My piggies always sound like they are in death throes, even when it is as small a something as having their feet cleaned up for inspection, or ears cleaned out to check for mites etc. When it is as serious as having ears notched, you'd think we were actually performing illegal torture on them. So, I am now somewhat deaf to their noises and try to look at the individual instead of listening to it (hard - it is a pretty insistent noise, a pig in pain...).
If he can sit and eat, I don't reckon he can have broken his back. Hopefully it is something ligament related - a bit like sciatica, maybe?
Aren't you glad you aren't a vet, though, when you have this sort of thing to try to work out...
Thinking of you all and hoping there's another good outcome for this little piggy xx