Damaged knee ligament. Computer artwork showing the cruciate ligaments (pink) in a knee joint. Ligaments are bands of inelastic fibrous tissue that connect bones to other bones. Those in the knee are the anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL). Here the ACL has torn right through (ruptured). These ligaments cross each other in an X-shape and connect the femur (thigh bone, top) to the tibia (shin bone, bottom centre), to prevent them from moving too much in relation to one other.