Implanted hearing aid uses bone conduction to bypass defective middle ear
There may soon be help for people who have been rendered functionally deaf by problems of the middle ear. Researchers from Sweden’s Chalmers University of Technology have developed an implant that bypasses the defective middle ear, transmitting sounds to the inner ear by sending vibrations right through the skull bone.
Developed by a team led by Prof. Bo Håkansson, the two-part Bone Conduction Implant (BCI) is intended mainly for use on “individuals who have been affected by chronic inflammation of the outer or middle ear, or bone disease, or who have congenital malformations of the outer ear, auditory canal or middle ear.” Regular hearing aids typically don’t work for such people, as they’re usually designed for dealing with problems of the inner ear.
The implant itself is a little less than six centimeters (2.4 inches) long, and is attached behind the ear, under the skin, directly into the surface of the skull.
It’s paired with an external sound processor, which is what actually receives sounds from the outside world. This unit is placed against the skin, directly adjacent to the implant, and is held in place by magnets in both devices. An inductive coil in the implant allows it to receive sound transmitted through the skin, from the processor. The implant then uses a miniature quadratic loudspeaker to relay those sound vibrations into the bone of the skull, through which they travel to the inner ear.
Sounds are picked up by the processor (top), transmitted through the skin to the implant, and then transmitted by the implant into the skull bone
Previous bone conduction-based hearing aids have required the patient to have a titanium screw permanently protruding from the skull through the skin, to which the external device itself is attached. Such a set-up can result in infections, and the possibility of the screw falling out. With the BCI, the skin is left intact (once it’s healed up, after the insertion of the implant), and the processor can simply be pulled off when not needed.
A deaf test subject received a BCI last month, although Håkansson and his team are still waiting for the incision to heal before turning the accompanying processor on. Sahlgrenska University Hospital's Måns Eeg-Olofsson, who has been in charge of the medical aspects of the research, performed the procedure.
If it works as hoped, clinical trials will follow, with possible widespread use of the BCI within one to two years.