Comparative study of cochlear damage with three perimodiolar electrode designs

Objective. To describe intracochlear insertion trauma caused by three perimodiolar cochlear implant electrodes. Study Design: Descriptive histological study of 15 human cadaver temporal bones. Methods. Fifteen cadaver temporal bones underwent surface preparation and were implanted with one of the following perimodiolar electrode arrays: Combi 40+PM (MedEl Corporation), HiFocus 11 (Advanced Bionics Corporation), or Contour (Cochlear Corporation). A cryosectioning technique was used to study horizontal sections at 200-mum intervals with the electrode in place. Image-enhanced videofluoroscopy and computer-assisted morphometrics were used to assess the mechanism of insertion trauma and to determine electrode position within the modiolus. Results: Histological examination revealed varying degrees of damage to the spiral ligament, basilar membrane, and osseous spiral lamina. Using a novel grading system for electrode trauma, there was no statistically significant difference among the three electrodes. A literature search of histological studies of a commonly used "standard" electrode showed damage equal to or greater than that seen in the current study. Conclusions: Insertion trauma caused by periomodiolar electrodes occurs to an acceptable degree. Refinement of electrodes based on mechanisms of trauma may be able to further reduce damage.