Three-dimensional stapes footplate motion in human temporal bones

The literature provides conflicting information on whether the motion of the stapes footplate is piston-like or some other type of motion, such as rotational or rocking. Examination of the three-dimensional (3D) motion of the stapes footplate appears to be an excellent way to understand this complicated motion. Five microsphere reflective targets were placed on the stapes footplate in ten fresh human cadaver temporal bone preparations, and their vibration measured through an extended facial recess approach using a laser Doppler vibrometer. The five target sites on the stapes footplate were center, anterior, posterior, superior and inferior. The stimulus was a sound input of 80-120 dB SPL at the tympanic membrane over a frequency range of 0.1 to 10 kHz. The 3D motion of the stapes footplate was calculated using the velocity amplitude and phase obtained for each target. For frequencies up to 1.0 kHz the vibration of the stapes footplate was primarily piston-like; this motion became complex at higher frequencies, with rotary motion along both the long and short axis of the footplate. When the cochlea was drained, stapes footplate motion became essentially piston-like for all frequencies.     

Ossicular vibration in human temporal bones

Vibration mode of the ossicles was investigated in twelve fresh human temporal bones using a video measuring system (VMS, Technical Instrument). This system allows one to observe the ossicular vibration and to measure its vibration amplitude (up to 0.2 micron) and phase angle. In this study the inner and middle ear was kept intact except for two small holes in the tympanic tegmen. These holes were for the observation of ossicular movement and were covered with a thin cover glass during the experiment. The vibration amplitude and phase angle of the umbo, malleus head, lenticular process and stapes head were measured at 19 frequencies between 0.1 kHz and 4.5 kHz. The umbo moved piston-like at 0.1-0.8 kHz and 2.6-4.5 kHz but in an ellipse at 1.0-2.4 kHz. The malleus head showed elliptical movement with its long axis anteriorly tilted around 45 degrees from the direction of the umbo vibration at 0.1 kHz. Both the lenticular process and stapes head showed similar movement; piston-like in lower frequencies and elliptical in higher frequencies. The umbo, lenticular process and stapes head vibrated parallel at lower frequencies. The position, displacement and phase angle of the rotation axis of the ossicles was calculated based on the displacement and phase angle of the umbo, malleus head and lenticular process. The axis was around the level of the neck of the malleus in frequencies lower than the resonant frequency, beneath the level of the short process near the resonant frequency and at the top of the malleus head in higher frequencies. The average axis displacement was 0.9 microns at 1 kHz but much smaller at frequencies lower than 0.8 kHz or higher than 2 kHz. This suggests that such axis movement may reduce the efficiency of the middle ear sound transmission.     

Complex Stapes Motions in Human Ears

It has been reported that the physiological motion of the stapes in human and several animals in response to acoustic stimulation is mainly piston-like at low frequencies. At higher frequencies, the pattern includes rocking motions around the long and short axes of the footplate in human and animal ears. Measurements of such extended stapes motions are highly sensitive to the exact angulation of the stapes in relation to the measurement devices and to measurement errors. In this study, velocity in a specific direction was measured at multiple points on the footplates of human temporal bones using a Scanning Laser Doppler Vibrometer (SLDV) system, and the elementary components of the stapes motions, which were the piston-like motion and the rocking motions about the short and long axes of the footplate, were calculated from the measurements. The angular position of a laser beam with respect to the stapes and coordinates of the measurement points on the footplate plane were calculated by correlation between the SLDV measurement frame and the footplate-fixed frame, which was obtained from micro-CT images. The ratios of the rocking motions relative to the piston-like motion increased with frequency and reached a maximum around 7 kHz.     

Reconstructing the absent lenticular process

When a surgeon encounters an absent lenticular process of the incus, he must either reposition the incus or attempt to bridge the small gap between the remaining incus long process and the stapes capitulum. Our solution to this problem is to place a Lippy modified Robinson stapes prosthesis on the stapes footplate and attach it to the remaining long process, thus bypassing the stapes superstructure. This modified Robinson prosthesis has a portion of the well removed allowing the eroded long process to enter from the side. The hearing results of 63 cases at 6 months (two-thirds of which had a concurrent tympanoplasty) are 67% within 10 dB and 91% within 20 dB of the preoperative bone hearing level. The use of an existing and proven prosthesis provides both stability and, to date, the most successful hearing results for reconstructing the absent lenticular process.     

Sequential motion of the ossicular chain measured by laser Doppler vibrometry

Objective: In order to help a surgeon make the best decision, a more objective method of measuring ossicular motion is required.

