Radiographic diagnosis of tarsal coalition.

OBJECTIVE: The objective of this study was to evaluate the sensitivity of unenhanced radiographic diagnosis of tarsal coalition.

MATERIALS AND METHODS: The study had two phases. The first was a retrospective case and control review. Radiographs of 37 feet (15 talocalcaneal coalitions and 15 calcaneonavicular coalitions) and of 17 patients with foot pain and no coalition used as controls were reviewed independently by three observers who had no prior knowledge of the cases. Each observer reviewed the cases for individual signs of coalition and then decided if coalition was present. The second phase of the study was a prospective evaluation by a single observer of 150 consecutive weightbearing foot radiographs obtained to evaluate nontraumatic foot pain. Patients diagnosed as positive for coalition underwent CT.

RESULTS: On retrospective review of unenhanced radiographs, observers achieved 100% sensitivity and 88% specificity in the diagnosis of talocalcaneal coalitions. Sensitivity and specificity for calcaneonavicular coalitions ranged from 80% to 100% and 97% to 98%, respectively. Several previously unpublished radiographic signs increased sensitivity of diagnosis. For calcaneonavicular coalition, the new signs were altered navicular morphology and visualization of the bar on the anteroposterior radiograph. For talocalcaneal coalition, the new signs were a dysmorphic sustentaculum tali, nonvisualization of the middle subtalar facet, and shortening of the talar neck. In the prospective phase of the study, three talocalcaneal coalitions were detected with no false-positive results.

CONCLUSION: Routine anteroposterior and lateral unenhanced radiographs are a valuable screening tool for tarsal coalition, even when used by inexperienced observers. The newly described signs increase sensitivity of radiographic diagnosis.