Tarsal coalition


 * Tarsal coalition represents abnormal fusion between two or more tarsal bones and is a frequent cause of foot and ankle pain.
 * Calcaneonavicular and talocalcaneal coalitions are encountered most frequently; fusion at other sites is much less common.
 * Tarsal coalitions may be:
 * Osseous
 * Cartilaginous
 * Fibrous
 * Initially, all patients with tarsal coalition are treated conservatively with orthotics, casting, nonsteroidal anti-inflammatory medications, steroid injections, or physical therapy.
 * Many patients fail conservative therapy and are then treated operatively.
 * Calcaneonavicular coalitions may be treated with resection.
 * Talocalcaneal coalitions are treated surgically with resection of the middle facet bony bridge, often with fat interposition.

Radiographs

 * Use of conventional radiography alone is often sufficient to diagnose most calcaneonavicular and talonavicular coalitions

Calcaneonavicular Coalition

 * Calcaneonavicular coalitions are best depicted on 45° internal oblique radiographs.
 * The calcaneus and navicular do not normally articulate. With osseous coalition, a bony bar that bridges the two bones is seen.
 * With fibrous or cartilaginous coalition, the bones are in close proximity, both have irregular surfaces, and the anteromedial calcaneus is abnormally widened or flattened.
 * On lateral radiographs, elongation of the anterior dorsal calcaneus may simulate an anteater's nose.
 * Hypoplasia of the talus may also be observed with calcaneonavicular coalition.

Talocalcaneal Coalition

 * The subtalar joint consists of the anterior, middle, and posterior facets.
 * Talocalcaneal fusion most commonly involves the middle facet at the level of the sustentaculum tali.
 * Talocalcaneal coalitions may be difficult to visualize on the three standard radiographic views of the foot because of the complex orientation of the subtalar joint.
 * A number of secondary radiographic signs of talocalcaneal coalition have been described, including a talar beak, narrowing of the posterior subtalar joint, rounding of the lateral talar process, and lack of depiction of the middle facets on lateral radiographs
 * A talar beak occurs because of impaired subtalar joint motion, which results in the navicular overriding the talus.
 * Another radiographic finding seen on lateral views in talocalcaneal coalition is the C sign.
 * A C-shaped line outlines the medial talar dome and posteroinferior sustentaculum.
 * The C sign results from bone bridging between the talar dome and sustentaculum, as well as the prominent inferior outline of the sustentaculum.
 * The C sign may be observed in both osseous and nonosseous coalitions. Variations in sustentacular size and orientation may affect the reliability of this sign.