Joint-specific kinematic deviations in asymptomatic flatfoot using biplane fluoroscopy

Asymptomatic flatfoot (AFF) is characterized by structural features of a medial arch collapse in the absence of pain, yet its dynamic biomechanical characteristics remain understudied. This study aimed to quantify and compare three-dimensional, multi-joint foot and ankle kinematics between individuals with AFF and healthy controls during walking and heel rise tasks using biplane fluoroscopy. Twenty-three participants (13 controls, 10 AFF) underwent weightbearing computed tomography to generate subject-specific bone models. Dynamic in vivo kinematics of the tibia, fibula, talus, and calcaneus were captured using biplane fluoroscopy during walking and heel rise. Joint kinematics for the tibiotalar, subtalar, tibiofibular, and talofibular joints were calculated using model-based tracking and analyzed using statistical parametric mapping. Range of motion (ROM) was also compared between groups. No significant differences in joint kinematics were observed between groups during walking. Walking ROM differences were observed only before FDR correction and were therefore interpreted as exploratory. During heel rise, AFF maintained a more everted subtalar position after SPM FDR correction and demonstrated reduced sagittal plane ROM at the tibiotalar and talofibular joint after ROM FDR correction. These findings indicate that significant group differences were detected during heel rise but not during walking within separate task specific analyses. These task dependent differences provide insight into biomechanical adaptations associated with AFF morphology, although longitudinal studies are needed to determine whether these differences are related to future symptom development or deformity progression.