Bone Anchored Hearing Devices / Aids
BAHD - Introduction
The first thing to say is that BAHD is the term that should be used for hearing devices that are implanted into bone, however, it is common to hear the term BAHA. Strictly, BAHA (bone anchored hearing aid) is the proprietary term for the implant made by the company Cochear. It's rather like calling a vacuum cleaner a Hoover, or a ballpoint pen a Biro. Despite this, and like those other brand names, BAHA has become common parlance.
BAHDs are implanted into bone and bind to the bone through a process called osseous-integration. The devices have three parts: an implant, an abutment, and a processor.
The implant is the inner most part that integrates with bone. The abutment attaches to the implant with a screw and sticks out through the skin. The processor clips onto the abutment and is the hearing aid itself. Below are two pictures, one showing the three parts of the system and one showing it implanted into bone.
The next image is of an abutment sticking out through the skin behind the patient's ear. You can see the arms of their glasses to the right of the picture. The processor clips onto the abutment.
Why do we do it?
The operation is offered to provide hearing to patients that cannot wear a conventional hearing aid but who need amplification of sound. This situation arises when the ear canal is too narrow or is absent, when the ear is chronically infected and discharges a lot, and it can be used for certain types of middle ear hearing loss too.
What are the alternatives?
A BAHD is usually discussed when all other options have failed. The Audiology Department will try to use a standard hearing aid wherever possible as these do not require an operation or expose the patient to the risks of an operation. However, for some patients standard aids are not suitable and an alternative must be found.
Is it the same as a cochlear implant?
No. A cochlear implant is used when there is severe or profound inner-ear hearing loss. A BAHD is used for mild to moderate middle and outer-ear hearing losses.
How long does it take?
Most operations are done within an hour. It can be done under general or local anaesthetic depending on the other medical needs and preferences of the patient.
How long does it take to recover?
Recovery from the procedure is quick with the majority of patients going home on the day of surgery. Healing takes a little longer.
The implant has a dressing placed over it at the time of surgery and this is removed after a few weeks. After around 4 to 6 weeks the implant will have integrated with the bone and the hearing aid can be applied.
What are the benefits of surgery?
The most obvious benefit is that the surgery improves hearing for an ear that won't take a conventional hearing aid. By being attached to the skull and not placed into the ear canal, it also can allow infections to settle.
Furthermore, as it is not an operation on the ear itself, there is no risk to hearing.
What are the risks?
All operations have risks. For BAHD implantation these are:
1. Infection in the skin around the implant. A degree of this is common and it can happen anytime after implantation. BAHDs must be looked after rather like teeth do - they need cleaning daily or else the flesh around them becomes infected and swollen.
2. Pain is usually associated with infections around the implant. However, a few patients get pain without infection and rarely it will be necessary to remove the BAHD.
3. The abutment can become loose with usage. This happens in about 10% of patients and is easily reversed in clinic by re-tightening it.
4. As with any hearing aid, the audiologists will work with the patient to get the best out of the hearing processor.