Cortical bone distribution in the femoral neck of Hominids: Implications for the locomotion of Australopithecus afarensis

Department of Orthopaedic Surgery, School of Medicine, Case Western Reserve University, Cleveland, Ohio 44106
American Journal of Physical Anthropology (Impact Factor: 2.38). 09/1997; 104(1):117 - 131. DOI: 10.1002/(SICI)1096-8644(199709)104:1<117::AID-AJPA8>3.0.CO;2-O

ABSTRACT Contiguous high resolution computed tomography images were obtained at a 1.5 mm slice thickness perpendicular to the neck axis from the base of the femoral head to the trochanteric line in a sample of 10 specimens each of Homo sapiens, Pan troglodytes, and Gorilla gorilla, plus five specimens of Pan paniscus. Superior, inferior, anterior, and posterior cortical thicknesses were automatically measured directly from these digital images. Throughout the femoral neck H. sapiens displays thin superior cortical bone and inferior cortical bone that thickens distally. In marked contrast, cortical bone in the femoral neck of African apes is more uniformly thick in all directions, with even greater thickening of the superior cortical bone distally. Because the femoral neck acts as a cantilevered beam, its anchorage at the neck-shaft junction is subjected to the highest bending stresses and is the most biomechanically relevant region to inspect for response to strain. As evinced by A.L. 128-1, A.L. 211-1 and MAK-VP-1/1, Australopithecus afarensis is indistinguishable from H. sapiens, but markedly different from African apes in cortical bone distribution at the femoral neck-shaft junction. Cortical distribution in the African ape indicates much greater variation in loading conditions consistent with their more varied locomotor repertoire. Cortical distribution in hominids is a response to the more stereotypic loading pattern imposed by habitual bipedality, and thin superior cortex in A. afarensis confirms the absence of a significant arboreal component in its locomotor repertoire. Am J Phys Anthropol 104:117–131, 1997. © 1997 Wiley-Liss, Inc.

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    • "Here, the evolutionary process would have favored locomotor phenotypes that were not only generally fit to the mosaic forest-grassland habitat features of East and northern Central Africa, but also minimized energy expenditure in that habitat (Wheeler, 1991a,b; Leonard and Robertson, 1997). The emergence of the genus Australopithecus, ca. 4 mya in East Africa, appears to have coincided with the evolution of " obligate bipedalism, " in which the anatomy supporting efficient stride is so specialized that it substantially limits habitual arboreal climbing (Jungers, 1982; Latimer et al., 1987; Latimer and Lovejoy, 1990; Ohman et al., 1997; Haile-Selassie et al., 2010). Obligate bipedalism—involving an arched foot, non-opposable big toe, and a strongly disto-medially angled femur—is first documented among fossil traces of Au "
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    • "Concerning the femur, the femoral neck demonstrates also a complex architecture in accordance with its biomechanical role. A strong asymmetric crosssectional distribution of the cortical bone along the femoral neck has been observed in humans (Lovejoy, 1988, 2005b; Ohman et al., 1997). Although this character is not a distinctive human feature, as it was observed in other primate species (Rafferty, 1998; Matsumura et al., 2010), a strong relationship between asymmetric cortex and locomotor behaviour has been demonstrated. "
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    • "The cortical bone structural asymmetry exists through the length of the femoral neck but is reported to achieve a maximum at the neck-trochanteric junction (Ohman et al., 1997), where the stress differential is theoretically maximized (Frankel, 1960; Lovejoy, 1988, 2005). The human condition contrasts with the more equally distributed cortical bone in the femoral neck of climbing/suspensory nonhuman anthropoids (Great Apes and atelines) (Lovejoy, 1988; Ohman et al., 1997). This cortical bone structure in climbing/suspensory species presumably is a response to larger axially compressive loads on the femoral neck that result from the higher femoral neck angle (Rafferty, 1996). "
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