Bone Anchored Hearing Aid
Encyclopedia
A Bone-anchored hearing aid is a type of hearing aid
Hearing aid
A hearing aid is an electroacoustic device which typically fits in or behind the wearer's ear, and is designed to amplify and modulate sound for the wearer. Earlier devices, known as "ear trumpets" or "ear horns", were passive funnel-like amplification cones designed to gather sound energy and...

 based on bone conduction
Bone conduction
Bone conduction is the conduction of sound to the inner ear through the bones of the skull.Bone conduction is the reason why a person's voice sounds different to him/her when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own...

. It is primarily suited to people who have conductive hearing losses, unilateral hearing loss
Unilateral hearing loss
Unilateral hearing loss or single-sided deafness is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.-Signs and symptoms:Patients with unilateral hearing loss have difficulty in...

 and people with mixed hearing losses who cannot otherwise wear 'in the ear' or 'behind the ear' hearing aids. The name Baha
Cochlear Baha
The Baha is a bone conduction hearing system designed, developed and marketed by Cochlear. When Cochlear bought the Swedish company Entific Medical Systems in 2005, the acronym BAHA was trademarked into Baha, since it is not considered a hearing aid by insurance companies.The Baha is a...

 is a trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

.

Background

Hearing impairment
Hearing impairment
-Definition:Deafness is the inability for the ear to interpret certain or all frequencies of sound.-Environmental Situations:Deafness can be caused by environmental situations such as noise, trauma, or other ear defections...

 is the most common physical handicap in the in industrialized world. There are two different reasons for poor hearing. One is due to lack of function in the inner ear
Inner ear
The inner ear is the innermost part of the vertebrate ear. In mammals, it consists of the bony labyrinth, a hollow cavity in the temporal bone of the skull with a system of passages comprising two main functional parts:...

, the cochlea
Cochlea
The cochlea is the auditory portion of the inner ear. It is a spiral-shaped cavity in the bony labyrinth, making 2.5 turns around its axis, the modiolus....

, the other when the sound has problems in reaching the nerve cells of the inner ear. An example of the first is the age-related hearing loss. A patient born without external ear canals is one example of the latter and here it is obvious that a conventional hearing aid
Hearing aid
A hearing aid is an electroacoustic device which typically fits in or behind the wearer's ear, and is designed to amplify and modulate sound for the wearer. Earlier devices, known as "ear trumpets" or "ear horns", were passive funnel-like amplification cones designed to gather sound energy and...

 with a mould in the ear canal opening is not possible to use. These patients often have a normal inner ear function as the external ear canal and the inner ear are developed at different stages during pregnancy. As the inner ear is normal, sound conducted via the skull bone could give normal/near normal 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 like discomfort and pain due to the pressure needed. The sound quality is also impaired as much of the sound energy is lost in the soft tissue over the skull bone. This is especially true for the higher sound frequencies so important for speech understanding in noise.

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 to use a hearing aid fitted in the ear canal. Direct bone conduction through a vibrator attached to a skin penetrating implant will overcome these disadvantages.

In 1977 the first three patients were implanted with a bone conduction hearing solution by Dr Anders Tjellström at the Ear –Nose- and Throat department at Sahlgrenska University Hospital in Gothenburg, Sweden. A 4 mm long titanium screw was inserted in the bone behind the ear and a specially designed bone conduction hearing aid was attached. The initial results were very good and since then about 100,000 patients all over the world have been treated according to this principle.

The implant in the bone is made of titanium and will osseointegrate according to the research performed by professor Per-Ingvar Brånemark
Per-Ingvar Brånemark
Per-Ingvar Brånemark is a Swedish orthopedic surgeon and research professor, touted as the "father of modern dental implantology." The Brånemark Osseointegration Center , named after its founder, was founded in 1989 in Gothenburg, Sweden....

