Yay for Casper! He must be so brave. Tell him I love him. My ratties send their undying love and hope.
I'm worried that if you go to a vet they'll suggest euthanasia. But I guess they can't make you. I'm just worried that they would talk you into it using fancy talk. I've found thats just how they work.
Anyway, I bet you could care for him on your own. Are there any open wounds? If so, you clean them, put peroxide on them, and bandage them. If the leg is swollen, you might want to get some advise or a Rx for an antinflammatory. I hear that sometimes human medicines in very small doses can work. You'd have to find out which ones.
If you put a cast on, I'm sure he'll chew it. Unless you make it taste really disgusting. Put vinegar in it or something.
Are you sure it isn't a tumor or something? The fact that its swollen disturbs me. Is it like, terribly unnatural? Or does it look normal for a broken leg?
You're probably handling the situation well, but still, I'm so worried....
I'll pray for you Casper!
Lila