BAHA (bone anchored hearing aid)

While it can be used like a conventional hearing aid, usually it is used in people who have good hearing on one side and no hearing on the other -- thus it is a surgically implanted version of the CROS aid. Most people with unilateral hearing loss are enthusiastic about BAHA aids because it works very well and it is unobtrusive. It requires "very good" hearing on the opposite side. It eliminates the head shadow effect, occlusion effect, and feedback.

BAHA (bone anchored hearing aid). This type of hearing aid works well in persons with severe unilateral hearing loss. The image to the left, from Prosper hospital, shows how a button is inserted into the bone of the skull above the ear. The middle image is from Island Hearing. The device is attached to the button within the skull. It is very unobtrusive (once the hair is put back into place).

Clinical indications:

The BAHA is most suitable for someone with a profound unilateral hearing loss (PTA > 90DB, WR < 20%). The other ear should have normal hearing.

The BAHA can also be used as a substitute for a powerful hearing aid or stapes surgery on an ear with a conductive hearing loss. It is less risky than stapes surgery, and probably more durable. The big disadvantage compared to stapes surgery, though, is that there is a visible "stud" protruding through the skin of ones skull, and also that one has to deal with batteries, and a device.

How it is implanted.

First, a titanium stud (called a fixture) is placed in the bone behind the ear. One then waits for 3 months until the titanium and bone heal together. After this, the sound processor is clipped onto the stud (it can come easily on and off).

How it works.

The sound processor converts sound into vibration, which is then transmitted to the titanium stud. Sound is transmitted through the bone of the skull to the other ear. Patients perceive sounds as coming from the deaf ear. Both ears remain free -- unlike the situation of a CROS aid which requires something placed into the good ear.

Testing in the office

A BAHA with a headband provides a quick way of telling if the BAHA will work for any individual patient.

Comparison studies.

Multi-institutional data show that the BAHA is superior to the CROS device for ease of communication, reverberation, background noise, and aversion to sound. Average patient satisfaction is 80%.

What it doesn't do: Sound localization

BAHA usually doesn't improve sound localization. People with normal hearing use timing differences between the ears to localize sound. This is not available in the BAHA because all sound ends up going to the good ear.

Risks and complications.

The most common problem is skin overgrowth over the stud, there also can be problems with infections, loose fixture, bone exposure, fixture loss. House and Kutz reported that postoperative problems requiring intervention occured in 12.8% of their patients (2007). Skin overgrowth occured in 7.4%, occuring on average 12 months after the initial procedure. Implant extrusion occured in 3.4% of patients. Wound infections occured in about 1% of patients.

Overall

The BAHA is a significant advance in the treatment of persons with single sided hearing loss.

References:

House JW, Kutz JW. Bone-anchored hearing aids: incidence and management of postoperative complications. Otol Neurotol 28:213-217, 2007