PSI - Issue 37

Ekaterina Smotrova et al. / Procedia Structural Integrity 37 (2022) 257–262 E. Smotrova et al. / Structural Integrity Procedia 00 (2021) 000 – 000

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1. Introduction Trabecular bone, a spongy component of many bones, functions as a supportive element, providing the lightweight and porous, yet strong and tough weight-bearing framework of the body. Trabecular bone is classified as a composite, structurally anisotropic, open-type porous solid material, formed by an irregular 3D lattice of interconnected plates and struts of bone, called trabeculae (Keaveny et al. 2001). The microstructure of trabecular bone is characterized by thick trabeculae oriented along the stress lines, which are supported by thinner orthogonal interconnected rods and plates. The complex microstructure determines the distribution of bone mineral density (BMD) across anatomical sites and, hence, plays an important role in the trabecular bone’s ability to sustain large deformations and its resistance to fracture. Aging and low-bone-mass disorders (e.g., osteopenia and osteoporosis) of humans are characterized by a significant decrease in BMD and transition from plate-like to rod-like microstructure of trabeculae, as reported by Li et al. (2013). Accurate measurement of BMD and microstructural parameters of trabecular bone is, therefore, vital for early diagnostics of bone loss and prediction of fracture risk. Dual energy X-ray absorptiometry (DXA) is an imaging technique that is widely used in clinical procedures for assessment of age- and osteoporosis-related changes in BMD. Despite such advantages as short scanning time, low radiation exposure and low cost (Celi et al. 2013), DXA has several limitations in prediction of bone fragility and fracture. First, due to its low resolution, DXA cannot provide information on trabecular-bone microstructure, which plays important role in determining mechanical properties of this bone tissue (Zhou et al. 2014). It was demonstrated by Muller et al. (2003) that BMD measured with DXA can explain only 50 – 80% of variation in the whole-bone strength. Second, the accuracy of DXA measurements is affected by increase in local BMD in patients with such medical conditions as osteophytes, vascular calcifications, scoliosis and bone sclerosis, as shown by Liu et al. (1997), Muraki et al. (2004) and Pappou et al. (2006). High-resolution peripheral quantitative computed tomography (HR-pQCT) is a novel technique of bone visualization, which, thanks to its resolution of 82 µm, allows depiction of individual trabeculae, ensuring the adequate assessment of trabecular-bone microstructural parameters. The results obtained from previous FEA simulations based on HR- pQCT data validated this approach for quantification of bone’s mechanical properties. However, the effect of material mechanical properties on failure modelling of human trabecular bone (HTB) is less analysed. The aim of this study was to determine the effect of different mechanical formulations of bone material on failure behavior of HTB. For this purpose, a 3D unit cell of trabecular lattice obtained from HR-pQCT scans of human distal tibia was developed. The finite-element (FE) method was implemented for the reconstructed model that was loaded in tension and compression in elastic and plastic deformation regimes to predict the onset of damage accumulation and failure in trabeculae.

Nomenclature BMD

bone mineral density

DXA

dual energy X-ray absorptiometry

FE

finite element

HR-pQCT

high-resolution peripheral quantitative competed tomography

HTB

human trabecular bone

2. Methodology 2.1. Processing of HR-pQCT scans

The HR-pQCT scans used in this study were acquired as discussed in Du et al. (2019). In brief, the scans of distal tibia of healthy women of 63.3 ±3.6 years with no fractures, diagnosed osteoporosis or any musculoskeletal disorders were obtained using a HR-pQCT scanner (XtremeCT, Scanco Medical). 110 slides in each scan corresponded to 9.02 mm axial scan length and had isotropic resolution of 82 μm. One scan of one participant was analyzed in this study.