The knee joint is a combination of three bones: the femur (thigh bone), the tibia (lower leg bone), and the patella, which connects the quadriceps muscle to the patellar ligament. The femur slides back and forth over the tibia so that the knee joint can be flexed and extended. These three bones are covered with a layer of flexible and soft cartilage, and the meniscus, which acts as a cushion between the femur and tibia, absorbs external shocks to the joint.