A noninvasive technique that stimulates the ear's vagus nerve could help reduce knee pain in patients with osteoarthritis, according to a pilot study involving 30 participants.
"This is the first study to evaluate the safety and efficacy of tVNS for people with knee OA," noted investigators.
The method, known as transcutaneous auricular vagus nerve stimulation (tVNS), showed preliminary evidence of being safe, feasible, and potentially effective in reducing pain by targeting the nervous system.
Participants underwent a single 60-minute tVNS session. Researchers measured knee pain, pain modulation, and heart rate variability—an indicator of parasympathetic activity—prior to, immediately following, and 15 minutes following the intervention.
Knee pain decreased by an average of 1.27 points on a 0 to 10 scale immediately following the session, and by 1.87 points 15 minutes later. Of the participants, 37% achieved a reduction considered clinically meaningful, reported Kosaku Aoyagi, of the University of Texas at El Paso, and colleagues.
Heart rate variability in the high-frequency range, which reflects parasympathetic nervous system activity, increased by 213 ms² immediately after the session and 234 ms² at 15 minutes. The results suggested that tVNS may activate the vagus nerve and influence mechanisms related to stress and inflammation.
The investigators also evaluated descending pain control using conditioned pain modulation, which modestly improved following stimulation. However, pressure pain threshold and temporal summation—other measures of central pain sensitivity—did not change, indicating a limited effect on those aspects of pain processing.
All 30 participants completed the full session. Two individuals reported brief nausea and dizziness, which resolved quickly. Most participants indicated willingness to return for future sessions.
Participants had a mean age of 55 years and an average body mass index of 33. The majority were women and of Hispanic background. All met clinical criteria for knee osteoarthritis and reported walking-related knee pain.
The stimulation device was applied to the cymba concha of the ear, targeting the auricular branch of the vagus nerve. It delivered pulses in 30-second on/off cycles during the session. No treatment was applied directly to the knee.
Although the study lacked a control group and involved only one session, the findings suggested that tVNS may help reduce knee pain by modulating the nervous system. Larger trials with longer follow-up and controlled conditions will be needed to confirm the preliminary results.
Full disclosures can be found in the published study.