Bone-anchored hearing aid

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Bone-anchored hearing aid
Baha user sound processor behind ear.PNG
A baha user with a sound processor attached behind her ear
Other namesBone-anchored hearing device [1]

A bone-anchored hearing aid (BAHA) [2] is a type of hearing aid based on bone conduction. It is primarily suited for people who have conductive hearing losses, unilateral hearing loss, single-sided deafness and people with mixed hearing losses who cannot otherwise wear 'in the ear' or 'behind the ear' hearing aids. They are more expensive than conventional hearing aids, and their placement involves invasive surgery which carries a risk of complications, [1] although when complications do occur, they are usually minor. [3]

Contents

Two of the causes of hearing loss are lack of function in the inner ear (cochlea) and when the sound has problems in reaching the nerve cells of the inner ear. Examples of the first include age-related hearing loss and hearing loss due to noise exposure. A patient born without external ear canals is an example of the latter for which a conventional hearing aid with a mould in the ear canal opening would not be effective. Some with this condition have normal inner ear function, as the external ear canal and the inner ear are developed at different stages during pregnancy. With normal inner anatomy, sound conducted by the skull bone improves hearing.

A vibrator with a steel spring over the head or in heavy frames of eyeglasses pressed towards the bone behind the ear has been used to bring sound to the inner ear. This has, however, several disadvantages, such as discomfort and pain due to the pressure needed. [4] The sound quality is also impaired as much of the sound energy is lost in the soft tissue over the skull bone, [5] particularly for the higher sound frequencies important for speech understanding in noise.

Medical use

A sound processor behind the ear The sound processor from Oticon Medical behind the ear.png
A sound processor behind the ear

Bone-anchored hearing aids use a surgically implanted abutment to transmit sound by direct conduction through bone to the inner ear, bypassing the external auditory canal and middle ear. A titanium prosthesis is surgically embedded into the skull with a small abutment exposed outside the skin. A sound processor sits on this abutment and transmits sound vibrations to the titanium implant. The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing. [6]

The surgery is often performed under local anesthesia and as an outpatient procedure. An important piece of information for patients is that if they for whatever reason are not satisfied with the BAHA solution, removing the implant is easy. No other ear surgical procedure is reversible like this.[ citation needed ]

By bypassing the outer or middle ear, BAHA can increase hearing in noisy situations and help localise sounds. In addition to improved speech understanding, it results in a natural sound with less distortion and feedback compared with conventional hearing aids. [7] [8] [9] [10] [11] The ear canal is left open for comfort, and helps to reduce any problems caused by chronic ear infections or allergies. In patients with single-sided sensorineural deafness, BAHA sends the sound by the skull bone from the deaf side to the inner ear of the hearing side. This transfer of sound gives a 360° sound awareness.

BAHAs may facilitate normal speech development. [12]

Chronic ear disease

This fairly common condition is often associated with continuous or intermittent drainage from the ear canal. These patients may also have a hearing loss and need amplification. A conventional air conduction aid with a mold placed in the ear canal opening may not be appropriate due to the drainage, and may even provoke drainage. If the hearing loss is significant an air conduction aid may have difficulty overcoming the dysfunction of the eardrum and middle ear bones. Bone conduction hearing device bypassing the middle ear may be a more appropriate treatment for these patients. Good transmission of sound in the bone, with reduced attenuation and distortion may be possible.

Single-sided deafness

A person with unilateral hearing loss may have functional difficulty hearing even when the other ear is normal, particularly in demanding situations such as noisy environments and when several people are speaking the same time. A complication in single-sided deafness is hearing impairment in the hearing ear. Conventional ear surgery involves a risk of hearing loss due to the surgical procedure. Ear surgeons may be reluctant to perform surgery on an only hearing ear. [13] The BAHA surgery avoids this risk and may be an appropriate treatment. An extended trial of a BAHA system with a headband prior to surgery led to more realistic expectations. In the trial, 50% of the candidates wished to proceed to surgery. [14]

External ear canal problems

Irritation in the external ear canal due to inflammation or eczema may be a condition for which a conventional air conduction aid is not an appropriate treatment. Direct bone conduction may be an option.

