PROQUEST: 304455744
Hip fractures exponentially increase with age and changes within the bone account for a portion of the increased fractures; however, litde attention has been given to aging changes in the metaphyseal cortex. The goal of this study is to investigate the age-related changes in cortical bone microstructure and mineralization within the female proximal femur.
Analysis was conducted using backscattered electron (BSE) imaging. A series of studies to determine the meaning, accuracy, and precision of BSE images were performed. BSE imaging was proven consistent and the BSE signal was highly correlated (r²=0.973) to the mineral content of bone. The BSE signal was converted to a weight fraction of calcium measurement using energy dispersive X-ray spectrometry with demonstrated precision (standard error of the mean <0.5% Ca).
BSE imaging was applied to 33 Caucasian female femora (age 17-95 years). On each femur, measurements of histomorphometry and mineral content were performed at eight circumferential locations at each of three levels (femoral neck, intertrochanteric region, and femoral diaphysis). Statistically significant (p<0.05) aging changes in histomorphometry and mineralization were measured. Significant variations were also present with respect to level and location, indicating that the three sites do not follow the same aging patterns. The largest agerelated changes in cortical thickness and porosity occurred at the femoral diaphysis. The largest changes in bone microstructure occurred at the metaphyseal region. Regions of hypermineralized bone were observed near ligamentous insertions and may represent calcified fibrocartilage.
The mineral content of osteonal and primary bone decreased with age (p<0.05), whereas interstitial bone mineral content did not significandy change (p>0.05) and hypermineralized bone increased in mineral content with age (p<0.05). The result was an increase in mineral heterogeneity with age. An animal model of mineral heterogeneity was mechanically tested to failure and revealed a moderate correlation (r²=0.41) between energy absorption and mineral heterogeneity. The animal model was, however, considered a poor model of the aging changes in human femora.
The results suggest that aging changes in the proximal femur are site specific. Any investigation of fracture etiology or prevention should consider the influence of variable mineralization and microstructure on bone mechanical properties.