I came across a fab baby bouncer that looked like a car in the sale and almost bought but mum said not to as they can cause spinal damage. A quick search on google returned this:
It makes sense really, if they're not walking then they're not designed to be in that upright position - their spine isn't strong enough. I have never been a fan of walkers as I think it makes them too reliant and not figuring it out for themselves. However had never thought about the health implications. I suppose it's down to each individual but we won't be buying any of these - spines are a very important part of the body and I wouldn't want to cause any damage to baby's spine.