Malformations

Patients with malformations are not always suitable for reconstructive surgery. Treacher Collins syndrome patients may have significant malformations with ossicular defects and an abnormal route of the facial nerve. These structures, as well as the inner ear, could be in danger at surgery.

Patients with Down syndrome may have a narrow ear canal and middle ear malformation leading to impaired hearing. Some part of the cognitive delay seen in these children may be partly due to their poor hearing.

The surgery can only take place once the skull is at least 2.5 mm thick. [15] [16] [ needs update ] Children with certain syndromes may have a slighter build, thinner bone, or unusual anatomy. Other children may have a thicker skull at a younger age, so it is difficult to give a specific age for surgery.

In the U.S., the Food and Drug Administration only approves BAHA implantation of children aged five years or older.

For infants and young children prior to surgery, the sound processor can be worn on a head band or soft band which the infant wears to hold it against the skull.

Side effects

Complications of BAHA systems can be considered as either related to the bone (hard tissue) or the soft tissue. [3]

Soft-tissue complications are much more common, and most are managed with topical treatments. Children are more likely to develop both kinds of complications than adults. Sometimes, a second surgical procedure is required. Complications are less likely with good wound hygiene. [3] Other drawbacks of BAHA include accidental or spontaneous loss of the bone implant, and patient refusal for treatment due to stigma. [17]

Surgical procedure

The bone behind the ear is exposed through a U-shaped or straight incision or with the help of a specially designed BAHA dermatome. A hole, 3 or 4 mm deep depending on the thickness of the bone, is drilled. The hole is widened and the implant with the mounted coupling is inserted under generous cooling to minimize surgical trauma to the bone. In a single stage procedure, the fixture and abutment are placed simultaneously. For children or patients who may damage the abutment prior to osseointegration of the fixture, a two stage procedure may be performed in which the fixture is placed first, and after osseointegration roughly 6 months later, the abutment is attached. In children, a sleeper implant may be placed to serve as a backup in case the main implant is damaged.

Some surgeons perform a reduction of the subcutaneous soft tissue. The rationale for this is to reduce the mobility between implant and skin to avoid inflammation at the penetration site. This reduction of the soft tissue has been questioned and some surgeons do not perform any or a minimum of it. The rationale for this is that any surgery will result in some scar tissue that could be the focus of infection. The infections seen early during the development of the surgical procedure could perhaps be explained by the lack of seal between implant and abutment allowing bacteria to enter the space. A new helium tight seal may be advantageous and prevent biofilm formation. This will also allow the surgeon to use longer abutments should a need exist. Three to six weeks later or even earlier, the audiologist will fit and adjust the hearing processor according to the patient's hearing level. The fitting will be made using a special program in a computer.

The original surgical procedure has been described in detail by Tjellström et al. 2001. [15]

Handling

An implant shown in actual size in adult hand Baha implant in hand.jpg
An implant shown in actual size in adult hand

An area where skin is penetrated requires care and cleaning because of the risk of inflammation around the abutment. Daily cleaning is required. [18]

Small children

Hearing is of importance for a normal speech development. [19] The skull bone in children is often very thin and softer than in the adult. Surgery is thus often delayed until the age of four to five years. In the meantime, the child with bilateral atresia can be fitted with a band around the head with a coupling for a BAHA. This may be done at the age of one month. Infants at this age may tolerate this well. [16] As described above, for children who may be at risk of damaging the abutment prior to osseointegration of the fixture, a two stage procedure may be performed in which the fixture is placed first, and after osseointegration roughly 6 months later, the abutment is attached. In children, a sleeper implant may be placed to serve as a backup in case the main implant is damaged.

History

Patients with chronic ear infection where the drum and/or the small bones in the middle ear are damaged often have hearing loss, but difficulties in using a hearing aid fitted in the ear canal. Direct bone conduction through a vibrator attached to a skin-penetrating implant addresses these disadvantages.

In 1977, the first three patients were implanted with a bone-conduction hearing solution by Anders Tjellström at the Ear, Nose, and Throat Department at Sahlgrenska University Hospital in Gothenburg, Sweden. A 4-mm-long titanium screw with a diameter of 3.75 mm was inserted in the bone behind the ear, and a bone conduction hearing aid was attached.

