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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  • 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.
    • 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.
    1. 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.
    2. B/L BAHA in B/L CHL: better than monoaural
    3. 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
    4. U/L BAHA in U/L CHL: alternative if problem with air mould
    5. U/L BAHA with B/L SNHL: less audio metric benefit
    6. U/L BAHA in U/L total impairment: no good evidence to support the use of  BAHA.
    7. BAHA  and OTOLOGICAL SURGERY: comparable to benefits of middle ear surgery
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