The knee joint joins the thigh with the leg and consists of two articulations: one between the femur and tibia, and one between the femur and patella. It is the largest joint in the human body. The knee is a mobile trocho-ginglymus (a pivotal condylar joint), which permits flexion and extension as well as a slight internal and external rotation. The knee joint is vulnerable to both acute injury and the development of osteoarthritis. It is often grouped into tibiofemoral and patellofemoral components. (The fibular collateral ligament is often considered with tibiofemoral components.)