Finite-element modelling of the mechanics of the coupling between the incus and stapes in the middle ear

The middle ear is a small air-filled cavity which contains a chain of three small bones or ossicles: the malleus, the incus and the stapes. There is a tiny bony bridge (pedicle) between the long process of the incus and the lenticular process, but little or nothing is known about the effect of the pedicle on the movements of the ossicles. The motivation of the work presented here is to improve our understanding of the mechanical behaviour at the pedicle and the incudostapedial joint, in particular the relative contributions of the two structures to sound transmission through the middle ear. A three-dimensional finite-element model of the pedicle and the incudostapedial joint was created, where the dimensions are based on examination of histological sections of a cat middle ear. Careful attention has been paid to the mesh generation of the model, especially for the regions of interest, such as the pedicle, that are very small relative to the overall structure. The issue of the compromise between the mesh resolution and the computational time will be discussed as well. Ranges of plausible values for the stiffnesses of the joint, joint capsule and pedicle were tested and the resulting displacements were examined for various loading conditions.