Bone conduction stimulation of the temporal bone with the inner ear: A finite element study

A numerical model of the human temporal bone with a precisely reconstructed cochlea was used to investigate bone conduction stimulation applied on the otic capsule. A passive cochlear model was used. Validation of the cochlea was based on the experimental data. The round window membrane and cortical bone were assumed as viscoelastic, with the storage and loss moduli defined as functions of frequency. Other solid tissues were modeled as linear isotropic, and the perilymph fluid was assumed as viscous and compressible. The model was subjected to harmonic analysis in the frequency range from 0.2 to 10 kHz. The bone conduction stimulation was applied as a harmonic force to the mass attached to the otic capsule surface. The boundary of the temporal bone was fixed on the sutures between the adjacent skull bones. The aim of the study was to examine: 1) the type of boundary condition applied on the surface of the petrous part of the temporal bone adjacent to the petro-occipital synchondrosis, 2) the value of the surface density used in the model to include the mass of soft tissues in the vicinity of the temporal bone, assumed as uniformly distributed on its outer surface (inside and outside the skull). Two conditions related to the mobility of the stapes were considered. The amplitude and phase of vibrations obtained from numerical simulation were used to assess the effects mentioned above, including the volume displacement on the round window membrane, displacements on the basilar membrane and at the spiral lamina along the cochlea, and vibration of the promontory bone at the edge of the round window. The values of forces needed for bone conduction stimulation corresponded to those used in previous experimental cadaver studies. The results from the numerical analysis were compared with the experimental data.