There are a number of different devices available that fall into this category. Essentially they all rely on the fact that bone is an excellent conductor of sound. Available devices include;
This has two forms, the traditional system were a small abutment is attached to the bone behind the ear and protrudes through the skin. A sound processor clips on to the abutment. It contains a transducer (sound source), which recreates the sound waves and then transmits them via the bone of the skull to the inner ear.
This device differs from the traditional BAHA above in that the skin is intact with no abutment protruding through the skin. Instead a magnet is attached to the skull and the skin closed over it. Once the wound has healed the same speech processor can be attached using a magnet. This has the advantage of having a lower risk of infection and a lot less maintenance. The sound transmission however is not quite as efficient.
More information can be found at the South Australian Cochlear Implant Centre
This device relies on the same properties of sound conduction of the bones of the skull. It uses a different approach however in that the transducer (sound source) is implanted surgically into the mastoid bone behind the ear. The sound processor attaches through the intact skin via magnets.
The sound processor transmits information to the internal transducer, which then creates the sound waves.
more information can be found here;
These devices can be very useful in a number of situations.
They are particularly useful when there is reasonable residual hearing but conventional hearing aids cannot be used due to poor fit or frequent infections when hearing aids are used.
They can also be useful in severe single sided deafness. In this scenario they are actually transmitting sound to the normal ear on the other side. This does not create true stereo hearing but gives 360° sound awareness. They will probably be used less in this situation as cochlear implants are now being offered for single sided deafness.
It is a complex area and the choice between these different devices will depend on the individual, their residual hearing, and their anatomy and individual preferences.
As such the decision will be reached after several in-depth consultations both with myself and also our implant audiologists.