Comparison of Alternative Coupling Methods of the Vibrant Soundbridge Floating Mass Transducer

The active middle ear implant Vibrant Soundbridge© provides a variety of coupling modalities of the floating mass transducer (FMT) to various structures of the ossicular chain and the round window. A retrospective analysis was performed on 125 subjects (n = 137 ears) (1) to compare the efficacy of the different FMT coupling modalities with increasing degree of hearing loss, (2) to compare the performance in speech outcome and the effective gain between the coupling types, and (3) to evaluate the risk of additional hearing loss of each coupling procedure. The patients were grouped according to their type of FMT coupling into incus vibroplasty (incus group, n = 59), round window vibroplasty with coupler (RWC group, n = 23), round window vibroplasty without coupler (RW group, n = 22), and oval window vibroplasty with coupler (OWC group, n = 33). For each coupling group, pre- and postoperative thresholds, the results of the Freiburg monosyllable test at 65 dB SPL, and the effective gain across frequencies (0.5-6 kHz) were evaluated. A logistic regression function was used to describe the relationship between word recognition scores (WRS, in % correct) and the mean bone conduction (BC) hearing loss. The surgical procedure had no clinically relevant effect on BC thresholds of patients in each coupling group. The BC pure tone average (PTA4) for 50% WRS predicted by the model function was similar for the incus (48.2 dB nHL), RW (47.8 dB nHL), and OWC (49.0 dB nHL) groups, but higher for the RWC group (67.9 dB nHL). However, the median WRS was 80% or better with no significant differences in speech perception between coupling types (Kruskal-Wallis test, p = 0.229). The effective gain shows an advantage for the incus coupling between 0.5 and 2 kHz over the other coupling types. The performance of the FMT coupling modalities is equally good for patients with a mild-to-moderate hearing loss, but the efficacy of coupling types differs for patients with greater hearing loss (>48 dB BC HL).