Audiology and Baha: Good... Good... Good Vibrations!

A hot topic in diagnostic audiology in recent years is superior canal dehiscence—a thinning or absence of the temporal bone above the superior semicircular canal. While doing some reading on this topic, I found the statement “A clinical sign of this phenomenon is the ability of patients to hear a tuning fork when it is placed on their ankle bone.” The ankle bone? That's a long way from the ear—at least for most people. Hearing by bone conduction is pretty amazing.

Figure. William Dick...

The efficiency of hearing via bone conduction has prompted numerous attempts to use this transmission means in hearing aids. The teeth are good transducers, which led to the patented “Dentaphone” of the 1880s, which was said to provide 30 dB of gain, assuming the user was willing to bite down hard on a wooden fan. Some say that this approach was invented by Beethoven, who reportedly had a rod attached to his piano.

In later years, there was the bone-conduction receiver as an option for body aids and, of course, the 1950s brought us every audiologist's nightmare, the eye-glass bone-conduction hearing aid. In most cases, the use of bone-conduction hearing aid was a last resort.

But that has changed. Today, when it comes to bone-conduction hearing aids, one product stands apart from all the rest—the bone-anchored hearing aid, or BAHA, which has become Baha, an osseointegrated cochlear stimulator. For some audiologists, working with Baha patients has become routine, and one such audiologist is our Page Ten guest author this month, William Dickinson, AuD.

Dr. Dickinson is an assistant professor at Vanderbilt University and the coordinator of the Hearing Technologies program at the Vanderbilt Bill Wilkerson Center. In addition to his teaching and management roles at Vanderbilt, he is clinically active seeing patients, training AuD students, and working with applied research projects.

Perhaps Bill's interest in the Baha and skull vibrations stems from his outdoor passions of hunting and fishing, where he has learned to understand the sophisticated hearing mechanisms of our underwater and feathered friends. He states that he is most fascinated with the hearing of the wild turkey, although we have yet to determine if he has attempted to put a tuning fork on the turkey's ankle.

While “good vibrations” are important for fish and birds, they also can be very important for your hearing aid candidates. This excellent article tells you why.

Gus Mueller

Page Ten Editor

1 I'm not an expert in the area, but I do know that the acronym in your title is for bone-anchored hearing aid. Shouldn't it be BAHA rather than Baha?

Good question. You have the words correct, and for many years the acronym was indeed BAHA, not Baha. Today, though, the term Baha is more of a generic reference to a bone-anchored hearing aid system. In 2005, Cochlear Corporation discontinued the acronym BAHA because the device was officially renamed an “osseointegrated cochlear stimulator.”

Late last year, Oticon Medical added a new dimension to what was a very limited market by releasing the Ponto Pro system of bone-conduction abutments and sound processors. This new system is based on the same circuit platform as its premium hearing aid technology and is fully compatible with other currently available bone-anchored hearing solutions. Hopefully, as with any consumer market, competing products will result in advances and innovations in technology that benefit the end user.

2 Interesting. Doesn't it break all rules of marketing to change the name of a well-known brand?

The name change was mostly an attempt to improve eligibility and reimbursement from third-party payers. Prior to this change, most insurance programs, including Medicare, would not approve the surgical request to implant a “hearing aid.” However, the name osseointegrated cochlear stimulator implies a surgical implant rather than a hearing aid. With its new name, Medicare and other third-party payers would approve the surgery, since the device was no longer classified as a hearing aid.

3 Okay, got it. Another thing about your title, since you're from Nashville, I'm not surprised to see you tie the Baha to music. But the Beach Boys and Good Vibrations? With all that good country music in Nashville?

Well, considering that we provide audiologic care to Baha patients almost every day, I'm hoping to clear up a few common misconceptions. There's a correlation that you missed.

Contrary to what many people think, the music industry in Nashville is not limited to country. Similarly, the Baha patient has become much more commonplace in routine audiology practices and is no longer confined to specialty surgical practices. Initially, Baha patient care was mostly limited to larger, more tertiary otolaryngology practices, and even in those settings the audiologist was minimally involved in Baha patient care. But today, working with the Baha devices, determining candidacy and counseling patients have become important components of the routine repertoire for many clinical audiologists—not just those associated with a specialized otology practice.

As for the Beach Boys, how could I pass up on tying bone-conduction hearing to “good vibrations”?

4 I am surprised that Baha care is such a large part of your hearing aid practice. Is that unusual?

Here at the Vanderbilt Bill Wilkerson Center, between our pediatric and adult hearing technologies program, we had around 300 patient visits last year for some type of Baha-related service. These included pre- and post-operative care, such as determining candidacy, pre-implant testing, counseling (and counseling and counseling!), delivery/orientation, verification, repair, and follow-up care.

