The Cochlear-Implant Side Effect You Should Know About

Cochlear Implants and Bone Formation: New Research

When undergoing health procedures, patients often face a risk that they’ll develop side effects. The implantation of cochlear implants (CI) for people who are hard of hearing or deaf is no exception. A new study indicated that many people who use this kind of device could face an issue known as new bone formation (or NBF), which may reduce the hearing benefits derived from cochlear implants.

First, let’s explain what cochlear implants are: These devices can restore hearing in people with severe loss, the kind that isn’t helped by hearing aids. The implant is a small electronic device that stimulates the cochlear, or hearing, nerve. The implant has an external part that sits behind the ear, picking up sound, and an internal part that is placed under the skin, behind the ear. This internal part is typically implanted during outpatient surgery .

Cochlea Parts

The exterior of the cochlear implant (blue) and internal components (grey) work together to deliver processed sound to the cochlear, or inner ear.

What did the study reveal?

Now, here’s the news: A December 2021 study from the Netherlands raises concerns about CI-induced NBF. The research team behind the study found that slightly more than two-thirds of 123 participants who had cochlear implants developed NBF, and that natural hearing declined the most in patients with NBF.

Floris Heutink, MD, one of the lead authors of the study, told HearingTracker that most patients do not use their natural hearing after the cochlear implant has been implanted. However, “there is a minority of patients in which a combination of electric [device] with acoustic hearing is used. These patients have good hearing in low frequencies,” Heutink said. “From our study, we can believe it would be best for these patients not to develop new bone formation. However, we do not have tools to control this yet.”

What exactly is new bone formation?

Here’s more detail on new bone formation. This side effect from CI implantation is a “marker of trauma inside the inner ear that occurs when you insert the electrode,” Chad Ruffin, MD, an ear surgeon, told HearingTracker.

Cochlear Nbf

New Bone Formation (NBF) is shown (gray) inside the cochlea, developing alongside the electrode array (stripes). Image courtesy the Radiological Society of North America.

“The new bone is really scar tissue that increases the distance between the electrode and the nerve. So new bone formation requires more power to cross that distance. This electrical current spreads to other sites of hearing and creates distortion” Ruffin said, explaining how the NBF can affect hearing.

This trauma can trigger new bone formation, which can cause a decrease in residual low-frequency natural or acoustic hearing. For people who have new bone formation, they may realize that their cochlear implants are working less effectively, according to neurotologist Douglas D. Backous M.D., FACS. In order to maximize their hearing with a cochlear implant, Ruffin said that patients with lots of residual hearing can benefit from wearing both cochlear implants and hearing aids.

“The biggest issue would be if you had new bone formation and you needed to have your device replaced for some reason, would you be able to get it back in?” Backous said. “That's a big challenge.”

Can new bone formation be avoided?

Finding ways to avoid new bone formation is an area requiring further exploration. This could allow more people to benefit from cochlear implants. For people with hearing loss who have a lot of low-frequency residual hearing, the potential damage from the new bone formation may outweigh the upside of getting cochlear implants.

“We're going to be implanting people with even more residual hearing as we find less traumatic ways of putting in the implant,” Ruffin said.

Research is being done on whether steroids can help prevent new bone formation, which Ruffin’s patients take during the implantation process.

“I have evolved towards using during preservation techniques and steroid protocol on all of my patients, regardless of whether they have residual hearing or not,” Ruffin said.

Backous also recommends that surgeons use techniques like a slower insertion rate and minimizing drilling around the inner ear to limit inflammation during surgery.

“Anything to make it less traumatic and decrease the inflammation or inflammatory response to surgery would minimize…new bone formation,” Backous said.

Should I still get a cochlear implant?

If you are considering getting a cochlear implant, and concerned about NBF, don’t be. Dr Ruffin, a cochlear implant wearer himself says “Your natural hearing may decline slightly after receiving a cochlear implant due to NBF, but in almost every case, your overall hearing will be better than it was with hearing aids.”