We had this done a few years ago for our big lab mix - he was only two! We'd rescued him at a year and a half. We thought he might have hip dysplasia from the way he was walking, but after x-rays the vet said it was an ACL tear. Our vet only did the extra-capular "fishing line" surgery, not the TPLO. Because Marley was about 95 pounds, the TPLO probably would have been the recommended surgery, but we were moving in two weeks - our vet could get us in then and we didn't have time to find someone who could talk to us about a TPLO. The surgery went really well, he had very little scar tissue, and everything - xrays, surgery, meds, etc - cost about $1500 altogether. His recovery was good; very hard first night but he felt almost too good at first and needed some fluid drained from his leg because he used it more than he probably should. Two and a half years later, you'd never know he'd had the surgery. We do have some Rimadyl on hand if we go for a long walk or hike and he looks stiff, but he's doing great. We would never have not gotten the surgery, especially at his age. If it happens again we will likely go for a TPLO to fix it, but knock on wood everything looks fine for now.
Our poor lab pup Daisy is another story - she's 2.5 and probably does have hip dysplasia/arthritis. Her hips sometimes look very stiff when she gets up, her back legs sometimes look stiff when she walks, she drags them when she gets off the couch and lays with them stretched out behind her, etc and it's been like this since she was little. We haven't done x-rays yet but the vet believes she does have problems so she's on Rimadyl daily which seems to help. We will probably be looking into potential surgeries to correct this as well. The Rimadyl is about $50 a month, so it would even make financial sense in the long run to have a surgery especially if it would fix things, but there are always risks so we're weighing options and seeing how the meds alone work for now.