Hand osteoarthritis is one of the most common arthritis, resulting in pain in finger and thumb base joints. The disease is characterized by pain and stiffness of the affected joints and is the most common cause of disability in aged people. Currently limited therapy options are available. Synovial inflammation is involved in the joint pain. Iguratimod is a small disease-modifying compound that can influence anti-inflammatory pathways in models of rheumatoid arthritis. It has an anabolic effect on the bone metabolism of infected joint by osteoclastogenesis inhibition and osteoblast differentiation. The investigators hypothesize that Iguratimod will alleviate pain of patient with inflammatory hand osteoarthritis, and that a beneficial effect of Iguratimod on pain will be accompanied by a decrease of synovial inflammation.

Inclusion criteria

Patients to be included must meet the following criteria:

1. Age of 45-75 years.
2. Men or women.
3. Hand OA according to the ACR criteria.
4. Symptomatic interphalangeal osteoarthritis for more than 3 months (at least every other day).
5. At least 1 IPJ (DIP/PIP/IP1st) with soft tissue swelling or erythema.
6. At least 1 IPJ with positive power Doppler signal or/and synovial thickening of at least grade 2 on ultrasound.
7. Finger pain which was more than 40 mm as evaluated by visual analogue scales (VAS) (0-100 mm) in the preceding 48 hours.
8. Be able to adhere to the study visit schedule and other protocol requirements. Capable of giving informed consent and the consent must be obtained prior to any screening procedures.

Exclusion Criteria:

1. Other known medical disease that may affect joints, e.g. rheumatoid arthritis, gout, psoriatic arthritis, reactive arthritis, ankylosing spondylitis, Lyme disease, Systemic lupus erythematosus, Sjogren Syndrome, Systemic sclerosis.
2. Psoriasis.
3. involving carpometacarpal [CMC] joints, without interphalangeal joints.
4. Existence of painful syndrome of upper limbs likely to interfere with the monitoring of pain (cervicobrachial neuralgia, incapacitating carpal tunnel syndrome, joint disorders of the elbow or shoulder, poly-articular chondrocalcinosis, fibromyalgia).
5. Trigger finger, injury in joints within past 6 months.
6. Slow-acting drugs for OA (e.g. glucosamine, chondroitin, diacerhein) initiated within the previous 3 months before the study.
7. Intra-articular treatments or aspirations of any kind of any joint in the hands 3 months before screening.
8. Intra-articular corticosteroids into any joint or use of systemic corticosteroids 1 month before screening.
9. Treatment with analgesics initiated within the previous 1 month and NSAIDs initiated within the previous 2 weeks.
10. History of hand surgery within 12 months prior enrolment.
11. Participation in experimental device or experimental drug study 3 months prior to enrolment.
12. Scheduled surgery during study participation.
13. Pregnant or lactating women，planned pregnancy within the study period, 3 months after end of study treatment for female fertile participant.
14. Known blood dyscrasias and coagulation disorders.
15. Elevated alanine transaminase (AST/ALT > 2x upper normal range).
16. GRF (MDRD) < 60 mg/min/1.73m2.
17. Known viral hepatitis B or C.
18. Uncontrolled diseases, such as asthma or inflammatory bowel disease, where flares are commonly treated with oral or parenteral corticosteroids.
19. History of peptic ulcer.
20. Patients who have severe comorbidities, including cardiovascular, nervous system, pulmonary, renal, hepatic, endocrine, GI disease. Known any other condition or impairment that, in the opinion of the investigator, makes a potential participant unsuitable for participation or which obstruct participation, such as e.g. psychiatric disorders.