My now deceased border collie had a problem like this - lumbar sacral stenosis, he was referred to an orthopedic vet - he recommended 6 weeks lead excercise and treated with steroids and not nsaids, if no improvement we would have done an mri scan and poss decompressive surgery, luckily at the time he was insured! However the 6 weeks lead exercise and PLT did the trick - however trying to convince a looney border collie that lead exercise was for his own good was another matter!!