Acoustics-structure interactions in the human middle ear produce variety of motion modes at the malleus-incus complex

Abstract

We developed a 3D finite-element model to simulate the dynamics of the human middle ear, using COMSOL Multiphysics software to solve the resulting acoustics-structure interaction problem. We validated the model by comparing numerical results with experimental data measured in the ear canal, on the tympanic membrane (TM), at the umbo, and at the stapes footplate. The results show that at low frequencies (up to 500 Hz), the conventionally accepted hinge-like motion of the malleus-incus complex dominates the response, with the angle between the rotational axes of the malleus and incus staying below about 5 degrees. However, above 5 kHz, this angle becomes significantly larger, indicating that the malleus and incus rotate about different axes. Near the upper frequency limit of 20 kHz, the angle between the rotational axes of the malleus and incus approaches 90 degrees as the malleus adopts a lower-inertia twisting-like rotation about its first principal axis. The model is also used to explore the effects, on ossicular motion and overall pressure transfer from the ear canal to the cochlea, of alterations to the mechanical properties of the TM, to the flexibility of the malleus-incus joint, and to the mass of the ossicles. [Funded by NIDCD/NIH.]