I would check out this site before you rush into surgery:
Dog ACL Injury-- Is Surgery Really Needed?
My story is kind of long, but I will shorten it- my DDB was diagnosed with a ACL tear (right rear leg) last fall. The vet said it was a surgical fix, but I decided to do some research, as well as join an internet group devoted primarily to Conservative Management for just this issue, and hold off on deciding about surgery.
I am so happy I did! I decided to do CM with Mateo-- I rested him and took short walks for awhile. Then, I found a dog rehab place downtown that specialized in water/treadmill rehab, as well as floor exercises, massage and cold laser therapy. We did a 10 week program, and by week 6 or so he really started to show improvement.
A few weeks after we finished treatment, he was about 85% better--- no limping, he could run a bit with no issue, and was going up and down stairs like before his injury.
Then, late April of this year, he took off after a squirrel and did some damage to his knee again. of course, i was devastated- even started thinking surgery again. But, to be honest, my funds were low---plus, I also kept talking with and hearing about how people had had the (TPLO) surgery and regretted it. It's a very painful procedure, with a long rehab. Plus, there is a 65% chance of recurrence on the other knee after surgery. I didn't want to put my boy through all of that.
So, we went back to basics: short walks, and no crazy stuff (not like he wanted to run around anyway.) Fast forward to today, and Mateo is almost back to being completely normal- no limp, and he is becoming very active again.
So, what I have learned is that it does take time. Lots of time, and patience. But the body heals, if given the chance.
I am still careful with him, as I do not want another setback, but he really is feeling and moving well; I couldn't be more pleased, and thankful.
Of course, every dog is different, and each situation must be taken on their own accord. But I would advise doing a ton of research to help with this difficult decision.
All the best to you and Duke.