Actually, accommodating Baha care in our hearing technologies program is really playing to our strength. We view ourselves more as rehabilitative clinicians than as dispensing clinicians. The care provided to Baha patients is focused on some of the most important principles of audiologic rehabilitation.

For example, a Baha candidacy evaluation could include testing and/or counseling that incorporates any of the following topics: SNR, audibility vs. intelligibility, localization vs. lateralization, head shadow effect vs. head diffraction, prescriptive fitting approach, digital signal processing and programming, hearing assistive technologies, pre-intervention inventories, unilateral versus bilateral fitting, and, of course, counseling on realistic expectations. I think we use some of our strongest audiologic rehabilitation skills and knowledge in these appointments.

5 Are you saying that the average audiologist practicing in Anywhere, USA needs to know about the Baha?

Probably so. The Baha, which has been available for almost 30 years, originally was designed as a hearing solution for patients with medically based, conductive hearing losses (e.g., atresia, congenital deformities, trauma, surgical, chronic draining/disease) who could not use or benefit from traditional amplification devices.

In 2002, the FDA expanded Baha candidacy criteria to patients with single-sided deafness (SSD), which has greatly increased the number of devices implanted annually.

Often a Baha patient may live a considerable distance from the surgical center where the device was implanted. So, the ongoing rehabilitative care and communication management could be, and likely should be, accommodated locally. Following Baha implantation, many patients need the expertise of a rehabilitative audiologist. In addition to repairs, maintenance, and device orientation, ongoing communication management is often needed, which may include audiologic rehabilitation and purchase of hearing assistive technologies and/or a hearing aid for the contralateral ear. Of course, as with hearing aids, counseling on proper use and realistic expectations is always needed.

Since the third-party payer often won't cover these services, the Baha patient should expect to pay out-of-pocket, thus creating a potential new revenue stream for the audiologist in Anywhere, USA. So, yes, I do believe any rehabilitative audiologist should be well versed in the principles of Baha care.

6 To be honest, although I often measure bone-conduction thresholds as part of a diagnostic evaluation, I haven't thought much about bone-conduction amplification since graduate school.

You're not alone. Most audiologists do relate bone-conduction (BC) hearing to diagnostic testing rather than rehabilitation. Even then, outside of learning how to mask, not much attention is paid to how we hear via bone conduction.

As you may remember, there are five significant contributors to bone-conduction hearing: (1) sound radiating into the external ear canal (osseo-tympanic), (2) middle ear ossicle inertia (inertial), (3) inertia of the cochlear fluids, (4) compression of the cochlear walls (compressional or distortional), and (5) pressure transmission from the cerebrospinal fluid.

While each factor plays a role in BC hearing, fluid inertia appears to be the greatest contributor in a healthy auditory system. Middle ear ossicle inertia can influence the mid-frequencies, while the external ear canal, especially if occluded, will dominate BC hearing sensitivity for frequencies below 1000 Hz. Bone-conduction hearing as a result of pressure transmission from cerebrospinal fluid (very low frequencies) and compression of the cochlear walls (very high frequencies) has been found to have a rather minimal impact on BC sensitivity.

7 Ahh, it's all coming back. So what has changed over the years?

Well, some things have changed significantly, like the technology options and our management approach. Yet, at the same time, other issues have not changed very much.

For example, the patient profile and the hearing handicap of candidates who need BC amplification have essentially remained the same. Patients with conductive/mixed hearing losses, medically based contraindications (e.g., atresia, stenosis, craniofacial anomalies, post-surgical ears), or profound unilateral hearing loss have always been challenging rehabilitative patients for the dispensing audiologist. Often there is limited success with either conventional air-conduction or bone-conduction amplification.

The traditional rehabilitative approach has included extensive counseling, speech reading, management of communication strategies and environment, or trial of contralateral routing of signal (CROS) amplification.

8 Oh, yes. Bone conduction and CROS hearing aids. We used to call those “boomerang” fittings. They may go out the door, but most will come back requesting a return for credit.

Aye, mate, you got that right! Bone-conduction amplification dates back to the 1940s. However, patients using an externally worn conventional BC hearing aid have reported limited satisfaction. Such dissatisfaction with BC hearing aids resulted from devices that were difficult to position correctly, uncomfortable to wear, and cosmetically unacceptable. Functionally, conventional BC hearing aids were limited because the vibrational energy was transferred through soft tissue mass in order to stimulate the skull. Such transmission caused considerable dampening of the output dB SPL and restricted the frequency range.

