Abstract
Aging, from 40 to +80 years old, causes geometrical and mechanical properties changes in the proximal femur. The subperiosteal width expands faster in men compared to women during aging, while the cortical thickness varies unequally in each sector and differently between men and women. Another change which occurs during aging is bone mechanical properties such as stiffness and ultimate strains. Numerical analysis allows us to study the potential effects of each of the age-dependent changes on the fracture forces separately and combined. We investigated the effects of the geometrical and bone mechanical properties changes due to aging on the femoral strength during a common falling scenario using a transverse isotropic continuum damage model. First, the femur model was adapted from a previously developed human body model named THUMS v4.02. Then, three sets of models were developed to address each of the changes separately and combined for both sexes. We found that the fracture forces in women are on average 1500 N less than in men of the same age. The age-dependent geometrical changes increased the fracture forces in men (25 N/decade), whereas it reduced the fracture forces by 116 N/decade in women. The mechanical properties changes reduced the fracture forces in men more than in women (354.5 N/ decade vs. 225.4 N/decade). When accounting for both geometrical and mechanical properties changes due to aging, the fracture forces decreased by 10.7% of the baseline in women per decade compared to 7.2% per decade in men.
Highlights
Adults older than 65 are at risk of a fall, and this risk increases as they get older (Ambrose et al, 2013)
The first set accounted only for age-dependent geometrical changes (GeomAge), the second set accounted only for age-dependent mechanical properties changes (MechAge), and the third set accounted for both changes in 4 decades of age (MechGeomAge), from 40 to 80 years old
It is noteworthy that the geometry was kept intact for various ages in the MechAge set
Summary
Adults older than 65 are at risk of a fall, and this risk increases as they get older (Ambrose et al, 2013). Houry et al (2016) estimated growth in the population of older adults, which without preventive plans, could lead to a 100% increase in the number of injuries caused by a fall in the year 2030. Women are at a higher risk of hip fracture comparing to men at a similar age (Courtney et al, 1995; Silva 2007; Ito et al, 2011), and the fracture risk increases exponentially as men and women get older (Beck et al, 2000; Ito et al, 2011)
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