Secular Change in the Femur Diaphyseal Biomechanical Properties of American Whites.

Over the past two centuries there have been documented secular changes in stature, weight, body proportions, and skeletal maturation rates in the United States. These changes along with a more sedentary lifestyle are likely reflected in femur morphology. Here we examine secular changes in diaphyseal cross-sectional size, shape, area, robusticity, and rigidity at midshaft and subtrochanteric of the femur using 395 adult white females and males from the United States born between the 1850s and the 1970s. The effect of secular change was controlled for an age effect. We also examine the relationship between femur length (proxy for stature) and femur head diameter (proxy for body weight) on measurements of diaphyseal size and biomechanical properties. The femur morphology of Americans born in the twentieth century reflects the combination of changes in stature, body build, and activity levels. Both sexes show significant changes in femur midshaft shape due primarily to a decrease in the mediolateral diameter. There are no significant changes at subtrochanteric in size or biomechanical properties in either sex after controlling for age variation. The results suggest that the changes in femur midshaft shape are primarily associated with a decrease in activity. The stability of the subtrochanteric dimensions and femur anteroposterior diameter may reflect a combination of decreased activity with a corresponding increase in femur length (moment arm) and a decrease in body breadth.