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.

Acoustic effects of a superior semicircular canal dehiscence: a temporal bone study.

A dehiscence of the superior semicircular canal is said to be responsible for a number of specific and unspecific ear symptoms and possible a conductive hearing loss of up to 40 dB. As in vivo a dehiscence would not be opened against air, but is naturally patched with dura and the brain, it was our aim to investigate the effects of an superior semicircular canal dehiscence on the air conduction hearing in fresh human temporal bones with different boundary conditions. At ten fresh human temporal bones, we investigated the transmission of sound energy through the middle and inner ear using a round window microphone and laser Doppler vibrometer for perilymph motions inside the dehiscence. After baseline measurements, the superior semicircular canal was opened. We investigated the change of the transfer function when the canal is opened against air (pressure equivalent water column), against a water column and when it is patched with a layer of dura. Opening the superior semicircular canal resulted in a loss of sound transmission of maximal 10-15 dB only in frequencies below 1 kHz. When covering the dehiscence with a water column, the conductive hearing component was reduced to 6-8 dB. Placing a dura patch on top of the dehiscence resulted in a normalization of the transfer function. If our experiments are consistent with the conditions in vivo, then superior semicircular canal dehiscence does not lead to an extensive and clinically considerable conductive air conduction component.

Nonlinear stiffness characteristics of the annular ligament.

The annular ligament provides a compliant connection of the stapes to the oval window. To estimate the stiffness characteristics of the annular ligament, human temporal bone measurements were conducted. A force was applied sequentially at several points on the stapes footplate leading to different patterns of displacement with different amounts of translational and rotational components. The spatial displacement of the stapes footplate was measured using a laser vibrometer. The experiments were performed on several stapes with dissected chain and the force was increased stepwise, resulting in load-deflection curves for each force application point. The annular ligament exhibited a progressive stiffening characteristic in combination with an inhomogeneous stiffness distribution. When a centric force, orientated in the lateral direction, was applied to the stapes footplate, the stapes head moved laterally and in the posterior-inferior direction. Based on the load-deflection curves, a mechanical model of the annular ligament was derived. The mathematical representation of the compliance of the annular ligament results in a stiffness matrix with a nonlinear dependence on stapes displacement. This description of the nonlinear stiffness allows simulations of the sound transfer behavior of the middle ear for different preloads.

In-plane motions of the stapes in human ears.

The piston-like (translation normal to the footplate) and rocking-like (rotation along the long and short axes of the footplate) are generally accepted as motion components of the human stapes. It has been of issue whether in-plane motions, i.e., transversal movements of the footplate in the oval window, are comparable to these motion components. In order to quantify the in-plane motions the motion at nine points on the medial footplate was measured in five temporal bones with the cochlea drained using a three-dimensional (3D) laser Doppler vibrometer. It was found that the stapes shows in-plane movements up to 19.1 ± 8.7% of the piston-like motion. By considering possible methodological errors, i.e., the effects of the applied reflective glass beads and of alignment of the 3D laser Doppler system, such value was reduced to be about 7.4 ± 3.1%. Further, the in-plane motions became minimal (≈ 4.2 ± 1.4% of the piston-like motion) in another plane, which was anatomically within the footplate. That plane was shifted to the lateral direction by 118 µm, which was near the middle of the footplate, and rotated by 4.7° with respect to the medial footplate plane.

[Vibration properties of the ossicle and cochlea and their importance for our hearing system]. / Schwingungseigenschaften der Ossikel und der Cochlea und deren Bedeutung für unser Gehör.

The investigations of movements of the eardrum and stapes have shown that at higher frequencies, complex spatial vibration patterns occur in which the individual elements move in very different spatial directions and phase angles. For the stapes, such movements can be divided into piston-like and rotational movements around its short and long axis (tilting or rocking motions). Unlike the piston-like vibrations, rotational rocking motions do not lead to a net volume displacement of cochlear fluid at a certain distance from the footplate. Therefore, according to the current theory of hearing, it is assumed that such tilting movements have no effect on hearing. A number of studies have shown, however, that tilting motions can lead to cochlear activity. Further research is needed to quantify this effect.

Acoustomechanical properties of open TTP titanium middle ear prostheses.

