title: Age-related factors affecting the postyield energy dissipation of human cortical bone.
abstract: The risk of bone fracture depends in part on tissue quality, not just the size and mass. This study assessed the postyield energy dissipation of cortical bone in tension as a function of age and composition. Specimens were prepared from tibiae of human cadavers in which male and female donors were divided into two age groups: middle aged (51 to 56 years, n = 9) and elderly (72 to 90 years, n = 8). By loading, unloading, and reloading a specimen with rest periods inserted in between, tensile properties at incremental strain levels were assessed. In addition, postyield toughness was estimated and partitioned as plastic strain energy related to permanent deformation, released elastic strain energy related to stiffness loss, and hysteresis energy related to viscous behavior. Porosity, mineral and collagen content, and collagen crosslinks of each specimen were also measured to determine the micro- and ultrastructural properties of the tissue. Age affected all the energy terms plus strength but not elastic stiffness. The postyield energy terms were correlated with porosity, pentosidine (a marker of nonenzymatic crosslinks), and collagen content, all of which varied significantly with age. General linear models suggested that pentosidine concentration and collagen content provided the best explanation of the age-related decrease in the postyield energy dissipation. Among them, pentosidine concentration had the greatest contribution to plastic strain energy and was the best explanatory variable of damage accumulation.
authors.affiliation: Department of Mechanical Engineering and Biomechanics, The University of Texas at San Antonio, San Antonio, Texas 78249, USA. jeffry.s.nyman@vanderbilt.edu
authors.forename: Jeffry S
authors.initials: JS
authors.lastname: Nyman
authors.forename: Anuradha
authors.initials: A
authors.lastname: Roy
authors.forename: Jerrod H
authors.initials: JH
authors.lastname: Tyler
authors.forename: Rae L
authors.initials: RL
authors.lastname: Acuna
authors.forename: Heather J
authors.initials: HJ
authors.lastname: Gayle
authors.forename: Xiaodu
authors.initials: X
authors.lastname: Wang
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D015519:Bone Density; D003094:Collagen / Q000502:physiology; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D012307:Risk Factors; D013718:Tensile Strength / Q000502:physiology*; D013977:Tibia / Q000502:physiology*; D013978:Tibial Fractures / Q000453:epidemiology / Q000503:physiopathology*; D016474:Weight-Bearing / Q000502:physiology
chemical_list: D003094:Collagen