Chapter 10 — Bone-conduction devices

BAHA, transcutaneous and percutaneous, skull-vibration modes.

A bone-conduction device (BCD) is a small electromechanical transducer that turns acoustic input into mechanical vibration of the skull. The skull conducts the vibration to both cochleae — which, if functioning, respond just as they do to conventional air-conducted sound. The BCD bypasses the outer ear and the middle ear entirely. For patients in whom the conductive apparatus is non-functional (malformed, scarred, infected, surgically absent) but the cochlea is healthy, the BCD provides a route to hearing that no air-conduction hearing aid can match.

This is the book’s shortest chapter — bone-conduction devices serve a small but clinically important population, and the relevant physics is straightforward once the bone-conduction route is understood. Three lessons:

• 10.1 Skull vibration and the bone-conduction route — how the skull transmits a vibration, the inertial / compression / osseo-tympanic modes, and the negligible interaural attenuation.
• 10.2 Device classes: BAHA, Attract, Osia, Bonebridge — percutaneous abutment vs passive transcutaneous vs active transcutaneous, and the tradeoffs.
• 10.3 Candidacy, outcomes, and closing the book — the four classical BCD candidacy populations, expected outcomes, and a closing reflection on the book.