The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)


The Bicondylar Angle in Modern Humans and its Relationship to Joint Stresses and Locomotor Economy

MARIA R. DARR1, HERMAN PONTZER2 and ANNA WARRENER3.

1Department of Anthropology, New York University, 2Department of Anthropology, Hunter College, 3Department of Human Evolutionary Biology, Harvard University

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The bicondylar angle (or “carrying angle”) evident in the distal femur of humans and fossil hominins has been suggested to increase the efficiency of bipedal walking by placing the foot closer to midline, below the body’s center of mass, during stance phase. In this study we analyzed coronal-plane hind limb joint moments and metabolic cost during walking to determine whether knee-joint stress or economy is correlated with carrying angle. We assessed moments at the knee in the coronal plane by using a combined modeling and experimental approach. Ten subjects (4 males, 6 females) walked along a trackway with an embedded force plate while kinematics and kinetics were recorded; inverse dynamics were used to calculate joint moments. During Control trials, kinematic markers were placed directly on the skin over skeletal landmarks. In Low-Angle trials, the right knee marker was modified to simulate a reduction in bicondylar angle. Analyses confirmed that simulated coronal-plane knee moments, and thus knee-joint stresses, were greater in the Low-Angle condition, indicating that the normal bicondylar angle reduces knee joint stresses. In a separate study of n=26 subjects, we compared bicondylar angle, determined via magnetic resonance imaging, and walking cost, measured via respirometry. Bicondylar angle was not significantly correlated with mass-specific walking cost in these subjects. The implications of these results for interpreting lower limb skeletal adaptations in the hominin skeletal record are also discussed.

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