Ossicles / Ossicular Chain
The ossicles are the three smallest bones in the human body, located in the middle ear. They form a connected chain, called the ossicular chain, that links the eardrum to the oval window of the inner ear. The three bones are the malleus (Latin for hammer), which is attached to the eardrum; the incus (anvil), which connects the malleus to the stapes; and the stapes (stirrup), the final bone whose footplate sits against the oval window and transmits vibrations into the fluid of the inner ear.
The ossicular chain acts as a mechanical amplifier and impedance-matching system, transferring vibrations efficiently from air (in the ear canal) into fluid (in the inner ear). Without the ossicles, much of the energy carried by sound waves would be reflected at the air-fluid interface and lost. The mechanical advantage provided by the lever action of the ossicles and the size difference between the eardrum and the oval window accounts for a gain of approximately 25 to 30 decibels.
Ossicular chain disruption or damage causes conductive hearing loss. Causes include middle ear infections (which can erode the ossicles), head trauma, otosclerosis (abnormal bone growth fixing the stapes), and tympanic membrane perforations that alter ossicular function. Surgical reconstruction of the ossicular chain (ossiculoplasty) can restore some or all of the conductive hearing loss in appropriate cases.
