This is very rare condition, but seems to be occurring under the wild species of hedgehogs, especially with the European Hedgehogs, Erinaceus europaeus.
Pop-off Syndrome is where the where the orbicularis muscle that runs around the hedgehog`s ‘skirt’ and enables him to roll up, pops over their body and move all the spikes up over the top of their body. This means they can`t roll up in a ball for self-defence. The ‘skirt’ is where the belly and side of hedgehog meets the beginning of their quills. The orbicularis muscle performs in a drawstring way, which enables them to ball up. Have you ever put your finger on a hedgehog stomach, and they quickly ball up? You will have difficulty removing your finger from that tight grip. That is the job of the orbicularis muscle.
So, how does this happen?
Normally when hedgehogs trying to crawl through very small spaces or holes, it causes for the muscles to physically pops out. Hence the reason for the name. This is not common under African Pygmy Hedgehogs, and no references could be found for other hedgehog species with this problem. It appears that it is not necessarily sized related, as the European Hedgehogs are very big, and you would think it might be related, as rescuers had found even juveniles with this problem.
See link with images and video that display this syndrome very well for you to get an better understanding of what is happening here.
Wildlives Wildlife Rescue and Rehabilitation Centre
In terms of our beloved African Pygmy Hedgehogs, it will be best to avoid small tubes or tunnels in their cages, not to create a possible scenario where something similar can happen to them.
Article by Lizl van Vreden.