The anterior cruciate ligament of the knee is located within the joint and is responsible for anterior stability and some rotational and lateral stability of the knee. It is not palpable on the body surface and it is difficult for the average patient to directly perceive an injury to this ligament. I. Clinical characteristics of ACL injuries. ACL injuries are generally associated with sports trauma, mostly inversion or valgus sprains, such as basketball landing sprains or direct external force on the knee joint by others; can also be seen in soccer when the “kick in the air” action caused by knee hyperextension injuries. Most patients experience pain in the knee joint and sometimes feel a tearing sound inside the knee joint, followed by restricted knee movement and subsequent swelling. Some patients may continue to play sports after the injury because they have good muscle strength and the external force of the injury is not significant, thus delaying treatment. Anterior cruciate ligament injury more than 6 weeks is old injury, old ACL rupture more instability symptoms, instability performance for the following three degrees: 1, serious instability: ACL rupture combined with poor muscle compensation of the knee joint, manifested as walking in daily life can feel the knee joint misalignment, this misalignment is generally manifested as the thigh bone and calf bone of the knee joint left and right misalignment. 2.Moderate instability: ACL rupture combined with moderate muscle compensation, manifested as not daring to accelerate fast running, not daring to stop or turn sharply when running fast. 3.Mild instability: ACL rupture combined with good muscle compensation, manifested as the patient can engage in general sports, the patient can run, carry the ball, but some movements in the game such as jumping up and landing on one foot, shooting with the healthy side of the foot with the affected lower limb support and other movements can not be completed, or need a reaction time to complete (reduced motor ability). Regardless of which instability the patient presents with, repeated sprains of the knee during sports or life are the hallmark clinical manifestations of ACL rupture. Second, the diagnosis of ACL injury. Patients with a history or clinical manifestation of the above injury must be seen promptly by a sports trauma-related specialist hospital or department. The diagnosis of ACL rupture is not difficult, and an experienced sports trauma specialist can diagnose most ACL ruptures by physical examination alone. The purpose of MRI is to: 1) confirm the diagnosis of ACL injury and provide diagnostic evidence for surgical treatment. A small number of old ACL injuries, because the upper stop is adherent to the lateral wall of the intercondylar fossa and other parts of the body, sometimes give the doctor a false impression, and it is easy to diagnose the ACL as unbroken or partially broken, MRI examination can help to clarify this situation. 2, to clarify the presence of articular cartilage, meniscus, other knee stability structure damage, for clinical diagnosis and treatment to provide reference. Third, the surgical treatment of ACL injury. ACL rupture generally requires surgical treatment, i.e., arthroscopic ACL reconstruction. The current mainstream technology is to use the autologous N cord tendon as a graft to reconstruct the ACL under arthroscopy as a single bundle, with mature technology and reliable clinical results. The reconstructive surgery uses the autologous N-tendon, two tendons of the medial thigh: the semitendinosus tendon and the thin femoral tendon. The reconstruction of the ACL requires the drilling of bone channels in the tibia and femur, and then the tendon is grafted into the joint cavity and the bone channels at both ends to replace the ACL. This fixation device is used as needed for the procedure and is usually a combination of absorbable and metal nails. Whether the internal fixation should be removed or not depends on the foreign body reaction at the site of internal fixation, and there is no pain at the site of internal fixation after surgery, etc. It is not necessary to remove it again. Patients can generally return to office work after 3-4 weeks of rest according to the doctor’s recommendation. For patients with smooth rehabilitation procedures, they can walk on crutches in January, remove crutches in February, walk normally with splinting in March, jog in April-May, general sports and fast running in six months after surgery, and confrontational sports in 10-12 months after surgery. Fourth, the special case of anterior cruciate ligament injury. It is worth noting that a fairly small number of patients have no clinical symptoms of instability after ACL rupture due to various factors such as muscle compensation. Clinicians faced with such patients must carefully choose ACL reconstruction surgery. The affected knee is protected by splinting during conservative treatment and no secondary injury occurs. Of course, if such patients have a combined meniscal injury, especially one that is judged to be sutured on MRI, early surgery is generally recommended to allow for the timing of the meniscal suture. Finally, it is important to remind the patients concerned that while waiting for surgery after the diagnosis of ACL rupture, they need to protect the knee joint (wearing a splint in the acute stage and a knee brace in the chronic stage), except for straight leg raising and other exercises to practice muscle strength (in the acute stage, they must practice the angle of knee movement and apply ice, etc.), and avoid walking and not exercising for a long time to avoid secondary injuries due to knee instability. Also, avoid infectious diseases such as colds and diarrhea, and protect the skin of the knee joint from insect bites and scratches.