3D Imaging for Hindfoot Alignment: A Comparative Study between MRI and Weight Bearing CT

CATEGORY: Hindfoot; Other INTRODUCTION/PURPOSE: Hindfoot malalignment is a common finding in multiple foot and ankle pathologies. In clinical practice, it is usually quantified through traditional weight bearing radiographs or, more recently, through cone beam weight bearing CT (CB- WBCT), which overcomes issues related to two-dimensional imaging. Interestingly, a few studies have suggested that hindfoot alignment can also be accurately assessed using non-weight bearing magnetic resonance imaging (MRI). The purpose of this study was to compare measurements of hindfoot alignment on non-weight bearing ankle MRI and CB-WBCT and to establish if there was any correlation. METHODS: In this Level III retrospective comparative study, a database review identified 51 feet in 47 patients (27 males, 20 females; mean age of 45 (range 13-79)) which had both CB-WBCT and MRI scans on the same day as part of standard care at our specialist tertiary referral Foot and Ankle Unit. Hindfoot alignment was assessed by independent Consultant Musculoskeletal specialists. The foot ankle offset (FAO), calcaneal offset (CO) and hindfoot alignment angle (HA) were assessed on CB-WBCT using dedicated software. The tibiocalcaneal angle (TCA) and calcaneofibular ligament angle (CFLA) were assessed on non-weight bearing MRI. Pearson correlation was used to evaluate the correlation between these measurements. RESULTS: We found a statistically significant positive correlation between TCA on non-weight bearing MRI and each measurement on CB-WBCT (Pearson correlation for TCA and FAO: 0.42, p=0.003; for TCA and CO: 0.46, p=0.001; and for TCA and HA: 0.40, p=0.005).We also demonstrated a moderate-to-low negative but significant correlation between CFLA and CO (Pearson correlation: -0.35; p=0.03). Conversely, the negative correlation between CFL and FAO (Pearson correlation: -0.29; p=0.07) and CFL with HA (Pearson correlation: -0.26; p=0.11) did not reach statistical significance. CONCLUSION: Weight bearing three-dimensional imaging has shown high degrees of accuracy and reproducibility for hindfoot alignment. The significant correlation between TCA on non-weight bearing MRI and hindfoot alignment measurements on CB- WBCT suggests that TCA should be reported during routine ankle MRI in order to put into context some of the soft-tissue findings. The CFLA shows a less significant negative correlation.