As the name implies, the talocalcaneonavicular (TCN) joint is a combination of the talonavicular joint and the subtalar (talocalcaneal) joint, which are both anatomically and functionally related (Fig. 16-17).157 The TCN synovial cavity is demarcated from the posterior subtalar cavity by the contents of the sinus and canalis tarsi. Ligamentous structures form an anatomic barrier between the posterior facet of the subtalar joint and its companion facets (the middle and anterior facets). This space houses the deep insertions of the inferior extensor retinaculum that cross anterior to the interosseous talocalcaneal ligament.