The Floating Mass Transducer of the Vibrant Soundbridge Interposed Between the Stapes and Tympanic Membrane After Incus Necrosis

Abstract

The floating mass transducer (FMT) of the Vibrant Soundbridge (VSB) can be interposed in the middle ear in case of an absent incus. The VSB is a middle ear implant in which the FMT is attached to the long process of the incus to directly drive the ossicular chain. In this case report, there was gradual deterioration in speech perception after VSB fitting and deterioration in hearing thresholds. During exploratory resurgery, it became clear that the ossicular chain was interrupted due to necrosis of the long process of the incus. The VSB could no longer function because there was no connection between the incus and stapes. Reconnection of the FMT to the anterior crus of the stapes on 1 side and the tympanic membrane on the other side. Reconnection of the FMT to the stapes head led to obvious improvement in audiometric results. The air-bone gap was reduced from approximately 35 to approximately 25 dB, which indicated that the construction with the FMT was working like a partial ossicular replacement prosthesis. At 1.5 years' follow-up, the aided hearing thresholds of approximately 45 dB hearing level were slightly poorer than those measured after the first procedure with classical positioning of the FMT. However, the speech recognition score in quiet at 65 dB sound pressure level was 70% with the classical FMT application and with the FMT connected between the stapes and tympanic membrane. It could be concluded that when the incus is absent, placement of the FMT directly on to the stapes is an acceptable solution.