Meeting Abstract

P3.130  Thursday, Jan. 6  Beyond Hinges: 6 DOF Joint Kinematics in Avian Bipedalism KAMBIC, Robert*; ROBERTS, Thomas; GATESY, Stephen; Brown University; Brown University; Brown University robert_kambic@brown.edu

The “erect” limb posture of birds has often led to the conclusion that, compared to “sprawling” lizards and crocodilians, their locomotor pattern is simple and planar. Although flexion/extension dominates limb kinematics, accurate data for abduction/adduction and long axis rotation do not exist. What are we missing by treating avian bipeds as 2-D? Until recently, it has been extremely difficult to study 3-D hind limb motion . Surface markers are insufficient to reconstruct six degree of freedom joint kinematics due to skin and muscle artifacts. A system developed at Brown (X-ray Reconstruction of Moving Morphology- XROMM) uses biplanar x-ray video combined with scan-based bone models to reconstruct highly accurate skeletal movements. When measured with an explicit joint coordinate system, animated bone models provide our first quantitative look at the three-dimensional motions of avian bipedalism. In guineafowl, we find that abduction/adduction is a relatively minor component at the hip, knee, and ankle during walking. However, the femur and tibiotarsus consistently counter-rotate about their long axes during each stride. During maneuvering, significantly greater long axis rotations occur (as much as 50° at the knee). Therefore, long axis rotation appears to be a critical component of avian hind limb motion. Although birds are close to parasagittal, this added degree of freedom provides the flexibility needed to modulate foot trajectory and provide single-leg support during locomotion. This research has been funded through the NSF and W.M. Keck Foundation.