Tarsal coalition is a congenital anomaly in which the tarsal bones fuse together, leading to a rigid flat foot, foot pain, and multiple ankle sprains. There are two types of tarsal coalition. The first is known as a Talocalcaneal Coalition, which is a coalition between the talus and the calcaneus. The second is referred to as a calcaneonavicular coalition which is a coalition between the calcaneus and the navicular. When talocalcaneal coalition occurs, it usually happens around 12-15 years of age. The calcaneonavicular coalition presents at an earlier age. About 50% of coalitions are bilateral, and around 20% have multiple coalitions in the same foot. Coalition may be fibrous, cartilaginous, or bony and occurs due to failure of segmentation. It could be associated with fibular hemimelia or Apert’s syndrome.
Symptoms typically consist of patient’s complaining of a painful foot, a history of repeated ankle sprains, and a flat foot deformity. Tarsal coalition may result in a peroneal spastic flat foot. During the physical examination, the physician may find hindfoot valgus. On toe standing, the arch does not reconstitute and heel cord contracture may also be evident during the exam. Furthermore, there may be restriction in the subtalar joint’s range of motion. It is important to check both feet as the condition may be bilateral.
The best imaging study is a CT scan. It can determine the size and location of the coalition. And MRI is also useful in detecting a fibrous or cartilaginous coalition. AP, Lateral, and Oblique view x-rays should be ordered. On a lateral view x-ray, the Calcaneonavicular Coalition can be identified by the “anteater nose sign” and the elongation of the anterior calcaneal process.
A lateral view of a Talocalcaneal Coalition may show talar beaking which is a traction spur that occurs due to the limited motion of the subtalar joint. Additionally, the C sign may be seen which is a radiological sign outlining the talar dome and the sustentaculum. A 45° oblique view is the best for showing calcaneonavicular coalitions.
Nonoperative treatment usually consists of anti-inflammatory drugs, modified activities, or the use of a brace or cast. Surgical treatment for the calcaneonavicular coalition usually consists of resection with an interposition of the extensor digitorum brevis muscle or a fat graft no matter the size of the coalition. Similarly, Talocalcaneal coalitions that involve less than 50% of the subtalar joint are also resected. A triple arthrodesis procedure is performed for large coalitions, failed resections, or advanced conditions.