The knee is a pivot-like hinge joint in the leg that connects the bones in the upper and lower leg. It is the largest joint in the human body. The knee is where the femur in the upper leg meets with the tibia and fibula bones in the lower leg. Another bone, the patella or kneecap, is at the center of the knee.The knee joint is composed of numerous tendons, ligaments, and protective elements, such as cartilage and bursa.any muscles that power foot movements begin as high up as the back of the knee and extend down to the foot. Possibly the most important structure in the lower leg is the Achilles tendon. It connects three muscles—the plantaris, calf, and soleus—to the heel bone.