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Fusion of the Ear Bones

Alternative Names: Otosclerosis, tympanosclerosis, incudomalleolar fixation, incudostapedial fixation.

Definition: Fusion or fixation of the ossicles (incus, stapes, and malleus) that help transmit sound from the eardrum to the inner ear.

What Is Going on in My Body? The ear consists of essentially two different components. The first component is the external ear, formed by the pinna and ear canal, which help to transmit sound down to the eardrum and the bones for hearing. Sound then vibrates the tympanic membrane and the malleus that is attached to it. The malleus and incus are joined by a joint similar to the joints in the finger. Therefore, the vibration of the malleus is transmitted to the incus. The incus has a joint to the stapes. Vibration of the incus is then transmitted to the stapes, which then creates fluid waves within the second compartment of the inner ear. The fluid waves in the inner ear are then transformed into nerve signals, which are transmitted by the nerve for hearing into the brain stem for central interpretation of sound. Because of the size difference between the eardrum and the small window in which the stapes sits along with the bones for hearing, the middle ear provides approximately 25 decibel amplification of sound.

Otosclerosis is one way in which fusion of the ear bones can occur. Otosclerosis is seen in approximately 3% of the population, but not all individuals affected have it impair their hearing. When otosclerosis occurs around the window in which the stapes sits, then that new bone formation can bind the stapes to prevent its vibration. If it is fixed, sound cannot be transmitted from the stapes into the inner ear, with resultant conductive hearing loss. Tympanosclerosis is an abnormal calcified scarring that occurs in the middle ear mucous membranes, or eardrum. If this abnormal scarring occurs where the ear bones are joined to each other, then that can impair their vibration, with conductive hearing loss. There are also rare instances of congenital abnormal bone formation such that there may be absent joint development between the incus and malleus or between the incus and stapes. Once again, transmission of vibration through the ossicles is impaired, resulting in conductive hearing loss.

What Are the Signs and Symptoms? If the problem is congenital, then the hearing loss may not be picked up until a school screening test is performed or if the parents notice that the child’s hearing is not what they think it should be. Fortunately infant screening tests can identify the hearing loss early so that appropriate intervention can occur. Often children who have congenital fixation of the middle ear structures also have abnormal formation of the external ear. For an individual in whom the fixation occurs by otosclerosis or tympanosclerosis, they may notice a progressive worsening of hearing. On physical examination there may be a completely normal examination in the case of otosclerosis, although at times there may be a red blush behind the eardrum next to the stapes (Schwartze’s sign). In the patient who has ossicular fusion occurring by infection, there is often a history of chronic or recurrent acute infectious ear disease. Therefore, there may be thickening and calcification of the eardrum. There are usually very few, if any, ear complaints, such as dizziness, tinnitus, pain, or drainage.

What Are the Causes and Risks? In the case of congenital ossicular fusion, it may be part of another congenital genetic syndrome. As mentioned above, chronic infectious ear disease can create tympanosclerotic fixation of the bones for hearing. Otosclerosis has a fairly significant family history, and absence of fluoride supplementation may actually be a causative factor.
 
How to Prevent the Disease: There is no means to prevent the congenital or otosclerotic fusion of the bones for hearing. Preventing tympanosclerosis involves aggressive management of ear infections.

How Is It Diagnosed? A hearing test will often show a conductive hearing loss. Ultimately it is not until the middle ear is explored surgically that the exact cause is identified.

What Are the Long-Term Effects? The long-term effects would be a conductive hearing loss. In some forms of chronic ear disease or otosclerosis there may be a non-preventable effect upon nerve function of the inner ear. Certainly in the child who has a conductive hearing loss that is not remedied, there will be some effects upon speech and language skill acquisition and even some concern about ultimate IQ levels and learning abilities.

Am I Putting Others at Risk? No.

What Are the Treatments? The individual who has only one ear affected by conductive hearing loss may elect to forego any form of treatment. However, for those individuals or parents desiring correction, hearing aids or surgical bypass of the fused bones are the main forms of treatment.

What Are the Side Effects to the Treatments? There are no side effects to wearing hearing aids except for irritation to the outer ear structures. The side effects of surgery have to do with structures in the middle ear. Side effects of middle ear surgery include taste disturbance, deafness, vertigo, facial paralysis, or failure to be able to bypass the fused bones. If artificial means are used to reconstruct the hearing mechanism, then these devices can either slip out of position or break and thus cause hearing loss.

What Happens After Treatment? Middle ear reconstruction is often very successful in reversing the conductive hearing loss in otosclerosis and congenital ossicle fusion. Surgery is less successful for tympanosclerotic fixation of the ossicles.

How Do I Monitor the Disease? Most causes of ossicle fixation cause a hearing loss that does not progress. Other than repeat hearing tests during the evolution of the process, there is no significant methods of monitoring this disease.