Methods: A laser Doppler vibrometer was mounted on a surgical microscope. To measure ossicular chain vibrations, eight patients with cochlear implants were investigated. To assess the motions of the ossicular chain, velocities at five points were measured with tonal stimuli of 1 and 3?kHz, which yielded reproducible results. The sequential amplitude change at each point was calculated with phase shifting from the tonal stimulus. Motion of the ossicular chain was visualized from the averaged results using the graphics application.

Results: The head of the malleus and the body of the incus showed synchronized movement as one unit. In contrast, the stapes (incudostapedial joint and posterior crus) moved synchronously in opposite phase to the malleus and incus. The amplitudes at 1?kHz were almost twice those at 3?kHz.

Conclusions: Our results show that the malleus and incus unit and the stapes move with a phase difference.     

An anatomically shaped incus prosthesis for reconstruction of the ossicular chain

An anatomically shaped incus replica prosthesis has been designed to reconstruct the ossicular chain. A series of in vitro studies on human temporal bones evaluated the acoustic performance of this prosthesis and compared it with a Causse partial ossicular replacement prosthesis (PORP). Pure tones in the frequency range 0. 125-8 kHz stimulated the tympanic membrane at sound pressure levels of 80, 90 and 100 dB. Measurements of the stapes footplate velocity were made with a laser interferometer. The acoustic function of the ossicular chain reconstructed with the incus replica prosthesis was found to be within 10 dB of that of the original intact ossicular chain, when both the upper and lower joints of the implant were rigidly fixed in place. It was shown that a rigid mechanical contact between the ossicular prosthesis and ossicles is a prerequisite for effective sound transmission. The anatomically shaped incus prosthesis gave a 15-dB improvement on the PORP at frequencies below 1.5 kHz.     

Acoustic Effect of Malleus Head Removal and Tensor Tympani Muscle Section on Middle Ear Reconstruction

In the reconstruction of ears with a missing incus, an incus replacement prosthesis (IRP) is commonly used to connect malleus and stapes. In some cases, it is necessary to resect the malleus head and/or section the tensor tympani muscle (TTM) tendon. The acoustic effects of these maneuvers have not been well studied. We performed experiments in a temporal bone model to measure the effect of these maneuvers on middle ear sound transmission. Measurements of umbo and stapes displacement were made before and after malleus head removal and TTM section plus incus replacement with an IRP. After malleus head removal, there was a peak gain in stapes displacement of 6 dB below 0.5 kHz and 8 dB above 2.5 kHz. TTM section had a similar but lesser effect. A clinical example is described.     

Ossiculoplasty with a cartilage-connecting hydroxyapatite prosthesis for tympanosclerotic stapes fixation

Many cases of tympanosclerotic stapes fixation are accompanied by fixation or erosion of malleus and/or incus. This status of the ossicular chain is one of the reasons that ossiculoplasty for tympanosclerotic stapes fixation is more difficult than that for otosclerosis. We conducted a retrospective review of seven patients who were operated on for tympanosclerotic stapes fixation between 2002 and 2006. All of the patients had abnormal conditions of the malleus and/or incus and underwent stapedectomy and total ossiculoplasty with hydroxyapatite prosthesis (Apaceram T-7 type), which has a planar-like head portion that contacts a piece of cartilage. Postoperative hearing results were assessed in all seven patients after at least 1 year. The postoperative air-bone gap (ABG) was closed within 10 dB in two of seven patients, and was less than 20 dB in six of seven patients. The mean postoperative ABG was closed within 10 dB at 1 and 2 kHz and less than 20 dB at low frequencies (0.25 and 0.5 Hz). There was almost no hearing improvement at high frequencies (4 and 8 kHz). There were no patients with postoperative sensorineural hearing loss. The present study shows that stapedectomy and total ossiculoplasty with cartilage-connecting hydroxyapatite prosthesis is effective and safe for stapes fixation accompanied by fixation or erosion of the malleus and/or incus.     

镫骨足弓进行性萎缩和镫骨足弓鼓岬粘连

目的介绍二种少见镫骨病变-足弓与鼓岬粘连和足弓萎缩引起传导性耳聋及其处理的结果.方法例1,女性17岁,右耳进行性听力下降伴耳鸣2年半.手术见镫骨头在颈部与足弓脱离,足板活动,镫骨苍白.取耳道薄骨片,修成叉柱状,尖抵足板,紧贴足弓叉起砧骨长突.术后语言频率(0.5-2KHz)气骨导差闭合到10dB以内.例2男性16岁,右耳非渐进耳聋3年.手术见砧骨长突较长,镫骨与砧骨豆状突连接紧密,但镫骨过于倾斜,足弓与卵圆窗下缘的鼓岬紧贴粘连,致镫骨活动受限.分离砧镫关节,切断镫骨肌,分离粘连,将镫骨足弓向上方移位并抬高.术后气骨导差闭合.结果分别在2年和1年后随访,听力保持术后水平.结论镫足弓进行性萎缩可能是局部缺血所致退行变,镫骨弓与鼓岬粘连可能是先天解剖变异加上后天炎症肿胀引起,临床上都少见.用不切开足板的微创方法解决青少年镫骨病变较为有利.     

