Knee joint is a large and complicated flexion joint of human body. It bears great stress and its structure is stable and flexible. Knee joint pain occurs from time to time, which is often ignored or arbitrarily considered as arthritis and other diseases. In fact, there are many reasons for knee pain. In daily life, most joint pain is not caused by trauma. Joint pain is mainly caused by long-term cold and huge temperature difference. Especially in autumn, alternating cold and warm, low temperature or huge temperature difference will lead to muscle and blood vessel contraction, causing joint pain. If you encounter this situation, first try to keep warm, you can use hot compress; The second is to reduce the amount of exercise and let the joints rest. If the above methods can't make the knee pain better, then you have to go to the hospital to find the reason. There are several common injuries that can cause knee pain: 1. Fat pad strain Filling the gap in front of the knee joint with fat pad can strengthen joint stability and reduce friction. The reason of fat pad strain may be due to trauma or long-term friction, which leads to congestion, hypertrophy and inflammation of fat pad and adhesion with patellar ligament, thus limiting knee joint activity. This kind of injury mostly happens to people over 30 who often walk, climb mountains or often squat. The patient will feel pain in the knee joint, and the pain will be aggravated when it is completely straightened, but the joint activity is not restricted. Symptoms are obvious after fatigue. 2. Meniscus injury Meniscus injury is a common injury for athletes. When the lower limbs are loaded, the feet are fixed, and the knees are slightly bent, if the knees are straightened suddenly by internal rotation or external rotation (for example, in a volleyball match, a player suddenly turns around and dives to save the ball when defending), it may cause meniscus tear. Meniscus injury will have obvious tearing sensation of knee joint, followed by joint pain, limited activity and limping. Joints show swelling and sliding sensation, and will suddenly break when they move. 3. Synovium of traumatic synovitis of knee joint is one of the main structures of knee joint. Synovial cells secrete synovial fluid, which can keep articular cartilage smooth and increase the range of joint activity. Due to factors such as trauma or excessive strain, synovium will be damaged, resulting in a large amount of effusion and increasing intra-articular pressure. If it is not eliminated in time, it will easily cause joint adhesion and affect normal activities. The patient will feel pain, swelling and tenderness in the knee joint, and the synovium will have the sound of friction and astringency. The most obvious feature of pain is that the pain in the lower part of the patella will be aggravated when the knee joint is actively and extremely extended, especially when the knee joint is extended with certain resistance, and the pain will be obviously aggravated when the knee joint is passively and extremely flexed. 4. Knee osteoarthritis is a common disease in middle-aged and elderly people, mostly women. Overload is the main cause of disease. The knee joint will be swollen and painful, and sometimes there will be a rubbing sound in the movable joint. The knee may be varus with medial pain. 5. The stability of knee ligament injury is relatively poor when knee joint flexes slightly. If the external force suddenly causes eversion or eversion at this time, it may cause damage to the medial or lateral collateral ligament. Clinically, medial collateral ligament injuries account for the vast majority. Taking this kind of injury as an example, the patient will have a clear history of trauma, including pain and tenderness on the inside of the knee joint, aggravated pain when the calf is passively abducted, swelling on the inside of the knee, and ecchymosis will appear a few days later. Knee joint movement will be restricted. The above five kinds of injuries that cause knee pain cannot be cured by daily health care alone. Experts remind: if you have the above pain characteristics, you should find a doctor as soon as possible to make a clear diagnosis, so as not to delay the best time for treatment.