What is an ACL?     The Anterior Cruciate Ligament (ACL) is one of four ligaments (ACL, PCL, Lateral and Medial Meniscus') that support the knee joint (www.medicinenet.com). Most ACL's are approximately 4 cm in length and about 1 cm in thickness (Remer et al. 1992). The ACL has four specific functions of support within the knee joint (www.sportsci.org):         1) It limits how far the tibia can slide forward with respect to the femur.         2) It does not allow hyperextension of the knee joint.         3) It provides support against forces on the inside of the tibia pushing out (valgus stress).         4) It controls how much the tibia rotates with respect to the femur. Title Page What is an ACL? How do you tear an ACL? The physics of an ACL tear How do you fix it? Bibliography