An anterior cruciate ligament (ACL) injury occurs when the ACL ligament within your knee is torn. This occurs most commonly while playing high intensity sports that involve a lot of quick, powerful changes in direction. People who play sports like basketball, tennis, volleyball, and soccer are most likely to suffer an ACL knee injury. For reasons that are not fully understood, ACL tears are much more common in women than in men.
ACL injuries typically happen when abruptly changing direction, landing awkwardly after a jump, or trying to pivot with your foot firmly planted, thereby overextending your knee. The first sign of a torn ACL is a loud popping sound as the injury occurs. Additional ACL injury symptoms include not being able to put weight on your knee, severe pain, and significant swelling.
A torn ACL should be treated by a medical professional immediately. The first course of action will be to reduce your pain through medication.