Coalition of the Calcaneus and the Navicular

Rigid flatfoot is generally considered to be the result of prolonged eversion and abduction, unrelieved by treatment. A failure of proper balance of the foot because of congenital or acquired weakness is considered the primary fault. The mechanism of the development of the alteration in relationship to the tarsal bones is dependent on the faulty position of the foot, which throws excessive and prolonged strain on ligamentous structures. The ligaments are not physiologically capable of resisting prolonged strain, and give way, allowing the tarsal bones to rotate into the typical deformity of flatfoot. The altered position of the tarsal bones and their articulations tends to produce a rigid foot. Although the rigid foot is less mobile than the normal one, it is frequently asymptomatic. In some cases, however, the foot remains painful, and the rigidity is greatly exaggerated by muscle spasm, chiefly of the peroneal group. This condition produces more