- 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.
- Transcutaneus abutment
- 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.
- Surgical technique:
- 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.
- COMPLICATIONS
- 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
- Air conduction aid:
Write short note on BAHA. Mention the various components of BAHA. Is the outcome of BAHA is better than that of AC hearing aids?
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