Two cases of supination-eversion grade II ankle fractures are presented. Both fractures were sustained during downhill skiing and both patients were wearing competition ski-boots with all buckles closed. The trauma mechanism is discussed. The only force that can act upon an ankle inside a ski-boot is a torsion of the calf on the foot. It is, therefore, interesting that the supination-eversion-type fracture can be reproduced with this violence. By considering the ankle and the subtalus joints as a torsion transmitter it can be shown that a supination leads to similar forces between the talus and the mortise as does an outward rotation of the foot. This explains why the two different trauma mechanisms lead to the same injury.