Bone Conduction Threshold Measurements in Patients with Bone Conduction Devices: A Comparison of Available Methods.

Background: The semi-implantable bone conduction devices connect the skull to the hearing device by means of an implant. This implant affords us 3 possible methods for conducting bone conduction evaluation, which may produce a different result for the same patient, and comparisons of results from different centers may therefore be interpreted incorrectly. Thus, the authors attempt to quantify the audiometric differences between the obtained auditory results and to check whether the results of standard pure tone audiometry could be replaced with the results obtained by alternative measurement methods.

Methods: Measurements were conducted in a group of 53 adult patients implanted with bone conduction devices in 3 modes: bone conduction-direct, when the bone conduction device itself is used to assess the audiometric threshold; bone conduction-pure tone audiometry with audiometric oscillator placed over mastoid aside of an implant; and bone conduction-indirect with oscillator placed on an implant.

Results: The analysis revealed differences between obtained results, which can reach up to 21.48 dB with a mean of 10 dB across all frequencies. The lowest values, regardless of the type of implant connection ("magnetic"; "snap"), were recorded for bone conduction-indirect mode whereas the highest mean all-frequency thresholds were recorded in the mode defined as bone conduction-direct.

Conclusion: The method that provides the most comparable thresholds is when the oscillator is positioned on the mastoid, aside from an implant. It should be the method of choice for any hearing evaluation in patients fitted with bone conduction devices, because of standardized equipment and the availability of preoperative data obtained with the same method.