1, chronic strain or injury knee synovitis: acute knee synovitis improperly handled will become chronic, clinically seen in the elderly, the body is more wet, or with knee inversion, knee valgus or other knee deformity patients, or have knee osteophytes, etc.. Patients complain of heavy discomfort in both legs, difficulty in knee extension and flexion, but there is no obvious obstacle to passive movement, pain is not intense, local redness is not hot, and functional examination of the knee joint generally has no obvious positive signs. The common phenomenon is: in the knee ligament on both sides of the knee eye bulge, full, palpation by hand, the place is soft, or even cystic feeling, joint fluid if more than 10 ml is positive floating patella test. 2, acute injury, knee hematoma: joint hematoma usually occurs immediately after the injury or within 1 – 2 hours afterwards, with extensive petechial hemorrhagic spots on the knee and lower leg. There is tension in the skin or swollen area on palpation and a positive floating risk test. There are often systemic symptoms, such as fever due to stasis of blood, and more localized heat. The disease is often a comorbidity of other injuries. Careful clinical examination is needed to prevent missed diagnosis. 3, long-term weight-bearing chronic strain and other: when the knee joint is directly hit by violence, long-term weight-bearing chronic strain, indirect knee sprain, injury during surgery, strenuous sports activities or super-intensity training, incorrect habitual movements, degeneration of the joint itself, knee joint reversion, and even improper shoe wear can cause traumatic synovial suffering injury, synovial congestion, swelling, synovial cells are active to produce a large amount of fluid, which contains plasma, white blood cells, phagocytes and so on. The fluid extracted by joint puncture is mostly yellow, clear, or pink with blood, and negative for bacterial culture. x-ray examination of synovitis bone is not abnormal, or there are degenerative changes, or there are intra-articular free bodies and bone spurs at the edge of the bone joint.