Defining Radiographic Threshold Values for the Progressive Collapsing Foot Deformity Classification System: A...

Area of Science:

• Orthopedics and Foot & Ankle Surgery
• Radiology and Medical Imaging
• Biomechanical Engineering

Background:

• Progressive Collapsing Foot Deformity (PCFD) classification currently relies on subjective interpretation of clinical and radiographic data.
• Existing classification methods for PCFD (Classes A-D) lack standardized quantitative thresholds, impacting diagnostic consistency.
• Objective measurement criteria are needed to enhance the reliability of PCFD classification for clinical and surgical decision-making.

Purpose of the Study:

• To establish objective, evidence-based cut-off threshold values for commonly used PCFD measurements.
• To assess diagnostic performance of these thresholds for PCFD Classes A-D using large patient and control cohorts.
• To identify independent predictors of symptomatic PCFD.

Main Methods:

• Prospective comparative diagnostic study involving 154 asymptomatic volunteers and 321 PCFD patients.
• Weight-bearing computed tomography (WBCT) was performed, with blinded segmentation for measurements including hindfoot moment arm (HMA), talonavicular coverage angle (TNCA), talus-first metatarsal angles (TFMA-A, TFMA-S), forefoot arch angle (FAA), and facet coverage (MF, PF, ST).
• Receiver operating characteristic (ROC) curves and Youden indexes identified optimal cut-offs; multivariate analysis identified independent predictors.

Main Results:

• Robust cut-off values were established for PCFD Classes A-D with high diagnostic performance (Area Under Curve [AUC] ≥ 80% for most measurements).
• Optimal cut-offs include: HMA ≥ 13.9 mm (AUC 85.3%), TNCA ≥ 38.7° (AUC 84.4%), TFMA-A ≥ 20.3° (AUC 82.1%), FAA ≤ 8.7° (AUC 83.9%), TFMA-S ≥ 18.7° (AUC 82.9%), MF coverage ≤ 73.5% (AUC 73.4%), PF coverage ≤ 84.5% (AUC 82.7%), and ST coverage ≥ 25.7% (AUC 84.4%).
• Hindfoot moment arm (HMA), talonavicular coverage angle (TNCA), middle facet (MF), and sinus tarsi (ST) coverages were identified as independent predictors of PCFD.

Conclusions:

• This study successfully established reliable cut-off values for PCFD measurements (Classes A-D), significantly improving diagnostic capabilities.
• These quantitative thresholds enhance the clinical applicability and reliability of the PCFD classification system.
• The findings support improved clinical and surgical decision-making and provide a foundation for future PCFD research.