Mechanical characteristics of bone in femoral capital aseptic necrosis.

Uniaxial compression loading of small cube-shaped samples in an Instron machine was used to study material property deficits of middle- and late-stage necrotic cancellous bone taken from adult human femoral heads. Although the experimental data should not be extrapolated to phenomena of viable trabecular response in a functioning osteonecrotic hip, they provide insight into the salient passive mechanical response characteristics of the pathologic tissue. Individual differences in the revascularization and/or collapse patterns occurring within femoral heads lead to substantial variability in the strength and stiffness of test samples taken from the involved regions. As an overall average, however, samples extracted from major infarct regions exhibit substantially reduced (52%) yield strength, severely reduced (72%) elastic modulus, and modestly increased (29%) strain-to-failure, relative to samples from normal femoral heads. However, statistically significant changes are not observed in the Poisson ratio, the post-yield modulus, or in the incidence of pre-yield load/deformation discontinuities.