Plain Radiographs Underestimate Tibiotalar Tilt in Progressive Collapsing Foot Deformity.

BACKGROUND: Accurate evaluation of tibiotalar alignment is essential for staging and surgical planning in progressive collapsing foot deformity (PCFD), yet plain radiographs are limited by their 2-dimensional nature and variability in beam angulation. This study pursued 3 objectives: to quantify discrepancies in tibiotalar tilt (TT) between plain radiographs (XRs) and weightbearing CT (WBCT), to compare the prevalence of significant valgus tilt between modalities, and to identify features associated with underrecognized deformity on XRs. METHODS: ≥ 4°) and No-discrepancy groups, and group characteristics were compared. Interobserver and intraobserver reliability were assessed using intraclass correlation coefficients (ICCs). RESULTS: < .001), suggesting anterior deformities visualized on WBCT are not reliably captured on radiographs. Interobserver reliability ranged from 0.80 to 0.86 and intraobserver reliability from 0.88 to 0.89 (ICC). CONCLUSION: Plain radiographs underestimate valgus tibiotalar tilt compared with WBCT, mainly because of limited visualization of the anterior joint. Surgeons should recognize that reliance on XRs alone may lead to underrecognition of ankle valgus alignment in patients with PCFD. As WBCT is not universally available, optimizing XR projection angles may better capture anterior tibiotalar alignment and improve preoperative planning. LEVEL OF EVIDENCE: Level III, retrospective diagnostic.