The floating mass transducer on the round window versus attachment to an ossicular replacement prosthesis

The Vibrant Soundbridge floating mass transducer (FMT) is part of a commercially available implantable hearing device in which the FMT can be placed in the round window (RW) niche or attached to a partial (V-PORP) or total ossicular replacement prosthesis (V-TORP) contacting the stapes head or footplate. The goal is to provide efficient transfer of sound vibration into the cochlea. The hypothesis is that the FMT location on the prosthesis is superior to the RW location.

No direct comparisons of the 3 FMT sites have been performed using the same measurement location.

A new measurement method called the third window method was used in eleven fresh human temporal bones to compare the sites. A small hole was made into the scala tympani of the temporal bones preserving the endosteum. A reflective target was placed on the third window endosteum and displacement of the cochlear fluid was measured using a Polytec HLV-1000 laser Doppler vibrometer. The input to the FMT at all locations was a constant 316 millivolts (mV); the frequency range was 0.5 to 8.0 kHz.

The V-PORP and V-TORP FMT locations both provided statistically significant better performance above 1.0 kHz than the RW site but not below that frequency. The V-PORP and V-TORP responses were similar at all test frequencies.

In this temporal bone model, the FMT provided better higher frequency performance when attached to a PORP or TORP than in the RW niche.