The anterior cruciate ligament (ACL) is one of four main knee ligaments, which holds the femur and tibia together. The ACL's job is to keep the tibia from coming too far forward from the femur. The most serious potential consequence of an ACL injury is an early onset of osteoarthritis in the knee joint. Other problems include lost time from school or work, poorer academic performance, damage to other major structures in the knee such as the meniscus, and high cost of rehabilitation and surgery. There are also psychological issues of anger and depression from loss of the ability to participate in athletics that may last for a very long time. Learn more