Finite element analysis of the osseous spiral lamina's influence on inner ear fluid flow during bone conduction...

Recent studies have investigated the anatomy and motion of the human cochlear partition, revealing insights into the flexible nature of the osseous spiral lamina (OSL). These investigations have primarily focused on air-conducted stimulation, leaving the impact of the OSL's flexibility during bone-conducted (BC) stimulation largely unexplored. By considering the OSL as either flexible or rigid in a finite element model of the human inner ear, we examined the effect of the OSL's flexibility on the fluid flow in the inner ear during BC stimulation, which was divided into contributors entering via the oval window (OW) and rigid body stimulation. Our results with rigid body stimulation indicate that the OSL facilitates an increased differential fluid flow at the round window compared to the OW, aligning with experimental observations interpreted as third window effects. Analysis of the OSL motion showed that this contribution results from a compressional motion of the OSL's vestibular and tympanic plates which is significantly lower in magnitude than the plates' translation in the direction of the stimulation. Separately applying OW input and rigid body stimulation provided insights into the interaction of BC sound entering via the OW and the reaction of the stapes to complex interior sound pressure distributions. Combined with the observations from a prior study (Kersten et al., 2024b) our results suggest a more important role for the OSL in BC hearing than previously understood. These findings enhance our understanding of the inner ear's response during BC and contribute to ongoing investigations into the interaction of BC mechanisms, while highlighting the need for further research into the deformation of the cochlear boundaries.