COCHLEAR WALL TITANIUM IMPLANTS FOR AUDITORY-NERVE STIMULATION

Genetically deaf dalmatian dogs and ototoxically deafened macaque monk eys were implanted with electrodes housed in cochlear wall titanium im plants to assess long-term stability, tolerance, and performance. Shor t-term human implantation, followed by trials of stimulation, was perf ormed in 4 unilaterally deaf patients. In the dog experiments, cochlea r wall electrode stimulation produced consistent electrophysiologic th resholds that were higher, by approximately 6 dB, than those obtained with bipolar scala tympani stimulation. Clinical testing revealed elec trically evoked middle latency response, auditory brain stem response, and/or behavioral detection responses in 3 of 4 patients, at levels b elow those for facial nerve activation and pain sensation. Electrode p lace discrimination studies, with controls for loudness cues, revealed near-perfect discrimination in a monkey subject. Eleven of the 12 ani mal implants were found to be rigidly fixed in the cochlear bone, with direct contact between bone and implant over 8% to 23% of the implant surface for the 6 implants examined in detail. These results suggest that long-term fixation of titanium cochlear wall implants occurs by v irtue of intimate implant-bone contact in restricted areas. This appro ach to prosthetic stimulation demonstrates encouraging performance cha racteristics in achieving auditory activation.