dog surgery: anyone have their pup's ACL repaired?

[GuyGene]

What is TPLO? Our mix chocolate lab, 11 1/2 years old, has bad back knee. It's been x rayed, 3 vets opinion, two said doesn't need surgery. Her regular vet office is the one that said she might, but they don't do it, a roving surgeon comes by, $2,500. Normally is $3,500 he said.