Bone-anchored hearing aids (BAHA) and cochlear implants are two surgical options for individuals with hearing loss that potentially cannot benefit from traditional hearing aids, though they are very different and have different candidacy and indications for use. This article will help to explain the difference between BAHA vs cochlear implants and how patients who are candidates for each might present clinically.
What is BAHA?
“BAHA” is a bit like “Kleenex” in that it tends to be used as the generic term for a bone conduction, or osseointegrated, hearing aid, though there is now considerable variability in how these devices function. Cochlear Corporation was the first to produce this device and they named it “Baha.” Oticon Medical and Med-El Corporation also manufacture bone-conduction devices and it is not uncommon to hear all of them referred to as BAHA, even though the other two companies have unique names for their devices and not all are actually bone-anchored at this point.
What Is Bone Conduction?
First, it is helpful to understand how the auditory system works and how it is professionally assessed. A diagnostic hearing test is performed in a soundproof booth. Pure tones are presented to each ear individually via headphones at octave frequencies from 250-8000 Hz, which is the range of frequencies that captures speech sounds. These tones are presented to determine the softest possible level you can hear at each frequency (pitch) in each ear. These thresholds are plotted on the audiogram to determine the degree of hearing loss, which can, and probably will, vary by frequency. These thresholds represent hearing ability using the traditional hearing pathway (ear canal, middle ear, inner ear).
This threshold seeking is then repeated via bone conduction. An oscillator on a tight-fitting headband is placed on the temporal bone, and the same pure tones are presented. The testing method means the tones go directly to the cochlea without traveling through the outer and middle ear spaces.
In many cases, the bone conduction thresholds will closely align with those obtained via the headphones (known as air conduction). This means that any hearing loss is known as sensorineural, originating in the inner ear. This type of hearing loss is probably the most common and is typically associated with aging, noise exposure, or ototoxicity, among other causes. If the bone conduction thresholds are better than the air conduction thresholds, they indicate conductive hearing loss or mixed hearing loss.
If the bone conduction thresholds are normal and the air conduction thresholds are not, the hearing loss is conductive; it is purely caused by something in the outer or middle ear. This could be something as simple and temporary as impacted earwax, an ear infection, or something more permanent like a malformation of the ossicles. If there is hearing loss present in both air and bone conduction testing but a gap between the thresholds, it is known as mixed hearing loss. Factors contribute to hearing loss in both the outer and middle ear and the inner ear.
How does BAHA work?
Like the testing performed in the booth, bone conduction hearing aids directly stimulate the inner ear (cochlea) via vibrations in the temporal bone rather than using the traditional hearing pathway (ear canal, middle ear, inner ear).
The first iterations of bone conduction hearing aids involved a surgical procedure in placing a small screw, known as an abutment, in the temporal bone to hold the device in place. Other devices are now fully implanted under the skin and attached to the external portion via a magnet. Still, others utilize a medical-grade sticker to hold the device in place.
Often when children are deemed candidates for a bone-conduction hearing aid, they start by wearing it in a headband. This is a way to test the device’s efficacy and avoid surgery at a young age, if possible. The bone conduction hearing device has microphones like traditional hearing aids, and the amplification is delivered based on the patient’s degree of sensorineural hearing loss.
Image credit: Oticon Medical
Who is A Candidate For A BAHA?
Bone conduction hearing aids have three common use cases: absence or malformation of the outer ear, which would prevent a person from wearing traditional hearing aids, chronic conductive or mixed hearing loss, and single-sided deafness. Patients with conditions such as atresia or microtia (total absence or malformation of the outer ear) are good candidates for a bone-conduction hearing aid.
Conditions like this vary in severity; sometimes, there isn’t enough of an external structure to support a traditional hearing aid; in other cases, there is a complete absence of an ear canal to put in an earmold or receiver to transmit the sound. The cochlea may be completely normal and functional (conductive hearing loss) or there may be some additional degree of hearing loss (mixed). In either case, direct inner ear stimulation via bone conduction is the best option.
There are other causes of chronic conductive or mixed hearing loss besides physical malformations of the outer ear. Audiologists may have differing opinions about what to recommend between a BAHA and a power hearing aid in this chronic conductive or mixed hearing loss situation.
