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Abnormal collagen cross linking via a glycine substitution
4%
72/1766
Mutation of the fibrillin-1 gene
5%
89/1766
Failure of mesenchymal segmentation
69%
1227/1766
Fracture through the hypertrophic zone of the physis
16%
289/1766
Fracture through the proliferative zone of the physis
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Talocalcaneal coalition is identified by the C-sign (Illustration A) and is caused by failure of mesenchymal segmentation of the subtalar joint. Tarsal coalitions are most commonly found to be calcaneonavicular (most common) or talocalcaneal. The vast majority, however, are asymptomatic and identified incidentally. When symptomatic, patients commonly report recurrent ankle sprains or persistent activity related pain just distal to the fibula (calcaneonavicular) or distal to the medial malleolus, as is present in this case. Most calcaneonavicular and talocalcaneal coalitions can be identified on plain radiograph as evidence by the anteater sign or C-sign, respectively. Mosca et al. review subtalar coalitions in pediatric patients. They report that the most common locations are between the calcaneus and navicular and between the talus and calcaneus. They suggest that initial treatment should be nonoperative, however if these attempts fail, surgery may be indicated. Surgery varies based on the location and type of coalition identified. Flynn et al. review subtalar coalitions in adult patients. They report that tarsal coalitions, while relatively uncommon, are typically identified in adult patients during an evaluation for ankle instability, sinus tarsus pain, and/or pes planovalgus. They conclude that the most common area of involvement of the subtalar joint is the middle facet, and heightened awareness should be present in adult patients with limited motion of the subtalar joint.Figure A and B are the AP and lateral radiographs of a pediatric ankle demonstrating the "C-sign" (lateral radiograph), which is indicative of a talocalcaneal coalition. Illustration A outlines this finding. Incorrect Answers: Answer 1: A glycine substitution resulting in abnormal collagen cross linking occurs with osteogenesis imperfecta and is not related to tarsal coalition. Answer 2: Coalition is not a common finding in patients with Marfan syndrome. Answer 4 & 5: Radiographs do not demonstrate a fracture in this patient. However, Salter Harris fractures do occur through the hypertrophic zone.
4.0
(5)
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