Age- and Sex-Specific Differences in the Factor of Risk for Vertebral Fracture: A Population-Based Study Using QCT

Authors

  • Mary L Bouxsein PhD,

    Corresponding author
    1. Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
    • Orthopedic Biomechanics Laboratory, RN 115, Beth Israel Deaconess Medical Center, 330 Brookline Avenue, Boston, MA 02215, USA
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  • L Joseph Melton III,

    1. Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
    2. Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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    • Dr Melton receives speaker's honoraria from Procter & Gamble, Merck & Co., and Amgen. All other authors state that they have no conflicts of interest.

  • B Lawrence Riggs,

    1. Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • John Muller,

    1. Orthopedic Biomechanics Laboratory, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts, USA
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  • Elizabeth J Atkinson,

    1. Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Ann L Oberg,

    1. Department of Health Sciences Research, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Richard A Robb,

    1. Biomedical Imaging Resource, Department of Physiology and Biophysics, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Jon J Camp,

    1. Biomedical Imaging Resource, Department of Physiology and Biophysics, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Peggy A Rouleau,

    1. Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Cynthia H McCollough,

    1. Department of Radiology, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Sundeep Khosla

    1. Endocrine Research Unit, Division of Endocrinology and Metabolism, Department of Internal Medicine, Mayo Clinic College of Medicine, Rochester, Minnesota, USA
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  • Presented in part at the 27th Annual Meeting of the American Society for Bone and Mineral Research, Nashville, TN, November 22–26, 2005.

Abstract

We used QCT scans obtained in 687 men and women, 21–97 years of age, to estimate the factor of risk for vertebral fracture, Φvert, defined as the ratio of spinal loading to vertebral strength. With age, vertebral strength declined and Φvert increased significantly more in women than men. Age- and sex-specific differences in Φvert closely resembled previously reported vertebral fracture incidence.

Introduction: Despite the high prevalence of vertebral fractures, little is known about the interaction between spinal loading and vertebral fragility.

Materials and Methods: We assessed the ratio of spinal loading to vertebral strength (i.e., the factor of risk, Φvert) in an age- and sex-stratified population-based sample of 700 women and men 21–97 years of age. We measured volumetric BMD (vBMD, mg/cm3) and cross-sectional area (CSA, cm2) of the midvertebral bodies of L1–L3 using QCT and computed vertebral compressive strength from these data using engineering beam theory. A biomechanical model of the trunk was used to estimate compressive forces applied to the L3 vertebral body during standing, bending forward, and bending forward while lifting 10 kg. The factor of risk for fracture, Φvert, was computed as the ratio of spinal compressive force to vertebral strength for each activity.

Results: Men had a higher vertebral strength at all ages, largely because of their greater CSA. Whereas both sexes exhibited a marked decline in vertebral compressive strength with age (p < 0.001), the decline was greater in women than men (−43% versus −31%, p = 0.008). Compressive forces on L3 were greater in men than women, because of their greater body weight and height. For both sexes, forces during bending and lifting were 8-fold higher than those experienced during upright standing. For all activities, Φvert increased with age, but significantly more so in women than men (p < 0.001). For bending and lifting, Φvert-bending exceeded 1.0 in 30% of women and 12% of men ≥50 years of age, values that are similar to the reported frequency of vertebral fracture.

Conclusion: These findings illustrate potential mechanisms underlying vertebral fractures and provide strong rationale for further evaluation of this QCT-based biomechanical approach for assessment of fracture risk.

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