. The hearing instrument is impedance matched and developed by professor Bo Håkansson at Chalmers University of Technology
Chalmers University of Technology
Chalmers University of Technology , is a Swedish university located in Gothenburg that focuses on research and education in technology, natural science and architecture.-History:...

 in Gothenburg, Sweden under the name of Baha. The initial design has been refined and improved first by the industrial partner Entific and later by Cochlear Bone Anchored Solutions both in Gothenburg. Since 2009 the Danish hearing aid company Oticon
Oticon
Oticon is the worlds second largest hearing aid manufacturer. It is situated in Denmark outside the capital Copenhagen. It was founded in 1904 by Hans Demant, whose wife was hearing impaired. Oticon is particularly well known for their loose management style referred to as "Spaghetti Organization"...

 has also developed a device based on the same principle. Osseointegration
Osseointegration
Osseointegration derives from the Greek osteon, bone, and the Latin integrare, to make whole. The term refers to the direct structural and functional connection between living bone and the surface of a load-bearing artificial implant...

 has been defined as the direct contact between living bone and an implant that can take a load. No soft tissue at the interface.

With Entific selling the trademark to Cochlear, Cochlear turned the acronym BAHA into a full-fledged trademark name, so to avoid unnecessary confusion between the "BAHA
BAHA
BAHA may refer to:*Bone anchored hearing aid*Cochlear Baha*Berkeley Architectural Heritage Association*Relating to the Bahá'í Faith*A misspelling of Baja...

" as a type of sound processor and technology and the Baha
Cochlear Baha
The Baha is a bone conduction hearing system designed, developed and marketed by Cochlear. When Cochlear bought the Swedish company Entific Medical Systems in 2005, the acronym BAHA was trademarked into Baha, since it is not considered a hearing aid by insurance companies.The Baha is a...

 as an hearing aid. This choice was motivated by the policy of insurances to distinguish between sound processors and a full bone conduction implant system for coverage's purpose. The other major brand of bone conduction device is manufactured by well-known hearing aid manufacturer, Oticon Medical

Use and operation

Bone-anchored hearing aids use a surgically implanted abutment
Abutment
An abutment is, generally, the point where two structures or objects meet. This word comes from the verb abut, which means adjoin or having common boundary. An abutment is an engineering term that describes a structure located at the ends of a bridge, where the bridge slab adjoins the approaching...

 to transmit sound by direct conduction through bone
Bone conduction
Bone conduction is the conduction of sound to the inner ear through the bones of the skull.Bone conduction is the reason why a person's voice sounds different to him/her when it is recorded and played back. Because the skull conducts lower frequencies better than air, people perceive their own...

 to the inner ear, bypassing the external auditory canal and middle ear. A titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

 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.

Both Cochlear and Oticon Medical's Baha bone conduction hearing solutions utilize a bone-anchored sound processor that convert incoming sound into vibrations. Cochlear Baha utilises a snap-lock coupling which allows them to clip onto the implanted abutment, The Oticon Ponto uses a spring based coupling. The sound processor units run on small circular batteries which last approx 6 to 14 days. The coupling is designed to detach upon impact as a safety feature to prevent damage to the bone or surrounding tissues.

Chronic ear disease

This is a fairly common condition often associated with continuously or intermittent drainage from the ear canal. As a rule these patients also have a hearing loss and often need amplification. A conventional air conduction aid with a mould placed in the ear canal opening is often impossible to wear due to the drainage – and may even provoke drainage. If the hearing loss is significant an air conduction aid may have difficulty to overcome the dysfunction of the eardrum and middle ear bones. The solution for these patients is a bone conduction hearing device bypassing the middle ear and stimulating the inner ear directly through the skull. Transmission of sound in the bone is very good with minimum of attenuation and very little distortion. In fact the hair cells of the inner ear cannot tell if the sound is coming the normal way through the external ear canal and middle ear or via vibrations in the bone.

Single sided deafness

A person who is deaf on one side
Unilateral hearing loss
Unilateral hearing loss or single-sided deafness is a type of hearing impairment where there is normal hearing in one ear and impaired hearing in the other ear.-Signs and symptoms:Patients with unilateral hearing loss have difficulty in...

 regardless of reason often has difficulties with his/her hearing even if the other ear is normal. This is especially true in demanding situations such as listening in noisy surroundings and when several people are speaking at the same time. A Baha could be of good help in lifting the head shadow to the deaf side. Hearing impairment in only hearing ear is another difficult hearing condition. Conventional ear surgery always involves a risk of hearing loss due to the surgical procedure. Most ear surgeons are thus reluctant to perform surgery on only hearing ear. The Baha surgery involves no such risk and is often a good solution.

External ear canal problems

Irritation in the external ear canal can be due to inflammation or eczema and makes it impossible or very uncomfortable to use a conventional air conduction aid. Direct bone conduction could be a very good option.

