The dual role of perichondrium in cartilage wound healing.

Cartilage structures from the head and neck possess a certain but limited capacity to heal after injury. This capacity is accredited to the perichondrium. In this study, the role of the inner (cambium) and the outer (fibrous) layers of the perichondrium in cartilage wound healing in vitro is investigated. For the first time, the possibility of selectively removing the outer perichondrium layer is presented. Using rabbit ears, three different conditions were created: cartilage explants with both perichondrium layers intact, cartilage explants with only the outer perichondrium layer dissected, and cartilage explants with both perichondrium layers removed. The explants were studied after 0, 3, 7, 14, and 21 days of in vitro culturing using histochemistry and immunohistochemistry for Ki-67, collagen type II, transforming growth factor beta 1 (TGFbeta1), and fibroblast growth factor 2 (FGF2). When both perichondrium layers were not disturbed, fibrous cells grew over the cut edges of the explants from day 3 of culture on. New cartilage formation was never observed in this condition. When only the outer perichondrium layer was dissected from the cartilage explants, new cartilage formation was observed around the whole explant at day 21. When both perichondrium layers were removed, no alterations were observed at the wound surfaces. The growth factors TGFbeta1 and FGF2 were expressed in the entire perichondrium immediately after explantation. The expression gradually decreased with time in culture. However, the expression of TGFbeta1 remained high in the outer perichondrium layer and the layer of cells growing over the explant. This indicates a role for TGFbeta1 in the enhancement of fibrous overgrowth during the cartilage wound-healing process. The results of this experimental in vitro study demonstrate the dual role of perichondrium in cartilage wound healing. On the one hand, the inner layer of the perichondrium, adjacent to the cartilage, provides (in time) cells for new cartilage formation. On the other hand, the outer layer rapidly produces fibrous overgrowth, preventing the good cartilage-to-cartilage connection necessary to restore the mechanical function of the structure.