Platform shoes are shoes, boots, or sandals with a thick sole, usually in the range of 3–10 cm (1–4 in). Platform shoes may also be high heels, in which case the heel is raised significantly higher than the ball of the foot. Extreme heights, of both the sole and heel, can be found in fetish footwear such as ballet boots, where the sole may be up to 20 cm (8 in) high and the heels up to 40 cm (16 in) or more. The sole of a platform shoe can have a continuous uniform thickness, have a wedge, a separate block or a stiletto heel. Raising the ankle increases the risk of a sprained ankle.