Without taking over Brittany's thread, I'll explain here.
Hypertrophic Osteodystrophy(HOD) is a bone growth dysfunction common in large breeds, especially Great Danes. In the age gap of 12 weeks to 7 months, when the Dane does the most amount of growing. Too much protein and calcium causes a 'build up' in their front knees, and become swollen and warm to touch. It can become crippling if not treated. Its suggested not to feed Danes puppy food as the protein levels are too high and 23% protein is a sufficient amount in a meal.
Minor case of HOD.
A friends rescue Dane, Julianna. She had a severe case of HOD, and sadly didn't survive.
Heres a site thats the closest to what I've learnt.
Great Dane Dog Breeder German Danes
Britt, I would call your vet and just have a chat about it, just to be sure.