Overview of Implantable Hearing Devices
Hearing loss can happen for many reasons, but it’s becoming more common as people are living longer. It’s important to support people with hearing loss so they can continue to interact with the world around them. The most common way to help people with hearing loss is through the use of hearing aids. These are small gadgets that fit discreetly in or over your ears and make sounds louder.
In certain cases, other treatment options might be better suited, such as implantable hearing devices. These devices can include bone-conduction hearing prostheses, which allow you to hear sound through the vibrations in your skull. Other options include middle ear implantable hearing prostheses, cochlear implants (which stimulate the auditory nerve directly to provide sound), and auditory brainstem implants (implants that stimulate the hearing part of the brain directly).
In this piece, we’ll be discussing bone-conduction hearing prostheses and middle ear implantable hearing prostheses in more detail. We’ll look at why people might need these devices, how they’re put in, any side effects, and their predicted outcomes. If you need more information on hearing aids, cochlear implants, and auditory brainstem implants, please look out for other chapters dedicated to these topics.
Anatomy and Physiology of Implantable Hearing Devices
The most frequently used method for improving hearing in people with hearing loss is hearing aids. These aids have improved over time and have become more comfortable and discreet, but they still have some limitations. Factors such as chronic ear infections, certain anatomical issues, lack of enough sound amplification, discomfort, and other issues can limit their effectiveness.
For patients with severe to profound hearing loss, standard hearing aids might not be very beneficial. However, newer types of implantable hearing devices can greatly improve hearing, although they are more expensive and require surgery. Therefore, doctors have to make sure they recommend the most suitable hearing devices for each patient.
One type of device, called a Bone-conduction hearing prosthesis, works by making the skull vibrate, which stimulates the hearing part of the inner ear (the cochlea). It can be a helpful option for people who can’t tolerate conventional hearing aids or are not good candidates for surgery. It may also be useful for people who have single-sided deafness, or who have hearing loss that cannot be treated with conventional hearing aids due to ongoing ear infections or anatomical issues.
There are two types of bone conduction devices: surgical and non-surgical. Non-surgical ones work by putting consistent pressure on a part of the skull called the mastoid cortex via an elastic band or eyeglasses. Although these systems have some limitations, they can provide temporary help for certain patients before they get surgically implanted devices, especially young children or patients who can’t undergo surgery.
Another newer development in the field of hearing devices are middle ear implants. These devices pick up external sounds and transmit them via an implant in the middle ear. This device then sends mechanical energy to the liquid within the inner ear. They can be good alternatives for people who can’t use traditional hearing aids or who can’t get bone-anchored devices. There are both partially implanted devices, which have an external component, and completely implanted devices, which don’t have any external parts.
Since the 1960s, Cochlear implants have been used to treat severe to profound hearing loss. These devices have improved a lot over the years, with better results and fewer complications. They work by having an implant under the skin behind the ear, which includes a piece that stimulates the cochlea. The procedure for placing the implant requires a specific surgical approach involving the mastoid part of the skull and inserting the electrodes into the cochlea. Commonly, this surgery is recommended for those with severe to profound hearing loss which can’t be helped with hearing aids.
All surgical devices for hearing loss have some limitations, including their cost and the need for anesthesia for the placement and replacement of the devices. In addition, some implants are not compatible with MRI, so this needs to be considered based on the patient’s needs.
Lastly, a device called an Osseointegrated Bone-Conduction Prosthesis works by creating a natural bond between titanium and bone. This concept was initially used in dental implants. This device improves bone-conduction of sound and has provided significant improvements in hearing, with an estimated gain in hearing ability.
Why do People Need Implantable Hearing Devices
Doctors use Bone-anchored hearing devices for people who have problems with their hearing. These issues could either be ones where sound isn’t properly conducted from the outer or middle ear to the inner ear, a combination of this type and another where the person’s nerve that sends sound to the brain is damaged, or cases where the person has lost hearing in only one ear. These devices can be useful in cases where normal hearing aids aren’t helpful, or if a person can’t use them.
Common reasons for needing these devices include ear diseases, birth defects of the ear canal, abnormal skin growth in the ear, chronic ear infections, and changes due to surgery. The device skips the problematic parts of the ear to provide better hearing.
For people who have lost hearing in just one ear, there are other options, too, like a type of hearing aid that sends the sounds from the deaf ear to the ear with better hearing. But research has shown that these devices can’t make up for all the issues related with hearing loss in one ear. That’s why bone-anchored hearing devices are now being used to help improve hearing in noisy situations and help localize sounds for people with hearing loss in one ear. The hearing loss can be due to genetic disorders, structural problems in the ear, treatments that cause hearing damage, physical trauma, diseases that affect nerves, sudden loss of hearing or a type of benign brain tumor called vestibular schwannoma.
Not everyone should get a bone-anchored hearing device. For instance, people with skin problems on the scalp or patients with bone structures that aren’t suitable for the device to attach and integrate well might want to consider other options. It’s also not suitable for those who need ongoing MRI evaluations, especially of the part of the brain responsible for hearing and memory, because of potential compatibility issues with MRI machines. Before surgery, patients expected to undergo future MRIs should discuss device-specific guidelines.