That said, some conditions can be considered contraindications for traditional hearing aids. For example, if a patient has a chronically draining ear, it is unwise to use hearing aids occluding the ear during waking hours. If a patient has a condition known as otosclerosis, which limits the mobility of the ossicles in the middle ear, most audiologists would say that appropriately fitting traditional hearing aids would be adequate treatment for this type of hearing loss.
The final use case which might warrant a recommendation for BAHA is single-sided deafness. This means the patient has profound hearing loss in one ear and either normal hearing or substantially better hearing in the opposite ear. Because the hearing organs are housed within the temporal bone and respond to vibrations, the better cochlea will always respond even if the sound is technically presented to the contralateral side.
A bone-anchored hearing aid would ensure that sound reaches the normal or near-normal cochlea, regardless of one side being completely deafened. It is important to note that there are other treatment options for single-sided deafness. The non-surgical option is a CROS device, which stands for “contralateral routing of signal.” A transmitter is worn on the deaf ear, and a receiver or hearing aid is worn on the opposite ear. The transmitter sends sound from the deaf ear to the opposite side, which may or may not be receiving amplification in addition to the signal from the other ear. The other treatment option for single-sided deafness is a cochlear implant, which we will discuss later on.
What Are The Pros And Cons of BAHA?
One of the biggest hurdles to obtaining a BAHA device used to be the surgery itself. The abutment is placed in the temporal bone behind the ear. It takes some time for the abutment to take hold and for the skin around the area to heal. It is something that needs to be kept clean and can be prone to infection. The Cochlear Baha and Oticon Ponto still function with a traditional abutment. There are other options now, which involve fully implanting a device under the skin and using a magnetic connection between the processor and the implant to stimulate the cochlea via bone conduction.
Med-El was the first to market with this device, and their latest generation is known as the Bonebridge implant used with the Samba 2 processor. Cochlear offers their Osia system as a fully implanted option rather than the abutment style used in their Baha system. Med-El also manufactures the ADHEAR device positioned on the temporal bone using a medical-grade sticker that can be worn for three to seven days before replacement. This non-surgical option appeals to individuals who want to try bone-conduction hearing aids before committing, particularly for children.
In general, an additional challenge to these systems is the placement of the microphones, which are positioned posteriorly to the ear and, therefore, not ideal. Traditional hearing aids can sit directly on or in the ears and pick up sounds as a user would with normal hearing. Directional microphone technology is quite effective in this way. That said, these devices incorporate technology to hear better in various difficult listening environments. Bone conduction hearing aids have many of the same great technology advancements as traditional hearing aids, including connectivity and streaming options and compatible accessories to assist with hearing better in more challenging listening environments such as in extreme noise or over distance.
What Are Cochlear Implants? How Do They Work?
Cochlear implants are comprised of two main parts: the internal cochlear stimulator, which is surgically placed under the skin and encompasses the internal electronics and the electrode array which is inserted into the cochlea, and the external speech processor which contains the microphones to capture sound. The acoustic sound from the environment is converted into electrical impulses which are delivered to the electrode array inside the cochlea, stimulating the auditory nerve and sending sound to the brain.
There are three FDA-approved manufacturers of cochlear implants: Advanced Bionics, Cochlear, and Med-El. You may have noticed that Cochlear and Med-El also manufacture bone-conduction devices. Oticon Medical, the other bone conduction hearing aid manufacturer, has pre-market approval for their cochlear implant in the US, but it is not yet commercially available.
All three companies have unique selling points, and, unlike most medical devices, the patient is typically the decision maker concerning which device they choose. The best way to make a device choice is to contact the local representatives from each company to talk through your hearing needs and lifestyle and get some personalized recommendations on what their company can offer.
Who Is A Candidate For A Cochlear Implant?
Cochlear implants are another surgical option for hearing loss, but they are designed for patients who present differently than those who qualify for a bone-conduction hearing aid. Candidacy for cochlear implants is based on two main factors: the patient’s audiogram and their discrimination ability with appropriately fit hearing aids.
