EARLY ONTOGENY OF THE HUMAN FEMORAL BICONDYLAR ANGLE

The presence of a femoral bicondylar angle consistently and significan tly greater than 0 degrees has been a hallmark of hominid bipedality, but its pattern of development has not been documented. We have theref ore compiled cross-sectional data on the development of the articular bicondylar angle for a clinical sample of modern humans and of the met aphyseal bicondylar angle for two Recent human skeletal samples, one p redominantly European in origin and the other Amerindian. All three sa mples exhibit a pattern of a bicondylar angle of 0 degrees at birth an d then a steady average increase in the angle from late in the first y ear postnatal, through infancy, and into the juvenile years. The two s keletal samples reach low adult values by approximately 4 years postna tal, whereas the clinical sample with a lowered activity level appears to attain consistent adult values slightly later (approximately 6 yea rs postnatal). In addition, two modern human individuals, one nonambul atory and the other minimally ambulatory, show no and little developme nt, respectively, of a bicondylar angle. These data, in conjunction wi th clinical and experimental observations on the potential and form of angular changes during epiphyseal growth, establish a high degree of potential for plasticity in the development of the human bicondylar an gle and the direct association of a bipedal locomotion and (especially ) posture with the developmental emergence of a human femoral bicondyl ar angle. (C) 1994 Wiley-Liss, Inc.