Predictors of Deformity in Patients with Progressive Collapsing Foot Deformity and Valgus of the Ankle

CATEGORY: Ankle; Hindfoot INTRODUCTION/PURPOSE: Markers of diagnosis and severity are well studied in patients with Progressive Collapsing Foot Deformity (PCFD). Medial facet subluxation (MFS) in weight-bearing computerized tomography (WBCT) has been established as an indicator of peritalar subluxation and an earlier detector of the disease. When the disease affects the ankle leading to a valgus talar tilt (class E), structures distal to this topography may behavior differently, trying to compensate proximal deformity. The aim of this study is to assess predictors of deformity in PCFD patients with and without valgus of the ankle. Our hypothesis is that MFS could not be used in class E patients as an accurate value for estimation and staging of PCFD. METHODS: In this IRB-approved retrospective case-control study we analyzed WBCT acquisitions of 21 consecutive patients with PCFD presenting valgus of the ankle and 64 controls (flexible PCFD with no ankle involvement). MFS (percentage of uncoverage), middle facet incongruence angle, middle cuneiform-to-floor distance, forefoot arch angle, talonavicular uncoverage angle, hindfoot moment arm (HMA), Foot and Ankle Offstet (FAO) and talar tilt angle (TTA) were obtained and compared between groups using oneway ANOVA. A multivariate regression analysis was performed to evaluate which of the measurements influenced the alignment. A partition prediction model was also constructed to find how the variables contributed to the deformity and its aspects. Statistical significancy was set in p values <0.05. RESULTS: We found differences among groups only for MFS, HMA, FAO and TTA, with a lower mean value of MFS in patients with valgus of the ankle. An inverse relation between MFS and TTA was obtained in this group, demonstrated by increase in the talar tilt and decrease in middle facet uncoverage. MFS affected FAO values in the control group (R2: 0.25) but not in the ankle valgus group (R2: 0.001), being that this last one was influenced mainly by the TTA (R2: 0.53). A FAO value higher than 12.14 was found to be a strong predictor of deformity at the ankle. CONCLUSION: MFS was lower in patients with PCFD and valgus of the ankle, demonstrated as a weak predictor of deformity severity. In this group of patients (class E), talar tilt angle and Foot and Ankle Offset should be used as disease markers. A FAO value above 12.14 must be appreciated as a possible sign of ankle involvement in PCFD patients.