Today’s blog is written by my friend Lisa Vaughan-Christensen. Lisa Christensen is the Audiology Program Manager at Cook Children’s Medical Center in Fort Worth, Texas. Dr. Christensen has devoted a large amount of her professional career to bone anchored hearing devices in children. Her other interests include pediatric diagnostics and amplification, and acquired hearing loss in children and adults. Dr. Christensen currently serves on the Board of Directors for the American Academy of Audiology.
What began as a treatment for children and adults with inoperable microtia/atresia most commonly seen in syndromes like Treacher Collins syndrome, bone anchored implants (BAI) have emerged with many more indications, such as mixed hearing loss, unilateral conductive hearing loss, and unilateral severe-to-profound losses. Traditionally bone anchored implants (BAI) are composed of three parts: a titanium implant, an external abutment, and a detachable sound processor. What makes the traditional Baha system work well is direct bone conduction achieved by a percutaneous abutment. Sound is conducted directly through the skull bone, bypassing the outer and middle ear and directly stimulating the cochlea. However this skin penetrating percutaneous abutment has opened the door to infection and in many cases an undesirable cosmetic appeal.
New Advances in Bone Anchored Implants
Recently Cochlear released an additional system, the Baha Attract, that does not utilize a percutaneous abutment. Instead it uses a magnetic attachment with the internal implant and sound processor. The sound processor picks up the sound vibrations and then passes the vibrations through the external magnet that ‘attracts’ to the internal magnet in the same way a cochlear implant speech processor connects. The internal magnet is attached to the titanium implant which is implanted in the skull and therefore starts the typical bone conduction process. Using magnets with implantable hearing technology isn’t a new concept, think cochlear implants. But does it work to use magnets as the ‘middle man’ to avoid a percutaneous abutment? Preliminary data at Cook Children’s Medical Center and The Texas Ear Clinic, both in Fort Worth, Texas, show this new technology as a viable option. This new across the skin or transcutaneous technology especially in children, could be beneficial because infection rates with the traditional percutaneous bone anchored implants tend to be higher for children (Lee et al, 2011).
Verifying The Attract
As with legacy bone conduction hearing aids and bone anchored implants, aided threshold testing is the method for verification of the Baha when used for bilateral conductive or mixed hearing losses. The speculation surrounding the Attract System is that it’s like a Softband fitting in respect to functional gain because of the removal of ‘direct bone conduction with the removal of the percutaneous abutment. This appears to be somewhat true. When the Attract System is compared to previous Baha Softband studies (Nicholson et al, 2011), the aided thresholds are within 10 dB for 500, 1000, & 2000 Hz. This gives average aided thresholds from 15-20 dB for these three frequencies. However, there’s more of a difference at 4000 Hz between Softbands and the Attract. From this preliminary work out of Fort Worth, 4000 Hz is about 17 dB worse than a Softband at 4000 Hz. This makes the aided thresholds average around 37 dB, which is clearly not best practice for pediatric fittings, especially considering how much important speech perception information and grammatical markers are in the high frequencies. It is important to remember that this is preliminary data that consist of only nine subjects with conductive hearing loss at this point. Also noteworthy is that almost all of these results were obtained at the initial fitting appointments where many times magnet strengths are still being determined. Getting the appropriate magnet strength and then deciding if magnet pads are need to be added for comfort can take more than one appointment for patients. Also important to acknowledge when working with the Attract System, magnet strengths become critical like the precision of the Softband fitting and can have some negative impact on aided thresholds. The best protocol for an accurate fitting is aided testing over a period of time to ensure comfort of the device and good responses to aided threshold testing.
Another solution to what has been noticed in this preliminary data is to simply give patients more gain at 4000 Hz. Many pediatric audiologists are uncomfortable with this solution as there’s no objective measures available at this current time to verify the changes, like a traditional hearing aid fitting with real ear measures. Even though this is not the normal course for many audiologists, you can and should adjust the gain within the programming software to make sure pediatric patients are hearing all sounds well across the speech spectrum.
Audiological data are promising and with care can be made to give pediatric patients access to the speech spectrum just as the legacy bone anchored implants have done. As results continue to emerge regarding the Attract system, it is helpful to remember that the traditional bone anchored implant is still an option for patients. Cochlear now refers to their traditional system as the Connect System and as always Oticon Medical has the Ponto as their bone anchored implant. These are both still great options for adults and children who could benefit from bone anchored implants.
Lee C, Christensen L, Richter G, Dornhoffer J. Complications of Bone-Anchored Hearing Aids: The Arkansas Experience. Otology Neurotology. 2011; 32:444-447.
Nicholson, N. Christensen, L, Dornhoffer, J. Martin, P, Smith-Olinde, L. (2011).Verification of speech spectrum audibility for pediatric baha softband users with craionfacial anomalies. Cleft Palate-Craniofacial Journal, (48)1: 56-65.