The effect of methodological differences in the measurement of stapes motion in live and cadaver ears

Methodological differences in sound-induced stapes velocity (Vs) measurements in live and cadaveric ears were examined using fresh cadaveric temporal bones. On average, differences in preparation (sectioning the stapedius tendon, removing the facial nerve, and widely opening the facial recess) had statistically insignificant effects on measured Vs. Differences in the achievable measurement angle (with respect to the axis of piston-like stapes motion) had a significant effect on measured Vs below 2 kHz. These results suggest that much if not all of the differences in Vs measurements between live and cadaveric ears can be explained by the differences in measurement angle between the two preparations. Measurement angle was found to have minimal effect on measured Vs above 2 kHz. This demonstrates that the commonly used method of estimating stapes translational velocity by dividing the measured velocity by the cosine of the measurement angle is not valid above 2 kHz.     

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.     

Studies on the mechanics of the normal human middle ear

The middle ear was studied in temporal bone preparations using a laser-Doppler interferometer. For measurements at a sound level of 80 dB SPL this method proved to be very reliable, as was shown by good reproducibility of results in experiments over more than 6 hours. The vibrations of the tympanic membrane and stapes footplate were studied from 200 Hz to 10 KHz and the results demonstrate a piston-like movement of the stapes footplate up to 120 dB SPL. The damping effect of the normal ear is located mainly at the footplate/cochlea level and the middle ear cavity per se does not contribute significantly to the stiffness of the middle ear system.     

Three-Dimensional Vibration of the Malleus and Incus in the Living Gerbil

In previous studies, 3D motion of the middle-ear ossicles in cat and human was explored, but models for hearing research have shifted in the last few decades to smaller mammals, and gerbil, in particular, has become a popular hearing model. In the present study, we have measured with an optical interferometer the 3D motion of the malleus and incus in anesthetized gerbil for sound of moderate intensity (90-dB sound pressure level) over a broad frequency range. To access the ossicles, the pars flaccida was removed exposing the neck and head of the malleus and the incus from the malleus-incus joint to the plate of the lenticular process. Vibration measurements were done at six to eight points per ossicle while the angle of observation was varied over approximately 30 ° to enable calculation of the 3D rigid-body velocity components. These components were expressed in an intrinsic reference frame, with one axis along the anatomical suspension axis of the malleus-incus block and a second axis along the stapes piston direction. Another way of describing the motion that does not assume an a priori rotation axis is to calculate the instantaneous rotation axis (screw axis) of the malleus/incus motion. Only at frequencies below a few kilohertz did the screw axis have a maximum rotation in a direction close to that of the ligament axis. A slight slippage in the malleus-incus joint developed with increasing frequency. Our findings are useful in determining the sound transfer characteristics through the middle ear and serve as a reference for validation of mathematical middle-ear models. Last but not least, comparing our present results in gerbil with those of previously measured species (human and cat) exposes similarities and dissimilarities among them.     

Malleus-to-footplate ossicular reconstruction prosthesis positioning: cochleovestibular pressure optimization.

AIMS: To determine 1) the best position for hydroxylapatite malleus-to-footplate (MFP), ossicular replacement prosthesis (ORP) in reconstructed ears, and 2) whether preserving the stapes superstructure (SS), when present, has acoustic advantages. BACKGROUND: Positioning of the MFP-ORP head beneath the neck of the malleus may produce maximal force, whereas positioning beneath the manubrium of the malleus may produce the greatest displacement. It is not clear which is the optimal placement position. In addition, we look at the effect of the SS on sound transmission to the inner ear in ossicular reconstruction. METHODS: The ear-canal air pressure and vestibular hydro-pressure were measured in human cadaver temporal bones with incus intact, removed, and replaced with the MFP-ORP; the ORP head was placed at three different positions on the malleus (head, mid-manubrium, and umbo) while keeping its base at the center of stapes footplate with intact or removed stapes SS. The vestibular pressure ratio between the ear with intact incus and MFP-ORP reconstructed ear is defined as Lmfp, the loss caused by the prosthesis in relation to the normal ossicular chain. RESULTS: The mean magnitude of Lmfp, averaged in the important speech frequency region of 0.5 to 3 kHz, is approximately 7.8 dB at the neck with stapes SS. In comparison, mean magnitude of Lmfp for mid-manubrium without stapes SS is 15 dB (p = 0.04), and with the stapes SS it is 16 dB (p = 0.05), whereas at the umbo without SS it is 15 dB (p = 0.03). In the 8 kHz region, the mean magnitude of Lmfp is approximately 1 dB with the stapes SS intact and approximately 8.5 dB when it was removed (p < 0.09). CONCLUSION: There are significant physiologic advantages to placing the hydroxylapatite MFP-ORP beneath the neck of the malleus and preserving the SS.     

