I had to google this! I hadn’t heard of it and was relieved to read that panosteitis is another name for growing pains, which disappear by the time they are two. Some of the websites said to take xrays of the joints, now and later on to compare progress. You could also ask for a second opinion.
Vets aren’t food experts, the market changes all the time. I hope someone can advise you. I would recommend ringing the customer service advisors of the decent dog food manufacturers that have a wide range of food, eg Millie’s Wolfheart, Nutriment,Royal Canin.. Can he manage to crunch a large dog style big kibble size?
Poor baby, it’s not fair when all he wants to do is run and play. As you say, there may be another reason for this. Keep speaking to the vet. Take videos of pup when he is having a painful episode to show them.