Who are candidates for a Bone Anchored Hearing System?
There are two main bone anchored hearing system (BAHS) candidacy indication categories, and one secondary indication category. Audiologically speaking, patients can be fitted with a Ponto system if they have conductive and mixed hearing losses, or if they have a unilateral profound hearing loss, also known as single-sided deafness (SSD). The secondary indication category includes patients who have other physical characteristics or other medical conditions that make wearing a conventional hearing aid impossible.
What information do we need to see on the audiogram to help us determine if an individual is a candidate for a bone anchored system? The first question we need to ask is if the device would be able to compensate for the inner ear hearing loss. This is obviously a key indicator for a BAHS fitting. To find this out, we examine the patient's bone conduction threshold. For a patient to be able to use a Ponto system, their BC thresholds can go up around 65 dB HL, on average. It's easy to calculate this average: you add up the thresholds, the four individual frequencies, and divide by how many there are. If it's less than 65 dB HL, then we can go with Ponto.
The second question in determining candidacy is a bit more complex: Is the use of a bone anchored device a better solution than traditional hearing aid? Research has shown that if the patient's air bone gap is on average, greater than 30 decibels, their speech recognition scores will likely be better than conventional hearing aids (Mylanus, van der Pouw, Snik & Cremers, 1988; de Wolf, Hendrix, Cremers & Snik, 2011). However, it is important to remember that the answer to this second question is not a requirement; it is simply a supportive indicator of benefit. It is not a hard and fast rule. If the patient had an air bone gap that was not quite 30 dB HL, it would still be worth trialing a BAHS, as they may still obtain benefit.
The two items that need to be calculated to determine BAHS candidacy of someone with conductive and mixed hearing loss are: the average BC threshold and the average air-to-bone gap. First, to determine the average BC threshold, calculate the average BC response at .5, 1, 2 and 3 kHz. The average BC that we can fit to is up to 65 dB HL. Add up all of these BC responses and divide by the quantity to obtain the average. The second criteria we need to look at is the average air-to-bone gap (ABG). First, calculate the average between the AC and BC responses at .5, 1, 2 and 4 kHz. The average ABG should be around 30 dB HL. Remember that this is just a rule of thumb.
This Ask the Expert is an excerpt from the CE Course, Bone Anchored Hearing Systems - Principles and Candidacy.
de Wolf, M. J., Hendrix, S., Cremers, C. W., & Snik, A. F. (2011). Better performance with bone‐anchored hearing aid than acoustic devices in patients with severe air‐bone gap. The Laryngoscope, 121(3), 613-616.
Mylanus, E. A., van der Pouw, K. C., Snik, A. F., & Cremers, C. W. (1998). Intraindividual comparison of the bone-anchored hearing aid and air-conduction hearing aids. Archives of Otolaryngology–Head & Neck Surgery, 124(3), 271-276.