In the United States, more than 9 million patients sought medical care for knee disorders in 2001. The knee joint is the most complex joint in the body and is critical to movement. Good extension and flexion stability is an important foundation for knee function. Two complete sets of ligaments, the cruciate ligament and the collateral ligament, ensure the stability of the knee joint. The cruciate ligament The cruciate ligament is located inside the knee joint and connects the femur to the tibia. It is made up of many bundles of fibers that hold the joint together like a rope during knee flexion and extension. This stability is necessary for normal knee movement. The name of the cruciate ligament indicates that the ligaments are arranged in a cross pattern and are essential to function within the knee joint. Not only are the cruciate ligaments located inside the knee joint, but they are arranged in an “X” shape. The anterior ligament is called the anterior cruciate ligament (ACL) and the posterior ligament is called the posterior cruciate ligament (PCL). ACL injuries prevent the tibia from moving toward the front of the femur and are often damaged in the following ways: 1) sudden change in direction of motion 2) deceleration during running 3) jumping from a height and landing on the knee 4) contact injury, such as a sprain from playing soccer. You may hear a popping sound and feel a loss of control of the knee, but you may not experience pain immediately. Two to 12 hours after the injury, the knee joint becomes swollen and painful when standing. Continuing to walk or run after an ACL injury can severely damage the cushioning cartilage in the knee joint, which can lead to a complete loss of knee function and may require consideration of an artificial knee in the future. Therefore, we should pay great attention to the diagnosis and treatment of ACL injury, not because we can still walk, or even run and jump after knee injury, and miss the best time for treatment. Diagnosis of ACL injuries The diagnosis of ACL injuries is based on a detailed physical examination. The physical examination, such as Lachman’s sign and axial shift test, can be used to understand the stability of the ACL, and even the results of the physical examination are directly related to the choice of treatment. X-rays of the knee, magnetic resonance imaging (MRI) or, in some cases, arthroscopic exploration of the knee will also be performed. Treatment of ACL injuries Depending on the nature of the ACL injury, surgical or non-surgical treatment methods may be used. Non-surgical treatment: 1, elderly people or those who do not require high exercise 2, those who have good knee stability 3, those who have done strength restoration exercises and often use crutches to maintain joint stability Surgical treatment (including incisional surgery and arthroscopic surgery) 1, usually using autologous or allogeneic patellar ligament or N cord tendon, through the ACL at the starting and ending points of the femur and tibia and reconstruction 2, can also use artificial ligament to reconstruct the ACL 3, postoperative muscle strength restoration exercises to maintain joint flexibility 4, according to the situation, our hospital mostly adopts the autologous N cord tendon double tunneling technology to maximize the restoration of ACL function, and has achieved promising results. At present, we have to complete about 300 cases every year, and good results have been achieved, and the reconstruction technology has been in line with the world’s leading technology. The incidence of posterior cruciate ligament injury is lower than that of the anterior cruciate ligament. It usually occurs during anterior knee impingement or sprain. The tibia is displaced posteriorly in PCL injuries, causing a breakdown in knee stability. Direct friction between the femur and tibial ends wears away the smooth, thin articular cartilage, leading to knee osteoarthritis. Treatment of posterior cruciate ligament injuries Because some patients do not have symptoms of knee instability after a posterior cruciate ligament injury, it often goes unnoticed. Moreover, the reconstruction of the posterior cruciate ligament under knee arthroscopy is technically demanding and complicated, and objectively some patients are not properly treated. Therefore, there is still a controversy on how to treat PCL after injury. We believe that some patients can be treated by exercise after PCL injury, but this treatment is not ideal because of the sacrifice of osteophytes and premature aging of the knee joint. Our opinion is that most of the patients with PCL injury or combined with other ligament injuries that seriously endanger the stability of the knee joint should actively use autologous N cord tendon to reconstruct the PCL, restore the stability of the knee joint, and make a good recovery of the knee function through a detailed rehabilitation program. The lateral collateral ligaments are located on the medial and lateral sides of the knee. The medial collateral ligament (MCL) connects the femur and tibia and provides stability to the medial side of the joint. The lateral collateral ligament (LCL) connects the femur to the fibula and provides stability to the lateral aspect of the joint. Medial collateral ligament injuries are usually caused by violence to the lateral aspect of the knee and are associated with severe pain on the medial aspect of the joint. Injuries to the lateral collateral ligament are relatively rare. Lateral collateral ligament injuries Because the medial collateral ligament is primarily a membranous structure, it has the ability to heal easily. When the medial collateral ligament is injured, most conservative treatment is effective, using the R.I.C.E. rule: rest, ice, compression bandages, and elevation of the affected limb: rest to give the knee time to heal; ice two to three times a day for 15 to 20 minutes; compression bandages to limit swelling, and elastic bandages and crutches; and elevation of the affected limb if possible. Rehabilitation program under the protection of a knee brace with locking. Surgery is required when the medial collateral ligament is completely ruptured or when the injury is not self-healing. With satisfactory surgical reconstruction, knee stability can be restored and many patients can regain their pre-injury level of motion. The lateral collateral ligament, because it is primarily a tendinous structure, does not heal easily after injury and often requires reconstruction after trauma with lateral instability. Neglecting the treatment of the lateral structures, especially when combined with other ligament injuries, will result in eventual failure of the surgery.