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.

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... ural 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 µm 3 vs 232 ± 106 µm 3 , P < 0.001 and 195 ± 86 µm 3 vs. 247 ± 106 µm 3 , P < 0.001, respectively). Lacunar density was also lower in both bone regions of the OVH group (40 ± 18 ×10 3 lacunae/mm 3 vs. 47 ± 9×10 3 lacunae/mm 3 in the lamellar region, P = 0.003 and 63 ± 18×10 3 lacunae/mm 3 vs. 75 ± 13×10 3 lacunae/mm 3 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. CA, Bellido T, Parfitt AM, Weinstein RS, Jilka RL, Manolagas SC. 2007. Skeletal involution by age-associated oxidative stress and its acceleration by loss of sex steroids. Busse B, Djonic D, Milovanovic P, Hahn M, Puschel K, Ritchie RO, Djuric M, Amling M. 2010. Decrease in the osteocyte lacunar density accompanied by hypermineralized lacunar occlusion reveals failure and delay of remodeling in aged human bone.