Bone anchored hearing aids (BAHA) are implantable hearing aids which works by directly stimulating inner ear via bone conduction.
It is the registered trademark of bone conduction hearing aid manufactured by Cochlear TM.
Its components are:
Titanium screw that becomes osteo-integrated in the skull bone behind the ear.
Ear level sound vibrator
The BAHA can also be fitted to headband and this is recommended in infants with congenital atresia unit about three years of age when they can undergo surgery.
Indication of BAHA :
Absolute: b/l canal atresia
Chronic ear infection when insertion of ear mould is a problem and discharge.
U/L deafness which cannot benefit from use of regular hearing aids
Eligibility for BAHA:
There should be adequate bone-conduction, pure tone threshold: BC averaged over 0.5, 1,2, and 3 kHz should be equal or better than 45 dB Hearing Loss (HL) for ear level aid and better than 58 dB HL for body level aid.
BC should be poorer in high frequencies compared to low frequencies.
Poor speech comprehension in speech audiometry is a contraindication.
LA or GA
Site for the implant is identified behind the ear and marked
A split thickness skin graft is raised using a custom-made dermatome
The subcutaneous tissue is removed leaving the periosteum intact
A countersunk drill is used to prepare the site to receive the implant
The titanium implant is slowly inserted under constant irrigation to avoid burning
The split skin graft is returned and fitted over the abutment in one staged. In two staged abutment is fitted after three months of implantation.
Damage to dura: rate, in children with craniofacial abnormality
Crusting and inflammation → granulation tissue(8%)
Falling out of screw (0.6%) or loosening of abutment (5%) : children because of thin skull bone and trauma.
OUTCOMES COMPARED TO :
Air conduction aid:
Acoustic benefits is marginal, discharged improved
If the patient is benefiting acoustically from an air condition-aid then disability from wearing of an ear mould has to be sufficiently great for BAHA to be substituted as this may give poor acoustic benefit.
B/L BAHA in B/L CHL: better than monoaural
U/L BAHA in B/L mixed impairment: provided a good acoustic seal by the air conduction aid and mould, changing to BAHA might result in poorer hearing benefit
U/L BAHA in U/L CHL: alternative if problem with air mould
U/L BAHA with B/L SNHL: less audio metric benefit
U/L BAHA in U/L total impairment: no good evidence to support the use of BAHA.
BAHA and OTOLOGICAL SURGERY: comparable to benefits of middle ear surgery