Anatomy
The stapes bone is the smallest bone in the human body. It is the innermost (most medial and nearest to the cochlea) of the ossicles inside the middle ear.
You can picture the stapes as a stirrup that’s hanging from a saddle and turned on its side horizontally. The top portion connects with the incus and the bottom portion lies against the oval window of the tympanic cavity.
On the head of the stapes are two limbs, the anterior and posterior limbs, which attach to the oval-shaped base of the incus. The head of the stapes connects with the incus via the incudostapedial joint. The stapedial membrane, a ligament-like structure aids this connection by spanning the width of the anterior and posterior limbs and base. On the medial side of the stapes, the stapedial annular ligament connects the base of the stapes to the oval window. The oval window is a thin membrane that covers the entrance to the cochlea.
The stapedius muscle is a muscle that runs from the pyramidal eminence of the mastoid bone to the neck of the stapes. When this muscle contracts in response to loud noise, it pulls the annular ligament and prevents excessive movement of the stapes bone.
Function
The stapes bone is essential to our ability to hear. Sounds vibrate the tympanic membrane (the eardrum) and travel through all three bones of the middle ear—the malleus, incus, and stapes. As the sound waves travel through the middle ear they are amplified.
The stapes, the last bone in the ossicular chain, hits the oval window, generating a wave in the fluid of the inner ear. This wave of fluid allows the initiation of a process in the inner ear that converts the sound waves into electrical signals, which can be interpreted by the brain.
Associated Conditions
Otitis Media with Effusion
Otitis media is an ear infection. When there is also fluid in the middle ear, it is defined as otitis media with effusion.
Infection and fluid in the middle ear, especially over a prolonged period, can damage the structures in the middle ear, including the ossicular chain. This can lead to temporary or permanent hearing loss.
This problem occurs more often in children than adults, but it can affect anyone. It is commonly associated with upper respiratory infections or allergies that can lead to congestion or prevent the ears from draining properly.
Sometimes this condition requires surgery to open up the auditory tube and allow the ear to drain. If damage to the ossicles occurs, it can sometimes be surgically repaired.
Otosclerosis
Otosclerosis is a condition in which abnormal bone remodeling of the ossicles causes the stapes to become fixed in place. The stapes is then unable to strike the oval window and produce the sound-producing fluid wave in the cochlea.
The cause of otosclerosis is not well understood, but it can be hereditary and most often affects middle-aged women.
Symptoms of otosclerosis include:
Hearing loss Tinnitus (ringing in the ears) Dizziness or balance issues
The hearing loss that occurs in this condition often begins in one ear and then moves to involve the other ear as well. Otosclerosis can be treated with hearing aids or a stapedectomy surgery.
Cholesteatoma
Cholesteatoma is a condition in which the skin of the eardrum grows abnormally. This can be congenital or can occur due to repeated ear infections that involve fluid in the ear. Cholesteatoma can cause the ossicles, including the stapes, to deteriorate.
Symptoms of cholesteatoma may include ear drainage, pressure in the ears, hearing loss, and tinnitus. Without treatment, cholesteatoma can lead to serious complications, including deafness, meningitis, and brain abscess.
The treatment depends on the extent of the growth and how much, if any, damage to the ear has been sustained.
Treatment
Getting treatment for chronic otitis media and otitis media with effusion in a timely and effective manner will help prevent deterioration and damage to the ossicular chain that can result in hearing loss.
Several treatments may be used:
Antibiotics if an infection is presentTreatment of underlying allergic conditions that may be contributingSurgical intervention when necessary
The surgical placement of synthetic ventilation tubes can open up the auditory tube to allow the ear to drain properly and restore normal pressure in the middle ear. This is a relatively simple procedure that is frequently done in the United States, with little risk of complications and a quick recovery time.
When damage affects the stapes bone as a result of cholesteatoma or other conditions, a surgical total or partial ossicular replacement, (TORP or PORP) can sometimes restore hearing. While the success rate of this procedure is relatively high, rare complications are possible and may lead to increased hearing problems.
Your healthcare provider will discuss the risks with you in detail before you make a decision to have ear surgery. Surgery is usually done as a same-day procedure. During the recovery time, you may experience some pain, as well as temporary vertigo, and your may stop getting worse or it may improve over time.
