BRIAN GADSBY / SCIENCE PHOTO LIBRARY BRIAN GADSBY / SCIENCE PHOTO LIBRARY
Knee extension and flexion. Two X-rays of a human knee joint seen from the side, in extension (straight, left) and in flexion (bent, right). The extended knee has the patella (knee-cap) at far left. The flexed knee has the patella at lower left. The femur (thigh bone) is at top in both images, with the upper part of the two lower leg bones (tibia and fibula) at bottom at left and at right in the image at right. As well as bones, the knee joint consists of muscles, cartilage, ligaments and tendons. The knee is a mobile hinge joint (ginglymus) that is also capable of slight internal and external rotation. X-rays help diagnose conditions such as arthritis or knee injuries.
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