Generally, an adult patient must have considerable hearing loss (moderate to profound), and it is typically sensorineural in nature. Occasionally, patients with mixed hearing loss can qualify for a cochlear implant. It is not designed for those with conductive hearing loss, as those patients have a functional cochlea. Patients with cochlear implants have typically been hearing aid users for some period of time. They are no longer getting an adequate benefits, as demonstrated by poor performance on aided tests of discrimination ability.
The patient must also be healthy enough for surgery and have an etiology of hearing loss that permits implantation (i.e., present and patent cochlea). Cochlear implant surgery can occur as early as 9-12 months of age if a baby is diagnosed with severe to profound hearing loss at birth or into old age if the patient is healthy enough for surgery.
What Are The Pros And Cons Of Cochlear Implants?
Cochlear implants restore access to sound for patients who can no longer derive adequate benefit from traditional hearing aids. Cochlear implants do not sound like hearing aids or normal hearing due to the difference in the sound pathway and method of stimulating the auditory nerve. However, the brain is incredibly plastic and can adjust to new input, allowing patients who had very poor speech understanding with hearing aids to substantially improve their ability to hear in a variety of listening environments.
The cochlear implant technology has advanced greatly in the last several years, with all three companies offering an MRI-safe internal device, Bluetooth and another streaming compatibility, waterproof options, and external processors, which are becoming increasingly smaller and lighter.
Most patients’ biggest obstacle to moving forward with cochlear implantation is fear of the unknown. Several factors can influence performance with a cochlear implant, including duration and etiology of hearing loss, age of implantation, amount of residual hearing, and other co-occurring medical conditions. There is no way to predict with 100 percent accuracy how well someone will do with a cochlear implant, even if they present as a fantastic candidate. Fortunately, most patients find improvement in their performance with hearing aids, and there is great potential to continue improving with a cochlear implant through increased wear time and aural rehabilitation.
BAHA vs Cochlear Implants
Aside from the overlap in manufacturers of these two surgical solutions for hearing loss, they are fundamentally very different. A BAHA relies on usable hearing in the cochlea, while candidacy for a cochlear implant essentially demands that the cochlea not be functional. A bone conduction hearing aid has different options for abutment vs. fully implanted vs. the sticker system, while the cochlear implant surgery is relatively identical regardless of manufacturer. The only real overlap between the two devices is cases of single-sided deafness, though cochlear implantation for this indication is still an obstacle regarding insurance coverage.
What Is The Evaluation And Implant Process? When Should I See A Doctor?
The evaluation and implant process for BAHA and cochlear implants would actually be relatively similar. If you are having difficulty hearing, seeing an audiologist for a complete diagnostic hearing evaluation is a good idea. The audiologist will be able to walk you through the results of your evaluation and let you know if you are a candidate for traditional hearing aids, a bone conduction device, or a cochlear implant.
If you are a candidate for a BAHA or a cochlear implant, the audiologist will refer you to an ear, nose, and throat specialist to discuss the surgical options and have a medical evaluation. Typically, this physician will be an otologist or neuro-otologist, meaning they have additional specialized training in ear surgeries. Imaging will also be ordered; most patients will have a CT scan, and some may have an MRI.
BAHA vs Cochlear Implant Takeaway
If you are a current hearing aid user having increasing difficulty with your hearing aids, you should talk to your audiologist about your candidacy for a cochlear implant. It could be that your hearing has changed, and your hearing aids simply need to be updated or reprogrammed to reflect your current thresholds, but it is also possible that you have progressed into the candidacy range for a cochlear implant.
Your team of providers will help you to walk through the solutions which can offer the best opportunity to improve your hearing. You may have some choice regarding the style and manufacturer of the device you choose, whether it is a traditional hearing aid, bone conduction device, or a cochlear implant. If you find a provider you trust, you should follow their recommendations for what is best. When in doubt, the best first step is a full hearing evaluation.
Erin Edwards received her Doctor of Audiology degree from Towson University in 2015 and her Ph.D. in Education and Leadership from Pacific University in 2022. She has worked with patients of all ages in a variety of settings and has a specific interest in cochlear implants, the relationship of hearing loss and dementia, and interdisciplinary healthcare.