Foot and Ankle International - 2026-07-07 - Journal Article
Defining Radiographic Threshold Values for the Progressive Collapsing Foot Deformity Classification System: A Large-Cohort Diagnostic Study.
Belayneh R, Lintz F, Mansur NSB, Talaski G, Anderson D, Ellis SJ, de Cesar Netto C
Topics
Key Takeaway
WBCT-derived cut-off values for PCFD classes A–D achieve AUCs of 73–85%, with HMA ≥13.9 mm, TNCA ≥38.7°, FAA ≤8.7°, and sinus tarsi coverage ≥25.7% as the strongest independent predictors of symptomatic PCFD.
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Summary
This prospective comparative diagnostic study used WBCT to establish ROC-derived threshold values for radiographic measurements across PCFD classes A–D in 321 symptomatic patients versus 154 neutrally aligned controls. Optimal cut-offs were: HMA ≥13.9 mm (class A, AUC 85.3%), TNCA ≥38.7° (class B, AUC 84.4%), FAA ≤8.7° (class C, AUC 83.9%), and ST coverage ≥25.7% (class D, AUC 84.4%). Multivariate analysis identified HMA, TNCA, middle facet coverage, and sinus tarsi coverage as independent predictors of symptomatic PCFD.
Key Limitation
Class E (ankle valgus) was excluded entirely, limiting applicability to the most advanced and surgically complex PCFD presentations.
Original Abstract
BACKGROUND
The Progressive Collapsing Foot Deformity (PCFD) classification categorizes deformity patterns into 5 classes (A, hindfoot valgus; B, midfoot/forefoot abduction; C, medial column collapse; D, peritalar subluxation; E, ankle valgus). Currently, the classifying process relies on surgeons' experience and interpretation of clinical and radiographic measurements. The goal of the present study was to establish cut-off threshold values for commonly used PCFD measurements assessing class A to D, using 2 large cohorts of PCFD patients and controls.
METHODS
This prospective comparative diagnostic study included 154 neutrally aligned or asymptomatic flatfoot volunteers (103 females, mean age 41.7 years, body mass index [BMI] 28.9) and 321 PCFD patients (136 females, mean age 50.7 years, BMI 29.8). Participants underwent weight-bearing computed tomography (WBCT). Measurements were obtained after blinded segmentation and included hindfoot moment arm (HMA, class A), talonavicular coverage angle (TNCA) and talus-first metatarsal angle axial (TFMA-A, class B), talus-first metatarsal angle sagittal (TFMA-S) and forefoot arch angle (FAA, class C), and coverage maps (middle facet [MF], posterior facet [PF], sinus tarsi [ST], class D). Receiver operating characteristic curves, Youden indexes, and areas under the curves (AUCs) identified optimal cut-offs. A partition prediction model refined those values, and a multivariate analysis identified independent predictors of symptomatic PCFD.
RESULTS
Optimal cut-off values (all P < .0001) included the following: HMA ≥ 13.9 mm (AUC 85.3%, class A); TNCA ≥ 38.7° (AUC 84.4%) and TFMA-A ≥ 20.3° (AUC 82.1%, class B); FAA ≤ 8.7° (AUC 83.9%) and TFMA-S ≥ 18.7° (AUC 82.9%, class C); MF coverage ≤ 73.5% (AUC 73.4%), PF coverage ≤ 84.5% (AUC 82.7%), and ST coverage ≥ 25.7% (AUC 84.4%, class D). HMA, TNCA, MF, and ST coverages were identified as independent predictors of PCFD.
CONCLUSION
This study established robust cut-off values for PCFD measurements across classes A-D using large comparative cohorts, significantly enhancing diagnostic performance (AUC ≥ 80% for most). These thresholds improve the clinical applicability and reliability of the PCFD classification, supporting clinical and surgical decision making and facilitating future comparative research.
LEVEL OF EVIDENCE
Level II, prospective comparative diagnostic study.