hi, the same thing happened to me when i was like 4 years old. i closed a washing machine on my finger and broke it but because i have such a high tolerance for pain i never went to a doctor and now it is bent and has a bump in it. i'm not a doctor but i'm pretty sure it's because when you break a bone it heals itself be creating more tissue and a cast is really to guide it into proper shape. because you had no cast the tissue was formed in an improper shape. my doctor said that i can get a surgery to fix it but i can't get it now.
It could be true, while i cant tell you anything for sure concerning your finger. I can tell you that a residual bump can take years to disapear.
When the bone heals, at the site of the break, it created some new fibers, wich in time harden, and become new bone.
But it always created these fibers AROUND the break, making, as you could say, a *ball* of bone around the break.
With time, this *ball* of bone, will gradually disolve any unecessairy parts, to finish closely to what the original bone looked llike.
However there is a chance it may stay that way for your life.
i hope this helps!