Medical history characteristics: ① Must have a history of violent injury, such as car accidents, falls, sprains, some patients can even hear the “bla” ligament rupture sound when sprained. ②After the injury, the blood vessels on the surface of the cruciate ligament are usually torn, resulting in intra-articular hemorrhage and peak swelling that night or the next morning. ③The post-injury swelling of the joint, after rest, usually decreases significantly in 3-4 weeks, and a better walking function can be restored. ④Afterwards, the symptoms of instability of ACL injury are manifested: the affected limb has decreased motility, cannot stop and turn sharply in sports, cannot make a single-leg basket, has difficulty running with a ball in soccer, has a feeling of not being able to eat and play softly down stairs, is worried about slippery roads or walking in snow, and even has repeated sprains. ⑤ Secondary symptoms of meniscal injury, such as pain and interlocking. Physical examination: positive anterior drawer test, positive Lachman’s sign, positive axial shift test. x-rays can indirectly suggest ACL injury in special cases combined with small avulsion fractures of the outer edge of the tibial plateau (i.e. Segond’s fracture), most of which are not positive. The presentation of ACL injury on MRI: edematous high signal changes after acute injury, but also tearing discontinuity at the upper stop, and also the appearance of a stump resorption after injury with no visible ACL signal. A higher quality MRI diagnoses ACL injuries with an accuracy of up to 97%. An experienced, hands-on specialist can correctly diagnose 95% of cases based on physical examination and history analysis. And while MRI can be a helpful aid, it is not always necessary as a routine examination.