Anterior cruciate ligament (ACL) injury can be defined in simple terms as a tear in the ACL. As we know, the ACL keeps the knee stable; but when the ligament is stretched way over its capacity limits (hyper-extended) and the knee is twisted in any way, the ACL may suffer injuries. Abruptly stopping from a speed run, turning awkwardly with one foot rooted to the ground, and clumsy landing subsequent to a jump with sudden deceleration, are common causes of ACL injuries. This is mostly true in sports, which rely heavily on the ACL such as football, basketball, soccer and skiing. Such ACL injuries are sometimes thought of as just “sprain”.