weak back legs and knuckling front right leg

Question
I have a 14 week old Great Dane.  For two weeks it seems his back legs are weak and is clumbsy.  Recently he started knuckling his front right . The last two weeks he also has gained 12 pounds.  Could his legs be growing at different rates?  I talked with the breeder Vom Hause Wagner who is a vet and he said it is common?  Im not sure.  What do you think?
Angela

Answer
You're feeding the wrong food. Your dog is growing too fast and his joints can't keep up with the weight he's gaining.
What are you feeding?? Wellness and Natural Balance both make foods that are low enough in protein and fat to help your baby stay within range. Right NOW put him on calcium supplements, vitamin C, E, b complex and bone meal. Get back to me with the type of food you are feeding
Best of luck
Cindi