Attend any rodeo with riding and roping competition and you’ll see them—competitors with four fingers on one hand and a nub where their thumb should be. It’s a common injury in the sport—a thumb gets caught between a rope on one end and a decent-sized steer pulling on the other, and the thumb is usually the loser. It’s not a career-ending injury, but the absence of a thumb changes things. Without using your thumb, try to brush your teeth or button a shirt or comb your hair or tie your shoes or even eat. That little overlooked member of your…