I also have the big bump on the knuckle of my right thumb. Mine was caused by bowling. I was also hoping to find out how to at least reduce it's size. But it looks like nobody has an answer. oh well. looks like it will have to stay that way...
I have the same bump. Family doctor told me it's callus. Have you found a way to get rid of it?
This just looks like excess cartilage/skin or a certain type of wart.
Next time you're at the doctor for a checkup or anything, ask him/her if they think it's appropriate to get it frozen off or removed.
Picking at it could cause an infection and that wouldnt be good!
Best of luck, David
Heres another view of it:
http://img262.imageshack.us/img262/7036/0327091216a.jpg