Meeting Abstract
The elbow joint in birds is typically considered to work as a simple hinge. However, some evidence from flying birds suggests greater complexity of movement. Additionally, the nature of the flapping wing likely places unusual demands on the elbow joint compared to other tetrapods. As the wing sweeps downward, the upward aerodynamic force would be expected to be greater on the distal wing, thereby generating a moment about the abduction/adduction axis of the elbow, perpendicular to its primary flexion/extension axis. We hypothesized specializations in the morphology and/or arrangement of the elbow ligaments to stabilize against this loading pattern, with particular focus on the ventral collateral ligament. In this study, we use X-ray Reconstruction of Moving Morphology (XROMM), to quantify the passive range of motion in turkey elbow by manipulating disarticulated wings. We also mapped ligaments onto digital models to explore their orientation during wing movement and explore which morphological features limit range of motion. We found ca. 90 degrees of flexion/extension, ca. 50 degrees of abduction/adduction movement, and ca. 40 degrees of long axis rotation at the humeroulnar joint (n = 4 wings). The range of abduction/adduction decreases with increasing extension of the elbow, suggesting that the ventral collateral ligament stabilizes the joint more effectively when the wing is fully extended as it is during downstroke of flapping flight. In order to achieve uniformity within interpretation of motion data for each trial, a standardized elbow joint coordinate system was established. This joint coordinate system used the inertial axes and key anatomical landmarks of the humerus, ulna, and radius, as the basis of its foundation.
