e-publications@RCSI

Abstract Compact bone makes up approximately 80% of the human skeletal mass, however there is a relative paucity of studies examining the effects of estrogen deficiency in compact bone. This study examines the effect of estrogen deficiency on compact bone turnover and associated geometrical structural adaptation over a 31 month period. Twenty –seven skeletally mature sheep were divided into control (n=16) and ovariectomy group (OVX, n=11). Animals were administered five different flourochrome dyes to label intracortical bone turnover and sacrificed at 31 months. Compact bone samples were analysed for cortical geometry, intracortical turnover at five time points, resorption cavities, porosity and compressive strength. Intracortical bone turnover was significantly increased in OVX, which demonstrated seasonal variation. Cross sectional area in OVX was significantly with an associated increased resistance to bending. Intracortical porosity was significantly increased in OVX, however there was no significant difference in ultimate compressive strength between the groups. Our results demonstrate sustained increased intracortical bone turnover, resportion spaces and porosity without adversely affecting compressive strength. Our results also support the hypothesis of geometrical adaptation of compact bone in response to estrogen deficiency. These results suggest an early structural compensatatory response in compact bone despite increased intracortical turnover. Key Words Compact bone, estrogen, ovine, bone turnover, bone geometry