Impacts of the Growth Environment on Cortical Bone Plasticity during Childhood.

Bone growth is plastic in its response to the environment, particularly during development. This research aims to examine the plastic response of cortical bone in the long bones of children via the examination of cross-sections of the femur, tibia, and humerus. The goal of this research is to identify some of the factors of the growth environment that impact cortical bone deposition, like biosocial stress, physical activity, and body mass, and to attempt to pull apart their impact on cortical bone distribution. The first paper is a preliminary study examining the intraobserver error from several rounds of cortical area measurements taken from computed tomography scans of dry and wet bone using both manual and algorithmic segmentation methods. The error rates and reliability coefficients for cross-sectional parameters taken from dry and wet samples are comparable, as are those between the manual and algorithmic methods, indicating that consistency of measurement is similar among both samples and al segmentation methods. The second paper develops body mass estimation formulae based on regression of known weight with several breadth measurements and torsional rigidity (J) of the femur and the tibia based on a modern sample of children (n=77). Body mass estimates created using the formulae developed in the study are then compared with documented weights to examine prediction error. Formulae using J values at the femoral mid-shaft produce the least amount of error and are accurate to ±12.62 kg for the overall sample, but surprisingly the formulae using J from sections of the tibia produce comparable results. The third paper examines the relationship between biosocial stress, mechanical loading, and distribution of cortical bone among 106 children from the Lisbon Documental Skeletal Collection (n=45) and the New Mexico Decedent Image Database (n=61). Results suggest that the amount of cortical bone deposited, and medullary cavity size are most impacted by biosocial stress, while bone strength and cross-sectional shape are more influenced by physical activity and, particularly in the lower limbs, body mass. This research demonstrates the importance of environmental context when examining cortical bone deposition in children. Biosocial stress and mechanical loading demonstrate distinct patterns of cortical bone distribution during development. The research also demonstrates the importance of examining multiple long bones, as different sections, bones, and limbs will have different plastic responses to the growth environment.