The knee joint joins the thigh with the leg and consists of two articulations. It is the largest joint in the human body.

The knee is a mobile joint which permits flexion and extension as well as a slight internal and external rotation. At birth, a baby will not have a conventional knee cap, but a growth formed of cartilage. By the time the child is 3-5 years of age, ossification will have replaced the cartilage with bone.