Three-Dimensional Distance and Coverage Maps in the Assessment of Peritalar Subluxation in Progressive Collapsing Foot Deformity

Abstract

Background: Progressive collapsing foot deformity (PCFD), formerly termed adult-acquired flatfoot deformity, is a complex 3-dimensional (3D) deformity of the foot characterized by peritalar subluxation (PTS). PTS is typically measured at the posterior facet, but recent studies have called this into question. The objective of this study was to use 3D distance mapping (DM) from weightbearing computed tomography (WBCT) to assess PTS in patients with PCFD and controls. We hypothesized that DMs would identify the middle facet as a superior marker for PTS. Methods: We analyzed WBCT data of 20 consecutive stage I patients with PCFD and 10 control patients with a novel DM technique to objectively characterize joint coverage across the entire peritalar surface, including both articular and nonarticular regions. Joint coverage was defined as the percentage of articular area with DMs <4 mm and impingement when distances were <0.5 mm. Comparisons were performed with independent t tests or Wilcoxon tests. P values <.05 were considered significant. Results: Overall, coverage was decreased in articular regions and impingement was increased in nonarticular regions of patients with PCFD with a significant increase in uncoverage in the middle (46.6%, P < .001) but not anterior or posterior facets. Significant increases in sinus tarsi coverage were identified (98.0%, P < .007) with impingement in 6 of 20 patients with PCFD. Impingement of the subfibular region was noted in only 1 of 20 cases but narrowing greater than 2 standard deviations was noted in 17 of 20 patients. Conclusion: Objective DMs identified significant markers of PTS in the middle but not posterior or anterior facets. We confirmed prior 2-dimensional data that suggested uncoverage of the middle facet provided a more robust and consistent measure of PTS than measures in the posterior facet. Level of Evidence: Level III, case-control study.