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

Abstract

Objectives: The active middle ear implant, Vibrant Soundbridge (VSB), can be implanted with a variety of couplers. Hearing outcome after implantation has been investigated in both temporal bone (TB) experiments and patient studies, but the relationship between experimental and clinical data is still weak in the literature. Therefore, experimental data from TB experiments should be compared with patient data in a retrospective study, in which the floating mass transducer is used with couplers of the third generation. Actuator coupling structures included the long (LP coupler) and short (SP coupler) incus process, the stapes head (Clip coupler), and the round window membrane (RW soft coupler). Methods: In the TB experiments, the sound transmission after vibroplasty on the above-mentioned actuator coupling structures was determined in 32 specimens by means of laser Doppler vibrometry on the stapes footplate. Data of 69 patients were analyzed. The main target audiometric parameters were the postoperative aided word recognition score (WRS) in the free field at 65 dB SPL (WRS 65 dB in %), the preoperative and postoperative pure-tone average (PTA4, including the frequencies 0.5, 1, 2, and 4 kHz) of the bone conduction hearing threshold (PTA4BC), the aided postoperative air conduction hearing threshold in the free field (PTA4FF) and the direct threshold (Vibrogram) at least 6 months postoperatively. The coupling efficiency of the actuator (Vibrogram—PTA4BC) as well as the effective hearing gain (PTA4FF—PTA4BC) was compared between the couplers. Results: The analysis in the main speech range (0.5–4 kHz) indicated that in the TB experiments, the LP coupler tends to have the best coupling quality at low frequencies (500–1000 Hz). This was up to 15 dB above the worst actuator (RW soft coupler). However, the results missed the significance level (p > 0.05). In the high frequencies (2000–4000 Hz), the Clip coupler showed the best coupling quality. This was 15 dB above the worst actuator (SP coupler). However, the results missed the significance level (p > 0.05), too. The postoperative WRS at 65 dB SPL and the postoperative PTA4FF were independent of the actuator coupling structure. The PTA4BC was stable at 6 months postoperatively. For the PTA4 of the coupling efficiency, there were no significant differences between the actuator coupling structures (LP 8.9 dB ± 12.9; SP 9.5 ± 6.5 dB; Clip 5.2 ± 10.5 dB; RW 12.7 ± 11.0 dB). However, the tendential inferiority of the RW soft coupler with regard to transmission in the low-frequency range and the tendential superiority of the Clip coupler in the high-frequency range that have already been displayed experimentally could be confirmed in the clinical results. However, the clinical results missed the significance level, too (p > 0.05). Conclusions: In vivo, there are no significant differences in the postoperative outcome stratified according to coupling the target structure. The differences known from the experimental setting were repressed by individual biasing factors. Howe...

The influence of intraoperative auditory brainstem responses on vibroplasty coupling-quality and analysis of the impact of different fixation steps on the coupling

“…Sufficient transfer of the FMT’s energy to the inner ear is a crucial factor for proper function and is referred to as “coupling-quality” [ 11 ]. While various, mainly retrospective studies that intraoperatively measure coupling-quality have been published [ 12 – 17 ], studies exploring the influence of different methods of FMT fixation are sparse and only available from retrospective temporal bone experiments [ 18 ].…”

“…Although no mean postoperative coupling-quality was provided, similar observations were reported by Fröhlich and colleagues, with narrow distribution of postoperative coupling- qualities between 0 and 15 dB for 18 or 23 patients in Bland–Altman plots [ 12 ]. In addition, Müller and co-authors observed stable coupling-qualities of 12.7 dB-HL approximately 6 months after RW-Vibroplasty without intraoperative ABR measurements [ 18 ]. A loss of approximately 12 dB-HL in Vibroplasty without intraoperative ABR measurement as observed in our study control group correlates with the literature.…”

“…In contrast to the number of available studies that assess coupling-quality via intraoperative measurements, studies that explore different methods of fixation of the FMT during Vibroplasty are sparse and only available from retrospective temporal bone experiments: Müller and co-authors retrospectively compared the transmission behavior of various FMT couplers in 32 specimens using laser Doppler vibrometry [ 18 ]. The authors observed a tendency towards better coupling-quality with LP couplers at low frequencies (500–1000 Hz) and Clip couplers at high frequencies (2000–4000 Hz).…”

“…However, both observations missed the significance level (both p > 0.05). The authors concluded that the differences in this experimental setting were minimized by individual biasing factors [ 18 ].…”