The document discusses bone conduction hearing devices (BCHDs) and their components, functioning, advantages over conventional hearing aids, and surgical classifications. It provides details on the normal routes of bone conduction, components of acoustic and implantable hearing devices, pathophysiology of cochlear deafness addressed by implantable devices, and terminology used. It also outlines clinical indications and criteria for BCHDs as well as some limitations.

1. Dr. Kanu Lal Saha
Associate Professor
Otology Division
Department of Otolaryngology and Head-Neck Surgery
Bangabandhu Sheikh Mujib Medical University, Dhaka,
Implantation Otology
Bone Conduction Hearing Devices (BCHDs)

2. Routes of Bone conduction
Three normal routes of bone-conduction of sound
vibrations to the inner ear
Route A: via the skull bone
Route B: via the ossicular chain
Route C: via the external auditory canal.
In a normal ear, when the skull is vibrated by bone-conduction, it not only
vibrates the cochlea via route A, but it also vibrates the tympanic
membrane and ossicular chain (route B) and the air in the external
auditory canal (route C).

3. Introduction
• The incoming sound vibrates tympanic membrane easily.
• The fluid-filled inner ear, which offers extremely high resistance (impedance) to an acoustic signal.
• The function of the middle ear is to force the inner ear to vibrate in response to incident sound by amplifying the
sound and by a process called impedance matching.
• Through impedance matching, even small sound pressure levels can induce a traveling wave within the inner ear.
• This traveling wave is too weak to stimulate the inner hair cells, which cannot “hear” sounds lower than 50–60 dB.
• The function of the outer hair cells is to amplify the tiny traveling wave 100–1000 times, enabling them to stimulate
the inner hair cells so that an acoustic signal is perceived . This mechanism is called the cochlear amplifier (CA).

4. Components of Acoustic Hearing Devices(ACHDs)
Hearing aids require
• a microphone to pick up the sound and convert it to
an electrical signal, electronic circuitry to amplify and
treat the signal
• a speaker—called a “receiver”—to convert
the signal back to sound waves.
• a battery to power the device.

5. Conventional Hearing Aid
• Conventional hearing aids operate with acoustic transducers.
• They transform sound into electrical signals, process and amplify the signals, and convert them back
into sound.
• Has tiny speaker that limit the hearing aid- amplified acoustic signal compared with the original
acoustic signal, although the processed signal is louder.
• The characteristic occlusion of the external ear canal can so alter it acoustic properties
• The output signal will undergo considerable distortion in the occluded ear canal.
• This distortion effect cannot always be corrected by adjusting the fit.
• The result for the patient may be an unintelligible speech signal at the tympanic membrane.

6. Conventional Hearing Aid- Disadvantages
 A certain percentage of hearing aid wearers perceive the sound fidelity and speech intelligibility of their devices as
unsatisfactory.
 The earmold can create an unpleasant occluding sensation in the ear canal, and some patients have recurrent bouts of
otitis externa.
 Acoustic feedback can occur between the speaker and microphone at high gain. In some hearing
aids, feedback can be eliminated by turning down the gain.
 Wearers are vulnerable to stigmatization, ridicule, and discrimination. Some patients stop wearing their hearing aid
because they feel stigmatized. Other experience social and/or professional ridicule and discrimination.
 Difficulties can occur with everyday activities and situations (swimming, showering, wind, rain).
Some patients cannot be rehabilitated to their jobs (e. g., athletic instructors, swimming instructors, cooks, secretaries,
receptionists, schoolteachers, doctors, workers exposed occupationally to heat, moisture, dust, etc.).
Despite good audiologic results, psychosocial rehabilitation may be unsatisfactory, resulting in social withdrawal and low
self-esteem.

7. Pathophysiologic aspects of Implantable Hearing Devices
The great majority of patients with sensorineural hearing loss have an underlying insufficiency of the cochlear amplifier(outer hair
cells).
 The cochlear amplifier is responsible for
(1) hearing sensitivity
(2) frequency selectivity
(3) the production of otoacoustic emissions
 Manifestation of failure of the cochlear amplifier:
a. positive recruitment
b. a partial or complete loss of otoacoustic emissions
c. raised threshold (hearing loss), and loss of speech discrimination.
In patients with cochlear deafness or very profound hearing loss, the damage goes considerably beyond failure of the cochlear
amplifier and includes a complete functional loss of the inner hair cells .

8. Implantable hearing device
Implantable hearing devices have several advantages over a conventional hearing aid
• Better sound fidelity over the entire audible range of frequencies
• Ear canal is left open (no earmold)
• No feedback
• contribute to directional hearing and the suppression of unwanted ambient noise.
• Not interfere with bathing, showering, hair drying, diving, etc.
• The implant is operational during sports activities and, if desired, during sleep (e.g., hotel wakeup call, mother wants to hear. baby).
• Vocational rehabilitation, even in difficult cases.
• Outwardly invisible
• Not irritating to tissues
• Good longevity
• No predisposition to infection

9. Components of Implantable Hearing Devices
An active hearing implant consists of four functional components:
1. Sensor for receiving sound (Microphone)
2. Electronic processor and amplifier
3. Electromechanical transducer (vibrator, actuator) which converts the audio
signal into a vibratory stimulus. The transducer may have an electromagnetic or
piezoelectric operating principle.
4. An energy source

