Anatomic mechanism The anterior cruciate ligament begins in the medial-superior region behind the medial surface of the femoral epicondyle and ends anteriorly and inferiorly at the medial aspect of the anterior intercondylar fossa on the non-articular surface of the upper tibia, mostly in front of the medial intercondylar ramus, with a small portion on it. Its fibers intertwine with the fibers of the anterior horn of the lateral meniscus. The fibers can be divided into two main bundles: the anterior internal bundle and the posterior external bundle, which spiral upward in the joint. The anterior internal bundle is tense during knee flexion, the posterior external bundle is tense during knee extension, and both bundles are tense during tibial internal rotation. The two bundles of the ACL act together to prevent the tibia from moving forward during knee extension and flexion. Pathophysiology The anterior cruciate ligament is often the result of a forceful hyperextension or hyperextension injury. Most of these injuries are compound injuries, with the lateral tibial ligament and joint capsule of the knee being injured at the same time. Simple ACL injuries can occur with forceful hyperextension under non-weight bearing conditions. ACL injuries can also occur with hyperextension of the knee. Posterior cruciate ligament injuries are much less common than anterior cruciate ligament injuries, with a ratio of 1:10. When the knee is hyperextended, the knee is in a hyperextended position, which first causes the posterior cruciate ligament to rupture, and the violence continues to cause anterior cruciate ligament injuries; the upper tibia is subjected to anterior to posterior violence, and the upper calf suddenly moves posteriorly, causing the tense posterior cruciate ligament to rupture. Continued posterior displacement of the upper tibial segment can lead to rupture of the posterior knee capsule; the role of posterior rotation violence: when the foot is fixed, the upper tibia is subjected to violence from the front and rotated at the same time, often resulting in a compound injury, the tibia is semi-dislocated posteriorly, which is more serious than simple posterior cruciate ligament injury. Clinical manifestations and self-diagnosis A. Anterior cruciate ligament injury: Some patients feel a tearing sound within the knee joint when forceful trauma occurs, followed by weakness of the knee joint, severe joint pain, rapid swelling, and restricted joint flexion and extension. In some cases, subcutaneous petechiae are seen around the joint. Examination may reveal a positive anterior knee drawer test (a few patients may have a negative anterior drawer test due to acute injury pain and protective spasm of the quadriceps muscle; examination under anesthesia can be more accurate) and a positive Lachman’s test. MRI may reveal an interruption of the ACL continuity or no display in the position where it should normally appear. Patient self-diagnosis: 1. joint instability: no obvious discomfort when walking on a flat road, but feeling unstable when running, jumping, turning, stopping, going up or down a slope; the affected leg cannot support the landing after jumping; if the affected leg is used as a support leg to land, it is easier to sprain again; 2. it is easier to swell and pain repeatedly. After the anterior cruciate rupture, the joint is unstable and loose, and it is easy to stimulate the synovial membrane to appear swollen. 3, meniscal interlocking or secondary injury: ACL loss is easy to combine with medial meniscal injury, if not repaired, it is easy to have joint interlocking and cannot move. And the instability of the joint is likely to cause overloading of the meniscus, resulting in rupture or accelerated metamorphosis. 4, articular cartilage wear: after the destruction of the static stability structure of the joint, the dynamic stability mechanism (muscle) will passively increase the load. This causes cartilage metamorphosis. 5.Muscle atrophy: Long-term instability causes patients to feel distrustful of the affected limb and afraid to exert force. Muscles develop disuse atrophy. 6.Decrease in activity: Patients involuntarily reduce the amount of exercise to protect the joint and avoid recurrent swelling and pain in the joint. Treatment 1.Fixation method Incomplete rupture of the cruciate ligament, fixed with a long-legged tubular cast in 0-30° of knee flexion, push the proximal tibia backward before the cast is set (pull the proximal tibia forward when the posterior cruciate ligament is twisted), and fix for 4~6 weeks. 2.Medication In the early stage, according to the evidence, the blood should be invigorated to remove blood stasis and other drugs, external use of four yellow powder or double cypress cream; in the middle and late stages to renew the tendons and strengthen the bones, internal use of kidney tonics and tendon soup or Jian Bu Hu Qian Wan, external use of lower limb injury washing formula fumigation. 3.Functional exercise: start quadriceps training from the 3rd day after fixation. If there is a controllable brace, the knee can be flexed and extended within the range of 30°~60° after the 3rd week. 4.Surgical treatment Indications for surgery of fresh ACL injury: complete rupture of ACL; tibial stop avulsion fracture of ACL with large displacement, closed repair is not effective; meniscus rupture and other injuries.