Sacramento, Calif.-- A new type of hearing aid for people who are unable to wear conventional ones because of chronic ear drainage, skin irritation or ear malformation is available from the Department of Otolaryngology at UC Davis Medical Center.
The new device, called a bone-anchored hearing aid, is implanted in the skull behind the ear. The unit consists of an implanted titanium fixture that attaches to a removable sound processor. UC Davis Medical Center is one of only four medical centers in California offering bone-anchored hearing aids. The others are located in the Bay Area and Los Angeles.
"Most people with permanent hearing problems can benefit from a conventional hearing aid, which consists of a sound amplifier that attaches in or behind the ear," says Hilary A. Brodie, associate professor and chair of the Department of Otolaryngology.
"Some people, however, are unable to wear these devices because they are born without an ear canal or outer ear, leaving no place to attach the aid. Others cannot wear them because of chronic ear drainage problems or skin irritation from the devices. This new device gives patients with conductive hearing loss a light weight and unobtrusive alternative to improve hearing and quality of life."
Doctors have long realized that sound vibrations transmitted directly to the skull provide a good alternative for people with conduction problems who cannot wear conventional hearing aids.
In conductive hearing loss, the inner ear is capable of transmitting sounds to the brain for interpretation, but the outer or middle ear has problems collecting the sounds. For example, ear infections or wax can temporarily plug ear canals, preventing complete transmission of sound waves to the inner ear.
Birth defects, though they are a less common cause, can also result in abnormalities or missing parts of the ear that are necessary for transmitting sound. Other options to conventional hearing aids are needed for patients who, for a variety of reasons, are unable to wear them.
"One type of alternative to conventional hearing aids depends on bone for the transmission of sound," says Brodie. "The most common unit incorporates a steel headband, which is both uncomfortable and cumbersome for patients. The new bone-anchored device is small and unobtrusive and can dramatically improve patient’s lives."
Consider John Keeter, a 48-year-old forklift driver from Proberta, Calif., who wore a headband since age 7. His hearing loss resulted from an ear defect caused by Treacher-Collins syndrome, a rare genetic condition that affects the development of the structures of the head and face.
"The headband gave me headaches and created a permanent groove in my skull," he says. Brodie implanted a bone-anchored hearing aid this year, and Keeter reports that "it’s meant freedom." He says that even combing his hair is now a simple task, whereas before the headband would interfere.
"I am hearing a lot more than before, like a dog barking outside or the piano at church," he says. His family has told him that his speech is softer now, which Keeter attributes to being able to hear his own voice better.
The device is implanted in two steps
The first step is accomplished under local anesthesia and takes approximately one hour. A hole is drilled in the skull behind the ear, and a titanium anchor is implanted. Titanium is a metal widely used for medical implants and surgical devices because of its strength and resistance to attack by body fluids. As the bone heals, the fixture is incorporated within the bone, forming a secure bond after a few months.
In the second stage, a coupling device for the sound processor is attached to the anchor. The sound processor, which is about the size of a matchbox, is worn externally behind the ear and is removable by the user.
The bone-anchored hearing aid is a popular device in Europe, but has only received FDA-approval in the United States in 1996. About 150 doctors currently perform the procedure nationwide.
Bone anchored hearing aids may be used in children, but are not recommended for children under 5 years old because of insufficient bone to properly anchor the devices.
Entific Medical Systems, based in Gothenburg, Sweden, is the manufacturer of the device.