OBJECTIVE: The purpose of the study was to identify acoustcomechanical properties of various biostable and biocompatible materials to create a middle ear prosthesis with the following properties: (i) improved handling including a good view of the head of the stapes or footplate and adjustable length, (ii) improved acoustical characteristics that are adequate for ossiculoplastic. The identified material should serve to build CE and FDA approved prostheses for clinical use in patients. METHODS: Test models made of Teflon, polyetheretherketone, polyethylenterephtalate, polysulfone, gold, Al2O3 ceramics, carbon and titanium were investigated for their potential to fulfill the requirements. Acoustical properties were investigated by laser Doppler velocimetry (LDV) in mechanical middle ear models (MMM). Measured data were fed in to a recently created computer model of the middle ear (multibody systems approach, MBS). Using computer-aided design (CAD) measured and computed data allowed creation and fine precision of titanium prostheses (Tübingen Titanium Protheses, TTP). Their handling was tested in temporal bones. Acoustomechanical properties were investigated using the MBS and mechanical middle ear models. MAIN OUTCOME MEASURES: Input impedance, mass, stiffness, and geometry of test models and prostheses were determined. Furthermore, their influence on the intraprosthetic transfer functions and on coupling to either tympanic membrane or stapes was investigated. RESULTS: Final results were FDA- and CE-approved filigreed titanium prostheses with an open head that fulfilled the four requirements detailed above. The prostheses (TTP) were developed in defined lengths of between 1.75 and 3.5 mm (partial) and 3.0 and 6.5 mm (total) as well as in adjustable lengths (TTP-Vario). CONCLUSIONS: The results suggest acoustomechanical advantages of TTPs because they combine a significantly low mass with high stiffness. In contrast to closed prostheses, the open head and filigreed design allow an excellent view of the prosthesis foot during coupling to the head or footplate of stapes, contributing to an improved intraoperative reliability of prosthesis coupling.

Resonant frequency pattern in multifrequency tympanograms: results in normally-hearing subjects.

This paper presents experimental data on the evaluation of middle ear resonances by multifrequency tympanometry. Multifrequency tympanograms (MFTs) of 18 normally-hearing subjects were recorded with a frequency resolution of 15 Hz. The fine structure found in the MFT patterns was compared with findings in literature. A first approach for the evaluation of this fine structure was made explaining the great variability of the main ossicular resonance frequencies described in previous publications. The consequence of the present investigation is that the concept of the main ossicular resonance has to be revised critically.

Dynamics of middle ear prostheses - simulations and measurements.

The efficient and systematic development of a middle ear prosthesis necessitates the use of computer models for the prosthesis itself and the reconstructed middle ear. The structure and parameters of the computer model have to be verified by specific measurements of the implant and the reconstructed ear. To obtain a realistic model of a reconstructed ear, three steps of modeling and measurements have been carried out. To get a first approach of the coupling elements a mechanical test rig representing a simplified reconstructed middle ear was built. The velocity of the stapedial footplate was measured with a laser Doppler vibrometer. The corresponding computer model was formulated, and the respective parameters were determined using the measured dynamical transfer functions. In the second step, a prosthesis was implanted into a human temporal bone without inner ear. Exciting this system with noise, the velocity of the stapes footplate was measured with the laser Doppler vibrometer. Based on the multibody system approach, a mechanical computer model was generated to describe the spatial motions of the reconstructed ossicular chain. Varying some significant parameters, simulations have been carried out. To describe the dynamical behavior of the system consisting of middle and inner ear, the computer model used in the second step has been enlarged by adding a simplified structure of the inner ear. The results were compared with in situ measurements taken from living humans.

Mechanical modeling and dynamical behavior of the human middle ear.

Very serious injuries may result from impulse noise applied to the human ear. To assess the hazard of a given impulse, its effects on the displacements and the velocities of the structures in the middle and inner ear have to be evaluated. Thus, it is necessary to consider the temporal pattern of applied pressure and the resulting temporal response of the ossicular displacements and velocities. These investigations have to be carried out in the time domain because the relations in the frequency domain known from steady-state motion do not hold. Mechanical models based on the finite-element approach and the multibody system method are presented to describe the spatial motions of the eardrum and the ossicles in the middle ear. The motion of all points of the ossicular chain can be calculated using these models. The free vibrations as well as the general solution of the excited system, consisting of a transient and a steady-state part, are analyzed. Three different sound pressure sources are considered and the dynamical response of the ossicular chain evaluated. It is not sufficient to assess a particular impulse only by its peak pressure and a characteristic time duration since the temporal response of the middle ear is strongly dependent on the waveform of sound pressure. In particular, it is shown that in most of the cases the first negative part of the pressure waveform is expected to cause the worst damage.

