ACL stands for Anterior cruciate ligament, which is a major ligament of the knee. Ligaments are basically strong bands of tissue and their function is to attach one bone to the other. The ACL helps to stabilize the knee joint by connecting the thigh bone to the shinbone. his ligament could get injured and torn due to sports, accidents, etc. And this torn and damaged ligament is then removed and replaced. This Ligament graft could either be taken from the patient body or donor.