STRUCTURAL DESIGN OF THE FEMORAL-NECK IN PRIMATES

This study investigates the structural design of the femoral neck with respect to phylogeny, locomotor behavior, and body size in a large co mparative sample of primates. Since a bone's strength is determined by the amount and arrangement of its constituent material, the amount an d distribution of bone in the femoral neck are the focus of the presen t study. Two types of data were collected. First, the total distributi on of bone across the femoral neck (perpendicular to the femoral neck axis) was examined using image analysis techniques. The distribution o f both cortical and trabecular bone are included in this analysis. Sec ondly, the external dimensions of the femoral neck and the thickeness of the superior and inferior cortices, measured from radiographs, were used to calculate femoral neck cross-sectional properties (cortical a rea and second moment of area). These data were input into a simplifie d cantilevered beam model that incorporates femoral neck-shaft angle a nd femoral neck length and is used to predict stress under one unit bo dy mass of loading on the femoral head. The patterns of bone distribut ion in the femoral neck between taxa are broadly similar for the analy sis that includes both trabecular and cortical bone and that which inc ludes only cortical bone. In all cases, there tends to be more bone on the inferior aspect of the femoral neck compared to the superior aspe ct. However, the nonhuman hominoids and New World monkeys (e.g., Atele s and Alouatta) have a more even distribution of bone across the femor al neck and have thicker superior cortices relative to inferior cortic es compared to the rest of the comparative sample, including humans. I t is proposed that the more equal distributional pattern in the nonhum an hominoids and atelines reflects less stereotypical, more generalize d loading orientations. Differences between species in overall strengt h of the femoral neck are a function of both body size and locomotor m ode. (C) 1998 Academic Press Limited.