Fracture toughness of human femoral neck: effect of microstructure, composition, and age.

The effects of porosity and pore size; osteonal area, size, and density; mineral content; water content; wet and dry apparent densities; and age on mode I (tensile) and mode II (shear) strain energy release rate were investigated for femoral neck cortical bone from human cadavers aged >/=50 years. The results suggest that porosity- and density-based parameters that are related to bone quantity are more consistently determinant for femoral neck fracture toughness than morphology-based parameters that are related to microstructural organization. Bone features examined here were more explanatory for shear than tension fracture toughness. Tension and shear fracture toughness did not change with age, unlike in previous reports investigating the femoral and tibial shaft. It was concluded that the femoral neck is different from the femoral and tibial shaft in terms of its microstructure and composition and in its relationship of fracture toughness to its constituents and age.