Dependence of trabecular damage on mechanical strain

Abstract

Trabecular damage may play a role in hip fracture, bone remodeling, and prosthesis loosening. We hypothesized that when trabecular bone is loaded beyond its elastic range, both the type and the amount of damage depend on the applied strains. Thirty specimens of trabecular bone from the bovine tibia underwent compression tests to one of three levels of strain (0.4. 1.0. and 2.5%) (n = 10 per group). The 0.4% level was a mechanically nondestructive control group that accounted for any systematic errors. Optical microscopy at magnifications as high as x200 was then used to quantify the trabecular damage for each group. The amount of damage in the yield group (1.0% strain) did not differ from that in the control group (p = 0.66), whereas damage in the post-ultimate strain group (2.5% strain) increased more than 3-fold (p < 0.0008). Four types of damage were observed: transverse cracks, shear bands, parallel cracks, and complete fractures, of which the first two were dominant. These findings therefore indicate that damage occurs within trabeculae at yield. By comparison with our previous work, it can also be concluded that substantial modulus reductions in trabecular bone (as much as 60%) are caused by damage primarily within trabeculae. The ability to detect such damage clinically may improve in vivo estimates of whole-bone strength by identifying regions of densitometrically normal but mechanically compromised trabecular bone.

Detection of trabecular bone microdamage by micro-computed tomography

“…The presence of microdamage decreases the apparent level mechanical properties of trabecular bone (Wachtel and Keaveny, 1997), and can propagate under loading (Wang, X and Niebur, 2006; Wang, X S, et al, 2005), which may increase fracture risk. Microdamage also stimulates adaptive remodeling (Burr, et al, 1985).…”

A non-invasive in vitro technique for the three-dimensional quantification of microdamage in trabecular bone

“…In cancellous bone, the understanding of microdamage is further confounded by the complexities of trabecular architecture and its interactions with loading [10,11]. Thus in order to fully understand the effects and localization of microdamage formation, it is necessary to develop a method to characterize and quantify microdamage that would also capture architectural information.…”

Bone Material Properties and Skeletal Fragility

“…For example, Young's modulus, yield stress, and peak stress are highly correlated. This is in part explained (for normal healthy bone tissue) by the observation that yield strain is similar across many ages and species [11,12,23,24].…”

“…The material properties of cancellous bone measured using relatively simplified mechanical tests (e.g., bending, tension, shear, bending) use the same mathematical analysis as for any other material. There are some special considerations to testing cancellous bone [5,11,12] but they are mostly related to practical matters of how to perform the mechanical test such as specimen grip design. There are mechanical testing methods for cancellous bone that rely on finite element analysis to estimate the hard tissue material properties directly, but these complex tests do not change how the quality of the tissues are associated with material properties.…”