Three-Dimensional Stapes Footplate Motion in Human Temporal Bones

Abstract

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.

Complex Stapes Motions in Human Ears

“…In previous studies (Békésy 1960;Kirikae 1960;Heiland et al 1999;Hato et al 2003), it has been assumed that due to the shape of the annular ligament and the mechanical stress and strain distribution in it, the in-plane motions of the footplate, which resulted from translational displacements in the x and y directions and rotations around the z axis, are much smaller by magnitudes than the piston-like and rocking motions. Though the restriction of the inplane motion of the footplate has not been proved and there still exists the possibility that the magnitude of the other components are comparable to the piston-like and rocking motions, it is assumed in this study that the piston-like and two rocking motions are the elementary components of the stapes motions.…”

“…To show the effect of the rotation, the linear velocities at the inferior and posterior edges of the footplate generated by the rotational velocities were calculated (Heiland et al 1999;Hato et al 2003). In this article, the edge velocities are defined as the velocities at the edges only due to the rotational velocities ω x and ω y .…”

“…It has been reported that the human stapes motions are piston-like at low frequencies and include rocking motions along the long and short axes of the footplate at high frequencies (Heiland et al 1999;Huber et al 2001;Hato et al 2003). Studies of rocking motions have been extended to other animals such as cat (Decraemer et al 2000) and gerbil (Decraemer et al 2007;Ravicz et al 2008).…”

“…Hato et al (2003) measured velocities at five points on the footplate and calculated the piston-like and two rocking motions of the stapes. Eiber et al (2007) also calculated the piston-like and two rocking motions from 3-D velocity components at a point on the stapes head measured using a 3-D LDV system.…”

“…In the work by Hato et al (2003), reverse calculation of velocities at the measurement points from identified rigid body motion components was used to verify consistency of measurement and calculation of the overall stapes motions. However, if contribution of a specific rigid body motion component to the entire stapes motion is relatively small, then good agreement between the original measurement and the reverse calculation does not guarantee accuracy of the rigid body motion component.…”