Bone Abstracts

Apart from analyses of well-known correlates of age-related hip fracture risk, such as low BMD, impaired external geometry and deteriorated micro-architecture, there is increasing interest to elucidate nano-structural determinants of fracture risk at the bone mineralized matrix level.

In this study we analyzed cortical bone specimens of the femoral neck region in five elderly women who sustained hip fracture and in four healthy women of corresponding age. Atomic force microscopy was performed at external cortical surface providing simultaneously topographical data and phase composition of the examined bone specimens, as well as measures of nano-structural roughness and surface complexity.

Simultaneous acquisition of 3D topography data and phase composition revealed granular organization of surface mineral phase. The results showed that distribution of grain size was skewed to larger grains in hip fracture cases with mean grain size 65.22±41.21 nm, whereas control cases displayed significantly smaller grains (36.75±18.49 nm, P<0.001). In contrast to the control group with unimodal grain size distribution, data deconvolution showed two distinct peaks in the fracture group reflecting two groups of mineral grains (peak positions: 36 and 87 nm; both occupying similar areas under the curve). Roughness analysis showed lower surface fractal dimension in fracture cases (1.40 vs 1.56) indicating lower and/or slower surface mineral deposition processes which might suggest a decreased periosteal apposition in patients who would suffer from hip fracture.

Based on previous observations that large-grained materials are accompanied by decreased mechanical properties in comparison with fine-grained fabrics, the findings of larger grains in fracture group offer additional explanation for decreased strength of the cortical bone. These results contribute to the understanding of nano-structural basis of age-related bone fragility.