Bone Anchored Hearing Aids

Hearing aids have been on the market in various parts of the world since the early 1940s. The earliest devices were simple amplification aids that were placed over the opening of the ear canal. While these devices worked for some people they didn't work for most hearing loss sufferers. That's because simple amplification isn't the issue for most people. Thankfully, as our understanding of hearing loss has increased, technology has also brought us new types of hearing aids for different purposes.

One of the newest types is known as the bone anchored hearing aid. This type of hearing aid is not something that can be temporarily placed in the ear and taken out at night. It involves a surgical process which implants part of the device into the skull where tissue then grows around it to make it a permanent part of the body. It should also not be confused with cochlear implants; they are something entirely different. Up until a few years ago, this type of hearing aid was only allowed in the United States with special FDA approval. Bone-anchored hearing aids are used for those suffering from:

• conductive hearing loss - an interruption in the sound waves anywhere in the hearing system which prevents those sound waves from getting to the nerves and being transmitted to the brain
• unilateral hearing loss - a condition in which a person suffers total hearing loss in one ear but little or no loss in the other
• a propensity to infection, or some other prohibitive medical condition, which prevents the use of in-the-ear or behind-by-ear units

The Mechanics Behind It

Regardless of the reason for using this type of hearing aid, the bone-anchored device is a conductive one which works by bypassing the ear canal and all of its inner workings. The implanted device causes the skull to vibrate, with those vibrations then being sent to the nerves which, in turn, transfer the signals to the brain and allow for a synthesized hearing. Bone-anchored hearing aids do not reproduce sound accurately, but they synthesize it close enough to allow normal daily functioning.

In order to use this type of hearing aid a titanium prosthesis is embedded in the skull just behind the ears with a post that protrudes from the side of the head. To that post is connected an electronic device which "hears" sound waves, translates them into electrical impulses, and then sends them to the prosthetic device. The prosthesis then vibrates the skull and the inner ear producing synthetic sound waves that reach the nerves.

The implantation of the titanium prosthesis has advanced to a state where it is a pretty straightforward process. However, in order to use the device properly, time must be given for tissue to go around the prosthesis and incorporate it into the bone tissue. This process is known as osseointegration. If osseointegration doesn't occur the prosthesis cannot properly cause the skull bones to vibrate. Usually the process takes about six months from the time of implantation to the point where the user can begin using his hearing aid device.

Programming the Device

Since every human skull is different, and every brain interprets sound waves differently, there's no such thing as a "one-size-fits-all" bone-anchored hearing aid. The brand-new user will have to undergo a lengthy time of therapy and testing in order to optimize his hearing aid. A hearing specialist will test the user in a wide variety of environments in order to determine how this new hearing device is working. Through those tests the technician is able to program the device's software in order to make it perform as effectively as possible.

The hearing aid itself connects to the post of the prosthesis and is designed to fall off on impact. This protects both the hearing aid and the user from harm in case of a fall, car accident, etc. Powering the exterior device is a small battery which typically lasts between 6 and 12 days.

When properly programmed the single biggest benefit of the bone-anchored hearing aid is the fact that it can restore 360° hearing to most users. This is something that standard hearing aids are incapable of. In fact, in some cases users of these devices report a near perfect ability to distinguish different sounds emanating from different portions of a room just like what is possible in someone with no hearing loss whatsoever.

The Downsides

As incredible as the bone-anchored hearing aid is, it does have its downsides. First and foremost is the fact that the external device is extremely fragile and expensive. At last count the cost in the United States was approximately $4,000. That could mean a pretty hefty bill if you are the type of person who is naturally clumsy or is careless with electronic devices.

The second downside involves the risk of infection. Because the post of the prosthesis protrudes from the skin the user will always be presented with some level of infection risk. He or she is required to clean the post and the skin surrounding it on a daily basis using a soft toothbrush and a cleaning solution like isopropyl alcohol. If infection does develop around the post, it could cause further complications which could potentially involve more surgery. Fortunately, such complications are rare thanks to modern technological advancement.