Problems with Microfracture

Microfracture as a method of cartilage repair has been much in the news lately.
Some celebrated athletes, including a major player for the Phoenix Suns, have had the procedure with decidely mixed results. Granted, the requirements of a NBA player are substantial, but according to the NY Times 9 out of 13 cases have failed to return to sport. In some cases, a return to athletics was attempte4d within about 6 months, which is far shorter than the originators of the technique have proposed. Nevertheless, there is no clear evidence that microfracture really works in a reliable way.
It would interesting to know of a comparable sample of players who have had cell based therapy, such as Carticel ( ACI).