Distance Mapping of the Foot and Ankle Joints using Weight Bearing CT: The Cavovarus Configuration

CATEGORY: Ankle; Hindfoot; Midfoot/Forefoot INTRODUCTION/PURPOSE: The cavovarus configuration sets the grounds for various pathological conditions, often involving the arthritic degeneration of the medial column. The objective of this study was to analyze the joint surface interaction at the ankle, hindfoot and midfoot joints using distance mapping on WBCT images in a series of cavovarus feet and compare them to normally aligned feet. METHODS: In this case-control study, a database containing WBCT datasets from 370 feet (189 patients) obtained in a specialized foot and ankle unit from July 2016 to October 2018 was used. Ten feet (10 patients) with asymptomatic cavovarus shape were extracted (cases group; N= 10) and compared to 10 matched-paired (by age, gender and body mass index) normally aligned feet (10 patients) (controls group; N=10). Colored distance maps were generated for the ankle, hindfoot and midfoot joints and divided in zones, therefore differences were assessed between the two groups. RESULTS: In the cavovarus group there was a significant increase in surface-to-surface distance at the posterior tibiotalar joint and a reduced distance at the anterior part, together with a greater distance at the posterior half of the medial gutter. Also, a decrease in surface-to-surface distance on the anterior half of the anterior facet and an increased distance on the posterior quadrants of the posterior facet of the subtalar joint were found. At the sinus tarsi, the lateral aspect of the talonavicular joint, the naviculocuneiform and the tarsometatarsal joints there was a statistically significant increase in surface-to-surface distance in cavovarus patients as compared to controls. CONCLUSION: In this study, the use of distance mapping analysis on WBCT images enabled to identify significant differences in surface-to-surface interaction at the foot and ankle joints between cavovarus and normally-aligned feet.