The fate of calvarias implanted into the epidural spaces of rats. A preliminary study

The histologic changes occurring in newborn rat calvarias implanted into the epidural space of adult rats were observed to determine whether this method was adequate as an experimental model of new bone formation in the spinal canal. Two weeks after implantation, all implanted calvarias of newborn rats grew with ossification in the epidural space. The grafted calvarias continued to grow gradually 6 weeks after this procedure. Six months later, 40% of the grafted calvarias showed progressive bone formation with osteoblasts, chondrocytes, and immature mesenchymal cells. In the other 60%, the implanted calvarias had developed into mature trabecular bone. Twelve months after the procedure, the calvarias had developed into mature bone in all cases, although the size of the grafted calvarias tended to decrease in size. It was concluded that this experiment had devised a suitable model for understanding the process of new bone formation in the spinal canal.