March 3 is World Hearing Day, observed globally and designated by the World Health Organisation. To mark the occasion, The Baha Blog has asked Dr. Anders Tjellström, the pioneering bone conduction surgeon, to reflect on the history of bone conduction and what developments the future could bring to the treatment.
By Anders Tjellström, M.D., Ph.D., D.Sc.hc
It is an old saying that to be able to look into the future you must know the past.
Hearing loss is the most common disability in the industrialised world. The World Health Organisation has estimated that more than 5% of the world population have hearing impairment, and that 1.1 billion teenagers and young adults are at risk of developing hearing loss due to high noise exposure. Around 50% of people between ages 12 and 35 are exposed to excessive noise due to different types of audio devices. How do we handle this situation? The key word is “prevention.”
However, when a patient has already developed hearing loss from noise exposure, hearing devices are often the only solution. In severe cases a surgical procedure placing a cochlear implant in the inner ear might be indicated. Even if sensorineural hearing loss is the most common cause of poor hearing, there is another group of patients who have severe conductive hearing loss. Some patients with congenital malformation and chronic ear disease could be helped with surgery, but for many this is not an option. Some of these individuals cannot use a conventional air conduction hearing aid where the amplified sound is presented through a mould in the external ear canal opening. For these patients, a bone conduction device could be of great benefit.
Direct bone conduction is based on the concept of osseointegration – the process by which bone bonds directly to the surface of an implant – a term introduced by professor Per-Ingvar Brånemark in Sweden. Bone conduction treatment for hearing loss starts with an implant made of titanium placed in the bone behind the ear, onto which a transducer could be attached. The sound goes directly to the inner ear bypassing any defect in the external ear canal and the middle ear. This is called direct bone conduction, and the treatment is indicated in patients with mixed or conductive hearing loss, or single-sided sensorineural deafness (SSD).
In 1977, the first patients were treated with bone conduction at Sahlgrenska University Hospital in Gothenburg, Sweden. This is now a routine operation all over the world, and it has been estimated that about 150,000 to 200,000 hearing impaired people have since been treated with bone conduction.
The hearing instrument and the surgical technique have of course been refined over the years. Engineers have applied modern technology to the early prototype of the 1970s, and today the sound processor is a highly sophisticated device.
Hearing technology has come a long way since the ’70s. The most recent Cochlear Baha 5 Sound Processor is the smallest bone conductor available and comes filled with many programming options that could be controlled wirelessly with the Baha 5 Smart App. It can be adjusted to fit a variety of listening situations with options like audio streaming and Bluetooth connectivity. The Cochlear Wireless Phone Clip allows hands-free use of your phone. Directional microphones make it possible to hold a conversation even in noisy places. Many of the wireless needs we encounter in everyday situations are already available in the Baha portfolio.
The Baha Attract System from Cochlear, where the sound processor is kept in place with a magnet without skin penetration, is already used by many patients. The SoundArc is also a recent addition to the Baha family. No surgery is needed as the high quality and power of the Baha 5 sound processors can overcome most of the soft tissue sound attenuation.
Cochlear is already making strides into the future with hearing technology, but where is bone conduction hearing headed? More and more of the electronic components of the sound processor have already been miniaturised and, looking to the future, could be placed in the implantable part. This means that eventually, the need of skin penetrating coupling might even become obsolete for direct bone conduction.
As bone conduction treatment evolves, more and more people will have access to helpful hearing solutions in the future. It is of course impossible to predict the future of bone conduction, but advances in the last 40 years can give us a clue to how advanced hearing technology could become just 40 years from now.
Anders Tjellström is an ENT-surgeon who performed the first surgery for direct bone conduction hearing in 1977 in Gothenburg, Sweden. He has published and presented bone conduction research at scientific conferences and surgical workshops in more than 50 countries. Tjellström remains active in the field of direct bone conduction as Professor Emeritus at the University of Gothenburg.