In the 1970s, the first percutaneous (through the skin) bone-anchored hearing aid was developed in Sweden. This approach provides greater efficiency in the direct transmission of vibrational energy to the mastoid.

9 So, how has the Baha evolved over the last several years?

Well first, regarding the actual surgery (i.e., the “bone-anchored” part), many things haven't changed much at all; but there have been many changes in the amplification device (i.e., the “hearing aid” part).

Bone-anchored hearing aids use a surgically implanted abutment to transmit sound by direct conduction through bone to the inner ear, bypassing the external auditory canal and middle ear. A titanium screw is surgically embedded into the skull with a small abutment exposed outside the skin. A sound processor or “hearing aid” connects to the abutment and transmits sound vibrations to the internal titanium screw. The implant vibrates the skull, which, in turn, stimulates the nerve fibers of the inner ear.

10 So, do you actually “screw on” your hearing aid?

Yes. Critical to the overall success of the Baha implantation is the principle of osseointegration, which is the direct structural and functional connection between living bone and the artificial implant. Osseointegration and the percutaneous nature of the implant are why the Baha is favored and considered superior to the traditional bone-conduction hearing aid with transcutaneous stimulation.

The hearing aid portion of the Baha has advanced considerably in recent years, evidenced by external sound processors that are completely digital for sound processing and multi-channel programming. They also include multiple memories and directional-microphone technology.

11 It sounds as if you believe that the audiologist should be involved in determining who is a candidate for the Baha implant. But since it's an implantable device, doesn't the surgeon determine candidacy?

Well, there is a big difference between an eligible candidate and a good candidate for implantation. Remember, when the Baha implant was initially brought to the market almost 30 years ago, it was intended for patients who could not be helped with traditional amplification devices. Specifically, the Baha was for conductive and mixed losses associated with congenital anomalies or for patients whose middle or external ear function was blocked, damaged, or occluded from surgery or trauma. For such patients, there were limited and often inferior amplification options.

Today, however, given the availability of much more advanced hearing technologies, as well as expanded surgical options with the SSD patient, the audiologist plays a very important role in assessing Baha candidacy. For instance, many potential Baha candidates are happy to learn they may benefit from other options such as a conventional hearing aid or CROS/BiCROS fitting, or even with an FM system or alternative wireless systems such as Bluetooth technology. Our role is to manage the communication impairment, not just audibility.

12 That makes sense. What is your audiologic protocol for a Baha evaluation?

We have modeled the Baha evaluation to be more like that for a cochlear implant. However, it is really more of an in-depth rehabilitative consultation. For example, since it is well documented that persons with single-sided deafness often report considerable difficulty recognizing speech in background noise, we take the time to carefully evaluate speech in noise performance, in both the aided and unaided condition. Using either the Connected Sentence Test (CST) or the Quick SIN, we compare unaided performance with various aided conditions. Aided conditions may include best fit unilateral or bilateral hearing aids compared to testing using the Baha demo device. We also conduct testing using FM systems or a more traditional CROS/BiCROS device may be evaluated.

Presentation of speech and noise is completed under conditions of maximal spatial separation of the speech and noise stimuli to show optimal device performance, as well as under conditions of minimal spatial separation for comparison to optimal performance. The intent is to provide a reasonable listening experience for the candidate with several different hearing technologies, while supplying the clinician with data to make the most appropriate recommendation to improve the overall communication ability of the patient.

13 I understand the Baha implant is appropriate for various types of hearing losses. Clearly, the conductive/mixed hearing loss population is very different from those with SSD. How do you handle those unique differences?

One thing that can be said of the Baha population with certainty is that it is not very homogeneous. Wearers have various types, degrees, and configurations of hearing loss. Patients present with conductive/mixed losses, asymmetrical SNHL (e.g., profound SNHL in the worse ear, mild-moderate SNHL in the better ear), true SSD (non-functional hearing in the worse ear, normal hearing in the better ear), or medically based contraindications for hearing aid use (e.g., chronically draining ear, radical mastoidectomy, cranio-facial anomaly).

I find that the more medically based the loss, the more straightforward it is for the patient to consider the Baha option. For such patients, alternative options have typically either been exhausted or are not applicable. For the SSD or asymmetrical SNHL population, deciding on the best recommendation usually involves dealing with shades of gray rather than black or white. This is why it is so important for the implant team to view the Baha as a rehabilitative intervention rather than a surgical intervention.

