help me to save my friend on his acl

The anterior cruciate ligament, or ACL, is one of the two major intra-articular ligaments of the knee (think deep inside) and the primary ligament of the knee that helps to stabilize and prevent the leg from falling forward. Additionally the ACL protects the knee against varus and valgus stress when the knee is in full extension. The ACL is comprised of 2 different bundles, the anteromedial bundle that tightens in flexion, and the posterolateral bundle, which tightens in full extension. The greatest amount of tension on the ACL is when the knee is flexed 30 degrees.