The term osseointegration was coined by Professor Brånemark. During animal studies, he found the bone tissue attached to the titanium implant without any soft tissue in between. He also showed an such an implant could take a heavy load. His definition of osseointegration was "direct contact between living bone and an implant that can take a load".

The first clinical application of titanium was in oral surgery, where implants were used for retention of dentures. Brånemark sought an acoustic way to evaluate osseointegration. A patient with implants in the jaws was fitted with a bone vibrator on one of his implants. When tested, the patient experienced very loud sound even at low stimulation levels, indicating sound could propagate very well in the bone. It has later been shown by Håkansson that the sound transmission in bone is linear, indicating low distortion of the sound.

The implant in the bone is made of titanium and will osseointegrate. The hearing instrument is impedance-matched. Osseointegration has been defined as the direct contact between living bone and an implant that can take a load, with no soft tissue at the interface.

Models

There are several models of bone-anchored hearing aids available. Most common are the BAHA from Australian company Cochlear, and the Ponto from Danish manufacturers Oticon Medical. [20] There are also other types of bone conduction hearing aids, such as implants and non-surgical devices.

Costs

In the US, the cost of the Baha device is about $4,000. In the Netherlands, the cost of the device is around €3000 (in 2008). The cost of the titanium implant, surgery, and aftercare from surgeon and audiologist must also be considered.

Related Research Articles

<span class="mw-page-title-main">Otorhinolaryngology</span> Medical specialty

Otorhinolaryngology is a surgical subspecialty within medicine that deals with the surgical and medical management of conditions of the head and neck. Doctors who specialize in this area are called otorhinolaryngologists, otolaryngologists, head and neck surgeons, or ENT surgeons or physicians. Patients seek treatment from an otorhinolaryngologist for diseases of the ear, nose, throat, base of the skull, head, and neck. These commonly include functional diseases that affect the senses and activities of eating, drinking, speaking, breathing, swallowing, and hearing. In addition, ENT surgery encompasses the surgical management of cancers and benign tumors and reconstruction of the head and neck as well as plastic surgery of the face, scalp, and neck.

<span class="mw-page-title-main">Cholesteatoma</span> Medical condition

Cholesteatoma is a destructive and expanding growth consisting of keratinizing squamous epithelium in the middle ear and/or mastoid process. Cholesteatomas are not cancerous as the name may suggest, but can cause significant problems because of their erosive and expansile properties. This can result in the destruction of the bones of the middle ear (ossicles), as well as growth through the base of the skull into the brain. They often become infected and can result in chronically draining ears. Treatment almost always consists of surgical removal.

<span class="mw-page-title-main">Anotia</span> Medical condition

Anotia describes a rare congenital deformity that involves the complete absence of the auricle, the outer projected portion of the ear, and narrowing or absence of the ear canal. This contrasts with microtia, in which a small part of the auricle is present. Anotia and microtia may occur unilaterally or bilaterally. This deformity results in conductive hearing loss, deafness.

<span class="mw-page-title-main">Otosclerosis</span> Condition characterized by an abnormal bone growth in the middle ear

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 hardened (sclerotized), which limits its movement and results in hearing loss, tinnitus, vertigo or a combination of these. The term otosclerosis is something of a misnomer: much of the clinical course is characterized by lucent rather than sclerotic bony changes, so the disease is also known as otospongiosis.

<span class="mw-page-title-main">Hearing aid</span> Electroacoustic device

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 such as personal sound amplification products (PSAPs) or other plain sound reinforcing systems cannot be sold as "hearing aids".

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 even if the ear canal is blocked. Bone conduction transmission occurs constantly as sound waves vibrate bone, specifically the bones in the skull, although it is hard for the average individual to distinguish sound being conveyed through the bone as opposed to the sound being conveyed through the air via the ear canal. Intentional transmission of sound through bone can be used with individuals with normal hearing — as with bone-conduction headphones — or as a treatment option for certain types of hearing impairment. Bones are generally more effective at transmitting lower-frequency sounds compared to higher-frequency sounds.

