Knee ligaments are bands of fibrous tissue that hold the knee joint in place. They are the medial collateral ligament (MCL), the lateral collateral ligament (LCL), the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL).
The MCL and the LCL are found on either side of the knee and keep it from wobbling from side to side. The ACL and the PCL are there to stabilize the tibia and the femur, the long bones in the leg that also make up the joint. The ACL keeps the tibia from slipping forward while the person runs, jumps or slows down. The PCL keeps the tibia from slipping backwards.