Bone Conducting HearingAid SolutionsDr Zeeshan Ahmad Department of ENT,M.S.(ENT,PGY1) NMCH,Patna. 27-09-2012
Hearing impairment is a common occurence.Most patients have abnormality of cochlear function and can be treated by use of conventional hearing aid.However, a significant number have conductive cause.Many of these can also be treated by conventional hearing aid but a proportion do not tolerate mould or insert in ear canal, so alternative means must be considered.
What is Hearing aid? A hearing aid is a battery-powered, electronicdevice that makes listening easier for peoplewith a hearing loss. A hearing aid consists of amicrophone, an amplifier and a receiver. Themicrophone picks up sounds in your acousticenvironment and turns them into electronicsignals. The amplifier selectively amplifies theacoustic electronic signals. The receiver is avery small speaker that changes the electricsignals back to sounds and delivers the sound tothe ear.
History1551- Bone conduction device consisting of metal shaft or spear.1670- Sir Samual Moreland, England invented a large speaking trumpet.1892- first patent for electric hearing aid in the U.S.1912- first volume control for a hearing aid.
History Contd….1931- first electric hearing aid eyeglass patent1937- first wearable vacuum tube HA in US1953- first all-transistor hearing aid1987- first commercially available implantable hearing aid system.1997- FDA approved BAHA®Recently- Oticon implants
MECHANISM of BONECONDUCTION HEARINGVibration of bone of skull is coupled to soft tissues of ear canal. More when ear canal is occluded.Some of sound energy transmitted directly to ossicular chain.Alternate compression and expansion of cochlear shell by vibratory forces on bone.
The BAHA ®BAHA® is the trade namefor bone anchored hearingaid system available FromCochlearTM.
BAHA system is comprised of threeparts: Titaniumfixture(3) Connecting abutment(4) Detachable sound processor(6)
How does it Work? The processor receives sound through the abutment and sends it to the functioning cochlea using the skull as a pathway to bypass the outer and middle ears
CandidatesChronic otitis media Acoustic neuromaCongenital aural Neurologic atresia degenerative diseaseMicrotia Meniere’s diseaseCholesteatoma Viral infectionMiddle ear Trauma dysfunction or disease
PrerequisitesMixed or conductive hearing lossBone conduction pure-tone average in the indicated ear is greater than or equal to 45 dB HLMonosyllabic word discrimination score ≥ 60%For single sided DeafnessFor bilateral fittings – candidates must have symmetrical bone conduction pure-tone averages between earsAge > 5 years
To anticipate a "high success rate" with BAHAPatients should have a PTA less than 45 dB, although improvements in hearing should still be expected for a PTA of up to 60 dB.(Hakansson B, Tjellstrom A, Carlsson P: Percutaneous vs. transcutaneous transducers for hearing by direct bone conduction. Otolaryngol Head Neck Surg 1990; 102:339-344.)
Operative TechniqueA. Posterior-based skin flap is elevatedB. Flap is thinned until all hair follicles are removed fromthe flap centerC. Soft tissues beneath and adjacent to the flap are excisedto create a smooth transition from surrounding tissue tothe thin central skin flap
Operative TechniqueD. 3- to 4-mm hole is drilled in mastoid or retromastoidcortex.E and F, A countersink creates a recessed surface forimplant placement.
Operative TechniqueG. The hole is tappedH. Titanium screw is implantedI. Titanium screw is tightened in place
Operative TechniqueH/I. The titanium screw is tightened into placeK. The skin flap is replaced
Operative Technique L/M. Metallic abutment for later attachment of thevibrating external hearing aid is attached to the screwN/O. A healing cap is placed to apply pressure to the skinflap
Perioperative Complications with theBone-Anchored Hearing AidLoss of Skin GraftGrowth of skin graft over the abutmentImplant extrusionInfection
The most important factor inobtaining a trouble-free bone-anchored hearing aid (BAHA) site is:A. Having thin, immobile, hairless skin around the abutmentB. Using a 4-mm fixture flangeC. Using a longer abutment – The longestD. Performing surgery in two stages
To Prevent Loss of Skin GraftHave thin, immobile, hairless skin around the abutment - This allows for placement of the fixture in a tissue bed that has minimal local tissue reaction to the implant and thereby minimizes chance of skin graft loss, infection or extrusionEnsure that the skin graft is firmly attached to the underlying periosteumEnsure that the fixture and skin penetrating abutment are firmly secured
To prevent growth of skin graftover the abutmentUse longest implant possibleObtain adequate removal of surrounding soft tissueApproximate the surrounding skin edges to the periosteum
To prevent implant extrusionAllow patients with poor wound healing and thin bones to have six months of osseointegrationFix any coagulopathies that the patient may have pre-operativelyMaintain proper hemostasis to prevent hematoma formationUse a 4-mm fixture if there is bone still present at the bottom after using a 4-mm drill guidePatients with thin, brittle bone should have a two stage surgery