Evaluating a theoretical and an empirical model of "side effects" in cancellous bone.

Accurate measurement of cancellous bone's apparent elastic modulus, E, is confounded by the experimental artefacts created when trabeculae are severed during specimen preparation. Although standardized axial testing protocols have been developed to deal with the so-called "end effects" caused by severed trabeculae at the loading surfaces, much less attention has been given to the "side effects" around the periphery and the specimen size dependence they create. Two models (one theoretical, one empirical) have been proposed in the literature to predict the reduction in E with decreasing specimen diameter.

Misalignment Error in Cancellous Bone Apparent Elastic Modulus Depends on Bone Volume Fraction and Degree of Anisotropy.

Cancellous bone is an anisotropic structure with architectural and mechanical properties that vary due to both skeletal site and disease state. This anisotropy means that, in order to accurately and consistently measure the mechanical properties of cancellous bone, experiments should be performed along the primary mechanical axis (PMA), that is, the orientation in which the mechanical properties are at their maximum value. Unfortunately, some degree of misalignment will always be present, and the magnitude of the resulting error is expected to be architecture dependent.

Failure behaviour of rat vertebrae determined through simultaneous compression testing and micro-CT imaging.

Skeletal fractures, including those resulting from osteoporosis, result in significant healthcare and societal costs on an annual basis. Therefore, it is important to understand the mechanisms by which these fractures occur. Incremental compression testing combined with micro-CT imaging has been used to visualize the progression of failure in trabecular bone samples; however, these studies have ignored the potential contributions of the cortical shell.

Effects of dehydration-induced structural and material changes on the apparent modulus of cancellous bone.

Dehydration is known to cause an increase in the elastic modulus of bone tissue. However, it also causes structural changes (i.e.

Specimen diameter and "side artifacts" in cancellous bone evaluated using end-constrained elastic tension.

In cancellous bone testing of cored samples, side artifacts are the underestimation of the true (i.e. in situ) mechanical properties due to the severing of the trabecular network during specimen preparation.

Minimizing specimen length in elastic testing of end-constrained cancellous bone.

End-constraint is needed when performing tensile and compressive testing of cancellous bone so that frictional and structural end-effects are minimized and the mechanical properties are not underestimated. Since many end-constrained testing techniques are limited to certain sites and species by the large specimen sizes required, reductions in overall specimen length would be advantageous. The following study examines the effect of specimen gauge length and aspect ratio on the elastic tensile testing of cancellous bone from the bovine femoral condyle.

Specimen size effect in the volumetric shrinkage of cancellous bone measured at two levels of dehydration.

Water is commonly removed from bone to study its effect on mechanical behaviour; however, dehydration also alters the bone structure. To make matters worse, measuring structural changes in cancellous bone is complicated by a number of factors. Therefore, the goals of this study were to address these issues by (1) comparing Archimedes' method and a helium pycnometer as methods for measuring cancellous bone volume; (2) measuring the apparent dimensional and volumetric tissue shrinkage of cancellous bone at two levels of dehydration; and, (3) identifying whether a size effect exists in cancellous bone shrinkage.