Improvement of the coupling quality of active middle ear implants with intraoperative auditory brainstem responses

Active middle ear implants are currently considered as treatment alternative to hearing aids in moderate to profound hearing loss. Sufficient transfer of the active middle ear implant energy to the inner ear is a crucial factor measured by the coupling quality (CQ). This study prospectively explores these influences comparing patients without intraoperative ABR. The influence of- a) intraoperative ABR, b) various fixation methods and c) safety is explored. Study patients (+ABR) were prospectively included and compared to a retrospectively generated group undergoing vibroplasty without intraoperative ABR (-ABR) by the same surgeon. Propensity-score-matching was performed based on preoperative bone-conduction-pure-tone-average-3 (BC-PTA3) at 1-, 2- and 4 kHz. Primary outcome parameters were: 1) postoperative CQ-PTA3, 2) intraoperative ABR threshold for the various fixation methods and c) postoperative BC-PTA3. A total of 28 patients (14 were+ABR and 14 –ABR) were included. Preoperative BC-PTA3, sex, age and number of previous surgeries did not differ. Mean postoperative CQ-PTA3 was significantly better for+ABR than for –ABR (1.79 vs. 12.26 dB HL; p=0.006). Mean intraoperative ABR threshold was superior for cartilage counter bearing and cartilage housing, compared to the fluid phase fixation (53 vs. 56 & 57 dB HL; p=0.039). Mean postoperative BC-PTA3 did not significantly differ between patients (41.43 vs. 41.79 dB HL; p=0.765). Intraoperative re-adjustment of the FMT based on unsatisfactory intraoperative ABR threshold was required in 7%. Intraoperative ABR measurement resulted in significantly better postoperative CQ. In 7% of the patients revision-vibroplasty was spared due to intraoperative ABR measurement.