Bone Conduction Hearing Loss
Hearing loss is a partial or total inability to hear. It can occur in one or both ears and can be present at birth or acquired later on in life. Hearing loss can be temporary or permanent.
There are three major types of hearing loss: sensorineural hearing loss, conductive hearing loss, and mixed hearing loss.
Sensorineural hearing loss is hearing loss caused by damage to the inner ear structures and the auditory nerve. It is the most common type of hearing loss in adults. Sensorineural hearing loss is caused by aging, exposure to loud noise, autoimmune inner ear disease, Meniere's Disease, etc.
Conductive hearing loss is hearing loss caused by damage to the outer ear or the middle ear.
This damage to the outer or middle ear prevents sound waves from passing through to the inner ear. In this case, the inner ear is appropriately functioning, but no sound gets to it.
Conductive hearing loss is caused by factors such as ear infections, eustachian tube dysfunction, ruptured eardrums, microtia, etc.
Mixed hearing loss is hearing loss caused by damage to the inner ear and the middle or outer ear. This is a combination of both sensorineural hearing loss and conductive hearing loss.
In this post, we will be examining bone conduction. This procedure is associated with conductive hearing loss. Let's get started.
Bone conduction is the conduction of sound to the inner ear through the bones of the skull. Bone conduction transmission is standard for people with normal hearing, but it can also be used to treat conductive hearing loss.
Normally, the sound is sent to the inner ear through two methods: air conduction and bone conduction.
The air conduction pathway is the standard mode of hearing where environmental sounds enter the ear through the ear canal and cause the eardrums to vibrate. The vibration sends sound signals to the middle ear from where it is sent to the cochlea in the inner ear.
If the process of air conduction is affected by damage to the outer ear or the inner ear, the transmission of sound to the inner ear is lost. In this case, bone conduction can be an alternative.
With bone conduction, sound waves cause the bones of the skull to vibrate. The vibration of this bone stimulates the fluid in the cochlea, which triggers the sensory cells and provokes the creation of electrical signals that the brain interprets as sound.
As already stated, bone-conduction transmission is normal even for people without hearing loss. We can listen to our voices through bone conduction. The process of bone conduction does not interfere with air conduction; it doesn't block the ear canal from receiving sound. But in a situation where air conduction is no longer possible as a result of conductive hearing loss, bone conduction can be used for hearing loss patients.
The reason bone conduction is used because, in some cases, conductive hearing loss patients may still not be able to hear with the aid of conventional hearing aids.
There is, therefore, a need to bypass the outer and middle ear to get the sound to the inner ear, where it can be sent to the brain for processing.
Bone conduction is done using bone conduction devices.
What are Bone Conduction Devices?
Bone conduction devices are also known as Bone Anchored Hearing Aids (BAHA). They are devices used in place of regular hearing aids by people with conductive hearing loss.
These devices transfer sound to the cochlea by bone vibrations.
For bone conduction hearing devices to function properly, the cochlea must be in perfect shape. This is because, even though the device can bypass the outer and middle ear when transmitting sound, the transmission of the sound to the brain is dependent on the functioning of the cochlea.
The basic function of bone conduction devices is the amplification of sound without an earmold in the ear. They may not restore hearing to normal, but they can help you get by until the cause of the conductive hearing loss has been treated.
Bone conduction hearing devices have two parts: an external part known as the sound processor and a surgically implanted part placed in the bone behind the ear.
The sound processor picks sound from the microphone and converts it into vibration. Simultaneously, the processor transmits the vibration through the bones of the skull to the cochlear in the inner ear. When this vibration gets to the inner ear, it is converted into electrical signals that the brain interprets as sound.
There are three major types of bone conduction hearing devices. This classification is based on how the sound processor of the hearing device is fastened to the head.
1. Abutment Implants
Bone conduction hearing devices with abutments are the oldest and original types of bone conduction hearing aids made. The sound processor is fitted through the skin and fastened in place with posts or screws (abutments).
Most cases of the procedure were successful, but sometimes, the procedure leads to complications. Also, the thought of having the processor held in place with screws is unsettling for most people.
The sound processor of bone conduction hearing devices can also be fastened to the head using a headband. The headband is usually a soft fabric or a hard plastic, and they are mostly used for children.
Headbands are risk-free and can be used for extended periods without any complications.
3. Magnets or Abutment-free
The sound processors of magnetic bone conduction devices are held in place with a magnet implanted behind the ear. The magnetic force from the magnet holds the sound processor in place. The magnet is often surgically implanted under the skin behind the ear.
