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Otosclerosis is a condition in which the bones in the middle ear become fixed and immobile, leading to hearing loss (usually one-sided).

Overview of Otosclerosis

In otosclerosis, the stapes, the bone near the junction into the inner ear, is affected. The stapes becomes more fixed with time, thereby impeding transmission of vibrations to the inner ear. In the beginning stages of the disease, sounds are dampened; however, clarity is preserved. With progression of the disease, the cochlea can be affected and clarity can decline. This is called cochlear otosclerosis.

The temporal bone anatomy is shown, including the ear canal, ear drum, middle ear, and inner ear.

A brief review of the anatomy of the middle ear allows a better understanding of how this disorder can cause hearing loss. Sound entering the ear canal causes vibrations of the tympanic membrane (eardrum). The eardrum is attached to one of three ossicles (bones) found in the middle ear called the malleus. Vibrations of the malleus bone are transmitted to another ossicle, the incus, which in turn transmits the vibrations to the smallest of the three ossicles, the stapes. Vibrations of the stapes bone are transmitted to the inner ear. The inner ear is made of a bony labyrinth filled with fluid and membranes. As the stapes vibrates, the fluid in the inner ear is set into motion. The cilia on the ends of hair cells within the inner ear are bent and an electrical signal is generated, which travels along the cochlear (hearing) nerve and then onto the brain. The inner ear is composed of the cochlea, which is responsible for hearing, and the semicircular canals, which detect angular acceleration of the head. This acceleration data, coupled with visual data and proprioceptive (position in space) data, determine our sense of balance.