Assessment of Lumbar Vertebrae L1–L7 and Proximal Femur Microstructure in Sheep as a Large Animal Model for Osteoporosis Research

Sheep have been widely used as a model for osteoporosis research. This study aimed to characterise changes in microstructure and composition in lumbar vertebrae L1-L7 and the proximal femur after implementation of a bone loss induction protocol (in this species). A sham control and experimental group (glucocorticoid-treated ovariectomized sheep) were used (n = 6/group), with a study duration up to the 24th postoperative week. Through micro-computed tomography, vertebrae and femoral head trabecular bones from the experimental group presented a consistent decrease in bone volume fraction (BV/TV), trabecular thickness (Tb.Th), and trabecular number (Tb.N) and an increase in trabecular separation (Tb.Sp) and total porosity (p > 0.05). The mineral density of the femoral heads from the experimental group showed a statistically significant decrease (p ˂ 0.05). The entire histomorphometric analysis of the vertebrae in the experimental group showed an increase in cortical porosity (Ct.Po) and a decrease in cortical thickness (Ct.Th) (p ˂ 0.0001 and p ˂ 0.001, respectively). Vertebrae L6 and L7 were the most affected, showing a significant increase in Ct.Po (p < 0.05) and a significant decrease in Ct.Th at the L6 level (p < 0.05). Regarding the trabecular bone at the vertebral level, only L4 showed a significant increase in Tb.Sp (p ˂ 0.05). In the femoral heads' subchondral cortical layer, the Ct.Po increased significantly and Ct.Th decreased (p < 0.01), and at the trabecular level, the BV/TV, Tb.Th, and Tb.N decreased significantly, while Tb.Sp increased (p < 0.05). In conclusion, the L4, L6 and L7 vertebrae seem the most suitable for further preclinical and translational studies of vertebral augmentation or spinal fusion in this animal model.