Oh Lynn...my heart breaks for you. We had to make the same decision...but we at least had almost 5 years.
It's awful to see them in pain...and a young dog that cannot run and play...really never gets to be a puppy or enjoy being a dog.
You are right about all of the weight going to their front...and if their front is no good...then nothing is good.
Our Bruno had developed quite the chest...but his back end was so much smaller.
When we got Baxter about 9 months after euthanizing Bruno...I would get tears in my eyes to see Baxter running and playing like a "normal" puppy...something that Bruno really never got to do, or he would be in pain.
RIP Quade and may you never be in pain again.
Gina