I Was Born With Only One Joint In Both My Thumbs. What Is Wrong With Me And How Can I Fix It?

My thumbs only bend at the first knuckle near the finger nail. I'm a mechanic and they get real sore and swell up if I try to unscrew too many small screws. Picture yourself trying to count to three with your fingers and when you get to three your thumb can't touch your pinky, so it looks like your holding up four because I have no joint there! I need a doctor!