Why does Iggy Pop limp?

According to the Rolling Stone interview with David Fricke:

Iggy Pop said.....

"I have a dislocated shoulder. I have a lot of cartilage lost in my right hip. Both knees are about to go. I have one leg about an inch and a half shorter than the other. When I was thirteen, I was run over by a big guy playing junior high football, and the right leg ended up a quarter-inch shorter. By my mid twenties, it was a half-inch. Then in the Eighties, I had no money and was taking packed economy flights everywhere, night after night. The combination of that schedule and a fall I took dancing on an amplifier left me with my spine twisted and a slight limp."