ACL. An anterior cruciate ligament, or ACL, injury is a a knee ligament that joins the upper leg bone with the lower leg bone . The ACL keeps the knee stable. Injuries range from mild, such as a small tear, to severe, such as when the ligament tears completely or when the ligament and part of the bone separate from the rest of the bone. http://www.miamisportsmedicine.com/ACLTears.html.
ACL location. Acl runs inside your knee from the posterolateral distal femur to the anteromedial aspect of the tibia, in the knee joint. I tell patients it roughly runs in the same direction as putting your hands in your pocket.
Let me show you. http://en.wikipedia.org/wiki/anterior_cruciate_ligament.