My hamsters leg!

Hey!
Thanks for reading, and I need help URGENTLY!!!!!
A couple days ago my I went to check on my hamster (snaggletooth) and saw he had his foot caught between the door of his cage and the cage its self. I helped him out by opening the door, and it was bleeding.
Naturaly I was shaken and crying.
When I told my mother she said he'd be fine, and now his leg is black, and when I look, I'm not Positive,
but I think I can see bone.
It looks like its wasting away.
He doesn't stand on it,
and sometimes I hear him running on his wheel,
but only for a few seconds. He can still climb, but he NEVER puts pressure on it.
I'm really worried,
and I just want advice on if I should get his leg amputated, or medication, because Im really scared! I love him very much, he was my first real pet,
PLEASE HELP!!!!!!!!!