The main function of the ACL is to prevent the tibia from shifting forward due to the course of its fibers and the location of its nodes, thus ensuring the stability of the knee joint. What actions in daily life and sports can increase the stress on the ACL and result in injury to this ligament? Studies have shown that there are two most common mechanisms of ACL injury: one is the rotation of the hip and thigh by the upper body after the lower extremity has been dropped and stepped on. Figure 1. This type of injury mechanism is very common in many sports that require running, stopping, turning, sudden acceleration and deceleration. Examples include soccer, basketball, tennis, badminton, and even table tennis. Soccer players (the two red arrows indicate the direction of landing and the direction of knee rotation, respectively). However, in non-land sports, special sports equipment can also cause similar forces on the knee. For example, in skiing, especially in snowboarding, when the snowboard is fixed at one end and the upper body happens to rotate in the other direction, or when the snowboard does not come off in time after a fall on the piste and gets stuck on the snow or on a protective net and the body is rolling – these are two common situations in which the ACL can be injured. The ACL is also very likely to be injured. Figure 4: Skier Injury mechanism #2: Knee hyperextension. When the knee is hyperextended by an external force, the tibia moves too far forward from the femur, and the ACL is there to prevent the tibia from moving forward by pulling on it. When the tibia moves too far forward and imposes a load on the ACL that exceeds its capacity, the ACL can tear or rupture. This mechanism of injury is more common in sports where there is physical contact, such as rugby and soccer where the opponent’s body is pressed head-on into his or her leg. The anterior cruciate ligament, the medial collateral ligament and the medial meniscus are tightly connected, and when the mechanism of injury occurs, all three are often damaged at the same time to varying degrees.