Structural and mechanical changes in trabecular bone during early development in the human femur and humerus

Introduction Many evolutionary functional morphology studies within biological anthropology assume a direct relationship between skeletal form and biomechanical function. Such studies often rely heavily upon the fundamental concept of “bone functional adaptation,” or the idea that bone tissue is responsive to and reflective of skeletal loading throughout an organism’s life. As a result, cortical and trabecular bone structure are treated as more or less faithful records of activity during an individual’s lifetime and are therefore generally considered robust indicators of behavior and behavioral variation in past and present populations and species. Many studies on human and non-human primates and other mammals have suggested a link between cortical bone cross-sectional geometric properties (Larsen, 1995, 2015; Lieberman, 1997; Bridges et al., 2000; Ruff, 2005b, 2009; Carlson and Judex, 2007; Shaw and Stock, 2009a, 2009b; Wallace et al., 2013) or three-dimensional trabecular bone structure (MacLatchy and Müller, 2002; Ryan and Ketcham, 2002b, 2005; Lazenby et al., 2008b, 2011; Barak et al., 2011; Wallace et al., 2013; Ryan and Shaw, 2012, 2015; Matarazzo, 2015) and the loads engendered during different physical activities. Other studies, however, have called into question the functional significance of cortical and trabecular bone structural variation in primates and other mammals (Fajardo et al., 2007; Carlson et al., 2008; Ryan and Walker, 2010; Shaw and Ryan, 2012; Wallace et al., 2014, 2015; Chapter 10). In order to gain a better understanding of the functional significance of cortical and trabecular bone structural variation in adult organisms, it is critical to develop a more robust understanding of the factors that contribute to bone development during ontogeny and that ultimately contribute to building adult bone morphology. Many morphological features of the vertebrate postcranial skeleton develop in response to specific behaviors and the resultant mechanical stimuli. Within humans, various important functional characters of the postcranial skeleton, including the femoral bicondylar angle (Tardieu and Trinkaus, 1994), the lumbosacral angle (Abitbol, 1987), epiphyseal morphology (Carter et al., 1989), cortical bone structure of long bones (Ruff, 2003a, 2003b; Shaw and Stock, 2009b), and three-dimensional trabecular bone architecture (Ryan and Krovitz, 2006; Gosman and Ketcham, 2009; Zeininger, 2013; Raichlen et al., 2015), have been demonstrated to be the products of an ontogenetic response to the loads induced during bipedal walking or running.