Technical development of the BAHA
- An historical review

By
 

Bo Håkansson, PhD
Professor in Biomedical Engineering

Contact address:

Chalmers University of Technology
Department of Signals and Systems
S- 41296 Göteborg
Sweden

Mail: boh@chalmers.se

Webb: www.chalmers.se

Background:

In the early 1950’s Prof Per Ingvar Brånemark made the remarkable and important initial discovery that titanium was accepted by living tissue as if it were part of its own structure. A thorough historical description of Brånemarks work can be found in Williams, E, 1992.

As in many medical fields it usually takes very long time between the initial discovery and the moment the treatment or product becomes available for general use. This was especially true when the new treatment involved a permanent penetration of soft tissues, first intra orally in dental implants and then extra orally in bone anchored hearing aids, and various facial prosthetic treatments. Historically, at that time when Brånemark made his first experiments, several attempts had failed to provide a long lasting anchorage to the bone and a subsequent permanent skin penetration.

Hence, it took until 1965 before the first patient Gösta Larsson successfully received titanium implants for a dental restoration. Interestingly enough Gösta also received a titanium implant for a Bone Anchored Hearing Aid (BAHA) twenty five years later in 1990. Unfortunately, Gösta passed away earlier this year (2006) at the age of 75, still using his implants.

In 1977 it was suggested by Brånemark and his associates at the ENT department at Sahlgrenska University Hospital that bone anchored and skin penetrating implants probably could improve the situation for patients with a significant conduction hearing loss who previously had to rely on conventional bone conduction (BC) hearing aids.

In bone conduction devices the sound is transmitted through the skull bone basically directly to the inner ear thereby by-passing the outer and middle ear. Thus this principle offers sound amplification for patients basically suffering from hearing disorders in the outer and middle ear i.e. typically chronic middle ear infections or atresia where a conventional air conduction hearing aid is contra indicated. Such devices were previously the only available alternative and consists of a small bone conduction transducer (sometimes just called “Bone conductor”) that is pressed against the skin over the skull bone by means of a steel spring arrangement and having the microphone amplifier attached to the opposite side (or body worn) with regard to the transducer as is illustrated in Figure 1 (the left picture is from our first publications and reminds of the pre PC era when all pictures were sketched or drawn by hand). For some patients these conventional BC devices worked so poorly that they rarely used them. Another alternative, and for some patients regarded as a more aesthetic one, is to incorporate the transducer (-ers) and the electronic components into the frames in a pair of glasses. That solution often suffers from poor output power and poor contact between the transducers and the skull.

Page 1      Page 2      Page 3      Page 4      Page 5

Page 6      Page 7      Page 8      Page 9      Page 10

Page 11    Page 12    Page 13    Page 14    Page 15