Middle Ear Implants

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


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


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

Documents

Middle Ear Implants