<span class="mw-page-title-main">Dental implant</span> Surgical component that interfaces with the bone of the jaw

A dental implant is a prosthesis that interfaces with the bone of the jaw or skull to support a dental prosthesis such as a crown, bridge, denture, or facial prosthesis or to act as an orthodontic anchor. The basis for modern dental implants is a biological process called osseointegration, in which materials such as titanium or zirconia form an intimate bond to the bone. The implant fixture is first placed so that it is likely to osseointegrate, then a dental prosthetic is added. A variable amount of healing time is required for osseointegration before either the dental prosthetic is attached to the implant or an abutment is placed which will hold a dental prosthetic/crown.

Osseointegration is the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant. A more recent definition defines osseointegration as "functional ankylosis ", where new bone is laid down directly on the implant surface and the implant exhibits mechanical stability. Osseointegration has enhanced the science of medical bone and joint replacement techniques as well as dental implants and improving prosthetics for amputees.

<span class="mw-page-title-main">Conductive hearing loss</span> Medical condition

Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles). If a conductive hearing loss occurs in conjunction with a sensorineural hearing loss, it is referred to as a mixed hearing loss. Depending upon the severity and nature of the conductive loss, this type of hearing impairment can often be treated with surgical intervention or pharmaceuticals to partially or, in some cases, fully restore hearing acuity to within normal range. However, cases of permanent or chronic conductive hearing loss may require other treatment modalities such as hearing aid devices to improve detection of sound and speech perception.

<span class="mw-page-title-main">Weber test</span> Screening test for hearing

The Weber test is a screening test for hearing performed with a tuning fork. It can detect unilateral (one-sided) conductive hearing loss and unilateral sensorineural hearing loss. The test is named after Ernst Heinrich Weber (1795–1878). Conductive hearing ability is mediated by the middle ear composed of the ossicles: the malleus, the incus, and the stapes. Sensorineural hearing ability is mediated by the inner ear composed of the cochlea with its internal basilar membrane and attached cochlear nerve. The outer ear consisting of the pinna, ear canal, and ear drum or tympanic membrane transmits sounds to the middle ear but does not contribute to the conduction or sensorineural hearing ability save for hearing transmissions limited by cerumen impaction.

Unilateral hearing loss (UHL) is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.

<span class="mw-page-title-main">Implant (medicine)</span> Device surgically placed within the body for medical purposes

An implant is a medical device manufactured to replace a missing biological structure, support a damaged biological structure, or enhance an existing biological structure. For example, an implant may be a rod, used to strengthen weak bones. Medical implants are human-made devices, in contrast to a transplant, which is a transplanted biomedical tissue. The surface of implants that contact the body might be made of a biomedical material such as titanium, silicone, or apatite depending on what is the most functional. In 2018, for example, American Elements developed a nickel alloy powder for 3D printing robust, long-lasting, and biocompatible medical implants. In some cases implants contain electronics, e.g. artificial pacemaker and cochlear implants. Some implants are bioactive, such as subcutaneous drug delivery devices in the form of implantable pills or drug-eluting stents.

<span class="mw-page-title-main">Microtia</span> Medical condition

Microtia is a congenital deformity where the auricle is underdeveloped. A completely undeveloped auricle is referred to as anotia. Because microtia and anotia have the same origin, it can be referred to as microtia-anotia. Microtia can be unilateral or bilateral. Microtia occurs in 1 out of about 8,000–10,000 births. In unilateral microtia, the right ear is most commonly affected. It may occur as a complication of taking Accutane (isotretinoin) during pregnancy.

A contralateral routing of signals (CROS) hearing aid is a type of hearing aid that is used to treat a condition in which the patient has no usable hearing in one ear and minimal hearing loss or normal hearing in the other ear. This is referred to as single sided deafness.

SoundBite Hearing System is a non-surgical bone conduction prosthetic device that transmits sound via the teeth. It is an alternative to surgical bone conduction prosthetic devices, which require surgical implantation into the skull to conduct sound.

Cochlear Bone Anchored Solutions is a company based in Gothenburg, Sweden that manufactures and distributes bone conduction hearing solutions under the trademark Baha. The company was founded in 1999 under the name Entific Medical Systems. When Cochlear bought the company in 2005, the name was changed to Cochlear Bone Anchored Solutions. The acronym "BAHA" was trademarked into Baha, as it is not considered a hearing aid by insurance companies.

