Bone Conduction Implants

Opening New Horizons in Hearing Rehabilitation

Untreated hearing impairment can result in disability and handicap, which ultimately reduces a patient’s quality of life. Some patients have conductive pattern hearing loss and are unable to wear conventional hearing aids due to chronic ear diseases.

Bone conduction implants (BCIs) are a type of implantable hearing aid that have opened up new horizons for hearing rehabilitation options in these patients. Another group of patients who can benefit from BCIs are those with unilateral hearing loss.


 

Much of our day-to-day communication is verbal. Communication is dependent on our ability to verbalise and understand spoken language. Both of these functions are actually dependent on our ability to hear with our ears. Development of our speech and language was possible because of our ability to hear, listen and understand in early childhood.

Hearing impairment, if left untreated, will result in communication difficulty. This disability can lead to decreased participation and opportunities in life, for example, in education and employment, with a consequent reduction in quality of life. Most patients with hearing impairment can benefit from the use of conventional hearing aids. Conventional hearing aids work by amplifying sounds before they get to our cochlear or inner ear.

DEFINING Hearing and Hearing Impairment

Sound travels as a form of kinetic energy through the air. Our cochlear is actually a fluid-containing organ.

Sound is captured and amplified by our ear drum and ossicular chain and sound kinetic energy in the air is converted into sound kinetic energy in the fluid of the cochlear. Within the cochlear, sound kinetic energy is converted into electrical signals that our brains can decipher.

There are two main types of hearing impairment, sensorineural and conductive. Sensorineural hearing impairment is the most common type and a manifestation of any decline in the function of our cochlear or its nerve supply. This can occur due to ageing, ototoxicity, excessive noise exposure, infection, inflammation or trauma.

Conductive hearing impairment occurs when there is compromised transfer of sound energy from air to the fluid of the cochlear. Conductive hearing loss can be caused by problems with the external ear canal, ear drum and/or ossicular chain. Ear canal problems include narrowing or atresia of the ear canal, which can be either congenital or acquired. Ear drum problems include perforation, retraction, fluid accumulation, abnormal thickening or scarring. Ossicular chain problems include ossicular chain discontinuity or stiffening secondary to infection, inflammation or trauma.

Some patients may experience a combination of sensorineural and conductive hearing impairment.

Implantable Hearing Aids

Conventional hearing aids tend to work well for patients with pure sensorineural hearing impairment, but less so for patients with conductive or mixed pattern hearing impairment. The ear abnormalities responsible for the conductive hearing loss actually act as physical barriers for the efficient transfer of sound kinetic energy in the air to the fluid within the cochlear.

Bone conduction implants (BCIs) are implantable hearing aids that work by transferring sound air kinetic energy into sound kinetic energy within the bone. We are familiar with the concept of the bone being an excellent sound conductor during tuning fork tests.

 

 

This bone kinetic energy is then converted into fluid kinetic energy within the cochlear, with subsequent conversion into electrical signals. Hence, BCIs work by bypassing the ear canal, ear drum and ossicular chain.

Some patients are unable to wear conventional hearing aids due to recurrent ear infections and they too can benefit from BCIs. BCIs can also help patients who have deafness in one ear only, that is, unilateral hearing loss. BCIs can route the sound from the deaf side to the working cochlear in the contralateral ear, hence enabling patients to regain some hearing in their deaf side.

There are two main types of BCIs in Singapore.

The Bone Anchored Hearing Aid (BAHA) utilises osseointegration and was invented by the same person who invented dental implants.

Osseointegration refers to the biological fusion of titanium implants with patients’ bone to form a very stable and secure fixation. This facilitates the efficient transfer of amplified sound from the air to bone via a tiny implant footprint. The second device is called the Bonebridge, which is more aesthetically pleasing as it utilises a transcutaneous coupling system. The traditional BAHA has a percutaneous coupling system but the latest generation offers a transcutaneous option.

Every patient needs to be carefully assessed to ensure they meet the anatomical and audiological criteria for either device.

Both BAHA and Bonebridge require an operation for implant placement. The operations are relatively straightforward, with very low rates of complication.

Multidisciplinary Hearing Clinic

In Tan Tock Seng Hospital, we initiated the multidisciplinary Combined Hearing Clinic two years ago, to assess patients with complex hearing difficulties who may benefit from various new hearing technologies. Since then, we have implanted more than a dozen BCIs. Many of these patients have struggled with their hearing impairment for a long time.

BCIs are more expensive than conventional hearing aids. We work closely with our Medical Social Workers to ensure that financial limitations do not limit patients' access to these devices.

BCIs have opened up new hearing rehabilitation options for patients whose conventional hearing aids had not been helpful previously.

 

Dr Ho Eu Chin 

Dr Ho Eu Chin is a Consultant in the Department of Otorhinolaryngology (ENT) in Tan Tock Seng Hospital. He completed his postgraduate ENT training in England. Dr Ho runs the Combined Hearing Clinic and Multidisciplinary Balance Clinic and has interests in providing holistic and individualised care to patients with complex hearing and balance problems. He devotes his time to teaching and research, and collaborates closely with colleagues from Nanyang Technological University, Singapore.