Acute sprain 1. Mild Knee sprain with mild pain and no swelling. It improves with rest for 3-7 days. It is generally a mild injury to the joint capsule, so rest is sufficient and normal activities are possible after the symptoms disappear. 2.Moderate There is pain when the knee is sprained, but it is still possible to move or walk, and it is judged according to the swelling after the injury. One is swelling within a few hours after the injury, which is usually combined with knee ligament injury or joint capsule tear. The second is swelling found the day after the injury, which is usually a meniscal or cartilage injury. The third is swelling that does not occur after the injury, but occurs with activity after the pain has subsided. The fourth is slight swelling after the injury, which is usually a mild injury to the joint capsule. The first three cases must be seen as soon as possible, the last one can rest and normal activities after the symptoms disappear. 3, severe The knee joint sprains with severe pain or immediate inability to move or a sense of dislocation, and swelling is apparent within a few hours after the injury. These need to be seen as soon as possible, some patients can still insist on walking after the injury, or even have a normal gait, but they should not delay the need for prompt medical attention. These injuries generally include large ligament tears such as medial patellofemoral ligament, anterior and posterior cruciate ligaments, meniscal tears or fractures of cartilage and bone, or even tendon ruptures. Chronic sprains: Inability to run fast, turn and stop sharply, difficulty jumping on one leg, inability to perform movements that were possible before the injury, ligament rupture, patellar dislocation injury or bony structural injury should be considered, and prompt medical attention should be sought. Painful popping in the knee, painful walking on level ground (especially clear pain in the medial or lateral space of the knee), or interlocking (sudden jamming of the knee joint that requires movement or help from others to unlock) should be considered meniscal or cartilage injuries and should be seen promptly.