Comparison of sheep and human middle-ear ossicles: anatomy and inertial properties.

The sheep middle ear has been used in training to prepare physicians to perform surgeries and to test new ways of surgical access. This study aimed to (1) collect anatomical data and inertial properties of the sheep middle-ear ossicles and (2) explore effects of these features on sound transmission, in comparison to those of the human. Characteristic dimensions and inertial properties of the middle-ear ossicles of White-Alpine sheep (n = 11) were measured from high-resolution micro-CT data, and were assessed in comparison with the corresponding values of the human middle ear. The sheep middle-ear ossicles differed from those of human in several ways: anteroinferior orientation of the malleus handle, relatively small size of the incus with a relatively short distance to the lenticular process, a large area of the articular surfaces at the incudostapedial joint, and a relatively small moment of inertia along the anterior-posterior axis. Analysis in this study suggests that structure and orientation of the middle-ear ossicles in the sheep are conducive to an increase in the hinge-like ossicular-lever-action around the anterior-posterior axis. Considering the substantial anatomical differences, outcomes of middle-ear surgeries would presumably be difficult to assess from experiments using the sheep middle ear.

Three-dimensional quasi-static displacement of human middle-ear ossicles under static pressure loads: Measurement using a stereo camera system.

The time delay and/or malfunctioning of the Eustachian tube may cause pressure differences across the tympanic membrane, resulting in quasi-static movements of the middle-ear ossicles. While quasi-static displacements of the human middle-ear ossicles have been measured one- or two-dimensionally in previous studies, this study presents an approach to trace three-dimensional movements of the human middle-ear ossicles under static pressure loads in the ear canal (EC). The three-dimensional quasi-static movements of the middle-ear ossicles were measured using a custom-made stereo camera system. Two cameras were assembled with a relative angle of 7° and then mounted onto a robot arm. Red fluorescent beads of a 106-125 µm diameter were placed on the middle-ear ossicles, and quasi-static position changes of the fluorescent beads under static pressure loads were traced by the stereo camera system. All the position changes of the ossicles were registered to the anatomical intrinsic frame based on the stapes footplate, which was obtained from µ-CT imaging. Under negative ear-canal pressures, a rotational movement around the anterior-posterior axis was dominant for the malleus-incus complex, with small relative movements between the two ossicles. The stapes showed translation toward the lateral direction and rotation around the long axis of the stapes footplate. Under positive EC pressures, relative motion between the malleus and the incus at the IMJ became larger, reducing movements of the incus and stapes considerably and thus performing a protection function for the inner-ear structures. Three-dimensional tracing of the middle-ear ossicular chain provides a better understanding of the protection function of the human middle ear under static pressured loads as immediate responses without time delay.

Assessment of a direct acoustic cochlear stimulator.

This study aimed to assess the functional results of a new, active, acoustic-mechanical hearing implant, the Direct Acoustic Cochlear Stimulation Partial Implant (DACS PI), in a preclinical study. The DACS PI is an electromagnetic device fixed to the mastoid by screws and coupled to a standard stapes prosthesis by an artificial incus (AI). The function of the DACS PI-aided reconstruction was assessed by determining: (1) the maximum equivalent sound pressure level (SPL) of the implant, which was obtained from measurements of the volume displacement at the round window in normal and implanted ears, and (2) the quality at the coupling interface between the AI of the DACS and the stapes prosthesis, which was quantified from measurements of relative motions between the AI and the prosthesis. Both measurements were performed with fresh temporal bones using a scanning laser Doppler interferometry system. The expected maximum equivalent SPL with a typical driving voltage of 0.3 V was about 115-125 dB SPL up to 1.5 kHz in reconstruction with the DACS PI, and decreased with a roll-off slope of about 65 dB/decade, reaching 90 dB SPL at 8 kHz. The large roll-off relative to a normal ear was presumed to be a relatively high inductive impedance of the coil of the DACS PI actuator at higher frequencies. Good coupling quality between the AI and the prosthesis was achieved below the resonance (∼1.5 kHz) of the DACS PI for all tested stapes prostheses. Above the resonance, the SMart Piston, which is composed of a shape-memory alloy, had the best coupling quality.

