What are double joints?

Double joints - is a capable of an unusual amount of movement, usually backward movement. Perhaps the most common demonstration of a double joints is to see someone bend his thumb downwards and backwards until it touches the inside of his forearms. A joint is a meeting place between different bones of the skeleton. Joints are divided into fixed and movable ones. Movable joints may be divided into gliding joints, such as the wrist and ankle; hinge-joints, like the elbow and knee; and the ball and-socket type such as the shoulder and hip.