We have a trip-pod too. Our lab mix tore her ACL chasing whatever it was she was after, rabbits or squirrels. It's slowly getting better.
That dog pizzes me off like no other sometimes, but you're right, they become part of the family and it sucks to see when they're hurting.
I was more concerned that it was cancer or something else, before we brought her to the doc. She's 10 years old now, so I know she won't be with us a whole lot longer.
