Hearing aids, used in people with hearing loss, vary in the way they deliver sound to the cochlea. Most of them are based on air conduction, while another group uses a different conduction route, which is bone conduction, the so-called BC or Bone Conduction.

Evaluation of BC hearing instruments

Conventional bone conduction hearing aids were fitted using various types of bands or, if the patient had them, using spectacle frames. However, this was very restrictive for the patient and, as a result, did not allow their widespread use by a large group of people. The 1950s, however, brought a breakthrough in this field, thanks to Professor Branemark, who discovered the phenomenon of osseointegration. This is the process by which bone tissue fuses with the titanium alloy to cover the surface of the implant. This phenomenon has been used in many fields of medicine, including dentistry as well as ENT.

BHTA system

In 1977, the first titanium implant with a bone conduction hearing aid was placed in a patient. This was the first solution of its kind to be used in the treatment of hearing loss. In contrast, a commercial device of this type has been available on the market since 1987 and is based on the BHTA system. The BHTA system uses a permanent connection between the titanium implant and the bone to transmit sound directly to the inner ear, through the skull, bypassing the skin and subcutaneous tissues.

Today, BHTA systems are widely used throughout the world to treat hearing loss, and what is more, they are also sometimes used to treat single-sided deafness.

Indications for BHTA

The indications for a BHTA implant, are the same for both children and adults. The only limitation is the thickness of the skull, which is sometimes not achieved
in children, and it is therefore recommended that children under the age of five do not undergo this procedure.

Congenital and acquired external ear atresia, microcephaly, syndromes based on genetic defects, bilateral conductive or mixed hearing loss, inability to use conventional bone conduction hearing aids and chronic inflammation of the skin or ear canals are all indications for a BHTA implant.

Surgical procedure

The surgical procedure itself to place the implant in the bone has also evolved from a two-stage to a one-stage procedure. Initially, the procedure consisted of an abutment brought outside the scalp on which the processor was placed. The technique described above, is a percutaneous technique that largely stigmatised patients in whom the implant and processor were visible.

The technique of implants using magnets hidden under the skin brought a breakthrough, thus eliminating the visibility of the implant to a great extent. In addition, the processor itself has undergone evolution and miniaturisation, which allows it to be significantly less visible and thus more comfortable. Another improvement related to the processor itself, are the innovative mechanisms for controlling it. Newer versions are compatible with a number of mobile devices, such as smartphones and iPods, where the processor can be set up and controlled in any way desired using the appropriate application.

photo: panthermedia

Effectiveness

In the opinion of patients with a BHTA-based implant, it is a superior solution to standard hearing aids. This is confirmed by patient studies, which have noted a significant improvement in quality of life, quality and audibility of sounds, especially with regard to hearing human speech or hearing words in noise. What is more, by freeing up the ear canal, skin problems associated with the use of a hearing aid can be eliminated. Bone anchored, bilateral implants improve patients' ability to localise sounds and hear human speech, regardless of the situation and conditions around them.

The significant improvement in quality of life that patients perceive applies to many different areas of life, ranging from situations in everyday family life, easier communication with others, improved ability to concentrate.

BHTA system in single-sided deafness

Bone anchored implants using BHTA systems are increasingly being used to treat not only hearing loss, but also single-sided deafness. They avoid the head-shadow effect, as the implants transmit sound via bone conduction to the healthy ear, collecting it from the area around the head. This significantly improves the quality of hearing and therefore also improves quality of life.

For patients with unilateral deafness, the rule of thumb is that each patient should wear the BHTA implant, fixed on a band, for a period of 14 days before deciding on an implant. This allows the patient to assess how far, this type of solution, is useful to them.

Limitations associated with BHTA implantation

The greatest difficulties in the decision to implant relate to childhood. This is mainly related to the anatomical structure of the skull, which is often too immature due to the child's age. In addition, the location in which the implant is to be placed and the risk of an adverse reaction to the implant are very important.

An additional consideration is whether auricular reconstruction is being considered. If so, it is necessary to plan the medical procedures and the location of the implant accordingly.

Depending on the type of implant, it is not always possible to monitor the osseointegration process, which should also be taken into account when deciding on an implant.

Another essential element is the bone thickness, which should be a minimum of 3 mm to be able to undertake the procedure. [1]