Assessment of an ectopic bone formation system with implantation of pelleted rat primary growth cartilage cells

To assess the ectopic bone formation system, growth cartilage (GC) cells were implanted to ectopic sites, and the effect of the implanting sites and gender of animals on bone formation were examined. Each 5 × 105 batch of GC cells from young rat ribs was pelleted, cultured in calcification medium, and implanted to ectopic sites (in a peritoneal cavity or on subcutaneous muscle) in female or male rats. The implanted pellets formed bone after 3–4 weeks at the ectopic sites. Histological examination concluded that, first, a subcutaneous muscle site is more conductive to bone formation than a peritoneal cavity site and, second, the pelleted GC cells implanted in male rats formed bone more effectively than those in female rats. Therefore, at present, the ectopic bone formation system of pelleted primary GC cells onto subcutaneous muscle of male rats is an appropriate system for the evaluation of bone formation.