middle ear implants
TRANSCRIPT
Middle ear implants
Definiton
Middle ear implants –
represent type of hearing aid designed for
induvisuals who are not complaining of
being unable to hear with conventional
aids , and are looking for improvements in
sound quality, comfort and cosmesis.
Indicated for both conductive and
sensorineural hearing loss
History
Wilska (1935 ) – used electromagnetic
induction to stimulate the middle ear.He
placed small pieces of iron on the
tympanic membrane and a coil within the
ear canal.The coil created a magnetic
field which in turn caused the iron and the
tympanic membrane to vibrate.Patient
reported gain in tone reception.
Principle
Works on direct drive principle
Transducer is directly coupled to
one of the ossicles or cochlear
windows
Drives ossicular chain directly
using mechanical vibrations while
leaving the ear canal completely
open.
Types of Middle ear implants
1. Piezoelectric device –
When a voltage is applied to a particular
ceramic causes proportional deformation
and hence displacement of that ceramic
Peizoelectric transducer in turn is coupled to
the ossicles and drives the ossicular chain by
vibration
Ex: Envoy, Rion, TICA
Disadvantage
power output is directly related to the size of
the crystal.
benefits only people with up to moderate
(about 60 dB) hearing loss
Advantage
Inert in a magnetic field and therefore
compatible with magnetic resonance imaging
(MRI)
Rion Device E-type
One of the earliest piezoelectric
devices
Used for both conductive and
sensorineural losses
Not gained FDA approval
partially implanted device
composed of an external ear-
level microphone and amplifier
and an internal electromagnetic
coil and vibrator element
( Transducer )
Microphone converts sounds into electrical
signals that are fed into amplifier
After amplification, transferred to
piezoeletric transducer which is connected
to stapes with a hydroxyapatite tube at one
end and anchored to the squamous portion
of the temporal bone with a titanium screw
at the other end.
Transforms electrical signals into
vibrations , vibrating stapes
Envoy Esteem
First fully implantable device
to use piezo electric
ceramics
Manufactured by St. Crois
company, Minneapolis
Not gained FDA approval
Consists of sound processor
and 2 piezo electric ceramic
units
1.Driver transducer
2.Sensor transducer
Sensor attaches to malleus
Detects movement of
malleus resulting from
tympanic membrane
vibration
Mechanical signal thus
generated is transformed into
electrical signal that is then
amplified
Amplified electric signal is
relayed to the driver which is
attached to the stapes and
causes stapes to vibrate
Totally Integrated Cochlear
Amplifier (TICA)
Totally implantable
Microphone is implanted in the
external ear adjacent to the tympanic
membrane
Digitally programmable processor
located on the mastoid processes the
signal
Piezoelectric transducer is coupled to
the body of the incus and drives the
ossicular chain by vibratory actions.
2. Elecromagnetic device –
Passes electric current into a coil which
creates a magnetic flux. This then
drives adjacent magnet that is
attached to the ossicles to transfer
vibrations to the cochlea.
Ex : Vibrant sound bridge, MET
1. Med-EL Vibrant sound bridge -
Earlier Manufactured by
Symphonix company, San jose,
Californiay , Currently by Med-EL
Semi implantable device
FDA approved
Has 2 components
Internal implanted part –
Also known as VORP (Vibrating
ossicular prosthesis ), made of 3 parts
Reciever, FMT ( Floating mass
transducer),conductor link between
the twoExternal wearable part
Known as audio processor
Worn behind the ear
Consists a microphone that picks up
sound from environment
Transmits across skin by
radiofrequency waves to the internal
reciever
The Vibrant Soundbridge system.
Candidacy profile
Age > 18yrs
Moderate to Severe SNHL ( PTA
>30dB)
SDS > 50%
Normal middle ear function
No h/o chronic middle ear disease
Prior h/o hearing aid trial and failed
Procedure
Done under GA
Type of incision – Reverse question mark
Simple mastoidectomy performed delineating
sigmoid sinus, tegmen , posterior bony canal wall
Horizontal SCC identified
Fossa incudis enlarged
Reciever positioned under skin over mastoid bone
Conductor link sloped into mastoidectomy
Facial recess opened ( posterior
tympanotomy ) and extended posteriorly
and inferiorly to visualise long process of
incus and incudostapedial joint
Facial nerve identified leaving thin layer
of bone over the nerve
Posterior buttress not to be removed to
avoid injury to posterior incudal ligament
FMT passed through facial recess and clip
portion of FMT positioned over long
process of incus
FMT not to make contact with
promontary, tympanic membrane ,
pyramidal eminence
widened tympanotomy
Floating Mass Transducer secured to the incus
6 to 8 weeks after the procedure,
external audio processor is fitted on the
back of ear
Processor is then programmed
Advantages of direct drive Hearing
devices
Provides mechanical energy directly to
ossicles bypassing ear canal and
tympanic membrane
Provides improved sound quality to
hearing impaired particularly in noisy
environment
Eliminates problems of conventional
hearing aids such as occlusion, feedback,
discomfort and wax related issues
Functional gain 6 weeks postoperatively
Otologics Middle ear Transducer ( MET )
Manufactured by Otologics
Not gained FDA approval
Indications - SDS > 20%, mod
severe to severe SNHL
Implanted via atticotomy
Electromagnetic transducer has a
probe which is coupled to the
body of incus and vibrates the
ossicular chain
Advantage
Offers better impedance matching
with more efficient transmission
of soundImplanted Middle Ear Transducer Ossicular Stimulator
The external sound processor
Sensor attaches to malleus
Detects movement of
malleus resulting from
tympanic membrane
vibration
Mechanical signal thus
generated is transformed into
electrical signal that is then
amplified
Amplified electric signal is
relayed to the driver which is
attached to the stapes and
causes stapes to vibrate
Advantages
Allows tremendous reduction
in amount of energy required
to drive the system with
potential battery life of
greater than 5 yrs.
Indications
Severe MHL with average
bone conduction levels for
the speech frequencies
not exceeding 50 dB and
SDS better tha 70%
Advantage
Provides natural quality of
sound very close to
physiologic hearing
without discomfort and
feedback
Disadvantages of middle ear implants
Though it provides good sound
amplification and sound quality to
patients there is potential risk for
Ossicular necrosis
Stereophonic hearing is lost
Insurance nor covered