Blame airbags, says NBC News, in a 2012 report that recently resurfaced on MetaFilter. They’re designed to protect your head and chest in a crash. But if your arms are too high up on the steering wheel, the deploying airbag can smash them into your face, causing injury. The chemical reaction that inflates the airbag can also injure your hands, sometimes requiring amputation.
Instead, put your hands at opposite sides of the wheel: “9 and 3.” An AAA representative tells NBC News that this position is also more ergonomic in general, giving the driver better control of the car.