Population-Based Analysis of the Relationship of Whole Bone Strength Indices and Fall-Related Loads to Age- and Sex-Specific Patterns of Hip and Wrist Fractures

Abstract

In an age-and sex-stratified population sample (n = 700), we estimated fall-related loads and bone strength indices at the UDR and FN. These load/strength ratios more closely simulated patterns of wrist and hip fractures occurring in the same population than did measurement of vBMD.Introduction: Areal BMD measurements, although associated with fracture risk, incompletely explain patterns of fragility fractures. Moreover, population-based assessments relating applied loads and whole bone strength to fracture patterns have not been made. Materials and Methods: Using QCT, we assessed volumetric BMD (vBMD), cross-sectional geometry, and axial (EA) and flexural (EI) rigidities (indices of bone's resistance to compressive and bending loads, respectively) at the ultradistal radius (UDR) and femoral neck (FN) and estimated the loads applied to the wrist and hip during a fall. We used fall load (FL)/bone strength ratios to estimate fracture risk. Results: vBMD in young adults was similar between sexes. Decreases in vBMD over life were also similar (30% and 28%) at UDR but were somewhat greater (46% and 34%) at FN in women versus men, respectively. In young adults, FL/strength ratios at UDR were 32-51% lower (better) in men than in women and increased (worsened) over life less in men (+4% to +22%) than in women (+20% to +33%). In young adults, FL/strength ratios at FN were only marginally better in men than in women but worsened less over life in men (+22% to +36%) than in women (+40% to +62%). Conclusions: The 6:1 female preponderance and the virtual immunity of men for age-related increases in wrist fractures are largely explained by the more favorable FL/strength ratios at UDR in young adult men (because of larger bone size and more favorable geometry) versus women and to maintaining this advantage over life. The 2-fold lower incidence of hip fractures in men versus women is largely explained by age-related increases (worsening) of FL/bone strength ratios that are only one-half of the increases in women. The moderate increases in these ratios with aging are insufficient to explain the >4-fold increase in hip fracture incidence after age 75 in both sexes, suggesting contributions of other factors, especially the well-documented increased frequency of injurious falls among the elderly.

Geographic variation of bone mineral density and selected risk factors for prediction of incident fracture among Canadians 50 and older

“…This result is consistent with prior studies that have reported that fracture rates are similar for 50-year old men and women but diverge with increasing age with a much higher fracture rate in older women [27,28]. Many factors may contribute to the increased differences between sexes in fracture rates with ageing, including differences in bone strength [29,30], propensity to fall [26], and the load placed on the bone [31]. The gradient of fracture risk by age varies not only by sex, but also by skeletal site [28,32].…”

The clinical contribution of cortical porosity to fragility fractures

“…As increasing bone size increases crosssectional moment of inertia (CSMI) and resistance to bending, 32 the increased odds for fracture with increasing bone turnover suggests that the positive effect of larger bone size on bone strength does not offset the negative impact of higher porosity and thinning of cortices produced by increased bone remodeling. 24,31,[33][34][35] This first evidence of association of in vivo measurements of proximal femur cortical porosity from clinical CT images with bone remodeling activity as reflected by PINP and CTX 31 confirm a previously reported association between distal tibia cortical porosity with PINP and CTX. 36 Cortical bone loss is the result of unbalanced and accelerated intracortical remodeling on the surfaces formed by the many canals traversing cortical bone.…”

Age-related patterns of trabecular and cortical bone loss differ between sexes and skeletal sites: A population-based HR-pQCT study

“…(42,48) This apparent sex difference in macrostructural changes with aging may partially explain the higher incidence of Colles' fractures in women than in men. (34) Despite a larger bone size, thicker cortices, and greater volume of trabecular bone in young-adult men, our estimate of sizeadjusted bone strength (ultimate stress) was not significantly different between young-adult men and women. Also, the predicted decline in size-adjusted bone strength was similar in magnitude in both sexes despite sex differences in the pattern of age-related bone loss in the trabecular and cortical compartments.…”

“…Consistent with previous population-based studies of adults in the United States (13) and the United Kingdom, (14) our results suggest that patterns of age-related bone loss differ between women and men and also between the cortical and trabecular compartments at the distal radius and distal tibia. The predicted macro-and microstructural changes with aging in our cohort may help to explain the significantly greater incidence of forearm fractures in women than in men, (34) as well as how age-related structural changes differ between weight-bearing and non-weight-bearing sites. Before discussing our findings in detail, we acknowledge that in this cross-sectional study we cannot determine true agerelated changes in HR-pQCT outcomes in women and men.…”

“…In particular, the observed trends for less periosteal expansion, more porous cortices, and a greater percentage of load carried by the cortex at the distal radius may contribute to the 600% higher incidence of forearm fractures in women. (34) Importantly, these findings must be confirmed in longitudinal studies that are able to accurately determine changes in trabecular and cortical microarchitecture with age in women and men.…”