Leg prosthesis. Front view of a prosthetic (artificial) leg with reflex foot action and a high activity knee module. At top is the coloured upper leg support and brace. The high activity knee module contains a piston that absorbs pressure from the leg as the knee bends. The foot moves by reflex action in relation to the leg using a spring-loaded mechanism. Most artificial limbs are fitted to replace amputated limbs following a disease or a severe injury. In some cases they substitute limbs missing from birth. An artificial leg such as this is highly successful in duplicating the movements of a natural leg.