The Anterior Cruciate Ligament (ACL) is the most important stabilizing structure of the knee joint and is one of the most common sports injuries to the knee. ACL injuries are common in sports and traffic injuries, mostly non-contact sprains or deceleration injuries, and are usually associated with hyperextension or internal rotation forces acting on the knee. (1) ACI injuries are usually traumatic. (2) There is a contusion or wobbling sensation between the femur and tibia. (3) There are repeated knee sprains after the first injury. From the above three points 95% can be diagnosed as an ACL injury. Symptoms of joint instability: (1) Inability to bounce normally. (2) Can not turn sharply and stop sharply. (3) Inability to run with sudden acceleration. From the above three points plus the femur and tibia between the contusion or wobbling sensation and repeated knee sprain, 99% can be diagnosed as ACL injury. Physical examination: increased forward knee mobility after ACL rupture is commonly examined in the following ways: (1) Lachman test; (2) anterior drawer test; (3) drawer test in the dropped leg position. If all 3 tests are positive, there is no doubt about the diagnosis of ACL rupture. If only one test is positive and the other is negative, the possibility of a partial rupture needs to be considered. Generally if the posterior external bundle is ruptured, it shows laxity on the Lachman test, while the anterior drawer test may not be lax, and conversely if the anterior internal bundle is ruptured it shows laxity on the drawer test and anterior drawer test in the hanging leg position, while the Lachman test may be less lax. (4) Pivot test, if this test is positive, it indicates that the patient has functional instability. (5) Zigzag test. If the patient cannot perform this test properly or with less amplitude than the contralateral side, it indicates that the patient may also have knee instability. Imaging: (1) X-rays: A simple plain X-ray can reveal avulsion fractures of the ligament stops or intra-articular osteochondral fractures, and Segond fractures have diagnostic value for anterior cruciate ligament ruptures. (2) MRI: It is very valuable for the diagnosis of ACL rupture, which shows ligament loss, continuity interruption, change of course, and signal change. Arthroscopy: The site and extent of injury can be observed under direct vision, and arthroscopic ligament reconstruction is performed in parallel.