Baha, when conventional devices won't do

Abstract

FigureThere is a different type of hearing device called the Baha® bone conduction implant, also known as an osseointegrated auditory prosthesis, that is made especially for people with a long history of sick ears and ear surgeries. Such patients tend to be frustrated with their poor hearing and are often nervous about the risk of another ear infection. They also want to avoid more ear surgery at all costs. If the health of the ear can be stabilized, which is often a challenge, a conventional hearing aid may be used. Unfortunately, ear infections tend to recur, making regular hearing aids contraindicated for long periods of time. Years ago we fitted people who had this problem with a bone conductor on a headband attached to a high-power, body-worn hearing aid. Some of these fittings brought much happiness to patients who after not hearing sound for many years suddenly could hear well. The down side of this type of fitting is the wear and tear that the vibrator and the headband inflict on the wearer's head. The band is often too loose or too tight. It is hard to keep in place, and it is uncomfortable to wear. Extended use of the vibrator leads to an indentation in the patient's head created by the constant pressure exerted by the bone vibrator, which eventually erodes the bone directly under the vibrator. We usually try to fix this problem by moving the vibrator to the opposite side of the head, but eventually patients move it back to the original spot because it allows them to hear better. Developed in Sweden in 1977, Baha received FDA clearance for use in this country in 1996. Cochlear purchased Entific, the company that made it, in 2005. HOW IT WORKS Implanting the Baha is a relatively simple surgical procedure. A prosthesis is screwed into the mastoid. Then, 3 to 6 months later, the Baha sound processor is attached to the prosthesis with a coupler. For people who have good hearing via bone conduction and poor hearing via air conduction, this can work extremely well. The amplified sound bypasses the defective outer and middle ear and goes directly into both inner ears. The quality of hearing is described as quite good. Currently, Baha implantation is restricted to people age 5 years and above. Before that age, a child may use a Baha sound processor worn on a soft band and used similarly to a conventional bone-conduction hearing aid. After surgery, the child may use the same Baha sound processor on the implant and abutment. The reason for restricting implantation by age is that younger children are thought to have immature bone density, which may not permit good osseointegration. To ensure osseointegration with pediatric patients, it is recommended that the sound processor not be attached to the prosthesis until 6 months after surgery. In adults the waiting period is usually 3 months. Figure 1 shows the parts of the Baha. The separate piece in the photo is the small titanium implant that is screwed into the bone behind the patient's ear. New bone tissue grows around the implant securing it to the head. The implant is attached to an abutment that connects it to the hearing aid. The main part of the system is the sound processor, which receives the sound, amplifies it, and then transfers it to the patient via vibrations.Figure 1: The Baha system.ADVANTAGES For appropriate candidates, Baha has several benefits over alternative fittings: Feedback is reduced or eliminated. There is no discomfort from wearing a large, tightly fitting earmold. The conductive hearing loss is bypassed so the power requirement is lower. Reducing the required gain results in less saturation and distortion. There is no headband to wear. Because Baha is perceived as a surgical procedure rather than a hearing aid, it is currently approved by Medicare and many insurance companies. ACCESSORIES Various accessories can be used with Baha. Direct audio input is available so the patient can connect to a stereo, TV, or MP3 player. The unit can be used with a Microlink FM receiver to help with classroom situations and hearing in noise. A telecoil unit can be used to improve telephone listening. SUMMARY If conventional hearing aids or ear surgery does not provide a patient with good hearing, then a Baha should be considered. Its use is indicated when feedback is intractable and/or when the patient suffers from irritated ears or has malformed ears or ear canals. The Baha is also sometimes recommended for single-sided deafness.