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Talocalcaneal coalition

DIAGNOSIS WITH THE C-SIGN ON LATERAL RADIOGRAPHS OF THE ANKLE

Frimley Park Hospital, Portsmouth Road, Camberley, Surrey GU16 5UJ, UK.

D. Sallomi, FRCR, Consultant Radiologist

Eastbourne District Hospital, Kings Drive, Eastbourne, East Sussex BN21 2UD, UK.

D. L. Janzen, MD, FRCP C, Assistant Professor; and P. L. Munk, MD, FRCP C, Professor

Department of Radiology, Vancouver General Hospital, University of British Columbia, 855 West 12th Avenue, Vancouver, British Columbia, Canada V5Z 1M9.

R. J. Claridge, MD, FRCS C, Consultant Orthopaedic Surgeon

Foot and Ankle Clinic, Mayo Clinic Scottsdale, 13400 East Shea Boulevard, Scottsdale, Arizona 85259, USA.

V. A. Kiri, PhD, FSS, Senior Statistician

Centre for Public Health Monitoring, London School of Hygiene and Tropical Medicine, Keppel Street, London WC1E 7HT, UK.

Correspondence should be sent to Mr A. Sakellariou.

We analysed 42 weight-bearing lateral radiographs of the ankle, 20 of which were from patients with a clinical and plain radiological diagnosis of talocalcaneal coalition (TCC) who subsequently had CT. The remainder were from 22 healthy volunteers with no clinical findings suggestive of hindfoot pathology. 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 comparison we calculated the sensitivity, specificity, accuracy, and positive and negative predictive values for the C-sign, and for other signs known to be associated with TCC. Similarly, we also calculated the interobserver and intraobserver reliability for these signs using the kappa statistic.

Our results suggest that the C-sign is highly sensitive and specific for TCC. It is an accurate indicator and significantly more reliable than other previously recognised radiological signs of TCC. Features of the C-sign, however, cannot be relied upon to indicate whether the TCC is fibrous or bony.