I read an article a while back that stated that dogs with cruciate tears (or as I say to my clients "you know that football player injury"), may not need surgery. This article went on to say that rest and anti-inflammatories along with a slow return to normal activity over a few months, is the way to go.
Since that time, though I've observed what I've seen in my patients. I still have always recommended referral and consultation with a veterinary surgeon. They can evaluate the dog and radiographs the best and in my opinion, their decision to cut or not is what I'd go with. And no, they don't all push to do so.
But I've been able to see in a population what happens when dog's don't get surgery. I have clients that don't or can't get the specialist's opinion. If the dog is small, then I can say, it may be ok. If they are large, invariably, there will be issues. There is often a subsequent issue with the other rear leg because of the extra strain put on it by the weight the dog shifts to that side. There's also a lot of tissue damage that gets done by the abnormal bone on bone contact, not to mention pain.
In this column a veterinarian explains why surgery is best for most dogs.