Cross-Sectional Morphology of the Femoral Neck of Wild Chimpanzees

To understand the mechanical effects of different modes of locomotion on the femoral neck of chimpanzees, we investigated the cross-sectional morphology of the femoral neck of 4 chimpanzees (Pan troglodytes schweinfurthii) collected from the Mahale Mountains, Tanzania. We performed serial computed tomography (CT) scans of the neck from the femoral head to the base of the neck perpendicular to the long axis of the neck. We measured the cortical thickness of the serial 5 cross sections of the neck region every 45° around the circumference, i.e., 8 points per section, and examined the cross-sectional properties of the mid-section. When we compared the superior and inferior parts of the cortical thickness of the femoral neck, the inferior part exhibited the greatest cortical thickness whereas the superior part had the smallest values in every specimen. Researchers have also observed such regional differences between superior and inferior cortical thicknesses in bipedal humans and other primates, although these differences are not as large in the chimpanzee as in bipedal hominini. The present study differed from the past study on hominini and chimpanzees in that the superior anterior (SA) part exhibited greater cortical thickness in chimpanzees. We believe these observations reflect the structural strengthening of parts of the chimpanzee femoral neck that is needed to accommodate the mechanical loads imposed by arboreal vertical climbing and terrestrial quadrupedal and bipedal locomotion.