There are also hearing devices that can be implanted in the middle ear. These are available for both adults and children five years and older who have problems with sound conduction or a combination of this and nerve-related hearing loss. These devices work best for those with stable, mild to moderately severe loss at frequencies that are important for understanding speech.
Misshaped inner ear structures are not necessarily a problem for these devices as they can usually bypass these abnormalities. However, you cannot have these implants if your hearing loss is due to a problem beyond the cochlea (the snail-shaped part that sends sound to the brain), if you have an active ear infection or if it would be risky for you to have general anesthesia. As with bone-anchored hearing devices, you should discuss MRI compatibility before surgery. In many cases, you might need to get a CT scan before surgery to help with planning the procedure.
How is Implantable Hearing Devices performed
Percutaneous Implants
The first step to get a percutaneous implant (a device inserted through the skin) is to decide where to place it. It’s usually along the side of the head, between 5.5 and 6 cm back from the ear. Many surgeons will mark this spot with a special dye before making a skin cut. But, they might also double-check these measurements after the cut is made.
The thickness of the skin at this location is then checked to decide on the right size implant. This is really important for proper function if the implant needs to connect through the skin. The surgeon measures these tissues accurately before giving any numbing medication.
After that, the surgeon makes a skin cut about 2 cm long, a bit ahead of or behind the implant site. This cut goes through the skin and the layer of fat beneath it, and reaches a firm layer called the periosteum. The surgeon then lifts the fat layer up until they reach the marked implant site.
Now, they make a little hole for the implant. Good cooling is needed when drilling to avoid any heat injury which can affect how well the implant settles in. They make sure to stop drillinh if they see any soft tissue or dura (a layer covering the brain and spine). If all looks good, they drill a tiny bit deeper.
The surgeon puts the implant inside the drilled hole using slow speeds and good cooling to avoid any heat injury to the bone. They tighten the implant to firmly secure it and then make a small hole in the skin to reveal the abutment (the place where the implant comes out of the skin). Finally, the surgeon stitches the surgical cuts back up.
Transcutaneous Implants
Transcutaneous implants are similar to percutaneous ones, but there’s no need to make a hole in the skin. Instead, the bone just around the implant site should be flat or made flat for the device to fit properly.
Percutaneous and Transcutaneous Outcomes
There’s quite a bit of research to show that both these types of implants can help with hearing. They’re good options to help with conductive hearing loss. If there’s also sensorineural hearing loss (nerve-related hearing problems), the percutaneous implants may provide a slight advantage.
Middle Ear Implantable Hearing Prosthesis (Device)
The steps for this kind of implant are similar to those above. But the location of the implant is usually at the back of the ear, near the cheekbone root. The surgeon will then make a cut behind your ear and create a space for the implant by removing some bone through a process called cortical mastoidectomy.
They then place the implant and secure it in the right location. It’s essential to make sure the device doesn’t touch any parts of the ear like the eardrum or the cochlear promontory. After the implant is placed, the wound is stitched up.
Outcomes
One systematic review shows that these devices can help improve sound localization and speech in noise. However, the outcomes and possible complications of these implants are still being researched.
Possible Complications of Implantable Hearing Devices
Problems can arise during and after surgery for bone-anchored hearing devices, but these are fairly rare. These devices improve hearing by using the bones in your ear to transmit sound. During surgery, complications could involve damage to nearby parts of the ear, which can lead to fluid leaks or bleeding. However, these potential issues are rare.
After surgery, the most common complications are related to the soft tissues around the implant. These issues might include infection, excessive tissue growth around the implant, or a lot of scar tissue. Thankfully, because of technology advancements and improved surgical techniques requiring smaller cuts and less tissue disturbance, these complications are becoming less common.
However, these complications are more likely in children and adults with certain health conditions, like being a smoker, having diabetes, or being overweight. Problems related to the bone happen rarely. One of those issues is failure of the implant to integrate with the bone properly. Fractures caused by the implantation process, along with factors like physical trauma, chronic infections, and poor bone quality at the implantation site, account for most issues related to the bone. A serious bone infection, called osteomyelitis, is an extremely rare complication.
There are also potential problems with a type of hearing implant placed in the middle ear. These risks are associated with the surgical procedure itself, which involves operating on a bone in the ear. Complications could include hearing loss, changes in taste, facial muscle weakness, fluid leak from the spine, or dizziness. Because of the way the device is placed, there is a higher risk for damage to the surrounding structures in the ear compared to other types of ear implant surgeries.
What Else Should I Know About Implantable Hearing Devices?
About half a billion people around the world suffer from hearing loss that impacts their daily lives. Not only is hearing loss one of the top reasons for disability globally, but it can also complicate various elements of day-to-day life like education, work, and social communication. Hearing loss can make it difficult for people to interact, which can result in feelings of loneliness and even lead to depression. Recent studies have even shown a link between hearing loss and a higher risk of cognitive decline, like dementia.
Many people with hearing loss can improve their hearing using traditional hearing aids. However, these may not work for everyone. In such cases, implantable hearing devices are an alternative treatment. These devices are surgically placed inside the ear and can be a good solution for people who don’t find regular hearing aids effective.