This European treatment for joint pain just passed a major scientific test

Participants with mild to moderate knee osteoarthritis experienced notable pain reduction and improved mobility within four months of receiving the treatment. The radiation exposure was only a tiny fraction of what is used in cancer therapy. Because the study included a control group that underwent a simulated treatment, researchers were able to clearly separate genuine treatment effects from placebo responses, which are common in osteoarthritis trials. Early results from this Korean study were presented at the American Society for Radiation Oncology (ASTRO) Annual Meeting.

"People with painful knee osteoarthritis often face a difficult choice between the risks of side effects from pain medications and the risks of joint replacement surgery," said Byoung Hyuck Kim, MD, PhD, principal investigator on the trial and an assistant professor of radiation oncology at Seoul National University College of Medicine, Boramae Medical Center. "There's a clinical need for moderate interventions between weak pain medications and aggressive surgery, and we think radiation may be a suitable option for those patients especially when drugs and injections are poorly tolerated."

Osteoarthritis is the most common form of arthritis, affecting an estimated 32.5 million adults in the United States. It develops as the cartilage that cushions bone ends wears away over time. The condition often targets the knees and hips, limiting mobility and diminishing quality of life. Typical treatment begins with lifestyle adjustments and pain-relief medications, with surgery considered when symptoms become severe.

Low-dose radiation therapy has long been used in European countries such as Germany and Spain to treat joint pain, where it is widely accepted. However, Dr. Kim noted that before this study, rigorous placebo-controlled evidence was scarce, and awareness of the treatment remained low among clinicians in other parts of the world.

"There is a misconception that medicinal, or therapeutic, radiation is always delivered in high doses," he said. "But for osteoarthritis, the doses are only a small fraction of what we use for cancer, and the treatment targets joints that are positioned away from vital organs, which lowers the likelihood of side effects." In this study, he explained, the radiation dose was less than 5% of what is typically used in cancer therapy, and no radiation-related side effects were observed.

The multicenter study included 114 participants with mild to moderate knee osteoarthritis, recruited from three academic hospitals in Korea. They were randomly assigned to one of three groups: a very low dose (0.3 Gy), a low dose (3 Gy), or a control group that received simulated (sham) radiation. In the placebo group, patients went through the same setup as those receiving treatment, but no radiation was actually delivered. Each participant underwent six treatment sessions without knowing which group they were assigned to.

To ensure the results reflected the true effects of radiation, the researchers restricted the use of additional pain relievers, allowing only acetaminophen as needed during the four-month follow-up period. The effectiveness of treatment was evaluated using internationally recognized standards, identifying a participant as a "responder" if they achieved meaningful improvement in at least two of three measures: pain, physical function, and overall assessment of their condition. Participants also completed separate questionnaires addressing pain, stiffness, and mobility. No treatment-related side effects were reported.

After four months, 70% of patients in the 3 Gy group met responder criteria, compared to 42% in the placebo group (p=0.014). Outcomes in the 0.3 Gy group were not significantly different from the control group (58.3% improved, p=0.157), indicating the 3 Gy regimen drove relief beyond placebo effects.

Meaningful improvements in the composite score of pain, stiffness and physical function were reported more often in the 3 Gy group (56.8%) than in the placebo group (30.6%, p=0.024). For other secondary outcomes, including the amount of pain medication needed, there were no significant differences.

Dr. Kim said this trial differed from previous research in two critical ways. "The sham-controlled design helped rule out placebo effects, and we limited stronger analgesics, which made differences between groups more clearly attributable to the radiation itself," he said.

"In previous studies, drugs such as NSAIDs or opioids were also used during the intervention or follow-up period. But using these pain relievers could mask the effects of radiation therapy," he said. Because analgesic use was limited to acetaminophen only during the four months of follow-up in this trial, "that means the differences between treatment groups are more clearly attributable to the low-dose radiation therapy itself."

Responses in the placebo arms were substantial -- about 40% met the criteria for treatment response without true radiation -- but are consistent with rates reported in prior osteoarthritis trials of injections or medications and in at least one similar European study, Dr. Kim said. "It was surprising, and it underscores how important placebo-controlled designs are in osteoarthritis research. We need to examine this more closely in future studies."

Radiation therapy may be best suited for patients with underlying inflammation and preserved joint structure, he explained. "For severe osteoarthritis, where the joint is physically destroyed and cartilage is already gone, radiation will not regenerate tissue," Dr. Kim said. "But for people with mild to moderate disease, this approach could delay the need for joint replacement."

He emphasized that low-dose radiation should be considered as part of shared decision-making alongside standard measures such as weight loss, physiotherapy, and medications. "In clinical practice, responses could be even stronger when radiation is properly combined with other treatments, and patient satisfaction may be higher than with current options alone."

The research team is completing 12-month follow-up to assess durability of benefits and to correlate symptom relief with imaging-based measures of joint structure. Planned studies also include larger, pragmatic trials to evaluate outcomes in specific subgroups and health-economic analyses comparing low-dose radiation with injections and medication regimens.