The talocalcaneonavicular joint (TCN joint) is a functional ball-and-socket articulation formed by the head of the talus fitting into a socket created by the navicular anteriorly, the spring (calcaneonavicular) ligament inferiorly, and the anterior and middle facets of the calcaneus inferiorly. It is the key joint of the medial longitudinal arch mechanism and is the primary joint corrected during flatfoot reconstruction surgery. Together with the calcaneocuboid joint it forms the Chopart joint complex.
The TCN joint is the most important joint in adult-acquired flatfoot deformity, where progressive spring ligament failure allows the talar head to plantarflex and adduct, collapsing the medial arch. Reconstruction of this deformity involves correcting the talar head position through osteotomies and spring ligament reconstruction, targeting the TCN joint. Isolated TCN arthrosis, though uncommon, produces medial midfoot pain reproduced by passive talar head palpation with forefoot loading, managed with orthotics or talonavicular fusion.
Progressive failure of the spring ligament and tibialis posterior tendon collapses the TCN joint, allowing the talar head to rotate plantarward and medially, producing a flexible then rigid flatfoot with subfibular impingement, managed with orthotics conservatively or calcaneal osteotomy and spring ligament reconstruction surgically.
High-energy injury disrupts both the TCN and calcaneocuboid joints, producing complete midtarsal dislocation that requires urgent closed or open reduction and stabilisation to restore the transverse tarsal axis.
