An ACL can be partially or completely torn. An ACL is considered sprained when the tearing is microscopic, and the ligament remains intact. Individuals typically report feeling or hearing a pop when they tear their ACL. Swelling of the knee is often associated with ACL tears. Individuals are typically unable to continue participating in the activity they were performing at the time of injury. Injured individuals also report instability of the knee with sudden changes of direction or pivoting movements.