Introduction
Bone-anchored hearing aids (BAHAs) are an accepted method of rehabilitating conductive hearing loss in conditions in which conventional hearing aids cannot be used. The BAHA system uses an osseointegrated titanium implant to conduct sound from a microphone-transducer unit through the temporal bone to the inner ear. Unlike conventional bone conduction hearing aids, the BAHA contacts bone without intervening soft tissue, which improves sound propagation to the cochlea.
In younger children, BAHA surgery is usually carried out as a two-stage procedure, with the fixture being allowed to osseointegrate for several months before an abutment is fitted through a skin graft. During the first procedure, it has been usual to place a reserve or sleeper fixture approximately 5 mm from the primary fixture as a backup in case the primary fixture fails to osseointegrate. The ipsilateral sleeper fixture is expensive ($1000 in the US, £298 in the UK; 2008 prices for self-tapping, flanged, 4 mm, CochlearTM fixture), is often not used, and is placed near the primary fixture in thinner calvarial bone.
For cases in which bilateral BAHAs are being considered and in which the second side is to be operated upon at a later date, we recommend placing the sleeper fixture on the contralateral side at the time of primary first-side surgery. In our series of seven cases, we found that contralateral placement of the sleeper fixture provided a reserve fixture in an optimal position, and also reduced the number of procedures for placement of a second-side BAHA.
Methods
Seven successive cases identified for bilateral bone-anchored hearing aid implantation, in which the second side was to be operated upon at a later date, were selected for the contralateral sleeper fixture technique, between 2004 and 2007. We placed a sleeper fixture on the contralateral side, using a 1.5 cm incision located at the optimal site for fixture placement.
With the patient under general anaesthesia, both sites were measured and marked through the skin with methylene blue dye on a needle. Symmetrical positioning of the primary fixture and the sleeper fixture was judged easily at the time of surgery. The child's head was turned to one side, prepared and re-draped, and a 1.5 cm, post-auricular incision was made over the intended fixture site. The fixture was placed in the standard fashion described by the manufacturer (CochlearTM, Weybridge, UK). Usually, a 4 mm-long sleeper fixture was implanted. A cover screw was attached to prevent tissue growth into the inner thread, and subcuticular 4-0 Vicryl was used for closure. The child's head was then turned to the other side, and the procedure repeated.
In older children, the primary site may be operated upon as a single stage procedure, with placement of a self-tapping fixture with abutment. The contralateral fixture is placed as described above.
Relevant literature was identified by searching Medline and Embase, using the keywords ‘BAHA’, ‘bone-anchored hearing aids’, ‘bilateral fitting’, ‘contralateral’, ‘hearing loss’ and ‘sleeper fixture’.
Results
Our paediatric cases ranged in age from five to 15 years, with a mean age of 10 years; in addition, a 20-year-old with learning disability was also treated (see Table I). Of the seven cases, three had bilateral discharging mastoid cavities, two had Down syndrome, one had Treacher–Collins syndrome, and one had a left unilateral discharging mastoid cavity and chronic suppurative otitis media in the right ear. In each case, the contralateral sleeper fixture was not needed as a backup fixture, but was used in four patients (57 per cent) as the basis for a second-side BAHA.
Table I Seven cases with contralateral BAHA sleeper fixture
No = number; bilat = bilateral; yr = years; BAHA = bone-anchored hearing aid; CSOM = chronic suppurative otitis media;
Discussion
The BAHA is indicated for treatment of conductive hearing loss cases in which conventional hearing aids cannot be used. Indications include microtia in Treacher–Collins syndrome, isolated microtia, Goldenhar syndrome, chronic suppurative otitis media and discharging mastoid cavities. In Down syndrome patients, who suffer a high incidence of glue ear, acute otitis media and stenotic external auditory meatus, BAHA can be a successful method of amplification.Reference Sheehan and Hans1
Bone conduction of sound from one source stimulates both cochleae, but attenuation by the skull can occur.Reference Stenfelt, Hakansson and Tjellstrom2 Bilateral BAHA implantation provides better sound localisation than monaural hearing and better speech recognition in both quiet conditions (diotic summation) and noisy conditions (when the speech and noise come from opposite directions).Reference Snik, van der Pouw, Beynon, Mylanus and Cremers3–Reference Dutt, McDermott, Burrell, Reid and Proops6 Bosman et al. demonstrated that sound localisation and speech recognition in noisy situations improved with bilateral amplification.Reference Bosman, Snik, van der Pouw, Mylanus and Cremers4 In the UK, it is common practice for children with bilateral conductive hearing loss to be fitted with bilateral behind-ear hearing aids. In those who require bilateral BAHA implantation, for reasons including acceptance of the device and cost, it is still more usual to fit a BAHA on one side and to plan to fit a contralateral BAHA at a later date.
In younger children, who have thinner and softer cortical bone, two-stage surgery allows time for osseointegration before the BAHA abutment is fitted. The two-stage technique described by Tjellstrom is generally used for children under 12 years of age, or in older children with cognitive difficulties.Reference Tjellstrom7, Reference Proops8 The weight of the BAHA abutment and the potential for knocking the protruding abutment are avoided during the osseointegration period in two-stage surgery. Two-stage surgery is also considered in adults with an increased risk of failure of osseointegration, such as after radiotherapy or in cases of fibrous dysplasia.
Sleeper or reserve fixtures are used in two-stage surgery to optimise the outcome. Zeitoun et al. reviewed the benefits of placing a sleeper fixture in children undergoing two-stage surgery, and noted that there may be incomplete insertion of the fixture in thin calvarial bone, or the fixture may be knocked out by injury.Reference Zeitoun, De, Thompson and Proops9 Loss of the fixture is a significant issue. One study found traumatic fixture loss in two out of 20 children under the age of five years after two-stage surgery, and in four out of 20 older children after single-stage surgery.Reference Davids, Gordon, Clutton and Papsin10
In cases of trauma or failure of osseointegration, the sleeper fixture obviates the need for a repeat first-stage procedure and consequent four- to six-month delay while osseointegration is awaited. In order to avoid this delay, it is current practice during two-stage surgery to fit an ipsilateral sleeper fixture in reserve; however, in our experience this ipsilateral sleeper fixture is not often used. At the time of writing, in our seven reported cases (see Table I), the contralateral fixture has not been needed as a reserve or backup, but it has found use in four of our patients as the basis of bilateral BAHA implantation, reducing the number of procedures these patients have needed.
