in the joint gap between the middle ear ossicles, the incus and stapes. The setup offers the advantage of a minimally invasive and reversible surgical solution. However, feedback between actuator and sensor due to mechanical coupling limits the available stable gain. We show that the system can be stabilized by digital control algorithms. The transducer is tested both in a finite elements method simulation of the middle ear and a physical model of a human middle ear. First, we characterize the sensor and actuator elements separately. Then, the maximum stable gain (MSG) of the whole transducer is experimentally determined in the middle ear model. With digital feedback control (using a least mean squares algorithm) in place, the total signal gain is greater than 30 dB for frequencies of 1 kHz and above. This shows the potential of the transducer as a high frequency hearing aid.

Influence of inner ear impedance on middle ear sound transfer functions.

Introduction: For experimental studies on sound transfer in the middle ear, it may be advantageous to perform the measurements without the inner ear. In this case, it is important to know the influence of inner ear impedance on the middle ear transfer function (METF). Previous studies provide contradictory results in this regard. With the current study, we investigate the influence of inner ear impedance in more detail and find possible reasons for deviations in the previous studies. Methods: 11 fresh frozen temporal bones were prepared in our study. The factors related to inner ear impedance, including round window membrane stiffness, cochleostomy, cochlea fluid and cochlea destruction were involved in the experimental design. After measuring in the intact specimen as a reference (step 1), the round window membrane was punctured (step 2), then completely removed (step 3). The cochleostomy was performed (step 4) before the cochlear fluid was carefully suctioned through scala tympani (step 5) and scala vestibuli (step 6). Finally, cochlea was destroyed by drilling (step 7). Translational and rotational movement of the stapes footplate were measured and calculated at each step. The results of the steps were compared to quantify the effect of inner ear impedance changing related to the process of cochlear drainage. Results: As the inner ear impedance decreases from step 1 to 7, the amplitudes of the METF curves at each frequency gradually increase in general. From step 6 on, the measured METF are significantly different with respect to the intact group at high frequencies above 3 kHz. The differences are frequency dependent. However, the significant decrement of rotational motion appears at the frequencies above 4.5 kHz from the step 5. Conclusion: This study confirms the influence of inner ear impedance on METF only at higher frequencies (≥3 kHz). The rotational motions are more sensitive to the drainage of fluid at the higher frequency. Study results that found no influence of cochlea impedance may be due to incomplete drainage of the cochlea.

The ostrich middle ear for developing an ideal ossicular replacement prosthesis.

The aim of the study was to investigate the validity of the avian middle ear model for researching the tympanoplasty mechanics. We studied the morphological details, acoustic transmission and quasi-static behavior of the ostrich tympano-ossicular system. The stained specimens of the ostrich middle ear were examined under a light microscope. The sound transfer function and quasi-static performance of the ostrich middle ear were evaluated using laser Doppler vibrometry. The application of pressure to the tip of the extracolumella causes a buckling movement of the ossicle between the cartilaginous and bony parts. Histologically, the intracolumellar connection can be identified as a junction zone between bone and hyaline cartilage. Sound conduction through the human middle ear is less effective than it is through the ostrich middle ear. The greatest difference (35 dB) was observed in the low-frequency region. Because the extracolumella bends, the medial displacements of the eardrum were not fully transmitted to the footplate. The amplitude of the ostrich columella footplate quasi-static medial displacements significantly exceeded that of the human footplate in both intact and reconstructed middle ears. The ostrich middle ear is a suitable model for designing total ossicular replacement implants. The main protective mechanism in the ostrich middle ear under quasi-static stress is a buckling movement of the extracolumella. The total ossicular prostheses of the new generation should contain an elastic element that allows an adaptation to greater quasi-static eardrum movements.

Auditory thresholds compatible with optimal speech reception likely evolved before the human-chimpanzee split.

The anatomy of the auditory region of fossil hominins may shed light on the emergence of human spoken language. Humans differ from other great apes in several features of the external, middle and inner ear (e.g., short external ear canal, small tympanic membrane, large oval window). However, the functional implications of these differences remain poorly understood as comparative audiometric data from great apes are scarce and conflicting. Here, we measure the sound transfer function of the external and middle ears of humans, chimpanzees and bonobos, using laser-Doppler vibrometry and finite element analysis. This sound transfer function affects auditory thresholds, which relate to speech reception thresholds in humans. Unexpectedly we find that external and middle ears of chimpanzees and bonobos transfer sound better than human ones in the frequency range of spoken language. Our results suggest that auditory thresholds of the last common ancestor of Homo and Pan were already compatible with speech reception as observed in humans. Therefore, it seems unlikely that the morphological evolution observed in the bony auditory region of fossil hominins was driven by the emergence of spoken language. Instead, the peculiar human configuration may be a by-product of morpho-functional constraints linked to brain expansion.

