Early ontogeny of the human femoral bicondylar angle

The presence of a femoral bicondylar angle consistently and significantly greater than 0" has been a hallmark of hominid bipedality, but its pattern of development has not been documented. We have therefore compiled cross-sectional data on the development of the articular bicondylar angle for a clinical sample of modern humans and of the metaphyseal bicondy- lar angle for two Recent human skeletal samples, one predominantly Euro- pean in origin and the other Amerindian. All three samples exhibit a pattern of a bicondylar angle of 0" at birth and then a steady average increase in the angle from late in the first year postnatal, through infancy, and into the juvenile years. The two skeletal samples reach low adult values by approxi- mately 4 years postnatal, whereas the clinical sample with a lowered activity level appears to attain consistent adult values slightly later (approximately 6 years postnatal). In addition, two modern human individuals, one nonambu- latory and the other minimally ambulatory, show no and little development, respectively, of a bicondylar angle. These data, in conjunction with 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 angle and the direct association of a bipedal locomotion and (especially) posture with the developmental emer- gence of a human femoral bicondylar angle. o 1994 Wiley-Liss, Inc.