Background: Compared with computed tomography (CT), magnetic resonance imaging (MRI) might overestimate the condition of osteochondral lesions of the talus (OLTs) owing to subchondral bone marrow edema and the overlying cartilage defect. However, no study has compared MRI and CT directly in evaluating OLTs with subchondral cysts. Purpose: To compare the reliability and validity of MRI and CT in evaluating OLTs with subchondral cysts. Study Design: Cohort study (diagnosis); Level of evidence, 2. Methods: An institutional radiology database was queried for inpatients diagnosed with OLTs with subchondral cysts who had undergone surgical treatment between May 2015 and October 2019. A total of 48 patients met the inclusion criteria. Based on our measurement method, 2 experienced observers who were blinded to the study independently measured the length, width, and depth of the cysts using MRI and CT. The classification of cystic lesions was also performed based on MRI and CT findings. Results: Interobserver reliability was almost perfect, with intraclass correlation coefficients (ICCs) ranging from 0.935 to 0.999. ICCs for intraobserver reliability ranged from 0.944 to 0.976. The mean size of cysts measured on MRI (length, 13.38 ± 4.23 mm; width, 9.28 ± 2.28 mm; depth, 11.54 ± 3.69 mm) was not significantly different to that evaluated on CT (length, 13.40 ± 4.08 mm; width, 9.25 ± 2.34 mm; depth, 11.32 ± 3.54 mm). The size of subchondral cysts was precisely estimated on both MRI and CT. The MRI classification and CT classification revealed almost perfect agreement (kappa = 0.831). Conclusion: With our measurement method, both MRI and CT were deemed to be reliable and valid in evaluating the size of subchondral cysts of OLTs, and the MRI classification was well-correlated with the CT classification. The presented measurement method and classification systems could provide more accurate information before surgery.

Background Current classifications emphasize the morphology of the coalition, however, subtalar joint facets involved should also be emphasized. Objective The objective of this study was to develop a new classification system based on the articular facets involved to cover all coalitions and guide operative planning. Methods Patients were diagnosed with talocalcaneal coalition using a CT scan, between January 2009 and February 2021. The coalition was classified into four main types according to the shape and nature of the coalition: I, inferiorly overgrown talus or superiorly overgrown calcaneus; II, both talus and calcaneus overgrew; III, coalition with an accessory ossicle; IV, complete osseous coalition (I-III types are non-osseous coalition). Then each type was further divided into three subtypes according to the articular facets involved. A, the coalition involving the anterior facets; M, the coalition involving the middle facets, and P, the coalition involving the posterior facets. Interobserver reliability was measured at the main type (based on nature and shape) and subtype (articular facet involved) using weighted Kappa. Results There were 106 patients (108 ft) included in this study. Overall, 8 ft (7.5%) were classified as type I, 75 ft (69.4%) as type II, 7 ft (6.5%) as type III, and 18 ft (16.7%) as type IV. Twenty-nine coalitions (26.9%) involved the posterior facets only (subtype-P), 74 coalitions (68.5%) involved both the middle and posterior facets (subtype-MP), and five coalitions (4.6%) simultaneously involved the anterior, middle, and posterior facets (subtype-AMP). Type II-MP coalition was the most common. The value of weighted Kappa for the main type was 0.93 (95%CI 0.86–0.99) (p<0.001), and the value for the subtype was 0.78 (95%CI 0.66–0.91) (p<0.001). Conclusion A new classification system of the talocalcaneal coalition to facilitate operative planning was developed.

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