Effects of middle-ear disorders on power reflectance measured in cadaveric ear canals.

OBJECTIVE: Reflectance measured in the ear canal offers a noninvasive method to monitor the acoustic properties of the middle ear, and few systematic measurements exist on the effects of various middle-ear disorders on the reflectance. This work uses a human cadaver-ear preparation and a mathematical middle-ear model to both measure and predict how power reflectance R is affected by the middle-ear disorders of static middle-ear pressures, middle-ear fluid, fixed stapes, disarticulated incudostapedial joint, and tympanic-membrane perforations. DESIGN: R was calculated from ear-canal pressure measurements made on human-cadaver ears in the normal condition and five states: (1) positive and negative pressure in the middle-ear cavity, (2) fluid-filled middle ear, (3) stapes fixed with dental cement, (4) incudostapedial joint disarticulated, and (5) tympanic-membrane perforations. The middle-ear model of Kringlebotn (1988) was modified to represent the middle-ear disorders. Model predictions are compared with measurements. RESULTS: For a given disorder, the general trends of the measurements and model were similar. The changes from normal in R, induced by the simulated disorder, generally depend on frequency and the extent of the disorder (except for the disarticulation). Systematic changes in middle-ear static pressure (up to 6300 daPa) resulted in systematic increases in R. These affects were most pronounced for frequencies up to 1000 to 2000 Hz. Above about 2000 Hz there were some asymmetries in behavior between negative and positive pressures. Results with fluid in the middle-ear air space were highly dependent on the percentage of the air space that was filled. Changes in R were minimal when a smaller fraction of the air space was filled with fluid, and as the air space was filled with more saline, R increased at most frequencies. Fixation of the stapes generally resulted in a relatively small low-frequency increase in R. Disarticulation of the incus with the stapes led to a consistent low-frequency decrease in R with a distinctive minimum below 1000 Hz. Perforations of the tympanic membrane resulted in a decrease in R for frequencies up to about 2000 Hz; at these lower frequencies, smaller perforations led to larger changes from normal when compared with larger perforations. CONCLUSIONS: These preliminary measurements help assess the utility of power reflectance as a diagnostic tool for middle-ear disorders. In particular, the measurements document (1) the frequency ranges for which the changes are largest and (2) the extent of the changes from normal for a spectrum of middle-ear disorders.

Vibrations in the human middle ear.

BACKGROUND: Middle ear surgery techniques can improve hearing destroyed by disease, but results of treatment are difficult to predict. Therefore, researchers use a Laser Doppler Vibrometer to measure vibrations of human middle ear ossicles. MATERIAL/METHODS: Measurements of ossicular chain vibrations are performed on fresh human temporal bone specimens using Laser Doppler Vibrometer. Vibrations of stapes are recorded in 3 cases: 1) for intact ossicular chain, 2) when incus long process is removed, and 3) after long process reconstruction with bone cement. A typical analysis of transfer function is completed by other methods applied in dynamics. RESULTS: Measurements and analysis of stapes vibrations in case of intact and damaged ossicular chain show regular and irregular behavior which can be recognize with the help of phase portraits, recurrence plots, correlation dimension, and Hurst and Lyapunov exponents. The long process reconstruction with bone cement gives good results in improving hearing. CONCLUSIONS: Recurrence plots, and Lyapunov and Hurst exponents used in the study complete information obtained from transfer function and can be employed to enrich the classical approach to ossicular chain vibrations.

Optimum Coupling of an Active Middle Ear Actuator: Effect of Loading Forces on Actuator Output and Conductive Losses.

