Distal Radius Microstructure and Finite Element Bone Strain Are Related to Site-Specific Mechanical Loading and Areal Bone Mineral Density in Premenopausal Women

Abstract

Peak bone mass is predictive of lifetime fracture risk, yet young adult women are not screened or counseled on strategies for improving their bone health. Thus, the purpose of this cross-sectional analysis was to identify measurable factors describing genetic and lifestyle characteristics predictive of bone macro-and microstructure and mechanical behavior. We hypothesized that serum vitamin D, current daily calcium intake, site-specific loading, and grip strength would be associated with favorable bone structure and mechanical properties. Seventytwo women aged 21-40 were included in this cross-sectional analysis. High resolution peripheral quantitative computed tomography was used to measure total bone mineral density (BMD), trabecular BMD, mean cross-sectional area (CSA), trabecular number, cortical BMD, cortical thickness, and cortical porosity (%) in the ultradistal radius. Quantitative analysis of clinical computed tomography (CT) scans of the distal forearm were used to calculate integral BMD, bone volume (BV), and bone mineral content (BMC) in the ultradistal and total distal radius, and mean energy equivalent strain in the ultradistal radius was calculated from continuum finite element models generated from CT images. Hierarchical regression models were used to assess the predictive capability of intrinsic (age, height) and modifiable (body mass, grip strength, physical activity) predictors. Vitamin D and calcium intake were not correlated with any bone parameter. Age and height explained 32% of the variance in variables related to bone size, with grip strength and adult loading due to physical activity each explaining an additional 5 to 19% in these and other measures. Body mass explained 10% of the variance in bone strain under a given force, with higher body mass being associated with lower strain (r=-0.210, p<0.05). Overall, results suggest that meaningful differences in bone structure and strength can be predicted by measurable subject characteristics. This highlights the contribution of modifiable site-specific mechanical loading on bone structure and strength.

Do mechanical strain magnitude and rate drive bone adaptation in adult women? A 12-month prospective randomized trial

“…During aging, trabecular structure is first lost from this region, and later from more peripheral regions 37 , thus maximizing moment of inertia for a given quantity of bone. We even observed age-associated declines in Tb.BMDinn within a large subset of the relatively narrow range of young healthy subjects measured here 38 . It is possible that in our cohort of young, healthy women, trabecular microstructure in the more peripheral regions was already at its physiologic maximum, limiting the degree to which it might be improved.…”