Influence of the coupling on the hearing outcome after implantation of an active middle ear implant – comparison of the transmission behavior in temporal bone experiments with clinical data

Objective  

Experimental data obtained by means of human temporal bone (TB) experiments should be compared to the postoperative hearing outcome after implantation of the floating mass transducer (FMT) in a retrospective study. Actuator target structures included the long (LP coupler) and short (SP coupler) incus processes, the stapes head (Clip coupler) and the round window membrane (RW coupler).

Design  

In the TB experiments, the transmission after vibroplasty was determined in 32 specimens by means of laser Doppler vibrometry on the stapes footplate. Audiometric target parameters of 69 patients were analyzed.

Results  

The postoperative aided speech understanding in the free field (WRS) at 65 dB SPL and the postoperative bone conduction hearing threshold (PTA4BC) were independent of the actuator target structure. The postoperative coupling efficiency (Vibrogram – PTA4BC) showed to be dependent on the actuator target structure. Over the frequencies of the main speech range, the SP coupler had the best coupling quality at 500 to 1000 Hz. This was 15 dB above the worst actuator (RW soft-coupler). The inferiority of the RW coupler with regard to transmission in the low-frequency range was also confirmed experimentally. At 2000 to 4000 Hz, the Clip coupler showed the best coupling quality. This was 15 dB above the worst actuator (SP coupler). The superiority of the clip coupler in the high-frequency range was also confirmed experimentally.

Conclusions 

In vivo, the postoperative aided WRS at 65 dB SPL is independent of the actuator target structure. However, the coupling quality is dependent on the actuator target structure. The TB experiments support these clinical data

Publication History

Article published online:
24 May 2022