dogs bones not showing up on x rays

Question
My dog Poppy a min chiwawa, collapsed yesterday ,couldn't stand ,took her to the emergence vets and they think she has a slipped disk,  she cant stand up or weight bear . the vets say she a good feeling in all of here feet (to pain nerves )
They took some x rays this am, and when they got them back they said her bones where not showing up very white.......so did blood tests, they thought it would be low calcium...but its fine.. the seem stumped..they say they cant see the x rays clearly so don't know why shes not able to stand , they are treating her for pressure on the spine..... but they don't know what to do now
they are going to refer  Poppy to a specialist to inject some dye in to her spine ,so any ideas what all this could be ?
oh Poppy is 13 and as she was found at the top of the stars we don't see how she could have fallen....when we first found her she was trying to scratch the left ear and it was very painful i told the vet but he said her ears were fine.. please help I'm going mad with worry. I've been trying to look up on the net about bones but cant seem to fine anything that helps
thanks Anne

Answer
Anne, it usually doesn't take much for a older little dog to sustain a cervical or lumbar spinal problem, whether it is a slipped disc or bulging disc, or a pinched disc or nerve.  Right now, the fact that they can't see her bones clearly may mean several things.  Maybe is was a temporary equipment or film development problem or an actual bone deficiency.  Your Vet hopefully is planning further films and/or researching the bone density situation.  The procedure they are talking about is a myelogram.  It is expensive and the sedation is risky at her age, but would identify a problem in the spinal column.  Has she been given, and is she responding positively to pain/anti-inflamatory medications?  If so, then by all means give them to her and try to keep her as still as possible.  I mean crate her if possible.  The more you restrict her movement, the faster she will improve.