Here is my guess how Junkrat lose his leg and arm:maybe it was an explosion with infection that infected Junkrat and maybe roadhog or himself cut OFF the leg and arm
It was diabetes. He used to be the size of roadhog, proportionally. They were munch buddies. Junkrats body reacted like a normal body and broke. Roadhog has always had severely lucky health considering the munching and meth inhaler