[A novel cryo-grinding technique for evaluating new cochlear implant electrodes after ex vivo insertions in temporal bone specimens].

Background: Prior to clinical application, newly developed prototypes of cochlear implant electrode arrays must prove their suitability with the smallest possible tissue damage in ex vivo temporal bones. So far, after insertion of the electrodes the temporal bone specimens have to be processed in a rather intricate technique, including embedding, sectioning or grinding prior to histological evaluation. The question remains whether for special indications this time-consuming method, which even causes artifacts, can be replaced by a new technique based on cryo-grinding.

Materials And Methods: The main principle of the method described is to grind the temporal bone with the inserted electrode in a frozen state, provided by a fixation device filled with dry ice. After creating a plane surface and staining it (still in a frozen state), the specimen can be examined and photographed with a projection microscope. This procedure is continued by subsequently grinding and examining new surfaces in defined distances.

Results: In numerous trial runs the method proved feasible, saving much time and manpower. After grinding, each plane could be examined sufficiently; the site of the electrodes and the corresponding tissue damage could be documented properly.

Discussion: The new concept of cryo-grinding provides relatively easy and fast examinations of temporal bones after inserting test electrodes. The examiner is enabled to correlate his "sensations" during the insertion (e.g., smoothness, resistances) almost directly with the morphologic findings, without having to wait a long time while the temporal bone specimens are being processed conventionally. Furthermore, this method avoids artifacts due to soft tissue shrinking during drying. In further steps of development, the grinding device will be optimized for standard use.