Cartilage conduction is a pathway by which sound signals are transmitted to the inner ear. In 2004, Hiroshi Hosoi discovered this pathway and named “cartilage conduction”. Hearing by cartilage conduction is distinct from conventional sound-conduction pathways, such as air or bone, because it is realized by touching a transducer on the aural cartilage and does not involve the vibration of the skull bone. Therefore, cartilage conduction is referred to as the “third auditory pathway”.

Alloplasty is a surgical procedure performed to substitute and repair defects within the body with the use of synthetic material. It can also be performed in order to bridge wounds. The process of undergoing alloplasty involves the construction of an alloplastic graft through the use of computed tomography (CT), rapid prototyping and "the use of computer-assisted virtual model surgery." Each alloplastic graft is individually constructed and customised according to the patient's defect to address their personal health issue. Alloplasty can be applied in the form of reconstructive surgery. An example where alloplasty is applied in reconstructive surgery is in aiding cranial defects. The insertion and fixation of alloplastic implants can also be applied in cosmetic enhancement and augmentation. Since the inception of alloplasty, it has been proposed that it could be a viable alternative to other forms of transplants. The biocompatibility and customisation of alloplastic implants and grafts provides a method that may be suitable for both minor and major medical cases that may have more limitations in surgical approach. Although there has been evidence that alloplasty is a viable method for repairing and substituting defects, there are disadvantages including suitability of patient bone quality and quantity for long term implant stability, possibility of rejection of the alloplastic implant, injuring surrounding nerves, cost of procedure and long recovery times. Complications can also occur from inadequate engineering of alloplastic implants and grafts, and poor implant fixation to bone. These include infection, inflammatory reactions, the fracture of alloplastic implants and prostheses, loosening of implants or reduced or complete loss of osseointegration.

A root-analogue dental implant (RAI) – also known as a truly anatomic dental implant, or an anatomical/custom implant – is a medical device to replace one or more roots of a single tooth immediately after extraction. In contrast to common titanium screw type implants, these implants are custom-made to exactly match the extraction socket of the specific patient. Thus there is usually no need for surgery.

A middle ear implant is a hearing device that is surgically implanted into the middle ear. They help people with conductive, sensorineural or mixed hearing loss to hear. 