After one or two fitting procedures, bone conduction hearing devices can become permanent. After the device is implanted, your doctor may recommend a four to twelve weeks recovery period before the device is programmed for the first time. This will enable the incision site to heal properly and eliminate any possibility of a complication.
You may be able to return to your regular routine a few days after the surgery. It is, however, advisable that you avoid lifting moderately heavy weights. Your doctor will brief you on other activities that should be avoided.
Eligibility for Bone Conduction
Bone conduction is unnecessary for some hearing loss patients, especially if there is no problem with the air conduction of sound into the ear. Most cases of hearing loss patients who need bone conduction are those with chronic conductive hearing loss.
Bone conduction hearing devices are most suitable for the following people:
1. People with Chronic Ear Infections
Ear infections are often characterized by the drainage of fluid from the ear canal, and they can cause conductive hearing loss. If you have frequent or chronic ear infections, the regular hearing aid may not be ideal for you. This is because the constant drainage of fluid from the ear will easily damage the hearing aid.
Also, using a conventional hearing aid with an ear mold can cause new infections in the ear canal, resulting in more drainage.
Using a bone conduction hearing device will bypass the ear infection and also leave the ear canal open for proper healing.
2. People with External Ear Canal Problems
People susceptible to external ear problems like irritation in the ear can be caused by inflammation or eczema will benefit more from bone conduction hearing devices. Inserting a conventional hearing aid into an ear canal that is prone to irritation and inflammation can worsen the problem.
3. People with Unilateral Hearing Loss
Unilateral hearing loss is loss of hearing in one year, even when the other ear is normal. Placing a bone conduction hearing device on the affected ear will enable the hearing loss patient to hear with both ears.
4. People with Malformed Ear Structures
Most people with absent or malformed ear structures caused by atresia, microtia, or anotia can enhance their hearing through bone conduction.
This malformation or absence of organs in the outer ear or the ear canal makes air conduction of sound impossible. In some cases conducting surgery to correct the deformity may cause more damage.
To avoid complications bypassing the outer and middle ear through bone conduction is the best option.
Bone Conduction Hearing Loss
Bone conduction procedures are beneficial to people with hearing loss. Unlike conventional hearing aids, bone conduction devices do not plug the ear canal and do not block out ambient sounds.
This makes them suitable for use by tinnitus patients. The noise that gets into the ear through air conduction creates a form of background noise that can drown the tinnitus noise.
Also, bone conduction devices do not need to be inserted into the canal, meaning that no damage is done to the ear canal.
These advantages notwithstanding, bone conduction can affect your hearing or result in certain complications in certain situations.
If the volume of the sound or music heard with bone conduction devices such as bone conduction headphones is too loud, it can damage hearing.
This is why it is important to have the volume adjusted to the normal sound threshold before being used.
Because the vibrations are being sent directly to the inner ear, if the sound is too loud, the structures in the inner ear, such as the hair cells, can get damaged, which will worsen the hearing loss.
Asides from damaging hearing, bone conduction procedures can also damage the bones and soft tissues around the ear. Below are some of such possible complications:
1. Failure of Osseointegration
Osseointegration is the ingrowth of bone into a metal implant.
In most bone conduction procedures, a metal implant is permanently and surgically anchored and integrated into the bone with the hope that the bone grows into the implant.
If osseointegration fails, the implant will fall out, and this will dislodge the bone conduction device from its position.
2. Infection or Inflammation
As with other surgical procedures, the risks of infection after a bone conduction procedure are moderately high.
The abutment area needs to be kept clean always to reduce infection risks.
3. Increased Risks After Injuries
The risk that any form of head trauma or accident can result in serious consequences is higher with bone conduction hearing aids than conventional hearing aids.
One of the complications that may arise from head trauma is the risk of the implant falling out. If this happens, repeat surgery for a new implant or a sleeper implant may be required.
Other complications that may arise after a bone conduction procedure include skin flap necrosis or death of the skin flap, persistent pain, hematoma formation, Overgrowth of skin over the implant, bleeding, and wound dehiscence.
While bone conduction may be appropriate for treating hearing loss, the device must be fitted appropriately to prevent further damage from being done to your hearing.
Most of the complications we enumerated above are common when there is poor wound hygiene. With good wound hygiene, you may have little or nothing to worry about.
Do you use bone conduction hearing devices? Have you experienced any side effects? Share your experience with us.
Drew Sutton M.D.
Drew Sutton, MD is a board-certified otolaryngologist. He has extensive experience and training in sinus and respiratory diseases, ear and skull base surgery, and pulmonary disorders. He has served as a Clinical Instructor at Grady Hospital Emory University for more than 12 years.