Meeting Abstract
Dynamic arthrology is the study of both structure and motion of joints. XROMM makes it possible to visualize and measure 3D shape and 3D motion within joints, both in living animals performing natural behaviors and in situ specimen preparations. Marker-based XROMM relies on radiopaque markers implanted into bones that then move rigidly with the bones. These markers are tracked in 3D from biplanar videofluoroscopy images, and combined with static bone morphology from a CT scan into highly precise and accurate reconstructions of bone shape and motion. From XROMM animations, 6 degree-of-freedom motion at joints can be quantified, and centers of rotation identified. Marker-based XROMM requires biplanar X-ray imaging, but in some cases, markers can be attached rigidly to bones but still visualized externally with standard video cameras. An example are the superficial bones in the heads of ray-finned fishes. Several of the skeletal linkages for suction feeding are visible externally, and miniature bone pins can be attached to the bones and tracked externally. A CT scan then yields bone shape and marker placement, and 3D bones can be animated as in XROMM. This new method, video reconstruction of moving morphology (VROMM), only works for superficial bones, but it provides all the same information about morphology and motion at joints. VROMM may also be applicable to the study of exoskeletal joints in some arthropods. Both VROMM and XROMM have the potential to yield high-precision joint motion, but a precision study with a frozen specimen should be undertaken as part of every XROMM or VROMM project. New, open-source software developed at Brown, the XMA Portal online data management system and XMA Lab marker-tracking software, are greatly increasing the speed and accessibility of XROMM and VROMM.
