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.
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 over three to six months after surgery in a process called osseointegration. The hearing aid can be used once osseointegration is complete, usually three to six months after implantation.
Entific's BAHA hearing aids have a patented[1] snap-lock coupling which allows it to clip into the abutment. The BAHA is then treated as a regular hearing aid, running on small circular batteries which last approx 6-14 days. The snaplock 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.
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, or a short general anaesthetic. Most patients are able to leave hospital within a few hours, or the day after their procedure with many not even requiring 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 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.
Procedure for Very Young Children - Two Stage Operation A double stage procedure is sometimes carried out for small children / babies or other medical reasons. The first stage involves peeling back a small 1cmx1cm section of skin behind the ear, 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 osseointergration (can be 6-8 months) the second stage os 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 and risks
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 (may be) 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 assists in minimizing infection.
Alternatives
- new open-ear hearing aids hearing aids
- Vibrant soundbridge [3]
Suitability is also confirmed by a series of audiological and basic medical tests.
Manufacturers
At present Entific Medical Systems, a Swedish company, is the only manufacturer of bone anchored hearing aids and has registered the acronym BAHA™ as a trademark[2] . On 4 March 2005, Entific was bought out by the Australian company Cochlear Limited[3] which was the first company to manufacture cochlear implants. They offer four types of system available. The Cordelle, Classic, Compact and Divino.
- 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 Feb 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 Jul 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.
References
External links
- Entific Medical Systems Free registration required to get full access to information.
- Patients' BAHA site "Run by baha users, for baha users."
- BAHA Nework Japan
- The Let Them Hear Foundation A 501(c)(3) non-profit who provides free insurance appeal assistance to individuals who have been turned down by their insurers for BAHA devices
A conference concerning microtia treatment options is sponsored by the Let Them Hear Foundation and held in Palo Alto, California. The conference is always the first Saturday in October. Conference attendees will be able to see presentations on both medpor and rib graft microtia reconstruction, atresia repair, prosthetics, jaw distraction and Baha devices.