INTRODUCTION: The desired outcome of the implantation of active middle ear implants is maximum coupling efficiency and a minimum of conductive loss. It has not been investigated yet, which loading forces are applied during the process of coupling, which forces lead to an optimum actuator performance and which forces occur when manufacturer guidelines for coupling are followed. METHODS: Actuator output was measured by laser Doppler vibrometry of stapes motion while the actuator was advanced in 20 µm steps against the incus body while monitoring static contact force. The occurrence of conductive losses was investigated by measuring changes in stapes motion in response to acoustic stimulation for each step of actuator displacement. Additionally, the electrical impedance of the actuator was measured over the whole frequency range at each actuator position. RESULTS: Highest coupling efficiency was achieved at forces above 10 mN. Below 1 mN no efficient coupling could be achieved. At 30 mN loading force, which is typical when coupling according to manufacturer guidelines, conductive losses of more than 5 dB were observed in one out of nine TBs. The electrical impedance of the actuator showed a prominent resonance peak which vanished after coupling. CONCLUSION: A minimum coupling force of 10 mN is required for efficient coupling of the actuator to the incus. In most cases, coupling forces up to 100 mN will not result in clinically relevant conductive losses. The electrical impedance is a simple and reliable metric to indicate contact.

Evaluation of Coupling Efficiency in Round Window Vibroplasty With a New Handheld Probe.

HYPOTHESIS: A handheld measuring probe was developed that analyzes the vibration characteristics of the stapes footplate after backward stimulation of the cochlea in round window vibroplasty. In temporal bone experiments, the measuring accuracy of the probe was tested. BACKGROUND: In round window vibroplasty, the effectiveness of the transmitted vibrations into the inner ear is provided with limited visual and tactile information. Currently, there is no objective measuring tool available. METHODS: In five unfixed temporal bones, a floating mass transducer was coupled to the round window membrane. During the excitation with different voltage levels (0, 5, 25, 100, 300 mV root mean square) corresponding to 0, 80, 94, 106, and 116 dB equivalent ear canal sound pressure respectively, the deflections of the footplate were recorded in parallel by laser Doppler vibrometry and the measuring probe. RESULTS: The probe allowed for differentiation of the coupling efficiency. The measured footplate vibrations from the excitation levels of 106 dB (and 116 dB) were statistically significant compared with the testing without excitation. The footplate deflections determined in parallel by laser Doppler vibrometry showed comparable results. CONCLUSION: In principal, the newly developed measuring probe allows for measuring the quality of retrograde cochlear excitation in a round window vibroplasty by detecting footplate vibrations. Further developments are directed for its application in clinical, intraoperative procedures.

Anatomical and functional aspects of ligaments between the malleus and the temporomandibular joint.

The aim of this paper is to investigate the anatomical topography and the relationship between the ligaments, malleus and temporomandibular joint (TMJ) and to determine the role of these ligaments on the movement of the malleus. The malleus, incus, petrotympanic fissure (PTF), chorda tympani, anterior malleolar ligament (AML), discomallear ligament (DML), malleomandibular ligament, sphenomandibular ligament and articular disc were explored in 15 skulls. Traction and tension tests were carried out to clarify their role in malleolar movement. In 12 of the cases, two separate ligaments were connected to the anterior of the malleus, whereas a single ligament from the anterior of the malleus to the PTF was observed in 3 cases. In 12 cases, the DML united the retrodiscal tissues. In the other 3 cases, the medial and the lateral parts of the ligament were connected to the retrodiscal tissue after passing through the PTF. The thickness of the ligaments differed among specimens. When tension was applied to the DML no malleolar movement occurred, but when the AML was overstretched, significant movement was observed in 5 cadavers; little movement in 6 cadavers, and no movement in 4 cadavers. This study suggests that extreme stretching of the condyle in conjunction with the ligaments between the ossicles of the inner ear and the TMJ could be the reason for unexplained otological problems.

[Ontogenic development of the incudostapedial joint]. / Desarrollo ontogénico de la articulación incudoestapedial.

OBJECTIVE: To study the development of the incudostapedial joint in human embryos and foetuses. MATERIAL AND METHOD: 46 temporal bones with specimens between 9 mm and newborns were studied. The preparations were sliced serially and dyed using the Martins trichrome technique. RESULTS: The incudostapedial joint takes on the characteristics of a spheroidal joint at 16 weeks of development. The cartilage covering the articular surfaces is formed by different strata that develop in succession: the superficial stratum at 19 weeks, the transitional between 20 and 23 weeks, and the radial from 24 weeks on. The subchondral bone develops after 29 weeks by the mechanisms of apposition and extension of the periosteal and endosteal bones, but it is not until week 34 that it completely covers the articular surfaces, following constitution of the bone fascicles transmitting the lines of force. The articular capsule is formed from the inter-zone, the surface zone develops the capsular ligament, and the internal surface develops the synovial membrane. CONCLUSIONS: At the time of birth, the incudostapedial joint is completely developed.