Real-time monitoring of middle ear prosthesis coupling.

INTRODUCTION: In reconstructive middle ear surgery, acoustic quality has received a high level of attention in recent years. Careful intraoperative selection and positioning of passive middle ear prostheses during tympanoplasty with ossiculoplasty is essential to ensure satisfactory sound transmission and postoperative hearing outcome. The reconstruction quality of the ossicular chain (OC) can be evaluated intraoperatively using a surgical assistance system which is based on a real-time monitoring system (RTM system) that acquires the transmission (middle ear transfer function (METF)) with electromagnetic excitation of the OC. In this experimental study, the METF with electromagnetic excitation of the (reconstructed) OC was compared to usual acoustic excitation and the benefit of the RTM system was investigated for the implantation of partial (PORP) and total (TORP) prostheses. METHODS: Laser Doppler vibrometry (LDV) was used to measure the middle ear transfer function (METF) in 18 human temporal bones (TB). The RTM system uses electromagnetic excitation of the OC with a magnet placed on the umbo. Comparatively, measurements with the usual acoustical excitation, using an earphone in the external auditory canal, were performed. The measurements began with the intact OC, followed by real-time monitoring guided OC reconstruction with PORP and TORP. In addition, during the simulation of an intraoperative setting, the influence of the influence of opening (tympanomeatal flap lifted and pushed anteriorly) and closing (tympanomeatal flap folded back) the tympanic membrane on the measurements with the RTM system was determined. RESULTS: Electromagnetic and acoustic excitation of the intact and the reconstructed OC provided comparable METF. The application of the RTM system significantly improved the quality of the OC reconstruction. The METF increased by up to 10 dB over the entire frequency range during implantation of the PORP with positioning control by the RTM system. When using the TORP, the METF could be improved by up to 15 dB. The opening of the tympanomeatal flap did not affect the measurements with the RTM system at the reconstructed OC. CONCLUSION: In this TB study, we demonstrated that the quality of OC reconstruction (improved METF as a benchmark for improved transmission) could be significantly increased by means of a RTM system. Intraoperative studies should now be conducted to investigate to which quantitative extent the intraoperative reconstruction quality can be improved and whether or not this improvement also manifests in an increased (long-term) hearing outcome. This will enable conclusions to be drawn about the contribution of the intraoperative reconstruction quality to the (long-term) hearing outcome in the context of the conglomerate of various factors influencing the postoperative hearing outcome.

In vivo microstructural investigation of the human tympanic membrane by endoscopic polarization-sensitive optical coherence tomography.

Significance: Endoscopic optical coherence tomography (OCT) is of growing interest for in vivo diagnostics of the tympanic membrane (TM) and the middle ear but generally lacks a tissue-specific contrast. Aim: To assess the collagen fiber layer within the in vivo TM, an endoscopic imaging method utilizing the polarization changes induced by the birefringent connective tissue was developed. Approach: An endoscopic swept-source OCT setup was redesigned and extended by a polarization-diverse balanced detection unit. Polarization-sensitive OCT (PS-OCT) data were visualized by a differential Stokes-based processing and the derived local retardation. The left and right ears of a healthy volunteer were examined. Results: Distinct retardation signals in the annulus region of the TM and near the umbo revealed the layered structure of the TM. Due to the TM's conical shape and orientation in the ear canal, high incident angles onto the TM's surface, and low thicknesses compared to the axial resolution limit of the system, other regions of the TM were more difficult to evaluate. Conclusions: The use of endoscopic PS-OCT is feasible to differentiate birefringent and nonbirefringent tissue of the human TM in vivo. Further investigations on healthy as well as pathologically altered TMs are required to validate the diagnostic potential of this technique.

Multimodal additive manufacturing of biomimetic tympanic membrane replacements with near tissue-like acousto-mechanical and biological properties.

