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.