Storage of the incus in the mastoid bowl for use as a columella in staged tympanoplasty.

OBJECTIVE: To evaluate whether the incus of the cholesteatomatous ear preserved in the mastoid bowl during the first stage of planned two-stage tympanoplasty can tolerate long-term implantation and be used in ossicular reconstruction during the second stage. METHODS: The study group included 24 ears of 23 patients who underwent staged tympanoplasty for the treatment of middle ear cholesteatoma. At the first stage, after removing the incus to eradicate the middle ear disease, it was returned to the mastoid bowl and stored there until use at the second stage. The average interval between the two stages was 8.3 months (range 6-12 months). RESULTS: The incus was identified in all cases at the second stage: 10 incudes were found to be covered with a thin mucosa layer, 12 were buried in fibrous or granulation tissue, and 2 were joined to the surrounding bone. Residual cholesteatoma was found in six ears, either in the attic (three ears) or tympanic sinus (three ears). It never occurred in the mastoid bowl where the incus had been preserved. In 19 cases, the incus was available as a short columella for ossicular reconstruction. The remaining five cases were reconstructed using a hydroxyapatite ossicle as a long columella, since the stapes superstructure was missing at the second stage. In one case, the stored incus underwent remarkable absorption between stages. CONCLUSION: Preservation of the incus in the mastoid bowl is an effective option in planned two-stage tympanoplasty, when the incus is considered useful for ossicular reconstruction at the second stage.

Middle-Ear Sound Transmission Under Normal, Damaged, Repaired, and Reconstructed Conditions.

HYPOTHESIS: We hypothesize that current clinical treatment strategies for the disarticulated or eroded incus have the effect of combining the incus and stapes of the human middle ear (ME) into one rigid structure, which, while capable of adequately transmitting lower-frequency sounds, fails for higher frequencies. BACKGROUND: ME damage causes conductive hearing loss (CHL) and while great progress has been made in repairing or reconstructing damaged MEs, the outcomes are often far from ideal. METHODS: Temporal bones (TBs) from human cadavers, a laser Doppler vibrometer (LDV), and a fiber-optic based micro-pressure sensor were used to characterize ME transmission under various ME conditions: normal; with a disarticulated incus; repaired using medical glue; or reconstructed using a partial ossicular replacement prosthesis (PORP). RESULTS: Repairing the disarticulated incus using medical glue, or replacing the incus using a commercial PORP, provided similar restoration of ME function including almost perfect function at frequencies below 4 kHz, but with more than a 20-dB loss at higher frequencies. Associated phase responses under these conditions sometimes varied and seemed dependent on the degree of coupling of the PORP to the remaining ME structure. A new ME-prosthesis design may be required to allow the stapes to move in three-dimensional (3-D) space to correct this deficiency at higher frequencies. CONCLUSIONS: Fixation of the incus to the stapes or ossicular reconstruction using a PORP limited the efficiency of sound transmission at high frequencies.

Biomechanics of the incudo-malleolar-joint - Experimental investigations for quasi-static loads.

Under large quasi-static loads, the incudo-malleolar joint (IMJ), connecting the malleus and the incus, is highly mobile. It can be classified as a mechanical filter decoupling large quasi-static motions while transferring small dynamic excitations. This is presumed to be due to the complex geometry of the joint inducing a spatial decoupling between the malleus and incus under large quasi-static loads. Spatial Laser Doppler Vibrometer (LDV) displacement measurements on isolated malleus-incus-complexes (MICs) were performed. With the malleus firmly attached to a probe holder, the incus was excited by applying quasi-static forces at different points. For each force application point the resulting displacement was measured subsequently at different points on the incus. The location of the force application point and the LDV measurement points were calculated in a post-processing step combining the position of the LDV points with geometric data of the MIC. The rigid body motion of the incus was then calculated from the multiple displacement measurements for each force application point. The contact regions of the articular surfaces for different load configurations were calculated by applying the reconstructed motion to the geometry model of the MIC and calculate the minimal distance of the articular surfaces. The reconstructed motion has a complex spatial characteristic and varies for different force application points. The motion changed with increasing load caused by the kinematic guidance of the articular surfaces of the joint. The IMJ permits a relative large rotation around the anterior-posterior axis through the joint when a force is applied at the lenticularis in lateral direction before impeding the motion. This is part of the decoupling of the malleus motion from the incus motion in case of large quasi-static loads.

