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

Participants with mild to moderate knee osteoarthritis experienced a significant reduction in pain and improved mobility within four months of receiving treatment. Radiation exposure was only a small part of what was used in cancer treatment. Because the study included a control group that underwent simulated treatment, the researchers were able to clearly separate true treatment effects from placebo responses, which are common in osteoarthritis trials. Early results of this Korean study were presented at the annual meeting of the American Society of Radiation Oncology (ASTRO).

“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 Byung-hyuk Kim, MD, PhD, principal investigator of the trial and assistant professor of radiation oncology at Seoul National University College of Medicine, Boramae Medical Center. “There is a clinical need for moderate interventions between weak painkillers and aggressive surgery, and we believe that radiation may be an appropriate option for these patients especially when they do not tolerate medications and injections well.”

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 protects the ends of bones wears away over time. This condition often targets the knees and hips, limiting mobility and reducing quality of life. Typical treatment begins with lifestyle modifications and pain-relieving medications, with surgery considered when symptoms become severe.

Low-dose radiotherapy 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 prior to this study, rigorous placebo-controlled evidence was scarce, and awareness of the treatment remained low among doctors in other parts of the world.

“There is a misconception that medical or therapeutic radiation is always delivered at high doses,” he said. “But for osteoarthritis, the doses are only a small fraction of what we use to treat cancer, and the treatment targets joints placed away from vital organs, reducing the possibility of side effects.” He explained that the radiation dose in this study was less than 5% of what is usually used in cancer treatment, and no side effects associated with radiation were observed.

The multicenter study included 114 participants with mild to moderate knee osteoarthritis, selected from three academic hospitals in Korea. They were randomly assigned to one of three groups: very low dose (0.3 Gy), 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 the treatment, but virtually no radiation was delivered. Each participant underwent six treatment sessions without knowing which group he was assigned to.

To ensure that 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. Treatment effectiveness was assessed using internationally recognized criteria, with a participant defined as a “responder” if they achieved significant improvement in at least two of three measures: pain, physical function, and global assessment of their condition. Participants also completed separate questionnaires addressing pain, stiffness, and mobility. No side effects associated with the treatment were reported.

After four months, 70% of patients in the 3-Gy group met response criteria, compared to 42% in the placebo group (P = 0.014). Results in the 0.3 Gy group were not significantly different from the control group (58.3% improvement, P = 0.157), suggesting that the 3 Gy regimen resulted in attenuation of 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 required, there were no statistically significant differences.

Dr. Kim said that this experiment differs from previous research in two important ways. “The sham design helped rule out placebo effects, and we limited stronger painkillers, making the differences between groups more clearly attributable to the radiation itself,” he said.

“In previous studies, medications such as NSAIDs or opioids were also used during the intervention or follow-up period. But the use of these painkillers can mask the effects of radiotherapy,” he said. Because the use of analgesics was limited to acetaminophen only during the four months of follow-up in this trial, “this means that the differences between the treatment groups are more clearly attributable to the low-dose radiotherapy itself.”

Dr. Kim said the responses in the placebo arms were large — about 40% met criteria for response to treatment without real radiation — but consistent with rates reported in previous osteoarthritis trials of the injections or drugs and in at least one similar European study. “It was surprising, and it highlights how important placebo-controlled designs are in osteoporosis research. We need to study this more closely in future studies.”

He explained that radiation therapy may be better suited for patients with underlying inflammation and preserved joint structure. “In cases of severe osteoarthritis, where the joint is physically destroyed and the cartilage is already damaged, radiation will not regenerate tissue,” Dr. Kim said. “But for people with mild to moderate disease, this approach may delay the need for joint replacement.”

He stressed that low doses of radiation should be considered part of the shared decision-making process alongside standard measures such as weight loss, physical therapy and medications. “In clinical practice, responses can be 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 a 12-month follow-up to evaluate the persistence of benefits and correlate symptom relief with imaging-based measures of joint structure. Planned studies also include larger pragmatic trials evaluating outcomes in specific subgroups and health and economic analyzes comparing low-dose radiation to injection and treatment regimens.