Articular Cartilage Chondrocytes are more Advantageous for Generating Hyaline-like Cartilage than Mesenchymal Cells Isolated from Microfracture Repairs

Articular cartilage lacks self-repair capacity. Currently, two methods employing autologous cells are used to stimulate repair of articular cartilage. Micro-fracture induced repair induces autologous mesenchymal cell migration from bone marrow. Autologous chondrocytes' transplantation involves in vitro expansion of chondrocytes, and later implantation. In 15 patients de-differentiated chondrocytes obtained by cartilage biopsy were compared to cells derived from repair tissue induced by micro-fracture. These patients all underwent micro-fracture during the cartilage biopsy procedure. Autologous chondrocytes' transplantation was performed at least two months later then the biopsy. Tissue bits from articular cartilage and micro-fracture repair tissue were incubated in-vitro and explant cell cultures established. The cell cultures were assessed by immunohistochemistry and induced to differentiate. Differentiation into bone tissue was stimulated by addition of basic fibroblast growth factor, ascorbate and dexamethasone. High density (micro-mass) culture was used to stimulate chondrogenesis. Both cell cultures consist of mesenchymal progenitors as indicated by fibroblast growth factor receptor 3 expression and anti-CD-34+ antibodies. However, the micro-fracture generated repair tissue consists of osteocalcin-expressing cells destined to become bone. Collagen type II expression does not occur in these cells compared to autologous chondrocytes. Inducible nitric oxide synthase expression by microfracture cells is likely to damage surrounding articular cartilage in vivo. In conclusion, cells recruited by micro-fracture are inferior for cartilage regeneration purposes to those from cartilage biopsies.