Patients with tarsal coalition will usually present with a rigid flatfoot (loss of inversion and eversion at the subtalar joint). Coalition is produced by a congenital fusion or failure of segmentation of two or more tarsal bones. The attachment may be fibrous, cartilaginous, or osseus. Tarsal coalition can be unilateral or bilateral and will often become symptomatic in early adolescence. The most common forms of tarsal coalition are calcaneonavicular and talocalcaneal.
The patient will usually present with hindfoot pain, which may radiate laterally due to peroneal muscle spasm. Symptoms are exacerbated by sports, and young athletes can present with frequent ankle sprains. There is a familial component. Pes planus is usually present in both weight bearing and non-weight bearing positions. There is usually a loss of subtalar motion, and passive attempts at joint motion may produce pain.
Anteroposterior, lateral, and oblique radiographs should be obtained, but they may not always clearly identify the disorder. The oblique view often identifies the calcaneonavicular coalition. Computed tomography (CT) is the gold standard for diagnosis of tarsal coalition. Even patients with obvious calcaneonavicular coalition on plain radiographs should have a CT scan to rule out a second coalition.
Coalitions that are asymptomatic (the majority) do not need treatment. Nonoperative treatment for patients with pain consists of cast immobilization for a few weeks and foot orthotics. The symptoms will often return, necessitating surgery. Surgical excision of the coalition and soft tissue interposition to prevent reossification can be very effective.