A middle ear implant is a hearing device that is surgically implanted into the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in t ...

. They help people with conductive, sensorineural or mixed

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken ...

to hear. Middle ear implants work by improving the conduction of

sound In physics, sound is a vibration that propagates as an acoustic wave, through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by th ...

vibrations from the middle ear to the

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in th ...

. There are two types of middle ear devices: active and passive. Active middle ear implants (AMEI) consist of an external audio processor and an internal implant, which actively vibrates the structures of the middle ear. Passive middle ear implants (PMEIs) are sometimes known as ossicular replacement prostheses, TORPs or PORPs. They replace damaged or missing parts of the middle ear, creating a bridge between the outer ear and the inner ear, so that sound vibrations can be conducted through the middle ear and on to the cochlea. Unlike AMEIs, PMEIs contain no electronics and are not powered by an external source. PMEIs are the usual first-line surgical treatment for conductive hearing loss, due to their lack of external components and cost-effectiveness. However, each patient is assessed individually as to whether an AMEI or PMEI would bring more benefit. This is especially true if the patient has already had several surgeries with PMEIs.

Active middle ear implant

Parts

An active middle ear implant (AMEI) has two parts: an internal implant and an external audio processor. The

microphone A microphone, colloquially called a mic or mike (), is a transducer that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, public address systems for concert halls and pu ...

of the audio processor picks up sounds from the environment. The processor then converts these

acoustic Acoustic may refer to: Music Albums * ''Acoustic'' (Above & Beyond album), 2014 * ''Acoustic'' (Deine Lakaien album), 2007 * ''Acoustic'' (Everything but the Girl album), 1992 * ''Acoustic'' (John Lennon album), 2004 * ''Acoustic'' (Love Amo ...

signals into digital signals and sends them to the implant through the skin. The implant sends the signals to the Floating Mass Transducer (FMT): a small vibratory part that is surgically fixed either on one of the three

ossicles The ossicles (also called auditory ossicles) are three bones in either middle ear that are among the smallest bones in the human body. They serve to transmit sounds from the air to the fluid-filled labyrinth (cochlea). The absence of the auditory ...

or against the round window of the

cochlea The cochlea is the part of the inner ear involved in hearing. It is a spiral-shaped cavity in the bony labyrinth, in humans making 2.75 turns around its axis, the modiolus. A core component of the cochlea is the Organ of Corti, the sensory or ...

. The FMT vibrates and sends sound vibrations to the cochlea. The cochlea converts these vibrations into nerve signals and sends them to the brain, where they are interpreted as sound.

Indications

AMEIs are intended for patients with mild-to-severe sensorineural hearing loss, as well as those with conductive or mixed hearing loss. They can be used by adults and children over the age of 5.

Sensorineural hearing loss

An AMEI can be beneficial for patients with mild-to-severe sensorineural hearing loss who have an intact ossicular chain and healthy middle ear, but who either cannot wear

hearing aid A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers su ...

s or who do not get sufficient benefit from them. Reasons for not being able to wear hearing aids include earmold

allergies Allergies, also known as allergic diseases, refer a number of conditions caused by the hypersensitivity of the immune system to typically harmless substances in the environment. These diseases include hay fever, food allergies, atopic derma ...

, skin problems, narrow, collapsed or closed ear canals, or malformed ears. In cases of sensorineural hearing loss, the FMT is usually attached to the incus.

Conductive or mixed hearing loss

An AMEI is also indicated for patients with conductive or mixed hearing loss with

bone conduction Bone conduction is the conduction of sound to the inner ear primarily through the bones of the skull, allowing the hearer to perceive audio content without blocking the ear canal. Bone conduction transmission occurs constantly as sound waves vibr ...

thresholds from 45 dB in the low frequencies to 65 dB in the high frequencies. In these cases, the FMT can be coupled to various parts of the middle ear, depending on the patient’s

pathology Pathology is the study of the causes and effects of disease or injury. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in ...

: * The oval window, causing stimulation of the cochlea in patients without an ossicular chain. * The round window, causing reverse stimulation of the cochlea in patients without an ossicular chain. * The mobile

stapes The ''stapes'' or stirrup is a bone in the middle ear of humans and other animals which is involved in the conduction of sound vibrations to the inner ear. This bone is connected to the oval window by its annular ligament, which allows the foo ...

in patients with absence or fixation of other ossicles, usually in cases of chronic

otitis media Otitis media is a group of inflammatory diseases of the middle ear. One of the two main types is acute otitis media (AOM), an infection of rapid onset that usually presents with ear pain. In young children this may result in pulling at the ear, ...

or malformations.

Efficacy

AMEIs have been shown by several studies to be equal or superior to both hearing aids and bone conduction implants. Lee et al used the PBmax test to study speech intelligibility in patients before and after receiving an AMEI. All patients had used hearing aids pre-implantation. The researchers found that speech intelligibility improved with the AMEI, particularly in patients with a down-sloping hearing loss. These findings were supported by Iwasaki et al, who found that both speech intelligibility and

quality of life Quality of life (QOL) is defined by the World Health Organization as "an individual's perception of their position in life in the context of the culture and value systems in which they live and in relation to their goals, expectations, standards ...

improved after implantation with an AMEI, applied to the round window. AMEIs can also offer improved hearing performance over bone conduction implants for patients with mixed hearing loss. Mojallal et al found that patients whose mixed hearing loss was treated with an AMEI experienced both better word recognition and speech understanding in noise than those who received a bone conduction implant, providing that their bone conduction pure-tone average (0.5 to 4 kHz) was poorer than 35 dB HL.

Passive middle ear implant

Parts

Passive middle ear implants (PMEI) are ossicular replacement prostheses designed to replace some or all of the ossicular chain in the middle ear. They create a bridge between the outer ear and the inner ear, so that sound vibrations can be conducted through the middle ear and on to the cochlea There are two types of PMEIs: tympanoplasty implants and stapes implants. Tympanoplasty implants (also known as PORPs or TORPs) are suitable for patients with a mobile stapes footplate, ie. a stapes footplate that moves in the normal way. Either a partial or a total tympanoplasty implant can be used, depending on the condition of the stapes. If the stapes is fixed and cannot transfer vibrations to the inner ear, then a stapes implant would be used.{{Cite web, title=Passive Middle Ear Implants {{! MED-EL Pro, url=https://www.medel.pro/products/passive-middle-ear-implants, access-date=2021-12-13, website=www.medel.pro, language=en PMEIs are made from different materials including titanium, teflon, hydroxylapatite, platinum, and nitinol, all of which are suitable for use within the human body. Titanium implants can safely undergo MRIs of up to 7.0 Tesla.

Indications

Tympanoplasty implant

The tympanoplasty implant is indicated in cases of congenital or acquired defects of the ossicular chain, due to e.g.: * Chronic otitis media * Traumatic injury * Malformation * Cholesteatoma It can also be used to treat patients with inadequate conductive hearing from previous middle ear surgery.

Stapes implant

The stapesplasty prosthesis is indicated in cases of congenital or acquired defects of the stapes due to e.g.: *

Otosclerosis Otosclerosis is a condition of the middle ear where portions of the dense enchondral layer of the bony labyrinth remodel into one or more lesions of irregularly-laid spongy bone. As the lesions reach the stapes the bone is resorbed, then hard ...

* Congenital fixation of the stapes * Traumatic injury * Malformation of the ossicular chain/middle ear It can also be used to treat patients with inadequate conductive hearing from previous stapes surgery.

References

Medical technology