The thigh bone, called the femur, and the tibia, or shin bone, connect together to form one of the human body's most complex joints. Two smaller bones, the fibula and patella, are also parts of the knee joint.
The knee bones are connected by tendons to the leg muscles, which move the joint. Ligaments help make the knee more stable. Between the tibia and femur are the medial and lateral menisci, two C-shaped pieces of protective cartilage. These help absorb shock between the two bones. The knee also contains numerous fluid-filled sacs, called bursae, which help provide smooth movement of the knee.