Optimizing Bone Loss Across the Lifespan: The Three-Dimensional Structure of Porosity in the Human Femoral Neck and Rib As a Metric of Bone Fragility

Both accidental and non-accidental circumstances can produce bone fractures leading to decline and death. This differentiation in manner of death becomes increasingly difficult with age, as fragile bones easily fracture during accidental falls or spontaneously break in osteoporotic individuals. Bone mineral density (BMD) is commonly used to clinically diagnose osteoporosis, but it under-predicts fracture risk about 11-fold because it does not consider changes in tissue structure. Most long bone strength is derived from the cortical ""wall"" of the bone. Porous voids accumulate in the cortex with age as artifacts of the remodeling processes that renew and repair bone. Pores concentrate stress, initiating and propagating microscopic damage into fracture. The complex three-dimensional structure of pore networks has confounded inferences from traditional two-dimensional methods.

Researchers have a poor understanding of how aging changes the relationship between the mechanical strains that initiate remodeling and pore structures that result from remodeling. Defining this relationship has direct forensic application in using porosity to 1) assess accidental vs. non-accidental fracture based on bone fragility, 2) indicate general age range and pathology (e.g. osteoporosis), and 3) infer mechanical strain patterns to identify unknown bone fragments.

The sample used for this study is an adult age series of the human femoral neck and human fourth rib from sixteen cadaveric individuals, both male and female (Division of Anatomy, College of Medicine, The Ohio State University).

Research Design and Methods: The SkyScan 1172-D high-resolution micro computed tomography (micro-CT) (Department of Biomedical Engineering, The Ohio State University) will quantify the three-dimensional structure of pore systems over the lifespan. Pore systems will be given strain ""scores"" based on circularly polarized light microscopy of collagen fiber orientation in histological sections. Bone is hypothesized to direct pore expansion and coalescence towards regions that are under lower mechanical strain and incur less fracture-initiating microdamage. This distinction is hypothesized to break down with age, compromising biomechanical Integrity. Femoral neck scanning and analysis is projected for 2017 -2018, with a prospective renewal in 2018 -2019 for the rib.

MANCOVAs for repeated measures will test the effect of anatomical region and strain score on pore volume, connectivity, and orientation. Covariates will include age, sex, height, weight, femoral neck length/angle, and BMD.

In addition to publication and presentation, raw data on pore measurements, three-dimensional scans, and any predictive equations for strain score or anatomical region based on pore variables will be made available through a website.

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