The ACL, Anterior Cruciate Ligament, is a commonly injured ligament of the knee joint. This picture is a sagittal slice of a knee MRI clearly showing the intact ACL and the ruptured ACL. This time of the year, in Montana, we typically see this type of injury in basketball and skiing. Ligaments are tough bands of tissue that connect the ends of bones together. The ACL is located in the center of the knee joint where it runs from the backside of the femur (thigh bone) to connect to the front of the tibia (lower leg). Hence the name cruciate, or cross. The ACL is the main controller of how far forward the tibia moves under the femur. Therefore if the lower leg moves too far forward in relation to the upper leg , the ACL can rupture. The ACL is also the first ligament that becomes tight when the knee is straightened. If the knee is forced past this point when landing, the ACL can also be torn. Several Missoula Bone & Joint surgeons specialize in the arthroscopic surgical repair of several knee injuries, including the ACL, with successful outcomes. This type of injury is unexpected and very unfortunate, but if you find yourself with a knee injury, come straight to the specialists.