Low-Dose Radiation Therapy Eases Knee Osteoarthritis Pain in Rigorous Sham-Controlled Trial

Knee osteoarthritis is one of the most common and stubborn sources of chronic pain worldwide, and for decades the treatment toolkit has revolved around painkillers, injections, physiotherapy, and, eventually, joint replacement. Now a rigorously designed randomized controlled trial from South Korea has delivered the strongest evidence yet that a surprisingly old-fashioned and often overlooked option deserves a place in that toolkit: low-dose radiation therapy. The trial, known as LoRD-KNeA, tested whether a single short course of radiation, delivered at doses far below those used to treat cancer, could meaningfully relieve the pain and stiffness of arthritic knees. The results, published in BMC Medicine, show a clear short-term benefit at the higher of two doses tested, but also reveal how elusive and time-limited such benefits can be when measured against a convincing placebo.

The idea of using radiation to treat degenerative joint disease is not new. German-speaking countries in particular have a long clinical tradition of using low-dose radiotherapy for osteoarthritis, benign joint pain, and even conditions such as Dupuytren’s contracture and plantar fasciitis. The biological rationale is that very low doses of ionizing radiation can modulate inflammation, dampening the activity of inflammatory immune cells and altering signaling pathways involving molecules such as cyclooxygenase-2, transforming growth factor-beta, and interleukin-10, without destroying tissue. What has been missing, however, is the kind of high-quality, placebo-controlled evidence that modern medicine demands. Most prior studies were observational, unblinded, or lacked a sham control group, leaving open the possibility that much of the reported benefit was simply expectation effect. The LoRD-KNeA trial was designed specifically to close that evidentiary gap.

The study enrolled 114 patients with primary knee osteoarthritis across multiple centers in South Korea, including Seoul National University Hospital, Samsung Medical Center, and SMG-SNU Boramae Medical Center. To enter the trial, participants had to be at least 50 years old and to report baseline walking pain scores between 50 and 90 on a 100-point scale, ensuring that everyone had substantial but not end-stage symptoms. Participants were then randomly assigned to one of three groups: a sham irradiation group that underwent the full appearance of treatment without actual radiation, a low-dose group receiving a total of 0.3 Gray delivered in six fractions, and a higher-dose group receiving a total of 3 Gray in six fractions. Both active regimens were given as a single course, meaning patients completed all six sessions in a short treatment series and then received no further radiation. The trial was registered as NCT05562271 on ClinicalTrials.gov and approved by Korea’s Ministry of Food and Drug Safety and the institutional review boards of each participating hospital.

The choice of endpoint reflects how difficult it is to measure pain relief objectively. The primary outcome was the responder rate at four months according to the OMERACT-OARSI criteria, a standardized definition developed jointly by the Outcome Measures in Rheumatology group and the Osteoarthritis Research Society International. A patient counts as a responder only if they achieve either a substantial improvement in pain or function or a more moderate improvement across several domains simultaneously. This composite approach guards against the trap of declaring success based on a single, easily inflated measure. Secondary outcomes included the WOMAC index, which quantifies pain, stiffness, and physical function; the visual analog scale for pain; the patient global assessment; blood-based inflammatory markers such as C-reactive protein and erythrocyte sedimentation rate; and a battery of magnetic resonance imaging parameters, including the volume transfer constant known as Ktrans and the Whole-Organ MRI Score, which track joint inflammation and structural change.

The headline result was unambiguous at the four-month mark. In the modified intention-to-treat analysis, 70.3 percent of patients who received 3 Gray met the OMERACT-OARSI responder criteria, compared with 41.7 percent of those who received sham irradiation, a difference that reached statistical significance with a p value of 0.021. In practical terms, roughly seven in ten patients in the higher-dose group experienced clinically meaningful improvement within four months of a single six-session course, against about four in ten in the placebo group. The lower dose of 0.3 Gray produced a responder rate of 58.3 percent, which, while numerically better than sham, did not reach statistical significance. The per-protocol analysis, which included only patients who completed treatment as assigned, showed a similar pattern, reinforcing confidence in the primary finding.

