Sometimes happens when its been reared on crap then new owner pumps it full of good snap and its to much for pup to handle. Also slippy (tiled or laminate) floors dont help. Drop protien, you want something like an adult biscuit for large breeds and carpet kennel floor if possible for a bit so it can use its claws to strengthen bones, ligaments and muscle etc. Hopefully come right for you. Good luck. Atb