[First comparisons with laser vibrometry measurements and computer simulation of ear ossicle movements]. / Erste Vergleiche von Laservibrometriemessungen und Computersimulationen der Gehörknöchelchenbewegungen.

The dynamic behavior of the ossicular chain is very complex and is frequency-dependent. To date, this has still not been fully investigated or understood. There remains a lack of measurement procedures to pick up the motion of the ossicles and ear drum simultaneously with sufficient resolution. The presented paper reports simultaneous measurements with laser-Doppler vibrometry at two points of the ossicular chain of cadaver specimens. Motions not observed were derived using mechanical simulation models on a computer and then evaluating appropriate mathematical equations. Using a sound stimulus, the displacement velocities of the umbo and stapes footplate were measured, and the corresponding transfer functions were derived by Fourier transform. Results were used for verification of the computer models. In the current investigations these models were refined and allow for the detailed investigation of the dynamic behavior of the ossicular chain, facilitating the optimal design of passive and active middle-ear implants.

[Calculated displacements of the middle ear ossicles in static load]. / Berechnete Verschiebungen der Mittelohrknochen unter statischer Belastung.

To investigate the dynamic properties of human hearing, experiments in vivo and with cadaver specimens can be carried out. Furthermore, electrical or mechanical models can also be used to study specific phenomena and parameter sensitivities. Present electrical and mechanical models are often based on crude structural and kinematic simplifications in which testing is restricted to static loading or simplified investigations. To investigate both static and dynamic behavior of normal and pathological ears spatial mechanical models have to be established. The different parts of sound transmission--i.e., airborne sound, elastic membranes, fluids, and ossicles have to be represented by different mechanical systems. In this investigations, a rigid body model of the middle ear was investigated. For verification, simulation results with respect to static loads were compared with measurements reported previously by Hüttenbrink. In further investigations, the dynamic behavior of the model will be evaluated. Models for the tympanic membrane and inner ear will also be formulated in order to create a compositive model that describes the whole hearing process. By so doing the successful development of prostheses as well as diagnostic methods will be supported.

Hypertension and hyperlipidaemia: garlic helps in mild cases.

Forty-seven non-hospitalised patients with mild hypertension took part in a randomised, placebo-controlled, double-blind trial conducted by 11 general practitioners. The patients who were admitted had diastolic blood pressures between 95 and 104 mmHg after a two-week acclimatization phase. The patients then took either a preparation of garlic powder (Kwai) or a placebo of identical appearance for 12 weeks. Blood pressure and plasma lipids were monitored during treatment after four, eight and 12 weeks. Significant differences between the placebo and the drug group were found during the course of therapy. For example, the supine diastolic blood pressure in the group having garlic treatment fell from 102 to 91 mmHg after eight weeks (p less than 0.05) and to 89 mmHg after 12 weeks (p less than 0.01). The serum cholesterol and triglycerides were also significantly reduced after eight and 12 weeks of treatment. In the placebo group, on the other hand, no significant changes occurred.

MR imaging of intracranial arachnoid cysts.

The magnetic resonance characteristics of 16 intracranial arachnoid cysts were evaluated and several features identified that allowed the differentiation from other cystic lesions. Uncomplicated arachnoid cyst contents respond like CSF to both T1 and T2 weighted sequences. Signal from the contiguous brain is of normal intensity. The absence of signal from cortical bone and the ease of obtaining multiplanar views enable the margins of the cyst, its contents, and the full extent of the lesion to be easily defined.

"Photopenic" bone lesion secondary to erector spinae muscle infiltration by breast carcinoma.

A bone image demonstrating a "photopenic" vertebral lesion was found to be caused by tumor infiltration of adjacent muscle and probable secondary osseous ischemia. Magnetic resonance imaging was valuable in detecting the muscle abnormality.