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This study was designed to determine whether stapes movement is pistonlike or complex.The literature provides conflicting information on whether stapes footplate motion is only pistonlike or has other types of movement, such as hingelike or rocking.Using 10 freshly harvested human cadaver temporal bones, 3 targets were placed on the stapes footplate through an extended facial recess approach. The targets were 0.5-mm pieces of reflective adhesive material positioned on the long axis of the footplate at the anterior crus, central footplate, and posterior crus. Displacement and phase of the three targets were measured from 0.2 to 10 kHz at a 90dB sound pressure level input at the tympanic membrane. The measuring system was a sophisticated laser Doppler vibrometer (LDV). A computer program (Tymptest) calculated footplate displacement and relative phase at the three sites and the ratio of anterior-posterior rocking movement of the footplate long axis to displacement at the center.Below 2.0 kHz, stapes vibration is predominately pistonlike. Above 2.0 kHz, anterior-posterior rocking motion increases logarithmically with frequency, and, near 4.0 kHz, rocking and pistonlike motion are approximately equal.Stapes footplate vibration is primarily pistonlike up to 2.0 kHz but becomes more complex at higher frequencies because of an increase in anterior-posterior rocking motion. Hingelike movements were not observed. This information may be helpful in the design of ossicular replacement prostheses that mimic or improve upon normal stapes vibration.

We describe a laser Doppler system (LDS) that can be used clinically for the measurement of tympanic membrane (TM), malleus and prosthesis head displacement in response to sound inputs of 80-to 100-dB sound-pressure level (SPL). It also has the potential for use in the operating room to perform measurements of prosthesis and stapes displacement. The information provided by such testing gives the otologist knowledge of TM and ossicular function that is unique in evaluating middle ear function; it should help select the best type of reconstruction in a given case and direct us toward new and better methods of TM and ossicular reconstruction. The results of umbo displacement measurements in 95 human ears are reported. Examples are provided of LDS measurements in representative ears and how they can be of help to the clinician. The potential of multisite TM-displacement testing is demonstrated in two temporal bones, including before and after partial ossicular replacement prosthesis (PORP) insertion.

Many middle ear prostheses are available for reconstruction of a missing or damaged incus. Little is known of the relative acoustic performance of these prostheses in vitro and the parameters (mass, shape, tension, angulation, area of head) that modify this performance. This report describes experiments in a human temporal bone model comparing the effect on stapes displacement of six commercially available incus replacement prostheses (IRP). Measurements were performed using a laser Doppler vibrometer before and after incus removal and IRP placement between the tympanic membrane (TM) and stapes head. In addition, experiments were performed on the effect of increasing prosthesis mass, varying the tension between TM and stapes head, changing the surface area in contact with the TM, and comparing different TM contact sites. All prostheses tested showed reasonable acoustic performance compared to the baseline condition. Optimum tension between the TM and stapes head produced the best overall sound transmission. The mid-malleus and umbo locations were the best malleus contact sites; however, the posterior TM contact site also worked well. Increased mass improved low frequency transmission and impaired higher frequency transmission, whereas a larger contact area with the TM contributed to increased gain in the mid frequencies.

A commercial laser doppler vibrometer (LDV) was used to evaluate umbo displacement at sound pressure levels of 60, 70, and 80 dB SPL at the tympanic membrane (TM) of six subjects. Thirty-five pure-tone test frequencies, five per octave, were tested from 140 to 19,433 Hz. A computer program (Tymptest) produced and controlled the tones as well as improved the signal-to-noise ratio of the LDV. The test took about an hour to perform and provided reproducible results in all subjects. In addition, measurement of umbo displacement using the same system was made in 15 fresh human temporal bones for comparison. Results in the humans revealed a relatively flat umbo displacement from 140 to 1000 Hz, with a gradually sloping roll-off of -8.25 dB per octave from 1000 to 7000 Hz. From 8000 to 14,000 Hz the roll-off increased to -12.5 dB per octave. At the mean resonant frequency of the middle ear, 1000 Hz, and an 80 dB SPL input, umbo displacement was 0.045 micron. The human temporal bones showed similar results. Possible future clinical applications of this measurement include the identification of ears with acoustically inefficient TMs (tin ears). By identifying and studying such ears we should be able to develop methods to improve their function and produce hearing threshold increases of 15 dB or more at key speech frequencies. In addition, analysis of umbo and TM vibration in reconstructed middle ears should help us achieve better postoperative hearing results.