Purpose: The height of navicular bone from the floor is in proportion with the height of longitudinal arch of the foot. The study was conducted to evaluate correlation of navicular bone height with most often used angles, heel valgus and a foot print in order to simplify the procedure for the diagnosis of flatfoot. Methods: A total of 218 operated children (436 feet) because of flexible flatfoot were evaluated clinically and radiologically. Meary angle, lateral talonavicular angle, talocalcaneal angle, calcaneal pitch, heel valgus and arch index (Staheli) were evaluated pre-operatively and postoperatively. In 121 (242 feet) chosen children (age eight to 15) with all clinical values and pre-operative angles corresponding flatfoot, all postoperatively measured values were within the normal range. We got the navicular index by dividing length of longitudinal arch with navicular height. Values of navicular index were then compared with pre-operatively and postoperatively measured values. Pearson correlation and ROC test were used for statistical analysis. Results: Values of the navicular index for flatfeet were in the interval from 4.75 to 31.2 (median 8.98), and for normal-arched feet 3.58-22.6 (median 5.48). Pearson correlation of arch index and measured parameters were significant in majority, and degree according to Colton was good. Area under the ROC curve was 0.861 (p = 0.0001). The cut-off value with 86 % sensitivity and 75 % specificity was 6.7407. Conclusion: Navicular index can be used reliably, without measures of the other parameters, to differentiate flatfoot from normal-arched foot. Therefore, the navicular index has an ability to distinguish between the flatfoot and normal-arched foot.
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