The knee joint is made up of two parts. The part of the knee between the end of the thigh bone (femur) and the top of the shin bone (tibia) is called the tibiofemoral joint. The patellofemoral joint is between the end of the thigh bone (femur) and the kneecap (patella).
The knee joint is surrounded by synovial fluid which keeps it lubricated. The bones are covered by smooth joint surface (articular) cartilage that allows them to glide smoothly together without friction. If the joint surface is damaged through wear and tear or a knee injury, arthritis can develop.