The ligament is a dense fibrous connective tissue bundle or membrane that connects two adjacent bones of a joint or between cartilage, made of elastic and collagen fibers, commonly known as “tendons”. Ligaments are strong in tensile strength and have a certain degree of elasticity, and their function is to maintain the stability of the joint and limit its movement beyond the physiological range. Many sports enthusiasts or athletes have sprained the ligaments of the knee during sports, with ACL injuries being the most common and potentially causing short and long-term mobility problems. The most common cause of an ACL injury is an external impact on the knee joint during twisting. Here are four indirect external forces that can cause injury: 1, sharp stop or turn Firmly on the ground, the leg turns in the other direction such as a soccer or basketball player sharp stop and quick change of direction. 2, straight knee landing knee straight down, the foot hit the ground, such as water skiers in the jump after landing or gymnasts vault landing. 3.Knee joint hyperextension when the side emergency stop landing leg in the case of hyperextension suddenly stop, such as baseball players in the lateral slide to the base when the knee joint is subject to additional forces. 4. Rotation and sudden deceleration Natural deceleration and foot twisting can cause excessive knee rotation, such as a soccer or rugby player turning sharply after a sudden deceleration. Injuries to the ACL can cause short-term or long-term mobility problems. In ACL instability, there is a subluxation of the tibia and femur so that the meniscus is subject to abnormal fracture forces. In addition, knees with ACL insufficiency have a high chance of developing osteoarthritis. The clinical manifestations of the injury are localized swelling, pressure pain, or joint instability, and pain that increases when the joint is pulled in a violent direction. Inappropriate treatment may result in instability or traumatic arthritis. The principles of treatment are exact diagnosis, early management, and comprehensive repair.