Hi,
Well, just as a basic guess, breeding a kinked female could cause problems with the manipulation of the follicles and eggs along the body depending on the location and severity of the kink. Or the amount of calcium needed to coat and produce the eggs could be a problem if the female leached it from her bones - wierd articulation caused by kinks and weakened bones could be a nasty double act in something designed to protect a spinal cord.
I don't know if those are valid reasons or if they are the ones Ed was thinking of - they are simply the ones that occured to me first when I read your question.
dr del