Piecewise Regression Analysis of Secular Change in the Maximum Femoral Vertical Head Diameter of American White Males and Females.

Osteometric measurements of the femur are consistently used to estimate stature, sex, and race in constructing demographic profiles. The presence of positive or negative changes in the size of the maximum vertical diameter of the femoral head could potentially affect the validity of such profiles. Additionally, changes in femoral head size may be an indicator of the socioeconomic status, health, and nutrition of a population over periods of time. Two large data sets consisting of white male and white female femoral vertical head diameter measurements with birth years spanning 1841-1990 are used in this study. A combination of both LOESS and piecewise regression models determined the presence of secular changes in femoral head size. Tests of the residuals were also conducted to assess normality of the data and goodness of fit of the nonlinear models. The results indicate that white males and females experienced nonsignificant increases in femoral head diameter size before 1920 and significant decreases in size thereafter. The results of this study are consistent with other studies that have identified changes in body and skeletal morphology. Considerable changes and improvements in environmental conditions that humans have experienced since the mid-nineteenth century likely contribute to the decrease in femoral head size observed in this study.