Background
Hearing impairment is the most common physical handicap in the in industrialized world. There are two different reasons for poor hearing. One is due to lack of function in the inner ear, the cochlea, the other when the sound has problems in reaching the nerve cells of the inner ear. An example of the first is the age-related hearing loss. A patient born without external ear canals is one example of the latter and here it is obvious that a conventional hearing aid with a mould in the ear canal opening is not possible to use. These patients often have a normal inner ear function as the external ear canal and the inner ear are developed at different stages during pregnancy. As the inner ear is normal, sound conducted via the skull bone could give normal/near normal hearing.
A vibrator with a steel spring over the head or in heavy frames of eyeglasses pressed towards the bone behind the ear has been used to bring sound to the inner ear. This has however several disadvantages like discomfort and pain due to the pressure needed. The sound quality is also impaired as much of the sound energy is lost in the soft tissue over the skull bone. This is especially true for the higher sound frequencies so important for speech understanding in noise.
Patients with chronic ear infection where the drum and/or the small bones in the middle ear are damaged often have hearing loss but difficulties to use a hearing aid fitted in the ear canal. Direct bone conduction through a vibrator attached to a skin penetrating implant will overcome these disadvantages.
In 1977 the first three patients were implanted with a bone conduction hearing solution by Dr Anders Tjellström at the Ear –Nose- and Throat department at Sahlgrenska University Hospital in Gothenburg, Sweden. A 4 mm long titanium screw was inserted in the bone behind the ear and a specially designed bone conduction hearing aid was attached. The initial results were very good and since then about 100,000 patients all over the world have been treated according to this principle.
The implant in the bone is made of titanium and will osseointegrate according to the research performed by professor Per-Ingvar Brånemark. The hearing instrument is impedance matched and developed by professor Bo Håkansson at Chalmers University of Technology in Gothenburg, Sweden under the name of Baha. The initial design has been refined and improved first by the industrial partner Entific and later by Cochlear Bone Anchored Solutions both in Gothenburg. Since 2009 the Danish hearing aid company Oticon has also developed a device based on the same principle. Osseointegration has been defined as the direct contact between living bone and an implant that can take a load. No soft tissue at the interface.
With Entific selling the trademark to Cochlear, Cochlear turned the acronym BAHA into a full-fledged trademark name, so to avoid unnecessary confusion between the "BAHA" as a type of sound processor and technology and the Baha as an hearing aid. This choice was motivated by the policy of insurances to distinguish between sound processors and a full bone conduction implant system for coverage's purpose. The other major brand of bone conduction device is manufactured by well-known hearing aid manufacturer, Oticon Medical.
Read more about this topic: Bone Anchored Hearing Aid
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