Knee is the largest and most complex joint in human body. Knee pain can be caused by meniscus injury, osteoarthritis, chondromalacia patellae, bone tumor, hip disease, lumbar spine disease and connective tissue disease. 1. Meniscus injury: because the meniscus tear pulls the surrounding synovial tissue to cause pain, the pain is mostly fixed in the medial or lateral joint line near the fixed compression pain, and some patients repeatedly appear stuck, which is often referred to as the interlocking phenomenon. 2. Osteoarthritis of the knee joint: it occurs in middle-aged and old people over 50 years old, heavy load is the main cause of the disease, the cartilage of the articular surface degeneration, wear and tear, resulting in direct friction of the subchondral bone, which causes pain, joint swelling in the acute stage, fluid retention, walking difficulties. 3. Chondromalacia patellae: Chondromalacia patellae is mainly caused by pain in the front side of the knee joint, aggravated by sitting for a long time, standing up or going up and down the stairs, going up and down the slope, the joint is afraid of coolness, or the knee joint is swollen and fluid accumulated repeatedly. 4. Bone tumor: including benign and malignant, there will be severe pain caused by tumor growth. 5. Hip diseases:Hip diseases can lead to knee pain, common femoral head necrosis, osteoarthritis of the hip joint, hip dysplasia and other diseases, manifested as knee pain symptoms. 6. Lumbar spine disorders: Lumbar spine disorders such as lumbar disc herniation can show clinical symptoms of knee pain. 7. Connective tissue disease and metabolic disease: rheumatism, rheumatoid disease, gout and other diseases cause inflammation of the synovial membrane, knee joint pain symptoms. If the symptoms of knee pain persist without improvement, it is recommended that the patient go to the hospital to clarify the cause of the disease and receive regular treatment.