What are you feeding him? I was worried that my puppy was getting a touch of it with how much he was rapidly growing up without really gaining weight. I was adding in extra vitamin C and the only thing that one of the surgeons I work with recommended was getting him onto an adult food rather than a puppy food. Keeping him on large breed adult has seemed to do the trick. No more sudden yelping and keeping his front leg off of the ground.
Sadly the big factor in it is time. :/ Not something super well known about either at this point, but it definitely is obvious on radiographs. Did they take some to be sure it is pano rather than something else?