This could be a malformation or development problem. You will need to take this puppy to a veterinarian for an exam, best would be a veterinary orthopedic surgeon. Your puppy may need orthopedic care in order to facilitate normal use, if possible. I would need to do a hands-on exam in order to give you more conclusive information. Your puppy will definitely need radiographs as well in order to assess the condition properly. Please make an appointment with your veterinarian,