Histologic analysis of the implanted cartilage in an exact-fit osteochondral transplantation model

Purpose: Osteochondral transplantation is one of the useful treatments for articular cartilage defect. However, the histologic change of the implanted cartilage has not been reported in detail. We investigated the histology of exact-fit osteochondral transplants used to repair articular cartilage defects in an animal model. Type of Study: This was a nonrandomized control study using an animal model. Methods: Sixteen skeletally mature female Japanese white rabbits were used in the study. The region of the femoral groove was selected as the site for the osteochondral defect. A full-thickness cylindrical defect (7 mm in diameter and 7 mm in depth) through the articular cartilage and into the subchondral bone was made using the Osteochondral Autograft Transfer System (Arthrex, Naples, FL). The entire osteochondral fragment was removed and then returned to its original site in the femoral condyle precisely. Thus, the defect was repaired with an autogenous osteochondral transplantation of exactly the same size and configuration as the defect. Specimens were obtained 2, 4, 12, and 24 weeks postoperatively and were analyzed both macroscopically and histologically. Results: Macroscopically, there was smooth continuity of the articular surface and the integration of the graft to the normal host cartilage. However, histologic examination showed that the layer of the grafted cartilage was thicker than that of the normal host cartilage and the extracellular matrix of the implanted cartilage exhibited a stronger staining pattern with safranin-O fast green than the normal cartilage. Cell density was higher in the grafted cartilage, particularly in the middle and the deep zones. Round and polygonal hypertrophic clusters of chondrocytes were observed in the middle and deep zones of the grafted cartilage. Conclusions: The histologic properties of the exact-fit implanted cartilage were different from that of normal articular cartilage. Further investigation of mechanical and structural properties of grafted cartilage is necessary to verify the long-term effects of osteochondral transplantation.