Dependence of yield strain of human trabecular bone on anatomic site

Understanding the dependence of human trabecular bone strength behavior on anatomic site provides insight into structure-function relationships and is essential to the increased success of site-specific finite element models of whole bones. To investigate the hypothesis that the yield strains of hum an trabecular bone depend on anatomic site, the uniaxial tensile and compre ssive yield properties were compared for cylindrical specimens from the ver tebra (n = 61), proximal tibia (n = 31), femoral greater trochanter (n = 23 ), and femoral neck (n = 27) taken from 61 donors (67 +/- 15 years). Test p rotocols were used that minimized end artifacts and loaded specimens along the main trabecular orientation. Yield strains by site (mean +/- S.D.) rang ed from 0.70 +/- 0.05% for the trochanter to 0.85 +/- 0.10% for the femoral neck in compression, from 0.61 +/- 0.05% for the trochanter to 0.70 +/- 0. 05% for the vertebra in tension, and were always higher in compression than tension (p <0.001). The compressive yield strain was higher for the femora l neck than for all other sites (p <0.001). as was the tensile yield strain for the vertebra (p <0.007). Analysis of covariance, with apparent density as the covariate, indicated that inter-site differences existed in yield s tress even after adjusting statistically for density (p <0.035). Coefficien ts of variation in yield strain within each site ranged from only 5-12%, co nsistent with the strong linear correlations (r(2) = 0.94-0.98) found betwe en yield stress and modulus. These results establish that the yield strains of human trabecular bone can differ across sites, but that yield strain ma y be considered uniform within a given site despite substantial variation i n elastic modulus and yield stress. (C) 2001 Elsevier Science Ltd. All righ ts reserved.