What is a Bone Anchored Implant?
A bone anchored implant is surgically implanted. It is also referred to as a bone anchored hearing aid (although this term is incorrect because it is not a hearing aid), or a bone anchored hearing system. It is usually used for less severe hearing loss that is conductive, mixed, or unilateral. Bone anchored implants work by transmitting sound vibrations to the ear's cochlea through vibrations via bone conduction.A bone anchored implant is not to be confused with a cochlear implant. Unlike a cochlear implant, the bone anchored implant is implanted behind the ear instead of being implanted in the ear. The bone anchored implant has three parts and functions as follows:
- An external sound processor that collects sound.
- An implanted titanium part (screw) surgically implanted behind the ear.
- A button-like holder (abutment) screwed into the implanted titanium part. This abutment is visible, and it transmits sound to the implanted part.
Surgery for a bone anchored implant is relatively simple. The titanium screw fuses with the bone after surgery, in a process called osseointegration. The sound processor can not be worn right away. Patients must wait until the titanium screw has fused with the bone. After healing and the bonding of the screw with the bone, the sound processor can be attached via the abutment.
Manufacturers of Bone Anchored Implants
Bone anchored implants were developed in other countries in the 1970s , but not cleared by the United States Food and Drug Administration (FDA) until much later. The FDA approved the bone anchored implant for use by adults in 1996. In 1999, the FDA approved it for use by children five years and older. Finally, in 2002, it was approved for use for single sided deafness (also known as unilateral deafness).
Originally, the bone anchored implant was manufactured by Entific, which sold the product as a bone anchored hearing aid (BAHA). Then in 2005, Cochlear bought Entific. Cochlear re-named the product's name from "BAHA" to Baha, a bone anchored implant. (Yes, BAHA and Baha are the same except the case is different.) This was done to remove the association with hearing aids and emphasize that the Baha is a surgical implant. (The term bone anchored hearing aid is still in common use, however.)
Before 2005, Medicare had classified the BAHA as a hearing aid and did not cover it. In late 2005, Medicare reclassified the Baha as a prosthesis. According to the Medicare Benefit Policy Manual, payable prosthetic devices include "osseointegrated implants, i.e., devices implanted in the skull that replace the function of the middle ear and provide mechanical energy to the cochlea via a mechanical transducer." Therefore, a bone anchored implant is considered a prosthesis because it "replaces" a function, making it eligible for Medicare (and theoretically, other insurance) coverage.
Another manufacturer of bone anchored implants is Oticon Medical. Oticon Medical's first venture into the bone anchored implant market was called the Ponto. The FDA approved the Ponto in summer 2009 for use by both adults and children.
Candidates for Bone Anchored Implants
Typical candidates for bone anchored implants can not use regular hearing aids. They may have malformed ears due to conditions such as:
Children whose skulls are thick enough can use bone anchored implants. So can people with infected ear canals that cause chronic drainage.Risks of Bone Anchored Implants
There is a risk of skin reactions in the area where the abutment is. Any skin reactions must be treated because untreated skin reactions can lead to extrusion of the implant or infection. Skin thickness (defined as how high the skin reaches up towards the abutment) can also be an issue. A study of 248 adult participants found no relationship between skin thickness and implant loss or skin reactions. This study did find that 23 implants where the skin was too thick, had to have tissue reduction surgery. Another risk is of failed osseointegration of the implant.Support for Users of Bone Anchored Implants
Yahoo Groups has a discussion list BAHA_PPL. Cochlear also has a group of Baha recipients in its Cochlear Community.
Bone anchored hearing implants have also been discussed on the About.com Deafness blog: Cochlear Implant with Unilateral Hearing Loss? Discussions have also taken place on the About.com Deafness forum in these threads:
Sources:
Bone-Anchored Hearing Aid Implant Location in Relation to Skin Reactions. Archives of Otolaryngology - Head and Neck Surgery. 2009;135(8):742-747. http://archotol.ama-assn.org/cgi/content/full/135/8/742. Accessed September 2010.
Cochlear: Bone Anchored Hearing Solution
Medicare Benefit Policy Manual, Chapter 16
Taking the Ear Out of the Equation. Hearing Health Magazine, volume 20, number 3, September 1, 2004. http://www.drf.org/magazine/30/Fall+2004+Issue/article/187. Accessed September 2010.
