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 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 0.2MPa, whereas the contact stresses on the basilar membrane reduce from 0.075MPa (without lubricant) to 0.025MPa (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. References B. K. Chen, G. M. Clark, and R. Jones. Evaluation of trajectories and contact pressures for the straight nucleus cochlear implant electrode array --- a two-dimensional application of finite element analysis. Medical Engineering and Physics, 25:141--147, 2003. doi:10.1016/S1350-4533(02)00150-9. G. M. Clark. Cochlear implants --- Fundamentals and Applications. Springer-Verlag, New York, 2003. L. T. Cohen, J. Xu, S. A. Xu, and G. M. Clark. Improved and simplified methods for specifying positions of the electrode bands of a cochlear implant array. American Journal of Otology, 17:859--865, 1996. H. N. Kha and B. K. Chen. Determination of frictional conditions between electrode array and endosteum lining for use in cochlear implant models. Journal of Biomechanics, 39(9):1752--1756, 2006. doi:10.1016/j.jbiomech.2005.04.031. H. N. Kha, B. K. Chen, G. M. Clark, and R. Jones. Stiffness properties for {N}ucleus standard straight and {C}ontour electrode arrays. Medical Engineering and Physics, 26:677--685, 2004. doi:10.1016/j.medengphy.2004.05.001. R. Laszig, G. J. Ridder, and M. Fradis. Intracochlear insertion of electrodes using hyaluronic acid in cochlear implants. Journal of Laryngology Otology, 116:371--372, 2002. doi:10.1258/0022215021910816. E. Lehnhardt. In B. Fraysse and O. Deguine, editors, Cochlear implants: new perspectives, volume 48 of Advances in Otorhinolaryngology, pages 62--64. Karger, Basel, 1993. Noran Engineering Inc. NE/Nastran Version 8.2 User's Manual, 2002. J. J. T. Roland, T. M. Magardino, J. T. Go et al. Effects of glycerine, hyaluronic acid, and hydroxypropyl methylcellulose on the spiral ganglion of the guinea pig cochlea. Annals of Otology, Rhinology and Laryngology Supplement, 166:64--68, 1995. R. K. Shepherd, G. M. Clark, B. C. Pyman, and R. L. Webb. Banded intracochlear electrode array: Evaluation of insertion trauma in human temporal bones. Annals of Otology, Rhinology and Laryngology, 94:55--59, 1985. C. Todd, F. Naghdy, and M. Svehla. Force application during cochlear implant insertion: An analysis for improvement of surgeon technique. IEEE Transactions on Biomedical Engineering, 54(7):1247--1255, 2007. doi:10.1109/TBME.2007.891937. M. Tykocinski, E. Saunders, L. T. Cohen, C. Treaba, R. J. Briggs, P. Gibson, G. M. Clark, and R. S. Cowan. The Contour electrode array: safety study and initial patient trials of a new perimodiolar design. Otology Neurotology, 22:33--41, 2001. P. Wardrop, D. Whinney, S. J. Rebscher, J. T. J. Roland, W. Luxford, and P. A. Leake. A temporal bone study of insertion trauma and intracochlear position of cochlear implant electrodes. {I}: comparison of {N}ucleus banded and {N}ucleus {C}ontour electrodes. Hearing Research, 203:54--67, 2005. doi:10.1016/j.heares.2004.11.006.