Ligaments are structures that hold bones together.
They not only stabilize the knee joint, but more importantly they guide the motion of the knee. Because the ACL is located in the very heart of your knee joint and is bathed by the fluid of the joint, it will not heal on its own. About half the time when one injures the ACL, one will simultaneously tear the knee cartilage. Tearing the knee cartilage leads to pain at the joint lines and such symptoms as locking, catching, popping and swelling. The ACL is a stabilizer.