10. Terminology in Implantable devices
Active implant : Implantable hearing devices having an electric power source that is independent of the body.
CIs are active implants. Since active hearing implants are controlled electronically, they are also
known as electronic hearing implants.
Passive implant : Implantable devices don’t require power/battery
e.g.- Stapes prostheses, TORPs, and PORPs
Fully implantable hearing device : If all four components are implantable, with no visible
components in the external ear canal, the device is described as fully implantable or a
total implant. The TICA LZ .
Partially implantable hearing device : With a partially implantable device, one or more of the components are
visible externally on the head or body or are placed within the external ear canal

11. Amplifier implant (AI)
The amplifier in an implantable hearing aid for patients with moderate to severe sensorineural
hearing loss partially replaces (for hearing sensitivity) the physiologic cochlear amplifier.
Rather than being amplified in the inner ear, the acoustic signal is amplified in the implant.
The amplified micromechanical signal that is generated by the implant bypasses non -functioning
outer hair cells and directly stimulates the inner hair cells of the inner ear.
This type of implantable hearing device, designed to function as a micromechanical replacement for
the cochlear amplifier, is called an amplifier implant (AI).

12. Suggested nomenclature for Active Hearing Implants
• Previous nomenclature of most active hearing implants (e. g., CI, MEI, BAHA) is anatomically derived-implants are
named for their implantation site.
• The result is a variety of device names that give little information on their functions or indications. It is better to
designate a device according to its function.
• ITI (impedance transformation implant) for conductive hearing loss. This device does not replace the
physiologic amplifier. BAHA, Rion MEI .
• AI (amplifier implant) for recruitment-positive sensorineural hearing loss. The function of an
AI is to replace the function of the cochlear amplifier and deliver a signal to the inner hair cells. P-AI: Vibrant
Sound bridge, Otologics MEI, BAHA Cordelle.
• CI (cochlear implant). The CI completely replaces the inner ear, including the inner hair cells .
• ABI (auditory brainstem implant). An ABI replaces the inner ear and the acoustic nerve by directly
stimulating the auditory nucleus in the brainstem.

13. Surgical classification of BCHDs
Type of device Skin relationship
Percutaneous Passive
Transcutaneous
Passive (skin drive)
Active (direct drive)

14. BCHDs
• Baha (produced by Cochlear Americas)
• Ponto (produced by Oticon)
• Alpha 1 (produced by Sophono)
• The Ponto utilizes an implantable abutment while
the Sophono is an abutment-free aid that is placed
in the bone behind the ear.
• Baha has both an implantable (Baha 4 Connect)
and an abutment-free (Baha 4 Attract) device that
stays coupled via magnetic attraction.

15. Clinical indications of BCHDs
Conductive and mixed losses
• congenital causes such as atresia or microtia
• acquired causes such as chronic otitis media or ossicular pathology
• chronic discharging ear (such as chronic suppurative otitis media (CSOM) or recurrent otitis externa)
• inability to wear a hearing aid following radical mastoid surgery
• unilateral mixed hearing loss.

16. Single-sided deafness – sensorineural or conductive
• Trauma resulting in hearing loss.
• Unsuitable ear canal for a conventional hearing aid, e.g.
– in a radical mastoid cavity
– an extremely narrow ear canal
– ‘blind sac’ ear canal closure
– lateral temporal bone resection
– extensive cranial base surgery.

17. Criteria for BCHDs
1a :Patients with unilateral or bilateral conductive or mixed hearing loss within the manufacturer’s fitting criteria
AND
Stable BC thresholds (≤15dB deterioration in >2 frequencies in a 2-year period)
OR
1b. : Unilateral sensorineural hearing impairment (including SSD) where the better ear has BC hearing thresholds
within the manufacturer’s fitting criteria including SSD
AND
2 The patient has trialled an ACHA or wireless CROS/ BiCROS hearing aid for a minimum of 4 weeks, or is
anatomically or physiologically unable to undertake a trial of an ACHA
AND
3 Has trialled a BCHD on a softband or headband for a minimum of 14 days and shown benefit in speech tests.

18. Limitations of BCHDs
Not recommended
• patients with a bone disease that is unable to support an implant
• patients who have a sensitivity or allergy to the materials used
• patients with physical, emotional or psychological disorders that, despite suitable
treatment and support, would interfere with surgery or the ability to allow suitable
rehabilitation such that significant benefit would be unlikely.

19. BCHDs without surgery
Hard and soft headbands are available for Baha, Ponto, and
Sophono processors, making it possible for young children,
and occasionally adults, to use the bone-conduction hearing
systems without having surgery.

20. Trial processors - passive transcutaneous format
Sound Arc Cochlear ADHEAR

21. Percutaneous(bone-anchored) hearing devices

22. BCHD(Ponto)

23. BCHD(passive transcutaneous device)
Sophono BAHA ATTRACT

27. Active transcutaneous BCHD

29. Bonebridge

30. Bonebridge

31. Special attention
Some devices and device components cause difficulty with MRI scanning.
Devices may also cause issues with airport security systems.
Make sure clinicians, patients and parents are aware by consulting individual
manufacturer’s guidelines.

32. THANK YOU
Otology Dr Kanu BMMU Bangladesh
www.drkanuotology.com
drklsaha@gmail.com