This is one of the weirder “good luck” expressions, as generally speaking, breaking any bone isn’t so lucky.  In my super limited research, this notion comes from the expression “lucky break,” meaning not a literal break, but more like an awesome opportunity.  Now onto the drawing bit.  The first thing I thought of for this drawing was C-3PO and his broken leg, especially because it is not so gruesome to illustrate.  Additionally, I was flying on a plane, en route to visit my pal, Val, in Oakland, and too cheap to pay for Wi-Fi…and like a dummy, I didn’t keep any reference images on my phone of our gilded friend.  I wound up drawing 90% of this from memory, and then making some adjustments once I could confirm what the droid actually looked like.  Thankfully, being a nerd and giant star wars fan, made this task not too awful.