Stimulation efficiency of an actuator driven piston at the biological interface to the inner ear

Direct acoustic cochlear stimulation uses piston motion to substitute for stapes footplate (SFP) motion. The ratio of piston to stapes footplate motion amplitude, to generate the same loudness percept, is an indicator of stimulation efficiency. We determined the relationship between piston displacement to perceived loudness, the achieved maximum power output and investigated stapes fixation and obliteration as confounding factors. The electro-mechanical transfer function of the actuator was determined preoperatively on the bench and intraoperatively by laser Doppler vibrometry. Clinically, perceived loudness as a function of actuator input voltage was calculated from bone conduction thresholds and direct thresholds via the implant. The displacement of a 0.4 mm diameter piston required for a perception equivalent to 94 dB SPL at the tympanic membrane compared to normal SFP piston displacement was 27.6–35.9 dB larger, consistent with the hypothesis that the ratio between areas is responsible for stimulation efficiency. Actuator output was 110 ± 10 eq dB SPLFF @1Vrms ≤ 3 kHz and decreased to 100 eq dB SPLFF at 10 kHz. Output was significantly higher for mobile SFPs but independent from obliteration. Our findings from clinical data strongly support the assumption of a geometrical dependency on piston diameter at the biological interface to the cochlea.

Systematic Review and Meta-analysis of Endoscopic vs Microscopic Stapes Surgery for Stapes Fixation

Objective To systematically review the current literature regarding the operative outcomes of stapes surgery for stapes fixation via the endoscopic and microscopic approaches. Data Sources PubMed, Embase, and Web of Science. Review Methods An electronic search was conducted with the keywords “endoscop* or microscop*” and “stapes surgery or stapedectomy or stapedotomy or otosclerosis or stapes fixation.” Studies were included if they compared endoscopy with microscopy for stapes surgery performed for stapes fixation and evaluated hearing outcomes and postoperative complications. Articles focusing on stapes surgery other than for stapes fixation were excluded. Results The database search yielded 1317 studies; 12 remained after dual-investigator screening for quantitative analysis. The mean MINORS score was 18 of 24, indicating a low risk of bias. A meta-analysis demonstrated no statistically significant difference between the groups with regard to operative time, chorda tympani nerve manipulation or sacrifice, or postoperative vertigo. There was a 2.6-dB mean improvement in the change in air-bone gap in favor of endoscopic stapes surgery and a 15.2% increased incidence in postoperative dysgeusia in the microscopic group, but the studies are heterogeneous. Conclusions Endoscopic stapes surgery appears to be a reasonable alternative to microscopic stapes surgery, with similar operative times, complications, and hearing outcomes. Superior visibility with the endoscope was consistently reported in all the studies. Future studies should have standardized methods of reporting visibility, hearing outcomes, and postoperative complications to truly establish if endoscopic stapes surgery is equivalent or superior to microscopic stapes surgery.