Title: Talocalcaneal Coalition

Imaging Findings:
Figure Lateral radiograph of a patient complaining of a painful foot shows secondary sign of talocalcaneal coalition, the continuous “C sign” (arrows) (7).

Figure This same patients coalition is best depicted on coronal CT and MR imaging as a solid osseous bridge (arrows) between the talus and calcaneus.

Figure T1 axial (Image 5), T2 axial (Image 6) and coronal T1 (Image 7) MR images from a different patient shows partial bone marrow contiguity with osseous bridging and marrow edema (arrows) indicating reactive bone changes at site of nonosseous bridging.

Clinical:
Slight male predominance and bilateral in 50% of cases. Seen in 1%-2% of population. Young person presents with foot and ankle pain, typically during the second decade. Hindfoot pain or stiffness, often first noted after antecedent trauma, weight gain, or an increase in athletic activity. A common cause of peroneal spastic flatfoot or rigid flatfoot, though can be asymptomatic.

Etiology:
Abnormal congenital segmentation results in osseous (synostosis), cartilaginous (synchondrosis) or fibrous (syndesmosis) bridging of tarsal articulations which can produce abnormal mechanical stresses and pain. Osseous bridging appears to be progressive with age (1). Autosomal dominant pattern of variable penetrance is suggested. Calcaneonavicular and talocalcaneal coalitions account for 90% of cases, though other coalitions occur. Talocalcaneal coalition most commonly involves the middle facet of the sustentaculun tali (7).

References:
1. Newman JS, Newberg ALT. Congenital tarsal coalition: multimodality evaluation with emphasis on CT and
MR imaging. Radiographics 2000; 20(2):321-32.
2. Weschler RJ, Karasick D, Schweitzer ME. Computed tomography of talocalcaneal coalition: imaging
techniques. Skeletal Radiol 1992; 21:353-358.
3. Deutsch AL, Resnick D, Campbell G. Computed tomography and bone scintigraphy in the evaluation of
tarsal coalition. Radiology 1982; 144:137-140.
6. Resnick D. Talar ridges, osteophytes, and beaks: a radiologic commentary. Radiology 1984; 151:329-332.
7. Lateur LM, Van Hoe LR, Van Ghillewe KV, Gryspeerdt SS, Baert AL, Dereymaeker, GE.. Subtalar coalition: diagnosis with the C sign on lateral radiographs of the ankle;
Radiology 1994; 193:847-851.