In reply to Chris F: agreed, it sounds like one. if the centre of your hand was a watch face, it'd lie around 1-2pm. mine is about 8mm across, is easily felt if you run a finger over it.
my father has it, so look for hereditary links. i have started to carry that hand (left) with pinky and ring finger crooked, involuntarily. my gp suggested splaying the entire hand outward a few times a day to put a counter-stretch in and when i do it i do feel a resistance.
if you look at the site mentioned above (dup info site) you'll see theres a list of 8-10 other things it could be tho.
at 38, my fingers are pretty straight tho. not likely to kick in heavily till middle aged, i think.
ahunter