Fragility of Vertebral Trabecular Bone under Various Loading Orientations in Ovariectomized (OVX) Rats

We developed a new estimation system using rapid prototyping technology that focuses on the relationship between the architecture and mechanical properties of trabecular bone. The system uses three-dimensional acrylic resin models of trabecular bone constructed from micro-CT data to predict the mechanical properties of trabecular bone. We used this method to clarify the relationship between loading orientation and bone fragility in the vertebral trabecular bone of ovariectomized (OVX) rats. Twenty 6-week-old female Wistar rats were randomly divided into two groups (OVX and normal groups). Five rats from each group were killed at 3 and 6 weeks following operations and the L4 vertebra was removed. Bone specimens from both groups were scanned using a micro-CT system. Subsequently, resin models of the bone were fabricated at 60× magnification from the micro-CT data sets using laser stereolithography. The resin models were subjected to compressive testing in three orthogonal orientations corresponding to the craniocaudal, mediolateral, and anteroposterior anatomic axes. The results showed that the elastic modulus and ultimate stress were lower in the models of OVX rats than in the normal rats, the mechanical properties of trabecular bone structure from OVX rats deteriorated with increasing time postoperatively, and the elastic moduli in the mediolateral and anteroposterior axes were especially reduced relative to the decrease in the craniocaudal axis in the OVX rats.