Hi,

From what I know, weak hind legs are rather common for large breed dogs. 2 thing will cause this problem, either genetically from their parents, or due to lack of certain nutrition during growing years. The first thing I think you should do is to check what was the puppy feed on previously. Does the pup have sufficient protein, calcium, vitamins etc in his/her growing months? If the food that your pup takes previously is not sufficient for a large breed puppy, then that might be 1 of the coz so might want to start to give the pup a more balance nutrition food.

Like me, who is very worried about my GR having weak hind legs (my GR hyper active one), my vet advise me to give my GR glucosamine that is specially for large breed puppies. I normally don't give my pup human suppliments coz I worried their dosage and human dosage is different. Unless you know the dosage, better don't go for it. And yes, this suppliments seems to be very easily out of stock, I don't know why. I even tried calling the distributors if they can sell directly to me but unfortunately, they only can sell to vets. Luckily this distributor is so kind, he gave me a few vet addresses near my place where I can buy it. :)

My vet does not recommend X-ray for growing puppies because their bones and muscle is still fully develope yet and taking an X-ray now will not give a true picture of the puppy's condition. Wait till the pup reach adulthood or 1 year old, it will be more accurate and give your pup a better diagnose.

I haven't heard of dog to be injected with steriod also but I can ask my vet about it but I don't think it is a good idea to give steriod to a growing puppy. Not sure if it will upset its muscle growth. Later grow too big... :p