Bone conduction evaluation methods involve using specialized equipment, including an oscillator to produce vibrations at predetermined frequencies and amplitudes. Modern bone conduction evaluation is frequently performed as a component of audiometry testing, especially when it is clinically useful to distinguish between sensorineural and conductive hearing loss. Early methods involved tuning forks and including the Weber and Rinne tests, which are still used today. Methods for testing BC have existed since the 19th century.
Ultimately, both AC and bone conduction cause a vibration of the cochlea's basilar membrane, a structure attached medially to the osseous spiral lamina, resulting in stimulation of the cochlear nerve. Multiple mechanisms are involved in bone conduction sound transmission, including the inertial force affecting cochlear fluids and middle ear ossicles, pressure changes in the ear canal, and pressure changes transmitted through a third window of the cochlea (which is a pathologic, abnormal structure).
Bone conduction is in contrast to the route of sound transmission known as air conduction (AC), in which sound is transmitted in the air through the ear canal to the ossicles of the middle ear (malleus, incus, stapes) via the tympanic membrane, thus stimulating the sensorineural organs of the inner ear. Bone conduction (BC) refers to the phenomenon in which vibrations are transmitted through the bones of the skull to the cochlea and the associated sensorineural structures resulting in the perception of sound.
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