I've not heard of this condition. Perhaps someone else has and can offer some advice. Cooter had pano as a young pup, and his condition sounds alot like your Ben's. His limp would come and go, and it was always worst when his got up from sleeping. Pano can be detected in X-Rays though, I'm sure your vet would know this. Rimadyl did help Cooter though, and pups just grow out of the pano. I'm sorry for your Ben, and hope all goes well!