Finite element modelling of the insertion of an electrode array into the cochlear scala tympani with lubricant

Abstract

Cochlear implants, consisting of electrode arrays for electrically stimulating the auditory nerve fibres, have been developed to restore hearing for profoundly deaf people. The insertion of a straight electrode array into the spiral cochlear scala tympani has unfortunately been found to damage delicate structures within the inner ear, such as the spiral ligament and the basilar membrane. Although a number of studies suggested the use of lubricant for smooth insertion, little attempt has been made to quantify the effect of lubricant on the damage by the electrode array to the cochlear structures. We develop a mathematical model, using the finite element method, to predict the trajectories of the Nucleus standard straight electrode array during insertion into the scala tympani, and associated contact stresses exerted Contents C1050 by the array on the cochlear structures. Results from the model show that the use of a lubricant, such as glycerine, reduces the contact stresses exerted by the tip of the array on the spiral ligament from 0.31 to 0.2 MPa, whereas the contact stresses on the basilar membrane reduce from 0.075 MPa (without lubricant) to 0.025 MPa (with lubricant). These results suggest that the use of a lubricant is clinically important for minimising the likelihood of damage by the electrode array to the cochlear structures.