An anterior cruciate ligament injury occurs when the ligament is over-stretched or either completely or partially torn. This can happen when a person gets hit on the side of the knee (e.g, a football tackle), overextends the knee joint, or quickly stops and changes direction while running, landing, or turning. Basketball, football, and soccer players as well as skiers are at risk for an anterior cruciate ligament tear. In many cases, an anterior cruciate ligament tear occurs with tears of the MCL and lateral meniscus. Most anterior cruciate ligament tears occur in the middle of the ligament, forming a gap between the edges. These types of anterior cruciate ligament tears do not heal on their own and may require surgery. Those who have sustained an anterior cruciate ligament tears report hearing a “popping” sound when the injury is sustained and swelling in the knee within six hours of the injury. Most cannot place weight on the injured leg without pain or the leg giving way. Those who suspect an anterior cruciate ligament tear or sprain should stop sports and activities and immediately seek medical attention. Initial treatment may involve raising the injured leg above the heart, icing the knee, and taking over-the-counter (nonsteroidal) pain relievers (e.g., ibuprofen). Physical therapy treatment of an anterior cruciate ligament tear or sprain will involve stretching and strengthening muscles in the surrounding area to ensure a return to daily activities without pain.