Erfahrungen mit dem teilimplantierten Knochenleitungshörgerät B.A.H.A.

Abstract

Semi-implantable bone conduction hearing aids of the type Bone Anchored Hearing Aids (B.A.H.A.) consist of an external vibrator hearing aid that is attached to a titanium screw implanted in the mastoideal bone behind the ear by means of a transcutaneous connector. In this way sound waves are transmitted directly to the bones of the skull, from where they are conducted to the cochlea. The primary indication for a semi-implantable bone conduction hearing aid is hearing loss due to conduction failure that is not surgically correctable. This may be caused, e.g. by ear canal atresia and other malformations of the external auditory meatus and of the middle ear, by chronic ear infections or by persistent high grade conduction hearing impairment after radical mastoidectomy. Today B.A.H.A.'s largely replace the less convenient conventional bone conducting hearing aids as hearing glasses or hearing bands, in which a vibrator is pressed against the skull. In conduction hearing impairment on both ears B.A.H.A.'s can be implanted bilaterally and thus binaural hearing with sound source localisation are made possible. A novel application is in cases of unilateral deafness, where the device is implanted on the side of the deaf ear and the amplified sounds are transmitted through the skull to the side of the hearing ear. Here it serves as a substitute for a CROS hearing aid. In adults the implantation is performed under local anesthesia as an out-patient procedure. Implantation may be undertaken under general anesthesia on children after two years of age. In Berne, B.A.H.A. bone conduction hearing aids have been implanted in 112 patients (ages 2-82 years) in the past 13 years. The operations have proved simple and without intra-operative complications. The long-term post-operative incidence of complications was low. The transcutaneous screw caused only isolated cases of transient skin reactions or local infections. In 7% of cases, rejection of the implant or a traumatic loosening of the screw required a reimplantation procedure. Over 90% of patients reported themselves satisfied with their partially-implantable B.A.H.A. hearing aids.