Pediatric PCFD Exhibits Less Forefoot Abduction and Middle Facet Subluxation Than Non-Pediatric PCFD: A Weight-Bearing CT Analysis
Authors: Acker Antoine , Jesus Huanuco Casas Erik , Forin Valvecchi Tommaso , Joan Luo Emily , Kuehn Sally , Carvalho Kepler A.M. , Anastasio Albert T. , Easley Mark E. , Wang Chien-Shun , Cesar Netto Cesar de 
Published: December 2024

Category: Hindfoot; Midfoot/Forefoot Introduction/Purpose: Progressive Collapsing Foot Deformity (PCFD) is a symptomatic, complex, three-dimensional foot deformity that can occur in feet that were previously neutrally aligned or in those with congenital/pediatric flat feet. Once collapsed, it becomes challenging to differentiate the initial foot shape. This study aims to evaluate differences in Weight-Bearing CT (WBCT) parameters among a cohort of symptomatic PCFD patients with a history of pediatric flat foot (= pediatric PCFD), without such a history (= non-pediatric PCFD), and a control group without PCFD. We hypothesized that pediatric PCFD would display distinct WBCT parameters compared to non-pediatric PCFD, particularly with less forefoot abduction and middle facet subluxation. Furthermore, we sought to identify which parameters are the most predictive of pediatric PCFD. Methods: This retrospective comparative study included adult patients with symptomatic PCFD. Pediatric PCFD was defined as patients with flat feet since childhood, and non-pediatric PCFD was defined as patients with no history of childhood flat foot. A total of 37 symptomatic pediatric PCFD patients were compared to 52 symptomatic non-pediatric PCFD patients and 11 control patients. All patients underwent foot/ankle WBCT scans. Using dedicated software, both manual and semi-automated 3D measurements were carried out for the various PCFD deformity categories (A-Hindfoot Valgus, B-Abduction, C-Arch Collapse, and D-Peritalar Subluxation). The data underwent normality testing with the Shapiro-Wilk method, and comparisons were made via Paired T-tests or Paired-Wilcoxon tests. A p-value threshold of 0.05 or below was deemed significant. To determine which factors affect the presence of rigidity in PCFD, a multivariate nominal regression analysis was conducted. A partition prediction model was employed to identify threshold values that most accurately determine “pediatric PCFD”. Results: All parameters showed significant differences compared to control, except for BMI. Compared to non-pediatric PCFD, the pediatric PCFD group showed significantly less deformity in classes A, B, C, and D (all p< 0.002) and became symptomatic at a younger age (p< 0.001). Compared to controls, pediatric PCFD measurements for HMA (p=0.053) and SF (p=0.07) were not statistically significant. Multivariate analysis indicated that axial TFM (p=0.005), MFS (p=0.013), and ST (p=0.03) were the best predictors of pediatric PCFD (R2: 0.27). The partition prediction model showed that an ST distance >0.24 mm, axial TFM >24.28, and MFS >43.7% can rule out pediatric PCFD with 95% confidence. Conclusion: This study showed that symptomatic pediatric PCFD presents with distinct WBCT parameters compared to symptomatic non-pediatric PCFD, notably exhibiting less forefoot abduction, less middle facet subluxation, and less hindfoot malalignment and seems to become symptomatic at a younger age. ST distance >0.24 mm, axial TFM >24.28, and MFS >43.7% could rule out a PCFD with “pediatric origin.” These results suggest that a different threshold should be set to assess PCFD in patients with flat feet since childhood.