TRABECULAR BONE EXHIBITS FULLY LINEAR ELASTIC BEHAVIOR AND YIELDS AT LOW STRAINS

Using a protocol designed to reduce experimental artifacts associated with the conventional compression test for trabecular bone, we perform ed in vitro mechanical testing on bovine tibial trabecular bone to obt ain accurate descriptions of the elastic and yield behaviors. Reduced- section cylindrical specimens were preconditioned for eight tension-co mpression (+/-0.5% strain) cycles and then loaded to failure either in tension (n = 15) or compression (n = 14). We found that the pre-yield behavior for every specimen was fully linear, indicating that the ini tial nonlinear 'toe' is an experimental artifact. Analysis of variance on the moduli indicated that there was no significant difference betw een the tensile and compressive moduli before preconditioning. However , preconditioning decreased the tensile and compressive moduli on aver age by 8.8 % (p < 0.01) and 5.3 % (p < 0.01), respectively, with the d ecrease in tensile modulus being larger (p < 0.01). These small but si gnificant decreases in modulus suggest that initial yielding involves microstructural damage (as opposed to plastic slip) of individual trab eculae and also indicate that the tensile and/or the compressive yield strain of(bovine tibial) trabecular bone is less than 0.5%. The mean tensile strength was approximately 70% of the mean compressive strengt h, although this difference in strengths may have been affected by the preconditioning-induced damage. Taken together, these results suggest that there are more similarities between the elastic and yield behavi ors of trabecular and cortical bone than had been assumed previously.