14 Since these patients are implanted by a surgeon, who is responsible for determining if the device is working optimally and if it is making a difference in the patient's life?

The Baha implant is not a restorative or corrective implant, but rather a rehabilitative implant. It is a rehabilitative tool used to reduce, not remove, the hearing handicap, which we hope, in turn, will improve the overall quality of life of the person living with the residual hearing loss.

The Baha, like other rehabilitative products such as hearing aids or hearing assistive technologies, is an auditory prosthesis used by persons with hearing loss to mitigate the deleterious effects of hearing impairment. As such, it should be held to similar standards of verification testing to demonstrate its effectiveness and document that it is meeting certain technical standards. It is the audiologist's responsibility to verify that the product, service, or system is meeting clinically accepted regulatory or technical standards, and also to validate that the device is meeting the needs of the end user.

15 How do you determine if the Baha is really helping the patient?

Without doubt, Baha outcomes should be validated and documented. Actually, most of the standardized instruments we use to validate more traditional hearing aid fittings can also evaluate post-operative Baha outcomes.

To investigate validation, the use of well-established inventories such as the Glasgow Hearing Aid Benefit Profile (GHABP), Abbreviated Profile of Hearing Aid Benefit (APHAB), Hearing Handicap Inventory for Elderly/Adults (HHIE/A), or the Client Oriented Scale of Improvement (COSI) has been reported. There also is growing interest in using more quality-of-life (QoL) inventories, particularly with the SSD population, as the hearing handicap is unique for a patient with no functional hearing in one ear and normal hearing in the other ear.

16 What about evaluating the device to ensure that it is functioning appropriately and optimally?

Verification techniques, on the other hand, differ much more from what is used with conventional hearing aids. Currently, we often use sound field testing, which may include unaided versus aided pure-tone threshold measures or speech intelligibility testing using speech-in-quiet and speech-in-noise stimuli. As I mentioned earlier, the speech testing can be conducted using different azimuth orientations, which provide useful information for the SSD patients.

17 You mentioned aided sound field pure-tone threshold testing...

I know, I know. With traditional hearing aid fittings, we abandoned this procedure 25 years ago in favor of probe-microphone measures. The limitations of aided sound field testing are well established, and we need to take special care that none of the many variables contaminate the test results. Traditional probe-mic measures, of course, are not possible, so we believe that carefully conducted sound field aided thresholds are better than not collecting any threshold data at all.

As an alternative, there has been some promising work using a skull simulator (TU 1000) to calculate a bone-conduction RECD and then complete the Baha fitting using a coupler response. Additionally, for SSD patients in our clinic, we have experimented with the possibility of completing probe-mic measures in an occluded ear canal in the ear contralateral to the Baha implant. Such verification techniques are either cost-prohibitive (skull simulator) or still too preliminary to be recommended for widespread clinical use.

18 Some of this sounds like too much work for the busy clinician. What is the advantage for a private practitioner who is not working directly with an otolaryngologist to become involved with Baha care?

I'll give you four reasons: (1) new revenue opportunities, (2) new marketing opportunities, (3) new referral opportunities, and (4) simply having a contemporary practice.

A new revenue stream is possible from hearing aid sales to patients who choose not to proceed with the Baha surgery or are denied by their insurance. These patients may elect to obtain a hearing aid on the better hearing ear, instead of the implant. FM systems, Bluetooth connectivity devices, and other hearing assistive devices are often purchased by this typically younger and technologically savvy patient population.

There are numerous opportunities to market to end users, their family members, and new medical referral sources. The Baha option is an innovative and fresh message that is relatively unknown, especially in primary-care offices.

Lastly, it is important for all audiologists to be knowledgeable about new and contemporary aspects of audiologic practice. Most of us want to be viewed as the “go to place” for all types of amplification, not just the types shown in the full-page ads in the local newspapers.

19 So, do you have a take-home message?

I certainly do. It is encouraging to see our profession becoming more involved in the pre- and post-operative management of the Baha-implanted patient. However, there remains a significant opportunity for audiologists to help establish evidence-based candidacy criteria for rehabilitation with the Baha, not unlike those developed for other rehabilitative tools such as hearing aids and cochlear implants. Establishing verification techniques and fitting and fine-tuning protocols will facilitate optimal post-operative performance, as well as authenticate the value of the audiologist in the rehabilitative management of the Baha patient.

20 One last comment about your title. At least you didn't link the Baha to We Got the Beat by the Go Gos.

Oh, I agree. It's much safer to stick with the Beach Boys. So, just remember, when done correctly, the Baha will indeed provide better hearing and, hopefully, a better quality of life through good vibrations!