the tuber coxae is the common name for the hip bone. it forms the basis point of the hip and a fracture of this point is usually caused due to direct impact with another object.
Looking at the pictures, I would say ned is definately lacking in bum muscle (topline). I would be concerned that: he's had this injury; he needs to be ridden in spurs; and he can't spread out over a wider jump. It all sounds like there is an issue that either just needs some chiro/physio or maybe it's more. I am not a vet, so do not take my words as fact. I would, if I wanted him, ask my vet's advice.