AGING CHANGES IN OSTEON MINERALIZATION IN THE HUMAN FEMORAL-NECK

Age-related mineral changes are associated with material property changes in cortical bone, which may affect its ability to transmit loads and resist fracture from falling. Aging changes in the mineral content of the femoral neck cortical bone are partly determined by osteonal remodeling events. The objective of this study was to measure mineral differences within the osteonal unit in the human femoral neck. In this study, cadaveric femora from male caucasians of two age groups (25 +/- 7, n = 6; 64 +/- 4, n = 6) were sectioned at the midfemoral neck. Using backscattered electron imaging, osteons from each of eight circumferential cortical regions were analyzed to determine osteonal mineral differences between regions, between the two age groups, and due to radial location within the osteons. Graylevel values from the backscattered electron imaging method were calibrated in equivalent ash content (wt%) units to provide a better understanding of the magnitude of differences observed. A pattern (p < 0.05) of decreasing osteonal mineralization was observed with distance from the central Haversian canal. Additionally, osteonal mineralization was highest in the superior (most lateral) regions of the femoral neck from both age groups, indicating that circumferential location is an influencing factor. The average overall equivalent ash content of osteons from the 17-35-yr group was 59.4 +/- 0.4% (mean +/- SE) by weight, while osteons of the group aged 60-71 measured 52.0 +/- 0.4% equivalent ash content, a decrease of 12.4%. An average 8-10% reduction (p < 0.05) in osteonal equivalent ash content occurred at each circumferential location with age, providing similar age-related mineral reductions at each location. The data of this study demonstrate the magnitude of differences that could be expected in the cortex of the male femoral neck, and indicate that mineral changes due to osteonal remodeling may be one of the several factors that determine the failure site in femoral neck fracture.