Anatomy of the Malleus

Largest of Three Small Bones in the Middle Ear

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The malleus, also known as the “hammer” or “mallet,” is the largest of three small bones in the middle ear. The malleus functions with the other bones to transmit vibrations from the eardrum to the inner ear. Conditions that affect the malleus often impact the ability to hear.  

Anatomy

The malleus (“hammer”), incus (“anvil”), and stapes (“stirrup”) are the three bones, also known as ossicles, of the inner ear. The malleus is the largest and the outermost of the bones, which are part of the auditory system. Together, the three bones make up an area no larger than the seed of an orange. 

The auditory ossicles are suspended in the middle ear by ligaments. The malleus is shaped like a hammer, thus its Latin name. It sits in the middle ear between the incus and the eardrum. The parts of the malleus include the head, neck, and handle. A joint holds the head of the malleus and the incus together.

Malformations of the ossicles include hypoplasia (under-development) or displacement. Congenital aural atresia is a birth defect that results from a failure of the external auditory canal to fully develop. It may be associated with other congenital anomalies and is one of the most difficult to correct.

Function

The ossicle bones’ sensory role is hearing. The bones work together to transmit sound waves from the outer ear to the inner ear. They do this by taking the vibrational pressure from the eardrum to the malleus, then the incus, then the stapes, and finally to the cochlea.

The bones also serve a protective function. When exposed to loud noises, the muscles of the middle ear contract, reducing the ability of the eardrum to vibrate. This, in turn, reduces the movement of the malleus and the other two ossicles and limits the impact of the noise.

Associated Conditions

Due to the vital role the malleus plays in transmitting sound, conditions of the malleus often affect hearing.

Otosclerosis is a type of hearing loss resulting from abnormal bone growth in one or more of the ossicles. When this happens, the bones can become stuck together, limiting their ability to move and thereby preventing proper hearing. Hearing loss is the primary symptom of otosclerosis, which usually comes on gradually. Tinnitus and dizziness can also occur.

If your healthcare provider suspects that you have otosclerosis, they may order an audiogram and tympanogram to determine your hearing sensitivity. A computed tomography (CT scan) to view the ossicle bones may confirm the diagnosis.

Dislocation of the bone can occur following trauma. Known as ossicular chain dislocation, the condition can occur from a blow to the head, a loud blast, injury from an instrument used in the ear canal, and injury from barometric or water pressure. Symptoms of dislocation include hearing loss, facial paralysis, tinnitus, and vertigo.

Dislocation of the ossicle bones is usually diagnosed by a CT scan. Tympanometry and audiography can help determine the extent of hearing loss.

Cholesteatoma is a noncancerous abnormal skin growth in the middle ear. If it gets too large, it can damage the ossicles. Symptoms include hearing loss, ear pressure or pain, vertigo, drainage from the ear, and facial paralysis.

Diagnosis of cholesteatoma involves examining the ear with an otoscope. Your healthcare provider may also order a CT scan in order to see the situation more clearly.

Rehabilitation

Treatment for conditions affecting the malleus often, but not always, involves surgery. Treatment is provided by an otolaryngologist, a healthcare provider that specializes in conditions of the ear, nose, and throat.

Surgery to correct congenital aural atresia is one of the more challenging treatments for conditions affecting the malleus. The goal of the surgery is to restore hearing without the need for a hearing aid. The surgery usually happens when a child is 6 or 7 years old.

Bone conduction devices are a type of hearing aid that transmits sound vibrations through the bones in the head. They are a non-surgical treatment option for atresia. They can be surgically implanted or used with a magnet.

Recent technical advances have improved these devices and studies have shown them to provide good hearing outcomes. In order to be most successful, they need to be placed as early as possible.

Treatment for otosclerosis can be supportive (treating symptoms) or curative. Supportive treatments include hearing aids and vitamin and mineral supplements. Curative treatments involve surgery. Stapedectomy involves removing the damaged bone (usually the stapes) and replacing it with a synthetic implant.

Repair of ossicular chain dislocation most often involves surgery, called ossciculoplasty. The surgery involves reconstructing the ossicular chain with the goal of improving hearing. This surgery may be contraindicated if dislocation is in the person’s only hearing ear.

Cholesteatoma does not go away on its own and is treated by surgical removal. Often, prior to surgery, antibiotics and ear drops are prescribed to control infection and reduce swelling. 

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3 Sources
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