The knee (commonly known as the knee) is the largest joint in the body and is a joint that is prone to injury during sports, with approximately 5-6 million visits to orthopedic surgeons worldwide each year for knee injuries. As the number of people participating in sports in China (especially teenagers) grows, the incidence of knee sports injuries increases each year. Why is the knee joint (knee) prone to injury? 1, the knee joint weight, weight is easy to injury is not easy to recover. The hip and ankle joints also carry a lot of weight, but the knee joint is special because of its complex structure and the special functions given to it by the body. 2. The knee joint has a complex structure (mainly including bone, cartilage, ligaments and tendons), and if there are many structures, they are delicate and easy to injure. The structure of the knee joint is more complex than that of the hip and ankle joint. 3. The knee joint is the center of the lower limb activities, it has to complete various sports movements (flexion and extension, rotation, axial shift, lateral movement) in addition to weight bearing. Therefore, the knee joint needs to be flexible and weight-bearing at the same time, and has a higher chance of injury. In summary, the knee joint takes on loads from above and below the body and completes multiple dimensions of activity, making it susceptible to injury and slow to recover from injury. Familiarity with the anatomical and physiological structure and function of the knee joint is required to aid recovery from knee injury.