For German Shepherds an individual test for HD (usually an x-ray) is mandatory over here. It might be a good idea to introduce it for all other big breeds, too.
We've had a few dogs wit arthrosis. If yours has a very bad day, try a hot water bottle (not too hot, only nicely warm) It helps a bit. You might also want to talk with your vet about a mild pain killer. It doesn't heal arthritis/arthrosis but it takes the pain away and allows the dog to move. That's important because otherwise the joints will stiffen.
Our dog gets a special greenish powder in his food, containing vitamins and minerals and god knows what else. It stinks like rotting algae and it takes him hours to eat it, but the vet says it does slow the illness down a little bit.