Could someone please explain 羽目に（はめ） to me, I've read a load of sentences on the net, had a look in a Japanese dictionary and can't get it.
e.g. 右足を切断する羽目に使用していた

I think it basically means things have come to some kind of dilemma or other undesirable circumstances. In your example, someone used his right leg so much that he faces the dilemma of having it amputated.. probably not to be taken literally.

See http://dic.yahoo.co.jp/dsearch?p=%E7%BE%...=0&dtype=3 for more examples.