Bone Conduction Hearing Aids
Conventional air conduction hearing aids have a fundamental role in rehabilitating hearing loss, but they do have their limits. When it comes to severe sensorineural, conductive, or unilateral hearing loss, these sound amplifying hearing aids may not be a reliable option.
How do we hear?
Our ears are made up of three parts, the outer ear, middle ear and inner ear.
The outer ear – also called the pinna or auricle, acts as a funnel, collecting sounds to channel them into the ear canal.
At the end of the ear canal is the eardrum – this is where the middle ear starts. The eardrum is a thin piece of tightly stretched skin, made to vibrate when sound waves hit it.
This vibration is transferred through your middle ear by the three middle ear bones, the ossicles. The vibrations then enter the inner ear which contains the cochlea.
Inside the cochlea are structures including three fluid-filled chambers, outer hair cells, and inner hair cells. The cochlea converts the vibrations into an electrical impulse with the help of these hair cells. The impulse is then sent up the auditory nerve to the brain where the auditory cortex can interpret the sound, which we interpret as sound.
Types of hearing loss
Sensorineural hearing loss – this is usually caused by damage to the hair cells in your inner ear, or to the nerve pathways that lead from the inner ear to the brain. The two biggest causes are excessive exposure to loud noise and age. It is the most common type of hearing loss and is typically treated by air conduction hearing aids.
Conductive hearing loss – this affects the passage of sound through the ear canal to the inner ear. It is caused by some kind of physical interference that prevents the proper transmission of sound waves. This could be an obstruction or damage, and may only be temporary and treated with medication. If it is permanent, bone conduction hearing aids may help.
Unilateral hearing loss – total hearing loss on one side but normal hearing or a mild hearing loss on the other. This is also called single-sided deafness and can be treated with a bone conduction hearing aid on the non-hearing side.
Amplification only helps hearing loss if the inner ear, also known as the ‘organ of hearing’, or the cochlea, is damaged (but not too severely). All the other pathways have to be clear and working well in order for the sounds to be cleanly transmitted all the way to the inner ear.
What are bone conduction hearing aids?
Bone conduction hearing aids create vibrations that are sent across the skull to the inner ear, directly stimulating the cochlea where these vibrations are perceived as sound. So if there is an issue with the outer and middle ear components, the process of transmitting sound by air can be bypassed.
Bone Conduction Hearing Aid vs Bone Anchored Hearing Aid (BAHA)
Bone Conduction Hearing Aid
- These consist of a hearing aid which is worn behind the ear coupled with a bone conductor/vibrator.
- The bone conductor is either held in place by a headband, which presses the audio processor to the skull, or by an adhesive pad stuck behind the ear, which the processor attaches to.
- Often they are used as a temporary solution, especially for people waiting to have surgery to fit a Bone Anchored Hearing aid, or for children.
- They can be uncomfortable to wear for long periods as the headband needs to be worn tight in order to keep the bone conduction device pressed hard enough against your head, and they are not as efficient as traditional aids or a BAHA.
- The adhesive pad is generally as effective as the headband, but they are not yet available worldwide, so a discussion with your audiologist is recommended.
- When a bone conduction hearing aid is fitted, time needs to be taken to work with a professional. It can take a while for the brain to make sense of the new information it is receiving and interpreting into sound.
Bone Anchored Hearing Aid (BAHA)
- Bone-anchored hearing aids tend to consist of two parts: the implant and the audio processor.
- Either a magnet or abutment is surgically implanted to anchor the sound processor.
- Abutment – this is surgically positioned under the skin and fixed to the temporal bone behind the ear. When it has had time to heal and osseointegrate into the skull, you can clasp on an audio processor as the connection is exposed from the skin.
- Magnet – The implant is fixed to your skull and has a magnet under your skin, the audio processor also has a magnet so it can be positioned and removed quickly, there is no post sticking out of the skin with this option.
- The audio processor is held directly over the implant in both situations.
- The processor needs to be removed when showering or swimming as it cannot come into contact with water.
How Do Bone Anchored Hearing Devices Work?
The external audio processor is attached to the skull via an embedded abutment or magnetic attachment. The processor picks up sound waves and converts them into electrical signals. These signals are then transmitted through the skin or abutment to the implant which is fixed in the temporal bone.
The implant converts the signals into mechanical vibrations which are transmitted to the skull bone, these vibrations naturally move across the skull to the inner ear.
The inner ear processes the mechanical vibrations in a similar way to natural hearing and transmits this acoustic information to the brain. It can take some time for the brain to get accustomed to receiving this new type of information and recognising it as sound. It is recommended to work with a professional to make the initial period of adjustment as comfortable as possible.
How could they help me?
If you have a conductive hearing loss where the outer or middle ear is affected, to the point that transmission of sound is blocked, traditional air conduction hearing aids cannot be used.
Bone conduction hearing devices bypass the outer and the middle ear entirely, so vibrations of sound directly stimulate the healthy cochlea. A healthy cochlea is required otherwise stimulating it will not have any benefit over air conduction hearing aids.
For unilateral hearing loss (or single-sided deafness) the audio processor is worn on the side with little to no hearing where it picks up the sound from that direction. The vibrations are sent via the skull bone to the functioning inner ear on the hearing side. This transfer of sound gives the wearer the impression of an average degree of hearing that comes from healthy hearing organs on both sides.
One benefit of bone conduction hearing devices and aids is that the wearer does not need to wear an ear mould, or anything physically in the ear canal as the ear canal is not being used to send the sound waves.
Not having anything inserted into the ear canal can be useful for people who:
- Have sensitive ears
- Have issues with ear wax
- Have a hole in the ear-drum
- Have dislodged ossicles
- Have a middle ear infection
- Have fluid behind the ear
- Do not like anything covering their ears
- Want their hearing aid to be less noticeable
- Find conventional hearing aids uncomfortable
Keep in mind that the cochlea needs to be intact and hearing well for these devices to work.
How is a bone anchored hearing aid fitted?
- An audiological assessment is carried out which includes an audiogram with an air conduction test, a bone conduction test, a speech recognition test, and a test with a BAHA simulator.
- You can take a BAHA simulator away with you to try out in familiar environments.
- After this assessment procedure, you will have a consultation with an Ear, Nose, and Throat surgeon.
- It will be determined whether you are a suitable candidate for a BAHA.
- You will then have all the necessary knowledge to make an informed decision about proceeding with the surgery.
- The speech processor is fixed to the temporal bone during surgery.
- A six-week wait is required so that the bone can integrate with the titanium abutment, ensuring a secure fixture for the hearing aid to be connected to.
- After these six weeks, an appointment with an audiologist is necessary so that they can check the skin around the abutment and attach the device for the first time.
- The sound quality and level will be programmed to suit your hearing loss.
- Your progress will be monitored for around six months to make sure you are adjusting well to the device.
Features of a BAHA
- Wireless connectivity options allow the possibility to connect to mobile phones and assistive listening devices, meaning their functions can be controlled and adjusted easily.
- The covers of the sound processor can be interchanged, new designs and styles can be chosen.
- Bone conduction hearing aids and bone anchored hearing aids are both compatible with assistive listening devices like telecoils, FM systems and neck loops.
Over 90% of individuals with a hearing loss will require the use of traditional hearing aids as their best and only treatment option. The remaining 10% may not receive benefit from this aid. For individuals with a conductive hearing loss, mixed hearing loss or single-sided deafness, a bone conduction device may be helpful.
Not every hearing loss requires the use of traditional hearing aids, but there are treatment options for every type of hearing loss, the time just needs to be spent to find the best option for you. Click here to book a free hearing test now.