The telltale sign of an ACL injury is the POPPING sound it makes as the ligament tears. This is usually combined with INTENSE pain and instability of the knee to the point where it feels as if it's giving out. It'll become almost impossible to stand on. For hours afterward, swelling in your knee will continue to grow. If you suspect you've hurt your ACL, do NOT try to move your leg. It can only do more damage. Instead, splint your knee to keep it from bending until you've see a doctor for x-rays. For minor injuries, treatment includes ice packs, painkillers, and knee splinting. The patient will usually need physical therapyto re-strengthen the knee muscles and to regain full range of motion. Surgery and rehab is almost always necessary in severe cases. Because the ACL can't be stitched back together, a small piece of tendon from another part of your leg is used to replace it. The full healing process can take 4 to 6 months or even up to a year for some patients. To learn more about other common joint injuries, watch the rest of the videos in this series.