I'm 29 and had my first ACL tear at 19. 3 ACL recons later I have a large Grade IV lesion in my trochlear and Grade 2-3 on my patella as well.
I did the ACI in Feb. and had a scope 6 months later. That was how my surgeon noticed that the ACI patch had torn open. It had torn open somehow and I had hardly even been weight bearing at all. We think the problem was the rough cartilage on the patella that constantly catches and ripped the patch open. I was very depressed because I have been dealing with this knee for most of my life.
There was a bright side however. I could see from before and after photos of the large defect that the hole was smaller and that it was pikish which showed that the cells were still trying to heal and grow. It's now a year later and I am about to have my last operation to replace my lateral meniscus. I will let you guys know how the defect is doing when my doc takes the intra-operative photos next week. It will probably be the same or worse, because I feel now that in order to heal cartilage you have to be basically in a wheelchair for a year and just get out of it twice a day to do Straight leg raises and stretching. Unfortunately, I and most everyone find the prospect of no weight bearing for a year or so extremely difficult to accomplish.
I am going to try to do it, however, and I'm also seriously considering doing the IAGH as well, since I plan to be non-weight bearing for a long time.