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2018 Abstracts

Subtalar Kinematics in Patients Treated for Tibiotalar Osteoarthritis with Arthrodesis: A High-speed Dual Fluoroscopy Study

Spencer Kendell, University of Utah

Osteoarthritis (OA) of the tibiotalar joint is a major cause of ankle pain, and is currently treated using one of two methods: fusion of the tibiotalar joint (i.e. arthrodesis) and total ankle replacement (TAR). Although the ankle joint seems simple, it is actually comprised of two complex, articulating interfaces: the tibiotalar and the subtalar joint, which represent the interface between the tibia and talus and talus and calcaneus, respectively. While arthrodesis and TAR are able to relieve pain in the short-term, many patients develop complications from surgery that can be difficult to address. Furthermore, patients who have received a tibiotalar arthrodesis commonly develop OA in the subtalar joint, which is thought to be caused by the subtalar joint having to compensate for motion lost at the tibiotalar joint as a result of fusion. Due to the difficulties associated with measuring the motion of small bones in the foot and ankle, the precise joint kinematics of the ankle are not yet realized. This work will study the kinematic differences in the subtalar joint between subjects with non-pathological, native joints in one ankle and tibiotalar fusion in the other ankle. This will be done using dual fluoroscopy to image the ankle joints in vivo, while subjects perform a double-heel-rise activity. Computed tomography (CT) scans are acquired of each subject’s ankles and used to create three-dimensional computerized models of the tibia, talus, and calcaneus. These three-dimensional models of the ankle bones are then synced with the dual fluoroscopy images to determine the three-dimensional (3D) position and orientation of each bone throughout the heelrise activity. These bone positions are then used to calculate joint angles and translations (kinematics) throughout the activity. The kinematics of the fused ankle will be compared to the contralateral ankle to determine the effects of ankle fusion on subtalar mobility. It is expected that mechanistic differences between the subtalar joint of the contralateral and fused ankles will lend insight into the properties and motions of the joints. Specifically, it is hypothesized that tibiotalar arthrodesis will lead to compensatory hypermobility in the subtalar joint, since it is adjacent to the fused tibiotalar joint. Hypermobility of these adjacent joints may contribute to the development of OA in these joints, as observed clinically. Such findings will promote the development of improved surgical planning tools and novel techniques to treat tibiotalar OA.