Abstract: A joint structure for a knee brace in which the axis around which motion takes place is not fixed but rather simulates that of the natural joint, lengthening and shortening with it. The joint structure includes two slidably-coupled joint elements, the lower one of which has a ramp member and a pair of furcations. The head of the upper joint element is received between these furcations and connected thereto by a pin which passes through an elongated slot formed in the head. As the joint elements rotate toward each other from their fully extended position, the pin slides from the upper to the lower end portion of the slot, increasing the overall length of the joint structure with flection as does the human knee joint.