Bone conduction systems are designed for people with conductive or mixed hearing loss, or single-sided deafness. They work by utilizing our body’s natural ability to conduct sound. There are two ways we hear sound: through air conduction and through bone conduction. Bone conduction systems were developed for people with conductive and mixed hearing loss, or single-sided deafness, to bypass air conduction hearing utilizing the patient’s better bone conduction hearing. There are two types of bone conduction systems as of 2015:
- Bone conduction processor with abutment
- Bone conduction processor with magnet system
Both systems have an implanted titanium post placed behind the ear in the mastoid bone, and then use an abutment or magnet to obtain sound from an external speech processor.
Small Titanium Implant
Abutment without Sound Processor
Sound Processor on the Abutment
The external sound processor takes in acoustic sound and translates the signal into vibrations. Those vibrations are sent, via the implant and abutment, through the skull to a functioning inner ear rather than through problems in the outer and/or middle ear – a process known as direct bone conduction.
A bone conduction system is an auditory osseointegrated implant system, which is an alternative hearing instrument for those who can benefit when there is no other suitable aid. The device, originally called the Bone Anchored Hearing Aid (Baha), is implanted in the temporal bone behind the ear and actually fuses (osseointegrates) with bone behind the ear to provide transmission of sound via direct bone conduction. Patients with conductive or mixed hearing loss, or single-sided deafness benefit from this device. The Baha device will help users localize sounds and improve hearing in competitive noise situations to a varying degree dependent upon the degree of underlying hearing loss. The Baha implant has been used successfully for more than 30 years and has become a treatment of choice for tens of thousands of hearing impaired people worldwide.
Bone Conduction Magnet System: Much like the bone conduction system with abutment, in the bone conduction magnet system sound is translated into vibrations by the external speech processor. A magnet is attached to the external processor. The vibrations are then transmitted from the external sound processor and magnet to the internal magnet, then to the titanium implant. Sounds are then delivered to the functioning inner ear. This option leaves the patient without any abutment, but requires less hearing loss to be present.
Sensorineural hearing loss means that there is a problem in the inner ear (cochlea) or auditory nerve. A bone conduction device may not be the best solution for you, unless you have single-sided deafness (deafness in one ear and normal hearing in the other ear), or there is a reason that you may not wear a conventional hearing aid.
If you are deaf in one ear, also referred to as single-sided deafness (SSD), a bone anchored hearing system may be the most appropriate solution. Being deaf on one side reduces not only your ability to locate sounds but also your ability to follow conversations in noisy environments – a combination that can make everyday life quite challenging. Traffic situations, such as biking and jogging, and noisy situations such as meetings and social gatherings can be particularly problematic if you are deaf in one ear. A bone anchored hearing system can pick up sounds on your deaf side, convert them into sound vibrations and transfer them to your healthy ear via the skull bone. By reducing the head shadow effect and making it easier to understand speech, bone anchored hearing systems can take much of the work out of listening.
Sensorineural Hearing Loss
Conductive hearing loss happens when an obstacle somewhere in the outer and/or middle ear stops sound from reaching your inner ear at an audible volume. Conductive hearing loss is often caused by chronic ear infections. These can be aggravated by conventional hearing aids as they physically block the ear canal, which increases the risk of irritation and infection. With a bone anchored device, these problems can be reduced or avoided, as the ear canal is always open. Another common cause of conductive or mixed hearing loss is atresia, a malformation of the outer ear where the ear canal is either missing or very narrow. By transmitting the sound directly to the inner ear via the skull bone, without it having to pass through the ear canal and middle ear, sounds completely bypass these obstacles allowing for better hearing and speech understanding.
Conductive Hearing Loss
Mixed hearing loss is a combination of sensorineural and conductive hearing loss. Much like with conductive hearing loss, a bone conduction device concentrates on compensating for the sensorineural hearing loss by amplifying sounds without having to first break through the ‘road block’ in the ear canal or middle ear. The result is clearer, more natural sound quality.
Mixed Hearing Loss
Bone conduction systems are available for up to moderately severe conductive or mixed hearing losses. Possible Baha candidates may have hearing loss from:
- Malformation of the ear canal or middle ear
- Chronic ear infections (outer or middle ear)
- Congenital atresia
- Middle ear dysfunction/disease
- Sudden hearing loss
- Acoustic neuroma
- Meniere’s disease
Children may also be candidates for bone conduction devices. For children with hearing loss to successfully develop language skills, early stimulation of the inner ear (cochlea) is essential. A softband is ideal for children who are either too young to have an implant, or whose hearing problems are temporary. Wearing the sound processor on a softband, rather than on an abutment, is also a good way to evaluate how much the sound processor is helping your child, before deciding to have an implant placed. Softbands are elastic and adjustable, fitting any head size- even infants. The softband can also be moved to the optimal position for comfort and hearing. Children who need a processor on both sides can get a special softband for that as well.
Images provided by Cochlear and Oticon Medical