Mr. Wang insists on going to the sports field every weekend to play soccer, and has been doing so for years. But recently he always felt soreness and weakness in his right knee, and he couldn’t walk fast enough to play soccer, so his colleagues and friends said he had arthritis, but his knee could lift and turn, but he couldn’t stop and turn sharply when playing soccer. He went to the hospital many times, but the doctor always prescribed some anti-inflammatory and analgesic medicine. A few days ago, he couldn’t continue to play soccer, so he went to the sports trauma department and found out that the anterior cruciate ligament of his knee had been damaged during sports, and the lateral meniscus had been torn, so he had to undergo ligament reconstruction and meniscectomy. Cruciate ligament injury of the knee is one of the most common injuries in sports medicine, and the mechanism of injury is caused by sudden stepping while walking, sharp stops in running, and other actions, and also due to direct violence. The joint is often swollen immediately after the injury, but there are also cases where the swelling is not obvious, and the swelling tends to subside naturally after a month of rest. The incidence in China is 3-5% of the population, of which the underdiagnosis rate is 70%, and there are a large number of people in society who have not been diagnosed and treated for old cruciate ligament injuries! The cruciate ligament of the knee is the most important stabilizing structure of the knee joint, and its injury will cause structural instability of the knee joint, which will lead to secondary damage to other important structures such as meniscus and articular cartilage, and this injury will continue to worsen with time until severe osteoarthritis and even joint replacement. Therefore, the sooner the knee is repaired after a cruciate ligament injury, the less secondary damage there will be and the faster the recovery will be. Since the swelling subsides after an injury, even without a visit to a doctor, and after a period of rest, and there is generally no restriction in walking, patients may mistakenly believe that the injury is healed. Patients often go to the hospital only after a second injury, or even after multiple sprains, when they feel indescribable joint discomfort, looseness, inability to walk fast, inability to run and stop sharply, etc., or due to joint rattling or jamming (meniscus damage or cartilage loss into intra-articular free bodies, etc.)! In many cases, doctors who do not specialize in sports medicine often do not know enough about this, and treat minor bone and joint injuries as normal (such as taking medication and getting closed) without careful clinical examination. In fact, if you take an MRI, you will find that not only the cruciate ligament is torn, but often the meniscus and articular cartilage are also damaged. Therefore, we urge patients to pay attention to knee sprains and their secondary damage to other structures of the joint, preferably in a sports medicine specialty. When patients with knee sprains are seen by the general orthopedic medical staff, a careful and thorough examination must be done to avoid the occurrence of missed and misdiagnosed cases.