The three additive manufacturing techniques fused deposition modeling, gel plotting and melt electrowriting were combined to develop a mimicry of the tympanic membrane (TM) to tackle large TM perforations caused by chronic otitis media. The mimicry of the collagen fiber orientation of the TM was accompanied by a study of multiple funnel-shaped mimics of the TM morphology, resulting in mechanical and acoustic properties similar to those of the eardrum. For the different 3D printing techniques used, the process parameters were optimized to allow reasonable microfiber arrangements within the melt electrowriting setup. Interestingly, the fiber pattern was less important for the acousto-mechanical properties than the overall morphology. Furthermore, the behavior of keratinocytes and fibroblasts is crucial for the repair of the TM, and an in vitro study showed a high biocompatibility of both primary cell types while mimicking the respective cell layers of the TM. A simulation of the in vivo ingrowth of both cell types resulted in a cell growth orientation similar to the original collagen fiber orientation of the TM. Overall, the combined approach showed all the necessary parameters to support the growth of a neo-epithelial layer with a similar structure and morphology to the original membrane. It therefore offers a suitable alternative to autologous materials for the treatment of chronic otitis media. STATEMENT OF SIGNIFICANCE: Millions of people worldwide suffer from chronic middle ear infections. Although the tympanic membrane (TM) can be reconstructed with autologous materials, the grafts used for this purpose require extensive manual preparation during surgery. This affects not only the hearing ability but also the stability of the reconstructed TM, especially in the case of full TM reconstruction. The synthetic alternative presented here mimicked not only the fibrous structure of the TM but also its morphology, resulting in similar acousto-mechanical properties. Furthermore, its high biocompatibility supported the migration of keratinocytes and fibroblasts to form a neo-epithelial layer. Overall, this completely new TM replacement was achieved by combining three different additive manufacturing processes.

Development of electrospun, biomimetic tympanic membrane implants with tunable mechanical and oscillatory properties for myringoplasty.

Most commonly, autologous grafts are used in tympanic membrane (TM) reconstruction. However, apart from the limited availability and the increased surgical risk, they cannot replicate the full functionality of the human TM properly. Hence, biomimetic synthetic TM implants have been developed in our project to overcome these drawbacks. These innovative TM implants are made from synthetic biopolymer polycaprolactone (PCL) and silk fibroin (SF) by electrospinning technology. Static and dynamic experiments have shown that the mechanical and oscillatory behavior of the TM implants can be tuned by adjusting the solution concentration, the SF and PCL mixing ratio and the electrospinning parameters. In addition, candidates for TM implants could have comparable acousto-mechanical properties to human TMs. Finally, these candidates were further validated in in vitro experiments by performing TM reconstruction in human cadaver temporal bones. The reconstructed TM with SF-PCL blend membranes fully recovered the acoustic vibration when the perforation was smaller than 50%. Furthermore, the handling, medium adhesion and transparency of the developed TM implants were similar to those of human TMs.

Evaluation of Vibrant® Soundbridge™ positioning and results with laser doppler vibrometry and the finite element model.

The etiology of hearing loss originates from genetic factors and includes several other events including infections, working or living environment, as well as several endocrine and metabolic disorders. The Vibrant® Soundbridge™ (VSB) is an implantable hearing aid whose floating mass transducer (FMT) is attached to the long process of the incus. The device is used for pure sensorineural hearing loss with an intact middle ear. Variations in the manner of attachment may occur. Knowledge of the impact of such variations on the overall device performance may guide towards optimal transducer attachment during surgery. A mechanical modelling of the ear was first reported by von Békésy and indicated that the tympanic membrane (TM) moves as a stiff plate, and that the mallear and incudal ligaments act as a rotation axis for the ossicular chain at low frequencies. Experimental investigations and simulations with the model yield the same main results. The first fitting situation, where the FMT floats freely in the middle ear, provides by far the worst possible results. Contact to the stapes supra-structure of the FMT is necessary for optimal performance of the FMT. The mastoid specimen preserves its acoustic properties that have been shown to be similar to those in the vital human ear, under these conditions. Properly coupling the electromagnetic transducer to the ossicles can be difficult and it requires a certain degree of experience. A finite-element model (FEM) is useful for functional evaluation of the VSB since it enables easy modelling of the complicated middle ear structures and simulation of their dynamic behavior which makes it easy to understand it in detail without experiments.

Measurement of middle ear transfer function in temporal bones using electromagnetic excitation: Comparison to sound excitation and evaluation of influencing factors.

