Correlation of Talar Anatomy and Subtalar Joint Alignment on Weightbearing Computed Tomography With Radiographic Flatfoot Parameters

Background: Underlying bony deformity may be related to development of adult-acquired flatfoot deformity (AAFD). Multiplanar weightbearing (MP-WB) computed tomography can be used to identify subtalar deformity which may contribute to valgus hindfoot alignment. On coronal MP-WB images, 2 angles reliably evaluate the subtalar joint axis: the angle between the inferior facet of the talus and the horizontal (inftal-hor) and the angle between the inferior and superior facets of the talus (inftal-suptal). Although these angles have been shown to differ significantly between flatfoot patients and controls, no study has investigated their relationships with other components of AAFD. We hypothesized that these angles would correlate strongly with commonly used radiographic measures of AAFD. Methods: Forty-five patients with stage II AAFD and 17 control patients underwent MP-WB imaging and standard weightbearing radiographs. MP-WB measurements were correlated with standard radiographic measurements of AAFD. Differences between AAFD and control patients were assessed using independent samples t tests and Mann-Whitney U tests. To assess correlations between each MP-WB measurement and radiographic measurement, factorial generalized linear models (GLMs) were constructed. Results: Patients with AAFD differed from the controls in all measured angles (P ≤ .001 for each). After accounting for differences between flatfoot and control patients, inftal-hor was not significantly correlated with any of the radiographic angles. Inftal-suptal, however, correlated with the AP coverage angle, AP talar–first metatarsal angle, calcaneal pitch, Meary’s angle, medial column height, and hindfoot alignment after accounting for differences between flatfoot patients and controls. Meary’s angle alone explained 48% of the variation in inftal-suptal angles. Conclusion: As measured on coronal MP-WB images, patients with stage II AAFD had more innate valgus in their talar anatomy as well as more valgus alignment of their subtalar joints than did control patients. It is possible that this information could be used to identify patients likely to have progression of deformity and may ultimately guide the approach to operative reconstruction. Level of Evidence: Level III, case-control study.