Malformations

Patients with malformations are not always suitable for reconstructive surgery. Treacher-Collins
Treacher Collins syndrome
Treacher Collins syndrome , also known as Treacher Collins–Franceschetti syndrome, or mandibulofacial dysostosis is a rare autosomal dominant congenital disorder characterized by craniofacial deformities, such as absent cheekbones. Treacher Collins syndrome is found in about 1 in 10,000 births, ....

 patients could have significant malformations with ossicular defects and also have an abnormal route of the facial nerve. These structures as well as the inner ear could be at danger at surgery.

Down Syndrome
Down syndrome
Down syndrome, or Down's syndrome, trisomy 21, is a chromosomal condition caused by the presence of all or part of an extra 21st chromosome. It is named after John Langdon Down, the British physician who described the syndrome in 1866. The condition was clinically described earlier in the 19th...

 patients often have a narrow ear canal and also middle ear malformation leading to impaired hearing. It has been suggested that some part of the mental retardation seen in these patient is partly due to their poor hearing.

The surgery can only take place once the skull is at least 2.5 mm thick. Children who suffer certain syndroms may have a slighter build, thinner bone or unusual anatomy, where as other children may have a thicker skull at a younger age and therefore it is difficult to give an age estimate.

In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, stage one surgery for Baha has been implanted into children as young as 13 months at the Hospital for Sick Children
Hospital for Sick Children
The Hospital for Sick Children – is a major paediatric centre for the Greater Toronto Area, serving patients up to age 18. Located on University Avenue in Downtown Toronto, SickKids is part of the city’s Discovery District, a critical mass of scientists and entrepreneurs who are focused on...

 in Toronto
Toronto
Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

. Stage two surgery has been done as early as 22 months. In the U.S., the Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...

 (FDA) only approves Baha implantation of children aged 5 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 a Baha against the skull.

Benefits

The benefits of Bone Anchored Hearing Aid such as Baha
Cochlear Baha
The Baha is a bone conduction hearing system designed, developed and marketed by Cochlear. When Cochlear bought the Swedish company Entific Medical Systems in 2005, the acronym BAHA was trademarked into Baha, since it is not considered a hearing aid by insurance companies.The Baha is a...

 are well documented. By bypassing the outer or middle ear, Baha can increase hearing in noisy situations and help localise sounds. The benefit is not only improved speech understanding, hearing with Baha results in a natural sound with less distortion and feedback when compared with conventional hearing aids.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 (SSD), Baha sends the sound via the skull bone from the deaf side to the inner ear of the hearing side. This transfer of sound gives a 360-degree sound awareness.

Surgical procedure


In adults, surgery is often performed under local anaesthesia and as an outpatient procedure. The bone behind the ear is exposed through straight incision or with the help of a special designed 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 pre-mounted coupling is inserted under generous cooling to minimize the inevitable surgical trauma to the bone.

Most 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 only perform a minimum of soft tissue work. Three to six weeks later the audiologist will fit and adjust the hearing processor according to the patient’s hearing level.

The surgical procedure has been described in detail by Tjellström et al. 2001

Everyday handling of skin at implant site

A skin penetration has to be taken care of. It could be compared with brushing one’s teeth. If neglected there is a great risk of inflammation around the Baha coupling. Daily cleaning routine is of great importance. This is often more easy to do if there are no hair follicles close to the coupling. The use of a mild ointment is also often recommended.

One important feature with the Baha is that if a patient for whatever reason do not want to continue with the arrangement it takes the surgeon less than a minute to remove the whole thing. The Baha will not restrict the wearer from any activities such as outdoor life, sporting activities etc.

Risks

The surgical procedure is simple both for the surgeon and the patient. Very few and minor risk are at hand for the experienced ear surgeon. Minimal discomfort and pain is reported. Some numbness of the area around the implant is not uncommon as small superficial nerves in the skin are sectioned during the procedure. However, these problems often disappear after some time. There is no risk of further hearing loss due to the surgery.

Although designed to come off the post should they be contacted, the sound processor unit are quite fragile if impacted.

Cochlear has a warranty and repair policy. The audiologist or Cochlear may provide "loaner" unit.

