Three-Dimensional Distance Maps of Ankle and Syndesmotic Joints from Weightbearing CT in Progressive Collapsing Foot Deformity: A Retrospective Case-Control Study

Abstract

Category: Ankle Introduction/Purpose: Recently, weightbearing computed tomography (WBCT) has been utilized to provide more comprehensive and accurate assessment of complex foot and ankle deformities, notably to diagnose and stage Progressive Collapsing Foot Deformity (PCFD). The 3D data provided by WBCT has enabled the developed of novel tools like distance mapping (DM), coverage mapping (CM), and volume measurements. Over the past year, novel DM and CM have shown promise in providing sensitive automated measures of peritalar subluxation, a major component of PCFD. However, the early effects of PCFD on the tibiotalar joint have not yet been quantified. This study sought to use DM and CM to objectively characterize the effects of PCFD on the tibiotalar and tibiofibular joints. We hypothesized that changes seen in early PCFD will be identified. Methods: IRB approval for retrospective review of patient data from 2014-2020 was obtained to identify patients with clinical and radiographic diagnoses of PCFD. The first consecutive 20 patients with symptomatic flexible PCFD and high-resolution weightbearing CT examination without arthritis that had not undergone prior surgery were selected and compared with 20 controls. Fully automated volume measurements of the syndesmosis at 1cm, 3cm, and 5cm from the tibiotalar joint were performed as well as of the medial and lateral tibiotalar gutters based on models created in Disior Bonelogic. Distance Maps (DMs) were obtained for the tibiofibular incisura, tibiotalar joint, and gutters. Coverage maps (CMs) were created using the measured 3DDMs to identify joint interaction, subluxation, and impingement. Data were checked for normality using the Shapiro- Wilk W test. Two-tailed independent samples student t-tests or Wilcoxon Tests were used to assess differences between groups. Results: There were significant decreases in coverage of all 3 anterior regions of the tibiotalar joint in PCFD patients when compared to controls along with corresponding significant increases in coverage of all 3 posterior regions (Figure). There were no significant differences in mean or minimum distances in any region of the tibiotalar joint surface. Significant increases in average and minimum DMs of the anterior medial (36%, p<0.01, 19%, p<0.03) gutter were observed with significant decreases in coverage of both anterior medial and anterior lateral regions. Significant decreases in the average and minimum distances of the tibiofibular joint were found anteriorly in PCFD patients compared to controls (-26%, p<0.006). There were no significant differences in overall syndesmotic distance or volume at any level. Conclusion: The results of our study were able to identify that, compared to controls, patients with early stage PCFD demonstrated significant tibiotalar and tibiofibular joint changes ahead of developing the tibiotalar narrowing associated with arthritis and syndesmotic widening associated with instability. Decreases in anterior coverage with increases posteriorly support early plantarflexion of the talus in PCFD. When combined with plantarflexion of the talus and unchanged syndesmotic volume, decreases in anterior tibiofibular distances support the absence of syndesmotic joint instability in early PCFD. Novel tools may assist with clinical decision-making regarding restoration of normal tibiotalar and tibiofibular alignment during PCFD correction.