Introduction.
Originally, (conventional) bone-conduction devices (BCDs) comprised a bone
vibrator pressed against the skin in the mastoid region. This so-called
transcutaneous coupling works, but is not effective at all. Therefore, these
conventional BCDs needed very powerful amplifiers. Nevertheless, the gain and
output was limited and these devices were only applied if there was no
acceptable alternative, thus as a ‘last resort’ solution (e.g. in case of aural atresia
or chronic draining ears).
The first implantable BCD, the Baha, introduced in the late eighties, was more
powerful, owing to its (efficient) percutaneous coupling, bypassing the vibration-
attenuating skin and subcutaneous layers (Hakannson et al., 1985).
Effectiveness.
At that time, to establish the effectiveness of the Baha device, within-subject, pre-
post intervention studies were performed comparing Baha with the patient’s
own conventional BCD, and the beneficial outcomes were accepted by the
authorities as convincing evidence. Reimbursement was admitted in many
countries, e.g. by the FDA, with the restriction that the sensorineural hearing loss
component (SNHLc) had to be less than 45 dB HL.
Equivalence claims.
Since then, several new types of implantable BCDs have been developed and
marketed on the basis of presumed equivalence to Baha (e.g. implantable
transcutaneous devices). These devices have achieved approval based on the
assumption of equivalence, rather than based on clinical trials demonstrating
their effectiveness, and the same restriction as applied for Baha (SNHLc <45 dB
HL) was claimed. However, these implantable transcutaneous BCDs cannot
compete with Baha regarding gain and output (Chapter 3 and 4.1, this website;
van Barneveld et al., 2018); this means that the <45 dB HL criterion is an
overestimation. Table 4.1, Chapter 4.1, this website, presents the more realistic
criteria, per device type, based on objective data, (partly) validated by published
clinical data.
Widely, the equivalence rule is under debate owing to serious problems with
other implants (breast implants, pace makers etc.) that were allowed to the
market based on the equivalence principle, without appropriate effectiveness
studies (e.g. https://www.theguardian.com/society/2018/nov/25/revealed-
faulty-medical-implants-harm-patients-around-worldreference). To deal with
this public debate, before the introduction of a new device, effectiveness studies
should be performed aiming at the capacity (in audiological terms) and stability
of that implantable hearing device.
References
Håkansson B, Tjellström A, Rosenhall U, Carlsson P. The bone-anchored hearing
aid. Principal design and a psychoacoustical evaluation. Acta Otolaryngol.
1985;100(3-4):229-39.
van Barneveld DCPBM, Kok HJW, Noten JFP, Bosman AJ, Snik AFM. Determining
fitting ranges of various bone conduction hearing aids. Clin Otolaryngol.
2018;43(1):68-75.