How do bone anchored hearing aids work?

Bone Conduction

Have you ever wondered why you sound different on a recording, to what you thought you sounded like? Well, the answer to that involves bone conduction.

Basically, you are only hearing sounds transmitted via air conduction and missing the parts that come from bone conduction within your head. This means that your voice on a recording usually sounds higher and weaker than what you think it should.

There’s no need to worry though, everyone experiences the same thing. Just because it may sound different and funny to you, that doesn’t mean other people hear it that way as well. What you hear, is what they are used to hearing all the time!

Bone Anchored Hearing Aids

As the name suggests, a bone anchored hearing aid makes use of our bone conduction hearing, by transmitting sounds through our skull bone to our inner ear. This contrasts with conventional hearing aids, which amplify sound through the ear canal.

A bone anchored hearing aid fixes to a metal implant that is then inserted into the skull. There are two types of bone anchored hearing aids available, and those are abutment and magnetic hearing aids. The former has a connecting abutment poking through the skin, which is attached to the internal implant. The sound processor clicks in and out of the abutment, and it tends to be this option which causes the “ewww’’ reaction!

The latter uses an internal magnet hidden completely under the skin, which is attracted to an external magnet that the sound processor attaches onto. Each type of bone anchored hearing aid has its own advantages and disadvantages, and both require surgical procedures. A non-surgical alternative is to have a sound processor worn on a headband. This is a popular choice for children whose hearing is expected to improve with time.

Being Offered a Bone Anchored Hearing Aid 

So why might someone be offered a bone anchored hearing aid? They are primarily used for people with conductive hearing loss, who’s outer and/or middle ears do not transmit sound correctly. However, they are also used for people who suffer with single-sided deafness (unilateral hearing loss) who have been unsuccessful in trialing, or just unable to wear a traditional behind-the-ear (BTE) hearing aid.

Such reasons for the offer may include chronic infection, malformed ear canals or ears, ear allergies / irritation from standard BTEs, or even practical issues linked with using a CROS (contralateral routing of signals) system in the case of single-sided deafness.

In the younger paediatric population, bone anchored hearing aids worn on a temporary headband can prove an effective solution for those struggling with fluctuating hearing loss, which is commonly associated with ‘Glue ear’. Without a bone anchored hearing aid, these issues may otherwise be tricky to manage with conventional hearing aids.

For whatever the reason, for a bone anchored hearing aid to work effectively, the individual must have at least one inner ear (cochlear) that functions normally. This will then be ascertained by the audiologist in the hearing clinic. They can be used in the case of mixed hearing loss (loss affecting both the outer/middle and inner ear) but the underlying, cochlea hearing level still needs to be above a certain level.

How do bone anchored hearing aids work?

Very simply, once you click the sound processor onto the abutment, magnet, or headband, the bone anchored hearing aid picks up soundwaves in much the same way as a traditional hearing aid. However, instead of sending these soundwaves through the ear canal, it converts them into vibrations which travel through the surrounding bone. In turn, this sets up sounds waves in the inner ear that stimulate the hair cells, resulting in a firing of the auditory nerve. Essentially, we are talking about by-passing the outer and middle ear and conducting sound to the cochlea directly through bone.

Single-sided deafness can make everyday activities more challenging, including meetings, crossing the road, driving a car, and enjoying social gatherings in noisy environments. A bone anchored hearing aid transmits sound vibrations through the bones in the skull to the healthy inner ear on the opposite side. This offers reduction of the head shadow effect (head blocks sound in the same way it would block sunlight), as well as improved speech intelligibility. However, it is important to point out that it will not restore localization ability, not the person’s ability to hear in their poorer ear.

How Are Bone Anchored Hearing Aids Fitted?

Bone anchored hearing aids are considered specialty devices that are used to treat specific types of hearing loss and as such, it is imperative that you contact a hearing specialist who will conduct the appropriate assessments to determine suitable candidacy.

If you have any questions regarding bone anchored hearing aids, please feel free to contact our audiology specialists, who will be able to assist you with any hearing queries you may have.