Torn anterior cruciate ligament (ACL) facts: The anterior cruciate ligament is one of the four ligaments in the knee that provides stabilization. Torn ACLs are a common knee injury with more than 200,000 occurring every year in the U.S. Almost 100,000 ACL repair surgeries are performed each year. An ACL tear or sprain occurs when a sudden change in direction or pivot occurs on a locked knee. A pop, followed by pain and swelling of the knee are the most common symptoms of an ACL tear. Women are more likely to tear their ACL because of differences in anatomy and muscle function. Treatment goals are to return the patient to his or her preinjury level of function. Arthroscopic surgery may be required to reconstruct the torn ligament. It may take six to nine months to return to normal activity after an ACL injury.