Physeal replacement with cultured chondrocytes of varying developmental time: failure to reconstruct a functional or structural physis

Bioengineering and Characterization of Physeal Transplant with Physeal Reconstruction Potential

Damage to physes is of serious consequences in children. Currently available treatments are limited and results are unpredictable. In this study, we attempted to treat proximal tibial physeal damage in rabbits with transplanted bioengineered physeal tissue. Resting chondrocytes from the reserve zone of costal cartilages of 6-week-old rabbits were pellet cultured in centrifuge tubes. The pellets were characterized histologically and biochemically with reference to the normal physis. The bioengineered tissue was then transplanted into partially damaged proximal tibial physis. Histological changes and proteoglycan metabolism of the transplants were monitored until 7 weeks posttransplantation. Our results showed that chondrocytes cultured by three-dimensional pellet exhibited cell division and the derived cells arranged in short columns similar to normal physis. They synthesized and deposited cartilaginous matrix and differentiated into hypertrophic chondrocytes marked by increases in cell size and alkaline phosphatase activity. The transplant incorporated well in host tissue with no sign of rejection for up to 7 weeks posttransplantation. A further 3-fold increase in thickness of the transplant within the host was observed. Endochondral ossification was demonstrated at 7 weeks posttransplantation. These results show that the bioengineered physeal tissue may have great potential in clinical management of physeal damage in children.

Repopulation of laser-perforated chondroepiphyseal matrix with xenogeneic chondrocytes. An experimental model

Growth of chondrocytes into a xenogeneic chondroepiphyseal matrix was investigated in an in vitro experimental model by combining viable calf chondrocytes with chick epiphyseal matrix devoid of viable chondrocytes. The chondrocytes were harvested from the wrist joints of newborn calves and cultured for 2 days. The epiphyses were harvested from the distal femurs and the proximal tibias of fetal chicks after development was arrested at 17 days by freezing. The epiphyseal specimens were prepared in four ways. These included femoral and tibial epiphyses without holes and femoral and tibial epiphyses with holes made by a laser. These epiphyseal specimens were co-cultured with calf chondrocytes for various periods. After digestion of the epiphyseal matrix, viable chondrocytes were counted in suspension. Chondrocyte division in the matrix was assessed by [3H]thymidine incorporation. The growth of calf chondrocytes into the xenogeneic chick matrix was evaluated by fluorescence microscopy on fresh thick epiphyseal sections. The percentage of viable chondrocytes in the xenogeneic epiphyseal matrix increased with culture time to a maximum at day 21. The addition of laser-drilled holes was found to extend a plateau of chondrocyte viability until day 29. A decrease in cell viability was detected at later observation points. This study demonstrates that xenogeneic matrix may serve as a morphogenetic scaffold for chondrocytic growth.