Background. Post-menopausal osteoporosis is a common health problem worldwide, most commonly caused by estrogen deficiency. Most of the information regarding the skeletal effects of this disease relates to trabecular bone, while cortical bone is less studied. The purpose of this study was to evaluate the influence of estrogen deficiency on the structure and mechanical properties of cortical bone. Methods. Eight ovariectomized (OVH) and eight intact (control) Sprague Dawley rats were used. Structural features of femoral cortical bone were studied by light microscopy, scanning electron microscopy and synchrotron-based microcomputer-tomography and their mechanical properties determined by nano-indentation. Results. Cortical bone of both study groups contains two distinct regions: organized circumferential lamellae and disordered bone with highly mineralized cartilaginous islands. Lacunar volume was lower in the OVH group both in the lamellar and disorganized regions (182 ± 75 µm3 vs 232 ± 106 µm3, P < 0.001 and 195 ± 86 µm3 vs. 247 ± 106 µm3, P < 0.001, respectively). Lacunar density was also lower in both bone regions of the OVH group (40 ± 18 ×103 lacunae/mm3 vs. 47 ± 9×103 lacunae/mm3 in the lamellar region, P = 0.003 and 63 ± 18×103 lacunae/mm3 vs. 75 ± 13×103 lacunae/mm3 in the disorganized region, P < 0.001). Vascular canal volume was lower in the disorganized region of the bone in the OVH group compared to the same region in the control group (P < 0.001). Indentation moduli were not different between the study groups in both bone regions. Discussion. Changes to cortical bone associated with estrogen deficiency in rats require high-resolution methods for detection. Caution is required in the application of these results to humans due to major structural differences between human and rat bone.
Bibliographical noteFunding Information:
The following grant information was disclosed by the authors: German research foundation (DFG): SPP1420. The Helmholtz-Zentrum Berlin by allocation of synchrotron radiation beamtime (proposal 2011_1_101141).
This work was supported by the German research foundation (DFG) through SPP1420 and the Helmholtz-Zentrum Berlin by allocation of synchrotron radiation beamtime. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
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- Disorganized bone