Hearing a sound produces vibrations of the ossicles in the middle ear, which can be measured in the micrometer to nanometer range. Destruction of middle ear structures results most commonly from chronic inflammatory diseases. In these cases, passive and active middle ear implants are used for reconstruction of the ossicular chain. The positioning of the implants depends primarily on the surgeon's experience. So far, no objective assessment has been conducted to affirm if the chosen positioning is the best in each specific case. We have established a new method, allowing us to measure the middle ear transfer function (METF) intraoperatively. Using the new method, a magnet is placed on the umbo of the malleus handle and is stimulated by a coil positioned underneath the head. The resulting vibration is measured on the stapes footplate using Laser Doppler vibrometry (LDV). Acoustic and electromagnetic excitation show comparable METF in lower frequencies, which differ up to 10 dB in frequencies over 1 kHz. The position of the coil does not play a relevant part in the METF, whereas the location of the magnet on the tympanic membrane highly impacts the METF. This technique demonstrates reproducible results. Electromagnetic excitation is comparable to sound excitation and is suited for measuring the METF. A stable positioning of the magnet on the umbo is essential in order to acquire valid data.

Biomimetic Tympanic Membrane Replacement Made by Melt Electrowriting.

The tympanic membrane (TM) transfers sound waves from the air into mechanical motion for the ossicular chain. This requires a high sensitivity to small dynamic pressure changes and resistance to large quasi-static pressure differences. The TM achieves this by providing a layered structure of about 100µm in thickness, a low flexural stiffness, and a high tensile strength. Chronically infected middle ears require reconstruction of a large area of the TM. However, current clinical treatment can cause a reduction in hearing. With the novel additive manufacturing technique of melt electrowriting (MEW), it is for the first time possible to fabricate highly organized and biodegradable membranes within the dimensions of the TM. Scaffold designs of various fiber composition are analyzed mechanically and acoustically. It can be demonstrated that by customizing fiber orientation, fiber diameter, and number of layers the desired properties of the TM can be met. An applied thin collagen layer seals the micropores of the MEW-printed membrane while keeping the favorable mechanical and acoustical characteristics. The determined properties are beneficial for implantation, closely match those of the human TM, and support the growth of a neo-epithelial layer. This proves the possibilities to create a biomimimetic TM replacement using MEW.

Fully Implantable Active Middle Ear Implants After Subtotal Petrosectomy With Fat Obliteration: Preliminary Clinical Results.

OBJECTIVES: In patients with chronic middle ear disease, especially after revision surgery for ventilation problems and mixed hearing loss, active middle ear implants may provide an alternative treatment option. The fully implantable active middle-ear implant (FI-AMEI) is designed for implantation in a ventilated mastoid with an intact posterior canal wall. Until now, there have been no reports on audiometric results after implantation of a FI-AMEI in a fat-obliterated cavity after subtotal petrosectomy (SPE). STUDY DESIGN: Retrospective case review. SETTING: Tertiary referral center. PATIENTS: Twelve patients were included after numerous previous tympanoplasty surgeries for severe mixed hearing loss and FI-AMEI implantation. INTERVENTION: In five patients, the FI-AMEI was implanted in a cavity, with fat obliteration, after SPE. Seven patients received FI-AMEI implantation after intact canal wall (ICW) surgery. MAIN OUTCOME MEASURE(S): Audiometric results (pure-tone audiometry, Freiburger monosyllables) are demonstrated for 12 patients after an observation period of 3 months. RESULTS: The improvement in monosyllable score was 40 to 85% for the 12 patients. Free-field-aided thresholds showed high heterogeneity. CONCLUSION: FI-AMEI implantation combined with SPE provides an alternative approach to hearing rehabilitation to non-FI-AMEI implantation. Studies with a high number of patients and long-term observation periods are necessary to statistically verify these results.

Endoscopic Optical Coherence Tomography for Evaluation of Success of Tympanoplasty.

OBJECTIVE: After tympanoplasty, it is often challenging to differentiate between different causes of a remaining air bone gap (ABG). Optical coherence tomography (OCT) offers a new approach for combined morphologic and functional measurements of the tympanic membrane and adjacent parts of the middle ear. Thus, it provides valuable diagnostic information in patients with a reduced sound transfer after middle ear surgery. PATIENT AND INTERVENTION: A patient with history of tympanoplasty and a persistent ABG was investigated with endoscopic OCT before revision surgery. MAIN OUTCOME MEASURES: The oscillation behavior and the thickness of the reconstructed tympanic membrane was determined. The oscillation amplitudes of the inserted prosthesis were compared to a finite element model simulation and to the clinical findings and the audiometric data of the patient. RESULTS: OCT measurements showed a reduced oscillation amplitude of the prosthesis while revealing an aerated middle ear and good coupling of the prosthesis. Transfer loss measured by OCT showed a similar progression as the ABG measured by pure-tone audiometry with a mean divergence of 4.45 dB. CONCLUSION: Endoscopic OCT is a promising tool for the evaluation of tympanoplasty outcome. It supports established otologic diagnostics and can help differentiating between different causes of conductional hearing loss.

