Bone-anchored hearing aid

A Bone-Anchored Hearing Aid is a type of hearing aid based on bone conduction. It is primarily suited to people who have conductive hearing losses, unilateral hearing loss and people with mixed hearing losses who cannot otherwise wear 'in the ear' or 'behind the ear' hearing aids. The acronym Baha is a trademark. Note: Entific sold the rights to Cochlear. Cochlear realized that many insurance companies were having trouble distinguishing the BAHA as a sound processor and not a hearing aid, which makes a huge difference for insurance coverage. They removed the acronym and have since called it strictly the Baha.

Use and Operation

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 "post" 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 external abutment of the titanium implant. The implant vibrates the skull and inner ear, which stimulate the nerve fibers of the inner ear, allowing hearing.

The titanium fixture bonds with the surrounding tissue in a process called osseointegration. The hearing aid can be used once osseointegration is complete, usually two to six months after implantation.

Both Cochlear and Otticon's Baha bone conduction hearing solutions utilize a bone-anchored hearing aid . Both solutions utilize a snap-lock coupling which allows them to clip onto the implanted abutment. The Baha units are then treated as regular sound processors, running on small circular batteries which last approx 6 to 14 days. The snap-lock coupling is designed to detach upon impact as a safety feature to prevent damage to the implant or surrounding tissues.

Suitability

Bone-anchored hearing aids can help:

• people who have chronic inflammation or infection of the ear canal and cannot wear standard 'in the ear' air conduction hearing aids.
• people who have malformed or absent outer ear and ear canals as is common in medical conditions such as Treacher Collins syndrome or Microtia.
• people who have single-sided deafness.

Bone-anchored hearing aids have also been offered successfully to people with bilateral conductive loss due to ossicular disease e.g. Otosclerosis and for hearing impairments related to other congenital syndromes such as Down’s Syndrome.

Prior to undergoing the surgery, the patient can test the device. This involves a steel band which one can wear over the head (much like a hair band), which presses a contact against the skull on one side to which the Baha unit may be attached. The test strap is not as effective as the implant, as the skin and tissue between the contact and the skull damp the vibrations. However, it is useful in demonstrating the concept to prospective patients.

In Canada, stage one surgery for Baha has been implanted into children as young as 13 months at the Hospital for Sick Children in Toronto. Stage two surgery has been done as early as 22 months. For infants, an interim measure young infants can be provided with a Baha Softband allowing them to use a Baha. This is a tight headband which the infant wears to hold a Baha against the skull.

Surgical Procedure

In recent years, improvements to the surgical procedures have resulted in most patients being able to have a single-stage procedure carried out under local anaesthetic, or a short general anaesthetic. The new procedure developed in the United States involves a much smaller incision and is much less invasive to the patient. The photographs contained herin are from the earlier procedures and are NOT necessarily reflective of today's less invasive procedure.

Most patients are able to leave hospital within a few hours, or the day after their procedure; many do not even require analgesia in the following days.

Osseointegration is the process of the titanium fixture bonding to the bone. There is a high success rate for osseointegration—above 95%, according to the latest studies in medical journals. Occasionally, infection and other problems will prevent osseointegration from being successful. In these cases, the patient will be given time to heal, and further more-cautious attempts at the surgical procedure can be made.

In many cases, the surgeon will implant a second "sleeper" receptacle for use should the initial receptor fail or be damaged.

A double-stage procedure is sometimes carried out for small children or babies or for other medical reasons. The first stage involves peeling back a small 1 by 1 cm section of skin behind the ear, and then drilling one or more holes for the fixture. (Some surgeons will place a "sleeper" receptor.) The skin is then grafted back, and the child waits for the skull to continue to thicken and for osseointegration to occur properly. After osseointegration (can be 6 to 8 months), the second stage is performed. The second stage is another surgery in which the "post" is attached, and the skin is grafted around the "post". This will require healing for several weeks, at which point the BAHA would be fitted.

Dangers, Risks, Durability, Repairs

The titanium screw of the Baha is screwed from outside into the bone. Because of this open wound, there will always be a risk of infection.

Daily care is required. This consists of using a very soft toothbrush like tool to scrub around the post and skin area to keep it clean and not infected. Daily use of an antibiotic ointment such as Polysporin assists in minimizing infection.

Although designed to come off the post should they be contacted, the units are quite fragile if impacted only slightly.

Cochlear has a warranty and repair policy. The audiologist or Cochlear may provide "loaner" units during the repair period.

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). In America surgery cost can cost as much as $ 30,000 including the device and can vary depending upon the type and hospital.

Manufacturers

At present [Cochlear Limited] and [Oticon Medical] are the only manufacturers of bone-anchored hearing aids. Cochlear markets the baha100 brand device and Oticon markets the Ponto brand receiver. Both units plug onto the implanted abutement screw and act as receivers sending sound through the screw to the skull and then to the other ear. The two brands are distinguished from each other easily by appearance as the baha100 is rectangular and the Ponto is teardrop shaped. Cochlear has registered the acronym Baha as a trademark .

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 Baha Cordelle, Divino and Intenso. In 2009 the BP100 and Ponto pro were released.

• 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. Newly released in July 2005 this is the long awaited digital Baha which has a built-in directional microphone. While some people are disappointed that the digital options were not very flexible, new users are said to be very happy with it. Even though the Divino takes a while to get used to for adolescents, in the long run it has been proven to be successful for most ages.
• Baha Intenso. More power and clearer sound quality in all types of listening environments plus far less irritation from feedback.
• BP100
• Oticon (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. Many users have chosen the Ponto because they believe its shape makes it easier to hide in their hair, and others believe it provide a louder transmission to the patient's good ear.

External links

• Cochlear. The manufacturer of the Baha device. Free registration required to get full access to information.
• Baha implant activation video Folk musician Patrick Costello filmed the activation of his Baha implant.
• BAHA Patients' and users site. "Run by BAHA users, for BAHA users.".
• Les curieux de la prothese Baha. A French Baha forum for the users by the users.
• Baha Network Japan. Japanese Baha network.
• Spanish Baha network. Spanish Baha network.
• The Ear Foundation's BAHA pages. Detailed information about BAHA technologies from the UK-based charity.