References

  1. 1 2 Banga, R; Lawrence, R; Reid, A; McDermott, AL (2011). Bone-anchored hearing aids versus conventional hearing aids. Advances in Oto-Rhino-Laryngology. Vol. 71. pp. 132–9. doi:10.1159/000323711. ISBN   978-3-8055-9700-5. PMID   21389713.
  2. ↑ Janssen, RM; Hong, P; Chadha, NK (September 2012). "Bilateral bone-anchored hearing aids for bilateral permanent conductive hearing loss: a systematic review". Otolaryngology–Head and Neck Surgery. 147 (3): 412–22. doi:10.1177/0194599812451569. PMID   22714424.
  3. 1 2 3 Wazen, JJ; Wycherly, B; Daugherty, J (2011). Complications of bone-anchored hearing devices. Advances in Oto-Rhino-Laryngology. Vol. 71. pp. 63–72. doi:10.1159/000323583. ISBN   978-3-8055-9700-5. PMID   21389706.
  4. ↑ Raicevich, George; Burwood, Eric; Dillon, Harvey (2008). "Taking the pressure off bone conduction hearing aid users". Australian and New Zealand Journal of Audiology. 30 (2): 113–8. doi:10.1375/audi.30.2.113.
  5. ↑ Mylanus, E.A.; Snik, A.F.; Cremers, C.W. (1994). "Influence of the thickness of the skin and subcutaneous tissue covering the mastoid on bone-conduction thresholds obtained transcutaneously versus percutaneously". Scandinavian Audiology. 23 (3): 201–3. doi:10.3109/01050399409047509. PMID   7997838.
  6. ↑ "Cochlear Implants". NIH.
  7. ↑ Flynn, Mark C.; Sadeghi, Andre; Halvarsson, Glenn (2009). "Baha solutions for patients with severe mixed hearing loss". Cochlear Implants International. 10 (Suppl 1): 43–7. doi:10.1179/cim.2009.10.Supplement-1.43. PMID   19195004. S2CID   29486631.
  8. ↑ Lin, Li-Mei; Bowditch, Stephen; Anderson, Michael J.; May, Bradford; et al. (2006). "Amplification in the rehabilitation of unilateral deafness: Speech in noise and directional hearing effects with bone-anchored hearing and contralateral routing of signal amplification". Otology & Neurotology. 27 (2): 172–82. doi:10.1097/01.mao.0000196421.30275.73. PMID   16436986. S2CID   23406013.
  9. ↑ Hol, Myrthe K.S.; Snik, Ad F.M.; Mylanus, Emmanuel A.M.; Cremers, Cor W.R.J. (2005). "Long-term results of bone-anchored hearing aid recipients who had previously used air-conduction hearing aids". Archives of Otolaryngology–Head & Neck Surgery . 131 (4): 321–5. doi: 10.1001/archotol.131.4.321 . PMID   15837900.
  10. ↑ Watson, G.J.; Silva, S.; Lawless, T.; Harling, J.L.; et al. (2008). "Bone anchored hearing aids: A preliminary assessment of the impact on outpatients and cost when rehabilitating hearing in chronic suppurative otitis media". Clinical Otolaryngology. 33 (4): 338–42. doi:10.1111/j.1749-4486.2008.01698.x. PMID   18983343. S2CID   205926180.
  11. ↑ Snik, A.F.; Mylanus, E.A.; Proops, D.W.; Wolfaardt, J.F.; et al. (December 2005). "Consensus statements on the BAHA system: where do we stand at present?". Annals of Otology, Rhinology, and Laryngology . 114 (12 Supp. 195): 2–12. doi:10.1177/0003489405114S1201. PMID   16619473. S2CID   24204765. Archived from the original on 3 May 2014.
  12. ↑ Verhagen, C.V.M.; Hol, M.K.S.; Coppens-Schellekens, W.; Snik, A.F.M.; Cremers, C.W.R.J. (1 October 2008). "The Baha Softband". International Journal of Pediatric Otorhinolaryngology. 72 (10): 1455–1459. doi:10.1016/j.ijporl.2008.06.009. PMID   18667244.
  13. ↑ Althaus, S R (1981). "Surgery on the only hearing ear". Laryngoscope. 91 (5): 765–770. doi:10.1288/00005537-198105000-00009. PMID   7231025.
  14. ↑ Pennings, R.J.E.; Gulliver, M.; Morris, D.P. (2011). "The importance of an extended preoperative trial of BAHA in unilateral sensorineural hearing loss: a prospective cohort study". Clinical Otolaryngology. 36 (5): 442–9. doi:10.1111/j.1749-4486.2011.02388.x. PMID   21883961. S2CID   12637285.
  15. 1 2 Tjellström, A.; Håkansson, B.; Granström, G. (April 2001). "Bone-anchored hearing aids: Current status in adults and children". Otolaryngologic Clinics of North America. 34 (2): 337–64. doi:10.1016/S0030-6665(05)70335-2. PMID   11382574.
  16. 1 2 Papsin, Blake C.; Sirimanna, Tony K.S.; Albert, David M.; Bailey, C. Martin (1997). "Surgical experience with bone-anchored hearing aids in children". The Laryngoscope. 107 (6): 801–6. doi:10.1097/00005537-199706000-00015. PMID   9185737. S2CID   35501222.
  17. ↑ Håkansson, Bo (2011). "The future of bone conduction hearing devices". Implantable Bone Conduction Hearing Aids. Advances in Oto-Rhino-Laryngology. Vol. 71. pp. 140–52. doi:10.1159/000323715. ISBN   978-3-8055-9700-5. PMID   21389714.
  18. ↑ Gallant, Sara; Lee, Judy; Jethanamest, Daniel (1 December 2017). "Skin Necrosis in a Magnet-Based Bone-Conduction Implant". Ear, Nose & Throat Journal. 96 (12): 454–455. doi: 10.1177/014556131709601202 . ISSN   0145-5613. PMID   29236274. S2CID   44290100.
  19. ↑ Lieu, Judith E. Cho (2004). "Speech-language and educational consequences of unilateral hearing loss in children". Archives of Otolaryngology–Head & Neck Surgery . 130 (5): 524–30. doi:10.1001/archotol.130.5.524. PMID   15148171.
  20. ↑ "Bone-anchored hearing systems: What you need to know". Healthy Hearing. Retrieved 24 March 2022.
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