In this condition the internal arch of the foot is flattened so as to be in some cases abolished; at the same time the foot is rotated outwards and the astragalus is pushed downwards and inwards, the greater part of its head ultimately leaving the scaphoid. The condition arises from the weight of the body stretching the ligaments, chiefly the external calcaneo-astragaloid and the interosseous calcaneo-astragaloid. The loosening of these ligaments allows of the displacement of the astragalus, which is the essential element in the production of the lesion.