Special concerns in small children

Hearing is of utmost importance for a normal speech and social development. See review paper by Lieu 2004. The skull bone in children is often very thin and also softer than in the adult. Surgery is thus often delayed until the age of 4 – 5 years. In the meantime the child with bilateral atresia will be fitted with a sweatband round the head called the Baha Softband with a coupling for a Baha. This is often made already at the age of one month. These small babies often tolerate this arrangement very well. For further reading se Papsin et al. 1997.

The surgical reconstruction of a malformed or missing external ear canal is much easier when the child is older. One important advantage with the Baha is that the procedure is reversible. A child can be fitted first with a Softband and at the age of 4 – 5 years get an implant for a Baha. When the patient is older and radiographic examination has shown that the prospects for reconstructive surgery is good and can be successfully made, it is very easy to remove the implant.

Costs

In America the cost of the Baha device is approximately $ 4000. In The Netherlands the cost of the device is approx € 3000 (in 2008). The cost of the titanium implant, surgery and aftercare from surgeon and audiologist must also be considered.
In America surgery cost can cost as much as $ 30,000 including the device and can vary depending upon the type and hospital. In the UK the procedure is usually offered on the NHS, although not all areas will do this for patient who retain hearing in one ear.

Manufacturers

At present there are two devices available from Cochlear BAS and Oticon Medical. The vibrator is basically the same and the differences are mainly in the design and in some of the features of sound processing.

Cochlear markets the Baha 3 System and Oticon markets the Ponto brand receiver. Both units attach onto the titanium abutment and act as receivers sending sound through the implant to the skull and to the inner ear. The two brands are distinguished from each other easily by appearance as the Baha 3 BP100 is rectangular and the Ponto is teardrop shaped.
Cochlear has registered the name Baha
Cochlear Baha
The Baha is a bone conduction hearing system designed, developed and marketed by Cochlear. When Cochlear bought the Swedish company Entific Medical Systems in 2005, the acronym BAHA was trademarked into Baha, since it is not considered a hearing aid by insurance companies.The Baha is a...

 as a trademark
Trademark
A trademark, trade mark, or trade-mark is a distinctive sign or indicator used by an individual, business organization, or other legal entity to identify that the products or services to consumers with which the trademark appears originate from a unique source, and to distinguish its products or...

.

Models

There are different types of systems. The Baha Classic and Compact will not be manufactured anymore. In 2008 the following types are available: the Cochlear Baha Cordelle, Divino and Intenso. In 2009 the Baha 3 (BP100) and Ponto pro were released. May 2011 Oticon Medical launched a more powerful version of the Ponto Pro the Ponto Pro Power. and Cochlear released the Baha 3 Power which can be fitted to the same patients as the Intenso
  • Baha Cordelle II. A bodyworn Baha for people with a severe hearing loss who need more amplification than the other Bahas available. The Cordelle II consists of a transducer which snaps onto the abutment and a bodyworn unit. This is the only Baha to have an induction telecoil receiver built in.
  • Baha Classic 300. This is the older Baha device which has been mostly superseded by the Compact and Divino but is still worn by those with more severe and mixed hearing losses. This will be discontinued in February 2007, with repairs ceasing to out of scheme models after that.

  • Baha Compact. Rated as identical to the Classic but found to be slightly less powerful by a few users. The Compact is 33% smaller than the Classic and has added AGCo and improved shielding from mobile telephone signals. Until July 2005 the Compact was the latest model.
  • Baha Divino. Released in July 2005 this is the first digital Baha which has a built-in directional microphone.
  • Baha Intenso. More power and clearer sound quality in all types of listening environments plus far less irritation from feedback.
  • Cochlear Baha 3 (BP100) - released in 2009 the BP100 is a fully programmable, multi channel digital sound processor (http://www.cochlear.com/au/baha-bone-conduction-implants/baha-products/baha-3/sound-processor)
  • Cochlear Baha 3 Power (BP110) - released in 2011 the Baha 3 Power is a higher powered version of the fully programmable digital sound processor (http://www.cochlear.com/au/baha-bone-conduction-implants/baha-products/baha-3/sound-processor)
  • Oticon Medical http://www.oticonmedical.com/oticon_medical/com/AboutOticonMedical/About/Downloads/2a.product_overview_UK.pdf) Ponto Pro is a teardrop shaped baha receiver from a well known manufacturer of hearing aids.
  • Ponto Power added as a higher-powered version of Ponto, offering more volume with no discernable feedback.

External links

The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
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