How to find the right placement for bone conduction testing

Reading Time: 5 minutes
by Amber Morgan
Published 06/07/2022

What is bone conduction testing?

“Bone conduction is the conduction of sound to the inner ear, primarily through the bones of the skull, allowing the hearer to perceive audio content without blocking the ear canal.”1

Instead of using an earphone, bone conduction audiometry uses an electromechanical bone conductor which is placed on the skull (usually on the mastoid prominence or forehead) to stimulate the cochlea directly, bypassing the outer and middle ear.2

How does bone conduction work?

A bone conduction hearing device works by performing the role of your eardrums, transmitting sound vibrations through the bone. It’s designed to pick up sound, amplify it, and convert it into a vibration that can be received directly by the cochlea. The sound reaches the ears as vibrations through the bones (or skull) and skin, so the eardrum is never involved.

A bone conduction hearing device is an alternative to a regular hearing aid for those with problems in their outer or middle ears. It’s useful to note that it relies on a working cochlea to send sound to the brain.3

How to obtain accurate results

There are two placement areas for the oscillator: the forehead and the mastoid bone. To obtain the most accurate results, the bone oscillator must be properly placed. The positioning will depend on the audiologist or hearing professional's preferred way of working, but we’ll explore the options below:

Forehead placement

Many audiologists prefer the bone oscillator placement to be on the forehead, as it’s often perceived to be the simplest way to test. The oscillator is usually attached to a soft headband which can be easily adjusted to fit the size of the patient’s head.  Proper placement for the oscillator is in the center of the forehead just above the eyebrows.

Mastoid placement

According to a survey by Martin, Champlain & Chambers, mastoid is the most widely used type of placement.4 This is where an oscillator is attached to a metal headband and placed on the mastoid bone. It needs to be placed close to (but not touching) the pinna. 

Placement on the mastoid bone can be tricky, as they’re not all shaped the same. Head size can also play a factor in how well the headband will stay in place. If you have trouble with mastoid placement on one side, it’s a good idea to try the other side, to see if the oscillator will better stay in place there.

It is important to note that there is a difference in intensity levels when performing testing via the forehead and the mastoid. To obtain a response from the forehead, the intensity has to be 10 dB louder than when obtaining a response from the mastoid.5 The best way to work around this issue is to have your equipment calibrated for your preferred testing placement.  

 

 

bone-conduction-forehead-placement bone-conduction-mastoid-placement
Forehead placement Forehead placement

 

Diagnostic audiometers

Amplivox has developed a suite of innovative and user-friendly diagnostic audiometers to diagnose a range of hearing loss pathologies. 

The Model 270+ is an advanced two-channel diagnostic audiometer - a popular choice for audiologists, ENTs and hearing aid suppliers. It includes manual and automatic testing for bone conduction, as well as air conduction (Hughson Westlake and Békésy), plus intuitive tools that enable hearing professionals to diagnose hearing loss issues quickly and efficiently. 

With bone conduction testing, masking becomes vital to differentiate the side of hearing loss, so the masking assistant supports hearing care professionals to accurately diagnose this.

For more information on our range of diagnostic audiometers for bone conduction and other tools, please visit our webpage, contact our customer support team on +44 (0)1865 880 846 or email solutions@amplivox.com.

 

References

    1https://en.wikipedia.org/wiki/Bone_conduction

    2From: Handbook of Clinical Neurology, 2015

    3https://www.sciencedirect.com/topics/medicine-and-dentistry/bone-conduction

    4Martin, F.N., Champlin, C., & Chambers, J.A. (1998). Seventh survey of audiometric practices in the United States. Journal of the American Academy of Audiology, 9 2, 95-104.2

    5Martin, F. N., & Clark, J. G. (2019). Introduction to Audiology. Pearson