Chronic articular cartilage defects do not heal spontaneously.[1] However, acute traumatic osteochondral lesions or surgically created lesions extending into subchondral bone, e.g. by Pridie drilling,[2] spongialization[3] abrasion[4] or microfracture causing the release of multipotent mesenchymal stem cells from the bone marrow, may heal with repair tissue consisting of fibrous tissue, fibrocartilage or hyaline-like cartilage.[5] The quality of the repair tissue after these "bone marrow stimulating techniques" depends on various factors including the species and age of the individual, the size and localization of the articular cartilage defect, the surgical technique, e.g., how the subchondral bone plate is treated, and the postoperative rehabilitation protocol.[6]