Doctors tend to think that it's the position of the foot while landing from a jump. During a landing, the foot flexes upward and the heel presses slightly inward. The ankle joint takes the pressure of the landing, which could lead to injury.

A recent study suggested that there may be an additional ingredient. This study found that pointing the foot out is the main cause of a fractured ankle. When placed in the normal "landing position," ankles didn't fracture. But when the foot bent up and pointed outward, nearly all of the ankles tested broke. (The researchers used ankle bones from cadavers in their experiments.)

Researchers hope that more protective boots and bindings will prevent this kind of injury. Until then, snowboarders are advised to watch their foot position when landing.