Automated vs Manual Measurement of Middle Facet Subluxation in Progressive Collapsing Foot Deformity Using Weightbearing CT

Background: Peritalar subluxation (PTS) is a key driver of symptomatic progression in progressive collapsing foot deformity (PCFD). Middle facet subluxation (MFS) is an established weightbearing computed tomography (WBCT) parameter to quantify PTS, but manual measurement is time consuming and dependent on rotation and slice selection. Automated WBCT-based tools may streamline measurement and improve reproducibility. Methods: Retrospective, institutional review board-approved study including 66 PCFD patients and 25 normally aligned controls. Manual MFS (mMFS) was measured by 2 fellowship-trained surgeons, repeated for intra- and interrater reliability. Automated MFS (aMFS) was calculated using a developer-level version of BoneLogic (Disior). Agreement was assessed using paired tests, correlations, intraclass correlation coefficients (ICCs), and Bland-Altman analysis. Results: < .01). Across all cases, manual interrater ICC was 0.80, manual-automated ICC 0.76, and manual intrarater ICC 0.72. Agreement was moderate-to-good in PCFD but weaker in controls. Correlation between mMFS and aMFS was strong overall and moderate in PCFD. Bland-Altman analysis demonstrated minimal bias in PCFD (0.99%), within the a priori 1% acceptability threshold, whereas bias exceeded this threshold in controls (6.66%). Conclusion: This study evaluates agreement between manual and a predominantly automated WBCT-based MFS measurement. Automated MFS showed moderate to good agreement and interchangeability with manual methods in PCFD, whereas agreement was limited in controls. These findings support the potential clinical and research utility of automated MFS in PCFD class D assessment, following external validation. Level of Evidence: Level III, diagnostic study.