The effects of tensile-compressive loading mode and microarchitecture on microdamage in human vertebral cancellous bone

Abstract

The amount of microdamage in bone tissue impairs mechanical performance and may act as a stimulus for bone remodeling. Here we determine how loading mode (tension vs. compression) and microstructure (trabecular microarchitecture, local trabecular thickness, and presence of resorption cavities) influence the number and volume of microdamage sites generated in cancellous bone following a single overload. Twenty paired cylindrical specimens of human vertebral cancellous bone from 10 donors (47–78 years) were mechanically loaded to apparent yield in either compression or tension, and imaged in three dimensions for microarchitecture and microdamage (voxel size 0.7×0.7×5.0 μm3). We found that the overall proportion of damaged tissue was greater (p=0.01) for apparent tension loading (3.9±2.4%, mean±SD) than for apparent compression loading (1.9±1.3%). Individual microdamage sites generated in tension were larger in volume (p<0.001) but not more numerous (p=0.64) than sites in compression. For both loading modes, the proportion of damaged tissue varied more across donors than with bone volume fraction, traditional measures of microarchitecture (trabecular thickness, trabecular separation, etc.), apparent Young׳s modulus, or strength. Microdamage tended to occur in regions of greater trabecular thickness but not near observable resorption cavities. Taken together, these findings indicate that, regardless of loading mode, accumulation of microdamage in cancellous bone after monotonic loading to yield is influenced by donor characteristics other than traditional measures of microarchitecture, suggesting a possible role for tissue material properties.

Figure 1

A) The spatial correlation between microdamage and eroded surfaces was determined by selecting at random 30 points at locations of damage and 30 points distant from microdamage and determining if an eroded surface was nearby. B) The spatial correlation between eroded surfaces and microdamage was determined by selecting points on the bone surface within an eroded surface or distant from an eroded surface and determining if microdamage was nearby.

Figure 2

Differences in A) whole specimen DV/BV; B) volume of each damage site; and C) number of damage sites between specimens loaded in tension and compression. Lines connect specimens from the same donor. p value indicates significant difference between tension and compression (paired t-test).

Figure 3

DV/BV sustained in tension was positively correlated with DV/BV generated in compression from the same donor (DV/BV_tension = 1.2 + 1.3 * DV/BV_compression). The median damage volume of microdamage sites generated from tension was related to that generated in compression (DV site_tension = 1.6 * DV site_compression − 9 × 10³). The number of damage sites per bone volume was not related between tension and compression.

Figure 4

A) DV/BV was negatively correlated with ES/BS in specimens subjected to compression (DV/BV = 5.3 − 0.6 * ES/BS), and not correlated with specimens subjected to tension. B) DV/BV was negatively correlated with BV/TV in specimens subjected to compression (DV/BV = 4.5 − 0.4 * BV/TV), and not correlated in specimens subjected to tension. C) Regions of microdamage had larger local Tb.Th although D) overall DV/BV was not correlated with average Tb.Th.

Figure 5

A) The relative risk of finding an eroded surface around microdamage (p_damage/p_no-damage) and B) The relative risk of finding microdamage around an eroded surface are shown (p_{eroded surface}/p_{no-eroded surface}). The mean value for each relative risk is shown with error bars indicating the standard deviation. No significant differences from 1 were observed indicating no observable spatial correlations between microdamage and eroded surfaces.