One of ours turned up lame like that. We were just walking down the sidewalk and he went tripod. Foot was warm and swollen. Vet couldn't find a thing. No x-rays though. He wanted to give him time on the meds. Previcox for one week and he was okay. Off previcox and he started limping after walking on some grass and stopping suddenly. I was messing with his foot and hear an audible joint crack. He has been fine ever since. I think he just dislocated the outside toe or jammed it or something. It's been 10 days and he seems to be fine. I would think that the x-ray would show a joint misallignment, but could it have popped back in and is now stretched and sore? Just a thought. Paws crossed for you!