”Doctor, when the weather changed, my knee joint suddenly became swollen and painful.” Early in the morning of November 12, 63-year-old Ms. Jiang came to the orthopedic department of Zhongshan Hospital, where she was warmly received by Chen Zhongde. After careful examination, she was diagnosed with simple, acute synovial effusion of the knee. Due to the large amount of fluid, Chen performed an arthrocentesis on Ms. Jiang on the same day and provided symptomatic treatment, which quickly brought her condition under control. Synovitis is an aseptic inflammatory response to mechanical and biochemical stimuli caused by cartilage degeneration and osteophytes, followed by synovial edema, exudation and effusion. This is characterized by pain, edema, and limited mobility. If the disease is not treated in time, once the synovial hyperplasia and cartilage degeneration are transformed into chronic synovitis, the pain will be long-lasting, increasing the medical burden and even affecting work and life. Due to the sudden drop in temperature, the synovial membrane of the knee joint is superficial, and based on the principle of heat expansion and cold contraction, the synovial membrane is stimulated by cold and shrinks, making it easy to be injured during activities; at the same time, the circulation and metabolism of the joint fluid are slow after the temperature drops, and the stimulation of chemical factors produced by metabolites in the joint fluid can lead to joint pain and slowly produce effusion and more and more fluid, increasing pain and seriously The pain becomes worse and affects the functional activities of the joints. A few days ago, when the temperature suddenly dropped, five patients with acute synovitis were seen, and two of them had their fluids punctured and extracted. Reminder: middle-aged and elderly people, sudden changes in weather, joint warming. If your joints are swollen and painful and your squatting is limited, seek medical attention.