The above video is a southern flying squirrel. The finders found it in their yard and don't know how it got hurt. You're right--looks like some sort of spinal trauma. and that's what the radiographs (below) revealed. The sharp angle in the spine is a dislocation of the vertebrae:( this patient had to be euthanized.
The video below is a juvenile ring billed gull. He came in when we had a vet student working with us. He had a fracture, which healed well. After that, he refused to fly. The student ran every test in the book, which all came back normal. The student left, so I repeated the tests, and still there were all normal. Turns out, this was just a stubborn gull, who refused to fly for us! He was perfectly healthy:) so we started "creancing" him (see video) where you essentially have him on a rope and get him to fly for exercise. After a few weeks of this, he was released just in time for migration:)