In-vivo validation of a high-speed biplane videoradiography pipeline for foot and ankle joint kinematics

Pathological ankle conditions alter joint kinematics and contribute to degeneration in adjacent hindfoot and midfoot joints. Accurate in-vivo assessment of these motions is essential for understanding disease progression and guiding clinical interventions. Biplane videoradiography (BVR) is a tool for six-degree-of-freedom in-vivo bone kinematics, but validation against gold-standard radiostereometric analysis (RSA) is needed for each new joint of interest and BVR configuration. This study validated a BVR system using one participant instrumented with tantalum beads in the tibia, fibula, talus, calcaneus, cuboid, and navicular. Dynamic imaging was acquired during walking, step-up, step-down, and heel rise. Bone motions were tracked using model-based tracking (MBT) and compared to RSA. Root mean square (RMS) error and coefficient of multiple correlation analyses quantified accuracy and inter-/intra-rater variability, respectively. The mean angular MBT RMS error was 1.37 ± 0.23° across all joints. The greatest error was 1.66 ± 0.19° in the talonavicular joint and the smallest error was 0.97 ± 0.19° in the subtalar joint. The mean translational MBT RMS error was 2.05 ± 0.58 mm across all joints. The greatest error was 2.83 ± 0.21 mm in the calcaneocuboid joint, while the smallest error was 1.20 ± 0.29 mm in the subtalar joint. The coefficient of multiple correlations scores for intra-rater repeatability ranged from 0.545 to 0.996. Joint accuracy errors are more clinically relevant and exceeded bone accuracy errors, reflecting compounded tracking of multiple bones. These findings indicate that BVR MBT is accurate in assessing foot and ankle kinematics and can be translated to pathological research.