The incus transmits vibrations from the malleus to the stapes.
The vibrations then move to theinner ear.
Conditions involving the incus affect hearing and often affect the other two ossicle bones.
Anatomy
The incus sits between the other two bones, known asossicles, of the middle ear.
Themalleus(hammer) is the outermost bone and thestapes(stirrup) is the innermost.
Incus is Latin for “anvil, which is why it is sometimes referred to as such.
It gets its name from the shape of the bone.
The ossicles are held in place in the middle ear by ligaments.
The incus consists of four parts: the body, short limb, long limb, and lenticular process.
Joints connect the three bones.
The body of the incus is connected to the malleus and the lenticular process connects to the stapes.
Anatomic Variations
Defects of the ossicles can include hypoplasia (under-development) and displacement.
A birth defect calledcongenital aural atresiahappens when the external auditory canal doesn’t fully develop.
This condition may be associated with other congenital anomalies.
Function
Hearing is the primaryrole of the ossiclebones.
The ossicles also work to protect the ear from loud sounds.
Associated Conditions
Due to its role in transmitting sound, conditions of the incus often affect hearing.
In fact, conditions of the incus are rarely isolated and most often involve all three bones.
The condition is marked by bones that become stuck together, which limits their movement and impairs hearing.
Symptoms include:
Diagnosis usually involves audiography andtympanometry, which help to determine hearing sensitivity.
To determine the extent of hearing loss, tympanometry and audiography may also be used.
Cholesteatoma is diagnosed by using an otoscope to examine inside the ear.
You may also have a CT scan to confirm the diagnosis.
Congenital aural atresia
Congenital aural atresia is one of the more challenging conditions to treat.
Non-surgical treatment includes bone conductionhearing aids, which transmit sound vibrations through bones in the head.
These devices should be placed as early as possible to be most effective.
Otosclerosis treatment options can be supportive (treating symptoms) or curative.
Hearing aids and sodium flouride supplements are examples of supportive treatments.
Curative treatments involve surgical restoration.
Ossicular chain dislocation
Ossicular chain dislocation most often requires a kind of surgery calledossiculoplasty.
During the surgery, the ossicular chain is reconstructed to improve hearing.
Surgical removal of abnormal skin growth is usually necessary for cholesteatoma.
Related conditions usually involve all three bones and affect hearing.
Treatment will depend on the condition and may involve surgery and/or supportive treatments such as hearing aids or supplements.
National Institute on Deafness and Other Communication Disorders.Otosclerosis.
Stanford Medicine.Ossicular chain dislocation.
Keck Medicine of USC.Ossicular chain dislocation.
Lee MY, Cho YS, Han GC, Oh JH.Current treatments for congenital aural atresia.J Audiol Otol.
2020;24(4):161-166. doi:10.7874/jao.2020.00325
American Hearing Research Foundation.Otosclerosis.
