The knee joint is the largest joint of the human body. It joins the femur and tibia (tibiofemoral joint) and also articulates the femur with the patella (patella-femoral joint).
The ends of the bone are covered with articular cartilage. Two C-shaped wedges of cartilage are placed between the tibia and femur and act as shock absorbers. Essentially the knee joint is a hinge-type joint allowing flexion and extension. 
The range of motion is limited by the geometry of the bones and also by constraints of the stabilizing ligaments. In general up to 140 degrees of flexion is permitted and also a small amount of rotation and side movements are permitted. The knee joint is surrounded by a synovial capsule which produces lubricating fluid. The knee is stabilized by four ligaments. The inner (medial) and outer (lateral) ligament stabilize against side and bending movements. Two internal ligaments, the anterior and posterior cruciate ligament provide resistance against anterior and posterior movement.