Correlation of flexural structural properties with bone physical properties: a four species survey

The present investigation explores the relationship between animal and bone physical traits and the mechanical properties of whole bone from four species. Mechanical testing was performed using three-point flexure on the femora and tibiae of mice, rats, rabbits and cats. Interspecies correlations of the physical traits to the mechanical properties were used to elucidate the most likely physical predictors of mechanical properties within a single species. Physical traits measured were total bone length (BL), mid-diaphyseal cortical area (CA), body mass (BM), body mass times bone length (BMBL) and bone dry mass (DM). Bone mechanical parameters determined by flexure testing to failure were the structural properties of stiffness (S), elastic strength (Pe), maximum strength (Pm), and the material properties of modulus of elasticity (E), elastic stress (sigma e), and elastic strain (epsilon e). Linear regressions were used to relate the physical trait to the mechanical properties. Interspecies regressions of physical traits to mechanical characteristics implied bone dry mass (DM) is a significant predictor of bone structural properties. Further evidence of this relationship was obtained by exploring the linear relationship for the femora of a single species (rabbit, N = 17) in which age and bone size were allowed to vary. Strength at the elastic limit (in N) within a single species was described by the equation, Pe = 42.9*DM + 42.9 +/- 42.0N, where DM is in grams.