It seems that not many people are aware of this condition that usually strikes young dogs going through teenage growth spurts. I only know about it as one of my rescues developed it.
It is sometimes called wandering lameness as it isn't always apparent where the dog limps from and it comes and goes.
Pano comes on because of a mix of things - genetics, feed, exercise, etc.
A couple of sites to read
Panosteitis - Wikipedia, the free encyclopedia
Panosteitis in Young Dogs