Response of the human tympanic membrane to transient acoustic and mechanical stimuli: Preliminary results.

The response of the tympanic membrane (TM) to transient environmental sounds and the contributions of different parts of the TM to middle-ear sound transmission were investigated by measuring the TM response to global transients (acoustic clicks) and to local transients (mechanical impulses) applied to the umbo and various locations on the TM. A lightly-fixed human temporal bone was prepared by removing the ear canal, inner ear, and stapes, leaving the incus, malleus, and TM intact. Motion of nearly the entire TM was measured by a digital holography system with a high speed camera at a rate of 42 000 frames per second, giving a temporal resolution of <24 µs for the duration of the TM response. The entire TM responded nearly instantaneously to acoustic transient stimuli, though the peak displacement and decay time constant varied with location. With local mechanical transients, the TM responded first locally at the site of stimulation, and the response spread approximately symmetrically and circumferentially around the umbo and manubrium. Acoustic and mechanical transients provide distinct and complementary stimuli for the study of TM response. Spatial variations in decay and rate of spread of response imply local variations in TM stiffness, mass, and damping.

Coupling of an active middle-ear implant to the long process of the incus using an elastic clip attachment.

The active middle-ear implant Vibrant Soundbridge© (VSB) is used to treat mild-to-severe sensorineural hearing losses. The standard surgical approach for incus vibroplasty is a mastoidectomy and a posterior tympanotomy, crimping the Floating Mass Transducer (FMT) to the long process of the incus (LPI) (standard crimped application). However, tight crimping increases the risk of necrosis of the LPI, resulting in reduction of energy transfer and loss of amplification. The aim of this study was to develop a new coupling device for the LPI, that does not require crimping, and to test its vibrational transfer properties in temporal-bone preparations. An extended antrotomy and a posterior tympanotomy were performed in ten fresh human temporal bones. As a control for normal middle-ear function, the tympanic membrane was stimulated acoustically and the vibration of the stapes footplate was measured by laser Doppler vibrometry (LDV). FMT-induced vibration responses of the stapes were then measured for the standard crimped application at the LPI and for the newly designed elastic long process coupler (LP coupler). For the LP coupler, velocity-amplitude responses in temporal-bone preparations showed increased mean amplitudes at around 1 kHz (∼10 dB) and a reduction between 1.8 and 6 kHz (13 dB on average for 2 ≤ f ≤ 5 kHz). In conclusion, attachment of the FMT to the LPI with the LP coupler leads to generally good mechanical and functional coupling in temporal-bone preparations with a notable disadvantage between 1.8 and 6 kHz. Due to its elastic clip attachment it is expected that the LP coupler will reduce the risk of necrosis of the incus long process, which has to been shown in further studies. Clinical results of the LP coupler are pending.

A method to measure sound transmission via the malleus-incus complex.

BACKGROUND: The malleus-incus complex (MIC) plays a crucial role in the hearing process as it transforms and transmits acoustically-induced motion of the tympanic membrane, through the stapes, into the inner-ear. However, the transfer function of the MIC under physiologically-relevant acoustic stimulation is still under debate, especially due to insufficient quantitative data of the vibrational behavior of the MIC. This study focuses on the investigation of the sound transformation through the MIC, based on measurements of three-dimensional motions of the malleus and incus with a full six degrees of freedom (6 DOF). METHODS: The motion of the MIC was measured in two cadaveric human temporal bones with intact middle-ear structures excited via a loudspeaker embedded in an artificial ear canal, in the frequency range of 0.5-5 kHz. Three-dimensional (3D) shapes of the middle-ear ossicles were obtained by sequent micro-CT imaging, and an intrinsic frame based on the middle-ear anatomy was defined. All data were registered into the intrinsic frame, and rigid body motions of the malleus and incus were calculated with full six degrees of freedom. Then, the transfer function of the MIC, defined as velocity of the incus lenticular process relative to velocity of the malleus umbo, was obtained and analyzed. RESULTS: Based on the transfer function of the MIC, the motion of the lenticularis relative to the umbo reduces with frequency, particularly in the 2-5 kHz range. Analysis of the individual motion components of the transfer function indicates a predominant medial-lateral component at frequencies below 1 kHz, with low but considerable anterior-posterior and superior-inferior components that become prominent in the 2-5 kHz range. CONCLUSION: The transfer function of the human MIC, based on motion of the umbo and lenticularis, has been visualized and analyzed. While the magnitude of the transfer function decreases with frequency, its spatio-temporal complexity increases significantly.

