All puns are intended, FYI
First, you have to lose all or part of your limb in a terrible accident. Like, we could use one instance I know, a fighter jet crash explosion.
Personally, I don't recommend it. It's hot and painful. And it comes with some permanent damage, like limbloss.
I hate to be heavy handed here, but I just want to hammer home how serious it is.
Second, it also helps to be connected with friends with deep pockets who want to use you for PR purposes. "Friends" might be a generous definition. Like, another instance I know, say a well funded politician who runs on a platform of taking care of wounded vets needs a clear example to point to that people like looking at for his campaign.