Should perilymph be considered when modeling the lateral semicircular canal?

Abstract

The inner ear contains a set of sensors that detect head accelerations, and are responsible for our proper balance. Due to its small size and fragility, numerical models are an essential tool to compensate for the lack of direct biomechanical experiments on the inner ear's tissues. In existing models, the surrounding perilymphatic compartment is seldom represented, imposing rigid boundary conditions on the endolymphatic compartment. Using an original 2.5D finite element model of the lateral semicircular canal, we demonstrate that both perilymph dynamics and membranous labyrinth elasticity significantly influence cupula biomechanical behavior (cupula displacement amplitude and von Mises stress distribution). Based on the cupula's time constant, we also propose new viscoelastic law parameters to best describe its behavior. A numerical simulation of a reference clinical test, in which canal rotation was abruptly stopped within 100 ms, was implemented as a stimulus to the models. In the complete model incorporating the perilymph compartment, the cupula exhibited, as expected, a rapid deflection toward the canal followed by a slow return to its straight position. Conversely, in the absence of the perilymphatic compartment, the cupula demonstrated oscillatory-like behavior, deflecting initially slightly toward the canal and then toward the utricle before returning to its straight position. The implications of accounting for the anatomical (i.e., flexible) boundary conditions of the membranous labyrinth are discussed, highlighting their importance for accurately capturing vestibular mechanics and for improving the understanding of related pathophysiological conditions.

Keywords: Biomechanical modeling; Cupula; Endolymph; Finite element; Perilymph; Vestibular system.