Reference threshold measures for a non-surgical skin-drive bone conduction hearing device

Objectives Skin-drive bone conduction devices (BCDs) are indicated for individuals with conductive or mixed hearing loss. For individuals who are not surgical candidates (i.e., young children), non-surgical skin-drive systems are available. Prescriptive targets for abutment-worn, percutaneous systems are established; however, device-specific reference equivalent threshold force levels (RETFLs) are not available for some contemporary skin-drive systems. Equivalent threshold force levels (ETFLs) may serve as preliminary reference data to support prescriptive development. Because standardized RETFLs require multi-site validation and are not yet available for these coupling conditions, the values derived in the present study are referred to as ETFLs. This terminology is used to distinguish these preliminary, single-site estimates from formally established RETFLs used for clinical calibration. This study derived ETFL values for the MED-EL ADHEAR when coupled via a soft headband and adhesive adapter. Methods Thirty-six normal-hearing adults (18–25 years) underwent audiometric testing with a B-71 bone oscillator and in-situ threshold measurement using ADHEAR in the two coupling conditions. Force level output was measured on a skull simulator using the Audioscan ® Verifit 2. Dial force levels (DFLs) and ETFLs were calculated across 250–8000 Hz. Results Both ADHEAR coupling conditions produced significantly higher in-situ thresholds than the B-71 ( p < 0.001). Threshold elevation was frequency-dependent, with a pronounced increase at 4,000 Hz. DFL patterns differed between the B-71 reference data (measured on the Artificial Mastoid) and ADHEAR measured on the Verifit Skull Simulator using a direct coupling adapter, particularly at higher frequencies. Derived ETFLs were higher for both ADHEAR coupling methods compared to the B-71 across most frequencies. Conclusions These findings provide preliminary, device-specific ETFL data for the ADHEAR system. While not constituting standardized RETFL values, these results may inform future multi-site validation and prescriptive fitting approaches for these non-surgical skin-drive BCDs.