BACKGROUND: The size of talocalcaneal tarsal coalitions (TCCs) is one of the main factors that is thought to influence patient outcomes after resection. Magnetic resonance imaging (MRI) is increasingly being used to diagnose and characterize TCCs. However, there is no reproducible MRI-based measurement of TCC size reported in the literature. The purpose of this study was to create a method to reproducibly measure TCC size using MRI. METHODS: Twenty-seven patients with TCCs diagnosed by a hindfoot coronal proton density (PD) MRI between 2017 and 2020 were included. Five independent raters measured coalition width, healthy posterior facet width, and healthy middle facet width on individual slices of coronal PD hindfoot MRIs using discrete MRI measurement guidelines. Individual slice measurements were summed to determine total size of the coalition and the remaining healthy cartilage of the posterior and middle facets. Inter-rater reliability of MRI measurements between the 5 independent examiners was evaluated using intraclass correlation coefficient (ICC). ICC was calculated for total coalition width, total healthy posterior facet width, total coalition width/total healthy posterior facet width, total coalition width/total healthy middle facet width, total coalition width/total healthy subtalar facet width (posterior facet+middle facet), and total coalition width/total subtalar facet width (coalition+posterior facet+middle facet). RESULTS: The ICC scores for all but one of the MRI measurements indicated good to excellent inter-rater reliability among the 5 examiners. The ICC was 0.932 (95% confidence interval: 0.881-0.966) for measurement of total coalition width/total healthy posterior facet width and 0.948 (95% confidence interval: 0.908-0.973) for measurement of total coalition width/total subtalar facet width (middle+posterior+coalition). CONCLUSIONS: Measurements of coalition size using novel MRI guidelines were reproducible with good to excellent inter-rater reliability. These guidelines allow for determination of TCC size using coronal PD MRI. LEVEL OF EVIDENCE: Level II-diagnostic reproducibility study.
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