Yet the story becomes more complicated when the timeline is extended. The advantage of the 3 Gray group persisted at eight months, but by twelve months the difference between active treatment and sham was no longer statistically significant. In other words, the treatment effect was real but time-limited, gradually converging with the placebo response over the course of a year. This pattern matters enormously for how the therapy might be used in practice. If the benefit lasts roughly six to eight months, low-dose radiotherapy could function as a repeatable, non-pharmacological bridge, offering patients windows of relief without the gastrointestinal, cardiovascular, and renal risks associated with long-term nonsteroidal anti-inflammatory drug use, and without the needles and infection risks of repeated corticosteroid injections.

Perhaps the most sobering finding came from the secondary outcomes. Mean changes in the WOMAC subscales, visual analog scale scores, patient global assessment, inflammatory markers, and MRI-based parameters did not differ significantly among the three groups. The trial’s authors note that no distinct benefits were observed in these continuous clinical or imaging measures, even though the binary responder rate clearly favored the higher dose. This disconnect is a well-known phenomenon in osteoarthritis research: a patient can cross the threshold for a clinically meaningful response while the group averages shift only modestly, and structural imaging often lags far behind symptom change, if it changes at all. It also underscores that the mechanism of low-dose radiotherapy in degenerative disease remains incompletely understood, and that symptom modulation, rather than measurable alteration of joint biology on standard imaging, may be what patients are experiencing.

On the safety front, the trial delivered a reassuring verdict. No treatment-related toxicities were reported among patients receiving either active dose. This is consistent with the broader understanding of radiation biology at these exposure levels: 3 Gray in six fractions is a tiny fraction of the doses used in curative cancer radiotherapy, which often exceed 60 Gray, and it is delivered to a small, superficial field over the joint. The doses are comparable to what patients receive from a handful of diagnostic CT scans spread over several sessions, and the theoretical long-term carcinogenic risk at such exposures is considered very low, particularly in patients over 50. For a population in which long-term painkiller use carries well-documented risks, a treatment with no reported adverse effects in a controlled trial is noteworthy in its own right.

The trial’s design also offers a masterclass in placebo control for physical therapies. Sham irradiation is notoriously difficult to implement convincingly, because patients receiving real radiotherapy see the machine, hear its sounds, and feel the positioning procedures. By replicating the full ritual of treatment for the control group, the investigators ensured that the 41.7 percent responder rate in the sham arm genuinely reflects expectation and natural disease fluctuation. That the active 3 Gray arm beat this benchmark significantly is precisely what makes the result credible, and it explains why the authors emphasize that their findings demonstrate a treatment effect beyond an early placebo response.

What happens next will determine whether this century-old idea finally enters mainstream practice. The authors conclude that a single course of 3 Gray low-dose radiotherapy produced a significant short-term improvement in responder rates among patients with knee osteoarthritis, while calling for further investigation of the therapy as a conservative, non-pharmacological option for selected patients. Key questions remain: whether repeat courses can extend the benefit, which patient subgroups respond best, whether the lower 0.3 Gray regimen might work with a different fractionation schedule, and whether longer follow-up can clarify the durability of relief and any late effects. The trial was supported by a grant from Korea Hydro and Nuclear Power Company, which the authors state did not influence the design or interpretation of the study. For the millions of people whose aching knees limit every step, the message is cautiously hopeful: a brief, painless course of very low-dose radiation may buy several months of meaningful relief, and the scientific case for taking this approach seriously has never been stronger.

Subject of Research: Low-dose radiation therapy as a non-pharmacological treatment for knee osteoarthritis

Article Title: Single course low-dose radiation therapy in knee osteoarthritis (LoRD-KNeA): a randomized controlled trial

Article References: Single course low-dose radiation therapy in knee osteoarthritis (LoRD-KNeA): a randomized controlled trial. (n.d.). https://doi.org/10.1186/s12916-026-05287-9

Image Credits: AI Generated

DOI: 10.1186/s12916-026-05287-9

Keywords: low-dose radiation therapy, knee osteoarthritis, randomized controlled trial, sham-controlled, radiotherapy, pain relief, OMERACT-OARSI, WOMAC, placebo response, non-pharmacological treatment, clinical trial, radiation oncology