This aims of this study is to investigate the efficacy and safety of the glucocorticoid injection into the infrapatellar fat pad among knee osteoarthritis patients with an inflammatory phenotype.

Inclusion Criteria:

1. Diagnosed with symptomatic knee osteoarthritis (OA) according to American College of Rheumatology criteria;
2. Age > 45 years;
3. Have knee pain for more than six months and the knee pain over the past week assessed by VAS (100 mm) ≥ 40 mm;
4. Ultrasonography showed obvious synovitis with effusion in the knee joint;
5. Both MRI-assessed Hoffa-synovitis score (MOAKS method) and effusion-synovitis score (modified WORMS method) ≥ 1, and their total score ≥ 3;
6. Being able to listen, speak, read and understand Chinese, capable of understanding the study requirements and cooperating with the researchers during the study, and providing written informed consent.

Exclusion Criteria:

1. Allergy to glucocorticoids;
2. Knee injection of glucocorticoid or hyaluronic acid within the past six months;
3. Severe trauma or arthroscopy in the knee within the past six months;
4. Planned hip or knee surgery (including arthroscopy, arthroplasty, and other open joint surgeries) in the next six months;
5. Contraindication to having magnetic resonance imaging (MRI) (e.g., implanted pacemaker, artificial metal valve or cornea, aneurysm clipping surgery, arterial dissection, metal foreign bodies in the eyeball, claustrophobia);
6. Presence of other arthritis, such as rheumatoid arthritis and psoriatic arthritis;
7. Other physical condition that is more painful than their knee OA;
8. Malignant tumors or other life-threatening diseases;
9. Infection, diabetes, coagulopathy, osteonecrosis, or gastric/duodenal ulcer within the past 12 months;
10. Current use of oral corticosteroids, nonsteroidal anti-inflammatory drugs, or immunosuppressive medication;
11. Pregnancy or lactating female;
12. Use any investigational drugs or devices in the recent 30 days.