A 3D-printed functioning anatomical human middle ear model.

The middle ear is a sophisticated and complex structure with a variety of functions, yet a delicate organ prone to injuries due to various reasons. Both, understanding and reconstructing its functions has always been an important topic for researchers from medical and technical background. Currently, human temporal bones are generally used as model for tests, experiments and validation of the numerical results. However, fresh human preparations are not always easily accessible and their mechanical properties vary with time and between individuals. Therefore we have built an anatomically based and functional middle ear model to serve as a reproducible test environment. Our middle ear model was manufactured with the aid of 3D-printing technology. We have segmented the essential functional elements from micro computed tomography data (µCT) of a single temporal bone. The ossicles were 3D-printed by selective laser melting (SLM) and the soft tissues were casted with silicone rubber into 3D-printed molds. The ear canal, the tympanic cavity and the inner ear were artificially designed, but their design ensured the anatomically correct position of the tympanic membrane, ossicular ligaments and the oval window. For the determination of their auditory properties we have conducted two kinds of tests: measurement of the stapes footplate response to sound and tympanometry of the model. Our experiments regarding the sound transmission showed that the model has a similar behavior to a human middle ear. The transfer function has a resonance frequency at around 1 kHz, the stapes' response is almost constant for frequencies below the resonance and a roll-off is observed above the resonance. The tympanometry results show that the compliance of the middle ear model is similar to the compliance of a healthy human middle ear. We also present that we were able to manipulate the transmission behavior, so that healthy or pathological scenarios can be created. For this purpose we have built models with different mechanical properties by varying the hardness of the silicone rubber used for different structures, such as tympanic membrane, oval window and ossicle attachments in the range of Shore 10-40 A. This allowed us to set the transmission amplitudes in the plateau region higher, lower or within the tolerances of normal middle ears (Rosowski et al., 2007). Our results showed that it is possible to build an artificial model of the human middle ear by using 3D-printing technology in combination with silicone rubber molding. We were able to reproduce the anatomical shape of the middle ear's essential elements with high accuracy and also assemble them into a functioning middle ear model. The acoustic behavior of the model can be reproduced and manipulated by the choice of material. If the issues such as resonance of the casing and steep roll-off slope in higher frequencies can be solved, this model creates a reproducible environment for experiments and can be useful for the evaluation of prosthetic devices.

Fully implantable hearing aid in the incudostapedial joint gap.

A fully implantable hearing aid is introduced which is a combined sensor-actuator-transducer designed for insertion into the incudostapedial joint gap (ISJ). The active elements each consist of a thin titanium membrane with an applied piezoelectric single crystal. The effectiveness of the operating principle is verified in a temporal bone study. We also take a closer look at the influence of an implantation-induced increase in middle ear stiffness on the transducer's output. An assembly of the transducer with 1 mm thickness is built and inserted into six temporal bones. At this thickness, the stiffness of the annular ligament is considerably increased, which leads to a loss in functional gain for the transducer. It is assumed that a thinner transducer would reduce this effect. In order to examine the performance for a prospective reduced pretension, we increased the gap size at the ISJ by 0.5 mm by removing the capitulum of the stapes in four temporal bones. The TM is stimulated with a broadband multisine sound signal in the audiological frequency range. The movement of the stapes footplate is measured with a laser Doppler vibrometer. The sensor signal is digitally processed and the amplified signal drives the actuator. The resulting feedback is minimized by an active noise control least mean square (LMS) algorithm which is implemented on a field programmable gate array. The dynamic range and the functional gain of the transducer in the temporal bones are determined. The results are compared to measurements from temporal bones without ISJ extension and to the results of Finite Elements Model (FE model) simulations. In the frequency range above 2 kHz a functional gain of 30 dB and more is achieved. This proposes the transducer as a potential treatment for high frequency hearing loss, e.g. for patients with noise-induced hearing loss. The transducer offers sufficient results for a comprehensive application. Adaptations in the transducer design or surgical approach are necessary to cope with ligament stiffening issues. These cause insufficient performance for low frequencies under 1 kHz.

