Implantable System Replaces Traditional Hearing Aids

A new hearing system, which includes a magnet implanted in the middle ear under local anesthetic, helps alleviate the problems that some people experience with more traditional hearing aids. About half of the people fitted with standard hearing aids do not wear them because they can be uncomfortable. Some people have to turn up the volume on their hearing aid to levels that cause feedback, distortion and squealing. Sounds may seem muffled or garbled. A snug fit is required and the resulting air pressure within the ear may cause a feeling that the individual is speaking from within a tunnel or barrel.

Where a standard hearing aid uses air pressure to transport sound to the middle ear, the new hearing system's sound processor receives sound and converts it to electromagnetic waves. The electromagnetic waves are transmitted to an implanted magnet, causing it to vibrate. These vibrations are passed on to the small bones of the middle ear, providing clear, natural sound. The electromagnetic waves can increase sound levels without the volume amplification required by standard hearing aids. For many people the new systems are more comfortable to wear than standard hearing aids because the air pressure on each side of sound processor is the same.

The new devices, such as the Direct System from SoundTec, Inc., were recently approved by the US Food and Drug Administration for use in adults. The Medical College of Wisconsin offers this option and is preparing to conduct clinical trials of the system in children at Children's Hospital of Wisconsin, a Medical College affiliate.

The new hearing system consists of two components: a tiny magnet and a sound processor. In the implant procedure, the tissue between the eardrum and the ear canal is carefully cut so that the eardrum becomes a "flap," providing access to the middle ear. The micro-magnet, which has been hermetically sealed in a titanium canister, is then placed on a segment of the three tiny bones in the middle ear. Finally, the eardrum flap is closed, completing the simple procedure.

The procedure takes about 30 minutes and is performed in an outpatient ambulatory surgery center under local anesthetic. Patients receive pain medication and a mild sedative but remain awake during the procedure. After the incision heals, patients are fitted with a sound processor placed in the outer ear canal like a standard hearing aid. It takes about three months after the magnet is implanted before the new system can be used.

The new hearing system is appropriate for people who have mild to moderate hearing loss from nerve damage to hair cells in the inner ear, the most common cause of hearing impairment. They should be able to understand at least 60% of words they hear, as determined by hearing tests. Some individuals, including those with permanent damage to the middle ear, will not benefit from the new hearing system.

The chief drawback to the new device is that it cannot be worn during a magnetic resonance imaging (MRI) test. MRI uses magnets to provide views of the internal structures of the body. If an MRI is required, the hearing system's magnet and sound processor must be removed from the ear. The magnet can be reimplanted after the MRI. On the other hand, a CT or CAT scan (computed tomography) can be performed with the hearing system's magnet in place. Computed tomography is a type of X-ray technique also used to view internal structures of the body. In addition, insurance usually does not pay for hearing aids or for the new hearing system, so the entire cost is borne by the patient.

The Medical College of Wisconsin is offering the new hearing system in conjunction with Children's Hospital of Wisconsin’s ambulatory surgery center for an all-inclusive price of $5,500, which is about the same cost as the top-quality, digital air conduction hearing aids currently on the market.

MCW Health News presents up-to-date information on patient care and medical research by the physicians of the Medical College of Wisconsin.