This study will assess the efficacy of pulsed electromagnetic field therapy in patients with inflammatory knee osteoarthritis confirmed by MRI-detected effusion-synovitis. Fifty participants will be randomly allocated into two groups. One group will receive active PEMF therapy at a specific optimized parameter twice a week for 8 weeks, while the other group will receive sham treatment using the same device without PEMF signal. The primary outcome is the change in WOMAC pain score, and secondary outcomes include knee function, stiffness, quality of life, and MRI-quantified structural changes.

Knee osteoarthritis (KOA) is a leading cause of pain and disability, posing a significant socioeconomic burden. Current treatments often focus on pain relief with safety concerns, and no disease-modifying drugs are available. Pulsed electromagnetic field (PEMF) therapy is a non-invasive and safe physical modality with potential anti-inflammatory and analgesic effects. However, existing evidence for its efficacy in KOA is inconsistent, likely because KOA is a heterogeneous disease, and previous studies have not targeted specific subtypes. The inflammatory KOA subtype, identifiable via MRI, is the most prevalent and represents a critical target for precise intervention.

Methods This study is a double-blind, randomized, placebo-controlled pilot trial. Fifty patients with inflammatory KOA, confirmed by the presence of effusion-synovitis on MRI will be recruited. Participants will be randomly assigned to receive either active PEMF therapy at a specific, optimized parameter or sham treatment twice a week for 8 weeks. The primary outcome is the change in the WOMAC pain score at 3 months after treatment. Secondary outcomes include knee function and stiffness (WOMAC), quality of life (SF-12), and quantitatively assessed structural changes on MRI (e.g., effusion synovitis volume).

Expected Results The investigators anticipate that the group receiving active PEMF therapy will show a statistically significant and clinically important greater reduction in WOMAC pain scores compared to the sham treatment group.The investigators also expect to observe improvements in secondary outcomes, including better knee function and reduced signs of inflammation on MRI in the treatment group.

Conclusion This will be the first clinical trial to evaluate PEMF therapy specifically for the inflammatory subtype of KOA. Positive findings will provide crucial evidence for a novel, non-invasive, and precise therapeutic strategy for KOA management. This has the potential to improve patient care, alleviate the disease burden, and reduce healthcare costs.

Inclusion Criteria:

1. Knee visual analogue scale (VAS) pain of <40 mm (0-100 mm)
2. Effusion-synovitis or Hoffa synovitis MRI semi-quantitative score of ≥2 (used to determine inflammatory subtype KOA);
3. Kellgren-Lawrence (KL) grade II and III
4. Patients can listen, speak, read, and understand Chinese; understand the pilot study's requirements and are willing to cooperate with the investigator in conducting the pilot study
5. Willing and able to provide written informed consent

Exclusion Criteria:

1. Other inflammatory arthritis (e.g., gout, reactive arthritis, rheumatoid arthritis, psoriatic arthritis, and seronegative spondyloarthropathy) and systemic lupus erythematosus.
2. Participants with usual KOA interventions/ treatments
3. History of knee trauma
4. Contraindications to MRI
5. Administration of intra-articular, intramuscular, and oral glucocorticoids within the last 4
6. Pregnancy and lactation