Hydrodynamics of a vibrating stapes prosthesis in stapedotomy

In stapedotomy surgery (small fenestra stapedectomy), the superstructure of the stapes bone in the middle ear is removed and replaced with a piston-like cylindrical prosthesis that projects through a small opening of the oval window into the vestibule of the inner ear. The longitudinal oscillations of the piston generate an oscillatory flow that transmits a pressure wave into the cochlea to activate the sensory hair cells. In this paper, the oscillatory flow induced by the harmonic vibration of the stapes prosthesis is investigated by the boundary element method. The perilymph is assumed to be an incompressible Newtonian fluid whose motion is governed by the equations of unsteady Stokes flow. A theoretical model is proposed wherein the piston projects into the vestibule through an infinite plane wall, and the effect of the piston diameter on the amplitude of the pressure vibration is investigated. It is shown that a simple point source model is adequate for describing the pressure distribution sufficiently far from the piston.