Middle Ear Implant Devices - Indications and Advantages

Introduction

Hearing loss affects millions of people and prevalence increases with age. More than one-third of individuals above 65 years of age are known to have significant hearing loss. It has been estimated that approximately 20 percent of people with significant hearing loss actually seek amplification assistance. Of these 15 percent do wear devices due to discomfort, battery change or maintenance, irritation, acoustic feedback, or occlusion effect. Since the last decade, technological developments have improved the usage of conventional devices. An interest in middle ear implants has developed over the years significantly to facilitate the patients who are noncompliant with conventional hearing aids and do not receive their necessary benefits.

What Are Middle Ear Implants (MEI)?

Middle ear implants are hearing devices that catch sounds with a sound processor or audio processor located on the head and convert sounds into mechanical stimulation of the ossicles of the middle ear. It makes the structures vibrate similar to the normal sound that moves the bones in the middle ear by converting sounds into vibrations.

Middle ear implants consist of two parts- internal and external parts.

External Part: It is the sound processor or audio processor which contains a battery, a microphone, and digital signal processing. It basically converts sound into electrical signals that are transmitted to the implant. It should be worn on the head and is covered by the hair. It is held in its place by a magnet in the implanted part.

Internal Part: It is placed surgically under the skin towards the back of the head. A part of an internal component called the floating mass transducer (FMT) is attached to the vibratory structure of the middle ear. FMT specifically vibrates according to the patient's needs enabling the structures of the ear to vibrate. These vibrations are amplified and adjusted to compensate for various degrees and types of hearing loss. The FMT is the main component of middle ear implant and is smaller than the rice grain.

What Are the Indications for Middle Ear Implants?

The indications are:

• Sensorineural hearing loss.

• Conductive hearing loss.

• Mixed hearing loss.

The people who can use MEI are:

• Those with an obstruction of the outer or middle ear.

• Who cannot wear hearing aids or mold for some reason.

• Who does not benefit from sound amplification.

What Are the Middle Ear Implants Devices Available?

The implant devices are broadly classified into partially or totally implantable electromagnetic or piezoelectric systems.

1. Rion Device: It is the first piezoelectric device, an E-type Rion device used for conductive and sensorineural losses. This device is implanted partially with the vibratory portion attached to the temporal bone’s squamous region. It works by passing an electric current into a piezoceramic crystal attached to the incus or stapes capitulum. However, it showed less efficacy to the sensitivity of the ossicular vibrator caused by aging and to tissue reaction around the vibrator element impeding its function.

2. Vibrant Soundbridge Device: It is a common example of a partially implanted electromagnetic device. It was developed by Symphonix Devices, Inc. which was the first FDA-approved implantable middle ear hearing aid to treat sensorineural hearing loss, receiving the designation in 2000.

• It is unique in taking an innovative approach to make sound audible. It mechanically causes the ossicles to vibrate, and the amplified vibrations may be adjusted to optimally compensate for hearing loss. Particularly, the vibration of the device is transferred to the ossicles by delivering stimuli to the middle and subsequently inner ear.

• It is semi-implantable and is composed of an external microphone, sound processor and amplifier, an audio processor, and an interval vibrating ossicular prosthesis.

• The microphone is placed behind the ear to detect the sound waves that are then processed by the implanted receiver. The vibrating ossicular prosthesis conducts the sound to a magnet surrounded by a coil called a floating mass transducer (FMT).

This device works on a battery and its life depends on the usage and device settings.

3. Soundtec Direct System: It was introduced in the U.S. in 2001 and is a semi-implantable device that converts sound waves to electromagnetic energy, which in turn stimulates ossicular chains directly.

• A surgically placed neodymium-iron-boron magnet is placed around the neck of the stapes, an earmold embedded with an electromagnetic coil stimulates the magnet.

• The coil assembly is placed into the ear canal approximately 2 mm away from the tympanic membrane. A sound processor is fit typically either posterior to the auricle or in the external ear canal.

4. Totally Integrated Cochlear Amplifier: It is the first totally implanted device and is widely used in Europe it was first implanted in 1998.

• The transducer, the microphone, is placed beneath the skin of the auditory canal allowing the skin to cover the microphone membrane completely.

• A digitally programmable processor placed subcutaneously on the mastoid bone processes the signal which is then translated to a piezoelectric coupler in direct contact with the body of the incus.

• This device is implanted through mastoidectomy and is charged transcutaneously within 90 minutes. This battery is estimated to last for approximately five years.

5. Otologics: It was initially developed as a semi-implantable middle ear transducer, then as a totally implantable device is available since 2006.

• The device consists of the implant, programming system, charger, and remote control. The implant has electronics including a microphone, battery, magnet, digital signal processor, and connector.

• It uses the microphone located under the skin to catch the sound that is amplified and converted into an electrical signal. This signal is sent down to lead and into the transducer, and the middle ear transducer ossicular stimulator is coupled directly to the ossicular chain.

• The device can be charged while the user performs daily activities, it can be turned on and off and volume adjusted.

What Are the Advantages of a Middle Ear Implant?

The advantages are:

• It offers amplification without ear mold in the ear.

• It is comfortable.

• It provides more natural sound than conventional aids.

• Helpful in managing normal daily activities.

• It also enables the user to connect to a mobile phone, FM system, and MP3 player without compromising the sound quality.

Conclusion

Middle ear implants were established to overcome the side effects of conventional hearing aids such as poor sound quality, canal occlusion, discomfort, irritation, and other feedback. Middle ear implants are used to treat sensorineural, conductive, and mixed hearing loss. These implants are made available after proper research to reach technological sophistication, medical safety, and regulatory approval. The implants have proven to be safe, effective, and efficient with subjective outcomes.