DIFFERENCES BETWEEN THE TENSILE AND COMPRESSIVE STRENGTHS OF BOVINE TIBIAL TRABECULAR BONE DEPEND ON MODULUS

The conflicting conclusions regarding the relationship between the ten sile and compressive strengths of trabecular bone remain unexplained. To help resolve this issue, we compared measurements of the tensile (n = 22) and compressive (n = 22) yield strengths, and yield strains, of trabecular bone specimens taken from 38 bovine proximal tibiae. We al so studied how these failure properties depended on modulus and appare nt density. To enhance accuracy, trabecular orientation was controlled , and each specimen had a reduced section where strains were measured with a miniature extensometer. We found that the mean yield strength w as 30% lower for tensile loading. However, the difference between indi vidual values of the tensile and compressive strengths increased linea rly with increasing modulus and density, being negligible for low modu li, but substantial for high moduli. By contrast, both the tensile and compressive yield strains were independent of modulus and density, wi th the yield strain being 30% lower for tensile loading. Thus, the dif ference between the tensile and compressive strengths of bovine tibial trabecular bone depends on the modulus, but the difference between yi eld strains does not. This phenomenon may explain in part that conflic ting conclusions reached previously on the tensile and compressive str engths of trabecular bone since the mean modulus has varied among diff erent studies. Realizing that our data pertain only directly to bovine tibial trabecular bone for longitudinal loading, our results neverthe less suggest that failure parameters based on strains may provide more powerful and general comparisons of the failure properties for trabec ular bone than measures based on stresses.