Bone Anchored Hearing Aids (BAHA)

Bone Anchored Hearing Aids (BAHA). The bone anchored hearing aid or BAHA is a small vibrator that can be reversibly plugged onto a titanium screw that is implanted behind the ear. It transduces sound into vibration of the screw and stimulates the cochleae by means of the bone conduction pathway. The main indications are conductive hearing loss or mixed hearing loss with a moderate perceptive component when classical hearing aids cannot be worn, and rehabilitation of unilateral deafness. The indications, contra-indications, surgical technique and results are discussed in this paper. 46 G. E. J. Forton and P. H. Van de Heyning of transcutaneous devices such as a bone conduction hearing aid incorporated in a headset or spectacles. Most interestingly, acoustic feedback or Larsen’s effect does not occur with the BAHA . Indications and patient selection criteria 1. Audiological indications • A BAHA can be used in all cases of conductive hearing loss, even with an additional sensorineural hearing loss of up to 45 dB HL. For the BAHA Compact, the average bone conduction threshold should be better than or equal to 45 dB HL (measured at 500 Hz, 1 kHz, 2 kHz and 3 kHz). Recently, a BAHA with digital sound processing, the BAHA Divino, has been released. Its maximal amplification is identical to the BAHA Compact, but is has automatic gain control (AGC) capability and two microphones: an omnidirectional microphone and a directional front-facing microphone. The BAHA Cordelle II is a body worn device and has the more powerful K-amp amplifier, which yields an output that is on average 13 dB stronger than the BAHA Classic. • A maximum speech discrimination score better than 60% (phonetically balanced CVCwords scored on phonemes). • For single sided deafness, the pure tone average air conduction threshold of the hearing ear should be better than or equal to 20-25 dB HL (measured at 500 Hz, 1 kHz, 2 kHz and 3 kHz). • Using a test band or rod, the candidate can evaluate the sound quality and possible gain of the BAHA device prior to implantation. Pure tone and speech audiometry can be carried out and thus realistic expectations are obtained. 2. Otological indications • Congenital malformations with agenesis or atresia of the middle or external ear. In cases of microtia or a completely absent pinna, an epithesis can be provided with two additional fixation points. • Chronically draining ears that do not allow use of an air conduction hearing aid, such as mastoidectomy cases with poor sound transmission and recurrent problems of humidity, discharge or infection in case of occlusion by a hearing aid or recurrent external otitis. • Patients with unilateral conductive hearing loss (and not appropriate for or refusing surgical correction) or unable to be aided by conventional air conduction hearing devices. • Congenital or acquired unilateral total deafness, e.g. after acoustic neurinoma surgery where preservation of hearing was not possible. 3. Contraindications • An average bone conduction threshold worse than 60 dB HL (measured at 500 Hz, 1 kHz, 2 kHz and 3 kHz). • Mentally retarded or uncooperative patients; drug addicts... • Very small children (<2 years). In the USA, the lower age limit is 5 years.