Write short note on BAHA. Mention the various components of BAHA. Is the outcome of BAHA is better than that of AC hearing aids?

• 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 :
  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