The trabecular and cortical bone difference in ovariectomized sheep: a densitometric, histomorphometric and biomechanical study

Objective To observe the trabecular and cortical bone changes in ovariectomized (OVX) sheep. Methods 20 adult sheep were randomly divided into three groups: sham-operated group(Sham, 8 sheep), OVX-Month 4 group(n=4) and OVX-Month 12 group(n=8). At the time of operation, all sheep underwent dual energy x-ray absorptiometry (DXA) of the lumbar vertebrae. Sheep were sacrificed 4 months and 12 months after operation respectively, and BMD at lumbar spine, femoral neck, femoral shaft and femoral condyle was measured using DXA. The trabecular bone (spine, femoral neck and condyle) and cortical bone (femoral shaft) were harvested and for micro-CT scanning. Compression test was performed for trabecular bone, while the 3-point bending test was conducted for cortical bone. Results After OVX for 12 months, the BMD in trabecular bone was significantly lower than that of Sham group and OVX-Month 4 group (P0.01). The BS/BV, Tb.Th and Tb.N was significantly lower while the Tb.N and BVF was significantly higher (P0.01 for both) compared with OVX-Month 12 group and Sham controls. The maximum compressive strength of trabecular bone in OVX-Month 12 group was significantly lower than that of the other two groups (P0.01). 3-point bending test for cortical bone showed no difference among 3 groups. Conclusion BMD, micro-architecture and biomechanical properties of the trabecular bone decreased significantly after OVX for 12 months. OVX sheep was a suitable animal model for studying estrogen depletion osteoporosis.