A bone gap, in the context of hearing, refers to a significant difference between the thresholds measured during air conduction and bone conduction hearing tests in the same ear.
Understanding Air and Bone Conduction
To understand a bone gap, it's important to know the basics of air and bone conduction:
- Air Conduction: Sound waves travel through the outer ear, middle ear, and inner ear.
- Bone Conduction: Sound waves bypass the outer and middle ear and directly stimulate the inner ear via vibrations through the skull bones.
Defining the Bone Gap
An air-bone gap is considered significant when there's a difference of 10-15 dB or more between the air conduction and bone conduction thresholds at the same frequency in the same ear. For example, if a person hears a sound at 40dB through air conduction but at only 25 dB through bone conduction at a specific frequency, that would be a 15dB air-bone gap.
Significance of a Bone Gap
The presence of an air-bone gap usually indicates:
- Conductive Hearing Loss: This type of hearing loss occurs when sound waves are blocked or have difficulty passing through the outer or middle ear. The bone conduction pathway is relatively unaffected in these cases because it bypasses the outer and middle ear.
- Mixed Hearing Loss: This type of hearing loss involves both a conductive component (problem in the outer or middle ear) and a sensorineural component (damage to the inner ear or auditory nerve). The air-bone gap reflects the conductive component.
Bone Gap Example
| Frequency (Hz) | Air Conduction Threshold (dB) | Bone Conduction Threshold (dB) | Air-Bone Gap (dB) |
|---|---|---|---|
| 500 | 40 | 20 | 20 |
| 1000 | 45 | 30 | 15 |
| 2000 | 50 | 40 | 10 |
In this example, significant air-bone gaps are present at 500 Hz and 1000 Hz, indicating a conductive or mixed hearing loss.
In Summary
A bone gap is a measurable difference in hearing thresholds between air and bone conduction testing, typically indicating a conductive or mixed hearing loss and requiring further audiological evaluation.
