Relationship between mineralization density, age and mechanical adaptation of the human mid-shaft femur

H.M Goldman

One of several microstructural variables known to affect the mechanical properties of bone is the degree of mineralization of the bone matrix, which in turn is a consequence of time since formation, and hence remodeling rate. This study sought to determine whether mineralization density variation is spatially organized in relation to specific bending forces at the mid-shaft femur, and whether such organization varies with age. Mid-shaft femur cross-sections were prepared from an autopsy sample (n=40) of adult individuals collected from the Victorian Institute of Forensic Medicine, Australia. Montaged grey-scale images of entire cross-sections were obtained using backscattered electron microscopy (BSE), employing a standard to control for instrument drift over time. Using an automatic routine, BSE images were divided into 48 segments according to anatomical position. Average grey values were quantified for each segment, and one-way ANOVA with Tukey HSD post-hoc tests were applied to assess differences in average mineralization between segments. Degree of mineralization was considered relative to preferred collagen fiber orientation data previously obtained from the same sections, and to the location of second moments of area of each cross-section. Results showed low overall variability in mineralization density. Mineralization and age were negatively correlated, and individuals in the 45-64 age group were significantly less variable than either younger or older individuals. Degree of mineralization was significantly lower in the antero-lateral aspect, indicative of higher osteonal turnover, relative to the postero-medial aspect. Collagen fiber orientation data from this sample has indicated a predominance of longitudinally oriented collagen fibers in the antero-lateral aspect, and of transverse collagen fibers in the postero-medial aspect. These organizational differences were found to relate to the location of [I.sub.max] and are consistent with our present understanding of bending forces at the mid-shaft. The combined analysis of bone material and structural properties illustrates continued mechanical adaptation in the human femur throughout life. Age differences may reflect changing mechanical usage and efficiency. Examination of these variables in different temporal and geographic populations may be useful for studies of activity and behavioral variability in modern humans. Supported by L.S.B. Leakey Foundation and NSF pre-doctoral awards, and NSF funding to NYCEP and the Analytical Microscopy and Imaging Center in Anthropology. Alan Boyde kindly made available the BSE standard.

Relationship between mineralization density, age and mechanical adaptation of the human mid-shaft femur

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Relationship between mineralization density, age and mechanical adaptation of the human mid-shaft femur

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