What is the Anterior Cruciate Ligament (ACL) The ACL is one of the four important ligaments that provide stability to the knee. There are two cruciate ligaments that cross inside the knee (cruciate originates from the Latin for cross), connecting the femur (thigh bone) to the tibia (shin bone). #ACL How do most ACL injuries occur? Most ACL injuries occur during a non-contact injury whilst pivoting or twisting on the knee; often during sports such as football, skiing, netball