Ossicles

What are ossicles?

Your ossicles — the malleus, incus and stapes — are three tiny bones in your middle ear. They move sound vibrations from your eardrum to your cochlea, which is part of your inner ear. There, the vibrations convert into electrical signals that reach your brain so you can hear.

Your ossicles are the smallest bones in your entire body, but they have a big job. They’re essential to your hearing. Issues with your ossicles can lead to hearing loss.

What is the function of the ossicles?

Your ossicles interact to push sound vibrations from your eardrum (tympanic membrane) to your cochlea. They amplify (boost) the sound signal along the way. This means that the vibrations that reach your cochlea are bigger than when they leave your eardrum.

To understand how your ossicles work, think of them by their collective name: the ossicular chain. Each bone is an individual link in a chain reaction, where one movement leads to the next. Here’s how your ossicles help you hear:

1. Sound waves enter your ear and strike your eardrum, causing it to vibrate.
2. The vibrations pass from your eardrum to the malleus.
3. The malleus transmits the vibrations to the incus.
4. The incus sends the vibrations to the stapes.
5. The stapes sends the vibrations to the entrance of your cochlea, known as the oval window.

The vibrations inside your cochlea cause the fluid inside to displace sensory hair cells. The hair cells release electrical signals that your brain understands as sound.

Where are the ossicles located?

Your ossicles form an interconnected chain inside your middle ear. They’re in between your eardrum and the most important auditory (hearing) structure within your inner ear, your cochlea.

• The first auditory ossicle is the malleus (hammer).
• The second is the incus (anvil).
• The third is the stapes (stirrup).

Malleus

The malleus is also called the hammer because of its shape. Key parts include the head, the neck, the anterior and lateral processes, and the handle. The handle attaches to your eardrum. The handle moves the entire malleus when your eardrum vibrates.

The head of the malleus attaches to the incus via the incudomalleolar joint.

Incus

The incus is also called the anvil because the malleus (hammer) strikes it with sound vibrations. The parts of the incus include the body, which comes into direct contact with the vibrating malleus. The incus also has a short limb and a long limb.

The long limb of the incus attaches to the stapes via the incudostapedial joint.

Stapes

The stapes resembles a stirrup and sometimes goes by that name. It’s the smallest bone in the human body, measuring only a few millimeters in both width and height. It has a head, neck and two limbs attached to a base, or footplate. The head of the stapes is attached to the long limb of the incus. The footplate transmits sound vibrations to the oval window of your cochlea.

What are some of the common conditions and disorders that affect the ossicles?

Problems with your ossicles can lead to conductive hearing loss. This happens when sound vibrations can’t reach your inner ear. Related conditions that impact your ossicles (and can lead to hearing loss) include:

• Being born with abnormal ossicles. Rarely, babies are born with an absent, underdeveloped or overdeveloped ossicle. Sometimes, the bones are too far apart or stuck together.
• Otosclerosis. An ossicle (usually the stapes) fuses with surrounding tissue and can’t move freely.
• Cholesteatoma. With this condition, skin cells build up in your middle ear. They can damage your ossicles and prevent them from moving as they should to transmit vibrations.
• Chronic middle ear infections. Long-term infections can cause inflammation and fluid buildup that limits ossicle movement. Infections can lead to permanent damage without treatment.
• Ossicular-chain dislocation. Head injuries can move your ossicles out of position, so they can’t transmit vibrations. Abnormal growths and chronic ear infections can also break the ossicular chain.

What are common symptoms of a condition impacting the ossicles?

Symptoms include:

• Muffled hearing or no hearing in one or both ears
• Ringing in your ears
• Ear pain
• Pus-like ear drainage
• A feeling of pressure or fullness in one or both ears
• Balance issues (if the condition also impacts the vestibular system in your inner ear)

What are common tests to check the ossicles?

Your healthcare provider may perform the following tests:

• Otoscopy,which uses a lighted instrument to see inside your ear
• Hearing tests to check for hearing loss
• Tympanometry test to check for signs of fluid buildup in your middle ear
• CT scan to check for signs of damage to your ossicles and nearby tissue

What are common treatments for conditions impacting the ossicles?

Treatments depend on the condition causing the problem. These may include:

• Antibiotics to fight bacterial infections
• Hearing aids to help you hear better
• Surgery to remove growths or repair your ossicles

How can I keep my ear ossicles healthy?

The best thing you can do for your ossicles is to take steps to prevent ear infections and seek treatment if you’re noticing changes in your hearing. Conditions that affect your ossicles are often treatable. But delaying treatment can lead to long-term damage. It’s best to see a healthcare provider as soon as possible.