Distance mapping and volumetric assessment of the ankle and syndesmotic joints in progressive collapsing foot deformity.

The early effects of progressive collapsing foot deformity (PCFD) on the ankle and syndesmotic joints have not been three-dimensionally quantified. This case-control study focused on using weight bearing CT (WBCT) distance (DM) and coverage maps (CM) and volumetric measurements as 3D radiological markers to objectively characterize early effects of PCFD on the ankle and syndesmotic joints. Seventeen consecutive patients with symptomatic stage I flexible PCFD and 20 matched controls that underwent foot/ankle WBCT were included. Three-dimensional DM and CM of the ankle and syndesmotic joints, as well volumetric assessment of the distal tibiofibular syndesmosis was performed as possible WBCT markers of early PCFD. Measurements were compared between PCFD and controls. Significant overall reductions in syndesmotic incisura distances were observed in PCFD patients when compared to controls, with no difference in the overall syndesmotic incisura volume at 1, 3, 5 and 10 cm proximally to the ankle joint. CMs showed significantly decreased articular coverage of the anterior regions of the tibiotalar joint as well as medial/lateral ankle joint gutters in PCFD patients. This study showed syndesmotic narrowing and decreased articular coverage of the anterior aspect of the ankle gutters and talar dome in stage I PCFD patients when compared to controls. These findings are consistent with early plantarflexion of the talus within the ankle Mortise, and absence of true syndesmotic overload in early PCFD, and support DM and CM as early 3D PCFD radiological markers.