L-arginine for Knee Osteoarthritis Patients

Inclusion Criteria: 1. Age between 40 and 80 years. 2. Knee OA according to the American College of Rheumatology (ACR) clinical criteria. 3. Knee pain lasting 3 months or longer and a score of 7 or greater on the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) pain subscale (standardized to range from 0-20). 4. Kellgren-Lawrence (KL) grade 2 or 3. 5. Willing to and able to provide written informed consent. Exclusion Criteria: 1. Any use of NSAIDs or other analgesics in the past two weeks. 2. History of injections of corticosteroids in the past three months or hyaluronic acid in the past 6 months in the index knee. 3. History of arthroscopy or open surgery in the index knee in the past 12 months. 4. History of a knee replacement in the index knee or planning to receive such a procedure within 3 months. 5. History of a severe injury in the index knee. 6. Pain in the index knee caused by inflammatory, autoimmune, neoplastic diseases or other diseases. 7. Abnormal liver or kidney functions, as defined by alanine transaminase or aspartate aminotransferase \>two times the upper limit of normal, or blood urea nitrogen or serum creatinine \>two times the upper limit of normal. 8. Severe respiratory diseases. 9. History of coronary artery disease and heart failure. 10. Uncontrolled hypertension or diabetes mellitus. 11. Diagnosis of malignant tumors. 12. Pregnant or contemplating pregnancy or breast-feeding.