Vibrant Soundbridge Round Window Vibroplasty: Safety, Coupling Efficiency and Speech Outcome of the Most Common Coupling Modalities.

Abstract

Introduction The Floating Mass Transducer (FMT) of the Vibrant Soundbridge (VSB) is successfully used for reverse stimulation of the round window membrane (RWM) since 2005, enabling the treatment of conductive and mixed hearing loss. The FMT can be placed directly to the RWM, or indirectly by using an interposed material such as fascia and Tutopatch, or a coupler, e.g. the Round Window Coupler (RWC), the Round Window Soft Coupler (RWS), or the custom-made Hannover Coupler (HCV2). The aim of the study was to retrospectively evaluate the long-term outcome of the most common VSB RW coupling modalities in our clinic with regards to (1) safety and preservation of residual hearing, (2) coupling efficiency and (3) speech outcome. Methods A total of 111 Round Window (RW) vibroplasties, a surgical procedure including the implantation of the VSB, in 102 ears (95 patients) performed at the Hannover Medical School between 2006 and 2021 were analyzed. Seventy-nine RW vibroplasties in ears with available preoperative BC PTA4 were included in the safety analysis, focusing on adverse events (AE). Furthermore, the audiological outcomes were evaluated in 56 ears (52 patients, 4 bilateral implanted) preoperatively, at initial activation (6-8 weeks), 2 years (2Y) and 5 years (5Y), including bone conduction pure tone average (BC; PTA4 at 0.5, 1, 2, 4 kHz), coupling efficiency (Ceff, in situ measurement - BC PTA4), effective gain (EG, BC PTA4 - sound field threshold) and monosyllable word recognition score (WRS; Freiburg monosyllable test at 65 dB SPL). Results The safety analysis showed a total mean AE rate of 29.1%. A statistically significant decline over time in BC PTA4 was found in groups RWS and HCV2 by 7.6 dB and 8.8 dB (paired t-test, p=0.022 and p≤0.001, respectively), at 2Y. The WRS improved over time in all groups, resulting in an overall mean score of 81.1% in the range 70.0% to 90.8% at 2Y, with a statistically significant improvement between IA and 2Y and the best mean WRS of 90.8% at 2Y in group HCV2 (paired t-test, p≤0.001). While the Ceff was stable and below 25 dB at all time points in most groups, it improved statistically significant in group RWC by a total of 9.9 dB between IA and 5Y to 16.8 dB (paired t-test, p≤0.001). Conclusion The RW vibroplasty is a safe surgery, though complex and challenging. All investigated coupling modalities provided effective treatment for conductive and mixed hearing loss. Patients in group RWC and HCV2 tended to perform noticeably better in terms of aided speech understanding and coupling efficiency than those in the other groups.