3D displacement of the middle ear ossicles in the quasi-static pressure regime using new X-ray stereoscopy technique.

A novel X-ray stereoscopy technique, using greyscale information obtained from moving markers, was used to study the 3D motion in both gerbil and rabbit middle ear ossicles in the quasi-static pressure regime. The motion can be measured without visually exposing the ossicles. The ossicles showed non-linear behaviour as a function of both pressure and frequency. For instance, about 80% of the maximum umbo displacement occurs at a 1 kPa (peak-to-peak) pressure load, while a limited increase of the amplitude is noticed when the pressure goes to 2 kPa. In rabbit the ratio of stapes to umbo motion amplitude was 0.35 for a pressure of 2 kPa (peak-to-peak) at 0.5 Hz. From two stereoscopic projections of the marker paths, 3D motion of the ossicles could be calculated. This motion is demonstrated on high-resolution computer models in order to visualize ossicular chain behaviour.

On the coupling between the incus and the stapes in the cat.

The connection between the long process and the lenticular process of the incus is extremely fine, so much so that some authors have treated the lenticular process as a separate bone. We review descriptions of the lenticular process that have appeared in the literature, and present some new histological observations. We discuss the dimensions and composition of the lenticular process and of the incudostapedial joint, and present estimates of the material properties for the bone, cartilage, and ligament of which they are composed. We present a preliminary finite-element model which includes the lenticular plate, the bony pedicle connecting the lenticular plate to the long process, the head of the stapes, and the incudostapedial joint. The model has a much simplified geometry. We present simulation results for ranges of values for the material properties. We then present simulation results for this model when it is incorporated into an overall model of the middle ear of the cat. For the geometries and material properties used here, the bony pedicle is found to contribute significant flexibility to the coupling between the incus and the stapes.

Shape-memory stapes prosthesis for otosclerosis surgery.

OBJECTIVES: The aim of this study was to determine the efficacy of a shape-memory alloy, Nitinol, as a component of an improved stapes prosthesis. STUDY DESIGN: Prospective laboratory and clinical study to develop a Nitinol stapes prosthesis. METHODS: Various diameters of Nitinol wire and temperature transition variants were analyzed with regard to ease of deformation, response to heating, and strength. The size and geometry of the closed hook was determined by measurement of 50 incus cadaver bones. Several heat sources for activating the shape memory were evaluated, including electrocautery, lasers, and warm water. Trial surgeries were then performed on human temporal bones in the laboratory. The closure characteristics of the Nitinol loop were studied. Magnetic resonance imaging (MRI) testing at 1.5 Tesla was performed to determine safety during MRI studies. Preliminary human subject trials were then instituted. RESULTS: In all cases, a low heat condition was ample to activate the shape memory characteristics of the hook and return it to a closed position after it had been opened. Laser power was generally set well below the power needed for removing bone. The Nitinol loop closed snugly around the incus with application to the top of the hook with a low temperature laser setting. Almost any heat source was effective. MRI testing at 1.5 Tesla showed no movement of the prosthesis. Preliminary results in human subjects showed excellent air-bone closure. The Nitinol loop holds uniform contact around the incus. CONCLUSIONS: The Nitinol piston greatly simplifies the stapedectomy procedure by taking the need for a hand operated instrument out of the surgeon's hands. Because of the nature of the Nitinol wire, it can never over-crimp. All these characteristics make the prosthesis advantageous for otosclerosis surgery.