Weightbearing Radiographic Predictors of Middle Facet Subluxation in Progressive Collapsing Foot Deformity

Area of Science:

• Orthopedics
• Radiology
• Foot and Ankle Surgery

Background:

• Middle facet subluxation (MFS) is a critical indicator of peritalar subluxation in progressive collapsing foot deformity (PCFD).
• Current assessment of MFS primarily relies on weightbearing computed tomography (WBCT).
• The correlation between weightbearing radiographic (WBR) measurements and MFS requires further investigation.

Purpose of the Study:

• To determine which WBR measurements correlate with MFS in patients with PCFD.
• To test the hypothesis that hindfoot alignment parameters measured via WBR are associated with MFS.

Main Methods:

• Seventy-three feet with PCFD underwent both WBR and WBCT.
• Key radiographic parameters (talonavicular coverage angle, hindfoot moment arm, etc.) were measured.
• Regression and partition analyses identified WBR predictors and cutoff values for MFS.

Main Results:

• Talonavicular coverage (TNC) angle and hindfoot moment arm (HMA) were identified as combined predictors of MFS (R² = 0.524).
• TNC angle showed a moderate individual correlation (r = 0.68), while HMA had a weaker correlation (r = 0.39).
• Established thresholds (TNC ≥ 38°, HMA ≥ 11.4 mm) for MFS ≥ 18% explained only 27.3% of the variability.

Conclusions:

• TNC angle and HMA are the most valuable WBR measurements for detecting MFS in PCFD.
• These WBR parameters provide a practical assessment tool in the absence of WBCT.
• The identified cutoffs explain a limited portion of MFS variability, indicating other factors are involved.