(1) Recurrent knee pain within the last 1 month. (2) X-ray (standing or weight-bearing position) shows narrowing of joint space, subchondral bone sclerosis and/or cystic changes, and bone redundancy formation at the joint margin. (3) Clear, viscous joint fluid (at least 2 times) with WBC <2000/ml. (4) Middle-aged and elderly patients (≥40 years old). (5) Morning stiffness ≤ 3 min. (6) Bone rubbing sound (sensation) during activity. The diagnosis of osteoarthritis of the knee can be made if 1+2 or 1+3+5+6, or 1+4+5+6 are satisfied.