Another update:
Vet called with blood results and said they were good, nothing in them to cause her leg weakness. When shown the x-ray yesterday he pointed out a spot on her spine near the last lumbar and sacrum. I asked today what that was and he said "spondylosis" (definition:
http://www.web-dvm.net/spondylosis.html)
He believes that because my cat was not eating well and has had irregular stool (soft) for most of the past month that this could have made her weaker and it's likely she strained her hind area from a jump or fall. She was given a steroid shot last evening and her legs no longer spread out but she is delicate on her back feet.
So i'm hoping this was just a strain that will heal and not a sign that the spondylosis is showing effects. He said fish oil and accupuncture can help. So for now i'm keeping an eye on her and hoping the I/D food she is on ends her soft stool symptoms. She really likes this food and has been eating more than she has in the last few weeks. She's also had more hairballs than usual even though i brush her daily, throwing them up and passing them in stool so i hope this food helps with that too.
My 16 year old girl is well cared for and i would do anything for her. Thank you for all your responses, i will keep you posted. If anyone has a cat with arthritis or spondylosis and any advice that would be great. Thanks
