There has been strong support from some contributors to this thread that spanking can cause spinal damage, and therefore it is too dangerous an option for a responsible parent to consider.

There are many references on the Web to that this indeed so - but you will only find them on web sites set up to promote anti-spanking propaganda.

The source of this theory is very hard to track down.   

As far as I can tell, it all comes from a single report in 1994 that 3 children had "unusual" spinal damage.   The attending physician thought that spanking, shaking or other similar causes may explain how the damage occurred.   No evidence, no facts, just an opinion of what may have triggered it.

And that's the only study I can find.

I now feel comfortable in dismissing the "a spank damages the spine" theory on the grounds that there is not yet one single documented case of it ever having happened.