COCHLEAR IMPLANT DEEP ELECTRODE INSERTION - EXTENT OF INSERTIONAL TRAUMA

We have recently undertaken deep insertions of the Combi-40 cochlear i mplant electrode (Med-Er Corp., Innsbruck, Austria) into apical region s of the scala tympani using a cochleostomy approach. In order to exam ine the extent of the insertional trauma, 12 fresh human temporal bone s were implanted with original Combi-40 electrodes. The specimens were histologically processed with the implants in place by employing a sa wing and grinding technique. In most cases, only very discrete distort ions of the epithelium of the spiral ligament occurred within the midd le cochlear turns. Furthermore, a slight displacement of the basilar m embrane caused by the electrode was occasionally seen. However, in 2 c ases more severe damage such as basilar membrane rupture and electrode displacement was found. Attempts to insert the electrode beyond the p oint of first resistance resulted in electrode kinking within the basa l cochlear turn with subsequent fracture of the osseous spiral lamina. According to our results, deep electrode insertions do not aggravate the insertional trauma provided no force is applied when resistance is felt.