Otosclerosis is a bone disease affecting the ear. With normal hearing, sound is transmitted to the tympanic membrane or eardrum. The eardrum vibrates, as do the three bones of hearing, the malleus, incus and stapes. These three bones are suspended in the middle ear and are connected like a chain to the vibrating tympanic membrane. At the other end of the chain, the vibrations are transmitted to the inner ear by the last vibrating bone, the stapes. The inner ear or cochlea has nerve endings that transmit the sound to the brain. Abnormal bone deposition by otosclerosis near the stapes bone keeps it from vibrating and therefore a hearing loss occurs.