There isn't a formula worked out to predict recovery (or failure) from osteochondral grafting of the knee. Many studies have looked at specific types of treatment. Researchers are trying to find the best way to treat this complex problem.
One factor to consider is how much and what kind of other damage was done. Often when the cartilage is pulled away from the bone, other soft tissue and bony structures are affected, too. For example, there may be ligament or meniscal damage along with the cartilage defect.
Any additional injuries complicates treatment and recovery. The smaller the cartilage tear, the better the chances are for a complete return to full function. In fact, many patients are able to go back to their chosen sport at the same level.
There are patients who do not practice sports at all after this operation. And there are others who return to a level lower than the preinjury level but they are able to play. Predicting who will be in each category isn't possible yet with the information we have thus far.