Regenerative and proliferative activities of chondrocyte based on the degree of perichondrial injury in rabbit auricular cartilage

Although the regeneration process for injured cartilage requires an intact perichondrium, few studies have addressed the importance of the intact perichondrial layer in the regeneration of damaged cartilage. In this study, we evaluated the role of the perichondrium on regenerative activities in injured cartilage according to different degrees of perichondrial injury. Auricular cartilage harvested from six New Zealand white rabbits was irradiated with a 1,460-nm diode laser at two different power settings (0.3 or 0.5 W). Irradiated cartilage was reimplanted into a subperichondrial pocket under three different conditions: non-injured perichondrium (NPI), unilaterally injured perichondrium (UPI), or bilaterally injured perichondrium (BPI). Rabbits were sacrificed at 1, 2, and 4 weeks after reimplantation and the auricular cartilage was reharvested. A histopathological study using hematoxylin and eosin staining, a live/dead viability assay, and immunohistochemical staining for proliferating cell nuclear antigen were performed to evaluate structural changes and regenerative and proliferative activities of the injured chondrocytes. A modified array and restored boundary of chondrocytes were observed in the NPI and UPI groups. Regeneration of chondrocytes was prominent in the NPI and UPI groups, but was not observed in the BPI group. Proliferative activity of chondrocytes was observed only when the perichondrium was preserved in the NPI and UPI groups. In contrast, proliferative activity was not observed until 4 weeks in the BPI group. The degree of perichondrial injury affected proliferation and regeneration in injured elastic cartilage. In the case of unilateral perichondrial injury, the surgeon should be careful to avoid damaging the other side of the perichondrium, because at least a unilateral perichondrial layer is needed for the regeneration of elastic cartilage.