Anterior cruciate ligament (ACL) is an important structure to maintain the stability of the knee joint, its injury is one of the clinically serious sports injuries, often resulting in partial or total loss of knee movement, except for a few people who can continue to exercise, most people can not perform running, jumping, emergency stop and other movements, in fact, those who can exercise also at the cost of damage to the cartilage and meniscus. The diagnosis of ACL is based on. 1, medical history: a history of acute trauma to the knee, rapid post-injury joint swelling and pain, and functional impairment. 2, physical examination with clear signs: acute phase of the affected knee joint swelling, pain, limited activity, and mostly able to draw blood accumulation. Patients in the chronic phase mostly report instability of the knee joint during daily life or activities, with weakness of the leg, evident when going downhill or accelerating to change direction or decelerating and braking. 3. Physical examination: (1) Lachman test: The patient lies in the supine position with the knee flexed at an angle of approximately 30°. The examiner fixes the affected foot with both knees, and the examiner fixes the distal thigh with one hand and the proximal calf (tibial tuberosity plane) with the other hand and tries to move the tibia forward. A positive Lachman test with a soft termination point indicates a complete rupture of the ACL; a positive Lachman test with a stiff termination point indicates a partial injury to the ACL or laxity of the capsular ligament alone; a negative Lachman test with a stiff termination point indicates a normal ACL. . (2) anterior drawer test: the patient lies supine, bending the knee at 90 degrees, the examiner sits on the back of the patient’s foot to fix, and pulls the upper tibia forward in three positions, such as external rotation, neutral position and internal rotation of the lower leg, respectively. The degree of forward displacement of the tibial tuberosity is observed, and a displacement >5 mm is considered abnormal. It is important to note that one must be alert to the possibility of posterior collapse of the upper tibia due to posterior cruciate ligament injury, which manifests as a false-positive anterior drawer test during forward retraction. (3) Axial shift test: The patient lies supine, the examiner holds the affected ankle with one hand so that the lower leg is internally rotated and the knee is straightened, the other hand is placed below the fibular tuberosity, both hands exert external rotation force, and gradually the affected knee is gradually flexed. At this point, the anterior pulling action of the posterior femur and the iliotibial bundle (at this point the iliotibial bundle is located anterior to the instantaneous center of the femoral epicondyle) causes anterior subluxation of the lateral tibial condyle. When the knee is flexed to 20°-30°, the iliotibial bundle moves to the posterior side of the transient center of the femoral epicondyle, producing a strong posterior pulling force on the tibial epicondyle, forcing the subluxation joint to reset, and the examiner can feel or see the bouncing and misalignment during the reset, then it is positive. 4. Auxiliary examinations: (1) Orthoptic and lateral knee radiographs: there is diagnostic significance only in the presence of avulsion fracture at the ligament stop; orthoptic radiographs showing avulsion fracture at the lateral edge of the tibial condyle (positive Segond’s sign) indicate ACL fracture; or no obvious signs of knee fracture are seen. (2) MRI of the knee joint: If MRI can show the whole course of the ACL, it can accurately show the complete rupture of the ACL, but it still needs to be evaluated with the medical history and clinical examination. 5. Pathological classification: partial ACL rupture (less than 50% of ACL ruptured fibers confirmed by arthroscopic exploration), major or complete ACL rupture and compound injury (complete ACL rupture confirmed by preoperative MRI and intraoperative arthroscopic exploration).