Bone-anchored hearing devices are surgically implantable systems to treat hearing loss through bone conduction of sound vibrations, in contrast to regular hearing aids, which amplify acoustic sounds that enter the ear canal.
Bone-anchored hearing systems were developed by Dr. Per-Ingvar Branemark in the late 1960s. Through his research, he found that titanium screws would eventually meld and grow with bone in the skull, allowing firm anchorage without a thick layer of connective tissue. He called his discovery osseointegration, and it lead to the development of titanium implants to be inserted under skin. Branemark used these in 1965 during craniofacial and dental reconstructive surgery in the mandible with great success. Less than a decade later, his student at Sahlgrenska University Hospital in Gothenburg, Sweden, Dr. Anders Tjellstrom, began experimenting with the devices for direct bone conduction for people with hearing loss. The first surgically implantable devices were developed in the 1970s. The first patient fitted with a bone-anchored device was Mona Andersson in 1977, who noted that she could hear the birds singing for the first time since childhood. The bone-anchored hearing aids were first commercially available in 1987.
Bone-anchored hearing systems were approved for use by the Food and Drug Administration in 1996 for conductive and mixed hearing loss and then in 2002 for unilateral hearing loss. Today, bone-anchored hearing systems have been widely improved upon and are an effective hearing loss solution for particular types of hearing loss. Here's what to know:
Why bone-anchored hearing devices?
Bone-anchored hearing devices bypass particular problems by sending sound vibration directly to the inner ear through the skull bone. This can be helpful because middle ear and ear canal problems might prevent sound waves and signals from reaching the inner ear along the typical acoustic pathway.
People who are potential candidates include those who have chronic ear infections or allergies, outer or middle ear malformations and those with single-sided deafness.
Chronic ear infections
People with chronic ear infections are good candidates because they often have near continual drainage from their ears. Placing a hearing aid in the ear may exacerbate recurring infection by plugging up the ear canal, whereas a bone-anchored hearing device does not occlude the ear canal. A bone-anchored hearing device is also a potential solution for those individuals who have extreme allergies to the materials used to fabricate custom hearing aids and earmolds.
Malformations of the outer or middle ear
Malformations of the ear canal or middle ear, such as narrowing of the ear canal or a malformed or absent pinna (external ear) cause conductive hearing loss. These malformations are often congenital, or present at birth. A bone-anchored hearing solution works for these individuals because it delivers sound vibrations directly to the inner ear by being in direct contact with the skull bones.
Single-sided deafness (SSD) is a condition in which a person has lost hearing in one ear, while he or she may have anywhere from normal hearing to profound hearing loss in the other. Single-sided deafness makes it difficult for individuals to determine which direction sound is coming from (localization) and diminishes the ability to understand speech in noisy environments.
An individual with unilateral hearing loss also has to be careful to position themselves in lecture halls, classrooms, conversations and dinner parties so that the better hearing ear is directed toward the speaker.
An individual with single-sided deafness can wear a special pair of hearing aids that are set up to route sounds from the poorer hearing side to the better hearing side, but the bone-anchored hearing device may be preferable because it requires the use of only one discreet device.
Other conditions that might warrant a bone-anchored hearing device include:
- Acoustic neuroma
- Meniere's disease
- Middle ear disease or dysfunction
- Sudden hearing loss
How does it work?
Bone-anchored hearing devices have three parts: a titanium implant, a sound processor and an external connecting element. During an outpatient procedure that typically takes less than one hour, a small titanium implant - usually only 3 or 4 millimeters - is placed into the bone behind the ear. Over time, it integrates naturally with the bone. A tiny abutment is then inserted and juts out through the skin. A removable microphone and sound processor is then attached to the abutment. Some devices are now using magnetic connections between the processor and implant, like a cochlear implant.
After it is implemented, the bone-anchored hearing device works by taking advantage of the bone vibrations, a natural transmission pathway for sound to travel to the inner ear. Rather than delivering acoustic stimuli through the ear canal and middle ear, the sound processor of the bone-anchored device sends vibrations through the abutment (or via electromagnetic coupling) to the implant. In turn, the implant vibrates the surrounding bone, which sets up sound waves in the inner ear that stimulate the hair cells and result in the firing of the auditory nerve.
Because this type of device requires at least one functioning inner ear, it is not recommended for the most common hearing loss that exists, bilateral sensorineural hearing loss. It is a specialty device for those conditions which are described above.
Benefits of bone-anchored hearing devices
The biggest benefit of bone-anchored hearing devices is that they bypass the outer and middle ear structures. This type of hearing solution is the only option for those who have outer or middle ear malformations, allergies or chronic ear infections. Other individuals may choose the bone-anchored device over a traditional acoustic device because the ear canal is not occluded with an earmold, which can lead to a plugged up feeling, trap humidity inside the ear canal and occasionally cause discomfort and infection.
One downside of bone-anchored hearing devices is that they require surgery for implantation, which can be quite expensive. However, the device placement does not damage the inner ear, so it can be removed if necessary without causing any damage to the patient's existing hearing ability.
What's available today?
Currently, there are three manufacturers with FDA-approved bone-anchored hearing devices: Oticon Medical, Cochlear Americas and Sophono. The devices fit differently for children and adults, with a soft band option available for children.
Cochlear has had 35 years in the bone-conduction hearing aids market, making it one of the biggest providers. It has several systems, including the Baha 4 Connect, which is its newest bone conduction titanium device with an advanced abutments system, as well as the Baha 4 Attract, which uses a magnet to connect the sound processor to the skull so there is no external abutment visible to anyone.
Sophono bone-anchored hearing devices originated in Europe and were first introduced in the U.S. in 2011. They do not have external abutments but work with an implanted magnet, which is appealing to both adults and children who favor a discreet option.
If you think you may be a candidate for a bone-anchored hearing system, contact a hearing care professional for a hearing test.
- Bone Anchored Hearing Aid, Department of Otolaryngology, http://www.ent.uci.edu/clinical-specialties/ear-surgery/bone-anchored-hearing-aid