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2018 Abstracts

Kinematics of the first and fifth metatarsals as determined by high-speed dual fluoroscopy

Konstantinos Karpos; Koren Roach, University of Utah

The foot plays a vital role in understanding lower limb joint kinematics and kinetics, as it is the first link in the kinematic chain that contacts the floor during gait. Even with the advent of advanced motion analysis techniques, the foot is often studied as one single rigid body segment, despite the numerous bones and joints throughout. Several foot models have recently been developed to independently investigate motions of the hindfoot, midfoot, forefoot, and hallux. However, these models still combine multiple bone motions into one rigid body for each of these segments. The purpose of this research was to determine the motion of the first and fifth metatarsals as their own dynamic system, rather than consider them a rigid body as was done in previous research. Three subjects were imaged with dual fluoroscopy (DF) while descending a set of stairs. This technique uses two x-ray cameras, placed approximately 90° from one another, to record continuous x-ray images of the subject. This allows for in vivo bone motion to be determined within the three-dimensional (3D) volume of the combined field-of-view of the fluoroscopes. Separately, a CT image stack was acquired of each subject and the first and fifth metatarsals segmented. Projections through these segmentations were used to generate artificial x-rays of each metatarsal from numerous perspectives. A custom model-based markerless tracking software package was then used to align the artificial x-rays with the DF images to quantify the position and orientation of each bone in 3D space. A coordinate system was defined for both metatarsals. From which, the relative motions of the first and fifth metatarsals were compared during the weight bearing portions of stair descent. Since the metatarsals are dynamic systems, a rigid body assumption ultimately limits the understanding of foot kinematics. We hypothesize that the first and fifth metatarsals will demonstrate different motions during the loading and unloading portions of stair ascent. The comparison of the first and fifth metatarsals will allow us to determine if differences exist between first and fifth metatarsal kinematics, which could be particularly useful for future clinical diagnoses and investigations of various foot pathologies.