Laser Doppler vibrometry of the middle ear in humans: derivation dependence, variability, and bilateral differences.

OBJECTIVE: Derivation dependence, inter- and intrasubject/intertest variability, bilateral differences of the eardrum vibration characteristics have been investigated using laser Doppler vibrometry (LDV). MATERIAL AND METHODS: A total of 31 normally hearing adults were examined. In each subject, both ears were consecutively stimulated by the chirp acoustic stimulus that covered 500-3700-Hz frequencies. The laser beam was directed to and the reflection was consecutively picked up from the tympanic membrane surface. RESULTS: LDV curves derived from different eardrum loci possessed dissimilar characteristics. The derivation area dependence was particularly apparent for the stimulus frequency constituents above 1500 Hz. The intersubject variability of LDV parameters exceeded the intrasubject/intertest one. The intersubject divergences looked selectively distinct for the frequencies over 2000 Hz. Under repeated recordings, LDV parameters remained stable. The intertest differences, if appeared, concerned predominantly the magnitudes of separate frequency bands. LDV waveforms registered by experienced and beginner investigators were alike. Bilaterally derived LDV curves regularly differed from each other. In individual cases, the bilateral divergences approximated the intersubject deviation. CONCLUSIONS: The derivation area on the eardrum should be taken into account when estimating the actual LDV recording. Over repeated recordings in separate individuals, LDV waveforms are stable while the experience of investigator has slight if any influence on the principal LDV characteristics. Due to bilateral differences in the middle ear transfer function, in LDV testing of the ear suspected to the pathology, LDV recording from the opposite healthy ear could hardly be taken as an appropriate reference sample.

Vibroplasty combined with tympanic membrane reconstruction in middle ear ventilation disorders.

Although the Vibrant Soundbridge is one of the most frequently used active middle ear implants, data regarding how middle ear ventilation disorders may affect the transmission behavior of its floating mass transducer are still insufficient. Studies involving coupling the floating mass transducer to the stapes head are particularly lacking. This temporal bone study evaluated the influence of simulated middle ear ventilation disorders on the middle ear transfer function in the reconstructed middle ear. The middle ear transfer function was measured using Laser Doppler Vibrometry after vibroplasty onto the stapes head, with or without tympanic membrane reconstruction. Middle ear ventilation disorders were simulated through changes in static pressure via the external ear channel with a maximum pressure of +3 kPa. Slice thickness of tympanic membrane reconstruction material was measured using micro-CT. When the reconstructed ossicular chain and the reconstructed tympanic membrane were mechanically excited by the floating mass transducer under conditions of ambient static pressure, the transmission behavior was found to be independent of the type of tissue used. Increase in static pressure up to +3 kPa caused maximum low frequency transmission loss of 15 dB when elastic grafts were used and 5 dB when stiff tissue was inserted. At high frequencies, measured loss of up to 5 dB was relatively independent of the tissue stiffness. Increase in static pressure led to displacement of the tissues towards the vestibulum and caused stiffening, especially of the annular ligament. Stiffening-induced transmission losses were mainly found at low frequencies and could not be compensated by the floating mass transducer in this range. Above 1300 Hz, the continuous force spectrum of the actuator sufficiently protected against loss of amplitude. To minimize postoperative transmission loss due to persisting ventilation disorders, choosing a very stiff tympanic membrane reconstruction material seems to be appropriate.

Sensor-actuator component for a Floating Mass Transducer-based fully implantable hearing aid.

We propose a novel system based on the Floating Mass Transducer (FMT) to be used as the active component of a fully implantable, Vibrant Soundbridge-like middle ear implant. The new system replaces the external microphone used in the currently available design with an implantable piezoelectric sensor that is inserted into the incudostapedial joint and picks up the vibrations transmitted to the long process of the incus. The FMT is coupled to the round window of the cochlea. We characterize the system by measuring the gain in intracochlear sound pressure using laser Doppler vibrometry at a surgically installed "third window" into the cochlea of six temporal bones. Closed-loop feedback oscillations limit the system's available output. We show that using an adaptive control algorithm, a mean functional gain of up to 40 dB is achieved, which is similar to Soundbridge functional gain. The concept matches the FMT's one-point fixation philosophy and offers several advantages over other designs, namely an easy and time-efficient surgery, reversibility of implantation, and natural hearing for the prospective patient.

