Got knee pain? Stimulating the vagus nerve through the ear may help

EL PASO, Texas (May 22, 2025) – Tying shoelaces, getting into a car, picking things up off the floor and walking down stairs all involve flexing that most difficult of joints: the knee. But pain in the knee can significantly hinder those and many other routine activities.

Now, a rehabilitation scientist and his team at The University of Texas at El Paso are exploring an alternative way to alleviate knee pain. In collaboration with Harvard Medical School and Boston University, the team has conducted a pilot trial on an innovative method to treat osteoarthritis (OA)-related knee pain by stimulating the vagus nerve through the ear. The results are published in the journal Osteoarthritis and Cartilage Open.

“As a physical therapist, I saw many patients suffering from OA knee pain,” said Kosaku Aoyagi, PT, Ph.D., an assistant professor of physical therapy and movement sciences in the UTEP College of Health Sciences. “This motivated me to pursue research to improve their quality of life, and our results showed strong potential.”

Many treatment methods for OA knee pain are only modestly effective, Aoyagi explained, and often come with side effects. Moreover, common therapies tend to be based on the assumption that tissue damage to the knee is causing knee pain. Aoyagi’s unique approach instead targets central pain mechanisms, which control how the central nervous system and the brain respond to pain.

One component of the central pain mechanisms is the vagus nerve, Aoyagi said. The nerve plays an important role in the parasympathetic nervous system, which controls the body’s rest and digest function, and is countered by the sympathetic nervous system, which manages the body’s response to stress and danger.

“The current evidence suggests that individuals with OA knee pain have an imbalance of sympathetic versus parasympathetic activity in the body, which can cause pain,” Aoyagi said. “By stimulating the vagus nerve, we hypothesized that our treatment may rectify this imbalance.”

Aoyagi’s pilot study tested a treatment called transcutaneous auricular vagus nerve stimulation (tVNS) on 30 individuals with knee pain. Each study participant was treated with a tVNS device for 60 minutes. The device works by resting on the ear and sending a pulse to the auricular (ear) branch of the vagus nerve.

Overall, 11 out of 30 participants with knee OA felt a noticeable difference in their pain levels after receiving the treatment.

“Dr. Aoyagi’s research on knee osteoarthritis is an innovative step in identifying a treatment that successfully reduces knee pain,” said Stacy Wagovich, Ph.D., interim dean of the College of Health Science. “With future, large-scale studies, his team’s work has the potential to greatly improve treatment options available for knee osteoarthritis.”

tVNS is already approved by the Food and Drug Administration to treat some conditions, such as epilepsy and depression, but the UTEP clinical trial is the first of its kind in the U.S. to evaluate the therapy’s impact on knee pain.

The treatment is not yet available to the general public. Aoyagi said the next step in the research will be to conduct a randomized controlled trial with a larger group of people divided into two groups: one getting the tVNS treatment and a control group receiving a placebo.

About The University of Texas at El Paso

The University of Texas at El Paso is America’s leading Hispanic-serving university. Located at the westernmost tip of Texas, where three states and two countries converge along the Rio Grande, 84% of our 25,000 students are Hispanic, and more than half are the first in their families to go to college. UTEP offers 171 bachelor’s, master’s and doctoral degree programs at the only open-access, top-tier research university in America.