A. C. L.- three simple letters that strike utter fear in any athlete’s heart. There are approximately 100,000 to 200,000 ACL ruptures per year in the United States alone, most of which are females. That’s a scary number!! The ACL, standing for anterior cruciate ligament,  aids in side to side motions, like shuffling, sidestepping, or cutting. It is located on the inside of the knee, running from the femur (thigh) to the front of the tibia (shin), and also keeps the lower leg from shifting forward.                                                   Most people are surprised by how small the ACL is. It is only about the size of your pinkie finger!We need ACLs, obviously. Without an ACL, the knee is very unstable during lateral movement, meaning that players in positions or sports that depend on rapid side movements can’t play for a long time after injuring their ACL (think football, basketball, soccer, etc.) and generally wear a brace for a very long time, even after it heals.  When a successful athlete tears or ruptures their ACL, everyone freaks out. Will this be the end of their career? Truth is, it can be hard to bounce back after an ACL injury. For something that causes such a ruckus among the athlete community, a lot people have false beliefs about them.  So exactly what happens when an athlete tears an ACL?ACL tears usually happen in contact sports or sports that require a lot of start-and-stop running. Girls injure their ACLs much more frequently than male athletes, simply because of their bone structure, hormone levels, and landing mechanics. The cause is usually an abrupt twist of the knee or a hit directly to it.  The most common cause of injury is a blow to the knee.  When an outside force causes the knee to go inwards, the force causes the knee joint to “‘open’ (like a hinge), which can damage the ACL as well as the MCL (medial collateral ligament) and the meniscus (knee cartilage)”1 . When an athlete’s knee endures a twisting motion (non contact), the ACL can be damaged by stretching past its limit.  This can happen with improper running mechanics.