BACKGROUND: Although the function of active middle ear implants in cases of intact ossicular chains and ventilated middle ears is well known, information about sound transfer function to the inner ear in cases of chronic middle ear effusion and defective middle ear structures is needed. A temporal bone model was developed to measure (1) the coupling of the active middle ear implant Vibrant Soundbridge in cases of nonventilated radical cavities, and (2) the effect of effusion and cartilage shielding.

METHODS: Three fresh human temporal bone specimens were studied. After preparation of a radical cavity, the floating mass transducer was coupled to the stapes footplate. The transducer was stimulated with 50 mV multisinus signals and inner ear fluid vibration was measured using a microphone in the round window niche. Several coupling conditions were simulated with mass and stiffness variations and cartilage shielding.

RESULTS: Coupling modality and prestress have the most influence on the sound transfer function to the inner ear. Cartilage shielding may ensure better coupling of the FMT to the footplate. The effect of middle ear effusion is negligible.

CONCLUSION: The Vibrant Soundbridge provides good sound transfer to the inner ear not only in cases of coupling onto an intact ossicular chain in a ventilated middle ear but also in cases of coupling to the stapes footplate in non-ventilated radical cavities.