Static and dynamic forces in the incudostapedial joint gap.

Dynamic pressure at the tympanic membrane is transformed and subsequently transferred through the ossicular chain in the form of forces and moments. The forces are primarily transferred to the inner ear. They are transferred partly to the stapedial annular ligament which exhibits non-linear behavior and stiffens for larger static forces. In unventilated middle ears, static pressure is additionally transferred to the ossicles. The purpose of this study was to measure the force inside the ossicular chain as a physiological parameter. We determined the forces which act for dynamic sound transmission and for static load on the ossicular chain. The study is the first one which introduces these forces. The static forces have direct impact on clinically relevant questions for middle ear reconstructions with passive or active prosthesis. The dynamic forces have an impact on the development of middle ear sensors. Quasi-static forces in the incudostapedial joint (ISJ) gap were measured with two different sensor types in 17 temporal bones. The sensing elements, a single crystal piezo and a strain gauge element for validation, were bonded to a thin flexible titanium plate and encapsulated in a titanium housing to allow the acquisition of the applied force signal inside the ossicular chain. Dynamic forces were measured in 11 temporal bones with the piezo sensor. We measured a static force of 23 mN in the ISJ after sensor insertion. The mean force for dynamic physiological acoustic excitation from 250 Hz to 6 kHz was 26 µN/Pa. If the tympanic membrane is loaded with a static pressure, the static force in the ISJ increases up to 1 N for a maximum static pressure load scenario of 30 kPa.

Feasibility Study of a Mechanical Real-Time Feedback System for Optimizing the Sound Transfer in the Reconstructed Middle Ear.

OBJECTIVE: To evaluate electromechanical excitation as an alternative excitation mode for middle ear transfer function (METF) measurements as well as real-time feedback in prosthetic ossicular reconstruction. METHOD: In eight human cadaveric temporal bones, the ossicular chain was excited using acoustic and mechanical (floating mass transducer, FMT) stimulation to determine the METF. After disconnecting the ossicular chain and reconstruction with partial or total prosthesis the METFs were measured again. Continuous FMT stimulation was then applied to improve the prosthesis' position using real-time feedback of the METF. RESULTS: Mechanical stimulation of ossicular vibration showed characteristic differences to acoustic excitation resulting from the force characteristics of the FMT. Furthermore, the interspecimen METF variability was greater with electromechanical than acoustic stimulation because of interspecimen variability in the FMT coupling conditions. When the METF with FMT excitation was used as a real-time feedback tool, a measurable improvement in the quality of ossicular reconstruction could be achieved. CONCLUSIONS: Mechanical excitation is an effective and suitable alternative stimulation method in experimental METF measurements. The system provides real-time feedback for ossicular reconstruction in the experimental setting. Some influencing factors still need to be distinguished for reliable measurements. However, the method does not yet meet the requirements for clinical application as an intraoperative, real-time monitoring tool. However, the system could be an excellent model for high-end cadaveric temporal bone training in ossiculoplasty.

Function, Applicability, and Properties of a Novel Flexible Total Ossicular Replacement Prosthesis With a Silicone Coated Ball and Socket Joint.

HYPOTHESIS: A total ossicular replacement prosthesis (TORP) with a silicone coated ball and socket joint (BSJ) is able to compensate pressure changes and therefore provide better sound transmission compared with rigid prostheses. BACKGROUND: Dislocation and extrusion are known complications after TORP reconstruction, leading to revisions and recurrent hearing loss. Poor aeration of the middle ear, scar tension, and static pressure variations in conjunction with rigid prosthesis design causes high tension at the implant coupling points. METHODS: A novel TORP prototype with a silicone coated BSJ has been developed. Experimental measurements were performed on nine fresh cadaveric human temporal bones of which five were used for a comparison between rigid TORP and flexible TORP tympanoplasty. The middle ear transfer function was measured at ambient pressure and at 2.5 kPa, both positive and negative pressure, applied in the ear canal. RESULTS: The flexible TORP design yields a better transmission of sound after implantation and at negative pressure inside the tympanic cavity, compared with rigid TORP. In average, it provides an equivalent sound transfer like the intact middle ear. At positive pressure, the flexible TORP performs slightly worse. Both performed worse than the intact middle ear, which is related to an uplifting of the prostheses. CONCLUSION: The findings may be considered preliminary as this experimental study was limited to just one of the many different possible situations of tympanoplasty and it involved a small sample size. Nevertheless, the results with the flexible TORP were promising and could encourage further investigations on such prostheses.