Perimodiolar electrodes in cochlear implant surgery

Perimodiolar-positioned cochlear implant electrodes have been developed in order to bring the electrode contacts as close as possible to the spiral ga nglion cells, which are the target of electrostimulation. This results in l ower electrical thresholds, higher dynamic ranges and less channel interact ion when compared with normal implant electrodes which are usually located peripherally within the scala tympani. In this study we evaluated 4 differe nt types of perimodiolar electrode: the Clarion Preformed electrode, the Cl arion Preformed electrode with positioner, the Nucleus Contour electrode an d the Med-El Perimodiolar Combi 40 electrode, These devices require differe nt approaches to achieve a perimodiolar electrode position. The electrodes a ere inserted in fresh human temporal bones. After processing these bones with the electrodes in situ by employing a sawing, grinding and polishing t echnique, the inner ear structures as well as the electrode positions could be evaluated in detail. All electrode types studied had a more or less per imodiolar position: however, each type produced a certain amount of trauma to cochlear structures which is discussed in relation to mechanical propert ies. Further human temporal bone studies with improved perimodiolar cochlea r implant electrodes are necessary in order to find an optimized type of el ectrode.