Quantitative relationships between microdamage and cancellous bone strength and stiffness

Abstract

Microscopic tissue damage (microdamage) is an aspect of bone quality associated with impaired bone mechanical performance. While it is clear that bone tissue submitted to more severe loading has greater amounts of microdamage (as measured through staining), how microdamage influences future mechanical performance of bone has not been well studied, yet is necessary for understanding the mechanical consequences of the presence of microdamage. Here we determine how stained microdamage generated by a single compressive overload affects subsequent biomechanical performance of cancellous bone. Human vertebral cancellous bone specimens (n = 47) from 23 donors (14 male, 9 female, 64–92 years of age) were submitted to a compressive overload, stained for microdamage, then reloaded in compression to determine the relationship between the amount of microdamage caused by the initial load and reductions in mechanical performance during the reload. Damage volume fraction (DV/BV) caused by the initial overload was related to reductions in Young’s modulus, yield strength, ultimate strength, and yield strain upon reloading (p < 0.05, R2 = 0.18–0.34). The regression models suggest that, on average, relatively small amounts of microdamage are associated with large reductions in reload mechanical properties: a 1.50% DV/BV caused by a compressive overload was associated with an average reduction in Young’s modulus of 41.0 ± 3.2 % (mean ± SE), an average reduction in yield strength of 63.1 ± 4.5% and an average reduction in ultimate strength of 52.7 ± 4.0%. Specimens loaded beyond 1.2% (1.2–4.0% apparent strain) demonstrated a single relationship between reload mechanical properties (Young’s modulus, yield strength, and ultimate strength) and bone volume fraction despite a large range in amounts of microdamage. Hence, estimates of future mechanical performance of cancellous bone can be achieved using the bone volume fraction and whether or not a specimen was previously loaded beyond ultimate strain. The empirical relationships provided in this study make it possible to estimate the degree of impaired mechanical performance resulting from an observed amount of stained microdamage.

Material heterogeneity in cancellous bone promotes deformation recovery after mechanical failure

“…Cancellous bone has long been recognized for the ability to recover large amounts of deformation after an overload; specimens compressed well beyond ultimate strain typically recover 61-94% of applied deformation (33)(34)(35). The ability to recover deformation in cancellous bone allows for recovery of shape of whole bone after a fracture, and is therefore a passive mechanism of setting or reducing a fracture.…”

Maximum principal strain as a criterion for prediction of orthodontic mini-implants failure in subject-specific finite element models

“…Fatigue causes irreparable bone microdamages to accumulate with subsequent bone resorption and reduction of bone strength, causing the OMIs to loosen. 28,29 Yeh and Keaveny 30 showed that microdamage may occur in cancellous bone at relatively low strains of approximately 0.2% (2000 mstrain). Frost 28 suggested that microdamages start to accumulate when strain exceeds 3000 mstrain.…”

Intermediate strain rate behaviour of cancellous bone: Links between microstructural and mechanical properties

“…The intermediate strain rate (ISR) regime (1 and 10/s) has been characterized [4,5] but the observed scatter was not investigated or linked to the upper ISR limit (100/s) and extreme strain rates. Detailed features of the micro-architecture of porous cancellous bone [6] have been linked to the quasi-static behaviour, to the dynamic and confined dynamic loading [7] to predict the fracture localization [8], the micro-damage [9] and the global mechanical response [10].…”