A new classification of talocalcaneal coalitions based on computed tomography for operative planning.

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.