Bone Conduction Thresholds

Bone conduction thresholds are hearing thresholds measured by applying a small vibrating device directly to the skull, typically placed on the mastoid bone behind the ear or on the forehead. This method bypasses the outer ear canal and middle ear entirely, transmitting sound vibrations through the skull bones directly to the cochlea. Bone conduction thresholds therefore reflect the function of the inner ear independently of any outer or middle ear pathology.

In a standard audiological assessment, both air conduction thresholds (measured through headphones) and bone conduction thresholds are recorded and compared. When air conduction and bone conduction thresholds are close (within 10 dB), this indicates that the outer and middle ear are transmitting sound normally and any hearing loss present is sensorineural in origin. When air conduction thresholds are significantly poorer than bone conduction thresholds, the gap between them (called an air-bone gap) indicates a conductive component, meaning the outer or middle ear is not transmitting sound efficiently.

Bone conduction testing is essential for determining the type of hearing loss (conductive, sensorineural, or mixed) and directly influences treatment planning. A large air-bone gap, for example, may prompt medical referral to investigate a surgically correctable middle ear condition.