Meeting Abstract
X-ray Reconstruction of Moving Morphology (XROMM) can be used to recreate skeletal motion of living animals by animating 3-d computer-generated models of the bones. Kinematic measurements from these animations require clearly defined joint coordinate systems (JCS). In most cases, anatomical landmarks from proximal and distal bones on either side of the joint can be used to orient a JCS. However, the alligator sternum is cartilaginous and is invisible in X-ray views and CT scan-based models of intact animals. Thus, the proximal end of the coracoid, which articulates with sternum, appears to “float” on the ventral aspect of the thorax. This makes orienting the JCS consistently between different individuals challenging. Here, we explore a method for reconstructing the cartilaginous elements to place of the coracosternal JCS. The JCS is then used to measure coracosternal motion XROMM data from four alligators performing the high walk on a treadmill. Models of the cartilages of the sternum and scapulocoracoid are derived from CT scans of a reduced dissection preparation with only cartilages and bone intact. These polygonal mesh models are then scaled and aligned to each of the experimental animals based on the bony interclavicle which runs within the midline of the sternum. Results suggest that while patterns of movement between individuals are highly consistent, there are offsets in the magnitudes for some axes in some individuals. These offsets may true variation between individuals or could be associated with slight variations in the orientation of the interclavicle within the sternal cartilage. Ideally, the sternum should be reconstructed from the anatomy of each individual which would distinguish between these two possibilities.
