Multichannel intracochlear electrodes: mechanism of insertion trauma.

Cochlear damage from electrode insertion, a potential cause of further neural degeneration, is a major concern in the use of intracochlear electrodes. A study was undertaken to evaluate mechanisms by which damage may occur. Fresh human temporal bone preparations were created to allow direct intracochlear observation during round window insertion of a free-fitting multichannel intracochlear electrode array. The path taken by the electrode, point of first resistance, and any resulting damage were documented. Tips of study electrodes in this preparation tended to embed in the outer wall of the scala tympani. The integrity of the basilar partition was largely maintained during insertion when this was stopped at the point of first resistance. However, insertion beyond the point of first resistance typically resulted in widespread damage to intracochlear structures.