Experimental study of an adjustable-length prosthesis in a temporal bone model

CONCLUSIONS: This prosthesis has the advantage of rapid adjustment at the time of insertion in order to achieve optimal tension and, as a result, optimal sound transmission. OBJECTIVE: To test the acoustic performance of a new, adjustable incus replacement prosthesis in a human temporal bone model. MATERIAL AND METHODS: Experiments were performed in seven human temporal bones, before and after removal of the incus and insertion of the prosthesis. The input comprised 406 pure tones ranging in frequency between 0.1 and 10 kHz at an intensity of 80 dB SPL at the tympanic membrane. The output measurement was stapes footplate displacement, determined by means of a laser Doppler vibrometer. Three lengths of the prosthesis were investigated: optimal, optimal +0.2 mm and optimal +0.4 mm. RESULTS: The optimal-length prosthesis produced similar results to those of an intact middle ear. The slightly longer prostheses decreased middle ear sound transmission at all test frequencies, except those near 1.5 kHz.     

Vibration properties of the ossicle and cochlea and their importance for our hearing system

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.     

Holographic observation of the tympanic membrane vibration after stapes fixation

Sclerosis of auditory ossicle was experimentally induced by fixation of the stapes, and its effect on the tympanic membrane vibration was examined using fresh 10 canine temporal bones by means of holographic interferometry. By changing the sound pressure (from 90 to 110dB) and the frequency (from 250Hz to 8kHz) in steps, vibration of the membrane was induced in a free field. At each frequency, the vibration of the membrane was photographed by the time averaged method using He-Ne laser. A small hole was created in the tympanic bulla and the stapes was fixed with an adhesive (Alon Alpha), followed by closure of the hole. Before stapes fixation, the posterior part of the membrane showed a simple vibration pattern, forming cocentric interference circles at frequencies from 250Hz to 2kHz. At 3kHz, segmental vibration began to be noted, and complex segmental vibration was seen at frequencies 4.5 and 6kHz. The vibration after stapes fixation became simpler at frequencies over 3kHz, accompanied by decrease in the number of segmental vibrations. Vibration amplitude in the posterior part of the membrane decreased from 250Hz to 3kHz, while it increased at frequencies over 4kHz. In the anterior part of the membrane, the amplitude decreased at frequencies under 2kHz, remained unchanged at 3kHz and increased at frequencies over 4kHz after stapes fixation. In the tip of the manubrium mallei, the amplitude decreased at frequencies under 3kHz and increased at frequencies over 4kHz. Thus, a shift of peak vibration to high sound region was observed after stapes fixation at every part of tympanic membrane.(ABSTRACT TRUNCATED AT 250 WORDS)     

Basilar Membrane Vibrations Near the Round Window of the Gerbil Cochlea

Using a laser velocimeter, responses to tones were measured at a basilar membrane site located about 1.2 mm from the extreme basal end of the gerbil cochlea. In two exceptional cochleae in which function was only moderately disrupted by surgical preparations, basilar membrane responses had characteristic frequencies (CFs) of 34–37 kHz and exhibited a CF-specific compressive nonlinearity: Sensitivity near the CF decreased systematically and the response peaks shifted toward lower frequencies with increasing stimulus level. Response phases also changed with increases in stimulus level, exhibiting small relative lags and leads at frequencies just lower and higher than CF, respectively. Basilar membrane responses to low-level CF tones exceeded the magnitude of stapes vibrations by 54–56 dB. Response phases led stapes vibrations by about 90° at low stimulus frequencies; at higher frequencies, basilar membrane responses increasingly lagged stapes vibration, accumulating 1.5 periods of phase lag at CF. Postmortem, nonlinearities were abolished and responses peaked at ~0.5 octave below CF, with phases which lagged and led in vivo responses at frequencies lower and higher than CF, respectively. In conclusion, basilar membrane responses near the round window of the gerbil cochlea closely resemble those for other basal cochlear sites in gerbil and other species.