Quasimodo has Short Spine Syndrome, a very rare condition among dogs. It's exactly what it sounds like, he was born with a spine that's shorter than a normal dog because he is missing some vertebra.
His condition doesn't cause him pain but he does need special medical attention for other health conditions. He's been getting lots of love from foster homes since being rescued. Now that he's in the care of Second Hand Hounds he's managed to bring some much needed attention to the organization that rescues dogs (and cats) in dire need and places them in foster homes.