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

The 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 quantitatively study the effect of lubricant on the damage by the electrode array to the cochlear structures. In this study, a mathematical model using the finite element method was developed to predict the trajectories of the Nucleus standard straight electrode array during insertion into the scala tympani and associated contact stresses exerted by the array on the cochlear structures. Results from the model have shown 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). The 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.