Driver stated was at the Transload Yard in Morenci at 1:30 am. While exiting truck from the drivers side, EE was maintaining 3 point of contact. When EE's left foot touched the ground, and EE put weight on it; EE's ankle buckled and gave out. This caused EE to fall backward. When EE put arm out to break the fall upon impact with the ground, EE hurt right wrist.