I had two OATS grafts done in Nov 2010. Around Apr 2011 (when my doctor had to perform an additional microfracture on my kneecap), it was discovered that one of the two (which was the smaller) grafts had failed. In July, I had a partial knee replacement to replace the failed graft.
I continued to complain to my doc about pain, which I've been doing since my original problem developed in Aug 2010. He kept telling me to "give it time". Finally, I went to another orthopedist, who immediately diagnosed that the other bigger graft had *never* taken, and now I have avascular necrosis (osteonecrosis = bone death) that has spread even further than the original injury. He surmises that I was originally given unviable donor material. Unfortunately for me, this means that I have to get a revision = total knee replacement in a couple of weeks.
Give the intense pain and very long recovery from the OATS done last Nov, I NEVER would have gotten this done and would have gone to a straight knee replacement. My life has been a living hell for over two years, and after the next surgery and recovery, I'll be looking at 1.5 years of constant knee pain.
My advice - don't bother with OATS - go straight to replacement. It's not worth the "risk" of hoping the grafts will take.
Best of luck.