Quantitative Relationships Between Microdamage and Cancellous Bone Strength and Stiffness

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 © 2014 Elsevier Inc. All rights reserved. Corresponding Author: Christopher J. Hernandez, Ph.D., Upson 219, Cornell University, Ithaca, NY 14853, cjh275@cornell.edu, Phone: (607) 255-5129, Fax: (607) 255-1222. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access Author Manuscript Bone. Author manuscript; available in PMC 2015 September 01. Published in final edited form as: Bone. 2014 September ; 66: 205–213. doi:10.1016/j.bone. 2014.05. 023. N IH -P A A uhor M anscript N IH -P A A uhor M anscript N IH -P A A uhor M anscript provided in this study make it possible to estimate the degree of impaired mechanical performance resulting from an observed amount of stained microdamage.