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Otosclerosis is an abnormal, microscopic growth of bone in the walls of the inner ear which causes the stapes bone commonly called the "stirrup" to become frozen in place or "fixed". Normally the stapes, the smallest bone in the body, vibrates freely to allow the transmission of sound into the inner ear. When it becomes fixed to the surrounding bone, it prevents sound waves from reaching the inner ear fluids and hearing is impaired.

In a normal ear, sound (which consists of vibrations of air molecules) is funneled by the auricle, or "outer ear", through the ear canal to the eardrum. Movements of the eardrum are transferred to the ossicles, the small bones of the middle ear. The eardrum and ossicles act as an amplifier and transducer, changing sound into a mechanical energy. 

At the end of this chain, the stapes vibrates in and out of the oval window, a thin membrane between the air-filled middle ear and fluid-filled inner ear. The vibration of the stapes sets up a wave of movement of the inner ear fluids. This, in turn, stimulates the fine sense organs (the hair cells) of the inner ear, which then stimulate the auditory (hearing) nerve, which carries the sound energy to the brain. It is this sequence of events that results in normal hearing. 

How is Otosclerosis Treated?

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Photo of a size comparison of dime and ear proshesesThere are a variety of middle ear prostheses available.

No medication has proven to be effective in the treatment of otosclerosis. Although a hearing aid can be worn successfully by most patients, natural hearing is preferred. Surgery has been found to be the most effective method of improving hearing loss caused by otosclerosis. 

Surgical treatment has been available for about 45 years. The first operation for this disease was the fenestration procedure, which required mastoid surgery and an artificial opening in another part of the inner ear. The attention of the ear surgeons then became focused on the diseased stapes itself and the stapes mobilization procedure was developed. With the improvement in surgical technique, the treatment of choice then became the stapedectomy. This operation was first performed in 1956. 

The stapedectomy operation involves the removal of the diseased bone and its replacement with an artificial substitute. Local or general anesthesia is used. The surgery usually takes place entirely through the ear canal so that no outer incisions are made. 

The stapedectomy is done using an operating microscope. The surgeon will first fold forward approximately one-half of the eardrum so that he or she can reach the area where the stapes is located. The upper portion of the stapes is removed with fine instruments. There are several ways to properly manage the fixed footplate, depending upon the individual case. Most commonly, a small opening is made through the fixed plate with fine instruments, a micro drill, or laser. 

In some cases, the entire footplate may be removed. There are a variety of artificial stapes or "prostheses" that are available to replace this diseased bone. The most common prosthesis used, is a "piston" which attaches to the incus and inserts into the vestibule of the inner ear, thus bypassing the fixed stapes footplate. 

The stapes bone (stirrup) is attached to the incus bone (anvil) by thin membranes and is separated.

The stapes suprastructure is then "down-fractured" leaving the footplate still frozen within the oval window.

A laser and drill are used to make a small hole in the footplate.

A prosthesis is placed over the incus and into the hole in the footplate. The surgeon then confirms that movement of the first middle ear bone, the manubrium (hammer), is transmitted through the incus and prosthesis into the hole and inner ear. Finally, the prosthesis is tightened around the incus to prevent sliding of the prosthesis away from the incus.