Talocalcaneal coalition - Diagnosis with the C-sign on lateral radiographsof the ankle

We analysed 42 weight-bearing lateral radiographs of the ankle, 20 of which were from patients with a clinical and plain radiological diagnosis of tal ocalcaneal coalition (TCC) who subsequently had CT. The remainder were from 22 healthy volunteers with no clinical findings suggestive of hindfoot pat hology. Four observers, blinded to the CT findings, independently evaluated the radiographs on two separate occasions. With the 95% confidence interval and using the CT findings as the compariso n we calculated the sensitivity, specificity, accuracy, and positive and ne gative predictive values for the C-sign, and for other signs known to be as sociated with TCC, Similarly, we also calculated the interobserver and intr aobserver reliability for these signs using the kappa statistic. Our results suggest that the C-sign is highly sensitive and specific for TC C, It is an accurate indicator and significantly more reliable than other p reviously recognised radiological signs of TCC, Features of the C-sign, how ever, cannot be relied upon to indicate whether the TCC is fibrous or bony.