title: Intrinsic material property differences in bone tissue from patients suffering low-trauma osteoporotic fractures, compared to matched non-fracturing women.
abstract: Osteoporotic (low-trauma) fractures are a significant public health problem. Over 50% of women over 50yrs. of age will suffer an osteoporotic fracture in their remaining lifetimes. While current therapies reduce skeletal fracture risk by maintaining or increasing bone density, additional information is needed that includes the intrinsic material strength properties of bone tissue to help develop better treatments, since measurements of bone density account for no more than ~50% of fracture risk. The hypothesis tested here is that postmenopausal women who have sustained osteoporotic fractures have reduced bone quality, as indicated with measures of intrinsic material properties compared to those who have not fractured. Transiliac biopsies (N=120) were collected from fracturing (N=60, Cases) and non-fracturing postmenopausal women (N=60, age- and BMD-matched Controls) to measure intrinsic material properties using the nano-indentation technique. Each biopsy specimen was embedded in epoxy resin and then ground, polished and used for the nano-indentation testing. After calibration, multiple indentations were made using quasi-static (hardness, modulus) and dynamic (storage and loss moduli) testing protocols. Multiple indentations allowed the median and variance to be computed for each type of measurement for each specimen. Cases were found to have significantly lower median values for cortical hardness and indentation modulus. In addition, cases showed significantly less within-specimen variability in cortical modulus, cortical hardness, cortical storage modulus and trabecular hardness, and more within-specimen variability in trabecular loss modulus. Multivariate modeling indicated the presence of significant independent mechanical effects of cortical loss modulus, along with variability of cortical storage modulus, cortical loss modulus, and trabecular hardness. These results suggest mechanical heterogeneity of bone tissue may contribute to fracture resistance. Although the magnitudes of differences in the intrinsic properties were not overwhelming, this is the first comprehensive study to investigate, and compare the intrinsic properties of bone tissue in fracturing and non-fracturing postmenopausal women.
authors.affiliation: University of Nebraska-Lincoln, NE, United States.
authors.forename: S
authors.initials: S
authors.lastname: Vennin
authors.affiliation: University of Nebraska-Lincoln, NE, United States.
authors.forename: A
authors.initials: A
authors.lastname: Desyatova
authors.affiliation: University of Nebraska-Lincoln, NE, United States.
authors.forename: J A
authors.initials: JA
authors.lastname: Turner
authors.affiliation: Osteoporosis Research Center, Creighton University, Omaha, NE, United States.
authors.forename: P A
authors.initials: PA
authors.lastname: Watson
authors.affiliation: Osteoporosis Research Center, Creighton University, Omaha, NE, United States.
authors.forename: J M
authors.initials: JM
authors.lastname: Lappe
authors.affiliation: Osteoporosis Research Center, Creighton University, Omaha, NE, United States.
authors.forename: R R
authors.initials: RR
authors.lastname: Recker
authors.affiliation: Osteoporosis Research Center, Creighton University, Omaha, NE, United States. Electronic address: akhtermp@creighton.edu.
authors.forename: M P
authors.initials: MP
authors.lastname: Akhter
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D015519:Bone Density; D001842:Bone and Bones / Q000473:pathology*; D000071556:Cancellous Bone / Q000473:pathology; D016022:Case-Control Studies; D000071538:Cortical Bone / Q000473:pathology; D005260:Female; D006801:Humans; D016015:Logistic Models; D008875:Middle Aged; D015999:Multivariate Analysis; D058866:Osteoporotic Fractures / Q000209:etiology* / Q000473:pathology*; D014947:Wounds and Injuries / Q000150:complications*
keywords: Bone quality; Fracture toughness; Intrinsic material properties; Nano-indentation testing; Osteoporotic fractures