The anterior cruciate ligament (ACL) is one of a pair of cruciate ligaments (the other being the posterior cruciate ligament) in the human knee. They are also called cruciform ligaments as they are arranged in a crossed formation. In the quadruped stifle joint (analogous to the knee), based on its anatomical position, it is also referred to as the cranial cruciate ligament. The anterior cruciate ligament is one of the four main ligaments of the knee, and the ACL provides 85% of the restraining force to anterior tibial displacement at 30 degrees and 90 degrees of knee flexion.