Bone Mechanical Properties in Healthy and Diseased States

Abstract

The mechanical properties of bone are fundamental to the ability of our skeletons to support movement and to provide protection to our vital organs. As such, deterioration in mechanical behavior with aging and/or diseases such as osteoporosis and diabetes can have profound consequences for individuals' quality of life. This article reviews current knowledge of the basic mechanical behavior of bone at length scales ranging from hundreds of nanometers to tens of centimeters. We present the basic tenets of bone mechanics and connect them to some of the arcs of research that have brought the field to recent advances. We also discuss cortical bone, trabecular bone, and whole bones, as well as multiple aspects of material behavior, including elasticity, yield, fracture, fatigue, and damage. We describe the roles of bone quantity (e.g., density, porosity) and bone quality (e.g., cross-linking, protein composition), along with several avenues of future research.

Keywords: bone quality; cancellous bone; cortical bone; multiaxial; multiscale; trabecular bone.

Figure 1

Stress–strain curves for (a,b) cortical bone tested along the longitudinal direction and (c,d ) trabecular bone tested along the principal direction. Panels a and c show monotonic tests in tension and compression, and panels b and d show load–unload–reload tests. Panels a and c are annotated with some basic material properties. The dashed lines in panels b and d indicate the perfect damage modulus, which is the secant modulus at the point at which the initial loading ramp is reversed to begin the unloading. Both types of bone tissue exhibit a reloading modulus that is initially equal to the original Young’s modulus but then decreases to equal the perfect damage modulus. Modified from References and with permission.

Figure 2

Microdamage in human vertebrae. (a,b) Linear microcrack. (c,d ) Diffuse damage. Panels a and c were acquired using bright-field microscopy; panels b and d were acquired using laser scanning confocal microscopy (stain is xylenol orange). Modified from Reference with permission.

Figure 3

(a,b) Crack propagation emanating from a notch (red arrow) in cortical bone. (c) Crack propagation in trabecular bone. Toughening mechanisms in cortical bone include uncracked ligament bridging ( yellow arrows) and crack deflection (black arrow). Modified from References and with permission.

Figure 4

Log–log plots for (a) Young’s modulus and (b) compressive yield strength as functions of apparent density. Lines indicating power-law exponents of one and two are drawn on the plots. Modified from References and with permission.

Figure 5

Increase in anisotropy with age. (a) Representative cross sections of cylindrical specimens from the trabecular compartment of the human proximal tibia from donors in the age ranges indicated below each rendering. (b) Degree of anisotropy plotted against donor age. Modified from Reference with permission.

Figure 6

(a) Total cross-sectional area, (b) marrow cross-sectional area, and (c) cortical cross-sectional area in the human femoral neck, all plotted as a function of age. Red, blue, and black symbols indicate premenopausal women, postmenopausal women, and men, respectively. Modified from Reference with permission.